Grounding of the Alternator? [Archive] - Chevelle Tech

: Grounding of the Alternator?


66ElkyBB
Jun 6th, 07, 8:45 AM
I wasn't getting much from the one-wire Powermaster 70 amp alternator when measured with a voltmeter across the battery terminals. Upon further checking I found out that the alternator case was not grounded. Apparently, my powdercoated beautiful looking Alan Grove steel brackets insulated the case from any ground on the engine. So, I bolted a ground wire onto a threaded hole in the back of the alternator and ran it to a head stud. Have I done anything wrong here? Also, would running an alternator without a ground have a tendance to fry diodes or anyting inside the alternator?

undee70ss
Jun 6th, 07, 2:09 PM
So, I bolted a ground wire onto a threaded hole in the back of the alternator and ran it to a head stud. Have I done anything wrong here? Also, would running an alternator without a ground have a tendance to fry diodes or anyting inside the alternator?
Did it start charging?

Jim Streib
Jun 6th, 07, 2:21 PM
When I install upgraded alternators they have this threaded hole in them also. Since I am running a new power wire from the alternators output stud to the battery I also add a new (same size as the power wire) ground wire from this threaded hole to the battery negative post.
If the alternator is not grounded the circuit cannot be completed to allow it to work properly. I've seen headlights grounded to newly painted radiator supports that the electrical connection between the radiator support and the rest of the car is very poor or non existant.
Ideally the less connections in a circuit the better.
Jim

66ElkyBB
Jun 6th, 07, 5:29 PM
Yes Greg, it did show it was charging after putting in the ground wire...same gauge as the wire from the alternator to the battery. When I checked the alternator by itself with engine running, it showed 36 volts....??? The alternator got extremely hot when connected to the battery and running, and when I removed the wire from the back of the alternator (one going to the battery) and started the car and then touched the wire to the alternator while it was running, it sparked and dragged down the idle a whole bunch and the fan belt even slipped some. Unconnected, the alternator spins freely. So where did I go wrong?

undee70ss
Jun 7th, 07, 2:03 AM
When I checked the alternator by itself with engine running, it showed 36 volts....??? Are you sure? Honestly, I have never checked voltage on alternator that wasn't grounded to a engine, so I don't know if that could be possible to get that much voltage, but it could be.


The alternator got extremely hot when connected to the battery and running, and when I removed the wire from the back of the alternator (one going to the battery) and started the car and then touched the wire to the alternator while it was running, it sparked and dragged down the idle a whole bunch and the fan belt even slipped some. Unconnected, the alternator spins freely. So where did I go wrong?
You really shouldn't do that. It can cause the alternator to spike and blow the diodes. Was that battery fully charged? Alternators are not battery chargers, and if the battery was low, the alternator was probably at max output, which would make it hot. This is one disadvantage of having alternators connect directly to the battery. It would be better to connect the alternator output wire to the horn relay buss bar, as this would limit current to the battery if its ever low. I would also not bother with a extra ground wire, clean up the brackets and bolt holes so there is a good ground path to the engine. Also check the bolt that you have in the back of the alternator, it has to be fairly short, if it was to long, you could have shorted the alternator internally. some Powermaster alternators can also be wired as a 3 wire, which is a lot better than a 1 wire.

66ElkyBB
Jun 7th, 07, 9:19 AM
Yes, battery was fully charged at 12.4 volts static. Bolt I used for ground is very short and doesn't go past the depth of the boss. Maybe I fried something in alternator when I measured between the lug and ground and got such high voltage. Cannot measure amps since I don't have a meter that can handle over 10. Oh well, I went ahead and ordered a new alternator since it appears pretty obvious to me now that this one is fried somehow. Don't want to go back to multi wire system since I have used one wire, clean looking setup on many applications and never had a problem. I use a 6 gauge wire from alternator to battery directly in the smugglers box under the bed in my elky....where the external regulator and cutoff switch is also located. The ground wire from the back of the alternator to the head stud is also 6 gauge. I think I need to be more careful about testing stuff with an alternator running....or learn more about electrical stuff which, til now, has been the only area I have tried to avoid.