Author Topic: The Ammeter's Major Design Flaw and Attempted Solutions  (Read 35216 times)

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Offline 4x4 440

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Re: The Ammeter's Major Design Flaw and Attempted Solutions
« Reply #100 on: March 29, 2012, 09:55:54 am »
Or you can make your own, 440.  A short length of 10-gauge, a pair of crimp-on terminals, some heat shrink tubing, and you're all set...   ;D

Correct. I made mine from a copy of the factory one because I had a roll of copper flat stock sitting at the house.
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #101 on: March 29, 2012, 10:15:18 am »
    "Shunt" is the general technical term used to describe any type of bypass for an electrical circuit, Kendall...

    http://en.wikipedia.org/wiki/Shunt_(electrical)

    In this case, the shunt wire shown merely halves the total current that passes through the ammeter at any given time thereby helping to protect it.  A resistive shunt of known value would be required to measure a voltage drop in order to determine an exact amount of current through Ohm's Law.  Our truck ammeters are only really designed to indicate the direction of current flow, hence the "D" and "C" labeling, so a resistive shunt is not required for such an application.   ;D
    Remember, electricity is going to take the path of least resistance, if your shunt has less resistance then the ammeter itself, the ammeter will not read anything.

    The gauges for the trucks with the 114 ammeters, are different then the gauges for the normal alternators, they are designed to work with the shunt provided, any change in the resistance of the shunt will change the reading of the ammeter.


    From your own link.

    Quote
    Use in current measuring


    An ammeter shunt allows the measurement of current values too large to be directly measured by a particular ammeter. In this case the shunt, a manganin resistor of accurately known resistance, is placed in series with the load so that all of the current to be measured will flow through it. The voltage drop across the shunt is proportional to the current flowing through it and since its resistance is known, a millivoltmeter connected across the shunt can be scaled to directly display the current value.

    In order not to disrupt the circuit, the resistance of the shunt is normally very small. Shunts are rated by maximum current and voltage drop at that current, for example, a 500 A, 75 mV shunt would have a resistance of 0.15 milliohms, a maximum allowable current of 500 amps and at that current the voltage drop would be 75 millivolts. By convention, most shunts are designed to drop 50 mV, 75 mV or 100 mV when operating at their full rated current and most ammeters consist of a shunt and a voltmeter with full-scale deflections of 50, 75, or 100 mV. All shunts have a derating factor for continuous use, 66% being the most common. Continuous use is a run time of 2+ minutes, at which point the derating factor must be applied. There are thermal limits where a shunt will no longer operate correctly. At 80 C thermal drift begins to occur, at 120 C thermal drift is a significant problem where error, depending on the design of the shunt, can be several percent and at 140 C the manganin alloy becomes permanently damaged due to annealing resulting in the resistance value drifting up or down.

    If the current being measured is also at a high voltage potential this voltage will be present in the connecting leads to and in the reading instrument itself. Sometimes, the shunt is inserted in the return leg (grounded side) to avoid this problem. Some alternatives to shunts can provide isolation from the high voltage by not directly connecting the meter to the high voltage circuit. Examples of devices that can provide this isolation are Hall effect current sensors and current transformers (see clamp meters). Current Shunts are considered more accurate and cheaper than Hall effect devices. Common Accuracy is 0.1%, 0.25% in North America and 0.5% in the rest of the World.

    The Thomas Type Double Manganin Walled Shunt and MI Type (improved Thomas Type Design) were used until the 1990s by NIST and other Government labs as the legal reference of an ohm until the advent of the Quantum Hall Effect. Thomas Type shunts are still used by Government and private labs to take very accurate current measurements, as using Quantum Hall Effect is a time consuming process. The accuracy of these types of shunts is measured in the ppm and sub-ppm scale of drift per year of set resistance.
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #102 on: March 29, 2012, 10:28:23 am »
    Here is a nice little interactive, that will show how different resistance values will affect the reading.

    http://www.phy.hk/wiki/englishhtm/Meter.htm
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    Offline 4x4 440

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #103 on: March 29, 2012, 05:52:37 pm »
    Quote
    The gauges for the trucks with the 114 ammeters, are different then the gauges for the normal alternators, they are designed to work with the shunt provided, any change in the resistance of the shunt will change the reading of the ammeter.

