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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?


Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


Cheers..


--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Thu, 9 May 2019 21:31:39 +0100, tony sayer
wrote:


Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.


They did!

It was quite effective but the caps were prone to short.

Reliability aside, valve heaters are resistive. Transformers have
inductive reactance. Guess where the "Wattless dropper" used to go.

Feeding heaters means very few hard sums. Everything is predictable so
its one over a pair of pies or fruitcakes or Brexiters- Take yer pick

Personally I wouldn't bother if you are driving with semiconductors.
It may get a trifle expensive.

Even when the reactance of the circuit is taken into consideration I
seem to recollect that the arcs and noise used to be pretty impressive
even with small caps when switching on and off.

Buy a couple of SMPS's off Ebay and ditch the tranny altogether.

Three sepeate aerials plus installation wouldn't be much more than an
RS low power transformer :-)


AB
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

I'd agree when these caps go the area tends to fill with very nasty smelling
smoke as well Also as this is for a radio receiver and one hads to think
weak signals, whatever power supply you use needs to be clean. Switch modes
can be clean, but most el cheapo ones are a disaster for rfi.
Some most definitely do not like inductive loads either, I'd still think an
auto transformer hidden away is a good solution myself.
Brian

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On Thu, 9 May 2019 21:31:39 +0100, tony sayer
wrote:


Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.


They did!

It was quite effective but the caps were prone to short.

Reliability aside, valve heaters are resistive. Transformers have
inductive reactance. Guess where the "Wattless dropper" used to go.

Feeding heaters means very few hard sums. Everything is predictable so
its one over a pair of pies or fruitcakes or Brexiters- Take yer pick

Personally I wouldn't bother if you are driving with semiconductors.
It may get a trifle expensive.

Even when the reactance of the circuit is taken into consideration I
seem to recollect that the arcs and noise used to be pretty impressive
even with small caps when switching on and off.

Buy a couple of SMPS's off Ebay and ditch the tranny altogether.

Three sepeate aerials plus installation wouldn't be much more than an
RS low power transformer :-)


AB



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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Fri, 10 May 2019 07:31:34 +0100, "Brian Gaff"
wrote:

I'd agree when these caps go the area tends to fill with very nasty smelling
smoke as well Also as this is for a radio receiver and one hads to think
weak signals, whatever power supply you use needs to be clean. Switch modes
can be clean, but most el cheapo ones are a disaster for rfi.
Some most definitely do not like inductive loads either, I'd still think an
auto transformer hidden away is a good solution myself.
Brian


Especially since an autotransformer can be considerably smaller than
an isolating transformer with the same VA rating.
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On 09/05/2019 21:31, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


Problem witha cap as a dropper is that the power consumption of te unit
will vary and if the motors are NOT running you might end up with a far
far higher votakge than you anticipate.

The answer is either a small autotransformer or simply get the mains
transformer rewound.,

Oddly enough one of te best ways to get a sm,all auto transformetr ois
to find say an old RS mains transformer that has two 110V promraies -
the type that could be uses in series or parallel to get 230/115v capability

Wire the primaries in series ignore the secondaries and take 115V from
the center tap and neutral. It wont be perfect, but it will be cheaper
than a custom auto

Or one of these ?

https://www.ebay.co.uk/itm/Step-Down...W/232415947981



Cheers..




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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Thursday, 9 May 2019 21:34:06 UTC+1, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


Cheers..


The issues...
1. Neither the motors, transformer nor the dropper cap are pf 1, nor is any BRed electronic load. So it's not as simple as treating them like resistors. However you could use that value as a starting point & tweak it until correct.
2. When load i is lower, V is higher. This may be a problem for the transformer and for the loads.
3. Dropper caps are vulnerable to shorting, so suitable fusing & thermal protection are wise, and in some cases overvoltage protection.

So in short, maybe, if you can address the load regulation issue.


