200/400 Amp Alternator, Drawbacks?

[Wire Fox]

Hey all, I know my A1 is going to be coming in with a weaker 60 Amp unit and it looks like it's missing parts, so I'm shopping alternators at the moment just in case it's truly DOA. I know that the 200 Amp dual voltage alt is the defacto go-to on these boards. It looks likes it's relatively compact, the installation kits are cheap, and there's not much to complain about except for the price when compared to an outdated 60 Amp. I also took notice that the 400 Amp is officially listed as the replacement for the 200 Amp units and in-service on the ECVs. It's hella-heavy at 120 pounds, appears to be larger, and the install kit for it is $200 more than a comparable 200 Amp kit.

I was a few pages in on a search for information about the 400A units and the only real commentary I picked up on was "you don't want the 400A one, you want the 200A." I guess I just want to know why. Are there any unforeseen drawbacks here, or have am I possibly not realizing how much larger/heavier the 400 Amp unit is over the 200 Amp? I'm worried about any possible reliability issues, maintenance troubles, engine wear, fuel consumption, or wiring issues (I'm assuming the cables in the install kits are all that's necessary-haven't done my homework to be sure) it might bring on? With the NOS Fleabay price being almost the same for the 200A and 400A alternators right now, it's really tempting to pay the extra $200 on the install kit to have literally double the power in order to be ready for any radio or shelter setup I could ever dream of.

Thanks everyone. Look forward to seeing what experience can be brought to the table on this.

 

[dilvoy]

Your belts are going to have to turn that heavier 400 amp armature so expect a bit of power loss when revving up the engine. There was a problem with the 200 amp alt when the first serpentine belt setup came out. When the engine would decelerate, the Armature would want to keep turning and would overpower the belt tensioner and the belt would go slack at the power steering pump and make it come off and get damaged. They put a pie plate type disk as a stop gap repair and then redesigned the serpentine setup on the later ones after trying a free wheeling on deceleration generator pulley. If you need 300 or 400 amps of charging capacity, it is a no brainer to install the 400 amp Gen.

 

[Wire Fox]

Your belts are going to have to turn that heavier 400 amp armature so expect a bit of power loss when revving up the engine. There was a problem with the 200 amp alt when the first serpentine belt setup came out. When the engine would decelerate, the Armature would want to keep turning and would overpower the belt tensioner and the belt would go slack at the power steering pump and make it come off and get damaged. They put a pie plate type disk as a stop gap repair and then redesigned the serpentine setup on the later ones after trying a free wheeling on deceleration generator pulley. If you need 300 or 400 amps of charging capacity, it is a no brainer to install the 400 amp Gen.

Anything at least pseudo quantitative on how much extra strain/power loss it will be? I couldn't find a spec on how much the 200 amp alternator weighed to be able to make a good guess. As well, has anyone on here driven both a HMMWV with a 200A and one with a 400A? Definitely would value that butt-dyno report. Just trying to guage out if I'd be kicking myself all the way up until the day that I actually would need that much power, which isn't today.

 

[Carrera911]

What is your reasoning for getting rid of the 60 amp? It's more than enough for a stock truck and still has plenty of headroom for accessories. It's almost all headroom because the only draws on the truck are the fuel solenoid, whatever lights you run and the heater blower. Remember that at 24 volts 60 amps, this is equivalent to 120 amps 12 volts. That is about what most new half ton trucks have with all the electronics, heated seats etc. If you want 12 volts, I was told that the 200 amp alt can't put out much on the 12 volt side anyway.

I went with a battery equalizer for 12 volts and can draw 40 (12v) amps constant and much more in surges (winches etc).

 

[mechanicjim]

the 200 amp weights about 70lbs for the dual voltage both the 200 and 400 only output max 50 amps on the 12v side. (if you pull all 50amps of 12v you only get 140 on 24v side) its a shared load system total output limited to combined loads. I think that there are a couple surplus sellers that have the data sheet for the 400 amp and that will show the output curve. on that curve the toque value is the power need to turn the thing if you find the same data sheet for the 200 amp you can compare at each RPM the torque difference to see how much "Power loss" the large unit will put on the engine. when searching use the Niehoff part numbers N**** sometimes you find more info with them.

 

[Retiredwarhorses]

I çant see a single reason for anyone to need a 400amp gen in a hmmwv for civ use.
if anyone other then me has ever worked on a 400amp equipped truck, they know you can't even change your fuel filter without removing the generator from the truck....so stupid of a design.
The 60amp is more then sufficient to do what it does....it's served on every M series's vehicle for how many years?

 

[Wire Fox]

Alright, time for some concrete numbers. I found the brochure easily for the N-1602, but couldn't find one for any of the 200A dual voltage models, so I just grabbed up one for the 140A and 260A units to just get an idea of what kind of numbers to expect. Check out these torque curves:




As you can see from the peak output on these graphs, the 140A requires 16 ft-lb, the 260A requires 30 ft-lb, and the 400A requires 40 ft-lb of torque to operate. Just taking a guess, it looks like you're gradually getting a better torque-to-power-output ratio as the unit gets larger, so I'll estimate the 200A alternator will require 21 ft-lb of torque to operate.

I also pulled this spec from Wikipedia for the GM 6.5 NA engine: Power / Torque (lowest):
155 hp (116 kW) @ 3,600 rpm / 340 lb·ft (461 N·m) @ 1,700 rpm (naturally aspirated)

I'm sure I'm doing the math on this with some pretty gross error and with flawed logic, but it's going to still help me visualize the power loss with each unit: 140A = 4.71% of engine power; 200A = 6.18% of engine power [estimated]; 260A = 8.82% of engine power; and 400A = 11.76% of engine power.

If we drop my non-engineering-grade math out of this, there's a pretty conveniently easy trend to see here: the torque required to operate each alternator is almost directly proportional to its output; we need about double the power to produce double the output. Losing nearly 12% of my engine's power output just to have extra power available that I won't need sounds...rather unreasonable, unless I had a real reason for it. Heck, if I were powering up shelters (mobile or ground-based), I'd probably be all for it; however, I'm just looking to keep radios and an inverter up and running, so I have to agree that it's absolutely overkill for me.

You guys were absolutely right and I appreciate your input on it. I really appreciate it when I really see why something is a good or bad idea, so I hope the extra information attached here aids the next guy well.