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Ammeter Safety?

Discussion in 'Intermediate CJ-5/6/7/8' started by dane71, Oct 13, 2019.

  1. Oct 13, 2019
    dane71

    dane71 Member 2019 Sponsor

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    I've read a few horror stories. I'm completely stock electrically, but is there anything I should do to improve the safety of the ammeter system? Add a fuse somewhere maybe? I read that it's internally shunted which is supposedly good.

    Also the needle barely moves, same with the old one too. Not sure if thats typical.

    Sunday thoughts...
     
    Last edited: Oct 13, 2019
  2. Oct 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    The internal shunt is just a low-valued precision resistor. Current through the meter causes a voltage drop across the shunt which is measured by the meter movement. There are external shunt meters available, used for marine apps (?). They are considered safer, since the total charging current no longer has to travel to the dash and back to the battery.

    Old, crusty ammeters are a prime source of dash fires in Wagoneers and J-trucks. I presume it's not as much of a problem in the CJ, given the steel dash and more direct wiring. I converted my J20 to a voltmeter, and changed the wiring like this:

    [​IMG]

    Above is before, below is after. The 14ga wire from splice K to the solenoid is the factory fusible link. The new wiring is essentially a copy of the factory scheme for the 1976 CJ. NB '75 and newer CJs have a voltmeter, not an ammeter.
     
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  3. Oct 13, 2019
    Twin2

    Twin2 wasn't me Sponsor 2019 Sponsor

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    I would ditch the amp gauge . and replace it with a volt gauge as tim suggested
    the one and only electrical fire I had in my jeep was a amp gauge installed by PO
    lucky for me the jeep didn't burn down
    I found a piece of scrap wire on jeep . hot wired the coil and drove home
    no lights or anything
     
  4. Oct 13, 2019
    MA74CJ5

    MA74CJ5 Member

    Bolton, MA
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    Yep. The only fire (well lots of smoke - no flames) I've ever had was due to full current running to the ammeter. In all fairness though it was the PO's hatchet job wiring that caused the problem. Still full current running to dash is sketchy.
     
  5. Oct 13, 2019
    dane71

    dane71 Member 2019 Sponsor

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    It seems weird to me that it wouldnt be fused. In the car audio world you'll see people running 4 gauge wires under the carpet and door sills etc but no fires since its always fused close to the source (battery).
     
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  6. Oct 16, 2019
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

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    I'll agree with the others, switch to a volt meter. I've had many car fires but one was caused by an el cheapo ammeter...never again!
     
  7. Oct 16, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

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    Ammeters were probably safe enough when new but after decades of exposure humidity & temperature swings corrosion will set in & corrosion + electricity = heat. Deteriorating wire insulation doesn't help either.
     
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  8. Oct 20, 2019
    Hellion

    Hellion Banned

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    Okay, I am scared hearing this new new-to-me revelation. :worry:

    My old heap came with a cluster of aftermarket gauges [oil pressure, water temp] and has an ammeter too which actually says AMPERES on the gauge face [I bet half the population doesn’t even know the word]. Have not looked at it to see the condition of the wiring but I must admit I am not quite understanding the issue here.

    Can someone explain what’s happening that causes a fire or the exact circumstances?
    Maybe some more pictograms?
    Can the ‘fire hazard just waiting to happen’ be mitigated enough to retain the ammeter?
     
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  9. Oct 20, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    André-Marie Ampère - Wikipedia

    By Ohm's law, P = I V = I^2 R in watts. The more resistance R, the more power dissipated as heat by a given current. The ammeter measures current, so all the current to charge the battery must flow through it. Normally this wire path through the ammeter has very little resistance, making negligible heat. When the connections to the ammeter, or internal connections, break down, resistance goes up and so does heat. Generally wires and such increase in resistance as the temperature goes up. I'd guess this becomes a run-away... positive feedback. More heat makes more resistance which makes more heat and so forth.

