Ronmar
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Mine is pretty steady/consistent. Another thing to look for is AC component(ripple) on the DC lines.
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This is what I'm getting today. The numbers are 13/25 during initial startup with AIH on full, then when AIH kicks off, the 14 leg climbs to 16 but is hovering above and below, I guess keeping the 3s timer from counting down and OVCO'ing. It settles a little to the numbers in the video. I tried disconnecting wire E in the reg on the fly but the 14v goes back to this high level. I'm wondering if the lack of lbcd capacitors is causing the abrupt AIH shutoff to percolate a transient that affects the regulator. Seems like nonsense but who knows.Mine is pretty steady/consistent. Another thing to look for is AC component(ripple) on the DC lines.
Answer to 2nd paragraph question is yes. The meter was reading 13.5-6 and flat, high side was 25.6 but flat. The amp reading going to the 24v+ battery is all over the place with The alt energized, goes from 0-13ish and everywhere in between. Maybe I got some internal alt issues. I'm wondering if this alt shamed the other regulator. I still have that original one. I might try it to see if it's actually bad but I was never able to get it to reset. The voltage when the ovco trips is very flat also. With 4 batteries it Runs 24 slowly down to 23.7 over a few minutes that's with the AIH already off.Those should be way steadier than that. One of 2 things is probably happening. Either the alternator regulator is not able to stabilize the voltage, possibly due to bad connections, or the load itself is unstable, possibly due to bad connections ect.
if you disconnect the exc lead from the regulator(forward screw terminal), or pull relay K11, the alt should stop generating power and that voltage should drop to battery voltage. Is that voltage stable With the truck running on batteries?
Another test would be to disconnect the alt from the truck, and connect it to a pair of batteries in series(ground, 12 and 24) separate from the truck, then start and run the engine on the installed batteries and see how the alt performs/stabilizes into the standalone batteries instead of the truck circuitry/load. You will have to apply 28V to the exc terminal on the reg from the battery set that is connected to the alternator ground point…
this alt regulates in 2 ways, like a traditional alt it monitors 28V and modulates the field to maintain that voltage. It also modulates the SCRs between the primary and secondary windings like the output of a switching power supply, to create the 14v. I don’t necessarily see one being low/unstable and one being high and unstable as a problem with the truck side of the equation…
I've not done the 2.2ohm test yet. But per chart4, I'm already at bad alt, since I'm already working with a new reg, except that it's not a "known good reg". So this is not definitive. I'll do chart 2 and 3 tomorrow. I effectively did chart 1 and 4 already with no real answers. Those EMP people have cursed me!!Have you gone through the troubleshooting manual and done the tests on the alternator itself?
Your ECM has a dedicated tach driver output so using the alternator VR is not necessary.
I would just get a J1939 tach. Such as:on the tach, I didn't know the ECM had that. Didn't see it in the online wiring schematics. I see tachs in some of the A0 pictures, so wasn't sure if it was same on my A1. Is that a terminal that's in the PDP? I just bought a nice Isspro 3k tach so I'm looking for ways to drive it aside from the crude wrap around pickup they provide.
The mil manuals/schematics don’t show the engine side of the ECU wiring on the 3126/c7 trucks…Cat ECM pinout does show the tachometer feed on the OEM side, though I have yet to find it in the schematics. It does read in the J1939 feed to diagnostics.
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I keep wondering if it is in the connector under the windshield 'behind' the heater in all units, like in A0 units; and running off the ring gear in all A0, A1, and A1R units. Who has seen different factory tachometers between different flavored units?