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Old 01-13-14, 01:48 PM
  #43  
turbo1889
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Location: Montana U.S.A.
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Bikes: Too many to list, some I built myself including the frame. I "do" ~ Human-Only-Pedal-Powered-Cycles, Human-Electric-Hybrid-Cycles, Human-IC-Hybrid-Cycles, and one Human-IC-Electric-3way-Hybrid-Cycle

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If they can take 5A per cell with no problems then your plan of using 3 cells in parallel by 13 in series sounds good to me (13s3p configuration).

As to charging, I've never tried to build a variable resistor charger like you are doing, I've just always used a charger or power supply circuit that provided my desired voltage straight out. Can't say it wouldn't work, but can't say it would either since I haven't done it. I've done a lot of parallel charging but I always used a charger/power-supply at the desired voltage instead of trying to use a variable resister like you want to do to step down a little higher voltage source. I always just matched to the desired voltage.

As to voltage tolerance range an extra cell or two won't cause problems with the motor usually, it's the controller that dictates that, does it have an absolute max voltage rating printed somewhere on the outside of the case? and if not then does the outer shell cover easily unscrew so you can read the max voltage rating on the side of the big capacitors? That is usually your top end limit since when stepping up the voltage beyond specs its usually a capacitor that you blow as the weakest link inside the controller as far as increased voltage is concerned. For example, I've seen 60V rated controllers that if you pulled the outer casing off of them the big capacitors on the inside (fairly obvious since they are one of the largest physically sized components often large round cylinder shaped) were rated for a max of 80V and that explained why people were getting away with running those controllers a little hot without problems. Always be extra careful when doing something like this and opening a cover to check the guts on a controller for stuff like this. And it's always the peak top charge voltage of your cells you compare to what the capacitors are rated for.

If you get lucky you might find capacitors inside your 48V controller that are rated for a little over 60V peak which means you could use 45-cells to build your pack in a 15s3p configuration consisting of five seperate 3s3p partial packs that could be charged direclty off of your 12V power supply reaching a peak "fresh hot off the charger" voltage of 4V per cell which would make for 60V "fresh hot off the charger" which would drop down to a normal voltage of about 55.5V after the first couple minutes of use and would make charging easy as well charging the cells in strings of three in series straight off the 12V power supply you have. Obviously that would be running the controller and motor well over design specs, the motor would probably take it, the big question mark would be whether the controller could, might and might not. It would be a risk and a calculated gamble. Less of a risk and gamble if you could confirm that the capacitors inside the controller were rated for a little over the 60V "fresh and hot off the charger" voltage that would be put out for the first couple minutes of use until the cells settled down to their nominal voltage in use. I'm not sure I would take that kind of a risk and attempted over volt "hot rodding" of the system on a first build especially. It's just you asked so that's my thoughts on it and I personally wouldn't even attempt going more then one cell over voltage without checking the capacitor ratings on the inside guts of the controller.
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