DC motors, master slave configuration, component selection

[MattQM]

This thread is regarding an application using DC motors in synchrony. Here are the salient points:

--- Two DC motors, 3/4 to 1 hp
--- 80 foot separation between motors (possible product)
--- One motor to be controlled for speed, the other is to follow it, i.e. master/slave
--- Low precision requirements
--- The closer to turnkey for the controls the better

Most of the parameters are still up in the air. For example, it is unknown whether brush or brushless motors would be better.

Here are some questions:

--- What direction would be best to pursue for the controls? Should I seek to use PLC, a PC running C to send instructions to digital drives, or what? Please provide manufacturers or links.
--- Are there reasons for using one technology over another? For example, PLC's might be more contained and closer to turnkey than other systems.
--- What are some concerns about voltage; eg, should I seek 300 or 24V?
--- Could we run multiple slaves?

The first of these questions is what I am mainly concerned with now. I would appreciate any advice as we get going with this design.

MQM

http://www.phoenix-engineer.com

 

[waross]

What is your application? It sounds as if you are trying to re-invent the wheel but aren't sure what an axel is. Most common applications have time proven solutions. Why DC?

What direction would be best to pursue for the controls? Should I seek to use PLC, a PC running C to send instructions to digital drives, or what?

You really haven't given us much to go on.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MattQM]

waross,

What is your application? It sounds as if you are trying to re-invent the wheel but aren't sure what an axel is. Most common applications have time proven solutions. Why DC?

The application is simple; so much so that I did not think it bore mentioning. We have two hose reels, and we want them to wind at about the same rate, regardless of whether one bogs down or not. That being said, it now sounds like not quite a master/slave, because if the slave bogs the master would not change speed like we'd like it to.

Your analogy is pretty apt, but to make it a bit more accurate I'd say I don't know what a ball diff is. I would not be surprised to learn that there is a time-proven solution available, I just do not know what it is.

The current is DC because of safety. Would it not also allow longer motor cables?

Thanks.

MQM

http://www.phoenix-engineer.com

 

[waross]

The current is DC because of safety. Not at 300 volts
Would it not also allow longer motor cables? Not at 24 volts.
I'm out of time just now, but hang in there, you should start getting some responses.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Is this on a mobile structure like a vehicle with 12 or 24VDC limitations?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TurbineGen]

MattQM,

Higher voltage is better for longer feeders. At 24 volts a 1 hp motor will draw about 35 Amps. So you're probably looking at 8 AWG wire depending on how long the run is. Assuming a maximum allowable voltage drop of 5% (1.2 volts), you can have a 25 foot run of wire. A 6 AWG gets you 41 feet, and a 4 AWG gets you 65 feet. If you can drop 10% voltage these runs double.

Now for 300 volts, the wires get significantly smaller and longer runs begin to be easily feasable. At 300 Volts your motor is going to draw a little under 3 amps. For this you can use a 16AWG wire if you want. Again assuming a 5% voltage drop allowance 16 AWG allows 550 feet, 14 AWG allows 900 feet! If your motors are both close to the DC source, then 24volts could be feasable.

If you must go with DC, can you split the difference and go with 115 or 180 Volts? there are hundreds of motors out there at these voltages. If that's too dangerous, consider 48 volts DC. Electric golf cars run on this voltage and so do some older control systems. Finding a motor and a drive at this voltage might be a bit harder, but you can go 4 times further on the same feeder compared to the 24 volt motors.

Another solution: 120 volts AC. Is that too dangerous? Surely much of the electrical equipment in the place is this voltage. There are countless numbers of motors and AC drives available at this voltage and they're cheap.

-Alex

------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[MattQM]

itsmoked,

There are no such limitations for this application.

MQM

http://www.phoenix-engineer.com

 

[Skogsgurra]

Go AC and VFD. Cheap, reliable, mainstream. There are very competent drives with torque control, master/slave configurability - even little PLCs built-in. You can't beat that with any other technology.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MattQM]

The feedback thus far is very helpful. A lot of it is lobbying for AC power. The main reason DC was pursued was the fact that the required torque is needed throughout the duty cycle, i.e. at startup. Is this a valid concern?

MQM

http://www.phoenix-engineer.com

 

[ScottyUK]

For sheer brute force and simplicity it's tough to beat a series wound DC machine for low speed torque if it has a big enough supply to draw power from. But (some) AC drives can maintain high torque right down to zero speed, and with appropriate choice of motor and drive I don't think you would have a problem. You wouldn't want a series DC machine for this type of application anyway. In many respects AC motors are superior to DC types - more rugged, less wear, less maintenance, smaller, cheaper.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

No DC requirement - then I agree with with Skogs and Scotty's AC comments..

Go with VFDs! That horsepower point is the sweet-spot too.

Keith Cress
kcress -

http://www.flaminsystems.com