I have just purchased these (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=2540326060&category=633&rd=1), for the princley sum of £10 + p&p. They should be arriving tomorrow, so I was wondering how I can safely test them? The guy says the resistance of the coils is good, but that means nothing to me. Also, I was wondering if anyone knew anything about these motors/manufacturers as i have no info on the motors apart from:
Evershed and Vignoles Ltd
London W4
Split Field Servo Motor
Type FB6A/A1/B
Serial No 1335473

Field windings are 1.74 k ohm
rotor is 11.5 ohm
Wt of each motor 4Kg
I have no servo drives, so testing with them is out, and unfortunately the company no longer exists! All help appreciated!

Hi Kong,

At least since the windings show a decent resistance reading, you'll know they aren't "open" (broken wire) and since they do not measure 0 ohms resistance, they should likely not be shorted out either, but there is no guarantee. :)

Can the seller tell you what application they came from? Maybe this will give you an idea of their power capacity.

I'm more familiar with permanent magnet servo motors, where no field winding is used. You might need a fancier drive amp to run that type, because of the live field windings. Maybe Google a bit and see what kind of info you can come up with on that general category of motor, or survey the online drive amps catalogues and see if they advertise what kind of motors they will run.

1) Connect the field coil and the armature to a power supply you intend to use with this motor.

2) Use a tach to measure the motor no-load RPM.

3) Calculate the Kv by dividing the supply voltage by the measured RPM and multiply the answer by 1,000. That will be the motor's Kv (volts per 1000 RPM)

4) Multiply Kv by 1.351 to get the motor's Kt. Kt is in-oz per Amp.

5) Calculate the max continuous torque by dividing the motor's rated voltage by its armature resistance. Multiply this by 0.2 and multiply the result by Kt from (4). That will be the maximum continuous torque you can use.

hope that helps.

Mariss

Please correct me if I have this wrong;
When you connect the field coil and the armature coil to the same supply, when the voltage polarity reverses the magnetic fields in both windings also reverse and the motor runs in the same direction.
If the above is true then you have to connect the windings separately so that the direction of rotation can be changed.

robotic regards,

Tom
= = = = =
In a perfect union the man and woman are like a strung bow. Who is to say whether the string bends the bow, or the bow tightens the string?
- Cyril Connolly, critic and editor (1903-1974)

Thanks for the help guys, but I'm still in the dark! I have searched google for quite a while and found nothing that I completely understand, and the seller does not know what app. they were previously used in. Unfortunately they haven't turned up yet, so I have no extra info.
As for testing them, hopefully the coils will be marked so I know which is which, but as for power supply, I have no idea what to go with. Oh, and I don't have access to a tachometer! It makes me wonder if the guy was selling them coz he was in the same boat as I am in now!

Partial success! I found the firm that deals with these motors, and a guy there sent me some data sheets. The thing is, they are way over my head! If someone has five minutes spare, would you mind looking over them please. Links to four pages:
page 1 (http://www.btinternet.com/~jasonrsmith/FB6A-A1-B_1.jpg)
page 2 (http://www.btinternet.com/~jasonrsmith/FB6A-A1-B_2.jpg)
page 3 (http://www.btinternet.com/~jasonrsmith/FB6A-A1-B_3.jpg)
page 4 (http://www.btinternet.com/~jasonrsmith/FB6A-A1-B_4.jpg)

kong:
The translation goes like this IMO (everyone else should look at this, too)

FB6A =
3.4 kg wt, 173mm length, 85.7mm flange, 10x24.6mm shaft, 1.2x3x17mm key

/AI =
80 mA field excitation (max), 220 Volt armature (max)

/B =
brush grade

It looks like you supply a constant 220Vdc (rectified mains supply) to the armature, and then vary the field current (maximum 80 mA) to control speed.

I think I would be concerned that these will produce enough torque to be useful for motion. It looks like the maximum torque produced is 33 oz-in, which in cnc machines is tiny :( . But let's see: 220V x 0.080 A = 17.6W. At 746W/horsepower this is 0.02. Yeah, they are very low power.

robotic regards,

Tom

Oh well, it was only a tenner! I think I may attatch some fins to them and call them fans! Thanks for the help.

