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.
Electronic – Charging a 12V battery bank while using it
batteriesgeneratorinverter
Related Solutions
There are many power supplies available for this purpose. As 0x6d64 says, these have a constant voltage output of around 2.3V per cell, ie 13.6V or 13.8V for a 12V battery. The power supply will need a current limit so that the battery will not be damaged if it is charged when flat. This would typically be about 0.1 of the capacity - so no more than 10A for a 100AH battery - probably 5A to be safe.
You can safely leave everything connected 24/7 with this arrangement and switch the mains on and off as necessary but some deep-discharge protection is advisable. This would cut the power output if the battery voltage drops below about 10V to prevent battery damage. Of course your connected equipment needs to be capable of operating at 13.8V for this to work. If 14V is the absolute maximum then this solution is borderline.
First, you really, really need to check how well your generator works when under load.
As brhans pointed out, you've got your battery connected wrong. Fixing this and adding a MOSFET will produce
simulate this circuit – Schematic created using CircuitLab
M1 is a p-type MOSFET, and when the generator output is zero the FET will be turned on. When the generator is charging the battery, the gate of the FET is high, and the FET is turned off. D4 compensates for the voltage drop in D2, and keeps the FET gate voltage from going the wrong way.
Best Answer
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.