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Technical Sun Amp gauge question

Discussion in 'Traditional Hot Rods' started by Eric Satterfield, Apr 11, 2021.

  1. Eric Satterfield
    Joined: Aug 2, 2018
    Posts: 286

    Eric Satterfield
    Member

    I’ve read the other threads on amp gauges and I’m still stupid on this. I bought a vintage set of Sun Blue line gauges as I’ve wanted a set of these gauges since the 1970s, I plan to install in a 56 Chevy gasser I’m building. I have the original shunt and all wiring for the amp meter new in the original packaging . My question Is the shunt itself matched to the gauge or to the device that’s providing the charge? What I’m asking is.? If one has a 100 amp alternator and a 50 amp gauge. Does it require a 50 or 100 amp shunt? Also the instructions show the large hole on the shunt connected to the starter post. Will my single wire alternator attach to the smaller provided hole in the opposite end of the shunt? I know this has been gone over before and would have loved to have had a volt meter in its place. But this is what I have and would like to see it function. Thanks in advance.
     
  2. BJR
    Joined: Mar 11, 2005
    Posts: 9,817

    BJR
    Member

    Your gauge should match the maximum output of your alternator.
     
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    The shunt is matched to the gauge.

    Since the alternator is on the load side of the ammeter, the ammeter won't see the full output of the alternator. You can wire it according to the instructions, and it should be fine.

    If you want us to double check the wiring before you connect the battery, take a lot of pictures, as well as a picture of the instructions.
     
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  4. Eric Satterfield
    Joined: Aug 2, 2018
    Posts: 286

    Eric Satterfield
    Member

    The shunt itself has the leads going to the gauge. I’m not ready to install as I still have the body off. I just didn’t understand the ratings. Thank You for the information.
     

  5. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    can you post a picture of the instructions?
     
  6. Eric Satterfield
    Joined: Aug 2, 2018
    Posts: 286

    Eric Satterfield
    Member

    Instructions and shunt.
     

    Attached Files:

  7. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    I would wire it up like shown in drawing B. Should work ok, just beware that it's easy to short that thing to ground and fry stuff...you want to insulate it well with tape or heat shrink or something.
     
  8. Eric Satterfield
    Joined: Aug 2, 2018
    Posts: 286

    Eric Satterfield
    Member

    I will for sure. Thank you again for the assistance
     
  9. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 513

    Fabulous50's
    Member
    from Maine

    Diagram B assumes all your load points go to the starter post. If you just have one cable going to the positive battery terminal then B will work.
     
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  10. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
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  11. deathrowdave
    Joined: May 27, 2014
    Posts: 3,519

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Man , please be sure you really want that . It can cause major electrical problems . OEM stopped them for a reason . Do it correctly and your good to go , short it and your not so good to go .
     
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  12. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 6,250

    Ebbsspeed
    ALLIANCE MEMBER

    The thing that many folks are afraid of are the ammeters with the internal shunt, as that requires the entire electrical load (except for the starter) be wired through the ammeter. The result is a couple of very heavy wires being run under the dash to the ammeter, and if there are loose connections or shorts there can be a fire hazard. With the external shunt that @Eric Satterfield has, the shunt is mounted somewhere else, typically under the hood and hopefully well insulated. The ammeter in the dash then is simply a very sensitive "centered needle" voltmeter, and measures the voltage drop across the shunt.
     
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  13. deucemac
    Joined: Aug 31, 2008
    Posts: 1,483

    deucemac
    Member

    the reason OEMs went with voltmeter is money, not safety. As electrical loads increased, current draw increased and ammeters for 100+ amp system are dreadfully expensive to saynothing of the fact that the average driver has no clue how to read or understand how to read an ammeter. Volt meters are cheap but don't indicate whether the system is changing or discharging, only system voltage. In other words, the volt meter reads 13.9. Is the charging system weak or not working at all and you are seeing battery voltage only? The cost of wiring and building a 100+ ammeter is prohibitive. Ammeterproblems occur from improperly sized ammeter in respect to load and not sufficient wire gauge to carry that load. Have had ammeters in my cars since I was a kid in 1962 and no problems. I have seen problems because of what I previously stated. Cost, not safety, caused the OEMs to change.
     
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    Mopar seems to have been the last one to use full current ammeters on cars, they had them well into the 70s. And they cause problems, because they didn't make them quite as well as they should have.

    Chevy switched to shunt type ammeters in the early/mid 60s on trucks. The cars had only idiot lights, since the 50s, except for a few such as vettes. I dont know what ford was using, besides idiot lights.

    I'm content with an idiot light....
     
  15. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 513

    Fabulous50's
    Member
    from Maine

    I've never had in idiot light fail me......

    Speaks to my intelligence (idiot) I guess....
     
  16. Eric Satterfield
    Joined: Aug 2, 2018
    Posts: 286

    Eric Satterfield
    Member

    It seems on my 56 the accessories are coming off the starter post along with the battery cable. I would assume this connection and the lead from the alternator will be coming into one end of the shunt and the other end will stand alone with the battery cable on the starter. Some pics of my project. So far. Powder coated frame. Rebuilt Muncie M22. 9” Ford.Chevy Performance SP 383 crate engine
     

    Attached Files:

    Last edited: Apr 12, 2021
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    that sounds right
     

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