Servo motor size question.

[Fabric8r]

This may be a stupid question but im not very good with this stuff yet. Im trying to figure out a power supply size. and im wondering what Volts and amps Im supposto use to calculate this. Here are the specks on my motor.

S.E.M Perm magnetic DC servo motor
Cont stall torque 3NM TENV
Max RPM 2400 Volts 142 Pulse amps 30
TACHO 9.5 Volts/1000RPM INSUL F

Thank you, Scott

[Al_The_Man]

If you have more than one motor then you want to allow for a common supply for all motors, Those SEM motors are nice motors and commonly are used with a buss voltage up to 160~180 DC with PWM drives to obtain control up to max motor rating.
The tach is not used in modern drives as the Torque or current mode of operation is used over the older velocity type drive, which required a tach.
They generally come with encoder fitted for feedback.
Al.

[Fabric8r]

How do you get the 160-180 Volts.
T%hank you, Scott

[Al_The_Man]

A 1 to 1 ratio 120 vac transformer (for isolation) will give you around 170vdc when rectified.
Al.

[Fabric8r]

All, Thank you for the input and info its greatly appreciated. I wasn't clear on my last question though. I was wondering how you came up with the 160-180 VDC as the required volts for this servo motor. Not how to get 160 Volts. although that info helps also.
Thank you, Scott

[mykow]

160-180 volts is really convenient because 1:1 transformers are relatively inexpensive. You get about 170 volts because rectification to DC multiplies your AC voltage by 1.41. Using PWM servo amps the extra voltage is not a problem. In software you can set the max speed to 2400 rpm and that will keep you from burning up the motor. Here's a 1:1 transformer that would work for you:

http://www.surpluscenter.com/item.as...tname=electric

I bought one of those to use in my servo power supply. They're brand new. You might be able to get one cheaper on ebay.

That, plus a bridge rectifier, and a capacitor bank, and you'll have a power supply that would drive three of those motors. You're going to need servo amps that will handle >170 volts though.

[Fabric8r]

Thank you guys for your information its looking good. I was looking at using 3 Rutex 2020 drives they are rated at 200V/40Amp. Does this sound like a good choice. Im still a little confused as to how you now I need 170V for these motors. Could you explane how you get this. I am also wondering If I have three of these motors How is 1 powersupply of 170V enough for all of them. Sorry but I like to understand.
Thank you, Scott

[Fabric8r]

How do I now what amp The tranformer has to be. does this have to be as big or bigger than my continues amps on the motor. So I would like to have around 6-7Amps and if im using 3 of these motors does it still have to be only 6-7Amps.
Thanks in advance.

[mykow]

This motor requires 142 volts, so ideally you'd use a 100VAC transforer and you'd end up with about 141 volts DC, which would be perfect. The problem? 100VAC transformers are vastly more expensive and harder to find than 1:1 120VAC transformers. Because it's not much of an issue to use a too-high bus voltage when you're using PWM servo amps, it's OK to just use a 120VAC transformer, rectify it to get 170VDC, and use that.

The voltage is shared by the three motors, because the amps are wired in parallel.

The current is not shared between the three motors. So take your 6-7 amps figure and triple it. There are a lot of mitigating factors when it comes to a typical mill's power supply, so it's common to use an even smaller power supply than that. But because 1:1 transformers are so inexpensive you might as well use one that will supply about 20 amps. The one I linked to in this thread would be good.

The rutex 2020 should work great.

You're going to want to make sure you have encoders. The rutex drives need them. If you don't have encoders then you can add them but you'll have to take the end caps off the motors and figure out how to attach them.

[Fabric8r]

Thank you so much for the information. is there an easy way to tell if my motors have encoders on them. from the discription on them it looks like they have tach's on them do I have to remove these.
Thank you, Scott

[Al_The_Man]

Most of the SEM motors the tachs are built in to the armature, so it is very difficult and also not necessary to remove, you just leave them unconected on a torque mode drive.
The servo's are an add on the rear shaft, usually the rear cover will house them, the ones I have used had small 1.5" dia ones. Koyo and Automation Direct make them this size.
Al.

[mykow]

One way to tell if you have encoders is to count the pins used to connect the motor (if you have an MS-style connector- the wires if you have no connector). If you just have a tach, then you might have only six or eight pins total. If you have an encoder you'll have the regular six or eight plus around four to eight for the encoder. I have an SEM motor with a tach and an encoder and it uses an MS 24-7P connector with about sixteen pins total.

Taking off the end caps shouldn't be hard, if you can't really tell from the pins. Make sure you don't unscrew the fasteners that hold the whole motor together- mine come from the shaft end, and the end cap screws come from the back at the end cap.

You'll probably have to take the caps off anyway to easily get the encoder pinout, if you have them. If you don't have encoders you'll have to take the caps off to install them.