[TR] Off topic electrical question

[Randall]

> When charging a car battery, I was always told to disconnect the
> battery
> terminals first, then connect the charger.

My opinion, there was a period in history where that was a good idea.  Now,
unless you are working on a car with early solid-state electronics (or an
early alternator) and using a poorly regulated battery charger, I don't
believe there is any point.  Unless perhaps the battery is run nearly flat
and you might get the connections reversed.

Some old car electronics (eg radios & alternators from the 60s) assumed that
their input voltage would never go above 20 volts or so.  Some battery
chargers (especially the old service station "fast" chargers) put out enough
voltage open-circuit to damage them.  When you connect them to a battery, it
takes the battery a few microseconds to start charging and pull the voltage
down.  Doesn't hurt the battery or charger, but could possibly damage a low
voltage transistor or solid-state diode.

But any device built in the past 30-40 years will be resistant to spikes
past 100 volts; and modern chargers are much better regulated, so I don't
believe it's an issue today.  Certainly I've never done it.

-- Randall