BMS Advice wanted, true balacer or just voltage monitor

[TiffTaylor]

Hi, I have a Hailong-3, 15 Ah 36V battery pack, the pack cut out on a ride the other day. On striping it down I found that one bank of cells had dropped to 2.8V whilst the others were at 3.6V.

Using a separate multi function charger, I charged and discharged that bank and found them to be ok. When charging the whole pack with the supplied 42V 2A charger, I noticed that not all cells were reaching 4.2V, but the BMS is switching the charge off (so leaving it on won’t make any difference).

So do these BMS's in this pack actually balance the cells (i.e., shunt the charged cells to allows the other to catch up), or just turn off when just one bank reaches 4.2V.

I am an electronics engineer so I have an understanding of how some of this stuff works.

Can anybody recommend a true balancer that I can replace this with?

Regards Tiff

 

[Nealh]

Some balance quite well and others are pretty aweful, like your one the worse ones don't do any balancing once a cell hits 4.2v.

30q cells also are known to be a bit erratic and self discharge, but in your case one expects the bms is the issue charging and leaving a bad imbalance.

I use this type of bms either same port or seperate port versions, can't say I've had any issues with them yet.

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[StuartsProjects]

Using a separate multi function charger, I charged and discharged that bank and found them to be ok.

Was the discharge capacity (once fully charged) of the problem bank the same as the others ?

 

[TiffTaylor]

Was the discharge capacity (once fully charged) of the problem bank the same as the others ?

Yes the bank looked good, capacity wise.

 

[Bikes4two]

Was the discharge capacity (once fully charged) of the problem bank the same as the others ?

I'm a battery newbie so can I ask, how do you go about checking the capacity of an individual bank (I'm assuming by 'capacity' you're meaning as in measuring Amp Hours or Watt Hours and not just the voltage).

 

[saneagle]

Hi, I have a Hailong-3, 15 Ah 36V battery pack, the pack cut out on a ride the other day. On striping it down I found that one bank of cells had dropped to 2.8V whilst the others were at 3.6V.

Using a separate multi function charger, I charged and discharged that bank and found them to be ok. When charging the whole pack with the supplied 42V 2A charger, I noticed that not all cells were reaching 4.2V, but the BMS is switching the charge off (so leaving it on won’t make any difference).

So do these BMS's in this pack actually balance the cells (i.e., shunt the charged cells to allows the other to catch up), or just turn off when just one bank reaches 4.2V.

I am an electronics engineer so I have an understanding of how some of this stuff works.

Can anybody recommend a true balancer that I can replace this with?

Regards Tiff

Transistors or other devices open up a path through bleed resistors when any cell gets over around 4.18v and it closes at the same point when the cell has bled down.

 

[StuartsProjects]

I'm a battery newbie so can I ask, how do you go about checking the capacity of an individual bank (I'm assuming by 'capacity' you're meaning as in measuring Amp Hours or Watt Hours and not just the voltage).

You need some device that measures the capacity, in mAhr, of a cell (or bank).

A lot of 'universal' chargers will do charge and discharge tests, and tell you how many mAHr went in and how many mAhr went out.

An example of the one I use, an iCharger 106B+.

You can do much the same discharge test with a known value discharge resistor, a stopwatch and a voltmeter.

If one of the cell banks has gone a bit bad, it might not have the same mAHr capacity as the other banks, so the whole battery will appear to cut out early. Nothing any type of BMS can do about that.

 

[TiffTaylor]

I'm a battery newbie so can I ask, how do you go about checking the capacity of an individual bank (I'm assuming by 'capacity' you're meaning as in measuring Amp Hours or Watt Hours and not just the voltage).

I have a Universal Charger (like the I Charger mentioned in a reply icharger-406-duo-1400w), so I can easily leave it charging & discharging as you tell it the battery type, so it wont over charge or discharge and will give you A/h in & Out

 

[TiffTaylor]

I use this type of bms either same port or seperate port versions, can't say I've had any issues with them yet.

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Any pros & cons between common port and seperate, my current one is seperate?

 

[Nealh]

Common port simply uses the same ouput for charge/discharge.
For the hailong one will probably stick with seperate port.

