Putting a HMMWV 400 AMP alternator on a Cummins NHC250. Has anyone done it? Need info

[goldneagle]

I just found some more info on the alternator and wanted to share it.

 

[patracy]

I will be watching this thread.... 12V supply would work a lot easier for my M931/MK48 project's gauges.

 

[goldneagle]

I will be watching this thread.... 12V supply would work a lot easier for my M931/MK48 project's gauges.

50 AMP output at 12 volts should be enough to recharge a 4 battery bank. 60 AMP alternators already do it on most of out trucks.

 

[Stalwart]

50 AMP output at 12 volts should be enough to recharge a 4 battery bank. 60 AMP alternators already do it on most of out trucks.

Not really, since the batteries are in series each see 60A on a 2 battery 24V system. In a 4 battery 50A 12V system each would see 12.5A which isn't very much to replenish batteries, not in a short period of time anyway, we are talking MANY, MANY hours.

 

[goldneagle]

Not really, since the batteries are in series each see 60A on a 2 battery 24V system. In a 4 battery 50A 12V system each would see 12.5A which isn't very much to replenish batteries, not in a short period of time anyway, we are talking MANY, MANY hours.

Thanks for the correction. So I guess I will have to set up all the batteries in 24 Volt groups and use a battery equalizer or inverter to get 12 volts out for the camper.

 

[Vintage iron]

I spoke to one of the manufactures of the alternators. He said the ratings on all the military is content duty not peak, like the civilian stuff. He also told he the the 400amp units take a
30 hp motor to run them in tests. Seeing that our Cummins 250 (240!) are already under powered. I don't think this would be a good idea?

I just replaced my 60 Amp alternator with a new one.

 

[Sephirothq]

a 250 cummins has more power to spare then a 6.2 or 6.5 does.

 

[Vintage iron]

I guess it comes down to your power needs. Every modification has it's pros and cons.

 

[goldneagle]

I might have to reconsider my mod. Since it is not a critical part of my RV mod I will hold off doing the project until i have more info available. I would like to get real data on the alternator, such as HP used in idle, and whether it puts an increasing load on the engine as power demand increases. Or does the alternator produce a constant load on the engine even under low power demand. I know that on AC generators the resistance and demand on the engine increase as you increase the load on the gen set. I do not want to loose even more fuel mileage on my RV, it is bad enough to start with.

As far as HP is concerned, if the truck is rated 20,000 payload highway, the RV conversion is not going to be anywhere near that capacity. If you deduct the weight of the cargo body and add the weight of the M109 box they probably cancel each other out, or close. SO all the RV add-ons will not put much weight on the truck. In other words, the truck will be carrying a light load. Adding a 30 HP drain on the engine should not effect performance.

 

[Vintage iron]

I am only trying to contribute to the conversation, but after speaking to the manufacturer I decided that a 60 amp is more than sufficient for my customers RV and my own power needs. As for the loss in hp, 30 hp is a lot! The guys here that are adding turbos to their Cummins 250 are only getting 20-30 hp out of that modification. Every hp counts in performance and fuel economy. Small changes to our trucks like a air operated fan, milled out front hubs or bobbing a axle of will bring a noticeable difference in the way our trucks perform.

 

[goldneagle]

I am only trying to contribute to the conversation, but after speaking to the manufacturer I decided that a 60 amp is more than sufficient for my customers RV and my own power needs. As for the loss in hp, 30 hp is a lot! The guys here that are adding turbos to their Cummins 250 are only getting 20-30 hp out of that modification. Every hp counts in performance and fuel economy. Small changes to our trucks like a air operated fan, milled out front hubs or bobbing a axle of will bring a noticeable difference in the way our trucks perform.

I do appreciate your contribution to the conversation. I am still in the early stage of my build. I may have jumped the gun on getting the 400 AMP alternator. I was assuming it would only put as much resistance to the engine as demand rose. So if i was not pulling 400 amps it would not put the same demand on the engine as when it put out only 200 AMPS. Did the manufacturer have any documents as to demand in HP vs. AMP output?

 

[frodobaggins]

I was assuming it would only put as much resistance to the engine as demand rose. So if i was not pulling 400 amps it would not put the same demand on the engine as when it put out only 200 AMPS.

You know what happens when you assume.. But in this case, you are assuming right. The resistance will be lower when drawing small loads and rise as demand rises. The 30+ HP draw is at max load.

 

[goldneagle]

You know what happens when you assume.. But in this case, you are assuming right. The resistance will be lower when drawing small loads and rise as demand rises. The 30+ HP draw is at max load.

If I remember the spec's on it, it is supposed to put out over 200 AMP at idle speed. I think it was part of the requirement from the military that it could produce over 200 at idle so they could run the equipment in the HMMWV .

 

[steelypip]

Several things I have learned from heavy duty vehicle electrical equipment (on first responder hardware in this case, but physics doesn't change just because it's painted green).

