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Thread: Fluctuating voltage problem

  1. #21
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Fluctuating voltage problem

    I should add that the old battery will read a pretty low voltage, but it's not consistent. It's generally 10.xx or 9.xx. All the crazy readings I was getting with my meter appear to be the result of that battery, but as you can tell, my electrical skills aren't the best.

    Why wouldn't you get an infinite reading on the battery with it in Ohm mode? I've done it many times with different meters over the years, and it's always read OL.

    ETA: Thanks for the comment. Some googling shows what your talking about and how I've apparently bought pretty decent meters over the years. I love learning things like this. It'll help to solve a lot of problems down the road.

    https://www.eevblog.com/forum/beginn...ery-terminals/

    Thanks again!

  2. #22
    Supporting Member II Turbo Mopar Contributor
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    Re: Fluctuating voltage problem

    yeah 10.xx and 9.xx definitely is not a good battery. Was this reading with the cables disconnected to rule out any load? Heck, even with a load that's not a good battery.

    Yes, as far as Ohms on a battery goes. I cannot think of a single reason to do that and in fact it could kill a meter. OL simply means "open line" You should get OL anytime you put any digital meter in ohms with the leads not connected to anything.

    Ohm readings are obtained by the meter sending a small voltage down the line and reading the loss as it returns to the other lead. That's it. By putting it on a 12V source you could in theory burn it out.

    Once you invest in a good meter never do that.

    If you're shopping for a meter I recommend spending the coin and investing in a Fluke.

    You cannot go wrong with one. Just don't spend extra for specialized ones such as "automotive" or stuff like that. They have features you're likely to never use.

    If it can read ohms, volts and current that's all you really need.

  3. #23
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Fluctuating voltage problem

    Those readings were with the battery out of the car. It'll still start the car with it in that range oddly enough, but it's a hard start. It's a very odd failure compared to every other battery I've had in a car.

  4. #24
    Supporting Member II Turbo Mopar Contributor
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    Re: Fluctuating voltage problem

    Yes that's very odd.

    The strangest one I had was my car was running fine. Been starting and behaving perfectly normal. Arrive at a destination. Shut car off. Try to start it a couple hours later. FLAT DEAD. Like ~0 volts flat dead!

    Battery had failed that hard that quickly.

  5. #25
    Garrett booster
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    Re: Fluctuating voltage problem

    try this test: run a temp ground (fat) wire from the block to the negative battery terminal
    (i had a rusty frame ground cause all sorts of over/under voltage problems )

  6. #26
    Supporting Member II Turbo Mopar Contributor iTurbo's Avatar
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    Re: Fluctuating voltage problem

    Seems like everything was covered pretty well. For whatever it's worth, I'll add my two cents.

    Car batteries: I like the Mopar branded ones. I've always had good luck with them lasting a long time. The original Mopar battery in my Caliber lasted 10 years before I finally had to replace it! I always get them for my older TMs and the dealership parts counter is good about prorating the warranty if I have an issue (once). Just make sure to stick the receipt in the glove box; plus, they look good underhood.

    As far as voltage irregularities, I had a major problem in my Omni GLH Turbo once. The voltage was spiking like crazy and it turned out that the brush leads on the Nippondenso alternator were worn out. The springs were fully extended and the shaft had deep grooves in it from the brush contact. Getting a new alternator fixed that.

    One thing I always do to determine if the battery cables are 'good' is to check with a voltmeter. With a probe on the negative terminal and the other probe on the alternator case, block, frame rails etc...I check for a voltage drop/difference. There should be very little. I would say if there is even 1 volt potential between the negative battery terminal and the block/alt case/frame rail....it indicates a problem.
    87 Shelby Lancer #127
    91 Dodge Spirit R/T
    08 Dodge Caliber SRT-4
    86 Dodge Omni GLH Turbo

  7. #27
    Supporting Member II Turbo Mopar Contributor 83scamp's Avatar
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    Re: Fluctuating voltage problem

    It's interesting to read some of the comments on this thread. As an employee of Johnson Controls, it makes me happy to see our batteries recommended. By the way, we also make Interstate, and Optima. As far as the regular batteries, there really isn't a difference across brands. They all come out of the same place. So save yourself a few bucks, and buy your batteries at Wal-Mart...

    Now, I will say Interstate's do follow a bit more rigorous testing and charging cycle. So if you for sure want a better battery, buy an interstate.

    Sent from my LG-H900 using Tapatalk
    83 Scamp GT, 2.5 TII/A-520
    89 Dodge Daytona ES turbo, Daily driver

  8. #28
    Supporting Member Turbo Mopar Contributor
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    Re: Fluctuating voltage problem

    Quote Originally Posted by firehawk618 View Post

    If you're shopping for a meter I recommend spending the coin and investing in a Fluke.

    You cannot go wrong with one..
    I have a Fluke 87 and I agree you cannot go wrong. But I only use in my electronic workshop. I use a 35 year old Metex in the garage and still works like a top

    Dave at EEVBLOG reviewed many lower cost but good meters.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    Project '87 CSX #432
    Donor car '88 Daytona Shelby Z, TII with S60 Turbo/smec, 3 bar.

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