Cherokee battery box repair

John Kunkel wrote:
: I've always assumed they were there to prevent the volotage induced by the
: collapsing magnetic field around the solenoid from spiking the electrical
: system.

I don't think so for two reasons:
1. The starter operating would require the master solenoid to be closed, so the
diode/resistor pair is shorted out and not a factor.
2. The direction of the diode is the wrong way to be a path for flyback current in the
starter solenoid.

Assuming the master solenoid stays closed, the battery should do a pretty good
job of absorbing voltage transients from the starter.

Good theory though.... I'm sure there are some setups where it's set up that
way... I just don't think this is one of them.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

I don't know Cherokee electrics, but does it maybe offer a way to (very
slowly) charge the battery thru the external service plug?

My Cessna 172M has a funny diode-resistor circuit like that in the
battery circuit in which that's the only reason I can see for it. It
is not described in the POH or even the service manual. Otherwise with
a completely dead battery, if I used the ground service plug to start
it, there still wouldn't be anything in the battery to initialize the
alternator.

Flyback diodes don't usually have a resistor in series with them.

Another good idea, but the schematic has rather clearly shown the
diode/connector setup for the external connection, but has it shown as "optional."
This diode/resistor is in addition to that.

nrp wrote:
: I don't know Cherokee electrics, but does it maybe offer a way to (very
: slowly) charge the battery thru the external service plug?

: My Cessna 172M has a funny diode-resistor circuit like that in the
: battery circuit in which that's the only reason I can see for it. It
: is not described in the POH or even the service manual. Otherwise with
: a completely dead battery, if I used the ground service plug to start
: it, there still wouldn't be anything in the battery to initialize the
: alternator.

: Flyback diodes don't usually have a resistor in series with them.


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

If it is for the external connection, then it is there to prevent the
external power from activating the master or external power solenoid
from energizing if the external source polarity is reversed.
Michelle

wrote:

Another good idea, but the schematic has rather clearly shown the
diode/connector setup for the external connection, but has it shown as "optional."
This diode/resistor is in addition to that.

nrp wrote:
: I don't know Cherokee electrics, but does it maybe offer a way to (very
: slowly) charge the battery thru the external service plug?

: My Cessna 172M has a funny diode-resistor circuit like that in the
: battery circuit in which that's the only reason I can see for it. It
: is not described in the POH or even the service manual. Otherwise with
: a completely dead battery, if I used the ground service plug to start
: it, there still wouldn't be anything in the battery to initialize the
: alternator.

: Flyback diodes don't usually have a resistor in series with them.

wrote in message
...
John Kunkel wrote:
: I've always assumed they were there to prevent the volotage induced by
the
: collapsing magnetic field around the solenoid from spiking the
electrical
: system.

I don't think so for two reasons:
1. The starter operating would require the master solenoid to be closed,
so the
diode/resistor pair is shorted out and not a factor.
2. The direction of the diode is the wrong way to be a path for flyback
current in the
starter solenoid.

I was thinking of the collapsing field around the master contactor solenoid.

John Kunkel wrote:
: I was thinking of the collapsing field around the master contactor solenoid.

The way it's configured, it wouldn't do that either.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************