Alternator Output

[ORCoaster]

The 11.5 vdc was the reading I got when I popped the hood and slapped the voltmeter across the terminals.  9.0 was what I got upon cranking the starter and it was slow but strong.

My alternator was flipping from 12.2 to 14.2 with a steady 1500 RPM showing on the Tiny Tach.

I swapped out the voltage regulator and the voltage is a steady 13.8-14.0 now even if I rev it up and down.  Before it would wander terribly.

[burn_your_money]

Have your battery load tested, a bad one will kill your alternator, and your starter too.

[ORCoaster]

B_Y_M,  I already took one 84 mth battery back after 3 mths as it was not holding a charge.  To date I have had the alternator tested for volts only.  14.2 -13.8 is current output.  Not sure of the amps but I will have a better idea of that later this weekend.  No rain in the forecast.  I have replaced the loose belt and the variable voltage regulator so far. 

I parked the car for the week at work and was traveling all week and guess what didn't have enough juice to turn the car over.  Almost but not quite.  So, I just jumped it but once I got it home I had to put it on the charger for like 6 hrs @ 2 amps to get it to come up on the meter on the charger to better than 75% but not quite to 100%.

Now that I have storage I am going to try to source out the leakage.  If I even have any.  All I am reading here is that my 0.02 amp draw is within spec.  And don't anyone suggest cleaning the terminals or the connections to the body and the starter.  They are already shiny and tight.

Very odd that the one car I have that uses the least electricity from the battery when driving is the one that is causing me the most trouble.

Oh, Murphy's law that's it.

[RunninWild]

Charge your battery on your trickle charger as full as you can get it. Then leave It disconnected overnight and record the voltage. If the voltage has dropped a significant amount with no load on the battery I'd say it's defective.

[TylerDurden]

A battery needs to be load-tested, resting voltage is a poor indicator of battery viability and capacity.

20mA draw should not kill your battery in two months much less a week.

[burn_your_money]

Check the water levels in the battery as well as low water can reduce capacity.

[ORCoaster]

Thanks for the additional tips guys.  I forgot to check the fluid levels for storage capacity.  Any time you start having high charge no charge stuff going on those Maintenance Free batteries need maintenance.  Why do they call them that?  Like a fuel free car?  Sure but it only goes 300 miles and you walk from there.

I will try the battery disconnect as well as I have a second daily driver I can use.  Any rules of thumb on the loss of voltage over night for reference? 

I do have test equipment back in hand and the wife's car is out of the driveway.  Time to go try and source out what I can. 

[TylerDurden]

I would not go by overnight reading. Too small a sample and you need to burn off the surface charge first. I'd put the ammeter in series with the battery in the car and look for parasitic losses while the car is off.

If your regulator was bad, that could have killed the first battery.

[mtrans]

Or diode,light is out after start right.

[fatmobile]

A dash-mounted voltmeter would be a great help.

[ORCoaster]

I actually have both an inline Amp and Volt gauge on the dash.  Trouble with the ampere one is it is really to coarse at O - 60 at the low end.  You know you are on the Positive side but not how much.  Am I getting 2 or 12 amps if I turn the lights on. 

Volt gauge is much better.  It was the one that tipped me off to a bad regulator in the Alternator.  It would jump around like it had a bad wire connection in the back on the terminals, but it really didn't.

So this afternoon I strolled out to the mighty VW Rabbit and measured 12.0 VDC on both meters I have and I pulled the negative side of the battery and will let it set for the better part of the week and see what happens.  It will get in the 40s at night and 60s in the day time so not much of a swing there but I should be able to find out if it is loosing it on its own and not connected to the battery at all.

[burn_your_money]

Once you do the standing test, hook the battery back up and turn the lights on. You should observe a very small drop in voltage. If it falls fast, time for a battery.

[mtrans]

Old school battery  test for 100 Ah one,
charge to full with 10 A or 14.5 V,next day discharge with 5 A load(1/20),with light 55 W, untill 10.8 V drop,URGENT STOP DISCHARGE then,measure the time.
If you discharge with 5 A for 8 hour, then you have 40 Ah battery.
That is true in my case, so change in shop next day.

[fatmobile]

12 volts on a sitting battery is bad.
 It should be around 12.7,.. unless it's really cold.

[ORCoaster]

Day one test one disconnected battery.  Still the same 12.0 volts DC I left it at yesterday.

Truck battery also measures 12.0 and have no issue with starting on it.  1 year old.  84 mth battery very similar to VW.