1078 Alternator question

[j_boucher]

Hello all and Happy 2024, I Just wanted to pick the brains of the sites seasoned owners, I'm working on a deal for a 1078, and when I went to look at it the alternator's 28V side wasn't pushing anything just the 14 Volts side. When starting the vehicle it goes to 28V for maybe a second then stops . I was curious if any of you have had a similar issue ? I'm trying to help troubleshoot this with the owner unfortunately Im 100 miles away, I was thinking it has something to do with the exciter wire and or the K11 relay, Any thoughts on this is appreciated

Thanks in advance

 

[GeneralDisorder]

14v is pulled from the center of the 28v windings so in general you can't have 14v if the alternator isn't making 28v. Where are you testing the 28v from?

 

[j_boucher]

W

14v is pulled from the center of the 28v windings so in general you can't have 14v if the alternator isn't making 28v. Where are you testing the 28v from?

When I was there we tested it at the 28V lug going to the batteries / Also the regulator has two lights and only the 14V was on

 

[GeneralDisorder]

If you have 28v at the regulator E terminal and the 28v LED is off that points to a bad regulator according to the Niehoff troubleshooting docs:

https://www.ceniehoff.com/Documents/Ctrl_Hyperlink/TG14_uid252021119472.pdf

Pretty common failure item on the 100a alternators.

 

[j_boucher]

If you have 28v at the regulator E terminal and the 28v LED is off that points to a bad regulator according to the Niehoff troubleshooting docs:

https://www.ceniehoff.com/Documents/Ctrl_Hyperlink/TG14_uid252021119472.pdf

Pretty common failure item on the 100a alternators.

Thanks for the help / / Any good references to obtain a new or used one? I see there is large range of prices just don't want to spend the money for a dud

 

[Ronmar]

I would be curious what you see at the 28v output terminal. The reg regulates the field based on the 28v output. That rotating field excites 2 series wired 14v windings to create a 28v output. It creates the 14V from the first winding like a switching power supply using SCRs instead of diodes to control and rectify the output of the first series winding.

Without field input that 1st winding wont have anything to work with...

 

[GeneralDisorder]

Thanks for the help / / Any good references to obtain a new or used one? I see there is large range of prices just don't want to spend the money for a dud

I wouldn't spend a dime to fix the 100a alternator. They were grossly undersized for the application. Any money spent toward the charging system should go toward upgrading it to the 260a alternator or one of the other options that are out there - the 200a HMMWV alternator, or a commercial 24v unit with a 24-12 converter for the 12v side.

 

[Ronmar]

I wouldn't spend a dime to fix the 100a alternator. They were grossly undersized for the application. Any money spent toward the charging system should go toward upgrading it to the 260a alternator or one of the other options that are out there - the 200a HMMWV alternator, or a commercial 24v unit with a 24-12 converter for the 12v side.

This right here! The amount you will spend on a Neihoff reg or any other repairs you might need will put you a long way along the road to a commercially available 24V alt and 24-12 converter… one real killer of the capability of the 100A dual volt is pulling half the power out of that first winding @14V. This kills ~1/3 of the possible output, knocking it down to ~1950W total, opposed to the ~2800W available from a straight 24V @100A alt.

in a straight single 24V config, the grossly oversized 240AH battery bank is actually still viable as it is only looking for 60% of the alt output worst case, at least that is the case for wet cells. 240AH in AGM, is looking for over 100A worst case, so it is still way off the 100A menu. These trucks only need 2 batteries, so regardless of what you do for an alt, i highly recommend you drop to 2 batts(cat specced a pair of group 31s for the equipment that uses these engines).

2 batts will only pull 30A wet cell bulk charging load(55A AGM) if they are really discharged/worst case. The truck itself only pulls ~20-25A@24V if you convert the 12V lighting loads(28A@12V), from 24, plus the native 24V loads. So even with 4 batts, that is still only ~85% alt load worst case…

A 100A 24V alt is a common and very cost effective item, commonly available, parts are common and these are easily repairable by any auto electric shop…

Victron makes a nice Orion 70A 24-12 converter which is a good size for the typical truck 12v loads…

 

[Third From Texas]

I wouldn't spend a dime to fix the 100a alternator. They were grossly undersized for the application. Any money spent toward the charging system should go toward upgrading it to the 260a alternator or one of the other options that are out there - the 200a HMMWV alternator, or a commercial 24v unit with a 24-12 converter for the 12v side.