NT
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Fri, 10 May 2019 05:53:04 -0700 (PDT), wrote:

On Thursday, 9 May 2019 21:34:06 UTC+1, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.


Bloody simple innit? Anyone spot the slight problem with the sums?



However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


Not so much a headache as a total incomprehesion of ac theory
methinks.


Cheers..


The issues...
1. Neither the motors, transformer nor the dropper cap are pf 1, nor is any BRed electronic load. So it's not as simple as treating them like resistors. However you could use that value as a starting point & tweak it until correct.
2. When load i is lower, V is higher. This may be a problem for the transformer and for the loads.


That's bloody deep! Where on earth did you find that useful little
snippet?

3. Dropper caps are vulnerable to shorting, so suitable fusing & thermal protection are wise, and in some cases overvoltage protection.

So in short, maybe, if you can address the load regulation issue.



For all the Brexit merchants out there!


https://www.electronics-tutorials.ws...s-circuit.html

AB
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

In article , tony sayer
scribeth thus

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.



Thanks for all the replies! In no real order, the aerial concerned is a
FUBA UK Stereo 8 this is a bit of a beastie its an old design but its
been "renovated" It has a very narrow forward acceptance angle if it
were as simple as using a couple of aerials I'd have done that!. But
there is a situation where one Transmitter is only a 100 kHz away from
another so as best possible discrimination is needed.

I think we'll give up with the cap dropper idea, they did back in the
day go short which was fun not! for the series connected valves but
there do look to be much better plastic poly whatever around today.

The problem using the Switch mode units is I believe the motors are AC
driven, there does not look to be any rectifier or switch mode built in
to the unit furthermore the transformer looks a bit fiddley to rebuild
and the extra wire needed for the UK mains may not fit so the idea of
using an existing tranny and tapping that at half way in autotransformer
mode seems OK and I do have a Toroid that would fit in there, but TNP's
reference to a simple 230 to 110 volts plug type reducer looks the job
so i think we'll go for that!

RS have one but its on flying leads and three times the price!

Cheers..

--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Friday, 10 May 2019 19:41:44 UTC+1, tony sayer wrote:
In article , tony sayer
scribeth thus


Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.



Thanks for all the replies! In no real order, the aerial concerned is a
FUBA UK Stereo 8 this is a bit of a beastie its an old design but its
been "renovated" It has a very narrow forward acceptance angle if it
were as simple as using a couple of aerials I'd have done that!. But
there is a situation where one Transmitter is only a 100 kHz away from
another so as best possible discrimination is needed.

I think we'll give up with the cap dropper idea, they did back in the
day go short which was fun not! for the series connected valves but
there do look to be much better plastic poly whatever around today.


Class X2 caps would get you better reliability in that respect. You'd probably need a bunch in parallel.

The problem using the Switch mode units is I believe the motors are AC
driven, there does not look to be any rectifier or switch mode built in


some ac motors are ok on dc, some aren't

to the unit furthermore the transformer looks a bit fiddley to rebuild


yep

and the extra wire needed for the UK mains may not fit so the idea of


it does. You use thinner wire.

using an existing tranny and tapping that at half way in autotransformer
mode seems OK and I do have a Toroid that would fit in there, but TNP's
reference to a simple 230 to 110 volts plug type reducer looks the job
so i think we'll go for that!

RS have one but its on flying leads and three times the price!

Cheers..


The only time a saleswoman made me laugh was when she told me they were cheaper than RS.


NT
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On 10/05/2019 19:36, Archibald Tarquin Blenkinsopp Esq wrote:

8


https://www.electronics-tutorials.ws...s-circuit.html


Not quite that simple..
if its a motor the moving magnetic field changes things too.
It depends on what type of motor it is.



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On Sat, 11 May 2019 09:44:59 +0100, "dennis@home"
wrote:

On 10/05/2019 19:36, Archibald Tarquin Blenkinsopp Esq wrote:

8


https://www.electronics-tutorials.ws...s-circuit.html


Not quite that simple..
if its a motor the moving magnetic field changes things too.
It depends on what type of motor it is.


