Want to replace AC motor 240V to a 12V DC, how to choose?

[apples]

I have a leaf blower that is mains powered, 240V 50HZ AC 1170 Watts.

I want to rip out that motor and hook it up to a DC 12v motor. How do I work out what size motor I would need to make it spin as fast etc. The power it needs to make is obviously 1170 watts, so how do you work out what size DC motor you need.

 

[crutschow]

One HP is 746W so 1170W corresponds to 1.56HP, neglecting efficiency. If you indeed need that much power it will require in the neighborhood of 100A @ 12V for the equivalent 12V DC motor. This would require a hefty car type battery size to power. Are you planning on carrying around that large a battery?

Most blowers designed for battery power use a much smaller motor, so that a reasonable size battery can be used to power them. (Mine uses a small 5AH 12V battery). Of course it doesn't have the air moving capability of the larger line powered ones but that's the compromise you must make to have it portable with a reasonable size battery.

 

[strantor]

leaf blowers have a universal motor, so they can run on DC as is, with no modifications. You can achieve 240VDC with hobby LiPo easily. see video.

 

[apples]

well yes I do have a car battery ready to go.
I am not going to use it as a portable leaf blower as such. I am using it for a fire,
I think that full power will be too much.

 

[strantor]

Try just hooking up your 12V battery to the leaf blower as is, and see if it puts out enough wind to stoke your fire. Are you making a forge? I'm an amateur blacksmith, and I tried to make a forge once with a leaf blower. It was waaay too powerful. I drilled large holes along the length of the thing to reduce the air, but it was still too much. I had to set the leaf blower 4ft away from the forge and blow air at it as opposed to into it. it didn't work well and I ended up scrapping the idea. But I bet if I had used a 12V battery instead of 120V mains, I might have had more success.

 

[ChrisP58]

It might be easier to just buy a 12 volt blower. I just googled "12v blower" and got lots of hits.

 

[apples]

Yep the 12volt battery made it spin, but not fast enough. I
Have pulled out the motor and will measure up the shaft size and
Maybe I can find a cheap DC motor off Ebay that will fit.

 

[colin55]

The 240v motor is a series motor. (universal motor) Try putting the armature and field in parallel.

 

[debe]

What i used on a pottery Kiln was a salvaged car heater fan with its 3 speed switch. Worked fine.

 

[apples]

Colin55 how do I pu the armature and field in parallel? I have included a photo of what I have and listed numbers beside it. Maybe you can say what numbers to connect to where.

What will be the result, faster spinning?
View attachment 64561

 

[colin55]

The rpm will not be greater. At the moment you have a"Universal Motor" and the RPM is the highest you can get.

You photo is not clear.


However: leave 2, 3, 4 together and cut the wire leading from this and going around the back of the motor. This is the postive lead.

Connect 1 to the other brush and this is the negative lead.

You will have to reverse the field to reverse the rotation as this is still an AC/DC motor. Try it on 12v.

 

[strantor]

wiring the field & armature in parallel will make the motor slower, and also may burn up the armature. Also I'm not sure that being in series (universal motor configuration) results in the highest possible speed. If you put the armature and field in parallel, and you put a resistor (any resistor with greater resistance than the armature) in series with the field, you would have a seperately excited (sepex) DC motor with field weakening. I think that may be faster, but never tried it, so I'm not speaking from experience.