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JAG35 Scooter Battery Charging & Discharge Capacity

egandalf

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Jun 25, 2021
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Not sure if this is the right place to ask or not.

I have bought some of the 36v scooter batteries from JAG35. Hooking up chargers (whether wall wart or solar controller) appears to work just fine through the discharge port - with the JAG35 dongles and arduino sending the keep-alive signal.

I have two main problems:

1. Charging via the smaller charge port. If I hook up a small, 2A charger to the charge port, it works fine, but takes about 11 hours per battery from drained (just under 50 watts). If I hook up a 36v/18a golf cart charger to it - nothing. It doesn't even recognize it's hooked up. The same is true of the solar charge controller. Hooking it up to the discharge port is fine but it fails to even recognize the charge port. Is there a workaround? I'm ok disassembling and soldering if that's what it takes.

2. Discharge capacity. I've been testing using these (2-4 batteries in parallel) to charge my Bluetti AC200P and I can get around 670wh from 2 cells when the rated capacity should (assuming 100%) be around 920wh. Seems like a big miss - or is this normal?
 
Since you haven't provided a link to any technical data, I'm just guessing.

1. SCC requires power from the battery it's charging. If the charge port is diode protected, which it probably is, or it otherwise only allows flow in one direction, SCC can't pull power from the battery, so it won't power on.

2. Assuming these are Li-ion 18650 cells, are you certain you're charging to 4.20V/cell?

Is there a built-in BMS?
 
Thanks for replying!

You're right, I neglected to link the pack:

It's a 40-cell 18650 pack with a built-in BMS. I haven't disassembled the pack to check any given cell.

For point one - is there a workaround? Should I jump the diode? Should I simply charge/discharge via the same port?

From what I understand, using the charge port engages the BMS whereas the discharge port... doesn't? This is the charge cable - I've wired 4 in parallel so I can charge/discharge in parallel in both ports. Charge with my custom dongle, discharge with the arduino-included dongle from JAG35.

From the description: "Charging via this cable allows the BMS to use overcharge protection."
 
I suspect that the presence of the two ports is for a separate port BMS. If you try to bypass either, you may disable any BMS protection function.

The packs should charge to 42V and discharge to 25V to capture their full capacity. If you're not charging and discharging to those levels, you can't compare it to rated.
 
I suspect that the presence of the two ports is for a separate port BMS. If you try to bypass either, you may disable any BMS protection function.
Right. Which is why I want to charge through the smaller charging port. However, my two chargers fail to recognize that they can do so. Probably due to aforementioned diode. Is it safe to bypass/remove the diode? Or is there some other hack to "inform" the charger that this battery can be charged.

The packs should charge to 42V and discharge to 25V to capture their full capacity. If you're not charging and discharging to those levels, you can't compare it to rated.

I see. I think I charged to 42 and discharged to roughly 30. So that makes sense. Thanks!
 
Right. Which is why I want to charge through the smaller charging port. However, my two chargers fail to recognize that they can do so. Probably due to aforementioned diode. Is it safe to bypass/remove the diode? Or is there some other hack to "inform" the charger that this battery can be charged.

If it's a separate port BMS, the "diode" function is likely in the BMS circuitry, and you can't bypass it without disabling that feature. Same on discharge.

I see. I think I charged to 42 and discharged to roughly 30. So that makes sense. Thanks!

Not a ton left below 3V/cell, but there might be another 15-20% at a guess.

Hmmm... This video seems to indicate that you can charge via the discharge port with the dongle once the battery is "awake" via the charge port?:

 
Hmmm... This video seems to indicate that you can charge via the discharge port with the dongle once the battery is "awake" via the charge port?:

Yes. That's how I've primarily charged. Can I set up charge / discharge simultaneously through the same port? There's a greater-than-zero chance I'm overcomplicating this.
 
If you can charge via the discharge port, I don't know why the SCC isn't working. I would presume that you can charge/discharge simultaneously. The result of a simultaneous charge/discharge is always either a charge or a discharge. There is only a NET current flow, and the battery will only see a net charge current if charge > discharge or a net discharge current if discharge is > charge.
 
If you can charge via the discharge port, I don't know why the SCC isn't working. I would presume that you can charge/discharge simultaneously. The result of a simultaneous charge/discharge is always either a charge or a discharge. There is only a NET current flow, and the battery will only see a net charge current if charge > discharge or a net discharge current if discharge is > charge.
Super helpful. Thanks!
 
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