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I Forge Iron

Making foot pedal blower electric


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Hi All,

For a while, I've been wanting to upgrade to an electric blower for my forge, but so far I have not found any affordable second hand options. Now I had a thought that I could use a variable speed electromotor to power the cast iron blower I currently use with a food pedal:

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After looking at some motors online, I found one that is pretty cheap, but I have doubts as to its suitability, as I have little to no experience with motors.

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This motor would have an rpm of 70 and a torque of 5 N.m. would this be suitable for use as motor for a forge blower, and if not, what RPM's and Torques should I be looking for? The cast iron blower has no internal gears so the rpm supplied is not multiplied by the blower itself.

Thanks for your thoughts.

~Jobtiel

 

 

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Interesting question. I would start by calculating the current range of speeds you’re getting with your foot-powered blower and then figuring out if the motor would be able to duplicate (or even extend) that range. 

Remember that low speed is important as high speed. You don’t want the lowest speed to be pumping in more air that you need for a gentle fire. 

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I checked this afternoon, and 70 rpm is about the rpm I spin on the big wheel, so that rpm is not suitable if I want to connect directly to the blower. Now if this motor has enough torque to spin the big wheel, I might get it. 

Time to do some more research on this.

~Jobtiel

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Thomas is correct. The small wheel attached to the fan isn't visible in your photo, but let's assume for the moment that its diameter is 1/10 the size of the big wheel. That would mean that when you turn the big wheel at 70 rpm, the small wheel is turning at 700 rpm. If you turn the big wheel at half speed (35 rpm), the small wheel would be turning at 350 rpm, while double speed of 140 rpm would turn the small wheel at 1400 rpm. Make sense?

Now, let's further assume that you put a pulley on the motor that's twice the size of the small wheel. That means that the small wheel would turn twice as fast as the motor, and since the motor runs at 70, 93, 140, 280, or 466 rpm, that would give you fan speeds of 140, 186, 240, 560, and 932 rpm.

So, what you need to do is to measure the diameters of the large and small wheels, which will allow you to determine the actual working speed of the fan. You can then calculate the size of pulley you'd need to put on the motor to give you the right range of motor-driven fan speeds.

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