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Technical Runtz resistors - do they burn out?

Discussion in 'The Hokey Ass Message Board' started by cederholm, Oct 23, 2014.

  1. cederholm
    Joined: May 6, 2006
    Posts: 1,748

    cederholm
    Member

    Hey guys,

    I've had nothing but issues with my gas gauge ever since converting to 12v on my '53 Chevy. It works intermittently. My last attempt at fixing it showed 12v at the "in" side of the runtz but 0v at the out. Clearly this is an issue. Do they burn out?

    Thanks,
    Carl
     
  2. Any resistor will burn out if you exceed it's power rating. If you are only using it to run your gas guage, it shouldn't have burnt out unless the ouput was shorted directly to earth.
     
  3. cederholm
    Joined: May 6, 2006
    Posts: 1,748

    cederholm
    Member

  4. If you are only running the gas gage it may be a simple fix to use the LM7806 electronic voltage reducer. I run one on my 37 Chevy and the gas gage works great. Few $ for the part and basic wiring work and your gage will be receiving 6v supply. Only drawback to the electronic voltage reducer is they have about 1 amp capacity, so good for gages, not good for heater fan or old 6V radios.
     

  5. odd that you have this problem, a buddy of mine also has a '53 chevy converted to 12 volts and has burnt out 3 of the LM7806 regulators...can't understand why, only running the fuel gauge. And they are mounted on heat sinks.
     
  6. JeffB2
    Joined: Dec 18, 2006
    Posts: 9,484

    JeffB2
    Member
    from Phoenix,AZ

  7. cederholm
    Joined: May 6, 2006
    Posts: 1,748

    cederholm
    Member

    Great info guys! thx
     
  8. i had a customer try to jump start his truck but hooked the cables up backwards. the gage stopped working, i had to change the runtz resistor.
     
  9. I have also used an LM7806 regulator, and used that to regulate a larger transistor.
    I run my 6v heater fan,, gas guauge and a couple of other 6v gizmos fom it.
    It has a 5 amp capacity, and i built it in a box with a heatsink and small 12volt computer fan for cooling. If anyone wants the circuit, I will post it up. If you can handle a small (20) watt soldering iron, you should be able to build it.
     
  10. squirrel
    Joined: Sep 23, 2004
    Posts: 55,944

    squirrel
    Member

    the Ford regulators wore ok on Fords, which have thermal gauges (Mopars used a similar system), but not so well on GMs with magnetic gauges.

    what exactly is the voltage reducer you are using? does it look like this?

    [​IMG]
     
  11. cederholm
    Joined: May 6, 2006
    Posts: 1,748

    cederholm
    Member

    Yes Jim, that's it exactly.

    ~ Carl

     
  12. post it!
     
  13. i have used the ford stepdowns for years and the LM7806 regulators also with no issues, i used to pull them out of old electronic boards.
     
  14. [​IMG]
    This circuit will increase your current capacity for the LM7806.
    Don't worry too much about the formulas, this circuit will be good for about 8 amps as long as the BD536 is on a good heatsink in some airflow.
     
    loudbang likes this.

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