Author Topic: h-bridge  (Read 2576 times)

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Offline odellTopic starter

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h-bridge
« on: August 20, 2012, 05:10:29 am »
can you use h-bridge on a pc fans? I like to control a fan air flow direction. so if in need more air going in. I can change the direction for the fans
 

Offline IanB

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Re: h-bridge
« Reply #1 on: August 20, 2012, 05:23:11 am »
Why don't you find out? If you have an old fan you are not too worried about damaging, try reversing the polarity on the input wires and see what happens. Just use a small 9 V battery and touch the wires briefly. (You can guess from this that I don't think it will work and a small 9 V battery will minimize the risk of letting the magic smoke out.)

Also, the fan blades are curved and are designed to move air in one direction only. If you examine them closely you can see this. If you did manage to make the fan run in reverse it wouldn't move air very well.
 

Offline EEMarc

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Re: h-bridge
« Reply #2 on: August 20, 2012, 06:23:53 am »
Most computer fans are not DC motors. They are AC motors in disguise with and on board AC motor controller that accepts DC voltages. They call them brushless DC motors as a marketing stunt to try to avoid losing customers scared away from the fact that it is an AC motor. It worked. The reason they are brushless and don't need a commutator is because the AC motors have a motor controller that take care of the switching requirements.

Reversing the fan blade may or may not be possible depending on the design of the motor controller. It may work, it may work poorly, or it may not work at all.

The fan blades themselves as IanB pointed out are designed for one direction and would not reverse well.

You really need a fan that is designed for bidirectional operation.
 

Offline G7PSK

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Re: h-bridge
« Reply #3 on: August 20, 2012, 08:55:10 pm »
Stack two fans back to back, turn one on for out flow and the other on for in flow, all the computer fans that I have used are polarity conscious and wont work with reversed current flow. Further the price of computer fans is such that the circuitry to do the reverse will cost more than the fan.
 


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