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#1
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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. |
#2
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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 |
#4
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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. |
#5
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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.. -- To ban Christmas, simply give turkeys the vote. |
#6
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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 |
#7
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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 |
#8
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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. |
#9
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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 |
#10
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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. |
#11
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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. But cpc are usually cheaper still. 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 |
#12
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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 |
#13
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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 |
#14
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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. |
#15
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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. |
#16
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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 |
#17
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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 |
#18
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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 |
#19
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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#20
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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. |
#21
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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 |
#22
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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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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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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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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Using a capacitor as a "wattless" dropper on 110 volt equipment?
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