Sketchy Battery Pack?

[jetpackjbd]

It almost seems like the cells inside the second battery aren’t connected inside. I think I’m only able to charge the capacitors inside the BMS, which is why it can’t provide enough power to keep the indicator light on on the scooter. I’ve contacted batteryhookup support and am waiting to hear back.

 

[DaLanMan]

Yeah, I would.. not use those.

I tend to error on the side of caution, and what you just described is a system in failure mode on it's last legs, so even if you got those 2 units for free, you just spent hours learning that they were not worth even free.

also...

These units come with inherent risks, (as in batteries, bikes, vehicles in general etc) best process is to try to minimize that risk wherever you can. Even kids out jumping freeways have put some time and effort into the safety process, then they do wildly unsafe things.
I ain't telling you to not do crazy, far be it from me to try and stand on that stump. I am just saying... think it through.

 

[amberwolf]

If the battery won't charge, it usually means the BMS detects something wrong with the cells inside and is preventing charge (just as it prevented discharge at first) to protect against damage that could lead to a fire.


BTW: Charging a battery from another battery is a great way to start a fire. If the BMSes of both batteries had actually allowed it, current would have flowed without any limit from one into the other. (the only limit would be the cell and interconnect resistances).

Unless the packs are very very close in voltage (a few tenths of a volt at most), I strongly recommend against ever connecting any cell or battery to any other cell or battery this way.

If everything is designed and working correctly (fuses, BMS) then they will probably prevent a disaster. But if anything isn't designed or working correctly, you could have a very bad day.


FWIW, a BMS doesn't usually have any capacitors (not like a controller). The voltages you detect on the output are whatever the actual cells inside are at, until any current tries to flow, in which case the BMS shuts off the FETs, or has already shut them off so the voltage you detect is just leakage thru them, at such a low current (microamps or less) that the voltage drops dramatically as soon as any load is applied.

 

[jetpackjbd]

If the battery won't charge, it usually means the BMS detects something wrong with the cells inside and is preventing charge (just as it prevented discharge at first) to protect against damage that could lead to a fire.


BTW: Charging a battery from another battery is a great way to start a fire. If the BMSes of both batteries had actually allowed it, current would have flowed without any limit from one into the other. (the only limit would be the cell and interconnect resistances).

Unless the packs are very very close in voltage (a few tenths of a volt at most), I strongly recommend against ever connecting any cell or battery to any other cell or battery this way.

If everything is designed and working correctly (fuses, BMS) then they will probably prevent a disaster. But if anything isn't designed or working correctly, you could have a very bad day.


FWIW, a BMS doesn't usually have any capacitors (not like a controller). The voltages you detect on the output are whatever the actual cells inside are at, until any current tries to flow, in which case the BMS shuts off the FETs, or has already shut them off so the voltage you detect is just leakage thru them, at such a low current (microamps or less) that the voltage drops dramatically as soon as any load is applied.

I guess I’m lucky the BMS was working properly to prevent my stupidity.. If there’s no capacitors I wonder what’s causing the weak voltage in the first “good” pack when the BMS shuts down.

 

[amberwolf]

I guess I’m lucky the BMS was working properly to prevent my stupidity..

That's the kind of thing BMSes are intended to do. They're not always well-designed for the purpose, but they can be.

If there’s no capacitors I wonder what’s causing the weak voltage in the first “good” pack when the BMS shuts down.

Same thing as in any pack with a BMS using FETs as switches to turn charge / discharge ports on / off: tiny current leakage thru the FETs.

Any load (resistance, etc) across the output of the battery will discharge that voltage by making a path for the current.

(even a multimeter set to a voltage reading range that has a low enough resistance on it can drain the voltage if connected long enough; many have high enough impedance that the charge builds about as fast as it drains so you may either not see it drain or it may take long enough to get very boring waiting for it. )

It's...kind of like capacitors, but it isn't actually separate discrete capacitors doing it.

 

[jetpackjbd]

That's the kind of thing BMSes are intended to do. They're not always well-designed for the purpose, but they can be.



Same thing as in any pack with a BMS using FETs as switches to turn charge / discharge ports on / off: tiny current leakage thru the FETs.

Any load (resistance, etc) across the output of the battery will discharge that voltage by making a path for the current.

(even a multimeter set to a voltage reading range that has a low enough resistance on it can drain the voltage if connected long enough; many have high enough impedance that the charge builds about as fast as it drains so you may either not see it drain or it may take long enough to get very boring waiting for it. )

It's...kind of like capacitors, but it isn't actually separate discrete capacitors doing it.

Oh ok, that makes sense. It seemed to be strange behavior for a capacitor since it would build back voltage out of nowhere but I didn’t know what else it would be. If I can’t return it, do you think it would be possible to revive this battery? For example, if I were to bypass the BMS and charge the cells directly, or is that too fire-hazard-y for a guy in his parents’ garage?

