LMTV ECU Voltage Regulator location?

[Dexis]

So I went out and disconnected all the batteries again and swapped in the voltage regulator off my reman alternator. Hooked everything back up and fired up the truck. Immediately the V gauge was almost rock solid around 28V.

Before the V gauge would bounce around between 24 and 28v wildly, until the huge spike under load at speed that tripped the trans codes.

I dont still have all 4 batteries connected and noticed while driving the truck back to the house that the V gauge was mostly around maybe 27.4-27.6V. So next step is definitely stepping down to 2 batteries to see if the alt can keep up then.

For now hopefully a pair of the 24’s will suffice. I’ll start working on getting a fresh pair of 27’s.

I still haven’t done any actual highway testing, and after all this I'm going to have a hard time trusting it until its got many MANY uninterrupted miles under its belt, but this looks the most promising so far.

 

[Ronmar]

The dual volt alt must have a proper connection to 12v in the middle of the 24v battery, with decent battery condition to regulate properly. It is not just a regulator it is also a balancer. If it does not see proper battery connection/response, this it will derate…
your loose connection at the alt could have also damaged the reg. Hopefully the spikes didn’t damage anything else…

 

[Dexis]

Went out for highway testing and it still threw the code. Same one, 1323. ECU volt high.

Volt gauge seemed more stable overall, less volatile jumping around, but still jumping around constantly.

Looking at the gauge this trip I realized some of my earlier figures were a bit off. I was thinking the line at yellow/green was 24V, just realized its 26V.

So before it was bouncing between 26 and 28V at idle like crazy. Under load that would jump into the 30-32 range periodically.

After new volt regulator at idle it was fairly solid just under 28V. Maybe 27.4-.6. As i got underway it would bounce around but less wide of a sweep. Maybe 27-29v average with the occasional ~30V. Now the more I drove that range became lower and lower. By the time I got home it was probably 25.8-26.6v range.

Threw high voltage again when it got up to full temp and around 45mph, about 80% of the way through the round trip.

Managed to make it back, parked it and grabbed the volt meter. 14.4 and 28.5 at alternator, and that was charging 14.3 and 28.4 at the batteries.

I also swapped down to 2 batteries before the trip. I threw the other two onto a charger but they were both at 100% in minutes, at least those two seem to be fine anyways.

So I'm not sure why my Volt gauge reads 26V and dropping. I guess maybe the alternator is bad? At this point all I can think to do is swap over the reman alternator and give it another shot.

 

[Dexis]

So i’m pretty sure I got burned on this alternator. Now that I think back they told me it was a “take off”, i originally asked if the had NOS, and the reman, but foe this model they just had the take off. I would think they’d test it before selling it. Maybe im wrong but here’s whats happening…

Bat disconnected, old alt out, new in etc…easy. Fired up truck. Immediately volt gauge began slowly surging 28V then crash to 20v, climb back…on repeat. Im pretty sure I read about this is another alternator related post. The only item that changed here was the alt. Volt regulator was working normally on other alt. Now i have green on 28V indicator light and flashing red on 14V light.

Alt charging excelent on 28V side but 14V wandering from mid 10V range to 15V.

 

[Ronmar]

The alt and batt are a system. The alt will not work right if there are connection and battery issues, so you must insure those things are correct before you can call it a bad alt.

 

[Dexis]

The alt and batt are a system. The alt will not work right if there are connection and battery issues, so you must insure those things are correct before you can call it a bad alt.

Well the other alternator didn't have this issue. Battery’s in the truck tested 12.7 each after over an hour of rest. The two I pulled showed 100% after just a minute or two on a charger. And aside from being undersized the batteries are fairly new, dated August 24.

The other alternator seemed to be slightly undercharging on both circuts. This one 28V seemed right were it should be and the 14V side dropping out to 10V every 2 seconds. Voltage regulator indicator lights showed proper function on other alternator and on this one shows a constant fault on 14V, confirmed with volt meter at 14V alternator post.