 

[TiffTaylor]

Common port simply uses the same ouput for charge/discharge.
For the hailong one will probably stick with seperate port.

Thanks, AliExpress not shipping that product to the UK, will have a search.

 

[Nealh]

I had no issue putting in my basket for delivery a moment ago.
There are quite a few sellers who stock it on Ali, one will likel find it on ebay or Amazon.

 

[Woosh]

Hi, I have a Hailong-3, 15 Ah 36V battery pack, the pack cut out on a ride the other day. On striping it down I found that one bank of cells had dropped to 2.8V whilst the others were at 3.6V.

Using a separate multi function charger, I charged and discharged that bank and found them to be ok. When charging the whole pack with the supplied 42V 2A charger, I noticed that not all cells were reaching 4.2V, but the BMS is switching the charge off (so leaving it on won’t make any difference).

So do these BMS's in this pack actually balance the cells (i.e., shunt the charged cells to allows the other to catch up), or just turn off when just one bank reaches 4.2V.

I am an electronics engineer so I have an understanding of how some of this stuff works.

Can anybody recommend a true balancer that I can replace this with?

Regards Tiff

I think bike4two made a good point:

I'm a battery newbie so can I ask, how do you go about checking the capacity of an individual bank (I'm assuming by 'capacity' you're meaning as in measuring Amp Hours or Watt Hours and not just the voltage).

The block that has lower voltage than the rest may have a faulty cell, it will discharge faster that the other blocks. When the difference becomes large enough, the protection system in the BMS will shut down the output to prevent fire.
On charging, the balancing circuitry starts only after all the blocks reach 4V or more. The bad block reaches 4V before the others thus prevents the balancer from doing its job.
When the balancer kicks in, you'll see the LED on the charger flashing between red and green for a few minutes before the charging ends.
If you can swap out the BMS then try that to see if the problem goes away. If not, you may have to buy a new battery.

 

[TiffTaylor]

I had no issue putting in my basket for delivery a moment ago.
There are quite a few sellers who stock it on Ali, one will likel find it on ebay or Amazon.

Thanks, even though I was logged in, the Language at the top was set to somewhere else, but this was not just the language of the site but the delivery country.

Now ordered, Thanks

 

[Nealh]

For the voltage imbalance one can simply charge to full and then disconnect the balance leads and let the pack sit for 24/48/72hrs and check the V's daily to see if any wander. If they do then the BMS isn't at fault, if they don't reconnect the balance and see if the cells drop over a similar period.

If the imbalance is happening during discharge then one has to suspect either a bad cell in the P group or simply cells that are failing (likely higher R).
The BMS doesn't do anything during discharge except shutting off due to lvc, any imbalance will be down to the cells. Like wise the BMS only top balances to keep the V's in check, it is possible any weak cells will top off the charge much quicker and then the voltage imbalnce is to great for any balancing to have an effect.

 

[Woosh]

I found once a battery with similar symptoms. It turned out that one of the cells had one of its welding spots undone.

 

[Nealh]

Yes a detached cell would also give a smilar result if a group is playing up.
I had the same issue/s with the vruzend kit and why I ditched it.

With any battery which has an issue it does pay to use a wooden or plastic tool to gently pry up any buss bars to check for movement.

 

[guerney]

Thanks, even though I was logged in, the Language at the top was set to somewhere else, but this was not just the language of the site but the delivery country.

Now ordered, Thanks

Well spotted! Very strange how the flag at the top repeatedly defaults to Afganistan. In the past, I've always found the same product for sale at the same price or cheaper on ebay, shipped from the UK. I may now order something from AliExpress for the first time ever.

 

[Bikes4two]

Well spotted! Very strange how the flag at the top repeatedly defaults to Afganistan......

Funnily enough, the same thing happened to me the other day and left me wondering why I couldn't order and ship.

 

[guerney]

Funnily enough, the same thing happened to me the other day and left me wondering why I couldn't order and ship.

It works fine in Chrome on Windows 7, but not the latest Firefox. Maybe they're still annoyed at Clint Eastwood for stealing their jet...