Alternator, Only getting 12.5V output |
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Alternator, Only getting 12.5V output |
hseymore1 |
Dec 23 2017, 10:45 AM
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#1
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Mid engine guy Group: Members Posts: 20 Joined: 14-November 10 From: washington state Member No.: 12,383 Region Association: Pacific Northwest |
I installed a new alternator and voltage regulator. I was told that you did not have to do anything to the new alternator to get it in charge mode, but I am only getting 12.5 volts output. Voltage regulator is good. Any suggestions of recommendations
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wndsrfr |
Dec 23 2017, 11:25 AM
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#2
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Senior Member Group: Members Posts: 1,429 Joined: 30-April 09 From: Rescue, Virginia Member No.: 10,318 Region Association: MidAtlantic Region |
I installed a new alternator and voltage regulator. I was told that you did not have to do anything to the new alternator to get it in charge mode, but I am only getting 12.5 volts output. Voltage regulator is good. Any suggestions of recommendations Check the bulb in the dash....it may be part of the circuit to excite the alternator.. |
BK911 |
Dec 23 2017, 02:59 PM
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#3
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Senior Member Group: Members Posts: 672 Joined: 19-February 04 From: Rocky Top, TN Member No.: 1,674 Region Association: None |
Could be lots of things.
You can ground the signal to the alt from the VR so alt goes to max output. If you get ~13.5Vs then vr or grounds are bad. |
BK911 |
Dec 23 2017, 03:01 PM
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#4
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Senior Member Group: Members Posts: 672 Joined: 19-February 04 From: Rocky Top, TN Member No.: 1,674 Region Association: None |
Oh, and you should polarize the alt even if you were told its ok.
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hseymore1 |
Dec 24 2017, 11:01 AM
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#5
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Mid engine guy Group: Members Posts: 20 Joined: 14-November 10 From: washington state Member No.: 12,383 Region Association: Pacific Northwest |
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ConeDodger |
Dec 24 2017, 11:05 AM
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#6
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Apex killer! Group: Members Posts: 23,588 Joined: 31-December 04 From: Tahoe Area Member No.: 3,380 Region Association: Northern California |
You could even have a slipping belt.
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Mark Henry |
Dec 24 2017, 11:12 AM
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#7
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
How are you reading the 12.5 volts.... gauge, meter?
Where is it connected? |
hseymore1 |
Dec 24 2017, 11:37 AM
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#8
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Mid engine guy Group: Members Posts: 20 Joined: 14-November 10 From: washington state Member No.: 12,383 Region Association: Pacific Northwest |
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Bartlett 914 |
Dec 24 2017, 12:49 PM
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#9
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Advanced Member Group: Members Posts: 2,216 Joined: 30-August 05 From: South Elgin IL Member No.: 4,707 Region Association: Upper MidWest |
How are you reading the 12.5 volts.... gauge, meter? Where is it connected? I have a voltmeter reading from the positive and negative to the console VDO meter You must read across the battery. Measure without the motor running then compare when the motor runs. Rev the engine a couple of times then measure. |
Spoke |
Dec 25 2017, 11:35 PM
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#10
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Jerry Group: Members Posts: 6,978 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
I installed a new alternator and voltage regulator. I was told that you did not have to do anything to the new alternator to get it in charge mode, but I am only getting 12.5 volts output. Voltage regulator is good. Any suggestions of recommendations Check the bulb in the dash....it may be part of the circuit to excite the alternator.. (IMG:style_emoticons/default/agree.gif) Assuming your alternator and VR are good, it sounds like you're not getting the alternator going. The armature (rotating part) needs current through the GEN light on the dash. Make sure the GEN light lights up when before cranking. And as mentioned before, measure voltage across the battery. The VDO gauge can have significant voltage drop WRT the battery voltage. |
Mikey914 |
Dec 26 2017, 10:12 AM
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#11
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The rubber man Group: Members Posts: 12,669 Joined: 27-December 04 From: Hillsboro, OR Member No.: 3,348 Region Association: None |
Does the Gen light come on with motor not running? You need it to make the circuit. May be as simple as replacing the bulb. Also NEVER use a LED for this.