Kong,

Don't give up hope! You can supply the field with the 80 ma and vary the armature with a gecko drive and it will work fine. As for torque, if it is indeed only 33 oz/in then yes they are not too powerful. But! They look too big to be only 33 oz in. The 80 ma is the field current, the armature current may be much more. We have 400 HP DC motors at work that have a 7 amp field current. The armature current is 750 amps max.

You need to know what the max armature current is to figure out the HP.

Eric

Eric:
You are correct, I completely forgot about the armature V-I when I did the horsepower calculation.
Unfortunately, the torque value (33 oz-in) came from the data sheet (chart - average motor characteristics, curve T/N(FB) ).
As to armature current: the table on the Electrical Data page says the armature current is 1.5 amps. So, 220V x 1.5A = 330Watts. Which is almost 1/2 horsepower (!!) at 746W/hp. I don't know how the field and armature powers inter-relate.
It sure seems like an awful lot of power in to produce only 33 oz-in torque out.

robotic regards,

Tom
= = = = =
i've been so wrong about so much so often that i probably ought to just shut the ---- up.
but that's no fun

yeah I saw the 33 oz/in...funny. I wonder if it's a typo? I know that you need to reduce the field current to overspeed the motor. In industry the drives increase the armature current to the max armature current, then they weaken the field to overspeed the motor. Want to see the motor scream? Turn off the field. Stand back as the motor comes apart!

Hooray, the motors turned up today, and they are huge! Well, by stepper standards anyways. So I'm itching to test them, but don't want to blow myself up. On the back I have six connectors. A1 A2, C1 C2, F1 F2. From page 3 of the manual, I see that A1 is armature + and A2 is -. As the voltage is 220dc max, i assume I could use a 12v or 24v supply, as that is all I have available at the moment. Now C1 and C2 are the two field coils positive, and F1 and F2 are negatives. It says to use only F1 or F2, I guess switching these will reverse direction? Also, it says max current 80ma, so I guess again that the voltage will be 220v max, so I should use the same voltage as the armature. The stupid question is how do I limit it to 80ma, or do I need to limit it at all, as I'm guessing it may only draw 80ma max from whatever supply I use. As you can tell, I know nothing about electronics, and even less about servos! Ok, looked up the current limiting and I obviously need a resistor to do it.
I can supply a photo of the connectors if needed. Thanks!:confused:

Do me a favor and measure the resistance of the field (between f1 and F2). From that info we can figure out the field voltage.

You can run the armature and field from the same supply. Reversing the field OR the armature will reverse the motor.

Be careful of hooking up the motor before we know the field resistance. Hooking the field to too low a voltage can cause the motor to overspeed and come apart. (bad)

Eric

Each motor has two fields. F1 and F2 are sperate fields. So the resistance between C1 and F1, and C2 and F2(same field) is between 1710 and 1780 ohms for the three motors. Is this "split field" going to cause a problem?

This topic is totally out of my league( but I'm interested :) ), but I can't imagine not using one field at all. Would they not have to be hooked up in parallel? This effectively cuts the resistance in half (or something) does it not?

The guy I bought them from pointed me here:
http://www.mae.ncsu.edu/courses/mae732/shih/00_motors.pdf
And told me to look at page 7 - shunt wound motors. These motors have their fields and armature wired in parallel,but surely then there would be a resistance between the two fileds? I understand a lot less than you, belive me!

2 equal resistors wired in parallel will pass twice as much current as a single one of those resistors, so this is the effect I am thinking about.

So split field is another term for shunt wound is it? Could be, news to me.

I'm thinking these motors would make better spindle drive motors than axis motors. I have this shunt wound DC motor and drive on my big cnc lathe spindle. It has a rather pricey Baldor drive to run it.

I'm thinking ahead to what kind of servo drive you're going to need to run these. This type of motor design allows control of the motor speed by using a rheostat (variable resistor) to vary the field voltage. This is if you connect the fields and armature windings in parallel as the diagram shows.

However, most servo drive amplifiers output a variable voltage which is the main supply for the motor. So, if you decrease the voltage to both the armature and the fields at the same time, what happens to the speed? Nothing? You simply lose torque? (I'm theorizing).

