No Alt. light after start up but battery not topping off .. Options

[Literati914]

My battery was bought last month.. Alternator light comes on with the key on, but goes out at start up. Battery keeps running low and eventually won't start the car. Does this point to anything usual - VR maybe?

[GregAmy]

Does this point to anything usual - VR maybe?

What is the voltage directly at the battery when the car is running?

post #15 in this thread is gold: http://www.914world.com/bbs2/index.php?showtopic=326479

https://www.pelicanparts.com/techarticles/9...roubleshoot.htm

https://www.pelicanparts.com/techarticles/9...roubleshoot.htm

[fixer34]

Could be several things but VR is a likely suspect. Had this same thing for quite a while, went thru several old style VRs (used). Voltage to battery was around 12, so enough to turn off the light but not adequately charge.
Finally installed Bosch electronic VR, that did the trick.

[TheCabinetmaker]

Check the belt tension

[Literati914]

Does this point to anything usual - VR maybe?

What is the voltage directly at the battery when the car is running?

I'm just getting back to this 'No charge at the Bat. and No dash light' issue.

Yesterday I charged my month old battery to like 12.77, did it with only the negative cable attached.. afterwards, I disconnected the charger and didn't go back to it until today.

Today I swapped out the VR for a spare one I have (they could both be bad - or both be good, I can't find any kind of continuity check etc for them). I then tightened up the belt which was maybe just slightly on the loose side. Then I checked the battery voltage before trying the starter... 12.33 now (sat overnight just the neg attached). Hooked up the pos. cable and started the car. It stayed right around 12.31V or so the while time.

What else can be checked before assuming it's a bad alternator?

[dtmehall]

I experienced similar symptoms about 4 years ago.

It turned out that my (original) alternator brushes had worn enough to not provide the proper charging.

Unfortunately, that meant replacing the alternator.

I hope this helps

[Spoke]

There is a quick test you can do on the alternator.

Start the engine.

Measure the voltage on all 3 wires going to the alternator with respect to chassis ground.

D- should be zero volts
DF should be 5-9V
D+ should be 13-14V

[Literati914]

just noticed that my alt bulb has blown after tightening the belt .. (IMG:style_emoticons/default/confused24.gif)

[Literati914]

update - the bulb is not blown. I can get it to light up with the ground provided by a test light.

[Literati914]

Alt light with ground provided by test light… lights the tester too.

[Literati914]

You can see the rat’s nest of wires here

[GregAmy]

update - the bulb is not blown. I can get it to light up with the ground provided by a test light.

You're aware that it's almost impossible to get the alternator to "excite" without a properly working GEN bulb? Make sure it's on with the key on. Once confirmed, start the car and recheck the voltage at the battery.

What else can be checked before assuming it's a bad alternator?

Read post #2 above..? (IMG:style_emoticons/default/confused24.gif)

[Literati914]

update - the bulb is not blown. I can get it to light up with the ground provided by a test light.

You're aware that it's almost impossible to get the alternator to "excite" without a properly working GEN bulb?..

Yes of course, I posted about the light as a new issue once the belt was tightened. The point being, that now my Alt light is not coming on with the key - when it was before.

[Literati914]

update - the bulb is not blown. I can get it to light up with the ground provided by a test light.

You're aware that it's almost impossible to get the alternator to "excite" without a properly working GEN bulb?..

Yes of course, I posted about the light as a new issue once the belt was tightened. The point being, that now my Alt light is not coming on with the key - when it was before.

Idiotic admission: removing the alt plug at the relay board in order to check the voltages of the wires there, like @Spoke suggested ^^ and forgetting you've done so, will cause the Alt light on the dash to no longer illuminate. I plugged it back in and the light on the dash works fine again. Sorry for side tracking everyone.

About those wires... with the engine running, the red wire is showing a (guessed) average of about 1.3V .. the brown and the green are both showing .002V . So, that's a bad alternator, no?

[Lockwodo]

Does this point to anything usual - VR maybe?

What is the voltage directly at the battery when the car is running?

I'm just getting back to this 'No charge at the Bat. and No dash light' issue.

Yesterday I charged my month old battery to like 12.77, did it with only the negative cable attached.. afterwards, I disconnected the charger and didn't go back to it until today.

Today I swapped out the VR for a spare one I have (they could both be bad - or both be good, I can't find any kind of continuity check etc for them). I then tightened up the belt which was maybe just slightly on the loose side. Then I checked the battery voltage before trying the starter... 12.33 now (sat overnight just the neg attached). Hooked up the pos. cable and started the car. It stayed right around 12.31V or so the while time.

What else can be checked before assuming it's a bad alternator?

If the battery voltage, measured at the terminals with battery not connected to car, really dropped from 12.77 to 12.33 overnight, then the battery discharged by 50% with no load on it and is defective. I would replace the battery before troubleshooting the charging system.

[Spoke]

removing the alt plug at the relay board in order to check the voltages of the wires there, like @Spoke suggested ^^ and forgetting you've done so, will cause the Alt light on the dash to no longer illuminate. I plugged it back in and the light on the dash works fine again. Sorry for side tracking everyone.

About those wires... with the engine running, the red wire is showing a (guessed) average of about 1.3V .. the brown and the green are both showing .002V . So, that's a bad alternator, no?

If you unplugged the alternator please plug it back in to test. The test I suggested is done with the plug connected as normal.

[Literati914]

If the battery voltage, measured at the terminals with battery not connected to car, really dropped from 12.77 to 12.33 overnight, then the battery discharged by 50% with no load on it and is defective. I would replace the battery before troubleshooting the charging system.

I did this again just to verify (bat. not hooked to any cables) :
Last evening the battery was charged via a manual charger to 13.02V .. today, less than 24hrs we're at 12.78V, no cables, bat. sitting in the rear trunk outdoors in the heat, to be specific - does this certainly indicate a bad battery?

[Literati914]

..
If you unplugged the alternator please plug it back in to test. The test I suggested is done with the plug connected as normal.

idleing:

D+/Red = 13.6v
DF/Green = 4.05 etc
D-/Brown = 0.05 etc

[Spoke]

..
If you unplugged the alternator please plug it back in to test. The test I suggested is done with the plug connected as normal.

idleing:

D+/Red = 13.6v
DF/Green = 4.05 etc
D-/Brown = 0.05 etc

Those are excellent numbers. The VR is working perfectly. The VR senses the voltage at D+ and adjusts DF to output 13.6V +/- 0.4V. I made up that tolerance but the bottom line is 13.5-14V is perfect.

I should have asked to also measure the battery voltage at the time of measurement. It runs open loop from the alternator diodes driving D+. If diodes are all good VBAT should equal D+.

What is the battery voltage at idle? Positive terminal to chassis ground.

What is the battery voltage from positive POST to the negative POST? Just want to see if the battery wires or connections are suspect. Post to Post or Pos Terminal to chassis should be identical if the wires/connectors are good.

[Literati914]

..
What is the battery voltage at idle? Positive terminal to chassis ground.

What is the battery voltage from positive POST to the negative POST? ..

Idleing:
D+ double checked still showing at 13.6v
Bat. + to Chassis ground = 12.49v
Bat. + to Neg. bat. post = 12.49v