1. If there's a one-way drive pulley on it, it's because the rotor of the alternator is so massive that full throttle up shifts result in the alternator shredding the drive belt as it slows down from ~13000 RPM to ~5000 RPM in the 500 milliseconds that the upshift takes. With the one way clutch, the alternator rotor can spin down independently of the engine and everybody is happy.

2. Cooling fan orientation and one-way clutch orientation must be changed to reverse-rotate an alternator. There might (but probably isn't) also be a need to change brush holder orientation.

3. The big problem with high amperage alternator is torque required at maximum charge at idle. Most belt drives can deliver enough power to run the alternator at maximum output above 5K rotor RPM, but turning that monster at 200A output at 2-3K rotor RPM is a killer, because the RPM is low, so the torque demand is higher than the belt can manage. That's why there are dual belts, wide multigroove belts, etc for these alternators. You'll note there are probably multiple alternator mounting brackets to lock the thing in place too - you need all of them - it will try to move around on you in a high load at idle situation. It will also try to destroy the bearings on any other belt powered accessory on the tension side of the belt between it and the crankshaft pulley.

4. 400A @ 28V is a lot of current and a lot of power. You WILL have to run big fat welding cable to the big loading points and you WILL need to put a fusible link in the output from the high power bus to the vehicle's existing bus, which is only rated for 60A or so. Cooling and ventilation will be an issue - both for the alternator and for electrical components (including batteries) that are absorbing that kind of power.

All of that said, it's a benign upgrade. Other than additional cooling fan load, it won't draw measurably more crankshaft HP than the existing alternator unless you're drawing that power to put it into a load somewhere. I would probably use a manual disconnect switch on the feed line running to the battery bank and maybe also a continuous-duty contactor as well wired into something that detects that the vehicle is probably moving, like a circuit running between the parking brake indicator light and the service brake light circuit (with appropriate diodes along the way) so that it tried to dump alternator power into the big battery bank only when the vehicle was actually moving.

 

[goldneagle]

Several things I have learned from heavy duty vehicle electrical equipment (on first responder hardware in this case, but physics doesn't change just because it's painted green).

1. If there's a one-way drive pulley on it, it's because the rotor of the alternator is so massive that full throttle up shifts result in the alternator shredding the drive belt as it slows down from ~13000 RPM to ~5000 RPM in the 500 milliseconds that the upshift takes. With the one way clutch, the alternator rotor can spin down independently of the engine and everybody is happy.

2. Cooling fan orientation and one-way clutch orientation must be changed to reverse-rotate an alternator. There might (but probably isn't) also be a need to change brush holder orientation.

3. The big problem with high amperage alternator is torque required at maximum charge at idle. Most belt drives can deliver enough power to run the alternator at maximum output above 5K rotor RPM, but turning that monster at 200A output at 2-3K rotor RPM is a killer, because the RPM is low, so the torque demand is higher than the belt can manage. That's why there are dual belts, wide multigroove belts, etc for these alternators. You'll note there are probably multiple alternator mounting brackets to lock the thing in place too - you need all of them - it will try to move around on you in a high load at idle situation. It will also try to destroy the bearings on any other belt powered accessory on the tension side of the belt between it and the crankshaft pulley.

4. 400A @ 28V is a lot of current and a lot of power. You WILL have to run big fat welding cable to the big loading points and you WILL need to put a fusible link in the output from the high power bus to the vehicle's existing bus, which is only rated for 60A or so. Cooling and ventilation will be an issue - both for the alternator and for electrical components (including batteries) that are absorbing that kind of power.

All of that said, it's a benign upgrade. Other than additional cooling fan load, it won't draw measurably more crankshaft HP than the existing alternator unless you're drawing that power to put it into a load somewhere. I would probably use a manual disconnect switch on the feed line running to the battery bank and maybe also a continuous-duty contactor as well wired into something that detects that the vehicle is probably moving, like a circuit running between the parking brake indicator light and the service brake light circuit (with appropriate diodes along the way) so that it tried to dump alternator power into the big battery bank only when the vehicle was actually moving.

Before we get crazy here with this alternator project, let me ask a question. What size alternator do i need to feed 4 batteries for starting and cab electronics and 6 deep cycle batteries for the Camper portion?

 

[frodobaggins]

If I remember the spec's on it, it is supposed to put out over 200 AMP at idle speed. I think it was part of the requirement from the military that it could produce over 200 at idle so they could run the equipment in the HMMWV .

Speed and load are not the same. If you draw 5 amps, it will pull less engine hp than 25 amps will. If you want to put it on your truck you are good. I don't however think you'll ever need that much power though.

 

[goldneagle]

Speed and load are not the same. If you draw 5 amps, it will pull less engine hp than 25 amps will. If you want to put it on your truck you are good. I don't however think you'll ever need that much power though.

