"RobertL" wrote in message
...
On Tuesday, March 17, 2015 at 8:52:20 PM UTC, Roger Mills wrote:
I see that Maplin have a 5000watt mains inverter on offer for £350
instead of £600

http://www.maplin.co.uk/p/maplin-dc-...paign=15P13-20

What possible use is it?

Someone who lives on a boat who wants to run an electric cooker off a
marine alternator?

Rather mad to have an electric cooker in a boat tho unless it's a microwave.

More useful for running motor driven power tools which need
a decent startup current but which don't actually use 5KW
continuously and which won't start when say a 1KW inverter is used.

Roger Mills wrote:
I see that Maplin have a 5000watt mains inverter on offer for £350
instead of £600

http://www.maplin.co.uk/p/maplin-dc-...paign=15P13-20


What possible use is it? How many people have got 12v batteries capable
of delivering 500 amps for more than a few minutes (more likely a few
*seconds"!)?

It worries me that the uninitiated are going to buying these things to
run lots of mains equipment off their car batteries - only to find that
they're totally useless. [I note that there are no reviews!]

It's a perfectly viable proposition on many small[ish] boats which aim
to be a sort of mobile bedsit. Even on our little 12 metre boat we
have 3 x 100Ah batteries which could supply 500 amps for half an hour
or so. Anyway a 5kW inverter is unlikely to run *continuously* at
5kW, it's the ability to supply this power occasionally for quite
short periods that is useful.

--
Chris Green
·

In article ,
"ARW" writes:
My Dad has a pure sine wave invertor. Just to power up the CH, the TV and a
couple of lamps and a small travel kettle if needed.

https://www.tlc-direct.co.uk/Products/SK652105.html

Several people said it would not work with his CH but it did:-)

I have the 300W version of that, for powering my central heating.
It didn't tie the neutral and ground together, which I had to do
to make the flame sensor in my Potterton Profile work, after
which it was fine.

I did previously run it from a modified sine wave inverter, and
it worked, but the pump made quite a bit of extra noise, and might
not have been running at correct power/speed.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
Roland Perry writes:
In message , at 19:44:43 on Wed, 18 Mar
2015, ARW remarked:
If you need them, pure sine wave inverters have come down very
significantly in price over last couple of years. They are basically
a sine wave generator coupled to a power amplifier with a 230V RMS
output. The amplifier is class D, i.e. high frequency switching, so
the efficiency is almost as high as the "modified" sine wave
inverters (or it can even match, as they're generally better designed,
and the efficiency of the appliance can also be higher in some cases).

My Dad has a pure sine wave invertor. Just to power up the CH, the TV
and a couple of lamps and a small travel kettle if needed.

I've got a 3KVA UPS which I hope produces something close to a
sine-wave. It's got about 30Kg of metal inside (as transformer cores)
and originally cost someone about $2000. I've never found anything that
objected to the output.

That sounds like an old type which basically bangs a low voltage
"modifed sine" wave (i.e. square-ish wave) into the primary of a
50Hz step-up transformer, and the transformer will do lots of
rounding off of the square corners. Won't be as efficient as a
modern one.

The output is probably something between the cheap modern modfied
sine wave inverters, and a real sine wave. In particular, the sharp
corners won't make it through the transformer (although the flat
peaks will probably decay on the output side too).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Wed, 18 Mar 2015 11:02:13 +0000, Syd Rumpo
wrote:

On 18/03/2015 09:56, john james wrote:

snipped


"Andrew Gabriel" wrote in message
...
In article ,
"john james" writes:
"Roger Mills" wrote in message
...

It would also depend on how sensitive your electrical equipment is to
waveform. It claims to produce a "modified" sine wave - whatever
that is.

It's a set of steps that are close to a sinewave than a square wave is.

It's often a square wave with the addition of an elongated zero section
at each zero crossing.

That's not modified sine wave.


'Tis, Google it. Rectangular pulses +ve and -ve with gaps between. I
designed one - filthy noisy thing.

I did the same thing over 20 years ago (a 500W 12v version) which I
ran off 2 12v banks of 225AH ex PABX lead acid cells that I'd revived
back to 80% capacity (200 hour rate mind you! :-).

I didn't use it in anger, just a very few hours on a 3 x150W test
lamp load. It's actually the reason why a 2 foot 20W fluorescent
fitting is missing its PFC capacitor to this day (the inverter didn't
like the capacitive load one bit).
--
J B Good

On Wed, 18 Mar 2015 19:57:17 +0000, Roland Perry
wrote:

In message , at 19:44:43 on Wed, 18 Mar
2015, ARW remarked:
If you need them, pure sine wave inverters have come down very
significantly in price over last couple of years. They are basically
a sine wave generator coupled to a power amplifier with a 230V RMS
output. The amplifier is class D, i.e. high frequency switching, so
the efficiency is almost as high as the "modified" sine wave
inverters (or it can even match, as they're generally better designed,
and the efficiency of the appliance can also be higher in some cases).

My Dad has a pure sine wave invertor. Just to power up the CH, the TV
and a couple of lamps and a small travel kettle if needed.

I've got a 3KVA UPS which I hope produces something close to a
sine-wave. It's got about 30Kg of metal inside (as transformer cores)
and originally cost someone about $2000. I've never found anything that
objected to the output.

I rather doubt you will. My ancient SmartUPS2000 surprised me by
taking the de-gaussing surge of a 19 inch colour monitor in its stride
and that's only rated at 2KVA / 1500 watts).
--
J B Good

On Wed, 18 Mar 2015 23:52:59 +0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
Roland Perry writes:
In message , at 19:44:43 on Wed, 18 Mar
2015, ARW remarked:
If you need them, pure sine wave inverters have come down very
significantly in price over last couple of years. They are basically
a sine wave generator coupled to a power amplifier with a 230V RMS
output. The amplifier is class D, i.e. high frequency switching, so
the efficiency is almost as high as the "modified" sine wave
inverters (or it can even match, as they're generally better designed,
and the efficiency of the appliance can also be higher in some cases).

