Powering Hybrid Battery Fan Externally

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by indel, Jan 12, 2026 at 3:15 PM.

  1. indel

    indel Member

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    I will soon be reconditioning my Prius battery and will take it out of the car to do so. That means, I will need to power the battery fan externally with a 12V power supply. Luckily, I have a spare Prius 12V battery laying around and it's putting out 12.5V consistently.

    1. Is it okay to use this battery to power the fan?

    2. What are the specs on the fan power connector? I would like to put together a harness that goes from the battery to the fan connector. Do they make any specific connectors on the battery end for applications like this?

    I found a video which suggests a frequency meter is needed to select fan speed on later generation Prii. I assume Gen 3 does not have such a function and the fan runs at a constant speed. Correct?
     
    #1 indel, Jan 12, 2026 at 3:15 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    Most people just put a big shot v
    Fan over the rack. I thought. At least that's what I see at my buddies set up wer he does this like production . 18 inch fan above table the racks are on wen charging in singles or complete racks of modules . And it's conditioned space the shop is .
     
    #2 Tombukt2, Jan 12, 2026 at 7:31 PM
  3. PriusCamper

    PriusCamper Senior Member

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    Or you could find a Gen2 Prius cooling fan at the junk yard... It will run straight off a 12v power supply. @ChapmanF pointed out the Gen3 wiring for the cooling fan on here once, but I don't remember what he said?
     
    #3 PriusCamper, Jan 12, 2026 at 7:32 PM
  4. indel

    indel Member

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    Yes I saw a couple of videos with that setup. But I feel like the factory cooling mechanism is much better at this.
     
    #4 indel, Jan 12, 2026 at 9:45 PM
  5. indel

    indel Member

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    Perhaps I am not understanding what you are saying, but what would be the advantage?
     
    #5 indel, Jan 12, 2026 at 9:46 PM
  6. PriusCamper

    PriusCamper Senior Member

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    @ChapmanF can explain better, but a gen2 fan is just two wires and gen3 fan is three wires so it's more complicated than a simple + and - connection to get the fan to run.
     
    #6 PriusCamper, Jan 12, 2026 at 10:58 PM
  7. indel

    indel Member

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    Gotcha. Sorry I just realized that you said Gen 2. Even if I went that route, I would then have to swap in the new fan in place and swap it out when I am done reconditioning.

    Does 3 pins mean the option to control the speed?
     
    #7 indel, Jan 12, 2026 at 11:01 PM
  8. rjparker

    rjparker Tu Humilde Sirviente

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    Gen3 has a variable speed battery cooling blower with pulse width modulation control.

    IMG_0176.jpeg IMG_0178.jpeg IMG_0180.jpeg

    IMG_0184.jpeg
     
    #8 rjparker, Jan 12, 2026 at 11:34 PM
    Last edited: Jan 13, 2026 at 12:13 AM
  9. Tombukt2

    Tombukt2 Senior Member

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    You're going to have to have the fan attached and all the duct work for cooling . All has to be removed to reaccess. The table fan notta. And uhhh big cfms more air from 18 incher with nothing fitted . And it's winter in many garages !
     
    #9 Tombukt2, Jan 13, 2026 at 6:12 AM
  10. Albert Barbuto

    Albert Barbuto Active Member

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    To prevent the slow degradation of module capacity, I do a once a year deep discharge of the entire pack, in the car. The cardboard box, along with a small fan, keeps the pack completely cold.
     

    Attached Files:

    #10 Albert Barbuto, Jan 13, 2026 at 8:16 AM
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  11. ChapmanF

    ChapmanF Senior Member

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    rj showed the wiring for the gen 3 fan. That SI0 terminal is for speed control, via a pulse train, with the property that the more time the pulse train stays low, the faster the fan. So just tying SI0 to ground, as the "Bench Test while Disconnected from Harness" drawing shows, is enough to run the fan at high speed.
     
    #11 ChapmanF, Jan 13, 2026 at 8:50 AM
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