I agree totally.

It's just a brief introduction for those that assume that a 50 Ohm
resistor has the same effect as a 50 Ohm impedance.


AB
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Sat, 11 May 2019 09:52:14 +0100, "dennis@home"
wrote:

On 10/05/2019 20:48, wrote:

8

The only time a saleswoman made me laugh was when she told me they were cheaper than RS.




There is quite a lot of stuff cheaper on RS than ebay.


????

By God RS have changed then.

I don't use RS now. I went off them when I found I could no longer buy
2.5mm Weidmuller terminals and 2.5 mm cable without doing a load of
cross referencing on the internet.

I did wonder when RS went AWG, whether they knew something was afoot
Brexit wise, and they went AWG around 5- 6 years back.

But cpc are usually cheaper still.



Had hassle with CPC, I always used my personal card for company
expenses, but CPC would not deliver to site on a personal card.
Farnell were a lot better, but oddly enough they seemed to have a lot
of stock problems and CPC usually had what they listed.

I use Ebay now. Some of the finished goods can be total junk, but most
of the cheapo Chinese components and basic electronic control
assemblies are amazing.

PID controller, N type T/C, SSR and a heating element all for less
than £20-00

Do that with a Eurotherm based system from CPC or RS :-)

AB



The hall effect switches I use on my train layout are 69p at CPC or £3
on ebay and amazon.

I thought about buying a few hundred and listing them myself but it not
going to make me a fortune.


This the sort of thing needed and its more likely to actually be safe
than one off some dodgy ebay trader from some unspecified place in china.

https://cpc.farnell.com/mercury/651-...W04236?st=110v
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On 09/05/2019 21:31, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

Do the secondaries need to be isolated from each other? If not then a
10-0-10 would be close enough to 9V and in series give 20V. I'm not sure
if there are many transformers with this output. 9-0-9 used to be more
common.

Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.

If you opt for 2 transformers remember they don't have to be so large.
The rotator power is also likely to be intermittent and that can be
reflected in the transformer rating.

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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On 11/05/2019 11:38, Fredxx wrote:
On 09/05/2019 21:31, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

Do the secondaries need to be isolated from each other? If not then a
10-0-10 would be close enough to 9V and in series give 20V. I'm not sure
if there are many transformers with this output. 9-0-9 used to be more
common.

Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.

If you opt for 2 transformers remember they don't have to be so large.
The rotator power is also likely to be intermittent and that can be
reflected in the transformer rating.

You could use the primary of any 0-120 0-120 or 120-0-120 transformer as
an autotransformer. Just keep an eye on the power rating but as the
rotator will have such a low duty cycle you will probably get away with
using something seriously under-rated.



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On Sat, 11 May 2019 11:38:17 +0100, Fredxx wrote:

On 09/05/2019 21:31, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
volts in has two secondaries of 20 volts power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

Do the secondaries need to be isolated from each other? If not then a
10-0-10 would be close enough to 9V and in series give 20V. I'm not sure
if there are many transformers with this output. 9-0-9 used to be more
common.

Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.

If you opt for 2 transformers remember they don't have to be so large.
The rotator power is also likely to be intermittent and that can be
reflected in the transformer rating.


Whoever reads the posts to you obviously failed to point out that the
person seeking advice is now fully furnished with a solution.

I do note that your posts indicate that you are being fed by a
constant stream of disinformation. Maybe it's time to sack your carer?

AB

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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On 11/05/2019 11:38, Fredxx wrote:
Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.


Correct. Autotransformers are wound with no secondary and lighter gauge
wire on the HV side of the primary.


But Tony only needs a few watts anyway. So I am thinking that a POS low
voltage split primary mains transforner will do the job


--
"First, find out who are the people you can not criticise. They are your
oppressors."
- George Orwell
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On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.


I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.


