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Author Topic: converting a fan to run backwards  (Read 208 times)

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Offline TrevL

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converting a fan to run backwards
« on: June 10, 2020, 02:29:23 PM »
A little help from you electronic wizards please.
My heatgun packed in yesterday after I dropped it.   The elements were broken in several places, so I canibalised it to recover the fan motor and blower.  I have a mind to make cyclone vacuum cleaner for use on my layout.
The problem I have is the motor only seems to run in one direction and acts as a blower.  I'm hoping to get it to run in reverse so it can act as a sucker.  I've tried the obvious and switched the polarity of terminals, but it still runs "forward".  I've tried to bypass the electronics using a 12vdc wallwart, and it runs normally as a blower, but switching the polarity, it does run in reverse, but very slowly. I thought I'd ask the collective geniouses here if they could point me in the right (wrong ;)) direction please, hopefully to get it to run a full speed in reverse?  TIA.






« Last Edit: June 10, 2020, 02:34:13 PM by TrevL »
Cheers, Trev.


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Offline themadhippy

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Re: converting a fan to run backwards
« Reply #1 on: June 10, 2020, 03:03:53 PM »
Theirs a bridge rectifier on the circuit board so thats forcing the polarity,,them 4 black cylinders with silver bands on em cut them  out and apply power to the 2 solder terminals  in the middle of the board
« Last Edit: June 10, 2020, 03:05:31 PM by themadhippy »
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Offline TrevL

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Re: converting a fan to run backwards
« Reply #2 on: June 10, 2020, 03:27:18 PM »
Theirs a bridge rectifier on the circuit board so thats forcing the polarity,,them 4 black cylinders with silver bands on em cut them  out and apply power to the 2 solder terminals  in the middle of the board

Awesome :thumbsup: :thumbsup: That works treat, thank you.
Would it be ok to cut the rest of the PCB off, except the two small brown jobbies attached to the motor brush terminals please?
Cheers, Trev.


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Offline Malc

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Re: converting a fan to run backwards
« Reply #3 on: June 10, 2020, 03:31:43 PM »
The PCB is superfluous, you can cut it off. I suspect the brown jobbies are spark suppressors and can be left.
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Online N_GaugeModeller

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Re: converting a fan to run backwards
« Reply #4 on: June 10, 2020, 03:45:28 PM »
You may find it's as efficient at sucking as it was blowing as you will be just running the blades backwards and if correctly designed they will be the wrong shape to effectively blow, the will not only be angled but also curved with the cup ofvthe curve scooping air, when you run it backwards you have the back of the blade tringbyhe push air and as its curved the wrong way performance will be reduced.

May not be an issue depending on how well the blades are designed but just something  be aware of during your build.
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Online chrism

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Re: converting a fan to run backwards
« Reply #5 on: June 10, 2020, 04:45:24 PM »
You may find it's as efficient at sucking as it was blowing as you will be just running the blades backwards and if correctly designed they will be the wrong shape to effectively blow, the will not only be angled but also curved with the cup ofvthe curve scooping air, when you run it backwards you have the back of the blade tringbyhe push air and as its curved the wrong way performance will be reduced.

May not be an issue depending on how well the blades are designed but just something  be aware of during your build.

If it's possible to physically reverse the mounting of the fan and motor, then run it in the original direction that may overcome any performance loss due to the shaping of the fan - assuming that the case can be modified to swap the inlet and exhaust.

 

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