"Panama" wrote in message
...
I have a 40 amp battery charger that has a 5 position switch to select
the battery charging voltage. Works great. Allows steps from about
13.2 to 17 volts. Prob done by a multi-tap transformer?

Trouble is - AC voltages in Mexico can be as high as 128-130 VAC and
other places can be as low as 105 VAC. The charger reacts by changing
the battery charging voltage up or down - a little but enough to vary
the DC amps that get to the batteries. I'm not going to replace the
charger.

I'm looking for a cheap variac/scr/triac something gizmo that I can
wire into the AC line to the charger and make the effective voltage
(RMS value?) go up or down by +/- 10% or so. The AC in is about max 9
amps. It could even be a big wired wound variable resistor I suppose.
Then I can set the AC line voltage to what my genset puts out and use
the charger at it's max 40 amps all the time.

Any ideas or products. Preferably cheap and never needs replacement
like the 27 years old charger.

I would not really worry about the voltage out as long as it is greater then
13.7vDC it should charge the batteries fine. You should be able to pick up
a used variac off ebay or get one new from fisher scientific. They
generally will supply from 0% to 120% of the input voltage. You should wire
a volt meter into the variac to see your output voltage before you plug the
charger into it. We use tons of them to regulate our furnaces at school so
they are straight forward to wire just keep in mind they supply a % of the
input voltage. So if you are overdriving the output and the input ramps up,
the output side may be more voltage then what the charger can tolerate.

good luck,
mark