Single or Dual alternators? - Diesel Forum

Bounty_Hunter · 02-08-2010, 10:41 AM

What are the pro's and con's to having a dual alternator system? Will the truck still operate if one fails? Are they the same alternator, just mounted different, so if you wanted to have a spare you'd only need to keep one on hand? I looked under the hood on one and there sure isn't much room for any extra anything.

Thanks

fxdwg · 02-08-2010, 12:03 PM

On my 2000, I've got the dual alts. I had one go out a little while back. The other picked up and did the job. Good and bad about this set up though. There was NO indication the first one had died from the truck. Nothing, no lights, no check engine, no decreased voltmeter readings, nothing. The only way I saw it was my Escort radar detector is also a digital voltmeter and it took much longer for it to come up to running voltage upon startup. They are different mounts on mine, so you can't just swap them, but the computer controls them so you don't have to do anything, the computer swaps them around. But one is primary, which is the top one on mine, and one is secondary. The primary one gets used most of the time.

So while I really liked being able to drive it until I was ready to change out the bad unit, you have to have a separate meter mounted to tell you when the first one fails.

444-4D · 02-08-2010, 01:05 PM

I think the PCM logic changed on the 6.0 to randomly turning off one alternator instead of always turning the same one off. I don't know how the new trucks are but the following is from the Ford service manual as it applies to my truck(a 2000 F-250).

"The optional dual generator package (7.3L diesel engine only) consists of an upper/lower dual generator system. The upper generator is a 6G 50/110 generator with a 2.49:1 pulley ratio. The lower generator is a 6G 50/110 generator with a 2.32:1 pulley ratio. Thus the upper and lower generators are not interchangeable.

This system is also monitored and controlled by the powertrain control module (PCM). The PCM monitors both the upper and lower generator I circuits to determine both generators' output and set possible fault codes (diagnostic trouble codes [DTCs]). The PCM only controls the lower generator by turning it on or off by opening or closing the lower generator off only when the glow plugs are commanded on by the PCM to avoid possible damage (excessive voltage) to the glow plugs.

Both generators are independent of one another and only control themselves (through their own internal voltage regulator). If one generator fails, the other generator can maintain system performance under light load conditions. Under a heavy load, the PCM should detect a problem, set a DTC and illuminate the warning indicator.

The PCM controls the charging system warning indicator and will command the light on if the PCM detects a problem on the monitored circuits. "

**SmokeyWren** · 02-08-2010, 01:09 PM

Quote:

Originally Posted by Bounty_Hunter

What are the pro's and con's to having a dual alternator system?

The main pro is more juice available to power high-draw equipment at idle or elevated idle RPM without killing your batteries.

Assuming a 2011 diesel:

Std is single altenator with max of 155 amps output.

Optional is heavier duty single altenator with max of 200 amps output. 200 amps is a bunch. Very few folks can use more than 200 amps.

But if you have an ambulance or off-road rock crawler with a million watts of lights and strobes and sirens and electric winches, etc., then you might need the optional dual altenators. The dual altenators put out a max of 355 amps, so I assume that's a primary alternator at 200 amps plus a secondary altenator at 155 amps. So no, the dual altenators are not identical twins.

Yes, it gets really tight around the front of the engine if you have dual altenators.

Bounty_Hunter · 02-08-2010, 05:30 PM

Thanks for the info. I'm planning to order a 2011 F250 pretty soon and just need to get my ducks in a row.

bbs · 03-03-2010, 12:25 PM

Years ago, ambulance builders had a heck of a time keeping alternators from burning up. The dual alternator setup was Ford's answer and it has worked pretty well. These days it isn't as much the lighting (lots of LED now), but climate control, air compressors for kneeling and airhorns and everything can add a lot of amps.

Other than a service vehicle like an ambulance or someone who constantly is on their plow controls I wouldn't think it would be an advantage.