LMTV Alternator replacement 24 volt

Keeping on the simple side didn’t you have to do other things to keep the dash indicator lights working properly?
Would love to see diagrams and part numbers of how you solved it.

Keith Knight said:

You’re killing me with abbreviations without stating what they are! LOL!!!

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AIH = air inlet heater
PDP = power distribution panel
IMHO = in my humble opinion
EE = Electrical Engineer
LBCD = Lateral Border of Cardiac Dullness
FWIW = for what it's worth
Alt = Alternator
COTS = commercial off the shelf

I know you already know these I'm just being redundant. Rick is way better at acronyms than I.

Keith Knight said:

Keeping on the simple side didn’t you have to do other things to keep the dash indicator lights working properly?
Would love to see diagrams and part numbers of how you solved it.

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Yes but only 1 wire. The "charging system" light control comes from the LBCD terminal B (FMTV
diagram page 23). I repurposed that 1853 wire with Ron's help to the i terminal of the new Alt. It needed a diode that's all since it's a sink, or low side control. Red wire in pics below.

the S terminal is a remote sense which I ran all the way back to the Batt with a sealed fuse at the 24v post. The Alt measures post voltage instead of the line voltage when charging. And now, I'm using the old "energize" wire off the old neihoff regulator to run a tach. 568A now goes to the R terminal and to the tach in the dash.

I used the diode shown below.
I edited the FMTV schematic but forgot to
Change 100 to 110

MatthewWBailey said:

So with all the accolades we're giving Neihoff at this point, perhaps there's a better question: Is it (100A) overloaded in a stock A1? Seems like the adjectives of "robust" and "rarely fail" and "no data" are ignored when it's considered overloaded. So is it overloaded? Yes or no? (Don't forget that hard pulsing 90A AIH draw)


my professional opinion (FWIW) is that this pulsing 90A AIH is an ALT wrecker or at least a Regulator wrecker. I'd have to test 2 units side by side to prove it thou.

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if you are only drawing 24v out of it, it would be no more overloaded than any other 24v alt. The Neihoff‘s Achilles heel rears its ugly head when you start pulling 14v out of it. The alt is rated 100A combined load, and since the 14 is pulled from the first half of the windings, it can only deliver ~60A max at 12v. An incandescent light load is ~25A, if you have the lights on and are pulling that, the alt can only deliver ~75A @24. The truck needs perhaps 15+ of that, you are now at 60 or less available. A 240A wet cell needs that if its discharged, and if they are really flat we are talking hours at max load to recharge.

At straight 24, you have 100A. Well thats 12.5 A for the lights, another 15 for the truck loads, that leaves you 70A. The batts are looking for 60A(25% AH), so <90% load. A much more favorable situation if you have several hours of charging ahead. Not an issue if you keep the batteries topped(float charger or run a lot of hours)

Of course AGM batts blow this situation up with their 45% of AH current draw(108A for a 240AH bank). Thats was probably a big factor in the 260A alt changeup.

now pick a vehicle, any vehicle. The daily in your driveway perhaps. Total loads, total battery demand(25 or45% of batt AH capacity based on batt type) and compare it against the alternator rating. I would be surprised if you find a worst case combination much above 50-60% of the alternators rating, and the batts will most likely NOT require hours to recharge.

As for loads like the AIH, still not thinking this is terrible. Again only fairly brief periods, and surely not as bad as say a winch Their voltage drawdown when on basically cuts off feed to the battery. The alt and batt are a team, so as the alt goes to full output and voltage drops, the battery steps in and makes up the rest, then the alt replaces it when the AIH cuts off. if your batts are kept up, not much of an issue IMO, and not thinking it is an alt killer. Lots of vehicles use them…

MatthewWBailey said:

So with all the accolades we're giving Neihoff at this point, perhaps there's a better question: Is it (100A) overloaded in a stock A1? Seems like the adjectives of "robust" and "rarely fail" and "no data" are ignored when it's considered overloaded. So is it overloaded? Yes or no? (Don't forget that hard pulsing 90A AIH draw)

For the record, I DO have a failed 100a Neihoff alternator at the local rebuild shop. Already dropped $800 on a failed regulator 2k miles ago with only 9k on the truck at the time. He tested it on his bench setup and it's putting out 50A max on his tester. So he's tearing into it. I'll know more once he's done. So apparently I'm the only person in the known universe that's ever had a bad Neihoff alt?, I should be shamed drawn and quartered. lol. Tyler screwed me again? I'm betting that's it.

