Easy alternator check

[riderdan]

I looked the the TM and didn't see an obvious answer...

The volt gauge is in the yellow when running and battery voltage shows 25 at the battery terminals. I was expecting 28v if the alt was charging. The old "hold a small piece of metal on the back to check field strength" thing didn't work. The little cover (over the pos connection) says not to remove w/o disconnecting battery. I suspect a bad regulator, and was hoping there's an easy way to check voltage at the alt.

 

[dilvoy]

That old check for magnetism works on Alternators.

 

[riderdan]

Probably a dumb question, but....I'm used to alternators with an external/separate regulator (I'm into classic cars) but can't seem to locate just a regulator, either in the TM or online. Is it necessary to buy an entire alternator if the regulator is bad?

On a different note, if I buy the 200 amp alternator and install kit, are there any pitfalls to the switch over? I've searched here (and other fora) and the physical installation seems to be the tricky part with that heavy son-of-a-motherless-goat. Is everything else pretty straight forward? I haven't been able to find a scanned copy of the MWO (if one exists) for the replacement. Looking on the evil auction site, it looks like a working used 200 is less than a reman 100... even if I add in the cost of the install kit.

 

[Wire Fox]

Probably a dumb question, but....I'm used to alternators with an external/separate regulator (I'm into classic cars) but can't seem to locate just a regulator, either in the TM or online. Is it necessary to buy an entire alternator if the regulator is bad?

On a different note, if I buy the 200 amp alternator and install kit, are there any pitfalls to the switch over? I've searched here (and other fora) and the physical installation seems to be the tricky part with that heavy son-of-a-motherless-goat. Is everything else pretty straight forward? I haven't been able to find a scanned copy of the MWO (if one exists) for the replacement. Looking on the evil auction site, it looks like a working used 200 is less than a reman 100... even if I add in the cost of the install kit.

Can't comment on the 60/100A regulators at this time. I do know that the 200A is clearly bolted onto the outside and is what also provides the 12V output.

Only real drawbacks I see to the 200A are the size, weight, and additional cabling that must be run. It just makes it a bit more difficult to work on things in that area, but it's nice having a more serviceable power unit where the things that seem to break are accessible without removing the unit. You're going to have an absolute ton of additional power that you won't put to use unless you start decking this thing with radios or massive lights or rows of ration heaters and coolers, plus you have a 12V power output without needing an additional discreet converter.

 

[riderdan]

Just to wrap this up... turns out it was operator headspace error. Or as they sometimes said down at the motorpool, 'Problem exists between steering wheel and seat."

Turns out the 24-1/2 volts nominal across the two batteries didn't mean they were good. Or at least, it didn't mean they were both good.

I'm attending an automotive restoration college degree program (sort of in my spare time, because who doesn't need a third college degree, right?). I talked to the electrical and electronic systems professor about taking a look at the charging system, and threw the batteries on a pair of battery chargers overnight. This morning the rear was dead as a doornail. Luckily it was under warranty, so I got a free replacement and she fired right up, the voltmeter went to green, and everything was ricky-tick.

At least I didn't drop $600 on a new, unneeded alternator, so only my pride was hurt, not my wallet.

 

[DatGuyC]

The 60 amp alternator does have a voltage regulator you can replace without replacing the whole alternator, its bolted to the back and has the fins. The thing you have to watch out for is that there are different versions of the 60 amp alternator and they each use a slightly different voltage regulator, but they all look almost identical.

 

[74M35A2]

A 12v battery reads 12.8v when fully charged. Any voltage over that is charging. Just double for a 24v system. Fully charged 24v system should be 25.6v with the engine not running. Takes more than 25.6v to push charge into the batteries. The higher the charge voltage, the more forceful it is. Anything above 14.4v per battery (28.8v on a 24v system) can boil the electrolyte (acid), depending upon ambient temperature.

 

[kc5mzd]

Having a 60a alternator on a 24 volt system is the same as having a 120a alternator on a 12 volt vehicle. In most cases 60 amp 24 volt alternator is very excessive and will keep your batteries charged. There are no radios, amplifiers or LED lights that are practical to use in a m998 that will use enough power to strain a 24 volt 60 amp system.
A 200 amp 24 volt alternator has the same power as a 400 amp 12 volt alternator. I am sure some one some where has seen one but I have never seen a modern car or truck with a 12 volt 400 amp alternator. The only thing I can think of where a 200 amp 24 volt alternator would be of benefit in a m998 would be if it was used to jump start a large number of other vehicles in a very short period of time. If you use a very large electric winch for extended periods of time it might help keep your batteries charged. The only other thing would be if you were using a very large power inverter.
The 100 amp system is more than enough for anything a civilian would likely use their truck for. If you try to charge your batteries to fast they can explode and make a very big mess!

 

[juanprado]

using the red dot military a/c kit for a hmmwv, they specify min 100amp 24v alt upgrade.

 

[kc5mzd]

using the red dot military a/c kit for a hmmwv, they specify min 100amp 24v alt upgrade.

I would guess it uses electric fans. It also leaves everything military spec which is to use the highest rated equipment that is feasible to do the job.
They also have requirements that call for the oversize military batteries to be drained to 0 then the engine started and the alternator fully charge the batteries in a very short time. Then the cycle has to be repeated a minimum number of times without any part failing.
I do agree that the 100 amp setup is very impressive. I also think the 200 amp setup is excessive for most of us, the money could be spent more efficiently on other "stuff".