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Old 01-15-2012, 04:59 PM   #50 (permalink)
thingstodo
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DC to AC inverter as a manual charger - OK so far

I checked after about an hour. The output current is down a bit at 2.3A. The NiCd battery string voltage has risen to about 101.3.

Just for the heck of it I started to increase the output voltage of the 12V power supply and I got it up to 13.8V Strange that it would not go over 13.33V earlier. Perhaps the adjustment on the voltage is not as wide when there is no load, or when the power supply is cold? Increasing the voltage to 13.8V raises the output current of the power supply to 36.5A. I tried a bit higher and the power supply shut down. It's close to high current, I guess, so 13.8V and 36.5A it is.

The output voltage is interesting. It is no longer 140VDC but has gone up to 154.4 VDC. Again, it has never been that high during my previous testing. But I was doing my adjustments when everything was unloaded and the electronics had not been running for long so nothing was warm. It is certainly warm now. The tests I did with the 120 VAC loads earlier had much higher current output - perhaps the two are related. The DC to AC inverter does not appear to regulate the DC intermediate voltage well, but the output voltage is very steady at 120 VAC RMS.

The DC output current is now up to 2.9A, and the voltage across the batteries has risen again, to 101.7V. With 71 batteries in series, that is 1.43V each. Still not the 1.45V minimum for doing a charge, and nowhere near the 1.7V I was shooting for, but I guess I'd need more input current to the DC to AC inverter for that as well.

Right now, I am wasting 154.4 - 101.7 = 52.7V at 2.9A or 153W ... over 1/3 of my available charging power, on a toaster to limit the current and allow the batteries to charge at all. I will have to address that, but for now this works. Efficiency is good, but that's an optimization. Things have to work first.

I'm trying to keep focused on the task - I want to test the 5 HP motor again, and that requires charged batteries.
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