11.2 volts,alternator tested ok

[courtal]

Something is draining my battery. The reading on my 85 is fluctuating between 11.6 and 10.9 volts. I put a new battery on and still the same readings. I had the alternator checked on the car and it tested bad. I removed it and had it tested at two different places and it tested good. Should i go and buy a new alternator? Any advice would be great. I'm new to vettes, but would'nt trade mine for anything.

 

[nyernga]

Put the alternator back in. Find a very dark spot to park so you can turn the car off and see if there are any lights staying on. This is the first most basic step to find a drain issue. Could be anything from the floor lights to the spare tire light. If no lights are on then it becomes a bit more involved in finding the drain.
Part of being a vette owner is becoming a gremlin finder expert...

Len

 

[I_R_DA_ONE]

You bring up several questions.......how old is the alternator...brushes could be worn out.... the voltage regulator in the alternator may be whats giving you trouble...or a weak diode inside

I got a trinkle charger from AutoZone for about $20.00 and mounted it above the battery....so when I'm done driving I can just plug it in....My VATS system will run the battery dead in about a week.....
I hope this will help
Mike

 

[courtal]

Thanks for the help. No lights are on that i can see. Also i failed to mention that my windows roll up and down very slow, almost like they are running directly off a weak battery. I just put in a new battery. I'll keep pushing forward. Thanks, again.

 

[jsinga]

You need a meter. The dash reading can be off substantially. A new hot battery usually reads over 13vdc Most good alternators will charge to about 14vdc. If you have less than 13vdc at 1500rpm, HOUSTON WE HAVE A PROBLEM! When you are convinced the battery is good and alternator is charging find current drain with an amp meter. Put an amp meter is series with a battery cable measure the current drain. Start pulling fuses until you find the circuit causing the problem.
My vette sat for 6 months while I was in Korea and it started right up when I got in it. Nobody touched it while I was gone.
If you get to the point where you aren't sure what normal current drain is, ask, I can check it for you. I think I remember it's normally less than .1amps for sure.

JS

 

[courtal]

I pulled each fuse and noticed no difference in the voltage reading. I'm going to try a new alternator, because i'm not 100% sure it's good. The battery is new. I'll post my results tomorrow( can't get an alternator today, it's Easter. Happy Easter, everyone and thanks. Tim

 

[WhalePirot]

dash indications MAY be inaccurate

Get yourself a digital Volt-ohm-meter (DVOM). They're not expensive; certainly less than a battery or an alternator

Check the voltage at your battery terminals with the car off: should be 12 +/-1 vdc.

Check again with the car running: should be 12.5-14.3 vdc. The voltage will be higher right after starting due to recharging after the starting drain. The higher voltage indicates a higher electical potential, indicating current flowing from high to low.

You can also turn on lights and fans to check if the alternator will adjust output to accommodate the added electrical demand. It may not fully 'cover' the load, at idle. An auto electric technician will run a VAT test.

A ground or positive connection might not be good. After wire brushing and cleaning the battery terminals [both sides] (I use a light coat of Vaseline, after, to keep them cleaner) look for other large wires and ensure those connections don't have dirt and/or rust inhibiting a good electrical contact.

The windows may move slowly due to wear/dirt on the mechanical parts or weak motors. That alone, is not a good battery test. mike

 

[I_R_DA_ONE]

Start the motor.....then disconect the ground cable on the battery while the motor is running.... the motor should continue to run.....then start turning everything on....lights ,,radio,, a/c ...rear flashers....if the motor continues to run the altinator is good .....but if the motor dies at any time replace the altinator

 

[WhalePirot]

I-R-da-ONE: RU certain that this won't damage any electronic components?

 

[courtal]

I forgot to mention the windows never moved slowly until the cooling fan relay went bad about a week ago. I replaced the relay, so the fan works now, but this is when my charging problems began. Thanks again for everyones help.

 

[courtal]

Found the problem!!! It was the positive stud on the back of the alternator. It was shorting out. Got that fixed and now i'm in the driver's seat, again. Thanks for everyone's help.