I think I'm in trouble finding servo drivers

[Danno]

I'm busy retrofitting a Hurco KMB-1 to mach 3, and to my dismay, the darn thing has 45volt servos. Where do I go now?
I was going to use the Larken Viper 200 drives, but they are only rated for 20 amps.
At 45 volts, I will be drawing twice the current of a 90 volt servo. Obviously this is a hobby mill, and if I have to replace the servos, I will scrap the whole idea of this retrofit.
Any ideas?

[joeybagadonuts]

Danno,

Where did you come up with the idea that the KMB-1 has 48 volt servos when all of them operate at 80-90 volts?

Have you checked the factory specified power supply voltage?

Maybe the person that is giving you the specs needs to eat a few more donuts.


JoeyB

[Danno]

They are 45volt. They are Electrocraft #0703 02 049

Check out this link http://www.servorepair.com/stock_servomotors.htm

I have also contacted Electrocraft, and they sent me the original blue-prints from these servos, and it states that they are indeed 45V.
Something just doesn't make sense!!
I removed the power supply that came out of the same machine that the servos are from, and the power supply is 90 volts DC. How is it possible that Hurco can be using 45 volt servos, and a 90 volt power supply?
I bench tested the servos this morning, and only put 115 volts ac to the transformer (1/2 of 230) so that I could try to run the servos at the recomended 45 Volts DC. At 45 volts DC, they are right on spec!! 1300 RPM
I then connected 230 volts ac to the transformer, so that I could try and run these servos at 90 volts DC. They were running 2600 RPM !! Twice the rated RPM. I am really confused, and would really appreciate anyone that can answer this Mystery. Thanks

[Al_The_Man]

Many drive manufacturers recommend the supply voltage to be 10% to 50% higher than the motor rated voltage, the 100% higher in your case appears a little high.
The higher voltage in and of itself does not harm the motor as the rpm can be controlled by the system itself, this is not the same thing as connecting a power supply up directly to the motor as you did.
Al.

[Danno]

I was reluctant to put full voltage on it, but since there was no load, I didn't think too much damage would occur.
Al, do you have specs on this motor? I would like to know what the torque rating is. It's the only info missing from the blue-prints.

[Al_The_Man]

Unfortunately I have nothing on that particular model, many were made for OEM's and full spec are not always available.
Al.

[tjs88yj]

Originally Posted by Danno They are 45volt. They are Electrocraft #0703 02 049

Danno,

I have a 1984 Hurco SM1 that has ElectroCraft servos they are part #0703 02 089. they look identical to yours, if yours look like the picture of the one in your link. I have a PDF file of the specs that I recieved from ElectroCraft. It states that the motor I have are

max terminal voltage: 45v
max continus speed: 1400 RPM (no load)
max peak torque: 2000 OZ-IN
max peak current: 45A
max continous stall torque: 427 OZ-IN
max continous current: 9.6A

I can email you the PDF if you are interested.

The electrical drawings that I have for the mill state a 60V power supply with a 35A fuse between the power supply and the servo drive board.

I am trying to figure out whether I need a servo drive that can handle the 45A max peak current and if I use one that has a lower amp rating if it will just reduce the torque of the motor or damage the drive.

Tom Jager

[Al_The_Man]

Originally Posted by tjs88yj I am trying to figure out whether I need a servo drive that can handle the 45A max peak current and if I use one that has a lower amp rating if it will just reduce the torque of the motor or damage the drive. Tom Jager

The continuous stall torque current should be used, the max peak current is the maximum current that can be applied before motor damage.
The drive usually has current limit setting to avoid over current situation.
Al.

[TOTALLYRC]

Originally Posted by Danno I'm busy retrofitting a Hurco KMB-1 to mach 3, and to my dismay, the darn thing has 45volt servos. Where do I go now? I was going to use the Larken Viper 200 drives, but they are only rated for 20 amps. At 45 volts, I will be drawing twice the current of a 90 volt servo. Obviously this is a hobby mill, and if I have to replace the servos, I will scrap the whole idea of this retrofit. Any ideas?

What you say about them drawing twice as many amp is only partially true.
If you wanted to get the same amount of output power they would have to run at twice the amps, but if you run the at the same amount of amps at 45 volts you will just get half the power.

http://www.larkencnc.com/dloads/viper-manual.pdf

According to the owners manusl they will peak to 50 amps.

