Starter Motor Post Mortem

Thanks Randy, but no secondary solenoid, standard/typical install. It worked for countless starts before this incident. This diagram does answer a question I had, that if one used a secondary solenoid (not sure the advantage) running a wire from the "I" post on the secondary solenoid to the "S" terminal on the starter completes the circuit to close the solenoid for start. In this picture the only way for continuous engagement of the starter would be a double failure of both solenoids or a failure of the starter circuit to discontinue power via the "S" & "I" posts. I see no benefit to add one. What are your suspicions, fess up......lol
 

Randy V

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Thanks Randy, but no secondary solenoid, standard/typical install. It worked for countless starts before this incident. This diagram does answer a question I had, that if one used a secondary solenoid (not sure the advantage) running a wire from the "I" post on the secondary solenoid to the "S" terminal on the starter completes the circuit to close the solenoid for start. In this picture the only way for continuous engagement of the starter would be a double failure of both solenoids or a failure of the starter circuit to discontinue power via the "S" & "I" posts. I see no benefit to add one. What are your suspicions, fess up......lol

The key advantage to running a secondary solenoid is that you don’t have a hot positive cable snaking its way though the engine compartment to the starter. It’s only hot when the starter button is pushed. This is huge when trying to make your car a bit safer in a wreck or a fire.
The “i” post on the secondary solenoid is to feed a full 12v to the ignition coil while the engine is being started.
 
Well good news today…..she lives!!!! Last part came in today, finally and pushed the button. Started back up like nothing was wrong.

after additional investigation, I suspect the heat blanket played the critical role in causing the hot battery solenoid wire to ground itself to the hot wire lead to the starter motor. There is black markings on the blanket to suggest this happened. The blanket will not be reinstalled.

I found it interesting that about 50% of the gear-heads I talked to about this never realized the exposed wire from the solenoid to the starter motor is actually hot when the circuit closes. So if you didn’t know, we won’t tell, but plan accordingly……I will now.
 

Howard Jones

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If we call the primary solenoid the one mounted on the starter and the second one the other one. Then if you locate the other one very close to the battery............. Like Randy says.

"is that you don’t have a hot positive cable snaking its way through the engine compartment to the starter. It’s only hot when the starter button is pushed. This is huge when trying to make your car a bit safer in a wreck or a fire."

This is an especially good idea if the battery is located at the other end of the car. Like in the nose behind the radiator. In most cars, the cable from the battery to the starter is always hot and if it's 8 feet long AND not protected with a breaker or a fuse! Then...............well you can see what we are talking about.

I'm happy to hear you have found your point of failure. That's always a good feeling,
 
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Neil

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A high current battery cut-off switch performs the same function as the "other" solenoid.
 

Neil

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Randy, maybe I didn't explain that clearly enough. The "extra" solenoid described above is just a high current contactor (relay) added in series with the existing starter solenoid and the + terminal of the battery. Located very near the battery terminal, this removes the voltage from the cable running back to the starter solenoid. Since a relay or contactor is simply an electrically-operated switch, it can be replaced by a manually-operated switch. Simple.

 
I designed a master cutoff whose primary purpose is two fold

1. To cut power to the electronics that drain the battery when not plugged into a trickle charger
2. Anti theft. There is a knob in the cockpit that you have to know it’s location and purpose to gain master power to activate all the cars systems.

I set up the power kill so I wouldn’t have to raise the bonnet to gain access. The knob is hidden in such a way that it’s not a distraction to the interior finish.
 
Hi Dan, one thing to keep in mind is that killing power to the ECU may wipe out adaptations. I have a kill switch in the car that I am not currently using because of this. I may end up plugging a 9V battery into my OBDII port to maintain juice to the ECU sufficient only to maintain memory, but not enough to run the car.
 

Ian Anderson

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Tom,
Run a (say) 2A / 5A fused circuit in parallel to the master switch that way the ECY will retain power but there will be a battery drain, And should anyone try to start the car the 2A / 5A fuse will blow!

Ian
 
Tom

while I haven’t used it often since the car stays hooked up to trickle charger mostly, the times I did pull the plug I did not notice any driving or startup differences from a memory loss. What gets saved?
 

Randy V

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Randy, maybe I didn't explain that clearly enough. The "extra" solenoid described above is just a high current contactor (relay) added in series with the existing starter solenoid and the + terminal of the battery. Located very near the battery terminal, this removes the voltage from the cable running back to the starter solenoid. Since a relay or contactor is simply an electrically-operated switch, it can be replaced by a manually-operated switch. Simple.


Having built and owned numerous competition cars and having served as an SCCA Tech Scrutineer, I’m quite familiar with the switch shown.
The only problem with these switches is they need human interaction to be thrown.
IE - If you are unconscious or unable to throw that switch, your system remains hot...
 

Neil

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Randy, that is precisely why in addition the SCTA requires an impact switch to disable the power electrical.
 
Tom

while I haven’t used it often since the car stays hooked up to trickle charger mostly, the times I did pull the plug I did not notice any driving or startup differences from a memory loss. What gets saved?

Hi Dan,

I think it depends on the ECU. I have a GM E38, and I believe long term fuel trims get lost when it's powered down.
 

Randy V

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Randy, that is precisely why in addition the SCTA requires an impact switch to disable the power electrical.

Curious what the current capacity in amps for this switch? The ones (inertia impact switches) we used to scab out of wrecked Fords was good for maybe 15 amps..
 

Neil

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I also used a Ford impact switch but used it to control a high-current contactor that was a master shut-off for all 12VDC power. I wired a toggle switch in series with the impact switch so I could hit the switch guard with my gloved hand in an emergency as well as having an automatic shut off in a crash.
 

Randy V

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I also used a Ford impact switch but used it to control a high-current contactor that was a master shut-off for all 12VDC power. I wired a toggle switch in series with the impact switch so I could hit the switch guard with my gloved hand in an emergency as well as having an automatic shut off in a crash.

So basically, you had a secondary solenoid in circuit like what was described above, only you used the Ford Inertia switch to trigger it? The only issue I can think of here is that you’re relying on a solenoid that is continually energized under normal conditions. Or did you use a normally-closed solenoid / contactor? Would you happen to have a wiring diagram? I’m always on the hunt for better / safer ways of doing things..
 

Neil

Supporter
Randy, I used a high current normally-open contactor that is held in the closed position by +12VDC from the battery, through the impact switch and through a manually-operated toggle switch. The toggle switch is an Airpax "switch breaker", a 3 amp circuit breaker that can be switched on and off like a toggle switch. Since my car is a mid-engine layout with the battery in an enclosed box in the passenger footwell (to balance the CG), the unprotected wiring is very short and of a light gauge (#22AWG) so it wouldn't conduct much current even if the car were totally wadded up.

It is important that the contactor (relay) be rated for continuous duty, not just intermittent. My complete schematic is rather complicated but I think you get the idea.
 

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