I've come across a large number of good laptop batteries containing mostly CGR 18650CG and CGR18650D Batteries, with capacities of 2250, and 2350 mah respectively. Recently our golf cart was left out on low charge in the cold, and many of its lead acid batteries are now dead. Time for a DIY solution...
The cart requires 48 volts at 200 amps when at full throttle (only will do so if on a hill), so by my calculations of a max current of 5A per cell, I would need a roughly 13s40p pack. To do this, I was thinking about making "Modules" that would consist of a 13s bms rated for 20A max discharge current -see link below- along with 13 sets of 4 cells in series.
There's a bit of intellegence to these batteries I would like to add, such as arduino controlled shunts for charge and discharge, temperature, and voltage, these arduinos across modules would be connected via i2c, and a single four pin connector, carrying 5v, ground, sda, sck. The last part is to add a relay that is controlled via the arduino that would shut off the battery discharge lead if the temperature gets too high, or if the user selects that option, the trouble is, the arduino relays are rated for 15amps at 125vac, 25% short of the 20A rating I'm looking for. My thought was just to rig two relays up in "Parallel" where the current flows through both relays, and both are triggered off of the same line. Would this be advisable?
-What is a safe maximum discharge current for crg18650 cells? I've looked on datasheets and found no discrete number, but on the discharge graph, they do pull 4.5A out of them.
-Can one run two relays in parallel to get more current capacity (both relays input and out are tied together)
-What is a low cost connector that is panel mount that can handle 48V at 20A, I found this connector that should fit the bill, but is bulky, and somewhat expensive compared to what I'm looking for: link
-Somewhat unrelated to the EV forum, but could this shunt support 20 Amps of current safely? The PCB does not look like it has large enough traces to do so. http://www.ebay.com/itm/181847127383
-Lastly, do any of you have suggestions of how to do this with 18650 cells? Different BMS? Configuration?
Thanks in advance