diy solar

diy solar

I have the poor connection blues - help me

I have (2) 280Ah 24V diy battery packs that I have had up and running for about a year now. I am off grid and these batteries have literally changed my life in so many ways, but I have had connection/corrosion issues that seem to crop up more and more and I am looking for a solution.

I am using the tinned busbars that came from Basen with my cells and when I initially put them together, I gave each connection (both the terminal and the busbar) a light sanding with 3M P320 sandpaper, wiped them down with isopropyl alcohol, and then a light coating of Ox-guard and tightened them up snug. This seems to work out fine for the short terms, but every month or two my BMS shows something strange on a cell and I need to take things apart near that cell and re-do them.

What is this "something strange"? also is it reoccurring on the same cell?

Do other folks who made a DIY battery have these issues? If you have had your batteries put together for longer than 6 months and aren't having any of these issues, can you tell me what you did to connect the batteries? Anybody see any issues with how I did the connections? Was it a mistake to lightly sand the tinned busbars? I am willing to invest in a new or better solution so any suggestions welcome. Thanks!

I have not had these issues in such a short time span.

320 grit probably a bit much. I would say light sanding with 1000+ would be ok.

What is your environment like? Very humid? Salt?
 
I used mg chem 847 and it's doing great on one set, and it is marginal on another. I'm looking at flexible bus bars to minimize movement. I'm also checking connections regularly now. I guess it's better than watering?

Btw, even the red loctite will most likely free easily on aluminum. You have to surface prep and use the aluminum mix.

Also, if you hand torqued, you could have over torqued. I used a torque wrench, and I certainly would have over torqued without it.

I don't think marginal connections are really noticable at low amps. Around 100amps it really shows though.
 
What is this "something strange"? also is it reoccurring on the same cell?



I have not had these issues in such a short time span.

320 grit probably a bit much. I would say light sanding with 1000+ would be ok.

What is your environment like? Very humid? Salt?
"something strange" is when the BMS shows a cell suddenly out of whack with the rest of the cells. This is usually only noticeable when charging and when it is in discharge mode everything looks like it should. I believe this happens because of greater resistance. It has happened in a variety of cells and happened first in a place where I needed to make custom busbars with copper (not tinned) - last few times it has happened where my regular tinned busbars are. Its only happened 5-6 times total and isn't a huge deal, but this thread trying to figure out how to prevent for next bunch of years when I am not so gung ho on babysitting the battery...

Good hint on 1000 grit sandpaper. Environment is upper midwest in a non-heated shed (battery box has heaters for cold months)
 
I used mg chem 847 and it's doing great on one set, and it is marginal on another. I'm looking at flexible bus bars to minimize movement. I'm also checking connections regularly now. I guess it's better than watering?

Btw, even the red loctite will most likely free easily on aluminum. You have to surface prep and use the aluminum mix.

Also, if you hand torqued, you could have over torqued. I used a torque wrench, and I certainly would have over torqued without it.

I don't think marginal connections are really noticable at low amps. Around 100amps it really shows though.
You are right that it is better than watering! These batts are a real life changer for off-grid living. I used to just have a chest freezer to fridge conversion and some lights. Now I have regular fridge, microwave, mini split, chest freezer, and induction cooktop. I have to pay attention to batteries when using mini split overnight, but that is only compromise currently and I hope to automate.

I am aware of the red loctite maybe not forever - that is why I use the hex on the stud head when tighten and loosening. None have broken free yet (out of 16), but I know it will likely happen.

Is overtorquing bus bars an issue with connection and corrosion?

I agree about the low amps not showing up as well. I plan to try to get things "right" and then if I am still having these issues, I plan to buy a flir camera and just look everything over once a month with a decent load and hopefully be able to "see" exactly what needs addressing instead of sorta guessing
 
"something strange" is when the BMS shows a cell suddenly out of whack with the rest of the cells. This is usually only noticeable when charging and when it is in discharge mode everything looks like it should.

So, out of whack. Is that higher or lower voltage. Can you give an example?

The reason I ask is because it's not uncommon at all for a cell (or more) to be higher than the rest during charging, especially after the cells reach 3.4v
 
So, out of whack. Is that higher or lower voltage. Can you give an example?

