How to charge this battery?

[wrybread]

I found a lithium battery pack in a recycle bin that seems to have a bit of life left in it. At least I hope so, ha.

The brand is Jetech, the name is 10S3P, it's 36 volts, and it has two large wires going to an XT60 plug, and three smaller wires (a black, blue and yellow) going to a smaller plug, with the label "7-BMS-SM3A".

Pic attached.

I picked up a 42 volt charger, but don't know which wires to attach it to.

Would it be two of those smaller wires?

Or does it charge thru the xt60?

Thanks for any help.

 

[john61ct]

danger will robinson

 

[e-beach]

The big wires go the the battery, probably discharging and charging port. The other wires probably went to a now missing BMS.

As advised "DANGER WILL ROBINSON!!!"

Use your DMM to meter the battery through the XT60? plug (more likely an XT30 plug) and check the voltage. It should be no higher then 42v. If it is 25v or lower, then dispose of it properly as it it a fire hazard. If it is over 25v you have a chance at a good battery, but due to it's age, It might be a fire hazard. If, you have a fire proof place to charge it to 42v you can test the battery to see what it does, but beware, it could also burn your house down.

 

[wrybread]

It's 35 volts, which is what makes me think it's still good.

It's definitely an XT60 jack.

I've never seen a battery pack of that size charge and discharge thru the same jack. Is it likely to be the same port used for both charging and discharge in this case?

And you don't think the bms is inside the battery case as in most 36 volts Batts?

I guess I could open it up to see whats going on inside but it's so nicely packaged I was hoping to avoid it.

As far as low voltage battery packs, I found another 36 volt battery pack that's 12 volts. This one has clearly labelled charging wires. I was going to bring it up slowly using a shop power supply set to .5 amps in a fire safe area (outside on pavement). Thoughts? Does it remains a fire hazard even after getting charged up and tested?

 

[amberwolf]

The fire hazard is specifically *after* it is charged (after having been overdischarged).

You should open up the 12v one to check each cell before you attempt a charge. Any cell below around 2v is damaged and is a fire risk. If you don't check the cells first, then the evidence of the problem will be gone and you won't know which are a a fire risk until the risk becomes reality.

The "12v" could simply be the residual voltage passed by a BMS that has shutdown to protect the cells from LVC. Any significant load would instantly drop that to nothing, if this is the case.


I would also recommend checking cell voltages on the other pack too, becuase if it doesn't have a BMS and it's unbalanced badly enough, *that* is a fire risk, too, as you may overcharge cells just charging it up to the normal voltage.

To be certain of finding out which connector does what, you'd have to open it up anyway.

If the main plug is *not* the charge connector (it could be), and it has a BMS, then it hasn't any way to stop unbalanced cells from overcharging, if charged thru the discharge-only port.

 

[wrybread]

I've never heard of a 36v battery pack without a bms. Do they exist?

And I think those 3 wires aren't enough for a bms anyway, am I right?

(Not saying I'm right, genuinely wondering).

 

[amberwolf]

It isn't likely to not have a BMS, but it's certainly possible, if the intended purpose was to be really really cheap (sometimes, a BMS will cost as much as the pack it's on).

 

[wrybread]

How could a 36 volt lithium pack cost what a bms costs ($10)? Doesn't sound possible. And googling, it looks like Jetech are good batteries, but I'm not getting any info on this one.

And it doesn't sound possible that the bms in a 10s3p pack has only 3 wires. But I'd love to get confirmation on that.

 

[dustNbone]

Those 3 wires could be for a few things:

-A remote power switch connection to the BMS, possibly with an extra wire for an LED voltage indicator. You might need to connect two of them together to "turn on" the battery.

-Output from a USB power converter inside the battery, to be connected to an external port

-Output from a 6V or 12V DC-DC converter for headlights, etc

-Other things?

You'll probably need to open it up to find out for sure, or do some trial and error from the outside if you're feeling brave.

 

[e-beach]

Post pictures of the whole battery so we can see what you have.

 

[wrybread]

I opened it up and it has what looks like a bms, but with no obvious charging tabs. It has the pos and neg wires going to the xt60 jack, then the other three wires are labelled TXC for the yellow wire, RXT for the blue and GND for the black.

There 2.8 volts on the RXT (blue wire), nothing on the TXC.

Attaching a couple of pics. Any ideas?

 

[fechter]

Well, there you go. It charges and discharges through the same XT60 port and the 3 small wires are serial data lines most likely for a battery gauge.

 

[wrybread]

Thanks for that. Is it common for a BMS to use the same wires for charging and discharge?

And would that be an indication that this doesn't have a LVD? Or maybe it can still charge when in LVD?

 

[dustNbone]

It can detect the direction of current flow, it can shut off the battery from discharge and then when it detects voltage at the port it will reconnect the port to the battery for charging.

Fairly common design, replaces a few big expensive parts with some brains.

SIgn of the times man....

 

[amberwolf]

How could a 36 volt lithium pack cost what a bms costs ($10)?

A BMS may cost hundreds of dollars, or only a few, or anywhere in between. Depends on it's design and complexity, etc.

No idea how much the BMS on these packs costs.

 

[fechter]

Right. You can still charge it if the low voltage cutoff is active.

 

[markz]

Besttech Power BMS' cost a lot of money!
http://bestechpower.com/
But you know its an excellent quality BMS.
^By the way, their MOQ is 2... more then likely the same as a few yrs back when I inquired.

Buy a generic, fleabay/alibaba/aliexpress bms or battery, then you have no clue what the quality of the bms is.

 

[john61ct]

crazy how many choices they offer

where is the published price list?

how do you **know** they're any good?