On the LBCD, I see 2 big capacitors and 2 diodes. The diodes can go in the PDP. The patent app discuses "ripple reduction during battery-less operation". If you eliminate "battery less operation" you don't need this mystical black box which imho as an EE does nothing but bust my balls. I gave mine away, with cash and bitcoin to a needy family along with the power relay. I shorted my manual disco terminals with bus bars for security but they're easily removable for maintenance. I'll post that another place. So I'm never in battery less mode

Further food for thought, convince me that at $800+ per regulator and god knows what for the alt itself ($1200), why isn't this thing able to produce 200% and never fail regardless of load duty? If I gave you $2000, could you buy a better more capable unit in the commercial market? With ALL the 12v load removed on mine with 2batts I'm pulling 115A during initial startup for several minutes. Is that an overload on a N1511?

my professional opinion (FWIW) is that this pulsing 90A AIH is an ALT wrecker or at least a Regulator wrecker. I'd have to test 2 units side by side to prove it thou.

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I have a stock lmtv alt that failed you could buy for parts if interested.

Thanks Matt

I think this question got overlooked.

Here’s the question that I find difficult to answer.
Why charge the same batteries with 24v and 12v?

With the 4 batteries in series parallel I’ve actually charged all four batteries with a 12v charger and with a 24v charger at separate times. Both methods have worked in a pinch.

Keith Knight said:

Thanks Matt

I think this question got overlooked.

Here’s the question that I find difficult to answer.
Why charge the same batteries with 24v and 12v?

With the 4 batteries in series parallel I’ve actually charged all four batteries with a 12v charger and with a 24v charger at separate times. Both methods have worked in a pinch.

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If you pull 14 out of the middle of a 28V battery, you have to also charge with 14 otherwise the batteries will not charge equally. A 28V alternator or power supply only knows 28V. It knows nothing of battery balance. So lets say you start to pull 14v power out of the middle. This drops the 0-14 battery voltage, lets say to 12v. The power source is applying 28 across both the batts, but since the 0-14 is now seeing 12 due to load, that means the 14-28v batt is now seeing 16. One never fully charges, and the other overcharges…

this is the same issue you run into with the dual alternator configurations as the two are independently regulated and the standard voltages for the two type alternators are not 1/2-double each other. 14.5V and 27.3v typically which will cause the same type imbalance. The best way to employ 2 alts would be to wire two 14V alts in series like the batteries, but you would need an alternator with a isolated ground to fill the 14-28 position. being separate regulators they would still regulate to slightly different voltages under load, but far closer than any dual alt setup i have seen proposed. it is Far easier to use a balancer or not pull 14 out of the middle at all, and use a 28-14 converter for the 14v loads.

The balancers deliver exactly 1/2 of the input, and maintain that relationship as load on the 14 changes, to maintain electrical balance between the 2 series batteries, that is where the middle of a series battery would fall naturally if you are not messing with voltage/load on that part of the circuit.

you can charge with 14 on each battery, or 28 across the pair, just not while pulling from the 14 in the middle…

So another thought. Can you leave the original 12v load wire connected to the LBCD and connect the 24-12 battery equalizer to the 12v battery terminal?


This is my battery configuration.

Deleted duplicate post.

You could also use a couple Victron balancers. I use two of these for my house battery bank that is composed of four 12v batteries but my solar charges at 24v. These burn power off whichever battery is higher to bring them back into balance. You can stick them between any pair of 12v batteries that are being charged by 24v.

Victron Energy Battery Balancer https://a.co/d/5JnoLHb

They are actually quite small too.

would connecting the battery equalizer directly to the 12v battery cause problems with the alternator?

Keith Knight said:

So another thought. Can you leave the original 12v load wire connected to the LBCD and connect the 24-12 battery equalizer to the 12v battery terminal?
View attachment 936001
View attachment 936002
This is my battery configuration.

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You could but it would then be doing what the alt already does(balanced charging), and would not really be reducing the 12v load applied directly to the alt which is the reason for this whole escapade isn't it?

The easiest option is to just replace the 100 with the 260 and be done with it. I've never seen or heard of a bad 260. They are built like tanks. You can carry a spare VR but that's about all you really need. And for an overland application - assuming you keep a large battery bank like the original 4 x 6TAGM - you can drive through a whole tank of fuel on just the batteries (with proper power management) and if necessary charge them via solar.

Sure they aren't cheap. But the truck wasn't cheap. Buy once, cry once..... The quality remains long after the price is forgotten..... Etc.

And if you do your homework and your legwork there are surplus channels and options that can reduce the cost. I run the HIMARS 300A alternator that mounts directly to the 260A mount and found them for under $800. Got a second one for a spare.... I'm not of the opinion I'll ever need it but it feels good to have it. Sadly the surplus on those has dried up for the moment. But they will show up again. It's a matter of waiting and watching and striking when it's available rather than waiting till you have a failure.

