xm3500li added battery

Iccarus's picture

I recieved my 3500li in september but it was damaged in shipping, so I had to refuse shippment.(that wasn't easy I wanted it bad) so I waited for my friend to get his. His came with slight chafing on right side of cowling (mine had hole worn clear through)but we accepted it. It works well but only does about 45mph stock. The first thing we did was replace all the lights with LEDs and added a switch so you can turn off the main headlight to save power. We haven't found an LED replacement for the main. Then we moved the breaker under the seat so you can remove the storage compartment for easy battery access. As I've seen posted a BMS is definatly needed. Some cells were getting significanly out of balance after a few charges. We are using balance pro balancer/monitors from commonsense rc. They can balance up to 6 cells per unit so you need 4 to handle 20 cells. You need to order leads also that the balancers plug into. These must be attached to all the batteries it's a bit of a chore but well worth it. Then we bought four 22.2v 10AH lipo batteries from a hobby supplier. These are then wired in parallel and hooked up to the system. they fit under the seat in the front part of the battery compartment,on top of the stock batts.(padding under and around them) Now you have added 22.2v to they're 63v-66v pack. Both being 40AH there is not a problem with uneven draw.This gives you about 88v@40AH we have gone through 4 charge cycles and have had no problems.(you have to charge the four 22v lipos using a differant charger...more$$$) The battery gage on the bike seems to work but drops rather quickly when getting low. We checked all cells after running and none were undervolt even after running the bike till it stopped. The bike did 57mph and we went 32 miles at mostly full speed with a little bit of 45mph and lower.We estimate 100mi range at lower speeds(estimate kind of pulled out of you know where though) We will do more testing and post results. The 22v 10AH lipos were $300 apiece ouch!But progress can be expensive I guess. Thanks for all the great tips I've been reading this site for months now!
Bill-

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reikiman's picture

I found commonsense rc - My question is that the only balancers I found on that site are for "lithium polymer". The cells in your bike are LiFePO4 and have different voltage thresholds than the normal "lithium polymer". The instructions I see at commonsense rc for their balancers do not say whether this accomodates the different thresholds for LiFEPO4.

Iccarus's picture

I think you're worried that the high voltage threshold on the lifepo4 could be exceeded when charging...because the treshhold on the polymer batts the commonsense rc balancers are used on are higher. However I read that thundersky says you can go to 4.25v.(I know other stats list it at 3.6v to 3.9v) I have seen up to 4.23 on individual cells using the stock charger. The balancer is already bringing it down at that point so I think it's doing it's job. The main thing is they keep each group of 5cells they're attached to within .05v of each other.so each group of 5 is separate and isn't balanced with the others, but they are staying within tolerance right now. You may have to leave them on overnite as they work pretty slow when the voltages get close.They also sell a balance pro+ I don't know what the + means but the balance pro can handle up to 6 cells and cycle through a digital readout of each cell to within.05v and green lights show which cells are balancing. They are about $40 each. Let me know if you hear of a better system. our pack fully charged is 93v@40AH and we get 57mph and about 32miles at that speed. I know Mountain chen says we may burn up the motor but so far so good. the dc to dc converter is handling the load and the hub motor is barely warm after long runs (5 to 10 mi.)
PS using a voltmeter the balancers only seem to be accurate to about .05v but they seem to be doing the job. I think it's a good idea to balance BEFORE and during charging to increase battery life.

2008 XM3500li Mods/Kelly KBL12251/84v 28cell 40AH pack/ Variable regen brake trigger on left brake handle/Givi/Cycle Analyst/Homemade BMS

KMX Typhoon Home build (recumbent pedelec) with two Astro Brushless 3220motors/twin castle Phoenix ICEHV 160/ Cycl

Iccarus's picture

I thought I would post the latest on our xm3500li mod. The bms seems to be working fine. When used during charging none of the cells get above 3.9v. (at first we were balancing after charging. Thats why we got some up to 4.23v)all cells are within .05v and as for low voltage. We tried leaving the bms hooked up and runnig the pack down and the balancers turn off well before the low voltage cuttoff in the speed controller trips. So if you forgot and left them hooked up you don't have to worry about the bms monitor LED's in the bms draining the cells to the point of damage after draining the pack. I may sound like I'm suffering from balance paranoia but lithium batteries aren't cheap.

Bill-

2008 XM3500li Mods/Kelly KBL12251/84v 28cell 40AH pack/ Variable regen brake trigger on left brake handle/Givi/Cycle Analyst/Homemade BMS

KMX Typhoon Home build (recumbent pedelec) with two Astro Brushless 3220motors/twin castle Phoenix ICEHV 160/ Cycl

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