BMS replacement questions

[rick_p]

Actually expected a worse case scenario. Your battery is NOT a lost cause and the BMS may be AOK -

I’m pretty sure the BMS is bad, the charging/balancing electronics are still working but there is no power at the discharge port and I’ve already tried resetting it. See this post from earlier in this thread where I posted a picture of the damage.
BMS replacement questions

The only question I have right now is, can I install a new BMS without any further balancing of the groups? I think it’s fine but would like to get confirmation on that.

 

[amberwolf]

With >0.1v difference between groups, the BMS may disable the output until you leave it on the charger long enough to rebalance. Depends on the BMS design, if not programmable, and on the settings if it is.

Might be why your original BMS's output port is not enabled. (aside from any damage it has that is not related)


The usual cause for that kind of voltage difference is a problem with that cell group that makes it's capacity and/or internal resistance different from the others that are the same voltage (it's common for companies to cheap out and build batteries so that none of the groups are the same as each other and to drift in voltage over time, which is why some BMS have a balancing capability in the first place).

The problem may not affect your usage (at least until the pack ages sufficiently), but it may require you leave the battery on the charger long enough for the BMS to rebalance this after every usage.

Note that not all BMS have balancers, so if yours does not, it will never re-adjust this and the imbalance will only get worse over time, lessening the usable capacity each cycle. I dont' see any passive balancers on the BMS in your pictures, but we can only see one side of the PCB, and they could be on the back or a separate board underneath the one we can see. Active balancers could be inside the chips on the board; to find out you'd have to look up the numbers on the chips to see what kind they are and if they have this function.

 

[eMark]

Group 4's BMS resistance discharge could be defective. Such that after each of the previous c/d cycles the voltage variance kept increasing ... 110mV (4.15V- 4.04V).

BMS replacement questions ... "but then I saw this and figured this can't be good."
... image is too small to make out what you say ... "can't be good".

Are you referring to a hot spot burn? It's possible that 10s battery was feeding a 30amp instead of a 20amp Controller. Even so with only a 20amp Controller and an inexpensive 10s battery a hot spot burn could be expected over time (abuse). Due too pulling between 15-20amps during most of the discharge cycle.

Yes! it's not a bad idea to have an external BMS as long as balance leads are long enuf and BMS well protected. However, whether it's a good idea is debatable. Instead of an external BMS you could add 2 - 5s balance extensions (5s jst-hx connector) for occasional external use with a cell monitor or an iSDT BG-8S ... Cut-off the male jst-xh ends for soldering onto bus bars. Same BMS bus bar locations, except for splitting 10s into 2-5s ... two negative sensing wires and 5 positive wires). In affect you are splitting the 10s into two 5s (can't buy a 10s cell monitor). It won't cause a short-cirucit if done correctly. If too confusing wire-in a 10s jst-xh extension with exposed female jst-xh connector for checking p-group voltages with dmm probes like you previously recorded. That way If/when necessary you could manually discharge balance the p-group(s) having excessive +voltge variance.

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First balance all ten p-groups (as close as possible) to 4.04 resting volts.

 

[RTLSHIP]

I see an ebay vendor selling 14s6p without any bms. I wonder if buyer is suppose to attach one or can just ride without. it takes over $100 of the pricetag

 

[eMark]

I see an ebay vendor selling 14s6p without any bms. I wonder if buyer is suppose to attach one or can just ride without. it takes over $100 of the pricetag

So typical of ebay ... BUYER BEWARE ... one would assume that the cells are anything but name brand cells

 

[amberwolf]

Without a link to the sale page (presuming there are specifications and details there), I couldn't say what they intend or what might be a good idea.

But based on typical packs I would guess it is not the best idea to run an "ebay pack" without a BMS, especially without a balancing BMS. It's just way too common for them to be built from badly mismatched cells (new or otherwise), so that monitoring whole-pack voltage is not safe as an LVC or HVC. (too easy to overdischarge or overcharge a cell (group) (or plural).)

 

[rick_p]

With >0.1v difference between groups, the BMS may disable the output until you leave it on the charger long enough to rebalance. Depends on the BMS design, if not programmable, and on the settings if it is.

When you say leave it on the charger long enough, do you mean leaving on the charger after the light turns green and has presumably stopped charging the battery? It's not programable as far as I can tell.

Might be why your original BMS's output port is not enabled. (aside from any damage it has that is not related)

I meant to ask how much difference there has to be between groups before a BMS will cut off the output port?

The usual cause for that kind of voltage difference is a problem with that cell group that makes it's capacity and/or internal resistance different from the others that are the same voltage (it's common for companies to cheap out and build batteries so that none of the groups are the same as each other and to drift in voltage over time, which is why some BMS have a balancing capability in the first place).

I'm certain the only way I will find out if the BMS is the problem or if it's something with the cell group is seeing if a new BMS with balancers fixes it. I don't know how to reduce the voltage on a single group.

Note that not all BMS have balancers, so if yours does not, it will never re-adjust this and the imbalance will only get worse over time, lessening the usable capacity each cycle. I dont' see any passive balancers on the BMS in your pictures, but we can only see one side of the PCB, and they could be on the back or a separate board underneath the one we can see. Active balancers could be inside the chips on the board; to find out you'd have to look up the numbers on the chips to see what kind they are and if they have this function.

Here are better pictures of the front and back of the BMS, which may not tell us anything if the balancers are inside other chips on the board. There is only this one board.

