Converting a HMMWV to 12/24V

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Augi
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Converting a HMMWV to 12/24V

Post by Augi » Thu May 02, 2013 12:10 am

The first question anyone asks ever about these trucks is "How do I get 12V to power my accessory stuff?" This is the way all the late model HMMWV's are set up so it's as close to factory as you can get.

Depending on where you get your alternator (the most expensive part, and the brackets and belts are the next), the price of the whole thing can be pretty decent too. This might have cost me $400 - $450 in total.

The reason I went down this path at all is because I need 12V power for the TCM for my 4L80 swap and I don't want to mess around with voltage converters etc. Also, since this is the factory method, it is way more robust. There are no cheapy electronics to get water in or otherwise explode due to the harsh environment the HMMWV spends it's time in.

Anyway, the concept is pretty simple. You just install a late model 12/24V Niehoff alternator (available in 100A or 200A output) on the truck and run a little bit of extra wiring. Now you can connect whatever you want to the +12V post of the lower battery and draw as much current as you need. The alternator will automatically keep the batteries at the proper voltages to charge them evenly so you don't kill one.

Image

Here's the parts list and where I got it from:
(1ea) 12/24V Niehoff Alternator with V-belt pulley (100A or 200A) -> 86humv
(1ea) 200A mounting bracket -> 86humv, NSN 5340-01-197-5548
(1ea) 200A tensioner bracket -> ebay, NSN 2590-01-444-4365
(1ea) 200A rear support bracket (braces the back of the mounting bracket to the head) -> Kascar, NSN 5340-01-292-8404
(8ft) 2/0ga battery wire -> Erik's Military Surplus
(1ea) 2/0ga crimp lug with 3/8" hole -> Erik's Military Surplus
(1ea) 2/0ga crimp lug with 1/2" hole -> NAPA
(2ea) red rubber boots (optional) -> Hummerpartsguy, NSN 5975-01-208-9618
(8ft) 8ga wire -> Erik's Military Surplus
(2ea) 8ga crimp lug with 7/16" (I think) hole -> NAPA
(2ea) black rubber boots (optional) -> ebay, NSN 5340-01-474-2315
(1ea) ground strap -> ebay, NSN 5999-01-372-5601
(1ea) 10" long 7/16 grade 8 bolt, washers and lock nut (reused all other mounting hardware) -> McMaster
(3ea) V-belts -> NAPA, #7640
(lots) zipties!

The alternators are drop in replacements for their 24V only counterparts in their respective sizes. I went with a 200A since that's what was available. Serpentine or V-belt on the alternator as you receive it does not matter as long as you have a pulley put on it to match what's on your engine. You can pull a serpentine pulley off an alternator and put the appropriate V-belt pulley on. You do have to pay attention though because the mounting brackets and pulleys are different for the different amperage alternators. The 200A alternator mounting bracket is way bigger than the 60A that it replaced and the pulley has grooves for three belts instead of two. The new brackets do bolt right up though. One note: I could only get the 10" long lower alternator mounting bolt from McMaster. It's the one the alternator pivots on when you tighten the belts.

Image

Wiring is super easy. Here's the only tricky part: for A0 trucks that originally had a 60A alternator, you connect the 8ga wire (5A) that was coming from the alternator output on the 60A to the SENSE (also called IGN) post on the new alternator. In the old harness Output (5A) and SENSE (568) are tied together anyway. The SENSE/IGN, A/C and Ground from the old alternator connect to the same spots on the new alternator. I had to extend my A/C wire a little bit.

Then there are three new additions. One is a heavy gauge ground strap. It connects to the outer bolt of the water crossover. Since I had a regular hex bolt in mine, I switched it with an unused stud out of the intake manifold so I could just run a nut down on it to secure the ground strap. The other two are the two cables you are about to make.

Wiring:
5A -> Connect to IGN
586 -> Connect to IGN
2A -> Connect to A/C
3B (I think, can't read the diagram) -> Connect to Ground
Ground strap -> Connect to Ground on the alternator and the water crossover on the engine.
2/0ga cable -> Connect to +28V output on the alternator and directly to the +24V side of the top battery
8ga cable -> Connect to the +14V output on the alternator and directly to the +12V side of the bottom battery

To make the cables I fed them through the truck following the engine harness where I could (look at the pictures below) and then ran along the top of the frame rail. Then I trimmed to length and terminated them. With 8ft of stock I think I trimmed a foot or so off of each. YMMV. The 8ga wire connects right to the middle battery (black boot in the photo), but I connected the 2/0ga wire to the power feed through stud in the battery box so I wouldn't have to connect and disconnect so many things when I unhook the batteries (red boot in the photo).

