[MN Driver]

A shorted cell will be fully discharged, a specific gravity reading would indicate that.

Unshorting a cell? Usually when a FLA battery has this happen, it's finished. Most people using these in EVs scrap it and replace. It's possible if you can blast enough current through it that you can blow up the short but if the separator is damaged, you will have no luck. Trying to do that might also burst the battery and with a 4D, it would be a huge mess of acidic fluid everywhere. With the battery sitting around for so long, you will need more luck than you can probably get because its probably sulfated terribly as well.

 

[alexcrouse]

Hooking a 25 amp load to it indicated that it still has a capacity in the 90Ah range. Free is good. Considering this is a school project and my budget is ZERO. Sadly, due to the design, i cant find a way to pump current through just that one cell.

A shorted cell will be fully discharged, a specific gravity reading would indicate that.

Unshorting a cell? Usually when a FLA battery has this happen, it's finished. Most people using these in EVs scrap it and replace. It's possible if you can blast enough current through it that you can blow up the short but if the separator is damaged, you will have no luck. Trying to do that might also burst the battery and with a 4D, it would be a huge mess of acidic fluid everywhere. With the battery sitting around for so long, you will need more luck than you can probably get because its probably sulfated terribly as well.

 

[MN Driver]

You mean to just charge one cell or to avoid the cell?

If you want to try to charge the dead cell(which if it really is shorted, you won't get far), you could stick a probe into the water fill hole to contact the plates of two cells next to eachother, once you probe and see no or very little voltage in comparison to other cells directly next to eachother, you know where to charge.

...but if its shorted, not sure what to tell you there, I'd say you are stuck.

 

[alexcrouse]

So after an overnight sit, i got out the hydrometer. No cells read even remotely charged. One is higher than others, but still in the red. I guess i don't have one dead cell, i have 6. Time to get out the welder and wake this baby up.

 

[MN Driver]

Wait, if they are all low, I wouldn't say you have 6 shorted cells. The welder likely won't help. I'm not sure what's up at this point as I don't know how to interpret the specific gravity readings in a diagnostic manner.

Are you sure the battery is fully charged? A 15 amp charger will take a long time to charge a 4D.

 

[alexcrouse]

not 6 shorted, just 6 weak cells. And welder is how i woke up the 3 batteries in the car.

 

[Harold in CR]

Could you explain how you did that on the car batteries ??? Thanks

 

[alexcrouse]

Treated the DC arc welder as a Power Supply. Turned off the feed, and touched the positive to the battery positive, clipped the negative to the other, and pull the trigger about 100 times. i monitored the voltage and current while doing it. At first, the battery drew very little at all, then the current rose as i went. Now they charge normally and have about 80% of their rated capacity. Not bad, considering they were flat dead for about 5 years.

 

[Harold in CR]

Ahhh, so it's Mig welder. I just have a cracker box, here. Mig is in Fl, along with all the other Metal Working Tools.

 

[Sunking]

Ok if this battery sit on a shelf for 5 years, it is not shorted cells, exact opposite. The battery self discharged and remained discharged for many years and the plates sulfated and the crystals hardened. What you have is very high internal resistance, that is why you cannot pump current through it to charge it up. The charger voltage goes up immediately because of the high resistance and shuts off. Put a load on the battery and you will see the voltage crash. The battery is toast and died several years ago.

Shorted cells cause the exact opposite, the charger just keeps pumping current and the voltage never comes up to indicate fully charged.