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Problem: Fuse 7B would blow whenever I started my engine ('95 NA Diesel).

This caused the Alternator to not charge my batteries, which would very slowly fail. Power loss failure was faster, of course, if I used heater/lights/radio. Everything would work, even starting, if I had enough charge remaining.

Fix: Drove two hours to my dealer (In snow, no heater!) Mechanic was unable to meter out any problem, so he called "Danny" at AMG who told him it could be the fuel heater assembly... although he'd never had this problem before. Changed it. No more problem.

Observations: The 7B fuse seems to concern itself with only initial-start related items like the fuel pre-heater, cold-start sensor, cold advance solonoid, cold-start solonoid, and maybe something else. We discovered (actually the mechanic did) that, if the fuse was replaced after the engine had really warmed up, the fuse failure didn't happen and the alternator maintained the battery charge nicely. Also, when the fuse was failing, it wasn't getting blasted black like a short-circuit would cause, but showed just a small separation in the element as in a slow overload.

Parts used: Heater Assembly, AMG #05742603. This part is made by "Standard" and the mfg part # is 29241. Also used several 20 Amp mini-fuses, blade type.

Recommendations: Look at the voltmeter occasionally. I didn''t know I was losing battery until it was so low that I was unable to start the car. Once jump-started I was able to drive nicely since there is very little power drawn if you don't use any of your accessories. After putting the charger on my battery overnight, I was able to drive for two hours without going below 11 volts.

Buy some mini-fuses. I was surprised to discover that very few places stock them, except for specialized auto stores.

Thank you for the many suggestions I received. Pete Gibbons in Ithaca.

Q: I was wondering about alternators. Is their an upgrade for an alternator for the diesel V-8? What would be the advantages of having a larger capacity alternator? Are their any downfalls to this? If you didn't have any accessories other than factory stuff would it be worthwhile to upgrade? Maybe Gerald or Scott could help me out here. I know what they do but I don't understand the advantages of higher voltage ones.


The military alternators are 24 VDC at 60, 100, or 200 amps...this is as good as a 120, 240, or 400 (!!!) amp 12VDC guy. Boy, I'm drooling again. They are really waterproof unlike most marine stuff. Marine waterproof usually means it can get a little wet. Mil. waterproof means it works perfectly under 30" of water continuously. The downside is that it's 24VDC of course and won't fit on a civ model b/c it mounts in a different location.

As Hal (?) said, Premier makes aftermarket alternators in the GM style case. AFAIR, they have 160, 190, and 220 amp models. The 160 and 190 can connect to the welder but the 220 is a high cap alternator only. The 160 and 190 put out 110 DC also...the 220 may too. Of course, this may have changed.

Why you ask? You can never have enough capacity to power stuff. The winch draws 365 suck your batteries dry really quickly. You can also recharge stuff faster. For example, on the Nevada trip, Everett drained 320 A-hr of sealed lead-calcium batteries halfway through the night running his heater in the truck. He had to start the engine. I managed to go though my 80 A-hr of similar batteries running my 12V ceramic heater in the truck by around 3 am. I had to grab my hat and burrow back into the sleeping bag. Anyway, with lots of current capacity, you can recharge faster.

It won't hurt you to have a larger alternator. There may be a slight efficiency difference or friction differences from design but for all practical purposes are second order effects. The only pain is from the wallet.


>Here may be a simple one for someone out there. I have a '94 4DHT with a
>peculiar problem. Being this is my first diesel I thought I would field
>I am noticing that when I am on the highway and my speed gets to 70mph
>my voltage guage drops below 12V to about 11V. If I sustain that speed
>for a while, the voltage approaches 10V. The strange thing is that if I
>drop the speed down to 45mph the voltage will register normal again.
>Does this phenomenon sound familiar to anyone else?

The alternator used with the Hummer is a "self excited type" that is, it relies on residual magnetism within the core to begin charging. You will note that just after starting, the voltmeter may read low for a fraction of a second until the magnetism builds to the point where the internal regulator begins working. The regulator is set (internally) for a voltage between 13.8 to 14.5 volts. This is not a current regulator. The current flow is assumed because of the battery's and other accessories internal impedances combined. The alternator just maintains the voltage up to the core saturation of the device. As the battery voltage rises, the internal impedance also rises, automatically reducing the current flow to the battery.

It is possible that your voltage regulator (internal) is drifting at what is called high head pressure in front of the regulator. That is, the voltage may be quite a bit over 14.5 volts before the regulator at higher rpm's. This increases the dissipation the regulator must deal with under these conditions. The heat build up may cause the regulator to "drift" resulting in your problem.

Another problem could be that one of the diodes in the three phase array may be intermittent causing reduced output capacity.

Remove the alternator and take it to an automotive electrical shop specializing in alternators. They can drive it under load using an electric motor test stand and load panel. After a few minuets, the problem should be noticed.

John W. & Kathe Watkins
96' & 98' Turbo diesels

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