NT
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On 11/05/2019 15:46, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), wrote:

On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.


I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point. A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.

I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.

'Wouldn't like to see the controllers replaced with LW tuning cap's,
it would make for a slow race.

AB

The Mistral digital clock kit I made in 1974 (maybe 1975) used a
capacitor dropper to generate the assorted voltages for the digital side
(GI AY-5-1220 clock) and a the heater and anode voltages for the VFD
display. Not a varying load though.



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On Saturday, 11 May 2019 16:08:07 UTC+1, mm0fmf wrote:
On 11/05/2019 15:46, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point. A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.

I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.

'Wouldn't like to see the controllers replaced with LW tuning cap's,
it would make for a slow race.

AB

The Mistral digital clock kit I made in 1974 (maybe 1975) used a
capacitor dropper to generate the assorted voltages for the digital side
(GI AY-5-1220 clock) and a the heater and anode voltages for the VFD
display. Not a varying load though.


VFD anode i certainly varies. A cap dropper doesn't help with heating filament life, but VDFs run so low it might be ok.


NT
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On Saturday, 11 May 2019 15:46:05 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.


I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point.


the point is obviously to reduce v and/or i

A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.


Lots of appliances use a C dropper to supply varying loads. It's cheaper.
Some loads need their v limiting with a zener, some can accept the variation.


I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.


the early ones just used a series lightbulb to the track, with IIRC 110v train motors. Yes, for children.


NT
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Sat, 11 May 2019 08:24:12 -0700 (PDT), wrote:

On Saturday, 11 May 2019 15:46:05 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point.


the point is obviously to reduce v and/or i

A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.


Lots of appliances use a C dropper to supply varying loads. It's cheaper.


I wasn't aware that it was common practice, I would have thought that
in practical terms battery charging or similar might be feasible.

What loads are you aware of?

Some loads need their v limiting with a zener, some can accept the variation.

The power dissipated by the zener must limit the practicality of the
Wattless dropper. A variation of any significance ie a few watts,
would be better served by a transformer.


I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.


the early ones just used a series lightbulb to the track, with IIRC 110v train motors. Yes, for children.


Happy days!

Would have been more fun with 240V.

AB
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Saturday, 11 May 2019 18:35:24 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 08:24:12 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 15:46:05 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point.


the point is obviously to reduce v and/or i

A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.


Lots of appliances use a C dropper to supply varying loads. It's cheaper.


I wasn't aware that it was common practice, I would have thought that
in practical terms battery charging or similar might be feasible.

What loads are you aware of?


it's used in a huge range of things these days.

Some loads need their v limiting with a zener, some can accept the variation.

The power dissipated by the zener must limit the practicality of the
Wattless dropper. A variation of any significance ie a few watts,
would be better served by a transformer.


C dropping can be used with much higher powers than that, even over half a century ago it handled far more than a few watts.

I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.


the early ones just used a series lightbulb to the track, with IIRC 110v train motors. Yes, for children.


Happy days!

Would have been more fun with 240V.

AB


It was 240v when a train wasn't running. Parliament was not happy.


NT
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Sun, 12 May 2019 03:34:56 -0700 (PDT), wrote:

On Saturday, 11 May 2019 18:35:24 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 08:24:12 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 15:46:05 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point.

the point is obviously to reduce v and/or i

A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.

Lots of appliances use a C dropper to supply varying loads. It's cheaper.


I wasn't aware that it was common practice, I would have thought that
in practical terms battery charging or similar might be feasible.

What loads are you aware of?


it's used in a huge range of things these days.


Well go on, enlighten me.

I cannot honestly see that it would have much place in anything but
resistive loads with a very small variation in consuption.

Can you nominate a few examples?

Some loads need their v limiting with a zener, some can accept the variation.

The power dissipated by the zener must limit the practicality of the
Wattless dropper. A variation of any significance ie a few watts,
would be better served by a transformer.


