A couple of ?s regarding factory Dual Alternators...

[SoCalDieselNewbie]

I was talking to Mr. Kennedy today regarding an order that I needed to place.

During our conversation, I mentioned that I was also in the market for a few SPAs gauges including the Volt/Volt guage to measure the voltage of both of my alternators.

I was under the impression that dual alts were an active system. In that both alternators worked 24/7.

I guess that I could see if I got output out of both... He mentioned that someone here (mdrag?) wrote that it was a passive system. In other words, only one alternator worked while the 2nd was just a backup.

While this is normally a non-issue, I have big plans. Plans that need power. :D

Between multimedia system w/ 4 monitors, the sound system, driving lights, Mr. Kennedy's high output Hella bulbs & harness, gauges, cb, scanner, power inverter & etc... Newbie needs the power!

Any information would save me the time of checking... though I probably should. ;)

[Kennedy]

Mdrag, Mdrag, he's your man...

[mdrag]

SoCalDieselNewbie,

Read throught his lenghty topic and it should answer some of your questions:

http://forum.62-65-dieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=7&t=001846&p=2


This is how I tested my dual alt set-up using a 125A battery tester:

I switched the 4 position alt connectors so the OEM was the primary and the PowerMaster the AUX alt. My battery tester is rated at 125A, which should overload the OEM Delphi alt rated at 102A max, and I believe about 60A at idle.

I started the truck after attaching a Fluke 77 digital multimeter to the jump start area and let the voltage stabilize to 14.5 volts. Hooked the battery tester to the PS battery. Hit the button for about 10 secs total.

Almost immediately the voltage on the meter dropped to approx 13.2 - 13.3V, within 1-2 secs the DMAX sound changed as if a load was added to the engine (RPMs did not seem to change to any significant degree).

At the same time as the engine sound change, the Fluke meter voltage reading increased to approx 14.3V and would fluctuate up/down by 0.1V. Held the test button for the remaining time to complete 10 secs. and the voltage was maintained at 14.3V +/- 0.1V. Button released (OFF) on battery tester and DMAX sound returned to normal. This all occurred very quickly.

I repeated this 3 times and even tried with PM alt as the primary alt and the OEM as the AUX alt. Same results each time. The PM alt should be putting out approx 100W at idle/235A max @ 13.6V - so the battery tester should overload it at idle.

From this, I reasoned that the AUX alt kicked in when there was a voltage drop (the increased load on the engine at idle I described above). Also, the added terminal to C1-32 is described as "Generator 2 Turn On Signal" throughout the Helm's manual...

However, Ronclyde later posted that he found full output from both alts at all times...so I'm not real certain what the answer is...

I haven't given this any more thought, especially since I've not had any problems....I can get my hands on a clamp meter that measures DC amps and I'll see what I can find out.


As to adding voltmeters, the output of both alts goes to the underhood junction block (Red jump start area) so just hooking up a voltmeter will read the voltage from the entire system and someone else will have to give you an idea how this could be done to make it work...

[ 06-12-2002: Message edited by: mdrag ]</p>

[redmax]

I checked the output on my dual alt. setup on my 2002 CC Duramax with a Fluke amp clamp. I was not running any load, just engine running at idle. I checked the output lead just behind each alternator one at a time and both showed output. Hope this helps.
redmax

[mdrag]

I took DC amp measurements of my '01 Dmax dual alts using a Fluke 337 digital clamp meter. All of
the readings were taken after the truck had been running long enough to
stabilize the battery voltage (14.4V), and temps up to normal operating
range.

At ~625 RPM idle with all accessories turned off (interior dome light off,
the under hood light was on for part of the time):

Primary alt Powermaster 200A: 23A max (range 18A to 23A) eventually
decreasing to 2A*
AUX alt OEM Delphi 100A: 14A max (range 10A to 14A) eventually
decreasing to 7A* - I double/triple checked this reading

Then I turned on everything I could find (without restarting the truck) - 4
lamp high beams with 70W low/100W high (Kennedy Diesel heavy duty HL harness), PIAA 80 Pro XT driving lights (120W ea), A/C, seat heaters on HI, rear window defroster (and outside heated
mirrors), OEM radio, scanner, power inverter, dome lights, running board
lights, bed lights - and again measured at idle:

Primary alt Powermaster 200A: 75A max (range 66A to 75A)
AUX alt OEM Delphi 100A: 43A max (range 29A to 43A)

I then shut off all the accessories and after a few minutes took one more
set of readings - this is where the 2A*/7A* numbers came from.

When I first started the truck, I obtained a max output measurement of 60.3A
for the AUX alt (right on the mark according to the Helm's manual for the
OEM 100A Delphi at idle). I did not get a measurement of the Primary alt (Powermaster 200A) at
cold start up and will do that the next time I think about it, to see how it
compares. This would be the time when the dash voltmeter is reading low
from the draw of the starter, glow plugs, and intake heater.

Ronclyde and redmax got it right - both alts are on line all the time. :D

[SoCalDieselNewbie]

Woooooohhhhoooooooo!!!!

Not only does that solve my power needs, it means that I can mount another SPA gauge as well. :D

[Kennedy]

Interesting! That's why I suggested asking Mittie. IIRC, though Mittie, wasnt there a point where you were thinking it wasnt running?

Next thing though is, Voltage will be Voltage for the most part, and pretty darn stable throughout the system so if you want to measure anything, measure amps OR measure volts at alternator(s) vs. volts at headlamps :D

[mdrag]

Kennedy,

Yes, I thought the AUX alt was not active all the time and provided power when needed...based on the limited info and descriptions of the dual set up in the Helm's manual and my crude load tesing...the DC clamp meter measurements tell the real story :D that both alts are active all the time.