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  1. #16
    Join Date
    Jun 2005
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    Townsville, Tropical Nth Qld.
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    225

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    Simon, Mag-pro in Melbourne has them @ $290, good starting point. BTW, anything out of China/eBay, is now taking 2-4 weeks.
    Rgds,
    Crocy.

  2. #17
    Join Date
    Aug 2011
    Location
    Melbourne
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    Thanks Crocy. That's a pretty good price if I go down that path.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #18
    Join Date
    Aug 2011
    Location
    Melbourne
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    Hi Baron,

    Here's another pic. Sorry it's best I can do for now. It's been a busy few days for me.

    I'll remove the board tomorrow. No big deal to remove the board and cut the wires as the board is a throw away anyway but I will need it for a template for where to place the micro switches if I choose to make a new board from scratch. Btw I've also emailed servo products on the off chance they may still have a copy of the PCB artwork. Remote chance but worth an email.

    Another option I have thought of is replacing the motor with a 250 watt DC motor from eBay. And buy a simple DC speed controller. Speed controllers are so small I think I could stuff it in the existing case and retrofit the DC motor as well. The power feed would look no different on the outside.

    A new board holding the micro switches would control direction as original.

    In the second pic you can see the brushes. They are brand new. I had already spent about $50 in parts for it from the US. Some parts are still available since they are used on later models.

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  4. #19
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

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    Hi Simon,

    From those two pictures I can't see any reason to want to replace the board, obviously I cannot see underneath so my opinion might be different. The motor windings look to have been getting hot at some time in its life, so the first thing would be to confirm that the motor is sound.

    Check the winding resistances, check for shorts to the frame. Put the armature back in and ohm between the brushes. You are looking for shorts and opens. You will get the values jumping up and down as you turn the armature, so look to make sure that the brushes are square on the commutator segment for each reading. Mark the shaft because you only need to rotate the armature 180 degrees in order to check every one.

    Lets see where this takes us.
    Best Regards:
    Baron J.

  5. #20
    Join Date
    Aug 2011
    Location
    Melbourne
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    Thanks Baron. That makes sense. I'll give it a go and report back.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  6. #21
    Join Date
    Aug 2011
    Location
    Melbourne
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    Hi Baron,

    Ok. The armature windings returned a DC resistance of between 4.0 - 4.3 ohms in every position.

    The field windings returned a DC resistance of 1.2K ohms.

    I don't have a megger but with my multimeter set to the highest setting (Mega ohms) it returned open circuit for both armature and earth and field winding and earth.

    I have cut the wires and freed the circuit board. You will notice a few of the wires are not original, I replaced those last time I had a crack at fixing it.

    Also one of the limit switches (one on LHS) is cactus. Does not switch. Looks over heated.

    Hope this helps..

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  7. #22
    Join Date
    Aug 2011
    Location
    Melbourne
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    Hey Baron,

    further to my last post, I'm a bit confused. looking at the circuit schematic it shows both a field winding and a shunt field yet physically looking at the motor and field windings, there are only 2 wires coming out. I can only assume that the motor has been changed over the years and it no longer has a shunt field?

    I think I'm only just realising why I may have been confused when looking at the circuit schematic when attempting to repair the wiring.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  8. #23
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    6,439

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    Hi Simon,

    You beat me to that one I was about to ask where the other two motor wires were !

    OK can you reassemble the motor so that you are able to apply a few volts to it. The field winding will be connected in series with the brushes. It doesn't matter at this point which way round they are connected. In the absence of a variable voltage PSU, I would start with 12 volts from a car battery or similar.

    All we are doing at the moment is making sure that the motor is sound.

    As far as the micro switches are concerned they are a fairly common one. You might actually find that the rollers will transfer from the old ones to the new ones. I tend to agree that the circuit board is in poor shape. If you want to go down the path of making a new one, I would carefully strip the components from the board and use it as a template for a new one.

    Circuit wise modern components would easily replace a lot of what is in there, indeed a triac could be used to replace the thyristors, though their equivalents are available.

    Anyway let's make sure that the motor is sound.
    Best Regards:
    Baron J.

  9. #24
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    Aug 2011
    Location
    Melbourne
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    Hi Baron,

    Ok so I connected the motor up. In series with a 12vdc supply battery to one brush other brush connected to a field winding and the other field winding to battery.

    Result: NOTHING!

    I then connected a variable 0 - 60v supply. Once again nothing. It drew about 20mA.