C dropping can be used with much higher powers than that, even over half a century ago it handled far more than a few watts.


I don't disagree. It could be used for an entire town or city as long
as they all staggered kettle/ heater/ lighting/ shower use to a strict
timetable.

C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".

I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.

the early ones just used a series lightbulb to the track, with IIRC 110v train motors. Yes, for children.


Happy days!

Would have been more fun with 240V.

AB


It was 240v when a train wasn't running. Parliament was not happy.

Unchuffed perchance ?

AB



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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

On Sunday, 12 May 2019 12:23:08 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 03:34:56 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 18:35:24 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 08:24:12 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 15:46:05 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point.

the point is obviously to reduce v and/or i

A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.

Lots of appliances use a C dropper to supply varying loads. It's cheaper.

I wasn't aware that it was common practice, I would have thought that
in practical terms battery charging or similar might be feasible.

What loads are you aware of?


it's used in a huge range of things these days.


Well go on, enlighten me.

I cannot honestly see that it would have much place in anything but
resistive loads with a very small variation in consuption.

Can you nominate a few examples?


google is your friend


Some loads need their v limiting with a zener, some can accept the variation.

The power dissipated by the zener must limit the practicality of the
Wattless dropper. A variation of any significance ie a few watts,
would be better served by a transformer.


C dropping can be used with much higher powers than that, even over half a century ago it handled far more than a few watts.


I don't disagree. It could be used for an entire town or city as long
as they all staggered kettle/ heater/ lighting/ shower use to a strict
timetable.

C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".


C droppers pass plenty of watts. They just don't dissipate them.


I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.

the early ones just used a series lightbulb to the track, with IIRC 110v train motors. Yes, for children.

Happy days!

Would have been more fun with 240V.

AB


It was 240v when a train wasn't running. Parliament was not happy.

Unchuffed perchance ?

AB


For sure


NT
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On Sun, 12 May 2019 08:26:17 -0700 (PDT), wrote:

On Sunday, 12 May 2019 12:23:08 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:


Can you nominate a few examples?


google is your friend


Go on, I tend not to use Google, but even so Duck Duck is not exactly
festooned with examples.

Google is no ones friend, it is only there to "rattle the stick in the
swill bucket".


Some loads need their v limiting with a zener, some can accept the variation.

The power dissipated by the zener must limit the practicality of the
Wattless dropper. A variation of any significance ie a few watts,
would be better served by a transformer.

C dropping can be used with much higher powers than that, even over half a century ago it handled far more than a few watts.


I don't disagree. It could be used for an entire town or city as long
as they all staggered kettle/ heater/ lighting/ shower use to a strict
timetable.

C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".


C droppers pass plenty of watts. They just don't dissipate them.


P = V^2/ R

P = I^2 R

P = V.I.cos [phase angle]

The last capacitor I had experience of handling any Watts at all was
many years ago when I stuck a 0.47uF 1kV in place of a Grundig flyback
tuning cap. It handled about twenty I would say. The 21st melted it.

An electrolytic stuck in backwards will also demonstrate what happens
when a capacitor "passes Watts".


AB




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On Sunday, 12 May 2019 17:47:43 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 08:26:17 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 12:23:08 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:



C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".


C droppers pass plenty of watts. They just don't dissipate them.


P = V^2/ R


precisely, so approximately no dissipation, despite it passing plenty of watts to whatever's downstream.


NT
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On Monday, 13 May 2019 05:41:52 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 16:20:32 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 17:47:43 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 08:26:17 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 12:23:08 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:



C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".

C droppers pass plenty of watts. They just don't dissipate them.

P = V^2/ R


precisely, so approximately no dissipation, despite it passing plenty of watts to whatever's downstream.


NT


Rubbish!

It passes no Watts.

The only time a capacitor will "pass" Watts is when it heats up.

Current is Amps, not Watts


If a capacitor had anything to do with Watts, you would specify said
value on ordering.

