ammeter reads negative @ idle
Thread Starter
Holley HP EFI w/TPI
Joined: May 2009
Posts: 553
Likes: 0
From: Kanata ON
ammeter reads negative @ idle
I'm assuming I need a larger amp alternator, but before I do, I thought I'd ask if there could be something else that is the root cause.
1974 SBC.
When headlights are on and dual electric fans are on, at idle, the ammeter dips just into the negative side.
If I rev the engine, it goes into the positive side.
Engine, dash and headlight harnesses are all new, grounds are good.
1974 SBC.
When headlights are on and dual electric fans are on, at idle, the ammeter dips just into the negative side.
If I rev the engine, it goes into the positive side.
Engine, dash and headlight harnesses are all new, grounds are good.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
With the radiator fans ON and lights ON, there will be about a 10-20 amp draw on your alternator. That is more than most alternators put out at idle speed. But, that shouldn't be a problem. The battery stores lots of 'juice' just for that purpose. As soon as you attain cruise speed, the ammeter should move to a positive reading...indicating that the alternator is recharging the battery...and then drift back to "0". As long as that appears to be the case, don't worry about it.
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
The 10SI series alternators were pretty weak at idle. Late in the C3 run they switched to the 12SI series that is much better. You can retrofit the 12SI if you want. Electrical connections are the same and your old pulley swaps over. Only issue is the case is larger and the distance between the mounting points is 1/2" wider. So some bracket surgery is needed.
