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Thread: Blower motor 3/4 speed tripped/reset c/b... but c/b is 40a

  1. #21
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    Quote Originally Posted by Ron View Post
    What kind of alternator is it?
    If it is a GM style and the light comes on when the key is on then goes off once running, a very common reason for low voltage is the pulley is to big. GM basically has 2 sizes, most of which are the larger one. They have a larger drive pulley than Ds...
    (It should never get down to 12V, running.)
    Itís from DMC-CA. The computer printed invoice says 105a, the handwritten one doesnít specify. Same part number (110101) on their website currently describes it as 120a. Mine is from 2011 though, so itís quite possible the actual item changed since then. The pulley is correct. I have fine voltage when driving, just at idle (especially when super hot) does it get low.

    A062C4C5-2709-413D-B717-CD3F89F3595C.jpgD4322FD1-954D-42D0-83DA-52E98D223D36.jpg

    Having low idle voltage should be a separate issue than the blower motor tripping a 40a c/b though, no?
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  2. #22
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    Quote Originally Posted by jackb View Post
    It’s from DMC-CA. The computer printed invoice says 105a, the handwritten one doesn’t specify. Same part number (110101) on their website currently describes it as 120a. Mine is from 2011 though, so it’s quite possible the actual item changed since then. The pulley is correct. I have fine voltage when driving, just at idle (especially when super hot) does it get low.

    A062C4C5-2709-413D-B717-CD3F89F3595C.jpgD4322FD1-954D-42D0-83DA-52E98D223D36.jpg

    Having low idle voltage should be a separate issue than the blower motor tripping a 40a c/b though, no?
    All 12V cars should keep the voltage at 12+ during idle (~13.5+ is normal). That's with stock accessories on. Ds are known to fall short with the stock alternators/age/etc., but one with an alternator rated 90 amps or more should never go below 12V. A D with a 105 Amp alternator shouldn't go below 13.5 volts. So, if you are getting "just above the mark between the 8 and 13" =? 11V while the engine is running, something is wrong.

    You didn't mention the voltage above idle, so I'm assuming it is ok (~13.5 or more). IF that is the case and the alternator itself is OK, it needs to turn faster -- You said the pulley is correct. How do you know?
    FWIW, it only makes sense, with the info so far, that the pulley is too big, to me. We've seen this a lot on after market units. And you report the problem goes away when you raise the RPM a little.....

    =====

    Yes. Although low voltage can cause things to heat up and make things worse, low idle voltage should be a separate issue from the breaker tripping.
    I agree that the 40 Amp breaker might be bad considering the Amp readings you are getting. But you might need to let it run longer and see what you read after the blower motor has had ample time to get 'hot'...
    You said you were going to replace the breaker with a 25 Amp. That's too low.

    EDIT: meant to say too "big" (fixed).

  3. #23
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    Wouldn't the alternator pulley be too large if it was not charging well at low RPM?

  4. #24
    Administrator Ron's Avatar
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    Quote Originally Posted by DMC-Ron View Post
    Wouldn't the alternator pulley be too large if it was not charging well at low RPM?
    Yeah, I said "big" in post 20 with an explanation as to why. ...no idea where the brain fart came from other than thinking about the remote possibility of the drive pulley being changed and dismissing it while typing...or ??

    THANKS Ron!!! ...um, it seems I'm talking to myself now...too...goodby.

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    Out for a drive today, I paid extra close attention to exactly what the voltmeter did under what conditions.
    Start it up, 13 volts. While still idling, within a minute, it dropped to 11.
    While driving it would get up to 13, but not always- Sometimes only 12.5ish.
    And pretty consistently if the engine was at idle speed (as in not pressing the gas pedal even while driving in gear) it would drop below 13. As low as 11 when stopped/idling in neutral.

    I pulled the alternator and brought it to Oreillys to get tested. It puts out 14.5 volts and passed all tests. I cleaned the grounds/bracket (there was no corrosion or anything to cause a poor ground anyway).

    The plug harness was in less than optimal condition it had a few breaks in the coating and corrosion. I ordered a new one and will get it tomorrow afternoon. I know this wire is only supposed to illuminate the battery light on the instrument cluster, but I want to eliminate any potential issues. The battery light does illuminate when the key is on/engine off, and turns off while the engine is running (despite the low voltage (the test indicated the light would turn on at 11v; the lowest I’ve gotten w/ a multimeter on the battery post in the engine compartment while idling is 11.5v)

    As for the original issue of the blower motor, I got a new 30a c/b and put ring terminals on each wire instead of the clip style. I did not have any issues today with the clip style connectors and the old c/b before I changed them.
    5 speed, grooved hood, grey interior (Nov '81)
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  6. #26
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    Quote Originally Posted by jackb View Post
    Out for a drive today, I paid extra close attention to exactly what the voltmeter did under what conditions.
    Start it up, 13 volts. While still idling, within a minute, it dropped to 11.
    While driving it would get up to 13, but not always- Sometimes only 12.5ish.
    And pretty consistently if the engine was at idle speed (as in not pressing the gas pedal even while driving in gear) it would drop below 13. As low as 11 when stopped/idling in neutral.

    I pulled the alternator and brought it to Oreillys to get tested. It puts out 14.5 volts and passed all tests. I cleaned the grounds/bracket (there was no corrosion or anything to cause a poor ground anyway).

