BYD BMS

Mtour

Solar Enthusiast
I powered the byd bms and left it connected for a week or so didn't seem to balance at all. Was thinking maybe the battery voltages may have to be high (+3.5v) to work...
 

JRP3

New Member
I had one cell hitting 3.65V during charging so I'll try to power up the BMS and see what happens.
 

JRP3

New Member
I wonder why they made it so low with such large cells? I guess I can bring down the high cells with an external resistor to get them in line and maybe the BYD BMS can keep them there.
 

Mtour

Solar Enthusiast
A .5amp balance would be lots for a cell of this size, 12amps per day...84amps per week... I have installed the Qnbbm active balancers on my bank of BYD's that have been interconnected, with say a 60mv imbalance nearing fully charged you only get about .7amp transfer. If the imbalance is around 20mv I only see 100ma of transfer, they advertise it being a 6amp balancer but your batteries would have to be out of balance by over a volt or more, so realistically the Qnbbm is really a 2amp balancer at best...

It would be great to figure out the factory byd bms....
 

Picasso

Solar Addict
I wonder why they made it so low with such large cells?


Signs are the BYD's got cycled fast, so I agree. I do know the one without the BMS board are slightly older. So at some point the 2nd board to balance was added to production but I dont think it solved the problem so all of these got pulled. Some BYD packs test good some have one bad cell.

as others noted is a sketch for someone post here for reading the CAN and converting to voltages. I just went Chargery but ended up pulling my six BYD packs.
 

Smarttowers

New Member
Signs are the BYD's got cycled fast, so I agree. I do know the one without the BMS board are slightly older. So at some point the 2nd board to balance was added to production but I dont think it solved the problem so all of these got pulled. Some BYD packs test good some have one bad cell.

as others noted is a sketch for someone post here for reading the CAN and converting to voltages. I just went Chargery but ended up pulling my six BYD packs.
Why did you end up pulling them?
 

Picasso

Solar Addict
because I didnt want to parallel cells in a few packs to one another to make up for the bad cells and wild drift I was seeing using them in 2s3p, I had them all balanced well and watched them all drift out over 3 months of use. BMS couldnt keep up with that. Taking apart and salvage cells is not a game I want to play. add to that re-strapping and trying to get good connections to the cells....I got way to many other things to take up my time. I was shafted by https://www.techdirectclub.com/ on the BYD's never got a refund from them. I'vr played with them in 24v and 48v configs just couldnt make them work good.
 
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Mtour

Solar Enthusiast
With my Byd's I bottom balanced the packs, then charged them and added one or two headways to the runners..

Once the headways were added, the difference between the 3.65v cell and the lowest cell in the pack would be +-5amps in capacity.

Then the cells were paralleled, this took many hours and around 200 fuses... The byd bank is 2s12p packs, 1350ah usable..

I added two 8s qnbbm balancers and a 1amp jkbms for monitoring. This gives a total of 3amps active balance for 1350ah power wall..

The Byd's are cycled 3.4v to 3v per cell, at 3.4v they are out max 60mv and once a load is added they settle to about 10-20mv...

These byd's have been beaten up pretty bad, only having 60% capacity remaining... But if you parallel the cells and only charge to 3.4v and let them absorb at 3.4v they will stay in balance.
These degraded lifepo4 are now behaving more like a lead acid battery. They need time at absorbtion voltage to bulk up... If you try and charge to 3.65v per cell there will be a runner in the pack. Once the absorbtion amps have tapered off which take about three hours it only takes 4ah to push an individual cell from 3.4v to 3.65v..It just not worth the extra ah to fight imbalances.

This morning is a typical 20% discharge of my power wall and there batts are 10mv out of balance.

I also wouldn't be surprised if all the Batts came with the two board bms from the factory and the one board was removed because the Batts were going too far out of wack for the software...
 

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Smarttowers

New Member
With my Byd's I bottom balanced the packs, then charged them and added one or two headways to the runners..

Once the headways were added, the difference between the 3.65v cell and the lowest cell in the pack would be +-5amps in capacity.

Then the cells were paralleled, this took many hours and around 200 fuses... The byd bank is 2s12p packs, 1350ah usable..

I added two 8s qnbbm balancers and a 1amp jkbms for monitoring. This gives a total of 3amps active balance for 1350ah power wall..

The Byd's are cycled 3.4v to 3v per cell, at 3.4v they are out max 60mv and once a load is added they settle to about 10-20mv...

These byd's have been beaten up pretty bad, only having 60% capacity remaining... But if you parallel the cells and only charge to 3.4v and let them absorb at 3.4v they will stay in balance.
These degraded lifepo4 are now behaving more like a lead acid battery. They need time at absorbtion voltage to bulk up... If you try and charge to 3.65v per cell there will be a runner in the pack. Once the absorbtion amps have tapered off which take about three hours it only takes 4ah to push an individual cell from 3.4v to 3.65v..It just not worth the extra ah to fight imbalances.

This morning is a typical 20% discharge of my power wall and there batts are 10mv out of balance.

I also wouldn't be surprised if all the Batts came with the two board bms from the factory and the one board was removed because the Batts were going too far out of wack for the software...

Wow I thought there would be more life in these. So if I'm calculating correct your only getting about 112ah per pack? Kind of a far cry from the stated 80% but i guess still a better deal than what they cost for new lifepo4 if they hold up. I paid just around $1800 for 8 cells at 180ah when i built my calb battery. Then put on a $500 bms. Now I'm going to build my own bms and about $325 a battery for the byd.

How many cycles have you put your byd batterys through so far and have you seen any noticeable capacity decrease yet?
 

