AC voltage killing my batteries?

[MattS]

I have been having some bad luck with batteries lately. Seems like every tractor I have needs one. Well, The other day I wheeled out my charger so I could add a gauge type voltage meter to it. I started probing with my digital volt meter and noticed it only put out about 2 volts dc. Just for the heck of it, I switched the volt meter to ac and it was putting out any where from 12 -15 volt AC. Any of the experts out there know if the batteries might have been damaged by this? Maybe I could recharge with a good charger and save them. I hope.

[mgonitzke]

Your battery cannot output AC voltage. Only the DC setting on the voltmeter will display the correct DC voltage.

[MattS]

I am talking about the output of my charger. I meant a battery charger, not a Dodge.

[wdeturck]

Your Charger seems to have bad ac to dc rectifiers and may even be the transformer as 15 V ac would only be max of 10.5 volts. I don't think it hurt the batteries but they won't have enough charge. Charge them back up on a low current setting if your next charger has one.

[mgonitzke]

Oops...didn't see the word 'charger' the first couple times I read that.

[jchabot]

Your Charger seems to have bad ac to dc rectifiers and may even be the transformer as 15 V ac would only be max of 10.5 volts. I don't think it hurt the batteries but they won't have enough charge. Charge them back up on a low current setting if your next charger has one.

It does appear that the rectifier is fried. The transformer is probably ok, most meters measure rms ac voltage.

[MattS]

I got a new charger, and so far only one battery that was in the "bad" pile is now ok.

[Tom Scott]

Unfortunately, lead-acid batteries don't like to be discharged. If they are going to sit awhile, a charger that can keep them at "float voltage" is the only way to go. That is hard too if you have lots of equipment and batteries. If you shop for one, they are not a trickle charger; an old time trickle charger will still eventually overcharge the battery. A charger that will maintain the float voltage has a voltage regulator to keep the battery at the exact correct voltage. One brand that I used for years was named a "Battery Tender". It worked well and lasted for years, but I think I killed it when I put it on a shorted battery.

[wdeturck]

Watch for those float chargers to be on sale at Harbor Freight. I have bought them for about $4 but they cost more lately. I use one on my diesel truck with 2 batteries and have 3 more for the Cubs.