Lead-acid batteries started to come on the surplus market and seem to be everywhere at hamfests (Amateur Radio Hamfest). I picked up a couple to play with. They must have been out of some emergency lighting equipment. I was just starting to build some QRP radios (low power radios) and equipment and was looking for a power source so that I could operate remotely. That is when I decided that I really need a charger for these type of batteries. He is a picture of a sealed lead-acid battery:
Lead-acid batteries presents something of a problem to charge them. A sealed lead-acid battery had the following charging requirements:
Irrespective of the discharged battery's initial state, a properly operating battery charger should charge the battery, give you an indication of the charging status and switch itself off when the battery is fully charged.
I found a great article from a March 1994 QST magazine. This one which the author named the Buzzard does all of this and it can also be used for charging sulfuric-acid-based car batteries. I will not go into the circuit description it would be to long to cover here. Hopefully you will find one of your local ham operators (Amateur Radio Operator) and he will have a source for the article. A good ham friend of mine help me make a printed circuit board for this project. Here is a picture of the circuit it is a poor quality picture but should print ok. It is a copy of a copy:
As you can see from the schematic it is pretty strait forward to build. I had a pretty hefty transformer from my junk box. It requires a transformer that has a output of 18 volts at 5 amp. I did not have a good box to build it in so I had some old PC power supplies that were bad and use them as a box to house my battery charger. Here is a picture of the finished product:
This battery charger has worked flawless since I have built it.