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Automotive battery question


doc47

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I've got a 100 amp-hour lead-acid battery that was left connected to a solar charging system with a faulty regulator. I'm trying to figure out if the battery is fried.

I connected it to a 6-amp charger and after 24-plus hours the battery is reading 12.7 v. I have a feeling it should be at 13 or above.

Any opinions?

(Well, hell! There are ALWAYS opinions here! Does anybody actually KNOW anything??) :rofl:

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Yeah....it sounds ok voltage wise. The big question is if it has any umph left in it. The only way to know is to put a load on it and see how the voltage reacts. If the voltage holds up under load, then it should be fine. Lead acid batteries can take some serious abuse

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DaveTheAffable

"A fully charged battery, without a drain or load, after the surface charge has dissipated, is 12.63 volts for a 12 volt battery.

Other states of charge are:

12.60 volts = 93% charged

12.55 volts = 89% charged

12.50 volts = 85% charged

12.45 volts = 80 % charged

12.18 volts = 50 % charged"

 

Courtesy of..... Batteries Northwest

(no affiliation)

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So I'm curious how you know that the regulator was faulty. How high was the voltage that the battery saw, and for how long? Did it boil?

 

Opinions are like armpits. Everyone's got a couple of them, and they usually stink.

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Eric, I was TOLD the regulator malfunctioned and that the batteries were left on circuit. Whether they boiled or not is up for grabs. Somebody said something about 15v. but reliable information here is as hard to find as Brough Superior SS100s.

I've seen load tests done but wonder if there's a way I could do one here.

And that's my armpit.

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I used to have a book or two on the topic, but who knows what happened to 'em with our recent move. At any rate it seems to me 14.7 is a normal regulator output, so 15, give or take shouldn't ruin anything. The voltage can vary depending on your system (auto, off grid, RV, whatever) and I forget how it goes.

 

My experience with this sort of thing (at least the African version) goes something like this: Put it in the car and pretend nothing happened.

 

To actually test it, I believe you put it in the car and check the voltage when running the starter. Like

 

a little more information: HERE.

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Gads! Too much for me!

The battery is actually a 100-amp-hour battery I bought to run a fan, a few lights, etc.

I guess the best way is to charge the thing and see if it works.

 

BTW, how long does it take surface charge to dissipate after charging?

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DaveTheAffable
Gads! Too much for me!

The battery is actually a 100-amp-hour battery I bought to run a fan, a few lights, etc.

I guess the best way is to charge the thing and see if it works.

 

BTW, how long does it take surface charge to dissipate after charging?

Just a few moments. Put a light load on it (i.e. a light), remove, and test.
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Just checked the battery after 3 days trickle (turkle?) charging and then off charger overnight: 10.4 volts. Afraid it's toast! Those solar panels done fried it.

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With a severely discharged battery, a trickle charger may not be sufficient to reawaken the near dead.

 

10.4 volts is on the edge of what many chargers would accept to recognize that a battery is connected. If you can connect another battery to the questionable one, then charge them both together, for awhile, you might be able to bring it back. Or.....It very well may be toast. Good luck.

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If it's a wet battery with removable caps, try to get your hands on a hydrometer and check the specific gravity of each cell. They should all be close to the same.

 

If you have to replace the battery, avoid getting an automotive starting battery and look for a battery made for deep cycling.

 

It is puzzling that the battery made 12.7 volts before and now is under 11 but I'm thinking you might find the battery has a bad cell that would show up clearly with a hydrometer. If not, charging at 6 amps or higher might wake it up but in the long run this is not a good application for an automotive battery.

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Good thoughts. I will try to find a hydrometer in The Gambia. Not much chance of finding anything down here in the rural Casamance. The Gambia, even though corrupt and bankrupt, has far more active commerce and access to products from Europe and America.

Would dumping the fluid completely and replacing it with new sulfuric acid be worth trying?

And, I do plan to be using real deep-cycle batteries for the solar system Im putting together. There are some 200 amp-hour gel cells available in The Gambia.

I just wanted to use this battery in the interrim to power a fan, if possible.

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I suspect that your battery has a shorted cell. If that's the case I don't think there is anything you can do to rejuvenate it even temporarily. Trying to recharge could even ruin a charging system that does not have some built in protection.

 

There are videos on youtube where people show various methods of refreshing a battery, probably ones that are weak but have acceptable internal resistance. I shudder to watch them because they often show a gross disregard for the potential dangers. A battery can produce hydrogen and self generate a spark, not a good combination. Acid burns especially to the eyes are a possible outcome. I would avoid messing with these procedures but I admit that my perspective is from relative luxury and with many alternatives readily available.

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Doc, I'm curious about the system you're building. Are you planning it yourself, or building from a kit or something? Have you got a book you're working from?

 

I've always been interested in off-grid energy production.

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Eric, I'm building this system myself. I've read a few books and have picked some brains around here. There are actually a couple of guys in town who make their livings doing solar systems, but they are beyond my budget.

The systems are actually not that complicated, especially when one is completely off-grid. When solar or wind are used to supplement an on-grid system it gets a little bit more complicated, but still do-able.

The main decisions are to estimate how much power is needed, then size the system appropriately.

I'll actually be running two separate systems: a 24-volt system for the water pump, and a 12-volt system for the house. At this point I will likely use smaller inverters at the point-of-use for items that require AC power. I may change my mind on that, however, and install a big honker of an inverter, say 2000 watt.

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Hey, that sounds like great fun! I've read a few books on the topic. Mostly regarding RVs or boats, but it's about the same as off grid.

 

Not that you'd be buying from them, but here's a couple of places I thought had some good info.

 

http://www.amsolar.com/

 

http://realgoods.com/

 

http://www.grapesolar.com/

 

https://tools.carmanah.com/src.web/GoPowerCalculator.htm?state=RvDiv

 

http://www.batteriesnorthwest.com/batteryschool.cfm?TID=10#ANC10

 

http://www.batterysizingcalculator.com/

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