    The plug harness was in less than optimal condition it had a few breaks in the coating and corrosion. I ordered a new one and will get it tomorrow afternoon. I know this wire is only supposed to illuminate the battery light on the instrument cluster, but I want to eliminate any potential issues. The battery light does illuminate when the key is on/engine off, and turns off while the engine is running (despite the low voltage (the test indicated the light would turn on at 11v; the lowest I’ve gotten w/ a multimeter on the battery post in the engine compartment while idling is 11.5v)

    As for the original issue of the blower motor, I got a new 30a c/b and put ring terminals on each wire instead of the clip style. I did not have any issues today with the clip style connectors and the old c/b before I changed them.
    Just for kicks, measure your (D)rive and (A)lternator pulleys.
    Your AlternatorRPM = D/A x EngineRPM, which should be 1800-2000 at idle for proper output.

    FWIW, the Brown/Yellow wire also feeds the internal voltage regulator's excitation or field circuit. Some of the later style regulators are self exciting (w/wo revving). Either way, once it kicks in, the alternator should perform correctly until the key is turned off. So, that connection shouldn't have been causing the low output.

    (Waiting on a fuse to blow is worse than, water to boil ;-)

  7. #27
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    None of this solves the original blower motor mystery, but hopefully that was just a bad c/b. Between the new 30a c/b and replacing the connections with ring terminals, hopefully it does not resurface.

    (5.8 crank/2.8 alternator) x 800 idle rpm (approx) = 1660. Pretty close.

    Voltage off - 12.38
    Key on - 12.0
    Idling - 14.0-14.3
    Headlights on - 14.18
    Aic conditioning only - 12.5
    Headlights and a/c - 12.3

    And then it hit me. Itís the cooling fans. The cooling fans are on almost constantly on my car. In hindsight I recognized the pattern. Iíve been doing very little highway driving and lots of street driving, in the summer, in Las Vegas. The a/c is almost alway running, therefore, my cooling fans are almost always running. And the controlled measurements of voltage confirm itís my cooling fans that are pulling all this current. They are the original style fans. One was replaced in 2005 by the previous-previous owner, and the other I believe is factory original.

    Of course, I just returned the ampmeter to Home Depot last night, so Iíll go rent it again and check the current each fan pulls.
    What is the normal/acceptable current per fan?
    5 speed, grooved hood, grey interior (Nov '81)
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  8. #28
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    Quote Originally Posted by jackb View Post
    Of course, I just returned the ampmeter to Home Depot last night, so Iíll go rent it again and check the current each fan pulls.
    What is the normal/acceptable current per fan?
    The Vendors low power fans seem to run between 7 to 9 amps each. I've tested a few OEM fans that run about 14 amps each but even those are ones that have burned up the fan fail socket and jumpers. Not sure what the currents are when the car is moving at highway speeds.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #29
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    Quote Originally Posted by jackb View Post
    None of this solves the original blower motor mystery, but hopefully that was just a bad c/b. Between the new 30a c/b and replacing the connections with ring terminals, hopefully it does not resurface.

    (5.8 crank/2.8 alternator) x 800 idle rpm (approx) = 1660. Pretty close.

    Voltage off - 12.38
    Key on - 12.0
    Idling - 14.0-14.3
    Headlights on - 14.18
    Aic conditioning only - 12.5
    Headlights and a/c - 12.3

    And then it hit me. It’s the cooling fans. The cooling fans are on almost constantly on my car. In hindsight I recognized the pattern. I’ve been doing very little highway driving and lots of street driving, in the summer, in Las Vegas. The a/c is almost alway running, therefore, my cooling fans are almost always running. And the controlled measurements of voltage confirm it’s my cooling fans that are pulling all this current. They are the original style fans. One was replaced in 2005 by the previous-previous owner, and the other I believe is factory original.

    Of course, I just returned the ampmeter to Home Depot last night, so I’ll go rent it again and check the current each fan pulls.
    What is the normal/acceptable current per fan?
    Those reading would indicate that the fans were drawing too much current if these regulators simply turned the alternators on an off like some of the older systems. But internal regulators increase and decrease the field circuit, varying the output, to keep up with the demand. So if the alternator is not at minimum speed at idle, it could already be putting out ~all it can at the point before you turn on the AC. When you then turn the AC (2 cooling and 1 blower fans) on, it wouldn't be able to keep up and the voltage would fall. So the readings might be misleading...

    Something not mentioned- If the voltage is actually being brought down too low (whether it is the pulley and/or fans), the system will start using the battery instead of running off of the alternator alone and the light should come on.
    Does it?

    Whether the fans draw too much or not, 1660 is not close enough -- 1800-2000 is a minimum!

  10. #30
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    No, the battery light only comes on before I start the car. It does not come on while running despite the low voltage indication on the gauge.

    The volts I listed above I took off the jump post in the engine bay (intake manifold for ground).

    I just measured the cooling fans current: one is 8.85 and the other is 9.00. (Tested by starting up the car and forcing them on by turning on the a/c).

    The alternator tested good when I had it measured the other day.
    B04E0ABD-EC8F-411D-8098-DA69A9B8D8E5.jpg

    Does this look like an alternator anyway? Or the pulley? (The pulley was replaced by DMCH when I changed the alternator in 2011. The 2.8” I measured was at the outside of the belts groove; what size should the pulley be?).
    Or something else entirely?
    Last edited by jackb; 08-20-2019 at 06:50 PM.
    5 speed, grooved hood, grey interior (Nov '81)
    Spax Shocks, DCUK springs, Delorean.eu LCA brackets, DPNW Poly swaybar bushings, DMCMW shock tower bar, Deloreana.com convex mirrors, DPNW Toby Tabs, DPI cat-less exhaust, C4 Corvette third brake light, PJ Grady tail light boards, Bitsyncmaster relays

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