Determining Alternator output
Thread Starter
Race Director
Joined: Dec 2007
Posts: 14,345
Likes: 4
From: Hartselle AL
St. Jude Donor '09
Determining Alternator output
Ordered a 100amp alternator to replace the stock 63amp due to the addition of electric rad fan, stereo amp and halogen driving lights. Got it from an e-bay seller that a member here posted about that rebuilds the stock cases with increased output.
It finally arrived today. First thing I notice is it says 55amp on the case. No big deal as it is supposed to be a rebuild and a 55 case was used.
Install it and put it underload - e-fan, stereo and driving lights all on and the dash gauge reads between 9 - 10
The e-fan is the biggest draw but the old alternator never dropped that low, even at idle.
Can I test this with a multimeter or do I need to take it down to the local parts store? Can their test tell the actual output?
Thanks
It finally arrived today. First thing I notice is it says 55amp on the case. No big deal as it is supposed to be a rebuild and a 55 case was used.
Install it and put it underload - e-fan, stereo and driving lights all on and the dash gauge reads between 9 - 10
The e-fan is the biggest draw but the old alternator never dropped that low, even at idle.Can I test this with a multimeter or do I need to take it down to the local parts store? Can their test tell the actual output?
Thanks
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
No a specific tester is needed, and I think they can test it at a local parts store.
Something to consider, when the SI alternators are rebuilt for more output, the idle amperage will almost always drop below what it already was. Yes it's probably a 100 amp alternator, but you'll only see that kind of output at a high RPM, and at idle it's likely less powerful than your stock unit.
SI alternators were never designed for more than 100 amps output anyway, and rebuilds usually give low end output for high RPM output.
If you want a good alternator, get a CS130 or CS144. At idle the CS130 puts out 60 amps, and at a higher RPM they're 100 amp. That's a stock CS130. The CS144 have several variations but generally they are 100 amps at idle and around 200 at a higher RPM.
Mounting either is not that hard. You can fix your V-belt pulley to them, and a 12 & 6 clocked CS130 is almost a direct bolt in. The CS144 will need the upper adjustable mount to be relocated, but it's still very easy.
The wiring is simple. A cheap plug from Autozone, spliced into the stock wiring harness, and that's it.
Something to consider, when the SI alternators are rebuilt for more output, the idle amperage will almost always drop below what it already was. Yes it's probably a 100 amp alternator, but you'll only see that kind of output at a high RPM, and at idle it's likely less powerful than your stock unit.
SI alternators were never designed for more than 100 amps output anyway, and rebuilds usually give low end output for high RPM output.
If you want a good alternator, get a CS130 or CS144. At idle the CS130 puts out 60 amps, and at a higher RPM they're 100 amp. That's a stock CS130. The CS144 have several variations but generally they are 100 amps at idle and around 200 at a higher RPM.
Mounting either is not that hard. You can fix your V-belt pulley to them, and a 12 & 6 clocked CS130 is almost a direct bolt in. The CS144 will need the upper adjustable mount to be relocated, but it's still very easy.
The wiring is simple. A cheap plug from Autozone, spliced into the stock wiring harness, and that's it.
Thread Starter
Race Director
Joined: Dec 2007
Posts: 14,345
Likes: 4
From: Hartselle AL
St. Jude Donor '09
Thanks DB 
The goal was to bump up the output enough to handle these additions and avoid going higher and the resulting increased wire size that may be needed.
The goal was to bump up the output enough to handle these additions and avoid going higher and the resulting increased wire size that may be needed.
