Alternator Suggestions?

We're installing a 24 volt rooftop AC unit on the cab of our truck. At max power, the AC unit draws 35 amps. I'm concerned that we could be pushing the limits of the 100 amp OEM alternator under certain circumstances. In a previous post, I mentioned that I was going to replace it with new C.E. Niehoff 24 volt 260 amp alternator, but as I was mocking things up in the engine compartment, I noticed that the non-pulley side of the new alternator will rub against part of the exhaust near the turbo charger. That concerns me.

In addition to that, I have repeatedly heard that these military alternators can be difficult to find in the field (especially when out of the country) and they don't have the greatest reputations for longevity. After thinking about it, I think we're just going to replace the OEM alternator with a more typical 24 volt alternator - one that wouldn't be so difficult to find and replace if it were to fail. I've been looking at 140 - 160 amp alternators, and I think either of those would give the alternator enough margin to operate comfortably.

Does anyone have any other recommendations? I've seen some youtube videos of similar conversions, but no one goes into any real detail about the swap. Will there be any issues with putting the old pulley on the shaft of the new alternator? Some of the alternators we're looking at have "single wire" hookups and others look like they have several wires. I don't know that much about alternators, so I'd like to get the opinions of others who do. Which would be better? I want to keep it simple. We have a well equipped shop and can manufacture mounting brackets, so I'm not concerned about that, and I'll down-convert for my 12 volt needs in the cab, but I've got to get this alternator issue resolved. Thanks

Kevin

BTW, if someone's looking for a new C.E Niehoff 24 volt 260 amp alternator, or an OEM 100 amp alternator with 1700 miles on it, let me know.

Where are you located?

Stick with the 260.

What year is your truck? The 260 requires the older trucks to change the mounting of the shock as they have the mounting slung a little farther out. If you cut the huck bolts and make two copies of the spacer plate behind the shock mount out of 1/2" plate you can bolt the shock bracket back in place and it will clear the 260 or the 300.

Don't worry about potential failures - carry a spare VR. The 260 is dead reliable and I've yet to see a confirmed winding or diode failure, etc. Even the VR's are very reliable. In any case if you stick with the 6TL/6TAGM setup you can drive through a whole tank of fuel on just battery if you observe some electrical discipline. And as an overland truck you'll have a secondary solar/generator system that can be shunted over to charge the truck batteries - this gives redundancy so carrying spares or sourcing them during the mission is irrelevant.

Carry a spare starter instead. You aren't push starting this garbage so without a starter you are HOSED. Without an alternator you are just mildly inconvenienced.

Hi Keith. We're in Hereford, Arizona (Next to Sierra Vista)

Thanks for the suggestions General - makes sense. I was hoping you'd chime in. I will consider them. Our M1083 is a 1998. The voltage regulator on the 260 has different cannon plugs going in and out of it, so one way or the other, I'm going to have to figure out the wiring changes no matter which alternator I end up using. I'd sure like to find someone around these parts who has experience making these kinds of changes to these rigs. Would be a big help. I made some calls to Fort Huachuca, which is not far from me, to see if anyone there would like to make a few $$$ on the side, but got no responses.

Thanks again

Kevin

There's no wiring changes AT ALL for the 260A. The chassis hookups are just the ring terminals on the case and the ring terminals for the VR studs which are the same. One is the E terminal that turns the alternator on, and the other is the AC terminal that runs to the LBCD. None of the cannon plugs go to the chassis they are from the VR to the alternator case. And one on the 260 is for the optional J1939 CANBUS data.

I missed you, 6 weeks ago we were in Tucson. We left flagstaff area yesterday heading towards Taos, NM. Then continuing north. I’m still running my original 100 amp alternator with 42,000 miles on her. Would have loved to got your 100 amp alternator for a spare. But shipping costs and not knowing where we can receive it while traveling is difficult.

What batteries are you running? The 100A dual volt alt really gets hamstrung pulling 12V out of its middle. it cuts the total wattage by nearly 1/3(1930 watts at max 12V and 24V load). Thats the real issue with the 100A alt. In the end, the truck load is perhaps ~35A total @ 28V if everything is converted to 28V(24-12V converter to power 12v loads) in straight 24V mode the alt is good for 2800W. in that mode even the 4 battery bank is doable as long as it is in wet cell(AGM's want twice the current during bulk charge).

so if the total truck load is 35A with all the lights on, and you want another 35 for AC, well that's 70A. If you have a sensibly sized battery(pair of group 31's for this engine) they are only going to be looking for ~25A worst case, so still under 100A worst case. If the service batts are charged, your down to 70A, if you don't have the lights on, well thats -15A, and I think 20A for truck running loads is also a pretty generous estimate(probably closer to 10-12A). so doable on 100A in the config described.

