Quote:
Originally Posted by vlad
I want to have them configured in 7S configuration. So, I will take some modules apart to extract individual cells.
The reason for 7S is here. I bought an efficient 24V 200 Amp military grade alternator (American Power Systems 55i-200ACT-28J). Nominal voltage is 28V.
I want to use a small diesel engine/alternator to directly charge 7S pack. 7s pack has a safe voltage of 4.2x7=29.4 V making some room from 28V charging voltage.
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I don't recall where I saw the video - likely on youtube somewhere - but the cans that hold the cells are kinda like sardine cans. You cut the seam to get the cells out and can't re-use the cans.
Most alternators use a regulator to limit the output voltage - I have no experience with this one, so I may be off base. If you are controlling the rpm on the diesel engine, you may be able to adjust the output of the regulator (or replace the regulator with an adjustable one).
I'd investigate that before splitting the cans up. You will have a bunch of cells in parallel anyway, so whether they are 2s2p inside the can should not be a big deal. If you are using off-grid inverters to boost the 28V to 120V, my experience is that they will take over 30V as input (8S) but will operate at 24V (6S). At 6S, since a lot of them assume Lead-acid battery packs, the inverter may shut down around 21V (3.5V per cell .. a bit high).
I have charged my Renault/Better Place pack to 4.1V as an average for each cell. I tediously bottom balanced the cells ...
- 4 cans in series, 12 cans in parallel
- connect a sinewave inverter to the 16.4V output that put the power into my house
- When the voltage dropped down to 15.9V for the 4S I got a modified sine wave inverter working and drew down the pack with one 1200W heat gun
- when the voltage dropped down to 14.8V I got a second modified sine wave inverter working and drew down the pack with a 12ooW hair dryer
- when the voltage dropped down to 11.5V, one 12P set of cans had the bottom set of terminals at 2.75V
- Turned off the hair dryer, voltages rose across the board
- ran the heat gun until 2.75V on the lowest set of cells
- turned to low heat and ran for a while longer, then stopped.
- Batteries bounced over 3 V with no load - very spoungy.
- Added another battery in series (LiPo4 CALB) to boost the output voltage and used a 250W inverter to draw down more power
- When drawing less than 10W from the inverter, I stopped.
- hand-trim the cells to 2.750V +/- 5 mv
I got maybe 55 A-h from 4.1V to 3.0V. The car is not on the road yet so I don't have any more data ... there is some debate on the forums whether charging to a bit less than 100% and discharging to 20% in worst case will result in a few more charge/discharge cycles.