Re: (ET) Deck Motor Alternate Use

["David Roden (Akron OH USA)" <etpost drmm net>]

On 9 Oct 2013 at 20:54, Robert Troll wrote:

> I need precise speed regulation that does not change with load. Think
> screwcutting... 

Do you need variable speed?  Maybe you said and I've forgotten.

> A universal motor is generally made to run at high speed. If you try to
> slow it down it is going to get angry. (technical term). 

In my experience, series motors play quite nicely with speed control.  

However, it's true that their speed regulation isn't great.  Speed can 
vary 
quite a bit with load, unless you incorporate some kind of feedback into 
the 
controller.   

> 
> DC PM motors are the preferred motor for this application. Second would 
> be
> a 3PH AC. 
> 

My understanding is that a PM motor will indeed try to maintain a constant 
speed, proportional to the applied voltage.  If the supply is capable of 
providing infinite current, the motor will happily destroy itself trying 
to 
maintain speed under load.

The speed regulation of an AC induction motor is also quite good.  
Induction 
motors also run at a speed determined by the frequency of the current 
powering them.  Because of the slip I mentioned before, it's a bit under 
the 
theoretical speed, which is why a 2-pole induction motor run on 60 Hz runs 
at about 3450 rpm.  

I don't know of any reason that a 3-phase induction motor would be any 
better at speed regulation than a 1-phase motor, but I'm not an engineer.  
Maybe you could explain this.

Or is it that you need variable speed?  Three-phase industrial motors, and 
speed controls for them, are more or less commodity items (and maybe 
available surplus). The problem is that most homes don't have 3 phase 
power.

> What started me down this route was simply wondering why i could buy
> 90v-120v DC motor controllers for stationary machines that operated on
> house current. After speaking with an engineer friend he tells me this is
> probably due to the fact that making a DC controller of that nature would
> probably be impractical. Simply because the 120VAC would first need to be
> converted down to the neighborhood of 36v using a large transformer or
> other type of converter. 

I'm sorry to say I don't understand any of this.  But I addressed the 
issue 
of 120+ volt DC controllers, and powering them, in an earlier post.

You seem to be pretty well set on using this 36v motor.  So the most 
straightforward solution I can think of is to buy a 100-300 amp, 36 volt 
golf car or similar controller and drive it with a 36-volt battery.  Add a 
36v charger and charge the battery as needed.  

I'll still recommend the 4QD controllers as they're high quality products, 
intended for PM motors.