 

[docw009]

Best thing to do is to ask Batteryhookup for a replacement on battery #2. If it didn't charge, it's their obligation to get you one that does.

 

[jetpackjbd]

Best thing to do is to ask Batteryhookup for a replacement on battery #2. If it didn't charge, it's their obligation to get you one that does.

I’m waiting on their reply, but I’m pretty sure they’re out of stock now. The link doesn’t work anymore so unless they’re holding onto a few in case someone received a dead one like mine, the best they’ll be able to do is get me a refund. I could buy used batteries on eBay but they’re a bit more expensive and I don’t trust them as much as batteryhookup.

 

[floydr]

Never hurts to ask. I have always found BHU to be a good source of quality cells and batteries. BHU gets the batteries quite often. Look at there main page Genuine Lithium Batteries for DIY Projects some times they move thing on the web page. or Products
later floyd

 

[amberwolf]

If I can’t return it, do you think it would be possible to revive this battery? For example, if I were to bypass the BMS and charge the cells directly, or is that too fire-hazard-y for a guy in his parents’ garage?

Well, the whole point of the BMS not allowing charge is there is something wrong with the battery; often that is a problem with a cell or cells that is caused by some form of internal failure, which means it could lead to a fire (not necessarily at that time--it could be at any time after that point).

If you were able to disassemble and diagnose and repair the battery by replacing the cells that were out-of-limits (assuming it's a cell issue; it could be an interconnect failure, and the cells could be fine, or even a failed BMS...but...you have to test to find out), then it might be safe to use.

But just bypassing the BMS and hoping for the best? I wouldn't.

 

[jetpackjbd]

Well, the whole point of the BMS not allowing charge is there is something wrong with the battery; often that is a problem with a cell or cells that is caused by some form of internal failure, which means it could lead to a fire (not necessarily at that time--it could be at any time after that point).

If you were able to disassemble and diagnose and repair the battery by replacing the cells that were out-of-limits (assuming it's a cell issue; it could be an interconnect failure, and the cells could be fine, or even a failed BMS...but...you have to test to find out), then it might be safe to use.

But just bypassing the BMS and hoping for the best? I wouldn't.

Nah, I wouldn’t bypass the BMS permanently, I’d just charge the cells without the BMS this one time. I’ve had a drill battery that refused to charge because the charger thought the battery was too low of a voltage, but I’m sure the cells would’ve been mostly fine seeing as they had maybe 100 cycles. I’m hoping it might be the BMS refusing to charge these as well but maybe not.
I wouldn’t be able to replace any cells myself or repair any welded connections, nor could I properly test any cells. Best I can do would be checking with a multimeter, charging with my school’s lab power supply and watching it, then testing with some lower power lights and motors to see if it holds a charge.

 

[amberwolf]

The point of a BMS shutting off the ability to charge (if that is what has happened, vs a BMS failure) is that the cells are beyond what is safe to recharge.

If you want to go ahead and do it, you should test everything first to find out *why* it shut off charge. If the cells are below the BMS LVC, then you are risking a fire, not just then, but at every moment of every hour of every day that the pack exists after that.

That's why the BMS is designed to do this, to prevent fires.

It doesn't matter if the cells had *zero* cycles; if they're damaged they're damaged. (which you can't know for certain--the only way to know if a cell is *going* to catch fire is *when* it catches fire...so the "safe" way to go about it is assuming any cell that's has had an excursion outside it's normal voltage range, or temperature, etc., is damaged). While LiFePO4 is probably safer than some other chemistries, it can still catch fire.

If the problem is not the cells, but a blown fuse, failed connection, damaged BMS, etc., and all of the cells are all above the BMS LVC and below it's HVC, then they're *probably* safe to recharge.

Up to you what to do.

Some people have successfully recovered even 0V cells...but the cells have still gone outside their design range and may be damaged, possibly in a way that can cause a fire. You just can't know.



You can check with K2 Energy to see what it is for those specific cells in those packs, but the usual LVC for LiFePO4 cells (probably what's in this pack from it's labelling) is about 2.4-2.5v. Below that there's little or no energy. Below about 2.1v, the likelihood of damage is higher the lower you go.

The usual HVC for those is about 3.65v, most of the time as they age they only retain about 3.4v after charging up to 3.65v. Above 3.65v, the likelihood of damage gets higher the higher you go.

 

[floydr]

Battery hookup has the K2 24V back on their web site.
Later floyd

 

[jetpackjbd]

Finally, I’ve got two good batteries. Batteryhookup paid for return shipping and sent me a new one. Great customer support.
Unfortunately, the scooter’s dead again. Currently trying to diagnose the BladeZ’s circuit board, I might end up swapping to a new one like Tabora is doing with theirs. Maybe I’ll go the lazy route and give it an on-off switch instead of a throttle.