24VDC Reversing Motor located 2700FT away from power source 2

[actnup]

I have a 24VDC reversing motor being moved 2700 feet from the controller power source. The motor requires 6 amps for normal operation but it is a torque motor in a valve actuator and requires 51 amps locked-rotor. Since it starts under a load the starting current is about the same as locked rotor, around 50 amps. I looked at a DC voltage drop calculator for a total of 5400 ft of #4 cable, I would need to start with about 100VDC to allow for the drop. Does this sound right? Thank you for any help offered.

 

[Skogsgurra]

Yes, your calculation sounds right. But the application sounds very wrong. Very low voltage cannot be used in an application like this. You need to use a few hundred volts AC and transform/rectify it near the motor. Then control the motor using any communication you find fit.

Gunnar Englund

http://www.gke.org

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

 

[itsmoked]

How often does it run? Depending, you could use phone wire.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[zdavesf]

Is there an existing AC voltage source near the motor that you can use? If so I would consider using that, if not Like Skogsgurra said you would be better off sending 120 VAC or better yet 240 VAC the 2600 feet and then rectifying it with transformer/diode and controlling it with two SPDT relays. pull 3 extra 12 awg wires for controlling the two relays wired back to a HOH switch (Hand off Hand).

 

[davidbeach]

And do it with 3-phase AC so that you only have the voltage drop of 2700 feet of wire rather than the voltage drop of 5400 feet of wire.

 

[itsmoked]

I wouldn't try to run any small motor over that distance. You guys priced wire lately? You're talking thousands of dollars!

Depending on the duty cycle I'd run phone cable.

Add a deep cycle battery at the motor. Charge the battery via one pair of phone wires and control the motor with another set. All DC so no long-line latch-up problems.

Use the charge lines as a dropping resistor. Feed the local end of the cable with the float voltage for the battery plus the calculated drop at its float current draw.

The battery will be a foot or two from the motor and can provide all the starting current the motor will ever need.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[actnup]

Thank you all for your help! I have never had an application to run a DC actuator so far out. I really appreciate the information and direction you all have privided. I am going to find out what available power is at the control site and what power is close to the valve location. The actuator has a total of 8 wires running to it right now. The 2 wires suppling the power to the motor which are from their reversing contactor, 3 wires from their controls, open/stop/close, and 3 wires for feedback to indicating lights. The control and light circuits are only feeding through limit switches at the actuator so they can use AC or DC control power. I am going to pass the information you all have provided on to the customer and depending on the power available and their budget they will be better able to decide what to do. itsmoked, the phone wire system is something I would never have thought about but it is very interesting. I will pass on the eng-tips website to their field engineer and maybe we will see a new participant in the forum. Also he may provide more questions about this application. Thank you all again for your help. It is very much appreciated.

 

[Skogsgurra]

Exactly my thoughts. The phone line cum battery twist was quantum jump out of the box. Nice, smoked.

Gunnar Englund

http://www.gke.org

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

 

[itsmoked]

Thanks Skogs.

Of course it all depends on the duty cycle. In any case, the wire size will always be waaaay smaller than if you directly tried to start the motor because you only need to send the average current down the lines. You might need to run CAT5 for eight wires. Of course you'd have to run all the numbers once the duty cycle is accurately known. You might even want to run 2 CAT5s as you could do other things or if the needed average current was greater you could pair them up.

BTW CAT5 is only $260 per 1000ft (8 wires)

Keith Cress
kcress -

http://www.flaminsystems.com