andychrist

What’s the risk, unless one is really inept at wiring?

I run two 52V Luna DireWolf 21Ah packs in parallel to power my dual 48V 500W Bafang hub drive cargo e-cumbent so that the batteries drain evenly and take the same amount of time to recharge (on my two Luna 52V Advanced 300W Ebike Chargers). No problems (so far! )

Rick CA

Yes Doc, I was referring only to the capacitors within the controller, not battery. They are obviously sealed within the controller housing so after the install I would not be concerned for any accidental contact. It currently has 63V capacitors. Best I can tell from online research, the 100V capacitor upgrade should not adversely affect the overall controller while likely smoothing out the voltage at the controller that tends to sag because of the voltage drop of the wire between the battery and the controller.

base2 

I really don't understand why you are so stuck on keeping this controller. It is only rated at 22amps & you are asking it to do 31.25+amps It is only 70% as big as you need. You are asking it to do 142% duty.

You wouldn't take your car engine rated at 6500rpm and ask it to do 9233rpm, would you? It's the same thing, literally.

Buy the proper controller with a minimum continuous duty of 35 or 40 amps current.

Rick CA

All interested:
I had some unrelated setbacks affecting my available time to experiment on my long term solution. Running the batteries in parallel was just my idea to learn if I could resolve the "sag" hypothesis with items on hand; it was not intended to be a final solution. If the sag (LV cut off) condition is eliminated then I can focus strictly on the power supply/battery. However, if the problem persists then it may still be a supply shortcoming of the LiFePO4 cells, or its then the shortcoming of the controller. Either way it costs me nothing to start with the parallel battery testing. I am eager to start building custom battery packs and while I've learned the LiFePO4s are not ideal for the ebike application, I do have (nearly new) three 48v 18ah LiFePO4s by which to (safely) experiment with...otherwise I'll be looking to sell them used on eBay. I'm not committed but my plan is to break them into two new custom packs: 52V 20Ah+ and only run one "new" battery on each of my two 1500W fat tire bikes...and pray that's enough to give me the performance I'm seeking.

Pop N Wood

Because of the issue of battery balance. Put them in parallel and you now have one large battery, but separate BMS controllers.

Good to hear it is working for you

Rick CA

I hear you and yeah, that's a logical path...BUT, as I mentioned before, this is a hobby and a journey. I enjoy tinkering and I have basic skills like soldering...and just about every tool you can imagine. Simply buying a new controller (if it's not absolutely needed) is not my style. What I have learned in the past few weeks is that what is labeled on the outside of a controller is not always what's factually found on the inside. But if a new controller is needed I will figure that out soon enough. Right now I'm seeking knowledge and this forum has been great for that! So If I can educate myself and learn a few new skills, which also entertains me in the process, that's a win! I'm hopefully bright enough to know when to say when; you know, that point of diminishing return. Until then I'm having fun and enjoying the process. Thanks amigo

Rick CA

If all goes well, this is my 10th post and I'll be off newbie probation =]

Doc_Wui

My opinion is that if the controllers were sold with the motor, they're matched. or it would be never ending grief for the seller. I also believe that they're really 1000W kits. However, the fact remains is you're shutting down.

This is not happening freshly charged is it? Did you ever report your full charge voltage? What's the rest voltage on the system when it does shut down.

While running parallel is never fool proof, if you ensure the packs are the same voltage when connected, I don't see a problem with a simple test run.

Pick up a $15 RC wattmeter when you have a chance, It will show you the miniumum vottage and peak amps, and you can easily tell if you hit LVC as well as the maximum current your bike/battery can supply,
,

Rick CA

1. Yes LVC happens at full, fresh charge
2. Full charge is 53V+
3. I can induce LVC as soon as I accelerate quickly on a fresh charge and reset shoots right back to 53V.

I can monitor the voltage on the LCD display as I ride. I can watch as the volts quickly drop as throttle is applied and when I reach 40V the motor cuts out. I release throttle, volts climb quickly on the meter and I can see the 53V resting state. I’ll look into the RC wattmeter, thanks for the tip! I do believe it’s a combination of the battery sag, which induces the controller to activate LVC. Hopefully by eliminating the sag I can avoid LVC. In the garage now, wish me luck! I’m balancing my two batteries (will ride one bike until I get the batteries at same level) before I connect in parallel. I need to create a harness so all will be connected with XT90S... and hope to have some results soon. Thanks again

Rick CA

Initial test complete and I will call it a success. Now, it would have been cheaper to correct if this was simply a controller problem (either by upgrading what I have or even to buy a new controller), but indeed the problem was battery sag.

I ran the LiFePO4s in parallel and had no low voltage cut off in testing with several riding conditions. Even from a dead stop I could activate full throttle and the motor ramped up (much tamer than I expected, too) and never cut out while cruising to full speed of nearly 30mph. I still plan to use all the “tools” you guys offered in this thread as they will be used throughout my development.

If I can somehow repay you all for the goodwill, please don’t hesitate to shout out.

2old

Excellent ascertaining the origin of the problem. Helped us in the process.

Pop N Wood

Yes, I had no idea about the limitations of LiFePO4s batteries. I can see why they aren't very common anymore

By the way, any idea what your bike weighs with both battery packs? 18 ah packs have to be pretty big.

I hear you on wanting to tinker. My coming project is converting a car alternator to a motor. See how long it takes me to burn something up.

Rick CA

Each battery weighs about 11lbs. I don't have an exact weight but I've lifted this build several times for various reasons. I'd say total weight single battery was about 50lbs, so maybe 60-ish when I rode it with the two? I've attached a coupe pics. I've already taken the batteries out of parallel. For the test ride I was able to strap the second battery on the frame tube just in front of the primary batt position; it was adequate for testing. Overall (now that I understand the LVC situation) I'm happy with this fairly custom conversion. I bought three of everything (bikes, conv kits and batts) and in total each bike will have cost me just under $750, to include rear cargo rack, riser bars (replaced flat bars for comfort), dual torque arms, LED headlight (not installed yet). Granted, it's a cheap fat tire bike with budget components, but really all I need for the riding we will be doing.

gsa103

If the batteries are imbalanced, when you connect them in parallel they will re-balance INSTANTLY, and draw VERY high current during the process. A 2V imbalance in the battery packs can result in 100A of current flow. I have no idea how the BMS would cope with the backflow, you'd have to check a typical data sheet.
I work with drones and RC aircraft. They have battery balancing jigs with high Wattage resistors to safely balance packs before connecting in parallel, 5Ohm, 10W is about right for mild imbalance. Those who don't, very quickly blow up batteries. Now, those are completely unprotected LiPo stacks, that have the lifespan of fruit flies. I'm sure a Luna pack is more robust, but you need to be very cautious unless you have something to regulate the balance.
Diode bridges can be used, a switch to select an individual battery pack, or even a 50W, 10Ohm resistor connecting the positive leads.

What you're doing with parallel charging and parallel connection is marginally safe, but it's not idiot-proof (unless you're sure the BMS protects you). If you accidentally ever get the batteries out of sync and connect them, you're risking a huge fire.

Pop N Wood

Those bikes look like a lot of fun. Sort of a rebel without a cause look with the fat front tire. Put some ape hangers and a Marlon Brando cut out on them.