I setup my alt to deliver just 28V, the only 12V connection under the cab is from alt to batt, as the alt reg requires this to regulate/balance properly. I convert 24 to 12 in the dash to feed the truck 12V loads so the battery only delivers 24V to the cab...

If the mil spec 100A ever hiccups, I will fit it with a Delco 110@24V alt. Common sized, readily available worldwide made by several other manufacturers like Bosche and Denso as well as Delco-remy. Easily rebuilt and serviced, parts available all over the place...

Not a fan of expensive unobtanium...

SO how many BTU does 24V@35A buy you in a big metal greenhouse in nevada...

Ronmar said:

Not a fan of expensive unobtanium...

SO how many BTU does 24V@35A buy you in a big metal greenhouse in nevada...

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I have yet to pay more than $650 for a Niehoff of any size. It's all about the surplus, the search, the legwork, the contacts, and horse trading. And in any case as I pointed out you can complete the mission without the thing - redundancy is key. There's plenty of time to find a replacement when you have planned for it in advance.

As for how many BTU..... Not even close to enough to warrant the damage it will cause to the cab and not nearly enough to make it actually comfortable. But you'll have a name for the truck..... "Cold Sweat"

Thanks all... and sorry we missed you Keith - next time.

General, the cab of the truck is being completely redone, including extensive thermal insulation all around. We have looked at a couple of LMTVs that have similar AC units and their owners claim that they cool their cabs well. (Both had additional insulation) The only real difference between our AC unit and theirs is, theirs are 12 volt and ours is 24 volts. I guess we'll find out if they were being honest with us.

Can you elaborate on the damage to the cab that will be caused by installing a rooftop unit? We're about ready to start cutting and if I've missed something, WHICH IS ENTIRELY POSSIBLE, I'd like to know. I don't think for a second that we've thought of everything (That's why I'm here) but we've studied this AC install closely and have come to the conclusion that the roof can easily support the AC unit, even when it's bouncing down a rough road.

In addition to installing the thermal insulation, I was also planning to install some additional structural support, to support the AC unit, although our testing, in the CAD and with a 250 lb. static load, indicates it isn't necessary. I just like to er on the side of caution. The images below represent static stresses on the roof (up and down) with a 45 lb. load on the roof. The AC unit will be rigidly mounted, so we don't think dynamic stresses will really be any different. The roof was modeled after our rig's roof and assumes a steel metal thickness of .08". Everything stays in the good range and that's without adding any additional support.

As always, thanks a LOT for the input.

Kevin

Ronmar... Here's the alternator I was looking at - for the same reason you mentioned... it should be relatively easy to find and replace in the field if I had to, but I have to admit that I like the General's logic about using the 24 volt House battery system as backup if it became necessary. It would definitely work until I was able to find and replace the military unit.

Having a brand new 260 amp alternator, which is more than capable of powering everything in the rig, including charging the House batteries with a DC to DC charger is enticing. (Especially since I already own the alternator) FWIW, I came up with the same results re: amp consumption when using the AC with the OEM 100 amp alternator. I'm just not comfortable with the margins being so slim, especially in a worst case scenario.

BTW, can anyone tell me if the fan belts in these rigs (at least my 1998 are 3/8" or 1/2"? I've measured them but they're right in between both numbers.

Thanks

Kevin

It still won't be powerful enough. The factory unit is 30k BTU for good reason. Smart people are great at justifying dumb things they spent money and time on and that they have no good real world performance comparison for. Usually they just assume that's as good as it gets and it's a coupe degrees lower and they pulled out some humidity. But it doesn't integrate with the HVAC so you get zero defrost benefits and the performance is lackluster and you get a big ugly wart on your cab for the trouble.....

The damage to the cab is not just from static loading. The hydraulic lift system and more importantly, where it's attached to the cab floor, is already too weak and many cabs (including my own) already have damage just from lifting their own weight. Adding additional weight all the way at the top where it puts the most leverage on the lift system is asking for problems. At the very least you will need the upgraded cab tilt cylinder and the floor reinforcement plates that are included with the up-armor lift cylinder kit. Have you seen the stencil that says do not exceed 200 lbs? It's not because of the static load......

