Design change to charger circuit required

Hi,

I built this charger years ago and it has served me faithfully ever since. It was a ETI Top Project and I like it, it is fool proof for guys like me as it;

- operates into a short circuit.
- is not damaged by, or will attempt to charge a reverse connected battery.
- can operate into a totally flat battery.
- is regulated for both current and voltage.
- can float a battery for extended periods.

My issue is that when it was designed (think 1979) car batteries were smaller by comparison than today. Ideally it is great for about a 50Ah battery and it puts out 4A. Things have moved on and I would like to double the output but don't have the know how.

I understand enough (I think) to know that the SCR would need upgrading to say a 10A device, as would the heatsink and transformer (mine could be OK as it was over spec to start off with). I already have a 80mm PC fan installed for additional cooling.

If this assists ...... when setting up a totally flat battery is used. Once connected RV1 is used to set the initial charging current. Currently when setting up I am unable to get more than about 4A. One would have thought that without current limiting that the battery would suck more that 4A? Is this a function of RV1 and does the value need to change?

The switch is as a booster for batteries below 4V.

Can the existing circuit drive the 8A load I would like?


Cheers
Andrew

Hi there,


I just wanted to mention that if you want to double the current
output then the first thing you would have to do is get a transformer
that puts out 8 amps instead of 4. Im not sure if you want to go
that far or not as this will be somewhat expensive unless you can
find a cheap transformer somewhere. The voltage needs to be
the same as the old one too. Of course increase the fuse
rating to 10 amps. You may also have to parallel the circuit board
traces with some copper wire to increase the current capacity
of those conductors too.
The rest would probably be easy, like double the SCR rating,
parallel the 0.25 ohm resistor with another one, double the
bridge rectifier rating, but this would need to be tested.

It would be cheaper to install another 4 amp transformer in parallel with the existing one. Then you have the 8 amp capability.

Does this work, or are there always going to be phase problems?

Hi again,


I would have suggested that but it may be hard to find another
4 amp transformer with the same impedance characteristic.
I guess it's possible though, but easier just to buy an 8 amp'er.