stevengerard

So after a few weeks of sitting I go to start the convertible and it barely turns over the first time. Second try nothing. Battery is relatively new and started right up this spring. So I take out my charger, hook it up to the battery, set it to "engine start" and I get some sparks, then the alternator starts to spin slowly on its own, right as I was unplugging it the charger automatically shut off. So I disconnected it, tried to start the car without the charger and nothing. What just happened? I have never jumped or used a charger on a car and saw the alternator spin. Must be a bad bad ground or short somewhere I am guessing

nsnarsk65cutlass

Low voltage or bad battery.What do you mean saw the alternator spin?Maybe parasitic draw caused low voltage?Nick

MDchanic

I haven't seen an alternator do this - I seem to recall it was more of a generator trick.

Without sitting down and thinking too hard, it sounds to me like a bad diode.
You can get the diode board at the auto parts store - it's not hard to replace, and cheaper than the whole alternator.

- Eric

gs72

I have seen this before. The alternator shorts internally at the diodes and the alt. starts acting like an electric motor. It also puts a huge draw on the electrical system (which is why your battery is dead). Try charging the battery with the alt. disconnected (you might be able to save the battery). With batteries charged if you connect the alt. and the pulley jumps or there is a big spark. The alt. is shorted.

stevengerard

thanks, I'll try disconnecting the alternator and charging the battery. If it accepts the charger than clearly its an issue with the alternator. Its an original alternator so I'll have to get ti rebuilt. I think I have an older replacement sitting around somewhere I can use in the meantime.

Yep it started spiining slowly backwards - pretty odd.

Tedd Thompson

X2 quite common with a generator not so much with a alternator...Tedd

rustyroger

I've seen this with dynamo generators, never seen an alternator do that though.
Well, I can learn something everyday, thanks guys.


Roger.

Octania

learn something everyday
===
new to me also
good to know

m371961

I never heard of it on an alternator either. I knew generators did it because I saw it on some old Wisconsin engines where it was used as a starter, then when running it charged the battery. I actually added one to a pull start Wisconsin making it electric start.

rustyroger

Hondas used a starter/generator on their N360 model in the early '60s - boy, have they come a long way since - and it was used in a lot of motorbikes too.


Roger.

stevengerard

so I disconnected the alternator and the car still would not start. I then left the alternator disconnected and tried to charge the battery, the charger shut off. When I disconnected the battery leads to the car and tried to charge the battery the charger worked fine. So something is causing a short somewhere that is draining the battery and causing the charger to shut down when the battery is connected to the car. Isn't the alternator as that was disconnected.

stan 65 cutlass

my mechanical voltage reg shorted internally, burned up some wires, worth a look

stellar

It sounds like it will be a large short. Follow the pos battery cable to see if it rubbed through or burnt thru on a hot area. The starter could also be stuck in the run position with solenoid contacts in the closed position. What it sounds like happened to me is you started the car on low battery and the solenoid contacts stuck. You may try tapping the starter or solenoid with a hammer and it may release.

stevengerard

Finally got around to looking at the car this weekend. Its what you guys thought, solenoid must have been stuck because of bad battery. I finally just took out the battery of the hardtop and stuck it in there, hooked it up, heard the solenoid snap back and car started right up.

On another note
1) now I know why the line was supposed to move the washer jug to the other side. I've been switching the battery all week with the changing weather - what a pain as my jug is on driver side on the convertible (Its staying there too)
2) The dang body shop lost the shims under the battery tray - they reinstalled the try without them. Guess it doesn't matter as its hard to tell but they were in there, nuts, I'll post a wanted ad to see if anyone has them
3) I just can't get myself to spend the money on a repo battery but boy I like the look of those - $280 plus shipping for a R71s or $100 for a good group 27. UGH

oldcutlass

The repro batteries are cool to look at but not worth the money in the long term. I had one on my Fury and it was more trouble than it was worth for the look. If you want to go that look by a cover for a good battery.