Taming Lester 7

Someone asked why I would bother fixing up this old transformer-based charger when my EV has a lightweight, modern charger installed in it:

I wouldn't want to carry the Lester around in the car, for that the K&W will suffice, but there are advantages to using a transformer-based charger:

1) ISOLATION: The transformer makes very sure that the traction pack is never "hot" with respect to the AC line, lessening the chance of getting a shock when servicing the batteries while being charged. I've gotten bitten many times this way, and it's not pleasant. I removed the GFCI from my charger very early in the game due to nuisance tripping.

2) BETTER POWER FACTOR: A transformer-based charger can match the output voltage to the pack voltage better, so less phase control is needed, improving the PF significantly. Residential watthour meters don't charge extra for low PF's, but commercial meters do. Either way, low power factor will cause heating in cordsets, connectors and fuses/breakers, which represents inefficiency and real power lost.

3) CHARGE RATE: There are only so many amperes you can suck out of a 120 volt outlet. 240 volt chargers allow you to step up the current while stepping down the voltage.

4) PACK VOLTAGE MATCHING: We luck out on the SCT's as fully charged voltage is about 130 volts, within the 156 volt peak of a 120 volt AC line, but if you were running 120 volts or more, you'd need a step-up transformer to boost the line voltage to match the pack voltage. If you are going to have to have a transformer anyway, might as well use it to give you the benefits listed here as well.

A high frequency, switching charger might be able to deliver some of the above advantages (not PF, though), but I like heavy iron, it's much more rugged, and can be worked on when it quits. Besides, I already had the Lester, and it was either fix it up or throw it into the recycle dumpster, I'm tired of having a lot of useless equipment laying around.

Part 8