The Vee belts used on the older trucks are "A" series belts.

A: 1/2"
B: 21/32"
C: 7/8"

They are probably worn and narrower than 1/2"

Kevin Means said:

...the cab of the truck is being completely redone, including extensive thermal insulation all around.

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Do you have a thread on your cab insulation efforts? Or would you share your plans for insulating the cab?

GeneralDisorder said:

It still won't be powerful enough. The factory unit is 30k BTU for good reason. Smart people are great at justifying dumb things they spent money and time on and that they have no good real world performance comparison for. Usually they just assume that's as good as it gets and it's a coupe degrees lower and they pulled out some humidity. But it doesn't integrate with the HVAC so you get zero defrost benefits and the performance is lackluster and you get a big ugly wart on your cab for the trouble.....

The damage to the cab is not just from static loading. The hydraulic lift system and more importantly, where it's attached to the cab floor, is already too weak and many cabs (including my own) already have damage just from lifting their own weight. Adding additional weight all the way at the top where it puts the most leverage on the lift system is asking for problems. At the very least you will need the upgraded cab tilt cylinder and the floor reinforcement plates that are included with the up-armor lift cylinder kit. Have you seen the stencil that says do not exceed 200 lbs? It's not because of the static load......

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We have a NOMADIC 24v rooftop unit. It hasn't made it through the summer as yet. Our charging system includes a 24v 200a alternator with 2 - 31's in series for the truck and another 2 - 31's inseries for the accessories, including the AC; each 24v battery bank separated by a Victron Cyrix - 230a for priority to the truck bank.

COOLING
We have (edited) found it acceptable into the 90's, though it certainly does not COOL the cab as well as our factory Jeep units in our Wrangler and Grand Cherokee. It is a huge improvement over the original "2-55" AC (two windows down at 55 miles per hour, as my dad used to say on our family trips in the 60's). Our cab insulation is yet to be completed: which we plan to include ceramic window tint, perhaps lizard skin, and painting the exterior cab white.

DEFROSTING
During the winter we set the unit to its highest temperature, 80.6° (it is not a heat pump) and it clears the windows crazy fast in 50° humidity or rainy weather. Even with our wet gear and dog. The moisture reduction is awesome using the ambient air from our factory heater, (which isn't the best either). It does not blow cold air in these conditions.

ROOFTOP LOAD
I can't respond to this other than the army had a gun on a turret there.

SMART PEOPLE
I agree we are justifying. A factory Red Dot unit would be more effective. We are settling with the rooftop unit and it fits our lifestyle. Having seen the threads on installing the factory unit and the difficulty I have had finding one, it is the path we chose.



In my experience here @GeneralDisorder is one of the most knowledgable and sharing people on the FMTV forum. Rick has helped us through a number of challenges with our unit. His advice is more than just worth considering; I am never looking for 'the round bin' when considering his suggestions.


I will note that my wife and I between us are 'outside' folks having spent all our time in the western US. A guide in Grand Canyon and Wasatch Mountains earlier in life and still involved in a primitive summer camp in the Humboldt Redwoods today. Folks who visit our home find it is warmer in the summer and cooler in the winter than they are used to. We find our Nomadic 24v rooftop unit a big improvement to our M1078A1. Would we install a Red Dot unit if we found one? Maybe, and I have looked for a couple years so far without success to find one. But we have lived much of our life outdoors dealing with desert heat and winter cold while on trips and the rooftop unit is much better than our '79 Toyota FJ40 Landcruiser with only a bikini top in Arizonia desert and the hard top in Utah's winter mountains back in the early 80's.

Thanks for the fanbelt info General. I kind of thought they were worn down half-inchers.

Hike, I really appreciate you chiming in. First... I couldn't agree more about the General's help. When I look back at the questions I've posted, he and Ronmar have answered most of them, and other than helping Ronmar dispose of a body, I hope to return the favor some day. The truth is, everyone who has responded to my questions have been very helpful. What a resource!

We don't have a thread on anything related to this project... as of yet. We're still in the information gathering stage, and most of the way through removing all the stuff that needs to be removed from the truck. We have purchased several things that we know we want (new Haldex air dryer, Eco-Hubs, Donaldson air filter system, larger fuel tank etc.) and we're most of the way through designing the box we want in the CAD. Your explanation of why you went with a rooftop unit is what we encountered too. Our rooftop unit is also a heat pump, which is something we wanted due to the reputation of the rig's heater-performance.