So this would be where you need a pretty intelligent drive amp to actually control the field voltage seperately and directly (no rheostat), on the basis of a +/- 10 v input signal (from your computer).

There is some other member of these forums that seems to be quite knowledgeable about this kind of stuff, let me see if I can find his name: Mariss Freimani

What you would do is hook the field up to a fixed power supply, and then vary the armature with a gecko. This would effectively make it like a permanent magnet motor. The problem is the gecko is only good for 80 volts. It may be easier to buy some different motors. Still, these may be fun to play/learn something with.

BRB

Eric

Thanks for the help guys, Hu, what you said makes some sense with what i have read on various types of motors, but yeah, the shunt thing doesn't quite fit. If you could find out the name of the "guy who knows", that would be great. - wow quick! I'll PM him later.
Balsaman, are you suggesting to use just the one field? Please excuse my ignorance!

It seems that the field coils need ~140 volts DC to draw 80 ma each. It's possible that they should only draw 40 ma each for a total of 80 ma for both, in which case they need 70 volts. Anybodys guess. I am not sure why there are two. I would wire them in parallel and hook it all up to the 24 volt supply and see what happens. Watch that it doesn't go too fast.

Eric

Originally posted by balsaman
What you would do is hook the field up to a fixed power supply, and then vary the armature with a gecko. This would effectively make it like a permanent magnet motor. ~snip~
Eric

Good thinking, Eric. :)

About the runaway motor condition if the field current drops to zero (broken wire or whatever): I think the plan there was to run the field current through the holding coil of a solenoid which controlled the main contacts for the armature current. Thus ,the power circuit to the armature would be cut if the solenoid opened (which it would if any kind of a field circuit failure occurred).

Yes, that is how it's done. It's called a field loss relay, and is wired as you say, witht the coil in series with the field, and contacts in series with the armature. But for now that won't be required, and if it's ever hooked to a gecko, the drive will fault if the motor ever tried to run away, which shuts the motor down anyways.

Eric

*/Rant mode on/*
Grrr, how annoying! I sent my motors off to a friend of a friend to be tested at 80v (for possible gecko usage), and they came back with a note today. They work fine, they were tested with the field coils connected in series, so reversing the polarity here will reverse the direction, but the annoying thing is that he had no way of testing the torque, so it just says, "You get good torque at 80v, but I'm not sure if it will give you the 200 oz-in you were looking for as I have no way to test it". So, do I go out and buy the necessary gear to test the motors, or search ebay for new ones! Hmm, it's a no brainer, I'll get the shopping list out!
*/Rant mode off/*
Anyhow, All I have is a 24v supply, so I'm gonna test with that. Can someone please confirm the test setup is safe!
Coils 80ma @ 24v
Armature 1.5A @ 24v
Obviously I'm going to need some nice resistor to regulate the current, but to adjust speed, I adjust the armature current, right?
Balsaman has scared me a bit with the thought of them coming apart!! Thanks for putting up with me!

Kong,

Don't worry about it too much. Hook it up. If the motor runs away you will know it. It will sound like it's going way too fast, like as in faster and faster and faster. If it's sounding like a jet turbine, unhook it.

You don't need any resistors to test it.

As for torque, you will probably just need to use a belt reduction if you want to use it on a cnc router, which is very common with servo motors.

Eric

No resistors? I'm a complete noob at electronics, unless I get told howto! So I just hook up the coils in series, then to the PSU, and then hook the armature to the same PSU, and switch on? Just making sure they'll just automatically draw their rated current! Thanks man.

They will draw less that the rated current because 24 volts is less than the rated voltage. They will draw the rated current when hooked to the rated voltage. (the field that is). The armature will draw the rated current when the motor is loaded to up the rated HP.

Eric

Thanks Balsaman, tomorrow be D-Day! Now I gotta find something heavy for them to push!

So how did it go? :)

Arvid

Lol, they are under my workbench! I bought some brand-new old stock of 24v 360 oz/in servos shortly after I bought these ones, so they remain in the box they came in! They were tested though, with a 60v supply, but thee wasn't a lot of torque there at that voltage. they are 220v, so the drivers for them would have beed expensive.