Mtour

Solar Enthusiast
The byd's have been cycling daily for seven months now. Since doing interconnects I have been able to raise the absorbtion-float voltage from 3.37v to 3.4v... I'm sure I could go higher but with the sunny weather we have had this summer I am back to 100% by 10am... So they float at 3.4v all day... By 1pm the bank is only drawing 5-8amps from solar... I am running three mpp lv5048 inverters connected to 17.5kw solar.. You can set absorbtion time but not end amps, this limits the absorbtion voltage due to the different daily depth of discharges, since I float at absorbtion voltage..

I would expect a really long service life from the byd's.. Who knows how long they have sat around after decommissioning.. If they were to say have a bad cell you would think there would be excessive voltage drop in that cell.
BCH tests the overall voltage before they leave, if they don't meet there number they are scraped.
Yah not the 80% warrantied for sure, I was going to let it go as buyer beware, but after Wills video on it I called BCH... Guy at BCH noticed the voltages marked in his book were below his voltage cutoff and sent a replacement set..I even offered to pay the $500 to ship but he said the mistake was on his end.. So I am miles ahead on new eve cells...

The byd powerwall I am running has been working great, it almost boring in a way... I chech the voltages once a week with the jkbms...


It would be fantastic to get these stock bms working...
 
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JRP3

New Member
Put 12V to these pins which had continuity with the 12V pins in the board, put a charger on the battery and took one cell up to 3.80V briefly and another was 3.70 and didn't see more than 0.05 amps on the 12V wires, not sure it's really doing anything.
Both the upper and lower plugs on the left were positive and upper and lower plugs on the right were negative, I plugged them in this way to keep the bare contacts further apart. I'm letting it sit like this off the charger for a while to see if anything happens.

Plug2.jpg
 

JRP3

New Member
I charged it so that 3 of the cells went over 3.60V, 2 of those were over 3.65, and I set my power supply for 0.50 amps hoping that the BYD BMS would keep the high cells from charging and allow the rest of the cells to catch up but it didn't work, the high cells kept increasing. Tried it on both of my BYD packs. So it seems that putting 12V to the BYD BMS doesn't do anything, unless it only happens above 3.70V which would make it fairly useless anyway since that's higher than they should ever get.
 

Smarttowers

New Member
I charged it so that 3 of the cells went over 3.60V, 2 of those were over 3.65, and I set my power supply for 0.50 amps hoping that the BYD BMS would keep the high cells from charging and allow the rest of the cells to catch up but it didn't work, the high cells kept increasing. Tried it on both of my BYD packs. So it seems that putting 12V to the BYD BMS doesn't do anything, unless it only happens above 3.70V which would make it fairly useless anyway since that's higher than they should ever get.
The BMS can't keep more than 1 cell from going to high unless it is capable of moving more current out than is incoming. That said I think the bms in these packs could have been externally controlled through the canbus.
 

jasonhc73

Cat herder, and dog toy tosser.
The next step in this Adventure of BYD pack.

The BMS I used, turned out to be junk. All four failed. The MOSFETs simply could not handle the current, even with 320 amps printed on the board and sticker. Geeze you'd think you could trust Chinese printers.

The BMS monitor works fine, but all the safety measures it provides are not satisfactory.

The next step is to add a 1S Balancer, a 4 AMP 1S balancer, it will be active and separate self contained unit in operation all the time, always balancing the cells.

This is what I am ordering:
2020-10-12 (3).png

I am getting 64 for my self, there is about a 12% discount if I order 100.

These will balance 4 amps between cells. Which in the balancing act, is huge. The "active balancer" on the BMS I had could only balance at 0.2 amps.

If you have a desire for a serious active balancer and want to save a few dollars, please PM me and I'll order the 100 and not the 64.

I am not bull shitting you, this is going to be ordered before the end of this week (October 16th, 2020). So don't dilly dally around. Expect $20 each with shipping.
 

Jesswrk88

New Member
The next step in this Adventure of BYD pack.

The BMS I used, turned out to be junk. All four failed. The MOSFETs simply could not handle the current, even with 320 amps printed on the board and sticker. Geeze you'd think you could trust Chinese printers.

The BMS monitor works fine, but all the safety measures it provides are not satisfactory.

The next step is to add a 1S Balancer, a 4 AMP 1S balancer, it will be active and separate self contained unit in operation all the time, always balancing the cells.

This is what I am ordering:
View attachment 24943

I am getting 64 for my self, there is about a 12% discount if I order 100.

These will balance 4 amps between cells. Which in the balancing act, is huge. The "active balancer" on the BMS I had could only balance at 0.2 amps.

If you have a desire for a serious active balancer and want to save a few dollars, please PM me and I'll order the 100 and not the 64.

I am not bull shitting you, this is going to be ordered before the end of this week (October 16th, 2020). So don't dilly dally around. Expect $20 each with shipping.
So now that the ANTs are a no go, what BMS will you be replacing them with?

I have two of the 24v BYDs that I will be using in parallel with the GroWatt all-in-one containing a 3000w 24v inverter. I was originally going to go with a 100a 8s BMS from Overkill Solar and was going to use one for each of my two batteries but was then advised I should be getting at least a 160a BMS for each battery to avoid potentially frying my BMSs during surge. Steve from Overkill told me that he's put his BMSs through much abuse with big inverters without damage but that if inrush current was too high I could get stuck in a loop of short circuit alarms as the BMSs try to restart and I might have to manually charge up the capacitors with a jumper wire in this case. I still feel a little uneasy about it though, last thing I want to spend a couple hundred on BMSs and then accidentally kill them if there is another reliable alternative at a semi-comparable price out there that does do 160+ amps.
 
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