mark |
hseymore1 |
Dec 26 2017, 10:47 AM
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#12
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Mid engine guy Group: Members Posts: 20 Joined: 14-November 10 From: washington state Member No.: 12,383 Region Association: Pacific Northwest |
Does the Gen light come on with motor not running? You need it to make the circuit. May be as simple as replacing the bulb. Also NEVER use a LED for this. mark The VDO gauge must be way out of calibration as my voltage across the battery with and without the engine running is about 13.5 - 13.8 as the gauge just reads 12V |
Mike Bellis |
Dec 26 2017, 12:24 PM
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#13
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None |
Does the Gen light come on with motor not running? You need it to make the circuit. May be as simple as replacing the bulb. Also NEVER use a LED for this. mark The VDO gauge must be way out of calibration as my voltage across the battery with and without the engine running is about 13.5 - 13.8 as the gauge just reads 12V It has to do with age & corrosion. Your wiring is 40 years old and the ground plane is just a bunch of rusty spot welds. Vehicle wiring is barely adequate for the circuit amperage. Oxygen starts to breakdown the copper at each connection point. There is enough resistance in the system to eat up 1V as voltage drop. The factory volt meter was never designed as a scientific instrument. It should be viewed as a relative measurement of voltage. Always measure at the battery. Rev the engine to 1500 rpm and ensure the voltage is slightly higher than idle. The alternator will usually not charge below 1200 rpm. |
Mark Henry |
Dec 26 2017, 12:33 PM
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#14
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
(IMG:style_emoticons/default/agree.gif)
The VDO gauge must be way out of calibration as my voltage across the battery with and without the engine running is about 13.5 - 13.8 as the gauge just reads 12V Why I asked how you were measuring it...13.5-13.8v is perfect, nothing wrong with your charging circuit. (IMG:style_emoticons/default/wink.gif) |
Elliot Cannon |
Dec 26 2017, 11:56 PM
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#15
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914 Guru Group: Retired Members Posts: 8,487 Joined: 29-December 06 From: Paso Robles Ca. (Central coast) Member No.: 7,407 Region Association: None |
(IMG:style_emoticons/default/agree.gif) The VDO gauge must be way out of calibration as my voltage across the battery with and without the engine running is about 13.5 - 13.8 as the gauge just reads 12V Why I asked how you were measuring it...13.5-13.8v is perfect, nothing wrong with your charging circuit. (IMG:style_emoticons/default/wink.gif) Shouldn't there be a bigger difference in voltage between checking it with the engine running and not running? Close to 14 volts with engine running and closer to 12 with it not running? (IMG:style_emoticons/default/confused24.gif) |
hseymore1 |
Dec 27 2017, 01:02 PM
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#16
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Mid engine guy Group: Members Posts: 20 Joined: 14-November 10 From: washington state Member No.: 12,383 Region Association: Pacific Northwest |
(IMG:style_emoticons/default/agree.gif) The VDO gauge must be way out of calibration as my voltage across the battery with and without the engine running is about 13.5 - 13.8 as the gauge just reads 12V Why I asked how you were measuring it...13.5-13.8v is perfect, nothing wrong with your charging circuit. (IMG:style_emoticons/default/wink.gif) Shouldn't there be a bigger difference in voltage between checking it with the engine running and not running? Close to 14 volts with engine running and closer to 12 with it not running? (IMG:style_emoticons/default/confused24.gif) I really appreciate all the feedback. First, all my harnesses are new, all ground are clean and good, no LED light in the volt meter, No Gen light at or above idle, Starts and runs at about 1200 RPM then settles down to 650-700 RPM (idle was higher until I took the aux air valve apart and repaired the stuck valve). So maybe I do not have a problem. I am taking it on its first shake down run after three year restoration project, as soon as I get a clear dry day. Then its just a matter of adjusting and tweaking all the little gremlins. Stay tuned! |
GeorgeRud |
Dec 27 2017, 06:17 PM
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#17
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Advanced Member Group: Members Posts: 3,725 Joined: 27-July 05 From: Chicagoland Member No.: 4,482 Region Association: Upper MidWest |
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