Ive gone through all the connections and everything is solid. Nothing is hooked up any different than the other alternator. If that one wasn't dropping in and out ever, forget 100% of the time like this new one I have a real hard time seeing how this alternator isn’t the issue.

 

[GeneralDisorder]

Welcome to 100A hell. Get a 200 or a 260.

 

[Dexis]

Does the 260 that is for the C7 engines work on the 3126?

 

[GeneralDisorder]

Does the 260 that is for the C7 engines work on the 3126?

The 260 is *THE* FMTV alternator now. It superceded the 100 and the 200 for all models. So the military has kits to install it on every single FMTV serial number back to 3116 trucks.

So yes. You can install the 260 on any FMTV with the right assortment of parts.

It's easier for serpentine trucks. The early C7 trucks are the easiest since the coil overs were designed to clear it already.

 

[Dexis]

The 260 is *THE* FMTV alternator now. It superceded the 100 and the 200 for all models. So the military has kits to install it on every single FMTV serial number back to 3116 trucks.

So yes. You can install the 260 on any FMTV with the right assortment of parts.

It's easier for serpentine trucks. The early C7 trucks are the easiest since the coil overs were designed to clear it already.

Any details or maybe just link(s) to swap procedure, parts, mods etc?

Ive seen a video of a 200A Humvee alt install with some basic modification. Only to read later in a post about needing to do something with the polarity protection as its only rated for 100A. And that was not done in the video I saw.

Long story short Id want to make sure I have the entire process and proper parts all lined out because Id assume slamming 2.6X amperage out into the systems incorrectly could have some devastating consequences.

 

[Ronmar]

The PPD isn’t an issue as the only current that goes thru it, is the current consumed by the truck via the dash power panel and that only changes if you add load… the PPD does serve as a tie point between alternator and batteries, but the 14 and 28 volt leads from alt and batteries are simply landed on the same studs on the ppd… if you keep those size batts, the batteries will never pull 260 anyway… Even 4 of the original size 6T batts in AGM are only ever going to pull 120A worst case… the cable between alt and batts is good for 200A+ at the installed lengths…

Your other option is to put in a 110A straight 24v alt(delco-remy, 350-450$ other manufacturers at lower prices) and use a 24-12 converter(170$) to power the truck 12v loads. Less expensive than any 260 you are going to lay hands on and very common/parts readily available. Any auto electric shop will probably have parts on the shelf for it… it can be fitted to the existing mount with some slight alteration… i reconfigured my power system to operate on straight 24 so I place no 12v load on the alt. It has a 12v lead from batt to alt only so the alt will regulate properly, but no 12v lead to the cab. I turn 24 into 12 under the dash in the cab.

if my dual volt alt quits(have yet to own a vehicle that has not needed an alt), I will fit the delco, should take about an hour to mod the mount and build a top strut. With all LED lights, and everything on 24V, my alt load worst case will rarely exceed 30-40A So I have quite a bit of power to send to my habitat if needed…110A@28(3KW) is plenty of power for me…

 

[that_one_alternator_guy]

I have a freshly remanufactured and tested 260 AMP. And I wouldn't mind a core 100 AMP so if you're interested let me know. 7866143640

 

[Dexis]

So I got to testing it again today and noticed the excite wire was only getting 23.7-23.8 when disconnected. Im assuming without a clean +24.0v this is going to cause issues. Perhaps the surging voltage 10v-15v on the 14v side and now it's doing it on the 24v side as well. I swapped the fuse and relay for the excite circuit and no difference there.

Hoping this excite wire V might be my culprit? Running out of ideas here. Anyone know where the excite wire routes to? I started to trace it back but it is quickly buried in the harness branching out all over the place. Could this also be a bad computer module at this point?

Any thoughts or input greatly appreciated, Im about to start pulling my hair out over here.

 

[GeneralDisorder]

No that is correct. It will only get the 24v from the PPD/LBCD which drops the voltage from the batteries across its Schottky diodes that have about a 0.4v forward bias.

