I am not sure what controls the output to the battery. I get 13.8 to 14.2 at the alternator. Over the day, it drops to 13.3 -13.4 at the battery and as indicated by Torque OBD. I am assuming this is the voltage regulator doing it job.

Any feedback ?

 

Mine does the same with different alternators, first with the stock alternator (Valero) and now with the P38 alternator (Bosch) I put in. I believe the lower voltage after a few hours of driving is just caused by thermal effects since the alternator heats up over time.

 

Hey Richard,

I hope the weekend 4 day run went well. I switched to this 150-amp alternator earlier in the year. I encountered similar voltage readings from my Ultraguage with the hot 90F-plus ambient temps on our run last month.

https://www.ebay.ca/itm/300369751057

 

@acg trip was gerast only one "bad" road, I had to leave monday night. Thanks to you and @Discorama I figured it might be heat related.

 

Its probably voltage reg. D2 has a parasitic drain. You can check your voltage before startup, likely significantly lower. VR will roll back voltage as battery reaches full charge.

 

The regulator can't detect the state of the battery. It sees the alternator output voltage only and then changes the current through the exciter coil to keep the generated voltage in a close range, otherwise it would fluctuate with rpm and load.

 

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Right, sorry, misspoke. Amperage is rolled back, not voltage. So to clarify after starting the battery has a lower charge, unable to resist the amperage input of the alternator so alternator output increases to charge battery. Over time as the battery becomes fully charged the amperage output of the alternator is decreased as the battery resist further charging. This change in amperage output likely shows up as small variations in voltage output. Yes the VR is trying to output a voltage, can't sense amperage, however that variation in amperage is likely causing the voltage variations you are seeing. Or maybe @Discorama can explain better.

 

@Extinct yea that was my problem trying to figure out the control system, to determine if I had an issue. Seems to be ok, as long as it stays above 13 V

It is worth going through this process if you have a problem :

To check if you have a bad connection either on the positive from the battery or the ground.

• Next follow the positive to the fuse box and verify you still have your 13.x between there and the body of the car.
• If not check between positive at fuse box and neg term on battery.
• If that's good you know the positive wire either has a sketchy connection or one of the crimped on terminals is loose or something.

I have some drops, so new battery cable ends on on my list, although I may have a set in my used wiring harness that I can rebuild.

 

So I have had sometime to do some detailed testing :

Alternator positive to alternator body 14.0 to 14.2
Alternator Positive to battery negative 13.8 (battery is pretty much charged)
Alternator to engine side of the negative battery cable 13.8
Alternator to battery cable mid point ground 13.4 or less it mirrors my voltage on Torque never below 12.9/8- this appears to be the an issue it should be 13.8
Engine Fuse box main positives to battery negative 13.4 mirroring the battery mid point ground

My assumption is there is a problem with Negative battery cable,at this point.

But as I am often mistaken any other suggestions ?