Alternator Suggestions?

[Kevin Means]

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.

 

[Keith Knight]

Where are you located?

 

[GeneralDisorder]

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.

 

[Kevin Means]

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

 

[GeneralDisorder]

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.

 

[Keith Knight]

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.

 

[Ronmar]

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...

 

[GeneralDisorder]

Not a fan of expensive unobtanium...

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

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"

 

[Kevin Means]

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

 

[Kevin Means]

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

 

[GeneralDisorder]

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......