4a Power Battery Charger

4a Power Battery Charger
question about secondry winding power transformer?

I had a car battery charger that was rated at 12V 4A I have had to remove the secondary windings from the transformer as they were burnt out.
What I would like to know is how many turns would I need when i re wind the secondary coils to up the ampage but keep the voltage @ 12V I would like to get at least 10-20 A
Please bear in mind that after doing this the transformer will be used in a power supply project

What you’re trying to do is hardly worth the effort, but here goes…. The turns ratio is 10:1. That means that for every 10 turns in the primary, there will be one in the secondary. That’s not going to change… regardless of the amperage. What you have to do to increase the amperage is increase the wire gauge in the primary AND in the secondary, while keeping the turns ratio the same. What does that mean? Simple… you would have to completely rewind the transformer with larger diameter wire. The problem is, your existing core is too small. Solution? Buy a new transformer. You can’t build a better one for anywhere approaching the cost of a new one and expect it to work.

IMAX B6 balance charging Stun Power battery with 2C / 4A