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Low voltage for motor powering

Low voltage for motor powering

Low voltage for motor powering

(OP)
We are in the process of ordering a power tool for our on site installation service. The tool has a requirement of 1kW.
It was proposed to enquire for a 24V supply voltage for the following reasons:

24 Volt is standard instrumentation supply voltage so readily available on any process plant

24 Volt does not give any safty concerns.


But in my opinion for a power tool 24Volt is not enough. We would need much to high ampere rating (about 40amps) in order to run the equipment.

My Question: Am I right in this assumption?

Does anyone have experiences with running a motor with such low voltage?

Any other problems to consider? I presume the high AMP is a major issue on plants?


:)

RE: Low voltage for motor powering

In my opinion that would be a total misuse of instrumentation control power.  Use 120 VAC.

RE: Low voltage for motor powering

The high current would result in a high copper loss in the 24 volt distribution system, plus that current level is beyond what would be expected in an outlet for instrumentation supplies.
I would recommend that you Use standard equipment and supply voltages.

Best regards,

Mark Empson
http://www.lmphotonics.com

RE: Low voltage for motor powering

Not a good idea.  In addition to other comments, you would experience a lot of voltage drop on the 24 vdc system as the motor loaded up, subjecting all of your instrumentation to voltage dips and sags they don't need to be subjected to.

24 V dc may be the standard voltage, but trying to draw 40 A from the power supply is definitely non-standard.  

If safety is the concern, put in a GFI breaker for the 120V supply.  

RE: Low voltage for motor powering

I doubt you will even find an option for 24V on a power tool of that size anyway. Your assumption about it taking 40A would be essentially correct. It's also doubtful that you will ever find a control power source with that capacity either.

Besides that, what davidbeach said is absolutely true. Plugging a power tool into a control power supply isn't a good idea, even if it is at the normal voltage. Power tools are notoriously noisy (electrically) and combined with the sudden power surge when you turn them on can cause other problems with the control equipment. I usually recommend to people that if they want a utility tool outlet, get a specific transformer or separate circuit for it. If you are in an area where you have 230V phase-to-neutral, use that.

JRaef.com
"Engineers like to solve problems.  If there are no problems handily available, they will create their own problems."   Scott Adams  
For the best use of Eng-Tips, please click here -> FAQ731-376

RE: Low voltage for motor powering

(OP)
Thanks,
what would be the implication if we connected it to the system. Would it trip because of the amperes drawn from it?

RE: Low voltage for motor powering

Uh, what "power tool" exactly are you proposing to order, and under what circumstances would you be using it?

Mike Halloran
Pembroke Pines, FL, USA

RE: Low voltage for motor powering

(OP)
Its a electrical mortor winch which assist for installation purposes. It is not ordered jet but power rating will be in the range of 1 to 2 kW

RE: Low voltage for motor powering

Unless it is a vehicle-mounted winch I can see no reason at all why you would want to use a low voltage DC machine in this application. At 2kW even a vehicle-mounted application starts to justify an on-board generator to allow a standard AC motor to be used. A 2kW DC machine is going to be bigger than an equivalent power AC mains powered motor, and much more expensive.

Even the biggest 24V systems we occasionally see for substation tripping & control are no bigger than 24V / 40A. The cost of the cabling and the volt-drop problems make it impractical to go any bigger, and I don't particularly like them this big because of the over-sized cables which are required. High DC currents are generally bad news for controlgear too although at only 24V I guess you can use relays designed for heavy automotive applications, e.g.truck engine starter motors, etc.
 

----------------------------------
  Sometimes I only open my mouth to swap feet...

RE: Low voltage for motor powering

With an automotive type winch, I would expect over 100 amps under stall conditions and under starting conditions. If the power supply cannot maintain the voltage under heavy load, the heavy current will persist.
Automotive winches are not noted for efficiency.
2 KW / 24 volts =  83 amps. At 80% efficiency, 104 amps.
Starting and or stalling, several hundred amps.
Wow, If your engineers designed the 24 V supplies with 200 A or 300 a excess capacity, by all means, go ahead.
Otherwise, either forget it or buy a model 8D battery, a hand cart to move it around, and a 40 amp charger to charge it at night.
respectfully

RE: Low voltage for motor powering

(OP)
I think the last comment clarified it quiet well.
So it is a no go!

thanks

RE: Low voltage for motor powering

Hi themroc;
The battery suggestion was not meant as sarcasm. It was a serious suggestion.
respectfully

RE: Low voltage for motor powering

I second waross' suggestion.  

That's a fairly serious winch; it's going to have high starting current whether AC or DC powered.  Almost by definition, winches have to start under full load.
Use during installation ( of ... something ) suggests that it may be most needed when the mains power is off.  



Mike Halloran
Pembroke Pines, FL, USA

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