Re: EV Beach Buggy Outing - long

[XURQ03A@prodigy.com ( LEE A HART)]

Andrew Delano wrote:
> On the subject of neighborhood voltage: I've heard that this can be a
> problem requiring a transformer to overcome and then there goes some
> of the charger efficiency.

Efficiency of a battery charger is not as easy as it looks. A rectifier in a
box looks efficient, but isn't.

Efficiency = PowerOut / PowerIn. DC power output is easy; Volts X Amps =
Watts. Volts and Amps should be RMS for resistive loads, but Average for
battery charging. Average values give you the power that went into
electrochemically charging the battery; RMS values give you the power that
went into charging, plus the power that went into heating up the battery and
its wiring.

But the AC input power is tricky. It is VoltsRMS X AmpsRMS X PowerFactor. Most
people don't use true RMS meters, and very few have the equipment to measure
power factor. Cheap equipment and sloppy techniques give you an exaggeratedly
high efficiency figure. It can actually exceed 100% with really crappy meters.

Adding inductors, transformers, capacitors, etc. to a charger actually
improves efficiency, by providing a better match between the AC line voltage
and load. Naturally, you can use bad enough parts so it is worse, but when
done right, efficiency improves. As a bonus, you can charge at a higher
current from a given AC outlet without tripping its breaker.

Lee Hart                     If you would not be forgotten
4209 France Ave. N.          Soon as you are dead and rotten
Robbinsdale, MN 55422 USA    Either write things worth the reading
phone (612) 533-3226         Or do things worthy of the writing
e-mail XURQ03A@prodigy.com   (Ben Franklin, Poor Richard's Almanac)