# First Bad Battery?



## F16bmathis (Jun 6, 2008)

I would consider myself lucky I haven't had a bad battery yet, but I did. I believe it was a loose connection and caused it to overheat and melt. So I ordered another from currentevtech back a month ago in Feb, it took some time before I got it, so its been in the truck for about a month, but I've been working on the truck, so I haven't put alot of miles on this battery.

I've got both the MiniBMS modules and the WiCom touch screen BMS system. The battery has been reading the same as the rest when fully charged, but when under load this one battery goes to a lower voltage faster than the rest till today when it got just over a volt lower than the rest!

Normally, I'd have expected the newer battery (3000 miles on older ones) to have better "hold" than the older ones. Never really made it to the break-in period. Just sent an e-mail to get a waranty replacement. I should be good for a warranty, right? And whats the normal way to get a waranty replacement?

The first melted battery actually reads good, but the case had melted a little around the post. Does anyone think I could still use it after I clean up the threads?


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## EVfun (Mar 14, 2010)

If that toasted battery has been holding it's charge then I don't see why not. Clean it up, match the SOC, and give it a try. I would keep it out if it goes dead on its own or showed excess sag under load, but not just because it looks ugly.


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## F16bmathis (Jun 6, 2008)

Yeah, I checked it last night and its still holding, though its only been about 2 months since its been removed. I'm going to clean up the threads and balance it to the others and see what happens!


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## dimitri (May 16, 2008)

F16bmathis said:


> The battery has been reading the same as the rest when fully charged, but when under load this one battery goes to a lower voltage faster than the rest till today when it got just over a volt lower than the rest!


Are you sure this new cell is fully charged? Did you top balance it to the rest of the pack?

Sounds like it just needs to be brought up to full charge along with the rest of the pack, i.e. fully charge the pack, then charge this one cell with single cell charger until red LED goes on on the BMS.


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## F16bmathis (Jun 6, 2008)

I only top balanced it once initially. Other than that, I've just had the MiniBMS running till last week, and this week I've had the WIcom BMS added so I can see each individual voltage.

Should I try re-balancing again? I did fully charge the pack last night, then turned it on twice more to top it off, not a balance charge in parallel though. This morning, it kept above 2.9V, but the others were .1V to .2V higher (all under load on a 13 mile highway drive taking it easy at 55). I'm trying to top charge it again for the ride home. Then fully charge to pack voltage, then remove and top charge by itself.


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## dimitri (May 16, 2008)

F16bmathis said:


> I only top balanced it once initially. Other than that, I've just had the MiniBMS running till last week, and this week I've had the WIcom BMS added so I can see each individual voltage.
> 
> Should I try re-balancing again? I did fully charge the pack last night, then turned it on twice more to top it off, not a balance charge in parallel though. This morning, it kept above 2.9V, but the others were .1V to .2V higher (all under load on a 13 mile highway drive taking it easy at 55). I'm trying to top charge it again for the ride home. Then fully charge to pack voltage, then remove and top charge by itself.


I still can't gather from this if you charged just this one new cell separately before putting it into the fully charged pack. There is no need for balance charge in parallel when adding just one new cell. You just have to make sure the new cell is fully charged ( i.e. reaching into the upper knee range, i.e. having red LED lit on it at the end of charge ).

If you have a single cell charger, then procedure is simple:
1. Charge entire pack.
2. Top off the new cell until it reaches the same level as the rest of the pack.
Since you have miniBMS modules, its easy to tell when the cell catches up to others, when its red LED starts to glow.

NOTE: Topping off the new cell must ONLY be done if the rest of the pack is full, otherwise you will imbalance it in the other direction.


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## F16bmathis (Jun 6, 2008)

Oh... Yeah, I went and fully charged the pack in the truck, including the new battery, then disconnected everything and hooked them up in parallel and charged. Then re-wired as a pack and installed the MiniBMS units.

The MiniBMS is working great, thing is, I have not been on a longer drive till last night, so the weak battery never got down enough to set off the BMS warning. My drive to work this morning was the same, no alarm, the battery didnt go under 2.9, but I can see it along with the others with the WIcom and its lower than the rest. Last nights drive was 25 miles and the low battery went way down, MiniBMS alarm was constantly going off and I could see with the WIcom it was a good volt under the other batteries.


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## dimitri (May 16, 2008)

F16bmathis said:


> My drive to work this morning was the same, no alarm, the battery didnt go under 2.9, but I can see it along with the others with the WIcom and its lower than the rest. Last nights drive was 25 miles and the low battery went way down, MiniBMS alarm was constantly going off and I could see with the WIcom it was a good volt under the other batteries.