    In Wagoneers, another common problem is modern alternators are too powerful for the ammeter. Back in the day, an OEM alternator made maybe 35 amps peak. Today you can walk into your parts store and buy a replacement that makes 100 amps. Nothing bad happens until the battery goes flat. Jumper the battery, start up and the alternator now sends 100 amps to charge the flat battery through a 40 year old ammeter that was intended to pass at most 35 amps. Not good ...

    If the ammeter connections are clean and the ammeter is in good shape, I suppose you could keep it. You run a gernerator? Alternator? Seems like current thinking is the voltmeter tells you as much, and it gets rid of the issue entirely. Can you understand the diagram I posted above?
     
    Last edited: Oct 20, 2019
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  10. Oct 20, 2019
    Hellion

    Hellion Banned

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    I run an alternator.

    I don't fully understand your diagram. On other diagrams I do ok, especially if they have a legend. Are all the white boxes splices?
    It doesn't really matter--when the time comes I'll probably follow a manufacturer's instructions.

    Anyone know where I can get a 2" dia chrome bezel volt gauge in the same style as this one? :D
    It's made by Equus and has that tall narrow font and orange needle I like.

    Equus Gauge.jpg
     
  11. Oct 21, 2019
    45es

    45es Member Sponsor 2019 Sponsor

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  12. Oct 22, 2019
    MA74CJ5

    MA74CJ5 Member

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    Tim's reply about too much alternator current through the gauge makes a very good point that i hadn't even considered. However, I think more commonly the issue stems from hacked wiring harnesses, wiring being incorrectly routed (too close to a hot manifold) or routing through the body without proper insulating grommets.

    What happened in my scenario was a combination of the PO hacking the wiring harness and not having the proper insulation grommet in the firewall. Consequently, the 10 gauge yellow ammeter wire rubbed against the steel body and over time through the wire insulation. Once the bare wire hits the steel body, it shorts to ground and you have as many amps as the alternator can muster tearing through a wire designed for 30 amps at most and it melts down almost instantly. And honestly after 45 years there is corrosion on the wire that generates resistance and as stated above, additional heat which only exasperates the issue.
     
  13. Oct 22, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    The short described above is worse than that. Unless you have a fuse or fusible link between the ammeter and the battery, any short in the charging circuit connects the battery via a 10 ga wire directly to ground. Does not matter if the key is on or off. The only way you can stop it is to pull the cable off the battery, or let the wire melt through. If the short is on the alternator side, the shorted current goes through the ammeter. Since the ammeter has more resistance than the wire, I would expect it not to get hot or melt but instead to burst into flames. A fully charged car battery is like a bomb under your hood - lots of stored power. The fusible links in newer car harnesses are there to protect the car from a direct short of the battery in case of a catastrophe - like a wreck or in this case the charge wire shorting directly to ground.
     
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  14. Oct 25, 2019
    shadetreetim

    shadetreetim New Member

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    I bought a USB outlet to replace my 12V outlet with, and the USB has a voltmeter built in. I'll run a relay to switch power off when ignition is off.

    I'm pulling the ammeter out and since I will already have the voltmeter in the USB outlet, I'm considering putting in an Autometer 2-1/6 Tach in place of the ammeter. Kind of small, but at least I would have one.
    2-1/16" IN-DASH TACHOMETER, 0-5,000 RPM, Z-SERIES

    I'm ordering the matching Autometer Oil Pressure gauge
     
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  15. Oct 30, 2019
    bigbendhiker

    bigbendhiker New Member 2019 Sponsor

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  16. Nov 2, 2019
    johnny_boy02

    johnny_boy02 New Member

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    I like the in dash tach, I had to mount mine to the steering column which works, but looks out of place.

    Got a link to the USB charger you are using?
     
  17. Nov 14, 2019
    shadetreetim

    shadetreetim New Member

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  18. Nov 15, 2019
    Focker

    Focker That's what I do, I know things and I fix stuff. Staff Member Sponsor 2019 Sponsor

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