High voltage drop

[jfever71]

Ok, I have tried to look this up myself, but I could not find anything.

I have a body dropped truck and the battery has been moved to inside the cab when I bought the truck it had a new alternator and I put in a new yellow top optima battery.

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I have the wire running off the alternator running a distribution block under the hood. The blue top wire is coming from the alternator the black wire on the left its going to the starter the blue wire on the right bottom is going to the fans and the yellow wire on the right is going to the battery in the cab.

The thing is when ever I turn on the electric fans our the ac on the voltage on the stock voltage gauge drops from 14 amps to 10 amps on the gauge. And my dakota gauge readings drop like 20 psi on the gauge.

Do I have a bad ground? I know that's too much drop in the voltage. I'm putting a Accuair in this truck in a couple of weeks and I don't want the low voltage sensor in the accuair to shut off the compressor when the fan comes on.

 

[jfever71]

Bump any ideas?

 

[jfever71]

Come on guys.

 

[borahshadow]

What awg is that blue wire from the alternator? Looks like it might be 8 awg. I'd upgrade that wire to at least a 4awg. Make sure that your grounds are solid and at least 4awg if not 1/0. Also check all those connections for corrosion.

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[1989GMCSIERRA]

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What's the rating on that alternator? You could be simply over running it. You may need to step up to a higher amp rated one or dual alternators or don't run all your accessories at the same time.

Does the voltage go back up once fans are at full output? Electric fans have a big amp draw when they start up. Once running the draw drops. What you may have is a accessory that's pulling too many amps and dropping the alternator output. You can disconnect in accessory if the distribution block. Whichever one draws the most and drops your voltage you may want to run that off a secondary battery and not straight off the alternator.
You'll burn up the alternator.

 

[jfever71]

Ok thanks for the info. Would it be better if i ran a bigger wire off the alternator strait to the battery?

 

[someotherguy]

Before buying or replacing anything, confirm with a voltmeter what's actually happening at the battery. When running, with all accessories off, you should see 14V or very close to it, give or take a few tenths of a volt, measured AT the battery. As someone else mentioned, e-fans will draw that down considerably when they start up. Once they're going if you don't recover near 14V then you should probably start looking at upgrading the wiring or even alternator, though your truck likely has a 100~105 amp piece which is good enough under most circumstances, unless you're also pushing a big stereo at the same time.

The dash gauge ground is a puny little wire attached at the metal tab where your ALDL connector is. Even with everything 100% stock it is VERY common to see the voltage gauge drop noticeably when other loads are kicked in, like the A/C fan, and it will drop in stages depending on your fan setting. You can clean up and tighten all your grounds and maybe see an improvement there, or consider upgrading that ground as well.

But first and foremost use a meter and check voltage at the battery. It's easy, free, and will tell you the truth vs. your dash gauge.

Richard

 

[jfever71]

Ok. Thanks someotherguy. Would it help run a bigger wire strait to the battery from the alternator?