Adding a second auxiliary battery pack to the existing stock pack.
Need some help/advice regarding a project to increase the range of my new Giant Quick-E bike. The stock integrated battery is 36 volts and 13.8 AH. Depending on conditions the expected range is between 40 and 80 miles. So far my experience is that these estimates are quite realistic. I'm a big guy of about 240 lbs and if I use the highest power setting I'm getting right at 40 - 45 miles. If I'm more judicious and only using levels 1 or 2 I've gotten 75 - 80 miles on a charge. I've completed the 10s10p pack using 100 LG MJ1 3500mah cells. The result should be a 36 volt, 35 AH battery. My plan is to wire it in parallel with the stock battery which will give me a 48.8 AH total. I'm using a weather proof junction box to house the 36v 10s BMS as sold by Vruzend and all the other connections. This box also houses the charging port for the auxiliary battery pack. I've identified the main positive and negative leads coming from the battery connector socket for the integrated but detachable battery and will run 4 gauge 364 strand copper cable from the motor/controller housing up to the junction box for the auxiliary battery pack. A run of almost 3 feet. I will use the Giant supplied 3 amp charger to charge the stock battery, and do so with it removed from the bike to prevent any incompatibility with the Cycle Satiator charger that will be used to charge the new auxiliary battery pack. The new battery will connect to the existing battery, negative to negative and positive to positive prior to the existing motor controller. With my limited understanding of such things I'm assuming that essentially the new battery pack simply increases the ampere hours of the existing battery. The voltage remains the same. I have not connected the P- lead from the auxiliary pack's BMS to anything. Essentially only using the BMS to keep the auxiliary cells balanced during the charging phase. Remembering that the two battery packs will be charged independently, and that I will verify that both battery packs are charged to the same voltage before reconnecting them to one another. Does anyone see a problem or issue with this arrangement.
Thanks Kyletom415. I've attached the wiring diagram. The various connectors are used to isolate the two batteries during the charging mode. So far, this configurations seems to be working for the most part. I have added a voltmeter which is not shown in the diagram so that I can both, monitor the system voltage, and also monitor each batteries voltages prior to connecting them together after recharging. Checking those voltages prior to connecting them ensures that they are close to equal to prevent excessive current flowing from the higher voltage pack to the lower voltage pack. The only problem so far is that the BMS that I added to the auxiliary didn't survive "the smoke" test when I first hooked it up. I don't know whether I miswired the balance wires or one of the other BMS leads or whether the the BMS itself was defective. Temporarily, I've removed the BMS and have been recharging the auxiliary pack without one. Just received a new BMS and will shortly double check the balance leads from the auxiliary packs and wire the BMS into the system. Overall, I'm pretty pleased with the modification. It appears that I have close to tripled the range of the bike given similar ride characteristics. But it's a little hard to resist the tendency to use higher power levels than I would have with just the factory battery alone.
Looked at your wiring schematic.
When you separate the battery packs to charge them, it's good that you check your voltage across both packs before you connect them. If the voltages aren't equal, I'd suggest getting a heavy duty power resistor and connecting both battery packs in parallel with the resistor in between.
Is there a reason why you just don't charge both batteries together with only 1 charger?
What's "the smoke" test? and out of curiosity, which BMS did you buy?
The charger supplied with the bike is a 3 amp charger and is not customizable as to maximum charge voltage or charge amperage. And it charges the much smaller capacity stock battery. I chose the second charger because I could program it to match the full charge voltage of the stock charger and it was capable of up to 8 amps of charging current. I currently have it programed to stop charging at 41.5 volts which very closely matches the stock charger's cut off. I've also limited it to charging at 5 amps reflecting the fact that the auxiliary battery pack it is charging is 35 AH as opposed to the 13.8 AH stock battery pack. Admittedly, the larger Cycle Satiator charger could handle both packs, but I felt it would be better to keep the stock charger and stock battery together. In addition, using both chargers simultaneously results in a shorter overall charge time.
The term "smoke test" was simply an attempt at humor, meaning when I first connected everything, a wisp of smoke started rising from the BMS after a few seconds. On inspection, it was evident that one of the MOSFETs in the BMS had been burned up. To be honest, I have to admit that I don't quite know just how the BMS functions and I only intended it to be used for its ability to balance the cell voltage during the charging process. And I only connected the BMS balance wires, B-, and C- wires, feeling that the P- wire would not be used as I would rely on the factory motor controller to control the current to the motor. My assumption was that since the P- wire was not used to provide voltage to the load, I could just leave it unconnected. Instead, the negative lead from the auxiliary battery connected to the B- lead from the BMS and the negative charger lead, and the negative lead from the stock battery.
The BMS used was the one ordered from this website for a 10s battery. I don't know if there is such a thing as a BMS that ONLY handles balancing of the various cells. But that is what I'm trying to do. Another alternative might be to invest in a charger with built in balancing functionality, but I haven't found one capable of balancing a 10s pack. 4s and 6s, yes. But not 10s. If you know of one, I'd be glad to get that information. If I could find one, even if it was a much lower amperage charger, I could use it every 10 charges of so to insure that the individual cells stay balanced.
Feel free to ask about anything else you need to know.