GeneralDisorder said:

The easiest option is to just replace the 100 with the 260 and be done with it. I've never seen or heard of a bad 260. They are built like tanks. You can carry a spare VR but that's about all you really need. And for an overland application - assuming you keep a large battery bank like the original 4 x 6TAGM - you can drive through a whole tank of fuel on just the batteries (with proper power management) and if necessary charge them via solar.

Sure they aren't cheap. But the truck wasn't cheap. Buy once, cry once..... The quality remains long after the price is forgotten..... Etc.

And if you do your homework and your legwork there are surplus channels and options that can reduce the cost. I run the HIMARS 300A alternator that mounts directly to the 260A mount and found them for under $800. Got a second one for a spare.... I'm not of the opinion I'll ever need it but it feels good to have it. Sadly the surplus on those has dried up for the moment. But they will show up again. It's a matter of waiting and watching and striking when it's available rather than waiting till you have a failure.

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I might hit you up on that 260 mount if you're sure it fits a 300. I have a NOS 300A N1313 with N3222 regulator. Before fiddling with the padmout, I stocked up on some Niehoff alts after I blew the regulator on the 100. Be nice to have as an alternative if I go back to J180. I got it for $500 plus shipping a couple years ago.

GeneralDisorder said:

The easiest option is to just replace the 100 with the 260 and be done with it. I've never seen or heard of a bad 260. They are built like tanks. You can carry a spare VR but that's about all you really need. And for an overland application - assuming you keep a large battery bank like the original 4 x 6TAGM - you can drive through a whole tank of fuel on just the batteries (with proper power management) and if necessary charge them via solar.

Sure they aren't cheap. But the truck wasn't cheap. Buy once, cry once..... The quality remains long after the price is forgotten..... Etc.

And if you do your homework and your legwork there are surplus channels and options that can reduce the cost. I run the HIMARS 300A alternator that mounts directly to the 260A mount and found them for under $800. Got a second one for a spare.... I'm not of the opinion I'll ever need it but it feels good to have it. Sadly the surplus on those has dried up for the moment. But they will show up again. It's a matter of waiting and watching and striking when it's available rather than waiting till you have a failure.

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I’m starting to feel the larger dual voltage alternator as a my choice. Never been about money. For me I like to way all options fully understand each then decide.
but which dual bolt alternator. I’ve seen the 200 amp humvee as another option.

So what's different about the 260 amp alternator that requires a different mount?

MatthewWBailey said:

I might hit you up on that 260 mount if you're sure it fits a 300. I have a NOS 300A N1313 with N3222 regulator. Before fiddling with the padmout, I stocked up on some Niehoff alts after I blew the regulator on the 100. Be nice to have as an alternative if I go back to J180. I got it for $500 plus shipping a couple years ago.

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Oh yeah. Absolutely. You will have to space the shock tower out and put a window in the backside of it. I just installed one on a 2004.5 A1R (non coil over) truck and I have the same mount I on my personal truck. Same one I posted above. Fits the 260 and the 300.

Keith Knight said:

So what's different about the 260 amp alternator that requires a different mount?

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It's larger in diameter and longer and requires a longer belt since it sits farther from the engine block. The 260A weighs 72 lbs. The 300A weighs 98 lbs. I think the 100A is around 50 lbs.

Keith Knight said:

I’m starting to feel the larger dual voltage alternator as a my choice. Never been about money. For me I like to way all options fully understand each then decide.
but which dual bolt alternator. I’ve seen the 200 amp humvee as another option.

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or a larger single volt alt... I would caution against overthinking this, that's what S&S did instead of critically thinking about it in the first place...

The dual vlts are only really used by the military, and the only thing that needs 12 on the vehicle is the lighting, and that's maybe 25A A 70A victron 24-12 converter is $150? remote switchable can be controlled by the ignition switch. 24v ALT, 24V battery, 24-12 converter for the lights. Simple, robust, commonly available parts with a reasonably consistent source of supply, unless you want to be your own parts warehouse and stock parts you may or may not ever need... in a pinch, you could pull 12 out of the middle of the 24 if you had a converter failure, until you can get it fixed...

Keith Knight said:

’ve seen the 200 amp humvee as another option.

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The HMMWV 200A is an option. But now your competing against not only FMTV owners, but also the whole HMMWV community for surplus. And they are designed to mount on the driver's side so mounting them on the FMTV is a dog's breakfast of bits and pieces and the regulator has to be remote mounted..... The 260 is more powerful and mounts correctly and cleanly for the 3126 and C7. At one point a whole crap load of them landed on the surplus channels and so for a while they were a "good deal" even if fitment was a literal sack of hammers. Now I don't think they are a very good deal unless you happen to score one for a significant discount.