On Sun, 23 Nov 2003 16:43:03 -0800, Panama wrote:

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.

(No I'm really not going to replace the charger.)

Seems like I answered this in another newsgroup, but if you missed it...

There are two types of auto-regulating transformers. The old kind uses a
swinging core. As the voltage varies, the core moves in and out to provide
a more or less constant voltage. I say "more or less" as they can seldom
act fast enough to block transients, those very short term spikes which can
damage electronic gear.

The second type are called "ferro-resonant" transformers. They work by
driving the core into saturation and operate in parallel with a
non-polarized capacitor to ensure that the output voltage always remains
the same. They offer a few advantages, the best being that they do not
transfer voltage transients (spikes).

Both are rated in volt-amps and both are available on the surplus market.

Good luck
--

Larry
email is rapp at lmr dot com