Please point out where you would buy a 10uF 5 Watt capacitor.

AB


Oh dear.


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On 10/05/2019 11:06, The Natural Philosopher wrote:
On 09/05/2019 21:31, tony sayer wrote:

Heres one I'd like to run past the leccy whizzes hereon for comment.

I have a need to twiddle a large FM radio aerial to three distant
transmitters that are 110 deg apart.

Managed to find a very nice aerial rotator on e-bay, brand new made by
RCA in America at a very reasonable price.

Unit has turned up and as expected its 110 volt AC operation now i was
intent on using a small autotransformer to power this but it might be
better if i could run the aerial cable to more than the one location
thats just a 3 core mains type flex but its a PITA lugging the
autotransformer around.

Now i could change the transformer in the unit that on a VARIAC at 110
voltsÂ* in has two secondaries of 20 voltsÂ* power for the aerial motor
and 9 volts for the microprocessor and display etc, but thats two
transformers and i can get them from RS and a few others but its going
the be a very tight fit so hence this idea of putting a series connected
cap inside the unit, there is space for that so that drops the volts and
doesn't get warm they used to this trick in some Valve telly's years
ago.

So unit says it is rated at 25 watts so thats about .227 amps on 110 at
full load so thats a resistance of 484 ohms on the supply

So assuming that we bung in a cap of around 6.6 micro farad thats equal
to 480 odd ohms then it should all work.

However it's a transformer load I'm feeding and it's also at 60 Hz
anyone see any snags in doing this at all that I've missed and a prolly
have with the bloody headache I've got at the moment!


Problem witha cap as a dropper is that the power consumption of te unit
will vary and if the motors are NOT running you might end up with a far
far higher votakge than you anticipate.


+1

The answer is either a small autotransformer or simply get the mains
transformer rewound.,


The other thing to watch is that some US stuff is really tight on the
power rating for the transformer and it may be close to saturating the
core when run at 50Hz instead of the designed 60Hz. Those crap mains
electric razors they used to sell at Xmas relied on a 60Hz mechanical
resonance to work. Sold in the UK they only lasted a couple of years.

Oddly enough one of te best ways to get a sm,all auto transformetr ois
to find say an old RS mains transformer that has two 110V promraies -
the type that could be uses in series or parallel to get 230/115v
capability


+1

Wire the primaries in series ignore the secondaries and take 115V from
the center tap and neutral. It wont be perfect, but it will be cheaper
than a custom auto

Or one of these ?

https://www.ebay.co.uk/itm/Step-Down...W/232415947981


You can get neat compact low power step downs intended for 50W loads.
Or DIY as above.

--
Regards,
Martin Brown
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On Thu, 9 May 2019 21:31:39 +0100, tony sayer wrote:

Unit has turned up and as expected its 110 volt AC operation ...


Late to the party, you have checked that the primary isn't two 110 V
windings in parallel haven't you? US mains is 110 V bi-phase and
neutral, most stuff is connected phase - neutral (110 V) but big
loads like washing machines at phase to phase (220 V). To be honest
I'd be suprised if it does have two primary windings but you never
know.

--
Cheers
Dave.



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On Monday, 13 May 2019 09:49:20 UTC+1, Martin Brown wrote:

The other thing to watch is that some US stuff is really tight on the
power rating for the transformer and it may be close to saturating the
core when run at 50Hz instead of the designed 60Hz. Those crap mains
electric razors they used to sell at Xmas relied on a 60Hz mechanical
resonance to work. Sold in the UK they only lasted a couple of years.


you mean Remington?
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On Monday, 13 May 2019 19:10:31 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 22:08:53 -0700 (PDT), tabbypurr wrote:
On Monday, 13 May 2019 05:41:52 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 16:20:32 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 17:47:43 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 08:26:17 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 12:23:08 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:


C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".

C droppers pass plenty of watts. They just don't dissipate them.

P = V^2/ R

precisely, so approximately no dissipation, despite it passing plenty of watts to whatever's downstream.


