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Thread: Dropping voltage as accessories are added

  1. #1
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,130

    My VIN:    11596

    Dropping voltage as accessories are added

    Got a bit of a power problem that seems like it's been getting worse. On a cold start, with no accessories on, the volt meter will read a bit above 13V for a few minutes until the car warms up and it drops to about 13V. I have checked with a multimeter and it reads like 13.4V between the jump start post and ground (intake manifold).


    As I add accessories, normally only A/C and headlamps, and the engine is hot, my gauge reads very low at idle (battery light not on though) and with a meter I am seeing only about 12.3V. This has actually been going on for a while but seems worse than usual tonight.

    I have an Interstate battery (less than a year old and it hasn't been found dead yet since I installed it), new DPI alternator kit (installed a month ago), the alternator is also grounded to a valve cover bolt, my battery connections are clean and tight, my battery light in the dash (regular bulb) lights up when I put the key in position II, and I replaced the three brown wires between the alternator and starter with a 4 awg welding cable and pneumatic crimped copper terminals. The ground on the trailing arm was also very recently cleaned and reinstalled with all new hardware when I did a full suspension rebuild last fall. I've also cleaned the grounds on the front frame extension and the one that goes to the frame under the header bottle.


    I had a Hervey CS130 D120 alternator prior to this new alternator and it did pretty much the same thing.


    New Gates 7495XL belt and it feels "fairly" tight. I might be able to crank it a tiny bit tighter but I really don't think it's slipping.

    As a test, I also took the single-wire plug off the alternator and started the car just to see what would happen and the battery gauge read even lower and my binnacle (LED) lights started flickering so I know the plug isn't periodically losing connection or else I'd see that happening sometimes.


    Any great ideas? I'd love to get this finally fixed.

    Here's my gauge at night with fans roaring, A/C on, and headlights on:

    PXL_20220626_041946586.jpg
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  2. #2
    Senior Member
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    Location:  Austin MN

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    If you still have the original battery cables I would just replace them. When I did mine they had significant corrosion really dark about 6 to 8 Inches up. I did the delorean tech YouTube video ground upgrades with 2 GA cable last year and picked up about a volt and half. This year I did the power side with a buss bar that's mounted to the jump start post. I eliminated all brown power wires and at each point got it's own cable. This got another almost half a volt. My car starts and runs a lot better. Just another thing to be replaced after 40 years.



    Dave B.
    Last edited by WHO1DMC; 06-26-2022 at 02:16 AM.

  3. #3
    Senior Member Bitsyncmaster's Avatar
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    Location:  Leonardtown, MD

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    As long as your problem is consistent, you can use a voltmeter with a longer test lead to find voltage drops. First would be to confirm the alternator is producing voltage (about 14.5 volts). So measure from the jump terminal to the case of the alternator. Then keeping the jump terminal as your meter reference, move the other meter lead to other 12 volt locations to read the voltage drops over those wire connections.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #4
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    As long as your problem is consistent, you can use a voltmeter with a longer test lead to find voltage drops. First would be to confirm the alternator is producing voltage (about 14.5 volts). So measure from the jump terminal to the case of the alternator. Then keeping the jump terminal as your meter reference, move the other meter lead to other 12 volt locations to read the voltage drops over those wire connections.
    Thanks guys. I have plenty of 4 awg made in USA welding cable so I made a new cable to eliminate the three brown wires that go to the positive stud in the ignition coil/ church window harness area. I ran it along the cable I already made to replace the other three browns from the alternator to the starter. My positive cable on the battery doesn't look that great so I'll probably just go ahead and replace that one and the battery ground cable too.

    Almost done re-wiring so I'll start it up and check actual output at the alternator case next.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  5. #5
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

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    My VIN:    11596

    Checked output at idle (about 800 RPM with A/C on, lights on, doors open) and checking at the alternator itself on the positive stud (with my two new cables connected) and the alternator casing, I'm getting about 12.8 Volts. I need to wait until my wife comes home to check output while giving it some gas, but if I get inside the car and rev it up a bit, the volt gauge does go up, maybe to 13 to 13.5V.

    I'll try to take some measurement while driving with the meter connected to a window switch this afternoon.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  6. #6
    Senior Member
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    Location:  Northern NJ

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    Measure the battery voltage at the battery with the motor off. Should be a little over 12 volts. Start the car and wait 2 minutes. Should be at least a few tenths above what you measured with the motor off. Now turn on the headlights, it should still be above what you measured with the motor off. Bottom line, if the system voltage while the motor is running is above battery voltage, the alternator is working. Too much voltage is not good for the battery or the electrical system. Use a good meter. The other thing you can do is measure voltage drops across connections. The grounding system is the weakest point in the Delorean's electrical system so that should be checked also. The gauge in the dash is not all that accurate.
    David Teitelbaum

  7. #7
    Senior Member
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    Quote Originally Posted by 82DMC12 View Post
    Checked output at idle (about 800 RPM with A/C on, lights on, doors open) and checking at the alternator itself on the positive stud (with my two new cables connected) and the alternator casing, I'm getting about 12.8 Volts. I need to wait until my wife comes home to check output while giving it some gas, but if I get inside the car and rev it up a bit, the volt gauge does go up, maybe to 13 to 13.5V.

    I'll try to take some measurement while driving with the meter connected to a window switch this afternoon.
    What you describe here is acceptable. A lot of alternators are weak at idle. As long as it makes over 12.5, you’re fine. (You won’t be discharging your battery. It might take longer for it to get the battery back up after a hard start. There are alternators that work better at idle. I did a write up on installing a 3G alt in the “how to” section.

    You might consider Dave’s Idle controller. It bumps up the idle a 100 rpm when the AC is on. Might be just enough to get the charge where you want it.

  8. #8
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

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    What is your voltage with no loads at idle and above 2000 RPM? You can read that voltage from the lighter socket. Since no loads all 12 volt and ground connections should be about the same.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #9
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,130

    My VIN:    11596

    Thanks for the good tips guys. I ordered this cig lighter display so I can check my voltage while driving. Another owner pointed it out to me and confirmed it works in his DeLorean. Should have more information later this week. I'm also definitely replacing both battery cables.

    https://www.amazon.com/dp/B085LKLCYX...8Qn-oMHZq0Jp18
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  10. #10
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,130

    My VIN:    11596

    Quote Originally Posted by 82DMC12 View Post
    Checked output at idle (about 800 RPM with A/C on, lights on, doors open) and checking at the alternator itself on the positive stud (with my two new cables connected) and the alternator casing, I'm getting about 12.8 Volts. I need to wait until my wife comes home to check output while giving it some gas, but if I get inside the car and rev it up a bit, the volt gauge does go up, maybe to 13 to 13.5V.

    I'll try to take some measurement while driving with the meter connected to a window switch this afternoon.
    Hey guys, this weekend I replaced both of my battery cables (sure is fun when you remove the 13mm bolt from the trailing arm bracket and everything shifts out of place....) and I also bought, on Amazon, a cig lighter USB adapter that displays the battery voltage in real time. Very easy to check from inside the car and while driving. I'm finding that when the engine first starts up cold, I'm getting like 14.2V and dropping down to around 13.4 when hot. As I add A/C, and headlights, the voltage does drop down to like 12.5V at idle but as soon as I'm off idle and driving I'm in the 13V range. I'll keep an eye on it but I think replacing the cables helped and I have the reassurance that I'm making juice. I put the same cig adapter in my Audi Q5 and found the voltage alternates from 14.2 to 12.8 to 13.2 to 12.8 etc as I drive but I'm sure that car has far superior voltage regulation and software.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

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