BMS

[Dimab]

My scooter battery BMS got water damage and I want to replace it with a basic one.
I am trying to source an inexpensive BMS to replace the existing damaged one. I have included a picture of the pack. Based on the picture and the output specs of 36V 15AH it appears that the arrangement of the cells are 10s p3. Please see the schematic I included for the INR 21700/5OE cells. https://batteryservice.bg/wp-content/uploads/2018/12/INR21700-50E.pdf. Based on this Spec sheet for the cell the Max discharge current for the cells is 9.8 A.

1. Does this mean that each P3 set can put out 9.8A x 3= 29.4A?
2. Do I need a 30A BMS?
3. Or do I need to get a BMS that matches the controller's MAX amps?
4. Do I need a 10s BMS or a 10s P3 BMS?
5. A friend suggested that if the 3P is in the end, then I must use a relay controlled BMS. I am not sure if that applies here. Please confirm if I have a P3 10s or 10s p3 or if it makes any difference.

The Kit I have is the EZEE by Grin:

• 500 watt internally geared eZee brushless hub motor
• A 25 amp (IRFB4110 mosfet) motor controller.

 

[Dimab]

My scooter battery BMS got water damage and I want to replace it with a basic one.
I am trying to source an inexpensive BMS to replace the existing damaged one. I have included a picture of the pack. Based on the picture and the output specs of 36V 15AH it appears that the arrangement of the cells are 10s p3. Please see the schematic I included for the INR 21700/5OE cells. https://batteryservice.bg/wp-content/uploads/2018/12/INR21700-50E.pdf. Based on this Spec sheet for the cell the Max discharge current for the cells is 9.8 A.

1. Does this mean that each P3 set can put out 9.8A x 3= 29.4A?
2. Do I need a 30A BMS?
3. Or do I need to get a BMS that matches the controller's MAX amps?
4. Do I need a 10s BMS or a 10s P3 BMS?
5. A friend suggested that if the 3P is in the end, then I must use a relay controlled BMS. I am not sure if that applies here. Please confirm if I have a P3 10s or 10s p3 or if it makes any difference.

The Kit I have is the EZEE by Grin:

• 500 watt internally geared eZee brushless hub motor
• A 25 amp (IRFB4110 mosfet) motor controller.

 

[glennb]

Very well documented question.

Good luck with it.

1. Does this mean that each P3 set can put out 9.8A x 3= 29.4A?

Yes

1. Do I need a 30A BMS?

Yes

1. Or do I need to get a BMS that matches the controller's MAX amps?

No, the BMS needs to be rated higher, or else it will cut power when you apply full throttle from a standstill.

1. Do I need a 10s BMS or a 10s P3 BMS?

10S BMS. The number of paralleled cells do not matter, the BMS sees them as single large cells rather than multiple smaller cells.

1. A friend suggested that if the 3P is in the end, then I must use a relay controlled BMS. I am not sure if that applies here. Please confirm if I have a P3 10s or 10s p3 or if it makes any difference.

No relay required. The P is for “parallel”, not for “poles”.

 

[Dimab]

Thank you Glenn for the quick reply and for answering all my questions.
Happy New Year

 

[glennb]

Thanks for making the effort to make it easy to help you

25A is a heavy load for these particular cells to sustain on a continuous basis. Battery could get a little too warm under certain conditions.

I’m sure you already have a few BMS on your shortlist. You’ll get more useful feedback about them here than from any amount of aliexpress reviews.

 

[Dimab]

Thank you Glenn for that guidance. I plan to use a Cycleanalist to limit the current to 15A with it Cycle Analyst V3 - Grin Products - Product Info. Do you think that will work?

 

[fechter]

In theory that would work but for motor current limiting it’s better to reprogram the controller. The latency in the CA makes it tricky to set up for current limiting.

 

[Dimab]

I have this 10s BMS which was for a 10s bank of 10,000mAh cells. I do not have the specs for these big rectangular cells but I am guessing that this BMS for them will be at least 30A. Are you familiar with these 10Ah cells? would there be any danger in trying it out.? Please see the pictures.
Cheers

 

[Dimab]

I left out that this battery bank has a 30A fuse on it. This is why I am assuming the BMS can draw at least 30A. Does that make sense?

 

[glennb]

Sorry, no idea about those 10Ah cells.

For the same reason that the BMS needs to be rated higher than the controller, so too must the fuse be rated higher than the BMS, So no, a 30A fuse is not grounds to presume a 30A BMS … far more likely to be a 20A BMS, or 25A tops.

20A BMS is ok if you reduce the controller current to 15A. You could consider modifying the controller shunts if the controller is not programmable.