    No the guages are the same part number in my 1978-1980 Parts Manual. The 114 amp alternator trucks got the shunt installed on the back of the circuit board.
    1978 Ramcharger 440/727 with NP 203/205 doubler w/twinstick, Dana 60F and Dana 70 rear w/3.54:1 gears and an 8" lift. Puttin' out 450 HP at the crank, a little to mild.

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #104 on: March 29, 2012, 06:08:34 pm »
    No the guages are the same part number in my 1978-1980 Parts Manual. The 114 amp alternator trucks got the shunt installed on the back of the circuit board.
    Interesting, I remember my 76 having different markings on the ammeter, maybe it was just a difference between years.
    77 W200, 360/727/NP203/D44HD/D60 (Wifes Toy)
    77 M887- 318/727/NP203 D44HD/D60
    78/86 Ramcharger.  360/727/NP203 D44/9&1/4
    85/89/90 D150/W250 5.9TBI/435/241 D44HD/D60HD
    85 W350 360/727/241 D44HD/D60
    97 B3500 5.9MPFI/518 D60HD
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    projects:
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #105 on: March 30, 2012, 01:10:09 pm »
    Remember, electricity is going to take the path of least resistance, if your shunt has less resistance then the ammeter itself, the ammeter will not read anything.

    Current flow can be divided and is inversely proportional to the resistance, George.  It's not an all or nothing deal like in a mechanical system such as an open differential.  LOL   ;)

    Our truck ammeters use a straight conductor, anyway.  A zero-ohm shunt will only decrease its sensitivity.   ;D
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #106 on: March 30, 2012, 01:44:31 pm »
    Current flow can be divided and is inversely proportional to the resistance, George.  It's not an all or nothing deal like in a mechanical system such as an open differential.  LOL   ;)

    Our truck ammeters use a straight conductor, anyway.  A zero-ohm shunt will only decrease its sensitivity.   ;D
    I never stated it was all, or nothing. The ammeter works by measuring the voltage drop across its terminals. A random selection of a shunt will make it useless. But sense you think the ammeter is only designed to tell you the direction of the current flow, a zero ohm shunt will work just fine, just do not keep looking for the needle to move, you might miss the red light.


     
    77 W200, 360/727/NP203/D44HD/D60 (Wifes Toy)
    77 M887- 318/727/NP203 D44HD/D60
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #107 on: March 31, 2012, 05:43:11 am »
    I never stated it was all, or nothing. The ammeter works by measuring the voltage drop across its terminals. A random selection of a shunt will make it useless. But sense you think the ammeter is only designed to tell you the direction of the current flow, a zero ohm shunt will work just fine, just do not keep looking for the needle to move, you might miss the red light.

    Technically speaking, our truck's ammeters are moving magnet zero-center types, George.  The bar magnet, attached to the indicator needle, is layered on the needle's pivot.  When current passes through the ammeter's zero-ohm straight conductor, the conductor generates a magnetic field which deflects the moving magnet and the needle providing an indication of the direction of current flow, either to or from the battery.  No coil is necessary as the straight conductor generates enough of a magnetic field to be usable by the moving magnet.  Placing a zero-ohm shunt wire in parallel with the ammeter's zero-ohm straight conductor will only divide the current flow, lessen the strength of the magnetic field generated by the straight conductor, and lessen the extent of deflection of the moving magnet thereby having the effect of decreasing the ammeter's overall sensitivity.

    Here's a bad pic of the assembly on the ammeter I broke where you can plainly see the straight conductor, the indicator needle, an insulator, and the bar magnet normally sandwiched on the pivot underneath the needle...   ;D
    « Last Edit: May 11, 2019, 06:30:14 pm by PowerWagonPete »
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #108 on: March 31, 2012, 07:52:59 pm »
    Thats good Pete, you just go ahead and keep thinking that way, When you get it all finished let me know.  Then you can enjoy your show only gauge.   ;)
    77 W200, 360/727/NP203/D44HD/D60 (Wifes Toy)
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    Offline Captain Obvious

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #109 on: March 31, 2012, 08:06:59 pm »
    They are pretty much "show only" even w/o bypassing them with random wires.

