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Thread: Cooling Fan Tripping Breaker

  1. #1
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    Cooling Fan Tripping Breaker

    I have installed the cooling fan from a 1998 Mustang 4.6 in my Roadster Mk 3.1. I have a generic fan controller triggering an 80 amp relay to run the fan, and the high power circuit on the relay is protected by a 50 amp breaker. My problem is that the fan trips the breaker after the fan has run for a few minutes. My research so far says that the fan draws 35 to 40 amps on high speed (I am running the fan on high speed), but that the start up current draw could be as high as 120 amps.

    Does anyone have a solution to the circuit breaker being tripped and does anyone know how this fan was wired in the original 1998 Mustang?

    Thanks.

    Wade

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    Seasoned Citizen NAZ's Avatar
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    https://derale.com/products/electric...n-probe-detail

    Sounds like you need a soft start controller. Perhaps this one would work or if not, something like it.

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    Quote Originally Posted by Driver_WT View Post
    My research so far says that the fan draws 35 to 40 amps on high speed (I am running the fan on high speed), but that the start up current draw could be as high as 120 amps.

    Does anyone have a solution to the circuit breaker being tripped and does anyone know how this fan was wired in the original 1998 Mustang?

    Thanks.

    Wade
    Wade, I just looked at the EVTM shop manual from the 94/95 Mustang with the 5.0 and the high speed fuse is listed at 60 amps. I suggest you run the fan on low speed, even on low that fan blows like a hurricane. Low speed has a 40 amp fuse.

    Frank

    FWIW the high speed was only used when the A/C was on and the EEC called for high temp from the coolant temp sensor.
    Last edited by i.e.427; 07-29-2018 at 07:16 PM.

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    Brandon #9196 TexasAviator's Avatar
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    Install this for 6 dollars in parallel with your 50 amp breaker to absorb the load. Your breaker will protect the larger load but this will supplement the start up of the fan, acting as a buffer. If the wire truly shorts out it will still pop the fuse and the breaker maintaining the safety of a short.

    https://www.amazon.com/dp/B06XS833Q5...&pd_rd_w=9ge4t

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    Quote Originally Posted by TexasAviator View Post
    Install this for 6 dollars in parallel with your 50 amp breaker to absorb the load. Your breaker will protect the larger load but this will supplement the start up of the fan, acting as a buffer. If the wire truly shorts out it will still pop the fuse and the breaker maintaining the safety of a short.

    https://www.amazon.com/dp/B06XS833Q5...&pd_rd_w=9ge4t
    With your solution the wire becomes the fuse...........Not a good idea. While it is OK to parallel wires, one source of over-current protection is a must.

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    Seasoned Citizen NAZ's Avatar
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    OK, I'm not an electrical engineer but from my limited electrical engineering 101 training many decades ago here's what I think I know.

    Running fuses or breakers in parallel for load sharing will increase the point at which the circuit protection (fuse or CB) trips if they are of equal amp rating. Lets say we need a 120A fuse but can't find one in that rating so we run two 60A fuses in parallel to achieve the 120A load rating. But load sharing is dependent on resistance so the load sharing will only be equal if the resistance in each leg is also equal. AND the wire as well as all other elements of the circuit had better be rated at 120A in this example or you are not really protecting the circuit.

    TA, what you're suggesting is already below the 120A load from the inrush current so I expect the fuse to blow very quickly and then the 50A CB will be carrying the entire 120A load just like it does now. And the CB should also trip just like it does now. Please correct me but it seems to me a better approach is to mitigate the high inrush current that results from instant start of the fan. A soft start ramps up the current over time lessening the inrush. Another suggestion was to run the fan at the slower speed which will also mitigate the high current condition.

    Or perhaps the current CB is faulty. CBs are usually slower to trip than a faster blowing fuse and can accept a margin of overload for a short time so can handle some inrush until the motor gets up to speed.

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    Quote Originally Posted by i.e.427 View Post
    Wade, I just looked at the EVTM shop manual from the 94/95 Mustang with the 5.0 and the high speed fuse is listed at 60 amps. I suggest you run the fan on low speed, even on low that fan blows like a hurricane. Low speed has a 40 amp fuse.

    Frank

    FWIW the high speed was only used when the A/C was on and the EEC called for high temp from the coolant temp sensor.
    Thanks Frank. I don't have A/C, so I guess I don't need to run the fan on High speed. I will try it on low speed and see how that works.

    Thanks for the detailed info.

    Wade

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    Quote Originally Posted by NAZ View Post
    https://derale.com/products/electric...n-probe-detail

    Sounds like you need a soft start controller. Perhaps this one would work or if not, something like it.
    Thanks NAZ. This controller will be my second option if running the fan on low speed does not work.

    Wade

  11. #9
    Brandon #9196 TexasAviator's Avatar
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    Quote Originally Posted by NAZ View Post
    OK, I'm not an electrical engineer but from my limited electrical engineering 101 training many decades ago here's what I think I know.

    Running fuses or breakers in parallel for load sharing will increase the point at which the circuit protection (fuse or CB) trips if they are of equal amp rating. Lets say we need a 120A fuse but can't find one in that rating so we run two 60A fuses in parallel to achieve the 120A load rating. But load sharing is dependent on resistance so the load sharing will only be equal if the resistance in each leg is also equal. AND the wire as well as all other elements of the circuit had better be rated at 120A in this example or you are not really protecting the circuit.

    TA, what you're suggesting is already below the 120A load from the inrush current so I expect the fuse to blow very quickly and then the 50A CB will be carrying the entire 120A load just like it does now. And the CB should also trip just like it does now. Please correct me but it seems to me a better approach is to mitigate the high inrush current that results from instant start of the fan. A soft start ramps up the current over time lessening the inrush. Another suggestion was to run the fan at the slower speed which will also mitigate the high current condition.

    Or perhaps the current CB is faulty. CBs are usually slower to trip than a faster blowing fuse and can accept a margin of overload for a short time so can handle some inrush until the motor gets up to speed.
    You're right it may not be the best solution. Fixing it right rather than a bandaid.

  12. #10
    Senior Member rich grsc's Avatar
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    A fuse is typically 150% of rated load, so your 50 amp fuse is too small. As Frank said 60 amp fuse, that would be minimum, and there isn't a need to run on high speed.

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