[GreenKeys] WU Modeal 2-A "Iron Horse" doesn't strike

[Ethan Blanton]

Jim Haynes wrote:
> The resistor-capacitor are there to protect the contacts that control
> the magnet by absorbing and dissipating the energy that is stored in
> the magnetic field when the contacts open.

Fair.  I assumed it was to reduce EM noise on the line, since the
current is pretty low, but that makes good sense.

> Can you measure the current draw from the power supply when you press a
> key?  Line voltage should be 120V DC and you can calculate what the current
> draw should be from the resistances you have measured.  Maybe
> something is increasing in resistance when the voltage is applied.

My line voltage is a little low.  As I meant to make clear in my
previous email (but on review it is not), there is 118 volts across
the two coils from end to end.

> Or try measuring the voltage across each of the coils when the contact
> is closed.

I hadn't checked them individually.  They each read about 59 volts, so
the current is balanced between the coils.

Curent through the two coils in series (checked by closing the circuit
via a DVM) is 162 mA.  That yields an AC impedance of 572 ohms plus
the DC resistance of 156 ohms, which seems within the realm of
plausible. Unfortunately I don't know what the current draw or AC
impedance are *supposed* to be.  That's a 20 W solenoid, though, which
I would expect to put out far more than a couple of ounces of force
even if it's rather inefficient.

Ethan