I wish I knew how much I need. I will have 4 starting batteries and up to 6 deep cycle batteries for the Camper. Any idea what size alternator would be right for that application? I can always sell the 400 AMP unit, and even makes some money on it, and buy a smaller one (once I know what size to get)

 

[steelypip]

Before we get crazy here with this alternator project, let me ask a question. What size alternator do i need to feed 4 batteries for starting and cab electronics and 6 deep cycle batteries for the Camper portion?

The question can't be answered as it was asked - you left out the most important variable: time. Most batteries are happiest being charged at a c/10 rate (check the manual - your battery may vary). So if you have, say, 40 amp-hours of batteries and they're 50% discharged, the optimum charge would be a 4 amp rate for 5 hours plus the topping/equalizing charge (or just float at ~2.3V /cell if they're wet cells and you're not going to do it for days on end). A lot of the time, however, you don't want to wait for the optimum rate charge to complete, so you go to something like c/5 or c/2 to get the time down until the impressed voltage comes up to the regulated value, then the effective charge rate drops off as the battery approaches full charge. That's pretty much what you get when you do a constant-voltage charge like most vehicles do, and they get away with it because starting batteries are seldom more than 20% discharged. It does, however, cost battery life and charging efficiency to charge at faster than a c/10 rate.

Where a big battery bank for the camper is concerned, I'd probably not worry a whole lot about managing charge rates myself and would just hook it up to a charge controller. Obviously a big bank can absorb a lot more amps than a small one can, so figuring out a maximum charge rate has to do with 1) how many amp hours you're charging, and 2) how long you're willing to wait for it to go from a declared minimum charge level (typically 30-60% for lead acid) to full charge.

As stock alternators on vehicles have grown in capacity, more and more of the OEM regulators I've seen have a current limiter function built into them to limit the maximum current delivery at low RPM precisely to avoid the problems I mentioned in my first post. Car alternators, in particular, are usually sized to deliver lots of current for a short period at about 5000 rotor RPM, with maximum output at about 7,000+ rotor RPM. They tend to be limited in current output below 5000 rotor RPM to keep from 1) frying the windings because of inadequate cooling air flow or 2) overwhelming the drive system with high torque demands.

If you ever want to know about alternator drive ratios, it's pretty simple: take alternator redline (usually about 13000 rpm) and divide by engine redline. You can also use this to figure out the design redline of an unknown alternator - measure the pulleys to find the drive ratio and then plug in the engine redline. I would do this with the 400A HMMWV alternator stock installation to verify the alternator redline before putting it on a different engine.

As for suitability of the 400A alternator - it's electrically completely suitable. You're going to have to either a) take an active role in battery management or b) install some intelligent electronics to do it for you with any large battery bank if you hope to get good life and performance from it no matter what you use for a current source, and you know for sure that the 400A alternator is big enough to do the job. That said, I'd probably look hard to see if I could get by with a physically smaller alternator just to avoid the installation problems you're looking at on the NHC250.

 

[Vintage iron]

Quote :As for suitability of the 400A alternator - it's electrically completely suitable. You're going to have to either a) take an active role in battery management or b) install some intelligent electronics to do it for you with any large battery bank if you hope to get good life and performance from it no matter what you use for a current source, and you know for sure that the 400A alternator is big enough to do the job. That said, I'd probably look hard to see if I could get by with a physically smaller alternator just to avoid the installation problems you're looking at on the NHC250.

I have discussed this at length with my customer. I like his design. He Separated the truck build from the camper portion. So we are using the 60 amp to charge the batteries and run the truck accessories. The RV power will come from a standard portable generator that may have a bank of batteries. The generator will be sized to handle the demands of the Camper portion. Having a portable generator will supply power on demand, can be run under times of high demand, can charge a bank for times of low demand, consumes less fuel, lower wear on the drive train and new generators are very quiet. Seems like a easy and sensible solution. This is what we did and I am not saying this will work for everyone. I will be interested to see what others will come up with. There are many ways to skin a cat.

 

[steelypip]

That was what my parents did with their vintage RV when they decided they wanted air conditioning and deep cycle charging on the road. Dad put a standard small utility generator on a swivel trailer behind the RV and it runs the big rooftop AC unit when they want AC underway (seldom - the RV has good ventilation and is white). Vehicle battery is always charged by the engine alternator. Dad put a battery isolator and disconnect switch in so that the deep cycle can be charged (slowly) and maintained by the vehicle alternator, or the deep cycle can be more rapidly charged by the 120V powered 10A+float charger hooked to the AC bus. In the event of a vehicle battery failure, dad can jumper cable from the deep cycle to the engine to get the thing running.

He has left it like that for about 15 years now, so it must work pretty well. He's still using the same 2KW Generac he bought originally, btw. It has also powered the house and well pump for days or even weeks after bad storms.