Hi gang!

I was talking with a mate yesterday and the subject of using a car battery with a charger across it as a cheap 12volt supply with high current capability. As opposed to using my 12v 35amp supply.. Note load is not constant, just occasional peaks.

So.. If I take my 12v 6amp charger.. And remove the 12v battery it is across... Why can't I just use that as a solid 12v, 6amp supply..?

I'm guessing it is because the voltage will be all over the place, seeing the load as a wavering battery ... But, practically speaking, what is the 'problem' with this idea..? I've just never actually looked at this in detail.

Cheers,

Ian

It would depend on the charger to some degree.
I have a CTEK 7 amp multistage charger which also has an option to operate as a 13.6v power supply. i have used that option many times and the output is stable (though I havent scoped it) and found it quite usable for electronic development.
The very old chargers were simply a transformer and rectifier with no voltage or current regulation other than the load characteristics of the transformer. the modern chargers are multistage and can act as constant current source, constant voltage source, pulsed voltage source etc depending on which stage they are running in.
Chargers can also be very noisy (electrically and radiation) which might affect your requirement.

You will find it will have an output of 14-15 volts unloaded and no filtering, with most cheap transformer chargers when you add some capacitors for filtering the peak voltage will be around 15 volts, and is why they overcharge batteries if left connected for long periods.

Go to Jaycar and buy one of their 5 amp x 12 volt switch mode supplys for about $30.00 and forget the battery, as in the long run it will be cheaper, with no acid fumes / hydrogen from over charging a battery on standby.

Pete.