Is That a Resistor Wired Between the Hot Side and the Switch Side of the Solenoid?

[jls]

And what's it for? Voltage spikes maybe? It's just under the voltage
regulator on the firewall of a 1966 172, which, btw, is a wonderful flying
airplane, as I can attest from experience.

Whoever installed this device did a sloppy job because the wire was out of
the oversized terminal on the switch side. Anyway it's apparently a tiny
resistor wired to the starter switch on the solenoid and the other end of
the wire runs to the solenoid's hot terminal.

Curious.

[John Kunkel]

" jls" > wrote in message
...
> And what's it for? Voltage spikes maybe? It's just under the voltage
> regulator on the firewall of a 1966 172, which, btw, is a wonderful flying
> airplane, as I can attest from experience.

It's a diode to prevent spiking the system when the field around the
solenoid collapses.
John

[MikeM]

jls wrote:

> And what's it for? Voltage spikes maybe? It's just under the voltage
> regulator on the firewall of a 1966 172, which, btw, is a wonderful flying
> airplane, as I can attest from experience.
>
> Whoever installed this device did a sloppy job because the wire was out of
> the oversized terminal on the switch side. Anyway it's apparently a tiny
> resistor wired to the starter switch on the solenoid and the other end of
> the wire runs to the solenoid's hot terminal.

Likely a 1n4007 Silicon rectifier installed to comply with a
Cessna Service Bulletin.

It is there to suppress a voltage spike caused by the collapsing
magnetic field in the coil of the starter solenoid. This happens
just as you release the starter key switch.

There should also be one on the master (battery) solenoid. If your
aircraft has "jump start receptical", then there should be a third
one on that solenoid, too.

MikeM

[jls]

"MikeM" > wrote in message
...
> jls wrote:
>
> > And what's it for? Voltage spikes maybe? It's just under the voltage
> > regulator on the firewall of a 1966 172, which, btw, is a wonderful
flying
> > airplane, as I can attest from experience.
> >
> > Whoever installed this device did a sloppy job because the wire was out
of
> > the oversized terminal on the switch side. Anyway it's apparently a
tiny
> > resistor wired to the starter switch on the solenoid and the other end
of
> > the wire runs to the solenoid's hot terminal.
>
> Likely a 1n4007 Silicon rectifier installed to comply with a
> Cessna Service Bulletin.
>
> It is there to suppress a voltage spike caused by the collapsing
> magnetic field in the coil of the starter solenoid. This happens
> just as you release the starter key switch.
>
> There should also be one on the master (battery) solenoid. If your
> aircraft has "jump start receptical", then there should be a third
> one on that solenoid, too.
>
> MikeM

Thanks to Mike and the others who responded to my questions about the
rectifier and leaky struts, making this newsgroup (and also because of so
many knowledgeable of courteous people here) a pleasure to visit.