At any rate that E terminal signal only needs to be present momentarily on the later units and that will turn the regulator ON. After that point it no longer requires that signal and it will continue to operate till it stops spinning.

I will have some 260's and installation brackets available soon as full install kits. Only applicable to the serpentine belt trucks at the moment. I don't have a 3116 truck around here to develop a kit for it. HUPP Aerospace designed all the 260A upgrade kits from what I have seen. At least they were the supplier of all of the one's I've seen.

 

[Dexis]

No that is correct. It will only get the 24v from the PPD/LBCD which drops the voltage from the batteries across its Schottky diodes that have about a 0.4v forward bias.

At any rate that E terminal signal only needs to be present momentarily on the later units and that will turn the regulator ON. After that point it no longer requires that signal and it will continue to operate till it stops spinning.

I will have some 260's and installation brackets available soon as full install kits. Only applicable to the serpentine belt trucks at the moment. I don't have a 3116 truck around here to develop a kit for it. HUPP Aerospace designed all the 260A upgrade kits from what I have seen. At least they were the supplier of all of the one's I've seen.

Well I just went and cleaned the ground strap from Alt and tried again. Getting 22v-23.4v at excite, disconnected. 10v-14v at 14v post and 22v-23.4v at 28V post. Something is off here and I'm really running out of things to check. Not sure where to look next.

 

[GeneralDisorder]

Does this alternator have the VR with the diagnostic LED's and if so what are they doing? You can also just completely disconnected the truck from the alternator and hook it to a couple batteries on the floor with jumper cables and hit the E terminal with a 24v lead to turn it on. If it acts normal then it's the truck not the alternator.

 

[Dexis]

Green on 24V side, but it cuts in and out. Amber flashing on 12V. But Ive swapped in another ALT/VR at this point and it acts exactly the same. Starting to think maybe its not Alt or VR.

 

[GeneralDisorder]

Do the test with batteries and jumper cables. The truck will just act as the rotational source.

 

[Ronmar]

What general said. If i recall from the neihoff troubleshooting manual, the E terminal input only needs to be above 21V . It comes from relay k11 pin 87A(de-energized contact) in the panel. K11 de-energizes to power/enable the regulator E terminal once you see 15PSI of oil pressure.

The only time I have seen these alts de-rate is when they do not see a good connection to the 12V in the middle of the 24V battery.

The 28V side of the alt works like any alt, the reg senses output voltage and regulates the field to maintain that 28V output. The 14V output works like a switching DC power supply with the regulator firing SCR's to pulse out a 14.1V output. I think when it sees a certain amount of field drive it is expecting to need to deliver a certain amount of SCR drive to make 14.1 within its load limits. if the drive to achieve this is too high or too low, it senses it as an issue and it throttles back the overall output(field drive) to 25ish volts(low float voltage) the 14V drive also will recycle/re-try at intervals looking for a proper output.

IE: if you disconnect the 12v to the batt/load, the 14v applies drive and without load, it takes very little to reach and exceed 14.1v, so it cuts off, resets and tries again.

if it does this wit 2 alts, I am going to suspect the truck wiring, so Generals test with 2 batts and external/jumper cables to the alt is an excellent test.

the grounds on these trucks are typically crap so don't forget to check them all also.

volt meters are great but unless you are checking voltage while the wiring is carrying it's rated load, or at least significant enough load, they will not show a hi resistance connection in the circuit. resistance resists current flow, not voltage, and you won't see a volt drop until you pull current thru the connection.

I like the garden hose analogy. you can kink a garden hose and still have full pressure(voltage) at the nozzle, until you open the nozzle and try and flow water(current) thru it. the kink will quickly cause pressure and flow to drop at the nozzle, but once you close the nozzle the pressure there will quickly build back to full pressure(voltage)...

 

[Dexis]

Do the test with batteries and jumper cables. The truck will just act as the rotational source.

So would that would look like Excite, 28V, and 14V wires are all disconnected from alt. Two 12V batteries wired into a single 24V. Jumper cables to alt ground and direct to excite on VR?