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Wanting to use my old 120 volt lead acid pack, that still have some life
left in them, to heat and cool with heat / ac combo window unit.


Solar charge during day, run unit overnight.





Question: How do you convert 120 volt dc to 120 volts ac?
I will need 20 amps





Thanks james
 

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Put your batteries into parallel/series as 5 in parallel and 2 in series, to get a 5x Ah capacity and 24V pack, and use an off the shelf 24V inverter.

There's not a lot of inverters for battery to AC above 48VDC. Since you'd have extra batteries if you did a 48V system, try a 12 or 24V system.
 

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Wanting to use my old 120 volt lead acid pack, that still have some life
left in them, to heat and cool with heat / ac combo window unit.


Solar charge during day, run unit overnight.





Question: How do you convert 120 volt dc to 120 volts ac?
I will need 20 amps





Thanks james
Hi james,

To invert directly (DC to AC), you'd need about 170Vdc to get 120Vac, RMS, sinewave. So what is usually done, I think, is invert to a lower AC voltage and step up with a transformer.

A commercial unit will be expensive. I suggest you look into used or surplus UPS, uninterruptible power supply. Often times they go for cheap because original batteries have died.

You'll probably have to oversize the unit to start the compressor motor on the heat pump. And most likely not use a modified sinewave inverter, but I think ones of suitable size will be true sinewave.

Good luck,

major
 

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so is there any difference in efficiency between converting 24VDC to 120VAC versus 12VDC to 120VAC? (assuming the same number of batteries just configured differently)

M
 

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12V directly is most common off grid, cheaper devices.

24V gives more oomph for high-current loads like winches, but then you need to convert for the 12V circuits, adds to cost.

Yes for long distances, 24V can save wire costs but only for a 30-40' boat would that be worth the above difference IMO.

Inverters are inefficient, good ones expensive, try to minimize their use only when necessary.
 
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