SLAs will be Tricky. If the supply you have is regulated, the variac is not
a very good idea. The transformer operation and efficiency is not an issue.
It will work just fine on the variac.


However, you really need a well regulated supply and accurate voltmeter and
to float them for full charge. I have two little SLAs sitting at 13.75 all
the time.

Read the lead-Acid sections of this first, then decide.
http://www.batteryuniversity.com/partone.htm

Having a good background in Lead-Acid basics, you can do some things, one
being:
For one battery at a time:
1- Measure voltage at start to determine charge state.
2- Calculate amp-hours to full charge (knowing the charge replacement
efficiency of YOUR battery).
3- Charge with known current (like a ni-cad charger) to somewhere under 90%.
4- Measure the open ckt voltage periodically, but after the required rest
period.
5- Stop before disaster happens.

OR

Just wing it. (:-)

73, Steve, K9DCI

Just kidding with the wing it thing.


wrote in message
oups.com...
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.