Alternator only charging on high rpm

[kilo64]

This is an extremely weird issue. All this time I thought my alternator was completely dead and out of the loop.

So today I decided to check up the electrical and I'm getting a healthy 12.8 volts on the battery.

Now all this time my car has been draining the battery like no tomorrow

Now, through extensive searching the information is compiled from another post on these forums and that I followed to see if the alternator was working.

"Needs to be 13+ volts when car is on /batt/alt

To test your battery:
Set the multimeter to DC and at about 20 volts. Connect positive to positive and negative to negative. Should give you a read out of 12.

To test your alternative:
Same procedure, just your car should be running. This time the read out should be higher (14 or so) to show that your alternator is actually charging your battery."

So thats exactly what I did.
Checked the battery and got a healthy 12.8v

Turned on the car and the battery slowly dropped by 2's until it fell below 11 and finally lost all power and died.

Recharged the battery and next day and dumped it back in to test other things. Upon testing the engine I decided to give it a few good rev's (5k~) and low and behold the battery voltage jumped to 13.8 and kept going until 14.8 and stayed there.

As long as the engine was doing some work other then idling the alternator kept its charge.

Now what can this be? I already checked the plugs on the alternator and the ground as well and everything seemed good. Also checked the 75a fuse i nteh fusebox and it checked out.

Now I'm not sure if its even the alternator to begin with.

Any input greatly appreciated

[Ceepo]

had the same problem, i replaced my alternator and it fixed my problem, does the battery light on the cluster come on slightly(very fade red light) or come on all the way, and then when you rev it it goes off... i would replace the alternator and go from there, that was my problem... hope this helps, pm me back for any more questions... my car was a sohc ka 2, i had this problem in 2 sohc ka's alternator fixed it both times :)

[Firestorm]

hows the tension on your belt? maybe it's a little loose so it slips at low rpm...
if that's not the issue, i would guess your alternator is broken.

[kilo64]

Belt tension is pretty tight. It gives a little slack when I pull itt (about 3mm movement?)

The thing is that the battery light never came on. And if I continue to high rev it, it will work perfectly fine.

I'm going to polish up the grounds and see if that does a thing later today. I'll keep you guys posted.

[let5l1de]

The problem may be internal with the alt.

Alternators have spring loaded brushes that make contact with a spinning component called a rotor. Its possible that the brushes have worn down/broken and or the spring tension has greatly decreased. The brush holder could have also broke, reducing spring loaded pressure.

Another area of concern is the stator to rotor tolerances, a break in the wire or faulty diodes. A number of issues from heat expansion to typical wear on parts may cause a symptom similar to the one mentioned above.

If the electrical is still in good condition and the belt tension is correct, i would just replace the alternator and cross your fingers.

I have a alternator available if you need one. (http://zilvia.net/f/sale-items/210365-garage-cleaning-s13-eng-int-misc-cheap.html#post2276729)

diagram of generic alternator below:
http://www.secondchancegarage.com/articles/images/alternatorLARGE.gif

[emayearecee]

I had the same problem last summer when I was in Connecticut, and had to push my car in that damn East Coast humidity.

Anyways, my car did the same. It would die at idle and work fine when driving (or revving), kinda like my alternator worked when it wanted to.

Long story short, alternator changed and PROBLEM SOLVED

[5t341tH]

yes its ur alternator. replace it and ur good.
happened to me too. i had to keep it reving so i could drive home...haha

[flip3d]

It's the voltage regulator. Go get an alt from AutoZone. They have a lifetime warranty so you can just get a new one everytime you have a charging problem :)

[ChicagoS14]

Yeah sounds like the voltage regulator, when that goes out the alternator has issues charging. As posted above me grab one from autozone and if you blow it or w/e get a new one.... gotta love lifetime!

[kilo64]

Woohoo on the alternator!

Thanks for the help guys! I figure I might as well pick up a new alternator now.

Now heres the big question; Whats the parts that I will truely need to swap over if I were to put a DOHC Alternator onto the SR?

The only information I pulled up so far is for the SOHC one; and that goes to replacing the pulley with the one off the SR and redrilling the tensioner hole. Is this going to apply to the DOHC one as well or is it direct drop in?

[flip3d]

you got it.

drill out the threads in the bracket/tensioner hole and swap the pulleys.

done.