My Dad has a pure sine wave invertor. Just to power up the CH, the TV
and a couple of lamps and a small travel kettle if needed.

I've got a 3KVA UPS which I hope produces something close to a
sine-wave. It's got about 30Kg of metal inside (as transformer cores)
and originally cost someone about $2000. I've never found anything that
objected to the output.

That sounds like an old type which basically bangs a low voltage
"modifed sine" wave (i.e. square-ish wave) into the primary of a
50Hz step-up transformer, and the transformer will do lots of
rounding off of the square corners. Won't be as efficient as a
modern one.

The output is probably something between the cheap modern modfied
sine wave inverters, and a real sine wave. In particular, the sharp
corners won't make it through the transformer (although the flat
peaks will probably decay on the output side too).

I doubt that a 3KVA UPS will be anything other than a pure sinewave
output type. It seems to be a very similar design to that SmartUPS2000
of mine. That uses a class D amplifier to drive conventional 50/60Hz
mains transformers in reverse (low primary input, mains secondary
output) from a 50 or 60Hz sinewave reference.

It's the type of design that's referred to as a "Line Interactive"
UPS where a relay is used to switch from mains input to inverter
output on full mains failure with additional relay switching of buck
and boost tappings to compensate for sags and surges in mains voltage
levels, eliminating the need to use battery power for the more modest
out of tolerance departures from nominal supply voltage. If I recall
correctly, the mains transformer also powers the battery charger
circuit as well.

It might seem rather cumbersome to digitally synthesise 50/60Hz power
at 28v rms to feed into a large and heavy mains step up transformer
but you have to remember that the transformer also serves as a
buck/boost device to reduce demands on the battery as well as act as a
charging transformer. At these power demands, portability wasn't
considered a high priority way back then.

These days, a modern UPS would do away with such large and heavy
mains frequency transformers[1] and simply synthesise a floating
fullwave "unsmoothed"[2] 325v peak DC voltage (230v rms case) with a
100% 100/120Hz ripple content connected to the load via a fullwave
thyristor commutator circuit to reverse the polarity at half the
ripple frequency.

[1] The smaller, sub 3KVA line interactive types may include a smaller
buck/boost autotransformer to retain the battery saving feature of
regulating poorly stabilised mains voltage supplies, probably only
weighing a tenth to a fifth of the weight of an Old Skool transformer
design like the SmartUPS2000.

[2] "Unsmoothed" only in respect of the 100/120Hz 'ripple', smoothed
in regard of the HF inverter pulses from the 'class D amplifier'.
--
J B Good

Dennis@home wrote:


Must have been a bloody big boat! I wouldn't fancy that sort of weight
except in the bilge!

Bill

Its a canal boat, they were used to carry 100 tons of stuff about, a few
small batteries doesn't matter unless you put them on the roof where
someone will knick 'em..

Someone very strong.

Bill

On Wed, 18 Mar 2015 22:09:17 +0000, wrote:

Roger Mills wrote:
I see that Maplin have a 5000watt mains inverter on offer for £350
instead of £600

http://www.maplin.co.uk/p/maplin-dc-...paign=15P13-20


What possible use is it? How many people have got 12v batteries capable
of delivering 500 amps for more than a few minutes (more likely a few
*seconds"!)?

It worries me that the uninitiated are going to buying these things to
run lots of mains equipment off their car batteries - only to find that
they're totally useless. [I note that there are no reviews!]

It's a perfectly viable proposition on many small[ish] boats which aim
to be a sort of mobile bedsit. Even on our little 12 metre boat we
have 3 x 100Ah batteries which could supply 500 amps for half an hour
or so. Anyway a 5kW inverter is unlikely to run *continuously* at
5kW, it's the ability to supply this power occasionally for quite
short periods that is useful.

Yes, but at TWELVE VOLTS! Even a 300W inverter takes a minimum of 25A
if we assume 100% efficiency, more like 28A assuming circa 90%
efficiency for a modified square wave type (or quasi-sinewave if you
prefer 'marketing speak').

I'd expect a 5KVA true sinewave inverter to require a minimum battery
voltage of 48 volts to retain any semblence of usability. Even
assuming an efficiency of 95%, that's still a maximum demand of 110A
off a 48 volt battery supply assuming the KW rating matches the KVA
rating.

Typical PF figures for such inverters are around the 75 to 80% mark
(true power handling limits of 3750 to 4000 watts). Assuming a 5KVA
80% PF rating, that's still a maximum demand of 88 amps.

Either way, you'd still need starter motor guage cabling between a 48
volt battery and the inverter's battery connecting terminals. A 12v
version just doesn't seem practical.
--
J B Good

"Andrew Gabriel" wrote in message
...
In article ,
"ARW" writes:
My Dad has a pure sine wave invertor. Just to power up the CH, the TV and
a
couple of lamps and a small travel kettle if needed.

https://www.tlc-direct.co.uk/Products/SK652105.html

Several people said it would not work with his CH but it did:-)

I have the 300W version of that, for powering my central heating.
It didn't tie the neutral and ground together, which I had to do
to make the flame sensor in my Potterton Profile work, after
which it was fine.


:-) I knew that I needed to do that. I was on a **** up with Geoff (CET)
when my Dad bought it.

I might fit a 300W version to the van to charge cordless tools

--
Adam