^THIS ^THIS ^THIS a thousand times THIS

100a on these trucks is anemic (simply idiotic when run with four TL6's). My 1960's 1600cc air-cool VW bug motors have more amperage.

Many owners don't realize that the 100a dual voltage Niehoff put's out 100a to the 24 side and 40-50a to the 12v side.
Then they add off-road lights and a stereo , or let's their four stupidly oversized batteries go flat and then wonder whey their alt melts down after a jump start (which is exactly why so many that come off GP blow the alts after jumping a flat set of batteries and the driving it to "charge then").

Do as GP and Ronmar suggests. Look to another alternator solution.

 

[Ronmar]

^THIS ^THIS ^THIS a thousand times THIS

100a on these trucks is anemic (simply idiotic when run with four TL6's). My 1960's 1600cc air-cool VW bug motors have more amperage.

Many owners don't realize that the 100a dual voltage Niehoff put's out 100a to the 24 side and 40-50a to the 12v side.
Then they add off-road lights and a stereo , or let's their four stupidly oversized batteries go flat and then wonder whey their alt melts down after a jump start (which is exactly why so many that come off GP blow the alts after jumping a flat set of batteries and the driving it to "charge then").

Do as GP and Ronmar suggests. Look to another alternator solution.

It doesn’t even do that. It is 100A total!,, about 60A@12 and 40A@24 max… Thats why a straight 100A delivers 25-30% more power than this 60/40 abomination…

 

[hike]

So, if I may bring this question from another thread, (and yes I have watched rronmar youtube many times):

So in an M1078A1 (>18550), over time?

1— one could simply disconnect the 12v feed from the LBCD to the PDP (TL80 TO X2); Adding a 24v-12v 70a between 24v bat (X4) and 12v bat (X2);
a— that would allow the factory alternator to essentially charge 24v at 100a as needed;



2— then disconnect two of the batteries while still providing a 12v connection to factory alternator;
a— that reduces the load on the alternator;



3— then when time to replace factory alternator arrives replace dual voltage with 24v 100+a alternator; remove LBDC; remove 12v side of polarity protection (leaving the 24v side allows the left knee and outside battery disconnects to remain functional; remove 12v to alternator (new alternator does not have).



These steps could be done over time, if done in order?

How to best reroute 'Charging System' indicator light in dash?

 

[j_boucher]

Thanks for all the info, I would rather just convert it to a commercial with the converter, anyone have a good part number for this alternator ? Right now I just need to get it home currently it has 2 group 31's in it . I plan to drive up and troubleshoot it again , dont know why I didnt check the excite wire at the time maybe because there was no light illuminated on the voltage regulator

 

[coachgeo]

Thanks for all the info, I would rather just convert it to a commercial with the converter, a...

there is no commercial alt. that will fit the alt bracket on these trucks. You have to re-configure yours or have one fabbed for you. Not something you can do on the road. Once home you can machine out bracket you have to install a commercial and convertor on it.

BTW- if your on the road and alt no working.... last resort is buy a very small generator, two 12v "smart" battery chargers... wire them up to each their own battery..... and drive home.

PS- you can go couple hundred miles on fully charged batteries with No alt. on these trucks.

 

[j_boucher]

there is no commercial alt. that will fit the alt bracket on these trucks. You have to re-configure yours or have one fabbed for you. Not something you can do on the road. Once home you can machine out bracket you have to install a commercial and convertor on it.

BTW- if your on the road and alt no working.... last resort is buy a very small generator, two 12v "smart" battery chargers... wire them up to each their own battery..... and drive home.

PS- you can go couple hundred miles on fully charged batteries with No alt. on these trucks.

Thats good news I was actually thinking of buying a 24V charger and my honda generator

 

[Third From Texas]

It doesn’t even do that. It is 100A total!,, about 60A@12 and 40A@24 max… Thats why a straight 100A delivers 25-30% more power than this 60/40 abomination…

I was under the impression that it was dual and the output number represented the 24v side.

