Car battery charger problem.

[malcscott]

Hi, i have just replaced the old finned selenium rectifier in a car battery charger. I have fitted a new bridge type. I have tested the o/p volts and it reads 22.5v !! The ac input from the mains t/x is only 14v. Will the o/p volts drop when it is loaded with a battery? Malc.

[Refugee]

Silicon rectifiers have a much lower forward voltage than selenium types.
Perhaps a silicon rectifier may need a transistor regulator added to limit the final full charge voltage otherwise it will have to be monitored as it is charging.

[malcscott]

I have loaded it with a car battery and the voltage o/p is now ok (13.9v) It is charging fine but the ammeter is makes a loud buzzing type noise? Any ideas? It never made any noise when the old rectifier was working.

[Refugee]

A series resistor should give the meter an easier time for sure.

[EDDINNING]

Hi Malc, if possible try reading the DC current into a charges battery. It should be under 1 Amp as the system is designed to taper charge, Add low value resistors to achieve this. You can then check what the current is on a discharged battery and it is normally not more than 3 A as the transformer is wound so as to limit the current.

Ed

[malcscott]

Hi Ed, the charger is rated at 1.5a max. The encapsulated bridge i fitted is rated at 20a. The battery i put on charge with it is now fully charged, just the noisy ammeter to sort out. Cheers, Malc.