Originally Posted by joeybagadonuts Danno, Where did you come up with the idea that the KMB-1 has 48 volt servos when all of them operate at 80-90 volts? Have you checked the factory specified power supply voltage? Maybe the person that is giving you the specs needs to eat a few more donuts. JoeyB

More doughnuts is always a good idea, especially paired with a nice cup of coffe and some good friends.

Originally Posted by Danno They are 45volt. They are Electrocraft #0703 02 049 Check out this link http://www.servorepair.com/stock_servomotors.htm I have also contacted Electrocraft, and they sent me the original blue-prints from these servos, and it states that they are indeed 45V. Something just doesn't make sense!! I removed the power supply that came out of the same machine that the servos are from, and the power supply is 90 volts DC. How is it possible that Hurco can be using 45 volt servos, and a 90 volt power supply? I bench tested the servos this morning, and only put 115 volts ac to the transformer (1/2 of 230) so that I could try to run the servos at the recomended 45 Volts DC. At 45 volts DC, they are right on spec!! 1300 RPM I then connected 230 volts ac to the transformer, so that I could try and run these servos at 90 volts DC. They were running 2600 RPM !! Twice the rated RPM. I am really confused, and would really appreciate anyone that can answer this Mystery. Thanks

Just thinking out loud here. The only time you will see max voltage on the motors is during rapid moves and possibly, during maximum cuts when the voltage applied goes up as the drive tries to apply more power to keep going.

Over simplifying it a lot, max voltage is a concern for 2 reasons, how long will the brushes last, and 2. will the motor windings stay together at the rpm it will spin with the new voltage applied.
If you are appling 90v at 20 amps, it is the same watts as 45v and 40 watts.

I will agree with Al_the_man completely, that a doubling of the voltage seems high, but as long as the motor max amps are being followed, you should be OK.

If they came on the machine and the power supply was 90, I would go with it and not worry about. I would bet those motors are way over built and have plenty of reserve in their specs.

Originally Posted by tjs88yj Danno, I have a 1984 Hurco SM1 that has ElectroCraft servos they are part #0703 02 089. they look identical to yours, if yours look like the picture of the one in your link. I have a PDF file of the specs that I recieved from ElectroCraft. It states that the motor I have are max terminal voltage: 45v max continus speed: 1400 RPM (no load) max peak torque: 2000 OZ-IN max peak current: 45A max continous stall torque: 427 OZ-IN max continous current: 9.6A I can email you the PDF if you are interested. The electrical drawings that I have for the mill state a 60V power supply with a 35A fuse between the power supply and the servo drive board. I am trying to figure out whether I need a servo drive that can handle the 45A max peak current and if I use one that has a lower amp rating if it will just reduce the torque of the motor or damage the drive. Tom Jager

According to the information that goes with my copley drives, the drives are a current limiting device, they will put out there max and no more. If I understand it correctly.
They will also put out double their continuos rating for 1 second or 2 seconds upon a direction change.

Again they will peak at twice the standard rating.
Seeing how the max ratings of the motor are just that, max and are only to be used for a second or so, I think you will be fine.

Mike

[Danno]

From reading the replies, it sounds like I may still be able to use the viper drives. I'm not too concerned about speed of the machine, because afterall it is just for hobby use.
Tom, I would love a copy of your motor specs. I can send you the info I have on mine. I had a feeling that Electrocraft made several versions of this motor.
I spoke to someone in england that has the same "looking" servos, but his state they are 100volt. Thanks, Dan

dantechfab@yahoo.ca

www.flickr.com/dantechfab

[bharbour]

Do you have the schematics on the driver boards? Are the output transistors set up in an H configuration on the driver board? The reason I am asking is that I have seen center tapped power supplies used with one side of the motor connected to the power supply center tap and direction control is done with only two output transistors instead of the 4 required for an H bridge. The 2X voltage factor is making me suspicious of this. I have no knowlege of the setup you have, this is just speculation on my part.

Bob

[Danno]

Bob; the power supply that I'm using to test these servos, is the power supply that came out of the mill. The transformer is 230 vac in, 60 vac out. After it goes through the bridge rectifier and capacitor (also from the same mill), I end up with around 90 vdc (60 X 1.4). Dan