DLX_Yoda

Good morning all!!

Within the past year or so, I purchased a 1995 DLX w/ 22re (approx 380k miles). When I purchased the truck, the OE alternator died on my travel back home. I was able to get the truck charged back up enough to make it to my house on battery power. After researching, I knew I'd want aftermarket items such as better head lights and radio. I replaced the OE alt with a GM 10si single wire alt (100a). In replacing the OE alt, I ran the single wire from the new alt straight to a 200a breaker. Then from the output side of the breaker, I ran it to my 80a fusible link as well as a leg straight to the + side of the battery. I ran this setup for approximately a year with no issues until recently. About a week ago, the rubber pad on my brake pedal fell off causing my brake light to stay on while I was inside working. It didn't drain my battery completely and I was able to start the truck. However, on the ride home, the truck shut off, stranding me on the side of the road. Wife came to get me and brought meter for me to check everything and battery was not getting charge from alt (dead)

Was able to get the truck back to the house and start troubleshooting. Here's where it gets wild.. I ordered a new alt thinking that diodes or regulators bad on original. New one came in (140a) and when I start the truck, the hot lead from the back of the alt (single wire) reads roughly 20v-35v when not under load from the battery. When engaging the 200a breaker, putting the alt under load, it cuts to the expected 13.8v being sent to the battery. The battery will then charge to approximately 13v and then will flip the breaker again, which cuts the alternator charge from the battery and send it back to high voltage reading.. I sent the alt back thinking that possibly the regulator was also bad on this one and the return they sent (verified working) had the same results

Aftermarket additions are radio speakers and headlights. Issues didn't present itself when these were installed however

Open to any/all suggestions

scope103

Standard headlights (~35watts) pull about 3 amps each. Upgrading to super-hot halogens would raise that to about 6 amps each (LEDs, on the other hand, down around 2amps). Super kick-ass speakers could draw as much as 10 amps continuously (their maximum thumping power isn't continuous). Your stock 60amp alternator could have handled all that while it napped.

I don't know what is wrong with your current system. Unless you're welding 1" steel while driving down the road, I think a 140amp alternator is doing nothing for you. Your stock alternator also has the Sense circuit and the Alt light. If it were me, I'd get a stock alternator and call it done.

DLX_Yoda

I went with the higher powered alt due to it being roughly the same cost as the OE. Not to mention, I am running HID head lights (ballasts), aftermarket radio with plans to add winch and other accessories. Just figured I'd get the OE generator/alternator out of the way early on seeing as that is a common issue some run into once they start upgrading

As far as the sense circuit and alt light. The new alt has both as well. I tried wiring it with and without the sense circuit but get the same results

DLX_Yoda

Got it figured out. It was the 200a breaker that was bad. It was hanging and the alternato9r never saw the load. Replaced the breaker and charging at a smooth 14.5

Blueman

FWIW, 14.5V is a bit on the hot side. You'll always have a full battery, but you're going to wear it out faster. That being said, there's not much you can do about it. Read more about 12V battery float voltages to learn more.

Glad you got it fixed!!

DLX_Yoda

Thanks and guess I could've specified a little more. It's an AGM and it charges at 14.5. Running voltage is roughly 13.8. Which is exact specs for alt and battery combo I have.

Blueman

@DLX_Yoda does your battery call out a float-charge of 14.5V? I ask because in a truck most of the time your battery is fully-charged and it's being floated while you're driving. As you note, 13.8V is often considered the optimal target float voltage so in a perfect world you'll see 13.8V nominal while cruising down the road.

I've yet to see an alternator that runs at a high voltage during charging, and then drops to a lower voltage later after the start-energy has been replenished. Smart chargers [can] do that, but the way your truck is wired the alternator can't tell where it's output current is going: into the battery or into those headlights+soundsystem+winch+.....