The reason I ask is because it's not uncommon at all for a cell (or more) to be higher than the rest during charging, especially after the cells reach 3.4v
During the spring, I would hardly open the BMS and glance at the batteries. But these days I check a little more often to see if okay to run mini split overnight.

The other evening I checked each battery bank. One said 82% SOC (Batt1) and the other said 93% SOC(Batt2). And when I looked at the amp draw, I realized that Batt1 was providing double the amps of Batt2 for the load I was pulling. I went to bed.

The next morning when I checked the banks, they were also charging at different rates and Batt 2 was charging at half as many amps as Batt 1. In Batt 2, cell #2 was also spiking voltage into 3.6V when the others were at 3.32ish(I don't remember exactly but it wasn't anything close to 3.4for any of the other cell. When I took Batt 2 offline with circuit breaker, all the voltages got real close again.

I figured there must be extra resistance in Batt 2 and I took off the busbars connecting 1>2 and 2>3 and cleaned up all connections and that fixed the whole problem.

Its always some variation of this and first evident on the BMS check.
 
During the spring, I would hardly open the BMS and glance at the batteries. But these days I check a little more often to see if okay to run mini split overnight.

The other evening I checked each battery bank. One said 82% SOC (Batt1) and the other said 93% SOC(Batt2). And when I looked at the amp draw, I realized that Batt1 was providing double the amps of Batt2 for the load I was pulling. I went to bed.

The next morning when I checked the banks, they were also charging at different rates and Batt 2 was charging at half as many amps as Batt 1. In Batt 2, cell #2 was also spiking voltage into 3.6V when the others were at 3.32ish(I don't remember exactly but it wasn't anything close to 3.4for any of the other cell. When I took Batt 2 offline with circuit breaker, all the voltages got real close again.

I figured there must be extra resistance in Batt 2 and I took off the busbars connecting 1>2 and 2>3 and cleaned up all connections and that fixed the whole problem.

Its always some variation of this and first evident on the BMS check.

I mean It really just sounds out of balance. It happens overtime, and the BMS built-in balancers really do not suffice with large capacity cells.

I limit my charge voltage to 3.4v - 3.45v per cell, and this helps dramatically with cell balance.
 
I mean It really just sounds out of balance. It happens overtime, and the BMS built-in balancers really do not suffice with large capacity cells.

I limit my charge voltage to 3.4v - 3.45v per cell, and this helps dramatically with cell balance.
I have the same cells as you. I had a similar problem and was plagued large voltage variations. Checking that each nut was tight did not seem to make any difference.

Eventually, I took everything apart ( except the studs) and cleaned every contact surface with a wet sand of 80% alcohol and 800 grit sand paper.

Put it all back together with an anti corrosion paste (very thin coat) and it's been fine for a year.

I think the aluminum oxide can form quickly on the cell terminals, and once it's there, it take some effort to remove. PIA with the studs in place.

Also, when charging your BMS will balance the cells, so that will make them jump around in voltage. Make sure that's not what you are seeing. 3.3v to 3.6v is extreme for a balance current however....
 
I mean It really just sounds out of balance. It happens overtime, and the BMS built-in balancers really do not suffice with large capacity cells.

I limit my charge voltage to 3.4v - 3.45v per cell, and this helps dramatically with cell balance.
My bulk charge is 3.42V(27.4V) and the float is set to 3.4v (27.2V).

I don't see how you think the issue I documented is just out of balance cell. After I cleaned those two busbars, not only did that cell no longer jump to such high voltage from 3.32V, but the charge/discharge amps divided between my two packs immediatly went back to approx 50/50.

If I hadn't seen such a weird Amps charge/discharge imbalance between my packs, I might have chalked up the issue to out-of-balance cell, but when the 2 batteries were so different in their charge/discharge Amps I suspected a resistance issue. And then when that totally went away (as well as the cell getting really really high voltage so fast) after cleaning up busbars - I took that as confirmation.
 
I have the same cells as you. I had a similar problem and was plagued large voltage variations. Checking that each nut was tight did not seem to make any difference.

Eventually, I took everything apart ( except the studs) and cleaned every contact surface with a wet sand of 80% alcohol and 800 grit sand paper.

Put it all back together with an anti corrosion paste (very thin coat) and it's been fine for a year.

