voltage at idle with and without accessories

[gmbellew]

1990 v1500 suburban, 350 TBI with stock 105amp alternator.

idle with nothing on - 13-13.2v at battery.

idle with ac, blower on high, rear air on high, lights on, aux fan on, radio on, fog lights on, basically everything that turns on is on - 11.8-12v at battery.

engine at operating temp in both scenarios.

is that within normal range, or is the 30yr old alternator on its way out the door?

 

[Matt69olds]

If that’s the voltage measured at the battery, with a meter, I’d say the alternator is weak, or your losing current in poor connections. Make sure the battery cables are clean and tight.

 

[gmbellew]

the truck has 2 batteries, wired together. that is the voltage metered at either one. it is dark outside and I didn't feel like getting tools out. but I couldn't tighten any of the battery cables with my man-finger wrenches.

 

[nabeshin]

Voltage should be over 14 volts with a healthy alternator and no electrical load, and over 13 volts with electrical load.

 

[gmbellew]

i couldn't resist getting some tools and checking the connections at the batteries in the dark. sure enough, one of the negative terminal bolts was basically stripped. i'll be off to the parts store in the morning to get a new bolt, and hope that brings up my voltage!

 

[gmbellew]

With a new terminal bolt snuggled in there, the battery voltage metered at 13.8v with no load and 12.9v with full load. So I picked up a volt under full load and am probably at the minimally acceptable range for voltage. I will keep an eye on things and check for other bad connections. But that may be all the 30yr old alternator can do....

 

[AuroraGirl]

With a new terminal bolt snuggled in there, the battery voltage metered at 13.8v with no load and 12.9v with full load. So I picked up a volt under full load and am probably at the minimally acceptable range for voltage. I will keep an eye on things and check for other bad connections. But that may be all the 30yr old alternator can do....

impressive if it IS the original

 

[Matt69olds]

The system voltage under load will probably improve once that weak battery fully charges. I bet a lot of the current that should have been charging the battery was lost as heat due to the poor connection.

 

[SirRobyn0]

The system voltage under load will probably improve once that weak battery fully charges. I bet a lot of the current that should have been charging the battery was lost as heat due to the poor connection.

I agree, but keep in mind no matter how you cut it no alternator will put out as much at idle, so there will be some fall off at idle underload even under ideal conditions.

 

[MikeB]

Your new voltages are just fine. 14.2 with no load is ideal, but it's not always gonna happen with older connectors. It also depends on the voltage at the point where the alternator "sense" wire is connected. Voltage at that point is what the regulator uses to control alternator output voltage. On my 82, it's a distribution block on the firewall.

More important is the voltage at the truck's "loads", such as headlights and distributor. That's where the rubber meets the road.