12v 0.5A auto trickle charger

[R791945]

The charger had its ends cut off. The cable from the charger does not indicate which is pos & neg. A volt meter across the end does not register because the charger seems to need a feed back voltage before it will charge. How can I test for which cable is neg and which pos?

 

[Externet]

Good question. The internals should give a clue, make a schematic + pictures of what you see and bring it here.
Many good modern chargers are discarded because as you say, need to detect the battery-to-be-charged is healthy, and refuse to work connected to a dead piece of junk residing years under backyard trash.

 

[R791945]

Thank you for that suggestion. I looked inside and it was obvious which cables were + & -. The board was marked.

I have an APC back-up CS 500. It suddenly stopped working. I looked at the MB and there was no obvious sign of burn out or damage. It looked in very good condition.

I wondered if the lead battery was finished. I have put a volt meter across it and it shows 5.8 instead of 12v. The trickle charger is not charging, presumably because the volt on the battery is too low. Is there any way to revive the battery or should I throw it out and hope that a new one will revive the battery backup?

 

[Bluejets]

I have put a volt meter across it and it shows 5.8 instead of 12v.

It is past it's use by date.
Get a new one.

 

[duke37]

Or try an old style charger which consists of nothing more than a transformer and rectifier.
If the battery has been sitting at 5.8V for a long time, then the plates will be sulphated and the battery will have no capacity.

 

[hevans1944]

I have lost track of the number of hours I have wasted over the years trying to revive dead, or almost dead, sealed lead-acid (SLA) batteries, discarded by the end-user and then "salvaged" by me from emergency lighting fixtures and small non-interruptable power supplies. Salvage means the object salvaged still has some value. Those batteries only value was in my time that I wasted trying to get them to accept and hold a charge.

@R791945 save yourself some grief and wasted time: just buy a replacement battery and get on with your life. Which is pretty much what @Bluejets recommended in his post #4, except I wouldn't bother checking the expiry or "use by" date on a battery that won't accept or hold a charge, unless it is still under warranty.