JK/Heltec smart BMS

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Last seen: 4 days 23 hours ago
Joined: Monday, August 19, 2019 - 05:37
Points: 11
JK/Heltec smart BMS

I have recently learned about an interesting 24S 200A smart BMS and active cell balancer available for under $200 (US): the JK-B2A24S20P, also sold as the Heltec 1026. Settings can be changed and cell voltage monitored via Bluetooth using an Android or iOS app. Of course, because gen1-2 LEAF modules are 2S2P, an 18-19 module pack would need 36-38S, or two of these BMS boards. At that point, it might be simpler (albeit more expensive) to buy a Vectrix universal BMS for $600+ shipped to the US.

Now's the part where I admit that I don't know very much about BMS hardware and what is compatible with what. Could this setup handle the 130V+ of our pack? I assume the 200A model--the highest available--is what we want because that also aligns with the 200A fuse (upgraded from the stock 125A) that's installed in a lot of our bikes.

The JK BMS is also CAN-capable and has a GPS port on it. The former certainly seems relevant to our usage, but I haven't been able to find much information about how that all works. Perhaps antiscab's Zeva BMS install video can help identify how the JK BMS might integrate with the Vectrix.

Most of the information I've found about this hardware pertains to DIY solar PV systems:

Any thoughts on using these JK BMS units? Worth the effort? I'm awaiting the arrival of the same cheap 20S balancer that israndy bought (~$15 each + shipping from AliExpress) until I can figure out what way to go for BMS. Of course, I wasn't paying attention and forgot to order two of them for my 38S setup...

UncleMike1's picture
Last seen: 2 weeks 2 days ago
Joined: Friday, October 29, 2021 - 08:35
Points: 21
Re: JK/Heltec smart BMS

I build a lot of batteries for e-bike and electric scooters. The Amp rating on the BMS is related to the current in and out of the BMS, current out being the greater of the two. I generally select a BMS capable of handling 2x the Amp consumption calculation. Since we have a Peak Wattage from Vetrix, we can use that and size slightly above.

The current I in Amps (A) is equal to the power P in watts (W), divided by the voltage V in volts (V): I(A) = P(W) / V(V)

For a VX-1, the motor is rated at 11kW with a peak of 35kW. The safest measure for us will be to use the Peak. For Volts, we use the nominal rating of 125v.

35,000W / 125v = 280Amps or you can use the calculator at https://www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.html

300Amp would be safe sizing for the BMS. What happens when you undersize the BMS is when the motor is under strain, going uphill or multiple riders etc, the motor will draw much more and the BMS will just shut down.

The alternative is to use the BMS only for charge in which case you have to measure input power and not output. The trade-off is you sacrifice high temp and low voltage cut-off features that keep the cells from being damaged during normal operation. If you only ride short distances at lower speeds, the risk is pretty low.

2007 Vectrix VX-1 Work In Progress

Last seen: 4 days 23 hours ago
Joined: Monday, August 19, 2019 - 05:37
Points: 11
Re: JK/Heltec smart BMS

Thanks for the info, Mike. Still trying to understand how this all works.

Worst-case-scenario amperage for me would be 35,000W at 136V (just above the 135V point at which Team Laird's 19-cell firmware goes into limp mode) = 257A. I suppose I'd be more likely to be using max motor power (highway speeds/hills) toward the top of the SOC (e.g., 35,000W/150V=233A). The JK BMS is rated at 200A continuous and 350A max, so I suppose that doesn't give enough margin when riding at higher speeds/loads.

It looks like Vectrix's universal BMS connects with both the charger and the motor controller, so I suspect that means it is not charge-only BMS protection.

2007 Vectrix VX-1 (19 gen2 Leaf modules, ESD charger)
2013 Nissan Leaf SV

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