Good trip to scrap yard

Alright, but why would you want a DC motor instead of AC? I was under the belief that the main reason to use larger DC motors was the power supply. Since AC batteries are uncommon, it's easy to power a DC motor with a multitude of car batteries. [I don't mean to be argumentative, I just want to understand.]

Should I look into making my grinder with my 4HP 24VDC motor instead of an AC motor? It's a leftover from a go-kart we didn't convert to electric.
 
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No one really powers a DC motor with batteries. You use a DC drive that converts AC to DC like the one Stacy has.

--nathan
 
OK, light bulb going off about powering the motor and what you mean by a DC drive

I still don't understand why you would want a DC motor instead of an AC motor.
 
Generally a DC motor can be smaller for a given power rating. They have certain applications in industries that require special tasks out of the motor above and beyond just running all day. Reversing, load holding, things like that you can't really do with an AC motor.

If Stacy has a large DC drive buying a 3-5HP motor to fit the drive is usually cheaper than buying an AC motor AND the drive for it. Drives are usually at least as expensive as the motor they power, with exceptions on vector drive motors with encoders built in, but that's another story.
 
The DC motor would be run at 180VDC on 240 VAC input ( 90 VDC with 120VAC in)
A DC motor is continuously variable by raising or lowering the voltage. With a good drive, torque is strong at all speeds. I bought the brand new Fincor drive for $30 ( about $1000 from the manufacturer). Hooking up a DC drive and motor is very simple.
AC drives get expensive above 1.5HP. The advantage is that good used 3Ph motors are really cheap. Wiring a 3Ph AC drive and motor is a bit more complex, but is still pretty basic.
Bottom line is that both work well for knife making purposes. The decision is mostly based on what you can find the cheapest.


Bart,
We used to put 3-4mm of water in a large steel trash barrel, throw in about 10cc of carbide, wait a minute, and toss a cigarette into the can......woof,bang.
I still have a carbide cannon I made from a 4" artillery shell . It has a spark plug in the primer hole. Add a little water and carbide, then press the button on a spark coil and it sounds like a howitzer.
To demonstrate the explosive power of gasoline, I used to take it to Scout groups. I would put in one drop of gasoline, shoot some oxygen in from a small tank, and put a piece of saran wrap over the mouth. When I pressed the button, the whole group would jump.
 
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