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #110 on: March 31, 2012, 10:08:00 pm »
    They are pretty much "show only" even w/o bypassing them with random wires.
    ;)  Don't tell Pete.   {dont}
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    Offline 712edf

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #111 on: March 31, 2012, 11:08:00 pm »
    I find a properly working ammeter very handy. I can tell immediately if alt isnt charging.... or if my brakes lights are on the fritz, just by watching that little needle.

    Bucky
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #112 on: March 31, 2012, 11:27:19 pm »
    My volt gauge does a pretty fine job of telling me if I am charging...and how much. Works great to tell me all that w/o the unneeded voltage drops and heat production.

    All this talk of "zero ohm [SUPER] conductors", don't know where anyone else is driving, but I don't drive or live in vacuums or liquid nitrogen baths. My wires all have resistance.

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #113 on: April 1, 2012, 07:28:27 am »
    ;)  Don't tell Pete.   {dont}

    Have you ever been to Niagra Falls, George?   {think}
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #114 on: April 1, 2012, 07:44:16 am »
    All this talk of "zero ohm [SUPER] conductors", don't know where anyone else is driving, but I don't drive or live in vacuums or liquid nitrogen baths. My wires all have resistance.


    Obviously negligible for our purposes here, Skipper...   ;)

    http://www.cirris.com/testing/resistance/wire.html   ;D
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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #115 on: April 1, 2012, 09:26:25 am »
    Have you ever been to Niagra Falls, George?   {think}
    Real close, but it was just a drive by, so it really does not count. What about you, Ever make it to the Intrepid museum?
    77 W200, 360/727/NP203/D44HD/D60 (Wifes Toy)
    77 M887- 318/727/NP203 D44HD/D60
    78/86 Ramcharger.  360/727/NP203 D44/9&1/4
    85/89/90 D150/W250 5.9TBI/435/241 D44HD/D60HD
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    projects:
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    Offline Nanuk

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #116 on: June 24, 2017, 09:02:40 am »
    Well, my 72 W200 is a go truck, not a show truck. I gutted the factory wiring after my fuse block melted. New fuse block, removed the bulkhead connector, soldered/heatshrunk all wires. updated wiring with relays, mega fuses, corrected factory BS for the charging system.

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #117 on: October 7, 2018, 07:45:57 am »
    Magic stuff right here...

    https://caig.com/deoxit-d-series/   {cool}
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    Offline deathrowdave

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #118 on: October 7, 2018, 09:02:54 pm »
    Not an issue soldering steel and copper or brass together . If you tend to still say no way . Just look at your OEM radiator tank and bracket . Seems as they have been doing this for many years .
    Have a great and safe day ,Dave

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #119 on: October 7, 2018, 10:32:19 pm »
    Not an issue soldering steel and copper or brass together . If you tend to still say no way . Just look at your OEM radiator tank and bracket . Seems as they have been doing this for many years .

    LOL Dave!!!  I probably should have said "shouldn't" instead of "can't".  What happens to those radiator tank to bracket connections once rust forms beneath the solder in even a mildly corrosive environment?  Planned obsolescence, perhaps?   ;D
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    Offline dodge82273

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    Re: The Ammeter's Major Design Flaw and Attempted Solutions
    « Reply #120 on: October 8, 2018, 02:45:46 am »
     I realize , recognize , this is a tech discussion as much as anything else .
     I walked under the falls , before the collapse ... trusted the detroits on the boat ride a couple times too . over 50 years ago now ...

     amp gauges told informed people if you were winning or loosing the keep the battery charged war when we had generators , and by how much either way , from which one could "judge" ( guess?) how long before the auto quit running .   Alternators came on around late 50's early 60's ( dodge was one of the first!) and with them the ability to charge at idle  . the need for the amp gauge sorta went away ... a idiot light and or voltmeter replaced it . working with equipment and such , I see the use of an amp gauge reading everything except the starter draw .

     so the best way to use an amp gauge is to correct the deficiency of the wiring system in the old dodge  ,install a completely pass thru gauge ,  then maintain the systems .  Now doing THAT  , AND maintaining a "stock" appearance may be a tad difficult ...   
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