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  1. #1
    Hi Guys,

    I am trying to find out some information about driving a 7.5Kw dc motor in a bridgeport interact 1 Mk2.

    This is the plate on the same motor type (taken from an ebay listing)...

    Click image for larger version. 

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    The main thing here is that i have never come across this type of motor before and it has rather confused me (i thought it was just a lumpy 3 phase until i read the plate!), as well as finding info on it seems to be pretty hard too. The original driver is not working and I am trying to find out if there is an alternative way to drive this type of motor but without understanding what i am looking at, it seems impossible!

    Does anyone know of A) Data sheet for this type of motor (i can't find one online but maybe I am searching wrong!?)

    or B) a resource where i can find more information on how this is driven


    or C) (if we have any motor specialists around here) if it can run in different ways, like using an AC drive instead of a dc drive

    Any help at all here would be greatly appreciated, even if it is just "pointing me in the right direction"

    Thanks,

    Mort

  2. #2
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Wow, that's quite a motor - 4.7kW at 6000rpm. Problem is, you need to drive a current in both the armature (rotor) and the field (stator) and be able to vary current in one or both to achieve speed control. Simply connecting them in series won't be a solution, even if you had a controller to regulate the current.

    If you can't mend the original drive, you may be best to fit a modern induction motor and matching VFD. Are you likely to be doing that sort of power at full speed? It would be fairly shifting material.

  3. #3
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 4 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    I did see a brief discussion about these somewhere very recently, and it seemed to be there were a few of these motors around, but the drives were rare due to them being the weak point, with no commonly available compatible replacements.

    I'd be looking at replacing the motor, but I'm guessing these probably aren't a standard fitment, so options may be limited.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  4. #4
    Quote Originally Posted by m_c View Post
    I did see a brief discussion about these somewhere very recently, and it seemed to be there were a few of these motors around, but the drives were rare due to them being the weak point, with no commonly available compatible replacements.

    I'd be looking at replacing the motor, but I'm guessing these probably aren't a standard fitment, so options may be limited.
    I was kind of hoping I could figure out how to drive one without the existing driver. I have a lot of motors and drivers and such but this is a new system to me and i don't really even understand how it works so I have no hope of getting it moving!

    Would love to swap it out for a better (read as: easier to control) one but it just isn't in the budget right now.

    Thanks for the reply though!

    Cheers,

    Mort

  5. #5
    Hi Muzzer,

    No, i would imagine that even if i could get half that power from this thing it would happily do what i want it to do! It really confuses me that this thing is feed from 3 phase 400v into the controller but is a DC motor!!

    I have looked into controlling various motors before from brushless dc (esc type controllers) to VFD controllers for the normal 415ish type three phase stuff, but this one is extreme (from my personal perspective) and even just knowing where to start is a real issue!

    Cheers,

    Mort

  6. #6
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 4 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    In theory, driving one is a easy.
    You put some current through the field winding, then by controlling the voltage applied to the main winding (well actually armature), you control the speed.


    The 150VDC is the easy bit, and could probably be done using something like a suitable KBIC SCR drive that could control the current.
    The issue is the variable 400VDC at up to 20A needed to provide motion.

    SCR drives are pretty common, but normally limited to a couple HP, as their main use now is basic speed controllers running from single phase.

    You could possibly get away with one small SCR drive set to give the required field current (the current control is more important than the voltage), then use another 240VACinput/180VDCoutput SCR drive for the armature, but that would limit the possible speed, to under half the rated speed.

    There is also aspect that reducing the field current/strength increases speed for any given armature voltage, so it's a bit of a juggling act.
    I think in normal use, whoever specifies/installs the motor will decide what speed they'd like, and will fix the field current to give their desired operating speed.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  7. #7
    If "only half the power" would be fine for you, then there's maybe an easy option. Use a 230V:115V stepdown transformer/rectifier/smoothing cap for the field winding, and a PWM regulator run off rectified 230V AC for the armature - last time i looked for one these they were available as an off the shelf module from a few suppliers. This will only give you 325V tops on the armature but hey that's still 4000...4500 rpm and at least 75% power.
    Last edited by Voicecoil; 24-07-2020 at 08:41 PM.

  8. #8
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Years ago I had a controller for one of these wound field motors that had no active controls in it. The stator had a fixed DC current generated by a bridge rectifier connected to the full mains voltage. I don't recall if there was a resistor or if the winding had an inherently high resistance - obviously you can't use its inductance when dealing with DC. The rotor current was controlled by a rotary knob. This turned either a variac or a rheostat, then the output was connected to the rotor via another bridge rectifier. The speed regulation of these machines is reasonably good in open loop, so it was adequate for the application which was moving a bogey on a large PTFE pipe convoluting machine.

    It was a very simple controller that worked fine until finally the insulation on the ancient motor windings broke down and the torque vanished.

  9. #9
    Quote Originally Posted by Muzzer View Post
    Years ago I had a controller for one of these wound field motors that had no active controls in it. The stator had a fixed DC current generated by a bridge rectifier connected to the full mains voltage. I don't recall if there was a resistor or if the winding had an inherently high resistance - obviously you can't use its inductance when dealing with DC. The rotor current was controlled by a rotary knob. This turned either a variac or a rheostat, then the output was connected to the rotor via another bridge rectifier. The speed regulation of these machines is reasonably good in open loop, so it was adequate for the application which was moving a bogey on a large PTFE pipe convoluting machine.

    It was a very simple controller that worked fine until finally the insulation on the ancient motor windings broke down and the torque vanished.
    I have 2 similar things sitting in the workshop, made by my late father for his watchmakers lathe & a mini pillar drill which were powered by Croydon 230V DC shunt wound motors - they use a variac to vary the armature current, the field current is set by the winding resistance which is in the high hundreds of ohms IIRC.

  10. #10
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Quote Originally Posted by Voicecoil View Post
    If "only half the power" would be fine for you, then there's maybe an easy option. Use a 230V:115V stepdown transformer/rectifier/smoothing cap for the field winding, and a PWM regulator run off rectified 230V AC for the armature - last time i looked for one these are available as an off the shelf modules from a few suppliers. This will only give you 325V tops on the armature but hey that's still 4000...4500 rpm and at least 75% power.
    Nice idea. You'd need to check if the field winding has enough resistance to limit the current to the required level but it looks as if it might be about right.

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