TV Inverter

[wooslehunter]

Sine-wave inverters are advertised as "ideal for a TV, DVD etc.......". This infers that square wave inverters are not OK for a TV.

Does anyone use a square wave inverter to power a TV? They're loads cheaper.

Thanks, Dave

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[robp]

Most of the inexpensive invertors that you see in the consumer market, are "modified" Sine Wave. These simulate a Sinusoidal and are OK for Video and Audio. 150 Watt = approx £30 to £35 retail.

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[MainlySteam]

Dave, I suspect most, if not all invertors are modified sine wave (or sine wave, more expensively).

We run a TV off a modified sine wave invertor (1kW Freedom 10) with no troubles whatsoever. We also run power tools, hi fi, various computers, voltage convertors for notebook charging, laser printers, toasters, cake mixers, etc off it and never found anything within its capacity that it will not run. We have not used a microwave however, which some say can be problematical.

The only issue I have experienced is that for high power devices which have large power transformers in them, the harmonics on the ac supply can set up strong vibrations in the transformer plates - but that use is an unusual circumstance, in my case being a 500 watt solid state radio transmitter.

Rounding that up, I would say you can have a high level of confidence in powering a TV with any off the shelf invertor of suitable capacity.

John

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[redhot]

I agree,
I bought an off the shelf unit from Maplins (£80 for 800W) and it powers everything I need to, TV, Video, Stereo, Digibox, Mobile phone chargers.

Thanks
Mike.

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[wooslehunter]

Thanks guys,

I threw some science at the idea and eventually thought I'd ask what people are doing since I couldn't see a problem. TVs over 75W have to be power factor corrected these days and it's done really cheaply with a large inductor in the power line. This could cause a problem with a pseudo-sine inverter trying to drive a highly inductive load. Smaller 14" TVs don't have this so I can't think of any other problems.


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[MainlySteam]

I cannot speak from direct experience with inductances used for power factor correction, but I think driving a TV with such correction would not be a problem. In my earlier post I mentioned driving a 500 watt transmitter with an invertor. It was 230v supply and drew approximately 1 kW on full power but being solid state it had a conventional tranformer/ rectifier internal dc power supply. I do not know what the inductance of the transmitter's internal transformer would have been, but I imagine fairly high. The inverter had no problem driving that, nor the transmitter being driven by it apart from the fact that the plates in the transformer "hummed" very loudly from the harmonics in the supply. It was also possible that the iron losses in the transformer could have been high.

I would imagine that a power factor correcting inductor would not suffer in that way. But in any event, as you say this is only relevant for larger tv's, but as you are alert enough to recognise the possible problem I add the above out of possible interest.

John

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[Alex_Blackwood]

Why worry about PF correction if you are running from an inverter? You really only need to worry if you are running off the shore supply. The correction is for their benefit!

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[MainlySteam]

No. The point is not to do with worrying about getting the benefits of power factor correction. The point is about how well appliances with inductive power factor correction built into them will run on a quasi sinusoidal invertor with high harmonics in its ac output.

John

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[wooslehunter]

The PFC inductor can be removed anyway if it's a problem. Correct - it's for the benefit of the power companys and not the operation of the TV. Anyone who doesn't know what they are doing, please leave well alone.

I think it's more important that the inverter drives the inductive load properly.

Thanks for the advice - I'll try it. It's still cheaper to buy a cheap 14" TV and replace my cheap inverter if I have to than it is to buy a 14" TV that runs from 12V.

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[Alex_Blackwood]

Point taken! Wooslehunter has said what I was trying to get across. If you know what you are doing you can take it out if you are worried about that particular component.
Any thing that produces harmonics will have an effect on inductive or capacitive components due to spiking and heating effects and can cause an eventual breakdown in insulation. They can also be detrimental to eletronic systems, computers etc. Good design of the inverter will reduce the harmonics, in other words the better (More expensive!) the inverter the less the harmonic problem. You could of course fit a harmonic filter, if you have a degree in electrical engineering and can cope with the maths! Or the money to pay for the design.
As a matter of interest. With some of the earlier Diesel-Electric propulsion systems in ships, they did not fit harmonic filters. One of the problems encountered was loss of fluorescent lighting circuits caused by the power factor capacitors in the light fittings short circuiting due to the effects of harmonics.
I am not trying to teach grandmothers to suck eggs. I am sure that some of you more a lot more about electricity than I do.

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