Smoker said:
Thanks for the reply
No prob -- always happy to help somebody not blow up their bike. And if you're looking to blow it up, Fechter's the expert.
When looking at that thread you made, I noticed a power strip with a buttload of ac adapters, are those for charging your ebike batteries?
Yes. There's 20 of these single cell chargers plugged into the strip -- one for each 15-cell parallel subpack.
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1231
If so what is the output voltage and do you charge your cells directly with them?
4.20 volts. This is the normal charging voltage for any lithium-ion, lithium polymer, or lithium manganese cell. Yes, the chargers connect directly to the batteries. I don't use any sort of BMS (battery management system, i.e. a little board with balancing/cut-off circuitry).
I'm thinking about buying 10 of these batteries. Converting each 12 cell battery to a parallel configuration for 3.7V and charging each "battery block" independently. Is this the optimal solution?
I think so. Some people prefer RC chargers -- but some of those have been known to misread the cell count, resulting in catastrophic overcharge. It's virtually impossible to overcharge lithium batteries with a single cell charger since when the cells are topped-off at 4.20 volts, the 4.20 volt charger doesn't have any more voltage to charge the cell any farther.
and when charging could I parallel all 10x 3.7v batteries?
Yes. Lithium cells wired in parallel act like one larger cell on both charge and discharge.
Or would it be wise to keep the batteries in their current 11v pack and try to charge them by finding 11v and ground in the "tabbed grooves" and slow charging them with around 13v?
If it was me, I'd pull all the cells out of their packs one-by-one, then load test each cell. Out of 300, I've had a couple bad cells. Then I'd rewire my 120 cells into parallel subpacks, each with its own charging leads, then wire those parallel subpacks together in series to get to the voltage I wanted.
What would you do in my situation?
In addition to the above, I'd first decide how many cells I needed in parallel, which since you're buying a fixed number (120) will determine how many subpacks in series. These laptop cells are only good for about a 1 to 1.5C amp draw. Let's suppose you've got a 35 amp controller (I don't know your kit's controller amperage offhand). Then in my experience you'd need at least 12 cells in parallel to safely provide the 35 amps (for 2200mah cells this provides a 1.3C max drain rate...2.2ah X 12 cells = 26.4ah subpack...35 amps / 26.4ah = 1.3C). I'd build 10, 12-cell parallel subpacks and wire those in series for 42 max volts (37 volts nominal).
If used without a BMS, cell voltage must be carefully monitored. These cells will overheat and die an ugly death if discharged lower than 3.70 resting volts. I killed part of my pack that way in early testing. So I'd use either the CycleAnalyst
http://www.ebikes.ca/drainbrain.shtml
or a voltmeter on my handlebars and quit the ride by 37 volts (37.5 - 38 just to be safe). I'd also take along a voltmeter for the first few rides at least and stop along the way to probe each subpack's voltage via its charging port to make sure all subpacks were draining at the same rate -- if one or more drained significantly faster than the others, I'd know either I had dud cells, or cells that weren't making a connection.
I don't know what your packs look like, but they may not have nice soldering tabs. If not, resoldering is more challenging.
Any dud cells can be replaced with other 18650s of the same capacity, like the 2.2ah ones I use:
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1643
If you decide to do this, keep us updated and if you like I can help you more along the way. These are great batteries for making a poor-man's lithium pack, but they're dangerous if mistreated, and they require some kind of monitoring to make sure each subpack's voltage goes no higher than 4.20 volts, and no lower than 3.7 volts -- when under full electrical load the voltage can go lower, but it's easiest and best to measure their resting voltages.
Here's a pic of a 12-cell subpack I destroyed. Note the ruptured cell in the top row.
