OT: motorcraft alternator and master disconnect

karl f · Jun 9, 2009

have a customer with an externally regulated motorcraft alternator. He bought a "one wire conversion" kit from us (it"s really a mini sized external regulator made by Victory Lap that bolts on back). If it was a street car, tractor, or similar i would not have a question; but this is a drag car that needs an emergency shutdown master switch accessible at the rear of the car. The battery is already at the rear.

I want to help him wire the switch correctly so that in worst case scenario--with the engine wide open and driver passed out--everything will kill yet at the same time prevent the alternator from being damaged during what he calls "tech" where they sometimes pull the switch to test that it actually works.
Right now he has a single pole master switch with only 2 terminals on it. Being a race car, i bet he spent big money on it, so if there is a way to do this with that swich, he"d probably like to go that route. If not, what is/are the other option(s)??
quick note about the regulator kit, all the wire connections are external, easy to get at, and have a few inches of wire coming out of the regulator, so any connection that needs to be modified can easily be changed.

thanks in advance
karl f

Owen Aaland · Jun 9, 2009

(quoted from post at 07:13:03 06/09/09) have a customer with an externally regulated motorcraft alternator. He bought a "one wire conversion" kit from us (it"s really a mini sized external regulator made by Victory Lap that bolts on back). If it was a street car, tractor, or similar i would not have a question; but this is a drag car that needs an emergency shutdown master switch accessible at the rear of the car. The battery is already at the rear.

I want to help him wire the switch correctly so that in worst case scenario--with the engine wide open and driver passed out--everything will kill yet at the same time prevent the alternator from being damaged during what he calls "tech" where they sometimes pull the switch to test that it actually works.
Right now he has a single pole master switch with only 2 terminals on it. Being a race car, i bet he spent big money on it, so if there is a way to do this with that swich, he"d probably like to go that route. If not, what is/are the other option(s)??
quick note about the regulator kit, all the wire connections are external, easy to get at, and have a few inches of wire coming out of the regulator, so any connection that needs to be modified can easily be changed.

thanks in advance
karl f

If it will pass the kill switch qualifications, wire the alternator to the battery side of the kill switch. That will allow you to cut power to all circuits but the alternator.

If all power must be cut from the battery, including the alternator, install a 20 volt zenor diode at the alternator. That will send to ground any voltage over 20 volts and should protect the alternator.

mkirsch · Jun 9, 2009

That's what I would suggest too.

Wire the alternator directly to the + post on the battery.
Put the disconnect between the + post and everything else on the car.

There's no way the car will run with the switch pulled this way.

Otherwise, I don't think it could be done with that switch. Why not ask the ruling board how they want it done? Why not ask other drivers how they do it? It's not like this is some big speed-enhancing racing secret or something...

"tech" being technical inspection I presume?

karl f · Jun 9, 2009

it's a case of a customer inexperienced with electrical and the parts store worker (me) trying to help yet having the customer do all his own work at his own house since we are not a shop. (seems to be the daily routine in this field). Little bits of information come out in a trickle since the details come out when something is said in passing. Unfortunately racing does not interest me so my experience and contacts are limited, I never would think of that switch and how it could be used because of what im familiar with. From what i've gleaned listening to this customer, it sounds like every track is different and most other drivers/owners have no idea about wiring either.
When i mentioned damaging the alternator/regulator when switching while running if the disconnect is not wired right, that was the first the customer heard of it, and the first time for another customer that was eavesdropping too (maybe also my manager with 25 years in a shop experience)! If they didn't ever check the switch in tech, i would not worry about saving the alternator, since emergencies cost way more than any fancy electrical.

I will ask him to look at his rulebook

thanks for the input
karl f

Bob M · Jun 9, 2009

Karl - I’ve successfully ruined Delco and Mopar (Chrysler) alternators by disconnecting the battery while running – no reason to think it will not smoke a Motorcraft alternator too(!)

A possible solution is to provide a dash switch wired into the alternator field circuit. The driver would open this switch and leave it open during the tech inspection. The alternator will thus be “turned off” (not providing current) and therefore unable to provide a burst of voltage and destroy itself in response to the sudden open circuit when the inspector pulls the battery disconnect.

A side benefit is the driver can leave switch off - thus the alternator disabled - during the run. Depending on the car's electrical load this might yield an additional 1 HP or so at the rear wheels during a run.

John G. Hasler · Jun 9, 2009

> A side benefit is the driver can leave switch
> off - thus the alternator disabled - during the
> run. Depending on the car"s electrical load this
> might yield an additional 1 HP or so at the rear
> wheels during a run.

I have to wonder why a drag racer would have an alternator at all.

JMOR · Jun 9, 2009

(quoted from post at 14:00:07 06/09/09) > A side benefit is the driver can leave switch
> off - thus the alternator disabled - during the
> run. Depending on the car"s electrical load this
> might yield an additional 1 HP or so at the rear
> wheels during a run.

I have to wonder why a drag racer would have an alternator at all.

One very good reason is that high performance, high rpm engines often need all the ignition energy you can get and that is often available at 14.7 volts, but not at 12 volts. Experience speaking.

Bob M · Jun 9, 2009

Indeed John - I kinda wondered about that too...

karl f · Jun 9, 2009

thank you to everyone for your help and added discussion. looks like a few of us learned about racing in the process too!
The customer did some online searching too, learned alot and talked himself into a double pole battery cut out switch.

this way safety is #1 while protecting the alternator during the tech test.

karl f

OT: motorcraft alternator and master disconnect

karl f

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Owen Aaland

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mkirsch

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karl f

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Bob M

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John G. Hasler

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JMOR

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