Timer charger - any way to mod for auto shutoff?

[rlw]

I got to thinking about the charger that came with my 83 Marathon. It's a timer-based charger. My neighbor's 98 TXT came with an auto-shutoff charger. It occurs to me that a circuit monitoring the current draw in the old charger could shut off the charger when the current drops to a certain level.

This sounds like something JohnnieB would know how to do, but if anyone has whipped up a retrofit for the old chargers, I'd be glad to hear about it.

I did a search for "timer charger auto shutoff", but couldn't find anything.

RLW

[simple man]

You may be able to adapt the newer timer board to your charger. I'm not that familiar with the newer style. I have two old Totalcharge manual timer chargers and a Lestronic II that I now use. The Totalcharge works fine, I just used to set the hours on it depending on how much I used the cart. I like the Lestronic II, cause it weighs a lot less than the Totalcharge! That makes a lot of difference to me, when I have to carry them around!

[JohnnieB]

Originally Posted by rlw

This sounds like something JohnnieB would know how to do.............

Never seen a manual/timer charger, nor a complete set of pictures of the innards. (Hint - Hint - Hint)

From what I can tell from a schematic I think might be a Manual/Timer type charger, they appear to be electrically the same (or similar) to the Automatic types except for the Primary circuit of the transformer.
The AC to the primary is switched on/off by a timer in the M/T type and by a relay on the control board in the Auto types.

Note: Activating and deactivating the AC relay is all the control board does. It does not control the amount of current going to the battery. That is done by the Ferroresonant Transformer and associated capacitor.
Basically, for the control board to turn on the charger, it has to sense a voltage of 27-30V (36V charger) and to shut it off automatically, it has to sense 44-46V, or if that voltage isn't reached sooner, a safety timer will cause the control board to deactivate the relay after 14-16 hrs has passed.

I suspect an industrious person with a little electrical/electronic knowledge might be able to figure out how to wire an off the shelf replacement control board in the transformer primary circuit and attach the battery sense lead to B- somewhere in the output circuit, but mounting it safely inside the case might be tricky.