Alternator Output

I bought a 270 amp HO alternator, and had it installed in my 07 DC a few months ago. Does anyone know if there is something like a stress test I can place on it that will determine the output is on par with it s supposed specs? I know there are analysers that can test charging systems, but not sure about showing potential amp output.

 

Absolutely, yes. A carbon pile load tester on the battery terminals to load the voltage to 12.0V with an amp clamp on the alternator charge cable will give you the numbers you’re after. This is the old-school way to test an alternator, before the current electronic “dummy proof” testers came along.

I’ll warn you though, you won’t have 270A at idle. I suspect your HO alternator came with a graph of it’s output at varying speeds though?

 

Yes. I ve studied the chart, and the specs, although the idle output is confusing. I m no expert, but I m thinking they are wrong numbers, because lower down in the chart it shows 179 amps at 2000 rpm. That s why I want to test the thing, and see just what it s doing. I do see that it "turns on" at 1230 rpm. Not sure what that really means. Maybe it starts charging battery at that rpm, and provide a set amount of amps below that rpm. Not really sure.

 

Pretty clear that 270 amp HO rating is happening around 7K rpm.

If that performance curve is accurate, it isn't "turning on" at 1230 rpm, but is generating a smooth curve of amp output from just under 1100 rpm (slightly fast idle) through 8K rpm. The curve is showing maybe 10 amp output at 1100 rpm (specified idle is 650-750 rpm). To compare the output to OEM alternators, you would need to know what rpm the OEM alternator was rated, or to have a similar performance curve for the OEM alternator.

 

Those specs are for alternator RPM, not engine RPM. I don’t know the pulley diameters off the top of my head, but I’d say the belt drive ratio is somewhere in the range of 2.5:1 to 3:1.

 

This man speaks the truth.

 

I tend to agree with your assessment. Although there s the 198 amp at-idle spec which sort of throws everything off. This is why I need to get this thing tested.

I did read about some HO alts, (Mechman), which use smaller than stock pullies to increase at-idle amps. This in turn causes problems with the ecu in some cases. I emailed DC Engineering, and specifically asked them if the pully was stock size, and they said yes it was.

 

No, that's actually about right. I thought the curve was versus engine speed, forgetting about the small alternator pulley. Using @landphil number of 3:1, just over 750 rpm engine idle speed would be about 2250 alternator rpm on the curve, which shows exactly 200 amp output. The specification table output matches the curve. The alternator is reaching it's rated 270 amp specification at about 2650 engine rpm.