So the 100 were 100/40, the 200 were 200/50, and the 260 were 260/140.

It was the reason I never looked into the 200a for my old AO truck (I was leaning towards a big 24va with a step down for the 12). Another 10a helps but didn't seem to be worth the trouble. I had seen it on the Niehoff site, but I very well could have been mistaken in my interpretation.

C.E. Niehoff Co. - Brushless Alternators - Commercial - Military - Mining - Construction

Generic Description Here

www.ceniehoff.com

 

[coachgeo]

Thats good news I was actually thinking of buying a 24V charger and my honda generator

two 12v better IMHO, if your not throwing a converter in there. If wanting to get home as is, two 12v smart chargers, may be your best bet sense one batt gets more 12v draw than the other, having the two smart ones to get you home then seems would with out needing converter. @Ronmar ?? would this work?

24v charger and a battery balancer may work?? ... but then again a 24v charger, step down convertor and/ or a balancer; these may not be something you can find on the road reasonably just to get you home..

 

[j_boucher]

two 12v better IMHO, if your not throwing a converter in there. If wanting to get home as is, two 12v smart chargers, may be your best bet sense one batt gets more 12v draw than the other, having the two smart ones to get you home then seems would with out needing converter. @Ronmar ?? would this work?

24v charger and a battery balancer may work?? ... but then again a 24v charger, step down convertor and/ or a balancer; these may not be something you can find on the road reasonably just to get you home..

Ok that makes sense to me now thanks

 

[Ronmar]

I was under the impression that it was dual and the output number represented the 24v side.

So the 100 were 100/40, the 200 were 200/50, and the 260 were 260/140.

It was the reason I never looked into the 200a for my old AO truck (I was leaning towards a big 24va with a step down for the 12). Another 10a helps but didn't seem to be worth the trouble. I had seen it on the Niehoff site, but I very well could have been mistaken in my interpretation.

C.E. Niehoff Co. - Brushless Alternators - Commercial - Military - Mining - Construction

Generic Description Here

www.ceniehoff.com

When Neihoff lists only one current spec, it was the combined total. Where they list two currents that is where they have altered the construction so one side is carrying significamtly more than 50% of the total current. The 1505 lists 100/40 for 28/14v like you mentioned, but we dont use the 1505...

We use the 1506, 1509 or 1511 in 100A. The 1506 and 1509 are not even listed on Neihoffs website anymore, but the 1511-1 is still listed @100A combined output...

Eriks Military still lists all the specs for the 1506 and 1509 @100A combined...

 

[Ronmar]

Ok that makes sense to me now thanks

Geo is right, a 24v charger will not charge equally pulling 12 out of the middle. But it will work ok for a short time to get you home. A pair of 12s would work better as long as they are not grounded/ground referenced(metal cases/3prong AC plugs) plastic cased chargers with 2 prong electrical plugs will work fine in series...

 

[Ronmar]

So, if I may bring this question from another thread, (and yes I have watched rronmar youtube many times):

So in an M1078A1 (>18550), over time?

1— one could simply disconnect the 12v feed from the LBCD to the PDP (TL80 TO X2); Adding a 24v-12v 70a between 24v bat (X4) and 12v bat (X2);
a— that would allow the factory alternator to essentially charge 24v at 100a as needed;

View attachment 914080

2— then disconnect two of the batteries while still providing a 12v connection to factory alternator;
a— that reduces the load on the alternator;

View attachment 914081

3— then when time to replace factory alternator arrives replace dual voltage with 24v 100+a alternator; remove LBDC; remove 12v side of polarity protection (leaving the 24v side allows the left knee and outside battery disconnects to remain functional; remove 12v to alternator (new alternator does not have).

View attachment 914082

These steps could be done over time, if done in order?

How to best reroute 'Charging System' indicator light in dash?

I would make dropping to two batts step 1, you can do it today, lift the leads off of a front(toward front of truck) or rear pair of battery posts and insulate them...

The LBCD controls the charging system warning light. This function could be recreated with an off the shelf voltage sense relay module, sampling the excite control voltage sent to the regulator by relay K11 after the engine starts. If that voltage doesnt go over say 27.6V, it would light the dash charge system light indicating the system is not charging.