250VDC Supply reduced to 24VDC motor

[actnup]

I have an application where I am replacing a 250VDC reversable motor with 24VDC reversable motor. I need an efficient way to reduce the voltage to the motor. Would I just use a DC-DC converter rated for the motor FLA? This would need to be up the line from the customers controls to reverse the motor. Is there a way to do it between the controller and motor without having to supply two converters? Note the FLA on the motor is only 7 amps but the LRA is about 50 amps. These motors do see a starting current of about 50 amps when started under a load.
Any help is greatly appreciated.

 

[DaveScott]

Use a buck circuit?

http://www.powerdesigners.com/InfoWeb/resources/pe_html/ch07s1/bas_ckt.html

 

[ScottyUK]

Yeah, that's a DC/DC converter really isn't it?

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I don't suffer from insanity. I enjoy it...

 

[itsmoked]

Sorry but you would need a DC - DC that can dish out the LRA.

You are going to find out that it would be far cheaper to stay with the original motor.. Just get it rebuilt!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

It all depends on what the existing controller does. If it is a simple relay/contactor thing, then you can feed the relays with 24 V. You will need about ten times as much current with 24 V compared to what you need at 250 V. So you need a really powerful 24 V supply (around 70 A full load and 500 A starting). And powerful contacts. And heavy-gauge wires.

The idea of using a DC/DC converter does not work. Those I know about do not accept reverse polarity (which is what it will see if you connect it in the motor leads). And if it existed (a bridge rectifier front end), it will not change output polarity when input is changed.

Gunnar Englund

http://www.gke.org

 

[ScottyUK]

It depends where you do the reversing! If it is reversed using either contactors or a semiconductor bridge on the low voltage side of the converter then of course it will work. Any regenerated power from the load could be problematic unless this was factored into the design.

Were the currents quoted for the existing 250V motor or for the proposed 24V motor? It wasn't clear to me. I doubt the economics of a 700A 24V supply are going to make sense. There is going to be a lot of copper!


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I don't suffer from insanity. I enjoy it...

 

[actnup]

I would like to thank all of you for your information. The 50A LRA is for the new 24VDC motor. I did not think I could use the DC-DC converter between the starter and the motor but I was not sure if I was finding the right product. Thank you for setting me straight there. It looks like any voltage reduction is going to be on the line side of the starter which is in the customers control panel. Also his starter will need to be reworked to handle the additional current required by the new motor along with his wiring out to the motor. It does look like the best thing would be to find another 250VDC motor so I would not impact the customers starter and controls. I will get some more info on what he has in the field right now and see where it take me.
I do appreciate all the help.
Best Regards,
Roger

 

[itsmoked]

Sounds like only a 1/4hp motor.

There are a lot of savvy motor people here. If you come back with specs I'm sure someone will point you in the right direction pretty quickly.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com