Image

Image

Image

Now you can connect a terminal block or whatever to the +12V post of the lower battery to power all of your 12V accessories.

Have fun with your new found power!

Augi

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Re: Converting a HMMWV to 12/24V

Post by Fenris » Tue Sep 20, 2016 6:29 pm

I just thought of something, wouldn't it be a better idea to have your massive 28 volt feed that goes to the batteries ran through a solenoid first? Theres always energy at the node point, thats one of the reasons why the control box disconnects the battery feed from the rest of the alternator. The line that goes to the excitation point (IGN) and the battery feed are spliced together inside your engine harness before it goes to the relay inside the control box. If you disconnect one of the lines you have to IGN (either the original excitation line or the original power feed) and connect it to a solenoid coil, then run your massive line back to your batteries through the high current contact, you would keep the rest of the circuit dead till you start up your truck :?
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Augi
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Re: Converting a HMMWV to 12/24V

Post by Augi » Wed Sep 21, 2016 6:19 pm

No.

The diagram in the TM shows direct connection to the batteries.

It's unnecessary, plus dealing with a 200 amp contactor sucks for a number of reasons.

Augi :)

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Re: Converting a HMMWV to 12/24V

Post by cptnblk » Wed Oct 05, 2016 11:54 am

I made a short video of pulling 12+ from the battery box last week.
https://youtu.be/NhFhChWhu6g

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Re: Converting a HMMWV to 12/24V

Post by MarioMP » Tue Apr 25, 2017 2:44 am

Do you guys have part numbers of compatible generators for M998s?
I'm trying to locate one and see that fleabay has one 200A and two 400A NIEHOFF units but I don't want to mess with modifications anymore than I have to.
If the old saying that 'mo is bettar' holds true, than I'll get the 400A unit, otherwise I should be fine with the 200A that seems to be popular.

Also, if anyone has sources for those, please let me know.
I'm seeing the 200A on fleabay for ~$500 which after brackets, wires, etc. should be somewhere around $620. If I can get what I need for less, I'm all ears.


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Re: Converting a HMMWV to 12/24V

Post by Retired War Horses » Tue Apr 25, 2017 8:19 am

Stay away from the 400amp unless you have a forklift to install it...and then available again to remove it just so you can change your fuel filter.
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Re: Converting a HMMWV to 12/24V

Post by MarioMP » Wed Apr 26, 2017 10:08 pm

I actually did just buy a forklift few months ago, although I know that you're just kidding.
With that said, are the any real world benefits to having 400A supply on M998 without any craziness?
Other than the 12K electric winch and maybe a light bar, I won't be doing much more to my rig.
Also, other than the weight, any downsides?

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Re: Converting a HMMWV to 12/24V

Post by 86humv » Wed Apr 26, 2017 10:50 pm

A 400 amp is way overkill, takes up to much room, need a hoist, or forklift, or 3 people { no room for that } to lift it.
A 200 will do all you need.
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Re: Converting a HMMWV to 12/24V

Post by MarioMP » Thu Apr 27, 2017 9:57 am

86humv wrote:A 400 amp is way overkill, takes up to much room, need a hoist, or forklift, or 3 people { no room for that } to lift it.
A 200 will do all you need.
Thank you.
86humv - I take it that you don't have the 200A units anymore? I PM'ed you either here or on SS last week with no replay.

In that case; does anyone on here have any for sale or am I'm looking at getting it from that one high volume dist/seller on FleyBay?

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Re: Converting a HMMWV to 12/24V

Post by metalman » Sat Apr 29, 2017 4:28 pm

Retired War Horses wrote:Stay away from the 400amp unless you have a forklift to install it...and then available again to remove it just so you can change your fuel filter.
Tell me about it, i picked up a truck with a 400 amp alternater last week, never seen one installed in person before, it's huge.
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Re: Converting a HMMWV to 12/24V

Post by LEIbuys » Mon Jul 03, 2017 12:05 pm

I have a new take off 200amp dual voltage alternator and new in box mounting kit with all hardware, wiring, belts, and instructions that I'm selling for $650. I had two of these kits one of them I recently installed in my M998. PM me if interested.


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Re: Converting a HMMWV to 12/24V

Post by luca » Tue Oct 02, 2018 1:39 pm

still have the 200A alternator?

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Re: Converting a HMMWV to 12/24V

Post by wooody1 » Tue Oct 02, 2018 4:59 pm

There is a guy on youtube with a humvee, he removed the motor, installed another unit then he runs 2 alternators on the same belt one on 24v and another on 12v, he has some good videos and tells you how he has worked it out, still a few bugs in it but he goes through the entire system, if you want the link let me know

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