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thingstodo · 01-15-2012, 04:44 PM

Can I use the DC/Ac converter as a charger for the NiCd battery bank? At 10.99V input, the output is 118.7V I can use a useless 6V or 12V lead-acid battery in series to 'drop' the voltage. It's worth a try. Using the 40A 12V power supply as the input to the inverter and adjusting the output to float where the batteries should be when the NiCd are 'full' will do a slow trickle charge. It's not the way it should be done - Saft recommend 0.2C for charging. That's 0.2 * 39A = 8A. Also recommended is 1.45 - 1.7V per cell. That sounds high so I guess I'll check - maybe I can't even charge the whole string with 140 VDC. 140 / 1.7 = 82. 140 / 1.45 = 96. But there is 71 - which would be 103 - 120.7 volts. Add 13.8V for a 12V battery - that gives 135V. Add another 13.8V for another 12V battery - that gives 148V. No way to adjust the current so I hope that it is somewhere around 8A. I can drop the voltage on the 40A power supply down to 11.06V and get an output of about 120.2V ... I guess we'll find out.

I adjusted the power supply down to 11.3VDC, which appears to be as low as it goes with no load. It remains at 11.3V when connected to the DC/AC inverter. The output voltage is 140.4V out of the DC section of the inverter, with no load.

I connected all of the NiCd cells in series. They were very discharged (to the point of battery abuse. It's been a while since I looked that these). They should be nominal 1.2 V per cell, or 85.2V and they were at 69.1V. Actually, they were lower than that. Several cells were at 0.5V which is far below fully discharged. None were 0V. In the time it took me to connect the cells together and check them a couple of times, the voltage rose from the original 55V (adding up the individual cell voltages) to 69.1 so I expect that the temperature rise from -5C outside to 15C in the garage helped a bit as well.

I connected the 140 VDC across the NiCd batteries - and the inverter shut off. Could be over-current and could be under voltage on the input. I guess it was too much load. No fuses blew.

I added a mostly-charged but still unservicable lawn tractor battery in series with the string to limit the current. The lawn tractor battery is not serviceable - not enough current delivered to turn the starter - and I have not traded it in yet so I'll use it as a current regulator. It's worth a shot.

The lawn tractor battery worked too well. There is a drop of 30VDC across it and the charging current does not register well on my clamp-on meter. Somewhere between 0.2 and 0.3 amps. Even after an hour, the current still has not risen. The voltage across the NiCd pack is up to 101V, which is 1.42V per cell or the minimum recommended floating charge voltage. I was looking for at least 4 amps, and would have liked 8 amps. Something about stirring up the electrolyte with bubbles?

01-15-2012, 04:44 PM	#47 (permalink)
thingstodo Master EcoModder Join Date: Sep 2010 Location: Saskatoon, canada Posts: 1,488 Ford Prefect - '18 Ford F150 XLT XTR Tess - '22 Tesla Y LR Thanks: 749 Thanked 565 Times in 447 Posts	DC to AC inverter as a battery charger? Can I use the DC/Ac converter as a charger for the NiCd battery bank? At 10.99V input, the output is 118.7V I can use a useless 6V or 12V lead-acid battery in series to 'drop' the voltage. It's worth a try. Using the 40A 12V power supply as the input to the inverter and adjusting the output to float where the batteries should be when the NiCd are 'full' will do a slow trickle charge. It's not the way it should be done - Saft recommend 0.2C for charging. That's 0.2 * 39A = 8A. Also recommended is 1.45 - 1.7V per cell. That sounds high so I guess I'll check - maybe I can't even charge the whole string with 140 VDC. 140 / 1.7 = 82. 140 / 1.45 = 96. But there is 71 - which would be 103 - 120.7 volts. Add 13.8V for a 12V battery - that gives 135V. Add another 13.8V for another 12V battery - that gives 148V. No way to adjust the current so I hope that it is somewhere around 8A. I can drop the voltage on the 40A power supply down to 11.06V and get an output of about 120.2V ... I guess we'll find out. I adjusted the power supply down to 11.3VDC, which appears to be as low as it goes with no load. It remains at 11.3V when connected to the DC/AC inverter. The output voltage is 140.4V out of the DC section of the inverter, with no load. I connected all of the NiCd cells in series. They were very discharged (to the point of battery abuse. It's been a while since I looked that these). They should be nominal 1.2 V per cell, or 85.2V and they were at 69.1V. Actually, they were lower than that. Several cells were at 0.5V which is far below fully discharged. None were 0V. In the time it took me to connect the cells together and check them a couple of times, the voltage rose from the original 55V (adding up the individual cell voltages) to 69.1 so I expect that the temperature rise from -5C outside to 15C in the garage helped a bit as well. I connected the 140 VDC across the NiCd batteries - and the inverter shut off. Could be over-current and could be under voltage on the input. I guess it was too much load. No fuses blew. I added a mostly-charged but still unservicable lawn tractor battery in series with the string to limit the current. The lawn tractor battery is not serviceable - not enough current delivered to turn the starter - and I have not traded it in yet so I'll use it as a current regulator. It's worth a shot. The lawn tractor battery worked too well. There is a drop of 30VDC across it and the charging current does not register well on my clamp-on meter. Somewhere between 0.2 and 0.3 amps. Even after an hour, the current still has not risen. The voltage across the NiCd pack is up to 101V, which is 1.42V per cell or the minimum recommended floating charge voltage. I was looking for at least 4 amps, and would have liked 8 amps. Something about stirring up the electrolyte with bubbles?