I think the aluminum oxide can form quickly on the cell terminals, and once it's there, it take some effort to remove. PIA with the studs in place.

Also, when charging your BMS will balance the cells, so that will make them jump around in voltage. Make sure that's not what you are seeing. 3.3v to 3.6v is extreme for a balance current however....
Thanks for the input. My BMS is JBD, so balance current really low. I am pretty confident my issue is corrosion. It would be nice to find a sanding pad for drill with middle cut-out for stud that I could use to clean up terminals.
 
3.42V is a very low absorption voltage and will require a very long absorption cycle to get anywhere near full (95%+) charge. It also doesn't give much room for balancing when it's typically set for 3.40V.
 
3.42V is a very low absorption voltage and will require a very long absorption cycle to get anywhere near full (95%+) charge. It also doesn't give much room for balancing when it's typically set for 3.40V.

Actually it's not bad. I have a 16s 100ah pack on my solar GPU mining rig. It's currently set to charge to 3.42v. It fully charges, I know this because I get the exact same run time as when I had it set to charge @ 3.55v.
 
Thanks for the input. My BMS is JBD, so balance current really low. I am pretty confident my issue is corrosion. It would be nice to find a sanding pad for drill with middle cut-out for stud that I could use to clean up terminals.

A bad connection can make a cell look like it is out of balance.

I would not use a machine for cleaning battery terminal surfaces. Get a Scotch-Brite pad and use that lightly. You want to remove surface oxides, not remove aluminum from the terminal. Clean the other surface (ring terminal, bus bar, etc.). After using the pad, clean the surface with mineral spirits or denatured alcohol and allow to dry. If corrosion is an issue, then use some anti-corrosion paste such as MG Chemicals 847 or No-Ox-ID or whatever you can find. Dielectric grease is not what you want. Use a very thin layer of paste. You don't need much. Less is better than more. Don't leave the surface untreated for very long if corrosion is a big problem.
 
Am following this thread …very interesting… I do have one honest question to the group in general..
” would using copper buss bars not solve many of the issues I am reading about here”. ?
what am I missing .?
There has to be a reason for choosing aluminum..
Why…?
 
Am following this thread …very interesting… I do have one honest question to the group in general..
” would using copper buss bars not solve many of the issues I am reading about here”. ?
what am I missing .?
There has to be a reason for choosing aluminum..
Why…?

Aluminum bus bar against an aluminum terminal = no galvanic corrosion between differing metals. Bare copper against aluminum requires an anti-corrosion paste. I use bare copper against tinned copper and still use the paste.

I bought aluminum flat bar last year with the plan to create new bus bars for between my cell terminals. Someday I'll actually get around to doing that.
 
Aluminum bus bar against an aluminum terminal = no galvanic corrosion between differing metals. Bare copper against aluminum requires an anti-corrosion paste. I use bare copper against tinned copper and still use the paste.

I bought aluminum flat bar last year with the plan to create new bus bars for between my cell terminals. Someday I'll actually get around to doing that.
Ok . I didn’t know they were aluminum terminals .. never built a diy battery.. I am horribly aware of the problem with aluminum and it’s interaction with other metals from my live aboard sailboat years..that’s why I was following the thread ……aluminum a great metal and yet sometimes awful too… just depends on how it’s used.. thanks for info… good luck to all on this topic..

Jim.
 
Ok . I didn’t know they were aluminum terminals .. never built a diy battery.. I am horribly aware of the problem with aluminum and it’s interaction with other metals from my live aboard sailboat years..that’s why I was following the thread ……aluminum a great metal and yet sometimes awful too… just depends on how it’s used.. thanks for info… good luck to all on this topic..

Jim.

If the battery is in a high humidity, and/or salinity environment, I would just use aluminum buss bars on batteries that have aluminum terminals (which is most of these prismatic cells)

Just have to go a little larger, no Biggy aluminum is cheap.

I would still use something to keep oxide layer from forming.
 
  • Like
Reactions: JRH
If the battery is in a high humidity, and/or salinity environment, I would just use aluminum buss bars on batteries that have aluminum terminals (which is most of these prismatic cells)

Just have to go a little larger, no Biggy aluminum is cheap.

I would still use something to keep oxide layer from forming.
Copy that…..thx..
 
Back
Top