 

[Dimab]

Those are great tips. I will contact Grin Technologies to learn more about the controller. I will share what I learn
Thank you

 

[Dimab]

Hi Glenn. I did not get a response from Grin. But I did install the 10s BMS . I did run the bike with it and drained it to about 33v. Now I have it charged to 40.76v. The Max Cut off voltage for these cells is 4.2 volts. Do you think its better if I not let it charge to a hundred % to 42V? Or as a test for BMS I should see at what voltage it cuts it off?

 

[Dimab]

I let it charge for another hour but the Voltage did not rise. Is it safe to say that the BMS cut it off because the Charger does have a 42v out put?

 

[rafalg]

just use a volt meter to check the charger voltage, but it should be at 42v
and if charging is stopped earlier it might be because BMS has disconnected it. It stops charging when some sections reach 4.2V limit (but then some other sections are lower than that - thats why total voltage is below 42V)
Does your new BMS do balancing as well?

 

[Dimab]

This is the same old BMS . After the charge I tested each cell separately and they were all exactly the same voltage. You were concerned about it drawing more current than 25A but the highest current It drew was 20A. I am noticing that the motor may have a problem. Sometimes it does not turn. I can here it trying with a bit of hum but no movement.

 

[Dimab]

I change the low voltage setting with the Cycleanlist from 31v to 27 and now the motor does not cutout at all. This is a good quality motor but since it is a 36v/48, I feel it will produce more power if I add more cells to make it a 48v bank. Any thoughts?

 

[glennb]

Each series group charged to 4.076V?

If so, it’s unusual, but not necessarily bad. Could be that the BMS is deliberately set to that voltage, but far more likely that the charger is only supplying 41V. Measure the charger output voltage while disconnected from the battery/BMS.

13S, all else being equal, will result in higher motor power draw. However, there’s fairly compelling reasons to avoid adding series cells to alter 10S to 13S. If the 10S battery is brand spanking new and you can obtain identical cells, then maybe. Otherwise, selling the 36V battery and buying a 48V replacement is preferable.

As to the 20A bottleneck, that will need more investigation. One thing at a time though … first figure out why the cells charge to 4.076V.

 

[Dimab]

My guess is the BMS may have something to do with it too because this BMS was for the big rectangular batteries which I cannot find the specs for. They could be Lifepo batteries. I checked out the charger output and it puts out 41.5v not 42v. In a way is this not good because avoiding a 100% charge for battery health?
Thank you

 

[amberwolf]

If you are not sure what chemistry the BMS is for, you should not use it. If it is intended for a lower voltage chemistry than you are using, then a few things will happen, and others could:
--it could damage the cell-level sense chips so the BMS cannot do any of it's functions (probalby woudln't, but it could depending on their design)
--it will detect cell voltages exceeding HVC and turn off the input to prevent charge--if it's an LFP BMS and say, NMC cells, you'll only be able to charge to half full
--it will detect cell voltages exceeding balance start point and drain them down to balance end point, so even if you charge to full it will empty the pack to half full as fast as it can
--probably others I haven't thought of


If it's the correct kind of BMS:

Are all the cells identical voltages?

If they are not, then the battery will not fully charge or equalize those unless the BMS is designed or programmed to balance within the voltage range the charger will charge them to. Most BMS only try to balance when cells have reached some voltage that is very near normal max full voltage for the chemistry the BMS is for. In those cases, if the charger does not go that high, the cells wont' charge that full, and the BMS will never balance them.

 

[Dimab]

I am sure they are either Lithium Ions or Lifepo4. I know this much because the Charger it cane with says Lithium Ion charger. I also know that this was this replacement battery for the seller I got it from. I found the manufacture name for it, Phylion from China. I will contact them to find out what the cells were.

 

[Dimab]

I was able to get into the charger and fine adjust the charger to 42.03v. The charger I have is this one HP High Power HP8204C 10s Li-ion Battery Charger 42 Vdc/2a eZip iZip XLR 36v for sale online | eBay

 

[Dimab]

This time even with charger at 42v it charged .4v less than 42. still an improvement from 40.67v .

 

[Dimab]

I am looking for a basic but reliable BMS with balancing circuit from ebay, or Aliexpress. Can you please recommend a few brands. Are you familiar with Heltec energy?Wholesale 10-14S BMS 12S 13S Wholesale 36V 48V 30A 40A 60A Manufacturer and Supplier | Heltec

Or something like this: 10S 30A 36V BMS Li-ion Battery Charge Protection Board Balance Charging Circuit | eBay