Aeroforce voltage reading inaccurate

[Comp04svt]

So I spent a good amount of time searching around. I found a few threads mentioning people with aeroforce gauges reading inaccurate voltage. The voltage seems to read .5 volts or so lower than measured at the battery. The few threads I found didn't really have much info, or resolutions.

While idling, I'm measuring 14.3-14.5 volts at the battery, and at the fuse block with a multi meter. My aeroforce reads 13.8-14.2 volts. Seems the gauge changes quite a bit, between 13.8-14.0 and the multi meter stays pretty steady at 14.5. I understand the aeroforce is reading whatever the ecm sees, so why would the ecm see .5 or volts less than what is at the battery/block/alternator? I cant imagine there would be that much of a voltage drop. At WOT the gauge drops down to around 13.5 volts up around 5500rpm, but I haven't checked to see if the voltage at the battery also drops some. but I assume some drop up near redline is normal.

Anyone out there dig into this before?

 

[whitedevil95]

I have seent hat same thing. Its about .5 less at the gauge than the battery. I always factor that into my readings.

 

[bullitt2735]

I've been wondering the same thing. My sctx4 is about .5 -.7 off from what my battery reads.

 

[DSG2003Mach1]

Im not sure Ive ever seen a good explanation of why that happens but its something in the factory wiring

 

[c6zhombre]

Ya, I've brought this up before on the mechman and nation alt threads....people seem pleased they're seeing above 14.5 on a pid volt reading, and I'm like "isn't that over 15 volts at the battery?!?" Seems excessive, but not sure if there's any harm to the battery

And counter wise....I'm not sure seeing 12.5 pid reading WOT in big time heat is necessarily a reason to panic that your current alt has taken a dump. That's 13.0 at the battery

 

[DSG2003Mach1]

tuner told me after adding that .5 back not to worry so long as it was 13 or more

 

[Comp04svt]

Yeah, I guess its not a big deal, but just makes me wonder what else isn't accurate you know? Like coolant temp, charge temp and all that.

I don't have any schematics, but I really wonder what in the factory wiring would cause the reading to be off.

 

[cj428mach]

The Aeroforce is reading the voltage the PCM is seeing, which could be different than what is being put out at the alternator.

 

[Bdubbs]

I'll have to check mine. Because on the gauge I'm at 14.3-14.7 volts. I'm running a nation's.

 

[RI-SVT]

Mine hangs around 13.5ish or so at the gauge

 

[Bdubbs]

So I just verified mine.

Battery: 14.5-14.8 volts
Gauge: 14.4-14.8 volts

Mine seems to be dead on.

 

[Comp04svt]

So I just verified mine.

Battery: 14.5-14.8 volts
Gauge: 14.4-14.8 volts

Mine seems to be dead on.

That's weird, I wonder why that is? I guess I don't get why the pcm would see different voltage than what is actually being put out.

 

[cj428mach]

That's weird, I wonder why that is? I guess I don't get why the pcm would see different voltage than what is actually being put out.

I believe some of it is the voltage lost through the system. Back in the Fbody days you'd lose a lot of system voltage going through the ignition switch.

Here's something I found on a vette forum.

"The PCM determines what the output of the alternator should be. So, if the PCM is happy at 13.1 volt output of the alternator, thats what you get. When you step on the brakes, turn on the HVAC FAN to HIGH ect..... and put a load on the charging system, the PCM has to see the drop in voltage and tell the alternator to increase output. This happens in fractions of a second but the delay is enough to cause a flicker in the lights and a movement on the gages.

If your seeing abnormal readings on the DIC or dash gage (what you perceive to be a LOW reading on the dash gages) put a voltmeter on the field terminal on the alternator and at the battery terminals and see what the ACTUAL readings are. You will be surprised in finding the actual battery voltages/alternator output is usually .5 to almost a full volt higher in some cases. So,,,,,,your 13.1 (which every one dreads seeing) is really 13.5 - 14.5.

"

So as you can see they have the exact same issue when reading system voltage from the PCM.

 

[Comp04svt]

Makes perfect sense. Thanks for the explanation!

I just found it weird the some people seem to have the .5 volt difference, and others, like bdubbs, don't. I remember while researching, I found threads of people with Nations or PA alternators needed to use a switched 12v for the generator, instead of the factory wire to resolve flickering battery lights. As in they would tap into the factory signal wire (I believe), one would go to the pcm, and the other to a switched 12v at the dash fuse block. What would really be interesting to know is if those with Nations or PA alternators, who have done the wiring change, would read actual output voltage, and the people without, would read .5v lower.