On Sat, 19 Feb 2011 13:13:23 -0500, "Wild_Bill" wrote:

I should've realized I'd leave out details since the post was composed
quickly.

The charger consists of a ferro-resonant transformer (third xfmr winding
wound over the xfmr secondary and 2uF AC capacitor), and a full wave
rectifier (2 diodes).

A relay handles the begin/stop-off control (xfmr primary energize/off), and
the charger has no high current components (other than the diodes).

I don't see what takes care of the 24V voltage regulation.

The battery does that, think of the charger as a current source.

The Lester control board has a small sealed pc-mount pot and 7 ICs, but no
power handling components.. only about a dozen resistors/capacitors/diodes,
and 2 TO-92 transistors.

741
4020
14001 (3)
14040
14093

The power for the circuit appears to be supplied by the to-be-charged
battery voltage.. so it seems that the circuit won't pull in the relay when
connected to a very low or dead battery.

So it drops out the relay when charge is complete? There's enough logic
to make a comparator (741) and timer stuff with logic to take battery through
to full charge. Wheel chair battery charging is cyclic, take battery up to
a voltage, if you are using old flooded cells then start a timer when voltage
reaches a certain point for a controlled over-charge.

Unsuitable for modern SLA or VRLA batteries due to that timed overcharge.

Maybe you're better off replacing the charger, unless you can reduce the
current for the top-off part of the charge cycle?

Grant.

The relay has a manual button to close the contacts, which is how the
charging cycle is initialized by the user (button is actuated thru front
panel).. this is the only start button (no on-off switch).

The output leads are just two 16 gage conductors.