8-Wire Stepper Motor Current

[itsme]

Hi there,

I'm busy sorting out the power supply and current set resistors on my system, but have a query about the current that my motors should be set at. I have got G201 drives.

My motors are 220Ncm 8-wire motors with specs as follows (from the data sheet that came with the motors):

Voltage: 7.5V
Current: 2.5A/phase
Resistance: 3 ohm/phase

My question concerns the current rating of these motors. Is this current rating likely to be the maximum current for series or parallel connection? I am going to be connecting them up in parallel, but am unsure if my current should be set to 2.5A on the Gecko (if the maximum motor rating is for a parallel connection); or something higher than 2.5A, if this rating is for series connection?

I obviously don't want to fry a motor by setting the current too high, but I'd rather not set it too low either, and have too much unused potential in the system.

Thanks
Warren

[pminmo]

The rating is per phase, or unipolar rating. So for parallel it should be 1.4 X the uniploar rating or 3.5A.

[Oldmanandhistoy]

Originally Posted by pminmo The rating is per phase, or unipolar rating. So for parallel it should be 1.4 X the uniploar rating or 3.5A.

I have always been led to believe most new steppers are rated series on the name plate. Also when I have looked at the data sheets that come with them it will state name plate value as bipolar series.

Did you work out the rating type via the specs provided? I’m not contradicting your post but would be good to be corrected if I am making wrong assumptions.


Itsme

May I ask where you bought your steppers from?

John

[itsme]

Hi,

Thanks for the replies.

I'd also be interested to know how you go about figuring out what these specs are refering to. I am unclear on what the definition of a "phase" is. I thought that maybe 1 phase was refering to 1 "coil" in the motor (where these motors have got 4 coils or phases). I then thought that perhaps 2.5A per phase (or per coil by implication of my previous logic) would mean that if I connected the phases (or coils) in parallel, then I would be able to apply 5A to the combination of parallel coils and each coil would then receive the maximum of 2.5A. Clearly my reasoning is flawed (and I had little faith in it) and that is why I asked this question here. I did not bring unipolar ratings into the picture, and I guess all my thoughts have been based around simple DC circuit theory. That is probably where my reasonaing has all gone wrong.

John, I got my steppers from Arceurotrade. These are the steppers that are going to be powering my XJ20. I am just getting ready to buy the power supply. For the time-being, I am going to base all my calulations on 3.5A for each motor. I have faith in you, pminmo !

Thanks again
Warren

Sorry, one last thing just out of interest. What would the current have to be set to if these motors were going to be wired in bipolar series mode?

[pminmo]

Originally Posted by Oldmanandhistoy I have always been led to believe most new steppers are rated series on the name plate. Also when I have looked at the data sheets that come with them it will state name plate value as bipolar series. Did you work out the rating type via the specs provided? I’m not contradicting your post but would be good to be corrected if I am making wrong assumptions. John

I possibly could have mispoken, I assumed the post said 2.5A/phase as a unipolar rating.

Seems like some manufacturers or distributors aren't putting nameplates on the motors. And even if they do, they may decide to put the information on the nameplate as they see fit. Bottom line, try to get the motor specification from the manufacturer.

Basically the relationship is:
Bipolar parallel current would be 1.4 * unipolar rating,
Bipolar series would be .7 * unipolar rating.

Phase current would be the total current as the drivers see it, not necessarily as the coil sees it. For example a 2.5A/phase current on bipolar parallel wiring would split that in half as the coil current. In a unipolar, bipolar series or bipolar half coil wiring arrangement the phase current and coil current would be equal.

[Oldmanandhistoy]

Itsme

I bought some steppers from the same source some time ago and actually contacted them to check how they had rated them. I’m not 100% but I do believe they give the bipolar series rating on their website. I would shoot them an email and double check.

Pminmo

No disrespect intended I just wanted to clarify and double check what I thought to be correct.

John

[pminmo]

I just pulled out two Vexta PK266 motors:
PK266-02B nameplate says 3.6V 2A
PK266-01A nameplate says 7.4V 1A
Looking at Vexta's documentation: http://www.orientalmotor.com/product...XTA/StPk26.pdf

That is the unipolar rating.

[Oldmanandhistoy]

Originally Posted by pminmo I just pulled out two Vexta PK266 motors: PK266-02B nameplate says 3.6V 2A PK266-01A nameplate says 7.4V 1A Looking at Vexta's documentation: http://www.orientalmotor.com/product...XTA/StPk26.pdf That is the unipolar rating.

I was not saying you were incorrect but the last 3 different stepper motors I have bought where not rated unipolar. The specifications came from the seller not the manufacturer. Two of the steppers had name plates on them stating series spec and one did not have a name plate. I think the seller should probably stick with the manufactures data sheets but think they use bipolar specs because most drives now sold are not unipolar.

John

[pminmo]

My gut feel is that there are sellers/distributors that are buying motors without nameplates from the mfg to put their "Own" name on the motor via a nameplate and putting info on it as they see fit. On the flip side if you buy a motor from a name motor manufacturer with their nameplate on it it will be the unipolar rating.

[Oldmanandhistoy]

Originally Posted by pminmo My gut feel is that there are sellers/distributors that are buying motors without nameplates from the mfg to put their "Own" name on the motor via a nameplate and putting info on it as they see fit.

I hope not but now you mention it some of my motors do get a little hotter than I would like even when run under their Amps rating. So you might just be onto some thing there.

John

[itsme]

Hello,

It seems this confusion is not limited to me. I'll contact Arc to see if they can give me some more details.

The datasheet that came with the motors is produced by Arc, not the manufacturers. They give details of how to wire the motor for unipolar, bipolar series and bipolar parallel, but there is no mention of what the specs are for. It really would be useful if the suppliers would provide this information.

I'll report back to this thread when I have more details.

Warren

[pminmo]

what is the P/N of the motor? Webpage?