NT


Rubbish!

It passes no Watts.

The only time a capacitor will "pass" Watts is when it heats up.

Current is Amps, not Watts


If a capacitor had anything to do with Watts, you would specify said
value on ordering.

Please point out where you would buy a 10uF 5 Watt capacitor.

AB


Oh dear.


Never mind, dont worry. Apology accepted.

It's a simple mistake to make really, getting units mixed up. Who
hasn't been guilty of confusing Angstroms and pH from time to time.

AB


I'm not sure why you're apologising to yourself, presumably for being a wally, but either way it's plonk time.


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On Mon, 13 May 2019 11:33:59 -0700 (PDT), wrote:

On Monday, 13 May 2019 19:10:31 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 22:08:53 -0700 (PDT), tabbypurr wrote:
On Monday, 13 May 2019 05:41:52 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 16:20:32 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 17:47:43 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sun, 12 May 2019 08:26:17 -0700 (PDT), tabbypurr wrote:
On Sunday, 12 May 2019 12:23:08 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:


C dropping never handled any Watt's incidentally, the clue is in
"Wattless dropper".

C droppers pass plenty of watts. They just don't dissipate them.

P = V^2/ R

precisely, so approximately no dissipation, despite it passing plenty of watts to whatever's downstream.


NT

Rubbish!

It passes no Watts.

The only time a capacitor will "pass" Watts is when it heats up.

Current is Amps, not Watts


If a capacitor had anything to do with Watts, you would specify said
value on ordering.

Please point out where you would buy a 10uF 5 Watt capacitor.

AB

Oh dear.


Never mind, dont worry. Apology accepted.

It's a simple mistake to make really, getting units mixed up. Who
hasn't been guilty of confusing Angstroms and pH from time to time.

AB


I'm not sure why you're apologising to yourself, presumably for being a wally, but either way it's plonk time.


Never mind, keep up the search for those high power capacitors old
bean.


AB


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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

In article l.net,
Dave Liquorice scribeth thus
On Thu, 9 May 2019 21:31:39 +0100, tony sayer wrote:

Unit has turned up and as expected its 110 volt AC operation ...


Late to the party, you have checked that the primary isn't two 110 V
windings in parallel haven't you? US mains is 110 V bi-phase and
neutral, most stuff is connected phase - neutral (110 V) but big
loads like washing machines at phase to phase (220 V). To be honest
I'd be suprised if it does have two primary windings but you never
know.


Its not Dave its just the one primary winding. It won't however be used
that much and for that long it just got to twiddle a large FM aerial
around.

Vid here by a yank "elmer ham;!


https://www.youtube.com/watch?v=3s0m-Hd0zjc
--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?


Do the secondaries need to be isolated from each other? If not then a
10-0-10 would be close enough to 9V and in series give 20V. I'm not sure
if there are many transformers with this output. 9-0-9 used to be more
common.


Yes they do one drives the motors at AC as best I can tell, the other 9
volt supply the microprocessor and display..


Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.


Thats what is in use at this moment. Pending the compact 230 volt step-
down..

If you opt for 2 transformers remember they don't have to be so large.
The rotator power is also likely to be intermittent and that can be
reflected in the transformer rating.

Indeed..
--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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Default Using a capacitor as a "wattless" dropper on 110 voltequipment?

On Mon, 13 May 2019 21:13:27 +0100, tony sayer wrote:


Do the secondaries need to be isolated from each other? If not then a
10-0-10 would be close enough to 9V and in series give 20V. I'm not sure
if there are many transformers with this output. 9-0-9 used to be more
common.


Yes they do one drives the motors at AC as best I can tell, the other 9
volt supply the microprocessor and display..


Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.


Thats what is in use at this moment. Pending the compact 230 volt step-
down..

If you opt for 2 transformers remember they don't have to be so large.
The rotator power is also likely to be intermittent and that can be
reflected in the transformer rating.

