Re: alternator
 

Those magic alternators that charge and discharge. I had one last year. Tom's solenoid solves the issue.

Re: alternator
 

Brilliant idea Tom!!
As usual thanks for sharing your knowledge.

Re: alternator
 

An alternative to the relay to shut the power off to the alternator when in the trailer or in storage is to use a Cole Hersee P/N 75912 double pole battery disconnect switch. The main battery cable gets wired to one pair of terminals and the alternator field cable to the battery goes through the other pair.

Re: alternator
 

I run master switches in everything, motorhome, bracket car, antique, Stocker. If there is a problem, I can turn the power off at the batt. (or if it's sitting for long periods)

Also, if an alternator is drawing power while not in use, you have a diode gone. You can unhook the cable or put a master switch on it, but that is a band aid to the real problem. Further, if one of the three diodes is gone and you have a batt light, you will see it flicker or come on at idle and go out when you add throttle. This also means the alternator is not putting out as much amps as it used to with three diodes.

I've never heard, and I'm trying to figure why, cutting the field wire would hurt an alternator. That is how it works, the regulator turns the charging on and off by regulating the power going to the field. It's how I test an alternator, spin it and add power to the field wire, if it charges, the problem is something else. (ford with FSAI wiring to the external regulator is mostly what I deal with)

Not saying anyone is wrong, I just don't understand how it could be a problem.

Re: alternator
 

Jack, I used to use those on all my builds ,but in recent years I and several of my customers experienced switch failures . .that prompted my switch to the relay which has been very reliable. The 75912 switch is US made now [previously it had been being made in Mexico] and is rated at 750 amps intermittent load . Some of the 4 post type switches that that are being sold by Jegs ,Summit and others have smaller gauge secondary terminal posts are only rated for a 30 amp load and will not survive the output from the alternator.

Re: alternator
 

Just spoke with tech support @ Tuff Stuff Performance which is one of the primary sources for the high output @ low rpm CS121 alternators.

He said it is unfortunately common that standard race car wiring and shutting off the master cutoff will zap the regulator.

I purchased another 7937ST and it is working fantastic.

Next time I have to go through a full tech, I will be removing the alternator belt.

Clark

Re: alternator
 

QUOTE:
Not saying anyone is wrong, I just don't understand how it could be a problem.

I don't think the problem is actually the "alternator" as it is the "regulator" that is getting zapped...

If the alternator is putting out a high amperage and the switch is turned off, it sends a spike through the regulator which is a bunch of made in china electronics, diodes/SCR's and such.
Electronic circuits don't like sudden changes in volts/amps.

Back in the day the external regulators were relays and ceramic wound resistors, and while not bullet proof, could handle a lot more in the way of hard use.