Charging system???
 

so the truck is a 01 f-350 srw lariat, it has the ambulance package-dual alternator package...can someone tell me why there would be two alternators on this truck instead of a good decent sized one, like any other diesel?? i noticed a few weeks ago while driving stopped at idle my trucks voltage was only at 12.1v, driving over 1000rpm it was normal about 14.3v, under load “lights and blower motor on” while driving 1800rpm i only had 13.4v when prior i would maintain 14.2-14.3v idle or high idle....full field testing of the charging system "110a alternators” primary pulled 30a and secondary pulled 8a, after the test system V was 11.9v...lights are dimming ect ect....i tested the batteries statically and in parrel, full field test was done with a VAT machine and a snapon detect, testing result bad diode in alternator, voltage ripple 385mV high idle....voltage drop across entire starter system and alternators test was 0.3v spec is 0.5v...would a bad diode cause my problem? i hear no wine or radio static ect....if one alternator is bad why isn’t the other one helping me out here??
thanks, mike

Dual alternators provide more amperage than a single alternator. With the ambulance package, it was designed to have a greater current load on the system.

Yes a diode can cause problems like this. They can cause all kinds of issues with t he electrical system. You need to swap out the bad one and you will be set.

Agree with Woodnthings on this - replace/test both alts. and then re-test and see how your voltage stands.

thanks for the reply’s guys...i figured that, just couldn’t figure buying two new alternators right now, but you gotta do what you gotta do...just the dual alternator set up........im a diesel mechanic and rigs that pull massive amounts of amperage 12v or 24v systems trucks or busses for the most part have one massive alternator....like or 92 f-custom 7.3L its or rescue truck at the firehouse, lights, sirens, generators, hurst tools, ect. ect....or even internationals TT444E the 7.3 in international MD trucks has one big alternator....just doesn’t make sense

I've often wondered why go with two alternators when a single large one could handle the load. Best I can figure is that maybe the E series have a hood clearance issue or more likely...the ambulance industry wants a secondary alternator as a back up just in case. When a patient's life depends on the ambulance getting to the hospital then redundant systems makes sense.

Just supposing though...I really don't know why Ford went with the duals either. :-huh

okay so i got the scoop today on the dual alternator set up...im a student at UTI and i talked to the ford fact teacher who claims to have specialized in the 7.3L for many years, he said both alternators work together at the same time, if one is bad, or if you disconnect the one, it will draw off of just one, since its trying to draw off of two, and its only drawing off of one, it full fields the alternator frying diodes, such as in my case. the idiot light doesn’t come on because its still charging a slight amount...ford did this because its cheaper then the 290a alternators they used in the newer “ambulance package” that alternator is $700, and it requires more room...basically ford did this to save money, i was advised to replace both of them...