    I would expect the motor should be at least 150watts. But given the field windings are about 1.2K how would you get the required current draw if they were run in series?

    Are you sure the windings don't need to be excited independent from the armature?

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  10. #25
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Simon,

    That's a little disappointing ! I would have expected the armature to at least try and turn. However you are right the field coils are separately excited from the armature as shown in the diagram. I suggested doing it the way that I did for the easiest. I used to test 220/250 volt washing machine motors using 12 volts. ***

    Motor Circuit.jpg
    This is a drawing of the basic circuit taken from the diagram. The field coils are inside a diode bridge that is directly wired across the AC supply. The negative junction feeds a pair of diodes that in turn feed the armature via the direction switches. The other side of those switches is the variable voltage from the thyristors.

    The transformer simply feeds a low voltage to the thyristor gates to turn them on. Because the transformer is centre tapped the thyristor gates are fed 180 degrees apart. This means that the thyristors are switched on, only on alternate half cycles of the incoming AC supply.

    OK, connect the whole 60 volts across the field winding and try the 12 volts from the battery across the armature, and see if it runs at all. It should do.

    That motor would only be 50 to 100 watts I would think. Does it say anywhere, on a rating plate ? I note that the one shown in your picture says 120 v 2Amp 60 Hz yet the indicator lamp has a 220 V label on it. The thought occurs to me that the motor might only be for 120 volts and not 220. In which case the field windings would be somewhat stressed at 220 volts even inside a rectifier bridge.


    *** The Sinclair C5 used the Hoover washing machine motor on 12 Volts.
    Best Regards:
    Baron J.

  11. #26
    Join Date
    Aug 2011
    Location
    Melbourne
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    Hi Baron,

    Thanks for the explanation and circuit.

    Wrt the lamp, yes the lamp and circuit breaker are non genuine parts that I sourced locally. They needed replacing and from memory they did not appear on the parts list in the US as available.

    The unit runs on 110V via a step down transformer that is mounted in a case on the side of the mill. I figured even at 110V the lamp would still give some indication when switched on.


    I'll try wiring up the motor with separate voltages to the armature and field winding.

    Really appreciate your help.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  12. #27
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Simon,

    That neon indicator lamp might not even light on 110 volts. The resistor value inside will be way too large in value. The 2 amp circuit breaker will be OK though.

    Thankyou for the additional information about the transformer power supply. Is it an Isolated output, not an auto transformer. The reason that I ask is if the transformer has an Isolated output then you are not at risk of getting yourself between live mains and earth by using it to feed the motor field windings inside a bridge rectifier as I show in my picture.

    We still need to confirm that the motor runs properly before we start to spend more time on it ! If the motor is indeed bad then a new strategy is needed.
    Best Regards:
    Baron J.

  13. #28
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    Aug 2011
    Location
    Melbourne
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    Hi Baron,

    Connected the armature to one variable independent DC supply and the field coil on another supply. Nothing. It is evedent that the armature is energised because it becomes difficult to move or turn.

    Then if I connect the field windings, still nothing happens. There is current flowing through both circuits but the motor has no interest in turning. Are you sure this thing does not need AC?

    I ran out of time to test an AC supply but I hope to do that tomorrow.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  14. #29
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Simon,

    Its a universal motor, it couldn't care less about using AC or DC. In use it will have DC across the field and armature. The field will be a constant voltage because it is inside a diode bridge that is connected directly across the supply, the speed will be controlled by the varying DC voltage coming from the thyristors, the direction determined by the voltage polarity from the thyristors with respect to the polarity of the field coils.

    I've just measured the field winding resistance of a similar size motor salvaged from a Kenwood food mixer. Its field winding is only just under 100 ohms !

    I'm beginning to suspect that the field winding is basically open circuit. The fact that the armature is sticking to the laminations suggests that there is no magnetic field to push it away.

    If you are absolutely sure that you have measured the field windings resistance correctly, you could look for the link wire between them and then measure each coil individually.
    Best Regards:
    Baron J.

  15. #30
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    Aug 2011
    Location
    Melbourne
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    Hi Baron,

    I'll have another look. 1.3K seems high doesn't it.

    I would have thought it would be the armature that burns out, not the field windings, but I only guessing about that. I must admitt to having very limited knowledge about such stuff!

    I'm not sure what you mean about mesuring each coil individually. You mean in the field windings? I thought that would be one single piece of copper wire?

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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