In article .com,
wrote:

Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.

I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?

Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

The transformer in your existing charger will probably function as you
expect if you reduce its input voltage with a Variac.

However, there's no assurance at all that your charger's DC output
voltage will behave. If the charger has a linear voltage regulator of
some sort inside, the regulator's not going to want to track the
reduced input voltage. It'll probably run "wide open", which means
that the charger's output voltage is going to be very critically
dependent on the Variac setting. Unless you are very careful in
setting the Variac, you'll either undercharge the battery, or hit it
with too high a voltage and end up gassing away much of the electrolyte.

You might be able to alter the DC regulation circuitry in the charger,
so that it would regulate down to a lower (switch-selectable) voltage.
You might need to do both in order to charge a lower-voltage battery
without overheating the charger - reduce the input AC voltage by about
half (to cut the raw, unregulated DC voltage) and then change the
voltage-regulator setting to produce the correct fast-charge or
float-charge voltage.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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