Bms for lithium

I’ve been having some issues with charging my Bosch lithium batteries when they are hooked up to bms. Not sure if I have it hooked up correctly.
Here is my bms setup


Here are the batteries. 20s bank charging to 84v

With the bms hooked up it seems to balance the batteries just fine. But when I hook the charger up through the bms it does not send any current to the batteries. If I hook up the charger straight to the battery bank bypassing the bms it charges just fine. I have the bms hooked up like the diagram shows. Any ideas?

Seller argues this is the correct bms for the Bosch batteries but it looks to me like these are for a 20s lifepo4 pack.

It’s either wrong or marked wrong. A 3.2v bms will balance 3.7v batteries but won’t allow charging over 73v.
Is your battery below 73v?
Are you planning to connect load as shown? As it’s only 60 amps.
This is a problem with dumb bms. There is no way to monitor cell levels, cell number, battery type, or even know if it’s working.
No reason the correct bms shouldn’t work for you. Have them replace it with a 72v model.

Is this from China or the “Bosch guy”?


Yep I think the guy I bought the batteries from pulled a fast one on me. Or didn’t know the difference. But I do see that they make these up to 200a constant. Would that be enough to hook up the discharge side on a gem car?

No, need 300a minimum, and i’m not sure if that will stand up to hot-rodding.
Nothing wrong with charge protection only.
Not a big deal. I think the one I pictured is like $50.

I know its too late for you but to anyone else reading this TALK TO INWO BEFORE YOU BUY! Dave sold me only what I needed, answered constant questions before and after the purchase and no matter what it is I’m doing next, he’s there to help. I don’t know who you bought these from so this might not apply, but there are guys on here and ebay that don’t care at all about your success, they just want to take your money. Avoid them!
Concerning 300a minimum, I have a 300a BMS and I have hesitated to connect it to the discharge path as I have had very occasional surges over 370a when monitoring via Sentry software. It will probably handle those blips but I’m not ready to fry it just yet.


Answer to pm.

To increase ah and kWh, more modules can be added in parallel.
Parallel modules cell to cell with balance leads.
This continues the practice of paralleling cells in the module themselves. Ie, a 60ah module may be made up of 3 pcs 20ah pouches welded together.
This forces all three to stay perfectly balanced. Even with slight differences in capacity or ir.
It is actually a good thing, as it averages out.

In your case connect balance leads from each 20s battery. Simply connect them like to like and then to bms.
Good practice connects the neutrals with heavier cable. I can explain later.

It won’t fry it. It will trip to protect itself, if not turned up too high, or too long a delay. It’s really nice to read amps from the dash. I love these bms.
The monitored armature current will not match bms current.

@Inwo I didn’t know it had that level of self protection. I guess that’s what that setting is for, to shut it down. That’s good to know. I’ll look into wiring it in soon.

So if I did a jst xh connector on the balance leads of each battery, and then used something like this, I could use just the one bms for a 20s2p pack?

Does the Bluetooth bms you sell come with any connectors on the balance leads?

In theory yes.
If it was me, I would have the balance leads from each set terminated in a terminal strip. Connecting them one at a time. B- to B- . 4v to 4v. 8v to 8v. Etc.
Then connect the free end of the xh wires to the terminal strip.

Or do the same twisting and soldering. Cover with wire loom to clean up.
Bms comes with 1 meter leads.

What do the Bosch leads look like?

I have looked but cannot find them online so far

the black connector and the grey connector are different

Measure the pitch of the pins. I think a generic header will plug in.

Getting the bms wired for you.


MVC-004F MVC-005FMVC-007F

Awesome! Will it come with leads soldered on for b- p- and c- if it has it?

Never mind I see them in The pic now. I like your idea of running everything to terminal strips. Do you have any nice water resistant ones you recommend ?

This is yours.
See leads. It is charge-discharge same. So connect B- to B- and load to C- .
I changed to 20s. Should be plug and play.
The usual Chinese warranty. If it quits, send it back to China.
Email me for android app, or download from anywhere. Several available.
4 temp. sensors and balance leads included.
The red fused wire powers bms and lcd.
RJ-45 is not an approved option. My own idea. At your own risk. Route away from power wires. They make shielded cat-5 if you want.

To test lcd, bluetooth etc. Connect 24v to 100v to B- and fused lead.

Long press bms button.
Press lcd button for display.

Ok I had some time to hook up the bms. I cannot get it to discharge. Am I missing something?

when I first power it up it only shows voltages for 20 cells which is correct. After a few minutes a reading for cell 21 shows up and changes voltage level constanstly from about 3.2v to 3.9v