# Inverters: quasi or true sine?



## mike800966 (May 1, 2005)

Looking to install a hard wired 1000W inverter as per the Clive M-G article in MMM but puzzled as to whether I need the luxury of the true sine versions? Intend to run run basically a 700w toaster,,, which I know shouldnt be fussy but no doubt will also be running or charging laptop, TV DVD and digibox etc.
About the only thing that I know insists on a true sine is the synchronous motor in the record turntable, but we wont be taking that with us!

Mike & Ann


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## 88870 (May 10, 2005)

Hi Mike and Ann, 

I don't have a true sine and everything - TV, Digibox, Playstation, DVD Player etc works fine. Even the hair clippers perform without a problem.  

It has had a detrimental effect on the Laptop battery though. It used to work for about 3-4 hours on a full charge, but now I am lucky to get an hour. Its only been this way since I started charging via the inverter. Even charging through the mains now will not alter the pitiful battery life


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## andyangyh (May 1, 2005)

Could just be what laptop batteries do. Mine now lasts almost 4 minutes on a supposed "full" battery. It was starting to lose storage capability long before I was charging it in the van. Ideally you should remove the bettery when on mains as a laptop battery (especially older ones) will only take so many charges before starting to wear out (probably a technical term for this but you know what I mean). So probably not an inverter problem - just a laptop problem the salesmen never mention


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## DABurleigh (May 9, 2005)

Mike/Ann,

Modified sine-wave is fine for that stuff. Only inductive loads can be a problem - motors, some lighting, some chargers (toothbrush). If you are really unlucky you might get some very mild audio/visual interference on TV, but not enough of a problem to justify the premium of a sine-wave inverter.

Dave


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## olley (May 1, 2005)

"Modified sine wave" is what the advertising people dreamed up, a more correct term is "modified square wave" just doesn't sound so good. :lol: 

Olley


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## mike800966 (May 1, 2005)

*Quasi Sine*

Many thanks, it seems that I could get away with it .
Just noticed a 5500w inverter on ebay going for £95, seems a bit overkill for a toaster. I can almost feel the battery protesting at the quiescent current!

Thanks agin

Mike (& Ann)


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## DABurleigh (May 9, 2005)

I should say that personally I think, unless you have a huge battery bank, using 12V to power a 700W toaster is not a wise move for a rack of breakfast toast. Just do the consumption sums for the Ah it will take out of the battery. Then multiply it up due to Peukert's formula because an Ah at the nominal discharge rate is not the same as an Ah at 65 amps ....

Dave


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## 101825 (Nov 18, 2006)

If you need a true sinewave for some low-consumption devices consider two inverters:

a) modified square wave - 1 or 2kw for heavy stuff
b) sinewave - 300w or less for small stuff that could be "sensitive"

This would cost considerably less than a big true sinewave.

Having said this, we use a modified sqaure wave without a problem.


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## Motorhomersimpson (May 9, 2005)

DABurleigh said:


> If you are really unlucky you might get some very mild audio/visual interference on TVDave


Not my experience using modified sine wave inverters, but I was using a TV/DVD combo "Ventura" (Tesco's & Argos) I think the name was, but it is labelled under various brands, only cost £149.00, shame as it was a nice unit.

The audio interference was quite loud and unacceptable, so much so, I returned the TV/DVD and have gone along the separate TV and DVD route.

I thought it best to mention this, just in case Mike, you have a similar LCD/TV/DVD set.

MHS...Rob


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## mike800966 (May 1, 2005)

*Inverters*

Thanks for the tip Dave.
I just looked at 700w @ 12v. 700/12 =58Amps +10% for the inverter loss =65amp. Seems a lot of amps but it should only be on for say 6 mins ie 0.1 hr which comes back to 6.5AH. Intending on going for 2x85ah batteries so its about 5% of capacity.

Still at the moment I havent spent anything and not even plugged the soldering iron in!

Mike


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## gromett (May 9, 2005)

*Re: Inverters*

TBH I would use the grill for toast if I were you. Gas toast is always better than electric toast. Real fire toast is even better.

I personally wouldn't use an electric toaster in my motorhome even with a 3K inverter and 800Ah. Use gas wherever possible its easy to replace. Use electric for what can't be powered by gas.

Just my opinion, don't know what other think?

Karl


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## DABurleigh (May 9, 2005)

Mike,

It's worse than you estimate for 2 reasons:

1) Peukert's formula, as I mentioned, reflects that fact that drawing double the current for half the time, say, consumes a lot more out of your batteries.

2) Battery terminal voltage, when it's cold, can quickly be pulled down by the high currents to below the inverter input voltage threshold. Everything stops. But, after a little while for the battery to recover, you will find it could continue to power lights, TV, etc. for days.

Dave


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## mike800966 (May 1, 2005)

*Inverters*

OK Dave and Karl, I think I give in!

The problem is that you havent seen where my grill is located, you need a PHd in origami to watch it as it cooks,,,,, slowly. I suppose that if I can mount the grillpan nearer to the heat that the inverse square law would cook it faster. 
So the inverter switching project might still go ahead just using the little Maplin 150w jobbie, at least the mains lighting that Ive installed (2x11w low energy bulbs and the socket for charging things from would be more useful.

Many thanks for the input

Mike (& Ann)


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## olley (May 1, 2005)

Hi what happens if you don't have a grill? like my RV, hob and combined microwave/oven only. 

So large 1800w inverter and 540amph battery bank, tried it for the first time at peterborough, lasted from Friday morning until Sunday afternoon when low battery voltage turned the inverter off. The xantex said 358amph had been used. (it was cold we had the heating on)

All that just for toast.  

Olley


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## DABurleigh (May 9, 2005)

Mike/Ann,

Get one of these instead:
http://www.argos.co.uk/static/Product/partNumber/0190800.htm

Dave


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## CliveMott (Mar 10, 2008)

*DONT OVER ESTIMATE PEUKERSS*

The battery has internal resistance. The applied VOLTAGE is increased by the charger to compensate during charging (or the charging current reduces). However Amps is amps equals electrochemical change. Ampere-hours in = ampere hours out less that consumed to split a little water into its component parts. You cannot convert heat losses due to I squared R into amps used for another reason. All the amps flow through the plates and the electrolyte whatever happens.
The basis of Peukert is that at high discharge (or charge) rates some parts of the lead paste is more accessible to the acid and therefor the current flow than others. At a high rates the easily accessible parts of the lead paste is converted first. Then that not so accessible gets used next but the effective internal resistance is increased, so the terminal voltage drops. If you continue until the battery appears exhausted at this discharge rate then Peukert constant applies.
However if you only have the high discharge rate for a small proportion of the available ampere hours then let the battery rest or work at a much lower discharge rate it recovers quite well and the paste equalises to a great extent.
This was one of the great concerns initially when battery electric fork lift trucks which take current at or in excess of the 1 hour rate during acceleration or during laden lifting went to pulse control but turned out to be a zero problem. The average discharge current over an 8 hour shift was a very good approximation to reality.
Hope that helps.
C.


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