Dual voltage alternator compatability question (1505 vs. 1506)

[clinto]

I have a buddy with a first generation M1078 (I can't bring myself to call it an A0). The alternator caught on fire. I'm fixing it.

Truck came to me with a 100A 24-12V alternator 76761-N1506-1.








And this is what I bought, not realizing the small differences. I bought a 76761-N1505-1.





So, can I run the 1505 on this 1078 or this there a difference other than cable connection points I'm not aware of?

Thanks

C

 

[coachgeo]

should be fine.... folk have installed hummer 28/14v niehoff 200amps alts. without issue so you should be fine if dimensionally it works.

 

[NDT]

I don't think that will work. The FMTVs are mostly 12 volt. That little yellow terminal on the regulator is not designed for the entire vehicle load, only for the transmission on a HMMWV.

 

[SausageGuy]

I think it will work. The one that came on my truck was a 1506. I replaced it with a 1505. The only difference I saw was the regulator for each was different and would not swap from one alt to another. The 1506 had the regulator with led lights on it. 1505 regulator did not have leds.

 

[Ronmar]

It is rated for 50A at 12v which should be plenty.

 

[NDT]

Do you feel lucky? Dun had one alt fire. Heater + wiper + headlights + clearance lights + trailer lights= ???

 

[coachgeo]

Do you feel lucky? Dun had one alt fire. Heater + wiper + headlights + clearance lights + trailer lights= ???

the alternator 12v side of the hummer and the FMTV as RonMar alludes to are BOTH rated at 50amp. Far as can tell from PDF's both Alt's outputs, maximums and minimums, cutoffs and other specs.. are the same except physical length and width between mount ears

 

[Ronmar]

Ok

Do you feel lucky? Dun had one alt fire. Heater + wiper + headlights + clearance lights + trailer lights= ???

ok, first off, wipers and blower are 24V. The peak light load(highbeams, markers, reverse, brakes hazard flashers) I calculated at around 25A... Not sure what the VIM uses, but I don't think it is 25A...

 

[MrMikey4026]

Would it be possible to just install a straight 24 volt alternator and center tap the batteries for the 12 volt loads? I worked on transit buses many years ago that were built that way.
Mike

 

[Ronmar]

Would it be possible to just install a straight 24 volt alternator and center tap the batteries for the 12 volt loads? I worked on transit buses many years ago that were built that way.
Mike

No, unless you like replacing batteries regularly. it imbalances the charge so one set gets overcharged and one gets undercharged... You can use a straight 24 alt but you need to use an equalizer/converter to maintain a balanced charge between 12 and 24v, or better still not tap the 12V from the batteries at all and make the 12v from the 24v in the converter(best for the batteries).

 

[ramdough]

Would it be possible to just install a straight 24 volt alternator and center tap the batteries for the 12 volt loads? I worked on transit buses many years ago that were built that way.
Mike

I would guess you would want a battery balanced and then you would be ok. As long as the balancer could keep up.


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[ramdough]

No, unless you like replacing batteries regularly. it imbalances the charge so one set gets overcharged and one gets undercharged... You can use a straight 24 alt but you need to use an equalizer/converter to maintain a balanced charge between 12 and 24v, or better still not tap the 12V from the batteries at all and make the 12v from the 24v in the converter(best for the batteries).

His Ronmar has a better answer. Knows more too!


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[clinto]

I've put about 100 miles on this now without issues.

Keeping my fingers crossed.

 

[Ronmar]

I've put about 100 miles on this now without issues.

Keeping my fingers crossed.

I don’t think anyone ever asked, but what battery config are you running? That will probably be what ultimately causes you issues(As it does most every other LMTV alt). On the stock alt, the battery bank is way to large a charging load and that was with wet cells, with AGM’s, which most of the 6T’s are now, the alt is grossly undersized. Probably the main reason the A1R went to a 260A alt.

With the 1505 limited to 40A on the 12v side, you need to avoid a depleted battery like the plague. A wet cell needs 25% of the AH capacity for acceptance charge. An AGM needs 45%. The 4 battery bank is basically two 240AH batteries in series, so it will be looking for 60A on a wet cell and over 100A on an AGM. If they are depleted that means a very very long overloaded charging session.

2 batts @ 120AH is a much better match for the stock alt, and a pair of group 31’s @100AH is even better. I would highly recommend dropping to two batts. I recommend it for everyone, but i would say especially in your case. Cat specs a pair of group 31’s in series for these engines in their loaders/tool carriers, and it is plenty of battery.

at the very least, you need a maintainer to keep the batteries as near fully charged as possible. These trucks have a 12v vampire load which doesn’t help the 12v side any...

 

[clinto]

4 6TLs



Thanks for all the technical assistance. I'll make sure the client understands to keep these on a tender, never let them discharge and consider moving to a two-battery setup