HELP WITH VOLTAGE DROP!

[blue95z71]

I have a 1995 GMC Sierra Z-71. I installed a pair of Hayden auxiliary electric cooling fans with dual fan/speed fan controller. I pull power from my fans directly from my battery(which is a brand new delco 800 cca battery). I performed the "big three" ground mod and upgraded the positive cables to 2 gauge as well. I installed a heavy duty headlight harness wired through relays that draw power directly from the battery also. Voltage at my battery and alternator are checking strong while running under heavy load (everything turned on) at 14.2V. however, when my fans kick on my volt meter drops about a volt and when my headlights turn on it drop by about another volt. With both my fans and headlights turned on at idle the gauge will drop below 12 volts and my a/c blower will run slower and it this is driving me crazy!!! sometimes the "check gauges" light will even come on. any help on this would be greatly appreciated!!

 

[laidbackbigun]

If you are running the stock weak alternator there is your issue.

 

[blue95z71]

forgot to mention I installed a DR244 240 amp alternator...

 

[RichLo]

was the pulley size different that the factory one?

Some of those high amp alternators will provide less amps at idle than even a stock one since they're designed to be run fast. If its possible, I would try to run a smaller pulley to get that thing spinning faster.

 

[laidbackbigun]

what size wiring is running to the junction block on the firewall? i found once i upgraded mine my dimming problems went away as well. could also be does this happen all the time or just once the truck is at running temp. i assume running temp because of the electric fan cuts in. alternators hate heat. it could be the alt is losing its capacity due to heat.

 

[blue95z71]

thank you RichLo it is running the small pulley. Nations alternator was great at helping me pick this one out.

laidbackbigun - interestingly when I first start the truck my volts appear to be just fine no matter what I turn on. as the truck warms up it gets worse. I paid a pretty penny for this alternator. its rated at 240 amp at 1300 rpm and 150 at idle. I hate to think it could be loosing that much????

 

[blue95z71]

oh and I'm running 2 gauge from he alternator to the battery and 4 gauge back to the junction box.

 

[Justin S]

i'd have that alternator load tested

 

[laidbackbigun]

i had a excessive amperage alternator on a sonoma i paid at the time 700 bucks for. 330 peak and supposedly 220 at idle. it was a beast until it got warm, once it got warm idle dropped to like 130 and peak was 215. but that was 10 years ago and technologies have gotten better. also look into a second battery as a reserve,

 

[90halfton]

What is the supposed current draw of all these things? #2 is not large enough for 240 amps if you're actually drawing close to that. Think even thhn is only good for 130 amps. And as was already mentioned, load testing may prove that 240 number to be exxagerated in the first place.