good alternator not charging help

[ecorl]

OK, according to a google search this is a very common problem. Here is the skinny of my specific application:
Running a 90 amp alternator (one wire) activates at 1500 RPM. It is mounted in reverse on the frame rail (spins backwards) but I don't think the diodes care???? I have had the alternator rebuilt and double checked and it checks out OK. Battery is trunk mounted, alternator wire (6 gauge) runs directly to positive side of the battery. According to voltmeter on the battery, it goes up to 13 volts at 1500 RPM, then drops to 12 volts and never comes back regardless of RPM. I don't think its a grounding issue as the alternator is mounted to the frame and the battery negative is also connected to the frame rail. My only other idea is to run a ground wire directly from the alternator housing to the battery neg post. Other thoughts?
ed

[Barry Donovan]

I did the same thing..ran in circles in my head for days.
the systems are so simple,
it is either running backwards avoiding diodal function as you said, or battery negative internal is busted.
one can exceed oem amp sizes, might need alittle bigger.
I did this with an msd digital ignition, needed 200cca beyond factory. (always approach that chore as a minimalist..)

I took on a lit subaru tin can (it even attracted lightning), busting battery negative internal is as weird as any of the problems can get. All else is ground checking.

the most rare of problems is nuclear...even that goes away if you an get it running.

one more weird thing happened to me.. the positive side coming from alternator filled with lead (dead nuke), stopped the wire dead at its connection to the underhood fuse synch. That may be the weirdest of all errors possible. Could not get any stranger than that.

[ecorl]

wow, you are more affluent with behavior of electrons than I am (and I am a PhD chemist). Your recommendations very much appreciated, will consider changes. Google search shows some folks NEVER found out what was wrong but when they bought a brand new alternator it solved the problem. Something inherent to the cca? Hmmm, will perform successive resistance checks distal from battery tonight and also look for specific circuits that might be problematic? Bizarre

[squirrel]

When it's running, measure the voltage between the alternator housing, and the battery negative terminal, Should be under one volt. If it's higher, then you have a loss of ground connection somewhere.


How accurate is the volt meter?

does the car have trouble starting? (ie. is it really not working, or is the low voltage reading the only indication of trouble?)

Do you have another car you can put the voltmeter on the battery and see closer to 14 v when it's running?

[ecorl]

Not to belabor this any more than we have to but.... does the reverse rotation affect the cut-in? My alternator (1-wire mini) from jegs is supposed to have a cutin RPM of around 1100. Will the reverse rotation prevent it from turning on?

[squirrel]

it's AC, should not affect it.

[anotheridiot]

Not to belabor this any more than we have to but.... does the reverse rotation affect the cut-in? My alternator (1-wire mini) from jegs is supposed to have a cutin RPM of around 1100. Will the reverse rotation prevent it from turning on?

I agree, they call them strikers in some alternators, I would think rotation would have alot to do with if its running opposite direction

[ecorl]

Thanks Guys...well I officially give up then. I can find no shorts, circuit drains, voltage drops, or bad circuits. I ran a 4 awg from the alternator housing to the negative post on the battery and checked the voltage directly off the alternator lug with two different multimeters....nothing! This thing just aint putting out so I am just going to replace it. Anybody got a recommendation for a mini alternator than I can safely spin to 7000?

[silver_bullet]

Most standard alternators will run fine to the rpm range you speak of, at that point, it is more a question of belt retention and slippage. This is why the DZ 302 Z-28s had deep groove pulleys. You may want to have a spin test at the local parts store, and see if they can test in reverse rotation as well...

[ecorl]

Problem solved! The positive output lug on the alternator itself was loose! I had to take apart the housing and tighten it up from the inside (its a new CS133 type alternator-fully enclosed). I found it when i was looking at the volt meter and noticed that it was jumping from 12-14 volts. After I tightened it.......14 volts, 90 amps!

thanks guys
ed

[silver_bullet]

glad to hear you got it sorted out! we had a similar issue with an alternator when the stud anchor IE rectifier plate was broken in the box... (no returns on electric components)