The Stovebolt Site Forums The Shop Area The Electrical Bay *High Output Altenator*

I have a 2001 5.3 Vortec out of a Tahoe in my 49. With my Walbro inline fuel pump running, electric fan, and the AC on my gauge drops just below 13 volts. Without the AC on it charges at 14 volts. Am I ok or should I be thinking about a high output Altenator? I have a new battery and don't want to drain it down.

At idle for stoplights and such it's probably ok, what voltage are you reading once it's off idle going down the road?

Stays about the same. The only time the needle jumps up is if I turn the blower down on the AC.

You want to see 13.2 or higher to keep the battery healthy. Make sure all of your connections are good then with everything turned on get an amp reading on the positive cable. you might need more alternator.

I have a Mechman 250 amp. It tested out at 260 amps and 180 amps at 800 rpm.

If it is the alternator that was used on a Tahoe, it sure will work on your truck. Just drive it. Gauges can be off a little, loose belt, failing alternator, bad grounds, some kind of charging system wiring issue or it's just plain normal. Sometimes a "one wire" alternator can be a problem. A/C has always been a large load on motor and battery. The compressor clutch and fan motor pull the amps. Together, could be 30A.
The 2001/5.3 Tahoe has a 105A and a 130A "standard". Pretty good.

Thanks for the info guys.

Few people will need an alternator the size of mine. polished it was about $500. I will also be running 2 batteries. I think my A/C pulls 40 amps at full load, might be 50. I also have 2 radiators with electric fans and 1 with electric water pump. Also the fan on the A/C condenser, electric power steering, electric vacuum pump for the brakes. My ignition is high power and fires continuously for 60 degrees of rotation per cylinder. Plus all the normal bells and whistles. I'm also working on a scissor lift for the bed that will run off 12 volt acme screws to access things under the bed. I don't know if that will work out.

If you buy used instead of new get an alternator off of one with the rear window defogger option, it will be a high output one. I don't think I have seen a Tahoe or any SUV in the last 30 years that doesn't have the rear defogger option.

Thanks guys. I've got a backyard project going on right now but when that's over I guess I need to look up the numbers on the alternator I have and go from there.

It started pouring down rain today so my yard project came to a halt. I made a trip to Harbor Freight and picked up a multimeter just to see what my charging system is doing as my in-dash meter (Classic Instruments) was showing below 13 volts at times with the AC on. This time the meter showed about the same as the multimeter. It never dipped below 13 volts.

Pic #1 - Engine running, electric fuel pump, and electric fan
Pic #2 - Engine running, electric fuel pump, AC on with blower on high
Pic #3 - Engine running, electric fuel pump, AC on with blower on high, radio on, headlights on

Readings look good, maybe the rain was the answer.

Haha....guess I just need to drive on rainy days. I think I'll carry my meter with me and the next time I see it below 13 volts I'll check it again to see if it in deed is my gauge reading low.

Since nobody wants to hear about the right way to resolve the problem, I'll just sit here and watch. I know exactly what the problem is
Jerry

ON my 1954 I replaced the alternator twice because it was keeping the battery charged. I then found out that some alternators will not activate until the RPMs are at a certain level so with my lower gearing my RPMS in town were not high enough to for the alternator to work. So I bought a new one from Jegs that would work. I would tell you the rpm but I don't remember because I have OMS.

Thought I would recheck the charging system again today in hopes of seeing the in-dash volt meter reading below 13 volts and it did. I wanted to make sure I'm still getting good reading across the battery while the in-dash meter is showing low. I feel better now. I was afraid the wife and I would drive somewhere and get stranded with a dead battery. Whatya think of these readings on the multimeter vs the in-dash meter? I don't know if there is any way to adjust the in-dash meter as sometimes it reads correct and some times it's a little off as the pic shows.

You've got a loose, dirty, or corroded connection that only works right when it's wet. Yes, it will leave you stranded one of these days unless you find it and fix it. It could be either in the hot side, or one of the ground connections.
Jerry

Hotrod,

I appreciate your info. Not sure about "when it gets wet" since my truck never see's water but I will check the connections.

Pouring rain = high humidity, right? if you've got a marginal connection somewhere, it's possible that just a wet, muggy day will provide enough conductivity to make things work right. Check every connection- - - -which means disconnect it, wire brush it clean, and reconnect firmly. Pay particular attention to grounds- - - -the mounting of the alternator to the engine, ground straps or cables between the body and frame, and the battery cable connections on both posts. One of my students many years ago brought his mother's car into the school shop. It was a Buick Electra 225 with a 455 engine that had a slow cranking problem on a hot start. It had already had two batteries, a starter, and three alternators changed without solving the problem. We did a series voltage drop test on the starting system and found a loose, dirty connection where the battery ground cable attached to the engine block. 10 minutes with a wire brush, plus a new bolt and lock washer fixed the problem for good. That one connection was dropping nearly 2 volts during cranking, leaving less than 10 volts to run the starter.
Jerry

Good example. I still think electrical problems especially intermitent ones are the hardest to find.Thanks