Indeed..


As you've surmised, the rotator motor is an ac only type (a universal ac/
dc motor will be unsuited on account of the interference produced by the
commutator/brush gear).

It will be a 120v 60Hz induction motor but the thing you have to
remember when running such motors off a 50Hz supply is that this makes
them a 100v 50Hz induction motor. You have to scale the voltage down in
proportion to the scaled down frequency to avoid excessive current draw
along with the real possibility of core saturation which will exacerbate
the increased I sq R losses in the motor windings.

TNP is in my killfile so I don't know what type of output his suggested
"compact 230 volt stepdown converter" is. If it's just a 9v smpsu to
power the electronics part, that won't be a problem but if it's a 230vac
to 110vdc converter that'll just fry everything.

It seems to me unlikely that a compact switching 240vac to 110vac
converter would be cheaper than a 50VA rated 240 to 100 volt
autotransformer, especially one made up from a readily available (or to
hand) 30 to 50 VA 240v split primary to 20v secondary transformer which
you can use to get 120v minus the 20 volt secondary connected in 'buck'
to get the desired 100v 50Hz motor supply.

Anyway, I just thought it might help to remind you about the need to
scale the motor voltage requirement with the reduction of frequency when
driving a 120v 60Hz motor off a 50Hz supply.

--
Johnny B Good
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Default Using a capacitor as a "wattless" dropper on 110 volt equipment?

In article , Johnny B Good johnny-b-
scribeth thus
On Mon, 13 May 2019 21:13:27 +0100, tony sayer wrote:


Do the secondaries need to be isolated from each other? If not then a
10-0-10 would be close enough to 9V and in series give 20V. I'm not sure
if there are many transformers with this output. 9-0-9 used to be more
common.


Yes they do one drives the motors at AC as best I can tell, the other 9
volt supply the microprocessor and display..


Maybe the cheapest auto-transformer is a standard one with 2 x 110V
primaries. I expect a true autotransformer with the same rating will be
smaller.


Thats what is in use at this moment. Pending the compact 230 volt step-
down..

If you opt for 2 transformers remember they don't have to be so large.
The rotator power is also likely to be intermittent and that can be
reflected in the transformer rating.

Indeed..


As you've surmised, the rotator motor is an ac only type (a universal ac/
dc motor will be unsuited on account of the interference produced by the
commutator/brush gear).


Don't think that would be a problem anyway your not normally using the
aerial/s whilst rotating them.


It will be a 120v 60Hz induction motor but the thing you have to
remember when running such motors off a 50Hz supply is that this makes
them a 100v 50Hz induction motor. You have to scale the voltage down in
proportion to the scaled down frequency to avoid excessive current draw
along with the real possibility of core saturation which will exacerbate
the increased I sq R losses in the motor windings.


I'm not a 100% sure it is AC it seems it might be. Haven't got it going
as yet but hopefully soon, do appreciate the 50/60 Hz bit it won't be
running that long or much either with the intended use.


TNP is in my killfile so I don't know what type of output his suggested
"compact 230 volt stepdown converter" is. If it's just a 9v smpsu to
power the electronics part, that won't be a problem but if it's a 230vac
to 110vdc converter that'll just fry everything.


It is AFAIK an AC one look like a small plug mounted type
autotransformer

It seems to me unlikely that a compact switching 240vac to 110vac
converter would be cheaper than a 50VA rated 240 to 100 volt
autotransformer, especially one made up from a readily available (or to
hand) 30 to 50 VA 240v split primary to 20v secondary transformer which
you can use to get 120v minus the 20 volt secondary connected in 'buck'
to get the desired 100v 50Hz motor supply.

Anyway, I just thought it might help to remind you about the need to
scale the motor voltage requirement with the reduction of frequency when
driving a 120v 60Hz motor off a 50Hz supply.

All noted I'll let everyone know how it goes when i get a aroundtuit!..

--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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