Solar charger, Over charging cell 1.

[Traderryan713]

Recently hooked up solar, and it seems to be wanting to overcharge cell 1.

I caught it earlier at 4.2v luckily and quickly discharged it down to spec and had all 4 cells back within .03 The 3 other cells were fine and stayed grouped very well.

My DC-DC charger does'nt cause this issue as easily, but it has gotten a cell or 2 off before. So i went and hooked up the solar charger correctly, (vs just directly to the battery + and -) running the negative to the BMS so it can read the solar incoming and prevent another over charge like that at least.

But im wondering what causes 1 cell to overcharge like that.

I never top balanced them when i got them, so i think i'll do that as well. Hoping that's it.

Preciate any input.

 

[Adam De Lay]

Recently hooked up solar, and it seems to be wanting to overcharge cell 1.

I caught it earlier at 4.2v luckily and quickly discharged it down to spec and had all 4 cells back within .03 The 3 other cells were fine and stayed grouped very well.

My DC-DC charger does'nt cause this issue. So i went and hooked up the solar charger correctly, (vs just directly to the battery + and -) running the negative to the BMS so it can read the solar incoming and prevent another over charge like that at least.

But im wondering what causes 1 cell to overcharge like that. I never top balanced them when i got them, so i think i'll do that as well.

Preciate any input.

The biggest thing is not running the Solar charge controller through the BMS.

If you ever top balanced your cells, there’s always potential for one to increase higher than it should because it’s at a higher state of charge than the other cells.

Sounds like you’re on the right track to prevent this from happening again.

 

[OTRwSolar]

Using cells with no BMS . . . especially when the cells haven't been top-balanced . . . is not recommended. Live and learn. A top-balance should correct this problem---if the cells are a well-matched set from the manufacturer/distributor. If not, then a top-balance may help, but won't eradicate the problem entirely.

 

[Traderryan713]

Right on.

Less of a possibility #2. I had reset the capacity on the app and so it showed if it was full @ 280ah, after moving the solar negative to the BMS.

but volts are more like 3.32-3.35 (40-50% charge) in reality. And just thinkn maybe the BMS was trying to top off cell 1 or wouldnt distribute volts evenly.

I did figure out how to reset to actual AH, so got the right reading there, and got em all equal now (.003).

I think it will charge equally now, but we will see. I'll report back to debunk my theory and how i need to top balance them really. lol.

Thanks.

 

[mikefitz]

Charging direct on the series cells sounds a realy good way of damaging cells due to over voltage. The point of using a BMS is to prevent this happening. Cell 1over charged because, the cells are not top balanced / did not use the BMS correctly/ perhaps used a high charge voltage.
The BMS doesn't distribute or top up. It's basically a protection device that stops charge or discharge when protection values are exceeded. Most have a limited balance facility that bleeds small amounts power from the high cell.
Cells at 3.32, 3.35 volts at rest are well over 80% SOC.

 

[Traderryan713]

Ya, no doubt on 1st statement.

I was going by some graphs i googled is where i got that info.

Here it is doing good around this level. I've had it full before a few times and in the top 20% with no "voltage runner" problem.


Its on the BMS now so it will stop at 3.65 if it does start to run. And ill top balance em if (when) it causes 1 more problem.

 

[Traderryan713]

Started to run/overcharge right after i posted. lol.

I'll get a charger and top balance them.


I'll let yall know how it works out once i get it.

Thanks.

 

[HRTKD]

Check your connections. Half the cell voltage problems seen on the forum are due to connection issues.

 

[Traderryan713]

Check your connections. Half the cell voltage problems seen on the forum are due to connection issues.

Ya, i bet. I did. I think the cell just has less internal resistance from 3.4v and up. But it only happened since i installed the solar. Im guessing the + solar wire going to battery is cell 1.

No overvoltage issue in the last year. Charger comes in today, So should have em top balanced in next few days.

 

[400bird]

Im guessing the + solar wire going to battery is cell 1.

Every BMS I have seen has the cell numbering starting at the negative. So the most negative would be cell #1

 

[Traderryan713]

edit: I re checked connections the neg. was a smidge widge loose. and got a 1/4 turn out of another post and a wee bit off +. Its a touchy ordeal. I got studs, but Dont wanna strip it. lol

I checked volts each cell with a multimeter.

Cell 1 is the negative coming from BMS to battery actually. Its the same spot my dc-dc charger negative is on.

Somethin fishy goin on im not aware of, i know that. lol.

 

[400bird]

Cell 1 is the negative coming from BMS to battery actually. Its the same spot my dc-dc charger negative is on.

Everything, including the DCDC should go through the BMS. Without knowing more about your set up, it seems like the DCDC negative connection should be moved.

 

[Traderryan713]

No, that wire is def. in right spot. 100% sure.

Im reading this thread... https://diysolarforum.com/threads/lifepo4-voltage-chart.3156/

I think my setting are just wrong and i dont trust this app b/c im not sure what to believe my real AH's are.

My full capacity is 280ah. I thought it should be at 3.6v @ 280ah. But apparently i misunderstand the SOC situation. And very minimal difference in SOC between 3.35 and 3.65. 2 days ago i was at 3.35 and it said 150ah. Now same spot and its 275-280ah if i "reset capacity".

After reading that thread im thinkn it actually is fully charged. at 3.4v potentially. Even if it isnt 100% its like 95% which is fine. So i change my overcharge limit to 3.5v.

 

[400bird]

No, that wire is def. in right spot. 100% sure.

If the current from/for the DCDC doesn't go through the BMS, how does the BMS track that energy usage to calculate your Ah and SOC? Also, how would the BMS provide protection from over charge/discharge due to the DCDC?

As you have it, the DCDC is bypassing the BMS. You might as well not have a BMS. But at least you get to see cell voltages.

Im reading this thread... https://diysolarforum.com/threads/lifepo4-voltage-chart.3156/

I think my setting are just wrong and i dont trust this app b/c im not sure what to believe my real AH's are.

My full capacity is 280ah. I thought it should be at 3.6v @ 280ah. But apparently i misunderstand the SOC situation. And very minimal difference in SOC between 3.35 and 3.65. 2 days ago i was at 3.35 and it said 150ah. Now same spot and its 275-280ah if i "reset capacity".

After reading that thread im thinkn it actually is fully charged. at 3.4v potentially. Even if it isnt 100% its like 95% which is fine. So i change my overcharge limit to 3.5v.
View attachment 143734

 

[Traderryan713]

If the current from/for the DCDC doesn't go through the BMS, how does the BMS track that energy usage to calculate your Ah and SOC? Also, how would the BMS provide protection from over charge/discharge due to the DCDC?

As you have it, the DCDC is bypassing the BMS. You might as well not have a BMS. But at least you get to see cell voltages.

No it does go through the BMS. DC to DC has always been fine. I had the solar charger hooked up like that, (direct to battery) but fixed it, so it goes thru BMS too.

I just change the settings in the app. Ima just call 3.4v 100% SOC. Overvoltage is now 3.45 so it stops there. It may only be 95% or so, but i dont need it to be perfect as long as this works good and i still get 95% or so. I just need to do some more real world usage/test and drain it down then see how it acts/charges from a very low SOC.

Preciate it.