 

[rick_p]

Group 4's BMS resistance discharge could be defective. Such that after each of the previous c/d cycles the voltage variance kept increasing ... 110mV (4.15V- 4.04V).

That is what I'm hoping for, so that a new BMS fixes all the issues and I'll have a working battery that will last a while.

Are you referring to a hot spot burn? It's possible that 10s battery was feeding a 30amp instead of a 20amp Controller. Even so with only a 20amp Controller and an inexpensive 10s battery a hot spot burn could be expected over time (abuse). Due too pulling between 15-20amps during most of the discharge cycle.

Knowing who I got this from, there is a high probability he was feeding a Phaserunner controller and programmed it for maximum voltage he thought the battery could handle.

Yes! it's not a bad idea to have an external BMS as long as balance leads are long enuf and BMS well protected. However, whether it's a good idea is debatable.

It's a last resort for sure, I have more important projects to work on that deserve fabrication much more than this battery does.

Instead of an external BMS you could add 2 - 5s balance extensions (5s jst-hx connector) for occasional external use with a cell monitor or an iSDT BG-8S ... Cut-off the male jst-xh ends for soldering onto bus bars. Same BMS bus bar locations, except for splitting 10s into 2-5s ... two negative sensing wires and 5 positive wires). In affect you are splitting the 10s into two 5s (can't buy a 10s cell monitor).

This is way over my head. Even if I knew what I was doing I doubt I would go this far for this battery.

First balance all ten p-groups (as close as possible) to 4.04 resting volts.

I wish I knew how. Hopefully a new BMS will take care of it.

 

[eMark]

I wish I knew how. Hopefully a new BMS will take care of it.

You NEED to first manually balance the 10 p-groups by discharging group 4 from 4.15V to 4.04V or at least 4.05V. You should do this before a FULL charging using either current BMS or a new BMS.

Attaching a new BMS before balancing the 10 p-groups won't give you the result you want. Instead the new BMS should stop charging when group 4 reaches 4.20V ... while the other 9 parallel groups are at 4.09V to 4.10V. With a variance of 100mV (0.10V) it will take a BMS hours and hours to balance the pack. Even then you may have to leave the charger plugged in with it's green light on for hours while the BMS balances the ten parallel groups. BMS balancing range is 25-30mV.

The easiest/quickest way to balance that 10s battery is using the top tool in the photo. Make contact with the two bare ends to the same two jst-hx contact points when you took a voltage reading of group 4 with the probes of your DC meter.

 

[rick_p]

You NEED to first manually balance the 10 p-groups by discharging group 4 from 4.15V to 4.04V or at least 4.05V. You should do this before a FULL charging using either current BMS or a new BMS. Attaching a new BMS before balancing the 10 p-groups won't give you the result you want. Instead the new BMS should stop charging when group 4 reaches 4.20V ... while the other 9 parallel groups are at 4.09V to 4.10V.

Got it

The easiest/quickest way to balance that 10s battery is using the top tool in the photo. Make contact with the two bare ends to the same two jst-hx contact points when you took a voltage reading of group 4 with the probes of your DC meter.

I can handle that, I'm sure I have some 12 volt auto bulbs in my spare parts box. I'll work on that today.

 

[rick_p]

The easiest/quickest way to balance that 10s battery is using the top tool in the photo. Make contact with the two bare ends to the same two jst-hx contact points when you took a voltage reading of group 4 with the probes of your DC meter.

The lightbulb trick worked like a charm. I left it on just a little bit too long and went to 4.03 volts, but that's OK, I haven't even ordered the BMS yet, so I'll charge it a little and balance the groups again just before I'm ready to install the BMS. Thanks for the tip.

 

[RTLSHIP]

So typical of ebay ... BUYER BEWARE ... one would assume that the cells are anything but name brand cells

Not true in this case. He sells these 14s with or without BMS. I asked him about it and he suggested that you can get by without it if you don't deep discharge etc. It depends on your usage.
These cells are made in USA , maybe San Diego. Green Horizon. Vendor has 100%

 

[eMark]

The lightbulb trick worked like a charm. I left it on just a little bit too long and went to 4.03 volts, but that's OK, I haven't even ordered the BMS yet, so I'll charge it a little and balance the groups again just before I'm ready to install the BMS. Thanks for the tip.

If you check the resting voltage today it could be higher 4.04V-4.05V (bounce back voltge). Especially if you took the 4.03V reading soon after discharge instead of waiting an hour before checking the (resting) voltage.

 

[amberwolf]

I don't really doubt that GH builds the batteries (though I always have some doubts about any battery builder until proven otherwise), but I seriously doubt they make their own cells. If they did, they'd probably be in a lot more search results, but the only results I can find relating to batteries are their packs on Ebay.

 

[pishta]

My controller has a lcd display that has "P settings" that allow you to set the undervoltage parameter, or battery cut off voltage. My 48v Fluid Freeride Horizon scooter has this throttle and it's set to cut the motor at 42v . I have come across 3 BMS issues on 4 scooters (low output voltage, voltage running down to 3v on power up, etc) I'm tired of their quirks frankly.. these are cheap scooters and don't need this finicky "protection" in my opinion.

 

[amberwolf]

Based on your other post, your problem isn't the BMS, it is the cells in the pack. See my reply to your other post here:

Strange BMS issue

I have a strange BMS issue. I change a bad BMS with a new one. The bad BMS outputs correct voltage, but as soon as it is loaded, it drops the voltage. The new one outputs 0.45v so something is bad with it. I change to another new BMS. I test the new one before soldering it and it outputs...

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