I have (4) 12V 190 Ah AGM batteries connected in series. I want to run a portable A/C unit through a 2000 watt inverter connected to those batteries and charge the batteries simultaniously with a battery charger powered by a generator. The A/C unit requires 7.5 amps continous and 15 amps surge. I would like to do this because with the A/C unit connected to the generator, every time the compressor kicks on the generator revs up which is just annoying. My plan is to use a 100 amp charger to contiually charge the batteries while im running the A/C. I calculate that the A/C will draw approximately 83 DC amps while running.
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1\$\begingroup\$ There's a problem here. 83 amps times 48 volts is 4 kW, and I have a hard time believing your inverter is only 50% efficient. Furthermore, most of the time the A/C will only draw about 7.5 amps, or 900 watts at 120 VAC. That will only be about 19 amps from the batteries, probably plus about 10 to 20% extra for inverter losses. \$\endgroup\$– WhatRoughBeastFeb 9, 2019 at 4:25
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2 Answers
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There is no problem with having a load drawing power while a charger is charging the batteries. The charger is pushing power into the system and the A/C is taking it out again. Most of the power will be going straight from the charger to the A/C, but that just means that your battery array will take longer to charge as it'll only be getting charged at 17A as opposed to 100A (100A-83A). This is the same as when you use your laptop or phone while it's plugged in.
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1\$\begingroup\$ I agree, but don't forget that lead acid batteries tend to prefer a slightly slower charge, and if your AC turns off, you will be charging your bank of batteries at 100 amps or a little more than c/2. Of all the types of lead acid batteries, I believe that AGM can take a faster charge than the others, but the general rule of thumb is c/3, so best to check with the manufacturer of your battery to make sure that when the AC turns off, your charger isn't too eager. \$\endgroup\$– FilekJun 23, 2016 at 8:21
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\$\begingroup\$ Good point @Filek, I wasn't even thinking about C rates \$\endgroup\$– SamJun 24, 2016 at 0:01
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While this is possible, I also wanted to point out that you are converting AC to DC and then back to AC in this setup. That's a whole lot of lost power. The little "rev" you get when the compressor kicks on is a small price to pay for the extra fuel consumption! Best of luck.
