Last summer I rebuilt my dying stock 63 amp alternator in my '82 Z with a rebuild/upgrade from alternatorparts.com.I used the part# HO-7011 105amp upgrade kit for a 10si alternator along with all new bearings.The rebuild was very easy and the car fired right up after I was all done and installed.Question/concern is the volts were/still are low upon startup and would/will not rise above 8 volts (which the gauge may be inaccurate I know) until I revved the car up to around 1,000 rpm or so.Still does this..but once it hits 1,000rpms or so the gauge jumps to 13-14 volts.It did not seem to do this as drastically before the upgrade/rebuild.I was close to parking it for the winter so i kinda let it go/forgot about it till last week when I started to begin the spring wake up.The car charges fine..never had any problems with it or the battery..just kinds wondered if that was the correct operation or not.That is what I am questioning..is this normal?I have searched on the boards and got that it is..but then some say maybe not?Like I said I have no problems with the electrical system what so ever..no major stereo system to support..a deck and 2 6x9's...dual electric fans wired with relays from a 91 Z..and a Holley "Black" electric fuel pump.Besides the normal lights..horn,etc..that is all the system has to support which I think 105 amps is more than enough.Basically..is this normal?Any and all help is appreciated.

 

High output alternators and conversion units require the alternator output to reach a certain threshold ( output voltage) before it kicks in.
This sounds like a single wire conversion regulator symptom. The manufacturers usually recommend swapping to a smaller pulley on the alternator so it spins faster.
One draw back is that it's also requiring more horsepower to drive it.

 

Question: Once you rev it up and volts jump, does voltage stay up when you let off the gas? If yes, then that’s “normal”.

 

Nothing is normal about what you say. Typical output votage wise is 13.5-14.5 at idle with accessories off on a normally working charging system. A higher output generator will have less current at idle since the larger stator changes the charging curve. Setpoint voltage for most GM internal regulators is between 14.5-14.9 volts. Make sure you use a voltmeter across the battery when testing. Sounds like you are missing a phase, meaning part of the stator is not connected. Verify correct guage operation then proceed from there. If the guage was reading correctly before the mod chances are it's something to do with the upgrade. Possibly the diode pack or trio was damaged. rarely to the regulators fail unless they are false biased somehow and that generally only applies to the newer ASVR units in the 130D units. Even with a low battery the alt should throttle up to almost 15 volts. Always start troubleshooting with a fully charged know good battery.

 

It is not a one wire conversion..I did the conversion with all the factory wiring.Yes once revved the volts stays up..unless the car is cold and starts to idle real low/try to stall..say 500rpm or less..then they will drop back down till I feather it to get it to idle normal.

Idle voltage once they come up with the initial rev is usually around 13.5-14.5 with accessories off.Cruising down the road at normal cruise rpm..usually around 2700-3000 yields 14-15 volts even with the fans on.How would I know when testing across the battery with a voltmeter if a phase is missing?The battery is a few years old..I think it is time for a new one regardless..but that is a good point..I overlooked the obvious.I did have to charge it to get the car fired up the first time this year.

 

Hey Bad Z,
Your Sig does not say what type of V8 is in your car, but I can guess from the symptoms that it’s a Carb. Right?
Most people are so use too fuel injection, that they have no clue how to start a 4-barrel motor.
I’m sure any alternator expert will tell you that your engine has to be spinning at correct idle speed for the Alt to work. Even a 144 amp Alt needs to spinning faster then 500 RPMs before it can put out enough current to maintain good voltage.

When my car developed cold start problems about 10 years ago, a carb expert said to spray the choke/fast start mechanism with WD-40. Much to my surprise after a few days, it fixed all the starting problems! Now I spray the outside of the carb twice a year and it always starts great.

 

65 Impala with a 396, Quadrajet and a Powerglide old enough? That's how long I have been rebuilding generators so I guess that qualifies me as a bit of an expert. He does not mention idle speed with the 8 volt scenario. Even a very low idle with a load only from the engine worst case scenario is he should be a little above battery terminal voltage. By a phase missing I mean that possibly one of the wires of the 3 heavy ones on the coil that sits around the rotor may not be connected. I have done a lot of the 140 amp CS upgrades, not any of the Si series so I don't know exactly how they behave since it uses a more simple and less exacting voltage regulator IC. The only time I ever saw the Si unit's exibit that condition is with a loose drive belt, could be that simple.

 

QUOTE:
"He does not mention idle speed with the 8 volt scenario."

He doesn't?

OK,
Let me try rephrasing.
I am not concerned about my Alt having a low voltage output when the engine is first started and not yet up to normal RPMs.
I‘m not concerned because once the engine comes up to speed, the Alt starts working fine and continues to work fine till the next “slow start”. The original 144 amp Alt did this (between rebuilds) and the replacement 105 does also.


QUOTE:
" The only time I ever saw the Si unit's exibit that condition is with a loose drive belt, could be that simple."

Very true. I like to keep my belts adjusted on the loose side to extended accessory bearing life.
Might be all you need to do 82z, is tighten the belt

 

Sorry, missed that part of the other post. Yes, if it is on the verge of stalling you may see that condition. It is not common for it to go below battery threshold unless there are accessories on.

 

The only load on the charging system when the car is first started is the elecrtic fuel pump...yes it is a carbed 355.So from the sounds of it I am experencing a normal occurance upon a cold startup.I am going to replace the battery next time I go out to start her up and begin driving/using it for the spring and summer since it needs it and could also be causing this.I will also be installing new belts as I do every spring so that should cover that possibility also.Many thanks for the replys..appreciate the help.Gives me some ideas to chase around...and reassures me this is normal.