10si or 12si GM Alternator Output at idle

[Learpilot]

Do any of the 10 si or 12 si alternators put out good amps at low rpms ?
There a lot claims in ads about 10si 100 amp chrome alternator putting out 80 amps at idle. I went to a CS130 105 amp alternator because of low amps at idle. I run a aux fan on my condenser with the compressor running.
I have a friend that has 12.5 volt at idle with his aux fan running. 14.4 volt with it off.
He has a Chrome 10si alternator he picked up at a swap meet that is suppose be a 100 amp.
Thanks for you input !!!

[BFS57]

Hello;
I don't know about amps output but I do have a chrome 100 amp alt not hooked up single wire that has voltage sensing and according to my volt meter, I have 14 volts no matter what!
Also, I found out that the pulley on the alternator has a lot to do with it keeping proper operation and can be changed to get the proper amount of voltage as well as amps at idle. (I don't remember where I read this but I think it was on the Powermaster web site.

Bruce

[Learpilot]

Hello;
I don't know about amps output but I do have a chrome 100 amp alt not hooked up single wire that has voltage sensing and according to my volt meter, I have 14 volts no matter what!
Also, I found out that the pulley on the alternator has a lot to do with it keeping proper operation and can be changed to get the proper amount of voltage as well as amps at idle. (I don't remember where I read this but I think it was on the Powermaster web site.

Bruce

Thanks I will look up powermaster's web site !

[Crosley.In.AZ]

the diameter of the pulley on the crank shaft / balancer plays a role in the alternator RPM at idle too.

[wayne petty]

i agree about pulley size...

it is also easy to upgrade the internals to higher amp windings...

do you junk yards?   86 87 cadillac fleetwoods and devilles with rear wheel drive have 12si alternators... same size as the 10si.. but many more winding on the stator.. and more windings on the rotor.. these require a special voltage regulator to handle the amp draw of the rotor... these have a drilled top hole where you normally find threads.

hi amp kits are also available... that have high output stator, rectifier bridge, voltage regulator.. some with the high amp rotor...

before you go swapping things around...   do some tests with the fan off...  and the battery fully charged...    charge the battery for 20 minutes at 10 amps...    with the engine off... turn the head lights on for one minute.. then off.. test the voltage...  

100% charge is 12.65v
50% charge is 12.45 volts..
25% charge is 12.25 volts

if the battery voltage is over 12.6... test the alternator... with the engine running.. and that aux fan off... the battery voltage should be over 14.1 volts... at idle...  

if it is not...   check the belt tension... with the keys in your pocket...  put a wrench on the alternator pulley nut...  turn the alternator .. it should not  really turn without turning the crank.. if it slips.. tighten the belt just until it does not slip...   it is a fine line for belt tension adjustment... too loose and it slips...  over tighten it and you will burn out the bearings in it and the water pump...

start the motor... turn on all the electrical... a/c , fan, headlights...    take your digital volt meter...  set at 20 volts dc... put on end on the negative battery terminal... the other on the body ground... should be less than 0.2 volts...   then from the negative battery terminal to the engine block...  should be less than 0.2 volts...  and the same reading to the alternator housing... less than 0.2 volts...   both will read some.. but not much..


then move the test leads over to the positive terminal on the battery and on the back of the alternator...  see how much you get there...  there should be less than 0.5 volts on that circuit... post what you find...

- bat to body
-bat to engine block
- bat to alternator rear housing

+ bat to alternator output terminal.

this test should take less than 5 minutes to do...


i ran across this site last week... they sell a lot of high amp parts , kits and complete units.. i have not purchased from them yet... but they have a lot of info on their site.

http://www.alternatorparts.com/


here is the direct page to 10si upgrades...

http://store.alternatorparts.com/10sialternator.aspx

see the difference in the insulation on the stator leads... on the 105 amp version..

[Learpilot]

i agree about pulley size...

it is also easy to upgrade the internals to higher amp windings...

THANKS for all the info. His battery is good. He has the small pulley. We had his alternator checked at a alternator shop and it was only putting out 50 amps. I had a 100 amp stator so we swapped that in and it is A-OK now.
THANKS again !!!

[enjenjo]

Another thing to check, is where the alternator bias voltage is picked up. That would be the small red wire on a three wire setup. If it is jumped to the large redwire at the alternator, the voltage is generally less that it is if the voltage is picked up at the ignition switch.

[Crosley.In.AZ]

I've got 1 of those chrome  1 wire  alternator from Summit... I do not remember if it was 80 amp  or 100 amp rated.

it's out put is sorta weak at idle in gear with stuff operating = lites , cooling fan running, brake lites on.

I have hooked up the additional wires to the alt for testing IF that helped the low power rate at idle =  did not help mine

[wayne petty]

tony.... do you have an amp clamp that reads DC amps.??

most of the parts stores have a battery load tester on wheels that can be wheeled out to the car...

one thing to remember..  to test the alternator output... the amp clamp has to be over all the battery cables on one side of the battery...  positive or negative.. it does not matter except which way the amp clamp faces...


when load testing batterys...  the amp clamp goes on the thick wires that come out of the tester...  one wire only positive or negative... not both..

on my brothers 164 volvo... he used to have charging problems... seems the local rebuilder was selling a 35 amp alternator and diode bridge for the 65 amp application..   their alternator testing machine ... analog type... was incorrect... probably rigged that way... so the lack of output would not be noticed... he pulled out his fluke RMS $500 digital volt meter and it showed 13.1 where their charging system tester showed 14 and a half..    i solved the problem by installing a 10SI... but i think it was off a chevette...  as the unthreaded thick mounting hole was farther from center ... i drilled it oversize.. hacksawed the back so it would be the same thickness as the factory motorola... never had another problem...

[BFS57]

Hello;
When I re-wired my car, the fuse block had all the wires coming from it to the usual places (From EZ) This was the first time I have used a 3 wire alternator. Since hooking this up I do not see any drop in voltages even with everything running, at idle!
I can say that re-wiring my car was one of the best mods I did to it!, Now if I can get the darn thing to look nice, I'll have a winner!

Bruce