Does it stand out from the rest only under load? Does it read same as others without the load? Do the terminals/bolts on this cell get noticeably warmer than others? Sounds like extra voltage drop is developed under load at this cell, but it could be inside the cell ( weak/defective cell ) or outside the cell ( poor/dirty/lose connection).

If BMS alarm goes off on this cell even when you let go of the throttle, that means the cell does not recover above LVC even when load is removed, which certainly points to a weak/bad cell. Or maybe this cell is simply much lower capacity than expected.

One trick I use to find lose/dirty connections is to measure the voltage drop between the actual body of the terminal and the busbar attached to it, while charging at max CC current. You should see just a couple millivolts or less on a healthy connection. Establish a baseline by checking all of them , most should be in same small range. If you find some significantly higher, clean and redo that connection.


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## dimitri (May 16, 2008)

Just tried it on my own cells while charging at 20Amp. I measure 0.2-0.4mV between the side of aluminum nut holding the terminal and the top of the busbar near the black shrink tube. Anything that stands out by 2x-3x from the baseline I would consider a poor connection. Actual baseline value might vary due to sensitivity of the meter, amount of current, etc. The idea is to compare the baseline with the cell in question to establish if external connection is clean.

BTW, such test done earlier would have definitely saved your original cell from melting. Live and learn....

I spotted a few poorly torqued connections in my own pack back when I built it 2 years ago, using this method. Never had a problem since then, knock on wood...


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## F16bmathis (Jun 6, 2008)

dimitri said:


> Just tried it on my own cells while charging at 20Amp. I measure 0.2-0.4mV between the side of aluminum nut holding the terminal and the top of the busbar near the black shrink tube. Anything that stands out by 2x-3x from the baseline I would consider a poor connection. Actual baseline value might vary due to sensitivity of the meter, amount of current, etc. The idea is to compare the baseline with the cell in question to establish if external connection is clean.
> 
> BTW, such test done earlier would have definitely saved your original cell from melting. Live and learn....
> 
> I spotted a few poorly torqued connections in my own pack back when I built it 2 years ago, using this method. Never had a problem since then, knock on wood...


Well that, or simply not passing over that terminal when tightening them all down. I had used a stainless wire brush to clean all the connections and buss bars every time I've had it apart. I've gotta try that measurement across the stud to buss bar. Right now I'm at work charging and slightly discharging to see if I can't get it closer to the rest of the pack. About three cycles so far today. I'll drive home and pull it and individual charge tonight after pack charging.


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## F16bmathis (Jun 6, 2008)

dimitri said:


> Does it stand out from the rest only under load? Does it read same as others without the load? Do the terminals/bolts on this cell get noticeably warmer than others? Sounds like extra voltage drop is developed under load at this cell, but it could be inside the cell ( weak/defective cell ) or outside the cell ( poor/dirty/lose connection).
> 
> If BMS alarm goes off on this cell even when you let go of the throttle, that means the cell does not recover above LVC even when load is removed, which certainly points to a weak/bad cell. Or maybe this cell is simply much lower capacity than expected.
> 
> One trick I use to find lose/dirty connections is to measure the voltage drop between the actual body of the terminal and the busbar attached to it, while charging at max CC current. You should see just a couple millivolts or less on a healthy connection. Establish a baseline by checking all of them , most should be in same small range. If you find some significantly higher, clean and redo that connection.


It does stand out when under load, and is also slightly lower than the rest when charged, but it does need a good individual charge to see if it can come up to the rest of the pack.

It scares me that I might have pressured the supplier to get me a battery. It had taken him two weeks before he even acknowledged that I bought one and that he'd send one as soon as he could. Then he said he had a friend that had one, and sent it to me. I'm worried that he sent me a used one. Plus, I've e-mailed asking about a replacement, and again, no response, though its only been 18 hours...


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## F16bmathis (Jun 6, 2008)

I'm going to hold off on a replacement for now... I'm trying to bring it back to full Voltage and see if it holds. I had the MiniBMS installed, and just recently installed the WIcom BMS which shows the actual voltages. Normally, I don't drive long enough to drain the bad battery to its lower limit, so I never got a warning. Now that I have the WIcom BMS, I can see it was going down the entire drive, and I drove almost twice as far as I normally go, so I had all the alarms.

I just drove with the bad battery disconnected to lower all the other battery voltages down to where the bad one sits at. 8 miles. Now I'm charging them all as a pack to see if I can get it back up with the others. I just started, but so far the bad battery is not showing as either the highest or lowest voltage, but I've got another 2-3 hours of charging to go. It'll need some tweaking if it works!


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