Fast acting device to protect a high current 6/12V charger during short circuit?

Thread Starter


Joined Dec 16, 2016

Which device best protects the rectifier and electronics inside an older style car battery charger? I have seen some manufacturers use an ATC blade fuse but I'm not sure if that will act fast enough to protect the circuits. I came across another device too, it's a Bussmann Circuit Breaker BP-UCB-10-RP. One advantage is that I don't need to open up the charger to replace the fuse if I go with the breaker. But one concern I have is which acts faster. Also, is there any other technique that you guys can recommend of these two are not really sufficient? I don't want to build a very complicated circuit either. Something simple that gets the job done.

The transformer inside is a Bosch 130VA 14/9VAC connected to a KBPC3510A full bridge rectifier (the original charger case was changed with a Schumacher charger since the orange plastic body had a burned section where the selenium rectifier originally was). But since the charger originally had a selenium rectifier which got damaged and was replaced with a silicon rectifier. But since selenium rectifiers have a higher voltage drop you can see the transformer output is 14VAC for the 12V setting & 9VAC for the 6V setting (had around 14.5VDC & 7.3VDC with selenium rectifiers) compared to silicon rectifier chargers where the transformer output is around 10-11VAC. Since the bridge rectifier had only a 1.1V the rectified output was too high and I ended up using a 35V 4700uF capacitor and then used two 300W DC-DC buck converters to step down the voltage to 14.4/7.2VDC and the current limited each unit to 5A since the specs say above 8A a fan is needed. So, it's now rated to the original max current setting. So, I want to protect the unit in case of accidental short circuits and the transformer mainly.




Joined Aug 21, 2008
I would be surprised that such a thing is needed if the charger was designed to charge large batteries. Consider what happens when a charger is connected to a totally discharged battery -the charger should survive such events or the manufacturer would have to placate a lot of very unhappy customers.