Test battery fan outside of the car?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Nov 5, 2021.

  1. pasadena_commut

    pasadena_commut Active Member

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    At some point I am going to pick up an extra battery fan or two at the junk yard. The one in our 2007 works but it does not spin as freely as I would expect, the airflow in high didn't impress me, and the battery seems to run a bit warm. If it was cheap to replace with a new OEM or aftermarket one I would do so, but those options are both stupid expensive for a silly little fan.

    If I have a couple of cheap ones to tear apart it will be possible to see if the drag in ours is typical of these fans, or if they can be disassembled and lubricated, or maybe even the motor can be replaced (if there are markings inside which are not visible outside, to identify it). Anyway, the only test I now know of that can be done in the yard is to measure the resistance across the pins to see if it is shorted or open. (And I need a better Ohmmeter than the one in my HF DVM - that cheap device cannot accurately read <10Ohms.) Are these fans PWM or voltage regulated? If the latter then probably putting 12V across it would be an OK test, but if the former, that might blow it up. It would be nice to test these in the yard so that I don't bring home a dead one.
     
  2. ChapmanF

    ChapmanF Senior Member

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    The Gen 2 blower just has a simple motor with two terminals and sees ~ 12 volts across it at full speed.

    It is speed controlled by a separate motor controller (mounted in the duct so the airflow keeps it cool) and that gets a PWM signal from the battery ECU. Giving a motor straight +12 to test it outside the car shouldn't hurt anything.

    In the car, that PWM controller lives on the low leg of the motor (between the motor and body ground), so the motor sees constant voltage matching the 12 volt battery + at one terminal (whenever the relay is on), and the other terminal sees a voltage that matches that when the blower is off, and goes lower (closer to ground) for higher requested speeds.
     
  3. Tombukt2

    Tombukt2 Active Member

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    Wow I didn't know these things are much of an issue I've got a bunch of them every time I grab a battery from the Gen 3 I get the fan with it and sometimes with the Gen 2 I'll go ahead and grab the fan because I got the panel off very simple design just like the blower motor

    SM-A715F ?
     
  4. pasadena_commut

    pasadena_commut Active Member

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    Thanks. Any idea how much current one of these draws normally when hooked up to a constant 12V source?

    Do the PWM controllers ever go bad? I doubt my controller is fried, the motor clearly responds to speeds, but it does not move very much air until it is at speed 6. That might happen if the pulse width for each speed was narrower than it was supposed to be.
     
  5. ChapmanF

    ChapmanF Senior Member

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    I haven't heard much about the controller going bad. I don't think it has much choice about the pulse width either; it's pretty much a big transistor following pulses sent by the battery ECU.

    No, I haven't heard much about those going bad and sending narrower pulses, either.
     
  6. pasadena_commut

    pasadena_commut Active Member

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    So the controller is probably not an issue. Dr. Prius thought my battery was running too hot (at 110F) but other sources say that a Prius doesn't do much to aggressively cool a battery until it hits 120F:

    https://www.eaa-phev.org/wiki/Prius_OEM_fan_control

    Unclear in that link what specific Prius is being discussed.
     
    davecook89t likes this.
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