Patman3 Solar Expert Posts: 62 ✭✭✭✭
I have 20 6V 225Ah US-145 batteries in series (electric car). 2 of these batteries are always about .1V lower than the rest after resting, and when charging, these 2 particular batteries reach 8V much sooner than the rest. One is second from the positive end and has a crack with some tape covering it. Also I noticed right after use it's terminal posts are very warm and tight, the other batterys posts are not this warm (after drawing 175 amps for a while). The other battery is about in the rear middle and I have not examined it as much as the bed must be raised. I think this means something but I'm not sure what. I am thinking of replacing those two batteries. As always, Thanks for your help.
0 · Share on Twitter
take those 2 batteries out of line and examine them closely along with your connections to them. charge up those 2 batteries seperately while observing proper water levels and such. if these 2 were on the ends of the string, put them in the middle now and those that were in the middle place them on the ends. in other words rearange the pecking order and see what happens to those 2 batteries and the ones that were shifted into their places.
after doing this and using as per the norm for a few cycles is the best time to check to see what difference that has made and if those 2 same batteries show the same then they are degrading faster than the rest of the bank. if you replace only 2 batteries then they will only be as good as the worst in the bunch and where there are 2 downgrading, the rest may not be far behind so i recommend replacing all of them in that case. let us know what the results are.
If these two batteries are as bad as I think, are they already pulling my system down, thus the heating? I assume replacing them will make the others better, at least as good as the third worst one now. I don't want to replace them all because they are only around 2 years old (cycles not sure of, I have about 12 cycles on it).
In general, in a series string of batteries, they should all be behaving the same... If you notice a couple warming, that is a sign of trouble. It may be the batteries themselves, or it may be the cable connections.
As always when working with large battery systems., the warning of taping tools and/or using insulated tools, usually lift the ground terminal first (to isolate the frame and help prevent accidental shorts) and be careful of what you are doing (or have somebody else do the work, if you don't know). (usual web safety warning--)...
If you can, place the batteries under load and use a DVM meter on millivolts and see if you can find any areas of higher than normal voltage drop (to isolate a bad or dirty cable/connection--removing the ground, then cleaning the "warm" terminals vigorously using wire brushes or sandpaper--and checking for bad cable crimps is worth doing). If all of the cables and connections look OK, then you are probably looking at problem batteries and replacing the two is probably worth the money (only 10% of cost of an entire bank). When the rest of the bank needs to be replaced, you should probably replace these two "newer" batteries too.
The cracked battery could be the result of handling or excess heat because of terminal or internal issues. If you have a "bad" jumper cable, not repairing/replacing it can cause the new battery to fail early too. If there is an acid leak due to the cracked case, it is possible that you will need to replace the cable.
The battery string is, pretty much, only as good as its weakest link(s). It sounds like you don't have very many charge cycles on the battery bank. Is the charger behaving properly? Proper voltages and times--no long periods of overcharging/dry cells or long periods of no charging while batteries are partially discharged?
wow, i'm slipping. a crack in the case and warm to the touch is a very bad sign. odds are you should replace the whole lot of them.
You aren't slipping - I added that info after reading your first response, sorry Niel.
relief and thanks for telling me that. replace the whole lot of them. if there's any semigood ones left over they may be usable in other applications, but not with the new battery replacements and i certainly would not consider them reliable.
nope, i think he's slipping. :-P
I replaced two batteries. The cracked one was a real mess. It had left some kind of greyish whiteish paste all over the bottom of the battery rack, I couldn't see until it was removed. It definetly had to be replaced and the area cleaned. The date code, I 5, means these batteries are only exactly 1 year old (I being September), so I will hold off replacing them all Niel, but I have a good feeling about it working better now, as it can only be as strong as the weakest battery. The other battery seemed to have a lower capacity as it reached maximum voltage sooner than the others and never stayed up in voltage after settling. Garages are HOT in the summer here in Las Vegas and maybe the heat shortened it's life, or excess DOD. New range is yet to be tested but I should be able to get almost 2 1/2 to 3 miles per battery, or 50 to 60 mile range, whereas before I would get maybe 44 miles.
The charger is a Zivan NG3 and seems to be working properly, changing from red LED to blinking red to yellow to green, around 152v at the end, or 7.6V per battery. Battery technology is THE MAIN disadvantage of electric cars.
Thanks for your help BB and Niel. While the pack was charging (around 20 amps or so) I measure the voltage drop in millivolts across each interconencting series cable/post combo (21 of these I guess). A 3 decimal place VOM is essential. Most cables read 3 to 5 mv or .003 -.005V. I found 6 cables over 35mv or .035V, one was 70mV! It wasn't the post to cable connection, it was in the cable itself!? Maybe acid got in there? Anyhow, bump the current up 10 times to 200 amps when driving and that voltage drop will become .7V, add in a couple more of those bad cables and I figure I can improve my car's voltage by almost 2v under load. I thought to myself, this is how we tune up an electric car. I am currently building some new cables that I soldered with a tourch.
Sounds like you got the problems nailed!
A couple of suggestions... Make sure that you only use rosin core solder/flux when soldering... Any plumber's solder or other types of acid solder will just cause those cables to fail again (sooner rather than later).
If you are going to be working on cables a lot for this vehicle (over the years), you may wish to look at getting the proper crimp connectors and crimp tool to use them (if available)--for many reasons, crimping is much preferred over solder connections and in the long run, you will probably have better results with crimping.
(solder flux can corrode copper over time, solder melts under heavy loads and a wire can come loose from its connector and short, solder stiffens the wire at the connection--and will cause cables subjected to vibration/bending to fail right at the end of the solder joint, crimp connections usually pass current better than solder connections over time--less corrosion/less broken wire strands due to work-harding at solder joint)
Wow that was a quick response. I used rosin core from RS, I figured it couldn't hurt to solder on top of a crimp if at least just to seal it up due to capillary action, but it does make the cable a bit stiffer there. Also, I have the vice type crimper that you use a sledge hammer to pound a crimp into the battery post lug. This is all 2/0. It was $35 vs. the plyers type crimper for >$200. I accidently crushed the cable with the mallet ( swing and a miss) on the first one I did.
Yes, it is the capillary action of the cable that draws rosin (and other corrosives) up the cable when soldering that you can't clean out and will start the corrosion process... Also, it is again the capillary action that draws the solder up the strands creating a point at where flexing will be focused and cause work hardening of the copper... Crimp connections just don't have these issues.
Like you, I always thought that soldering a crimp connection was a good "belt and suspenders" type solution for a long lasting electrical connections... However, over the long years of working around cars (such as trying to fix broken jumper cables) and designing/manufacturing/repairing computer systems, I have found that solder is almost always best avoided when attaching wires... At best, I did not find any advantages to using solder--and at worst, many reasons to not use solder.
Find or borrow a hydraulic crimper, much better crimps in large wires
A friend has an electric car, and loose cable connections have melted several terminals off the batterys at various times. A real battery shop (he has one nearby) can re-cast a terminal back on for $5
Improves a crimp joint * BUT * you have to use a special heat sink on the cable to keep it from wicking solder up the cable, wicked solder stiffens the cable, and causes it to crack.
Rosin flux is generally considered not corrosive, if you have new wires, or even silver plated stranded, it won't need much flux, heat it FAST (big iron or torch) and solder it quick.
many strands of fine wire are prefered over a fewer strands of heavy wire, it flexes more without breaking, Welding cable may meet your needs.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
gen: http://tinyurl.com/LMR-Lister ,