[GreenKeys] energizing relays and questions on voltage and current

[Craig Sawyers]

> Finally, there are thermal considerations.  Some electromagnets, relays
> and solenoids are designed for continuous duty.  Those you can leave
> energised forever.  Others are designed for intermittent duty.  With
> those, you should only pulse the power or you risk burning things up.
> That's why I recommend that the variac experiment be done quickly, in
> seconds, and then turn off the power.

I know it is kind of irrelevant considering the age of the technology here,
but the way this is done in more recent times is to whack in a high current
pulse of maybe a tenth to half a second to engergise the magnet and move
whatever it is shoving, then the current is reduced to the holding current.
The energizing current and holding current may differ by a factor of two or
more depending on the system (so the power difference is a factor of four).

Craig