I'm going to take a close look at how to best reinforce the floor as the General mentioned, and we'll definitely upgrade the cab-tilt cylinders. That information was VERY helpful.

As of now, the cab will be insulated with three layers - the first with Siless 3mm sound, noise and vibration dampening mats (butyl mats) the second will be with 3/4" Dynamat foam and the third layer will be with sound-deadening carpeting and floormats. For the most part, this will be done to the ceiling, walls and floor, including the underside of the cab. Any suggestions?

Kevin

Forget all that. Just use the two Lizard Skin products for insulation and sound. Spray on. Done. All that other stuff will take 10x the labor and won't work any better. Probably won't work as well since a spray can get in places like up against seams and corners and through holes in the reinforcement of the walls and ceiling, etc, and edges where it can more effectively immobilize the sheet metal from vibrating. Lizard Skin is NOT a scam. Many other products are. It's the spin-off consumer arm of Mascoat. Their coatings are used in commercial, industrial, and military applications. Dog houses for fire trucks, Navy engine room applications, etc, etc. it's the real deal not just butyl tree rubber and foil.

As for the larger fuel tank - consider the frame flex. Most of the "solutions" I've seen were far too long and if you ACTUALLY go off-road they could be put under too much torsional load and break a weld seam. Get a second factory tank and straps and have it modified to fit around the rear leaf spring shackle. Again - use what you can get for pennies on the dollar surplus and leverage it hard. This also provides redundancy against losing all your fuel from a single tank rupture or puncture. Used tank and straps to for $150 to $300 pretty much every day. Easy to find when so many people are choosing to throw away the good engineering and poorly redesign things that took decades of field testing to find all the flaws with. Then they wonder why their junk is broken the first or second time out with it.

Factory heater on these trucks is impressive actually. If it's working properly you won't need additional heat. Weak heater on A0 trucks was due to routing that preferenced the transmission cooler so you wouldn't get good heat in the engine or the cab till the whole transmission came up to temp. They fixed that with the A1 and put the routing back to the way CAT intended it and the heat is significantly improved.

The up-armor tilt cylinder kit includes the cab floor reinforcement plates.

Kevin Means said:

As of now, the cab will be insulated with three layers - the first with Siless 3mm sound, noise and vibration dampening mats (butyl mats) the second will be with 3/4" Dynamat foam and the third layer will be with sound-deadening carpeting and floormats. For the most part, this will be done to the ceiling, walls and floor, including the underside of the cab. Any suggestions?

Click to expand...

I don't think we have any suggestions. We used Dynamat Xtreme under the doghouse in the engine compartment, then added Dyna Core under that next to the engine. We have also added Dynamat Xtreme to the interior cab walls, ceiling, and door panels.

Right now we can hold a conversation, though it is still louder than we hope.

Currently, we are building out our power windows and door locks (door locks/latches are frustrating: debating GeneralDisorder and Ronmar's routes to solve), ceiling and center consoles, and behind seat storage while laying out map lights, radios, backup camera, and device charging. Once we have it all ready to go together we may add Dyna Core to the ceiling and rear air pockets before installing the carpeted ceiling, wall, and door panels.

We haven't added anything to the cab side of the doghouse yet, though will likely Dynamat Xtreme and cover with carpet. All the floors are getting Dyna Pad, no carpet.

I almost forgot...
We are thinking about using Lizard Skin Cl as an undercoat on the cab exterior prior to painting it white.

If life would stop while I was working on the truck we could have all our chassis work done by fall and start on the habitat—

Thanks Hike - interesting. General... I'd never even heard of Lizard Skin until it was mentioned here. I'll definitely check into it.

Kevin

Kevin Means said:

Thanks Hike - interesting. General... I'd never even heard of Lizard Skin until it was mentioned here. I'll definitely check into it.

Kevin

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LZ dropped the interior wall temps in my 1079 van by 20 degrees F before/after and that's testing it in 90+ degree temps heat soaking in the sun all day. That stuff WORKS. And the sound deadening adds mass which stops sound propagation by making the surfaces harder to accelerate.

Thanks Ronmar. I just got done watching and reviewing some material on Lizard Skin products. Very impressive stuff. Just ordered the application kit and buckets of the sound dampening stuff and ceramic heat stuff. I think it will work well in conjunction with some of the other stuff we got. Thank you!

Kevin