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  1. #1
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    Default Treadmill motor controller - will 220v scr be ok? Inductors needed?

    Just watched a video on how to control a treadmill motor with an SCR triac based speed controller and a bridge rectifier.

    Will the 220v ones for the US market work OK?
    https://www.ebay.com.au/itm/AC-220V-...wAAOSwk1JWd8W3

    Should I add an inductor to the treadmill motor lead? He suggested it in the vid. I'm just not sure on a source or Henry rating.

    Here's the vid. Took quite a bit of reading to understand TRIAC's.... Just remember TRIAC controller means it gives you AC voltage out, it doesn't convert it to DC.
    https://www.youtube.com/watch?v=_NmAFZMAfH8

    Thanks.

  2. #2
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    Default Treadmill motor controller - will 220v scr be ok? Inductors needed?

    The youtube video features a TRIAC based controller, whereas the controller in your link is SCR based. TRIACS are bidirectional whereas SCRs only pass current in one direction.

    I suspect these controllers are really designed for dimming lights, but the manufacturer or seller is passing them off as being suitable for controlling motors. Proper motor controllers are much more complex than light dimmers. It may work, but I don’t think it will work very well, nor last very long.
    Chris

  3. #3
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    Default

    Hi,

    You really need to allow for double the peak voltage that will be applied to the triac or thyristor ! So for a 220 volt mains supply that would be 220 X 1.414 = 312 volts peak. A triac rated at 600 volts or greater will be OK.

    I would not just add an inductor in the mains supply, you could get into all sorts of trouble doing that. I would recommend a proper mains filter. Something like these-

    EMI Mains Filters | Bulgin

    These devices have all the components that you need built in. Another source of a suitable filter is an old washing machine, all of them will have a mains input filter, usually fastened near or next to where the mains power lead comes in. Pity you are not in the UK, as I have boxes full of them. In fact I used one when I made my 4 facet drill sharpener.

    Both Triac's and Thyristors chop the sine wave such that only the power under the curve is made available at the output, the difference between the two is the Triac chops both halves of the sine wave.

    You should also fit a capacitor, say 1000pf at 1Kv across the brushes of the motor to suppress sparking and the associated RF interference.

    This web page might help.
    AC Motor Speed Controller Circuit

    HTH.
    Best Regards:
    Baron J.

  4. #4
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    Default

    There is always these

    https://www.ebay.com.au/itm/Input-AC...4383.l4275.c10

    The price concerns me as they are usually over $50.
    Gold, the colour of choice for the discerning person.

  5. #5
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    Default

    Have you checked the voltage of the treadmill motor, typically they are either 90V or 180V DC, I have a 180V treadmill motor powering my drill press and ended up using a 0 -180V version of a US made Kbic variable speed controller, very pleased with the end result.
    I was seriously considering a chinese made controller, but the Kbic came up at a good price so I went with it.

  6. #6
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    Hi Guys,

    It seems that most treadmill motors intended to be fed from 220/240 volt AC controllers are rated at 180 volts DC. This is not a problem because the losses in the controller and conversion to DC, unsmoothed DC I might add, become greater as the load on the motor increases.

    Sorry I have to go, No: 1 granddaughter has just arrived and is demanding my attention.

    Before I got ambushed, I was going to say that the simple circuit from AC Motor Speed Controller Circuit works very well.
    motor-speed-regulator-schematic.gif
    However I would still use a commercial mains filter to supply power to it. This one gets away with a 400 volt triac simply because most of the voltage is dropped across the motor. But note the components C1, R1, C2 and the choke L1. These components reduce arcing at the brushes of the motor, in turn suppressing radio frequency interference and protecting the triac from spike voltages which might damage it.

    The only caveat that I would add is to put the circuit into an earthed metal box or use a plastic box and a potentiometer with a plastic shaft, because the potentiometer is at mains potential.

    NOTE: There is no direct feedback of motor speed with this circuit.

    HTH.
    Best Regards:
    Baron J.

  7. #7
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    I'm no solid state electronics expert but that circuit looks suspiciously like a universal (AC/DC) brush motor speed controller, this type of motor is commonly found in mains powered hand tools - drills, angle grinders etc. the controller feeds AC to the motor, while I'm not 100% sure I think treadmill motors are DC only and if so this type of controller would not suit.

  8. #8
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    Wow, thanks. I just read about TRIACs (took quite a while from a high school knowledge of transistors) and now I want to understand that circuit.... Did you teach yourself or are you an electric/electronic engineer BaronJ?

    Yes familyguy I the one in the video was TRIAC based (AC output) and hence you need to rectify before the treadmill motor which are mostly I think DC.

  9. #9
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    I just watched the Youtube video, I believe commercial motor speed controllers have some form of feedback from the motor (back emf) to the controller, this feedback signal is used by the controller to help maintain a more constant speed regardless of the load on the motor. The Youtube video setup does not look to have this and while it does vary the speed of the motor, it may or may not work as you would like depending on the intended use, if you want it for a fan (constant load) then it will probably be fine but if you are thinking of say a drill press which will have a variable load depending on the drill bit size and also the amount of down force you are using to drill the hole then you may find the drill will start off at the right speed then slow to a crawl once you actually start making swarf - reason being the controller does not know the motor has slowed down and so can't compensate for the drop in speed.

  10. #10
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    Quote Originally Posted by familyguy View Post
    I believe commercial motor speed controllers have some form of feedback from the motor (back emf) to the controller, this feedback signal is used by the controller to help maintain a more constant speed regardless of the load on the motor.
    That's correct. As I said in my post above, proper motor controllers are much more complex than simple dimmer circuits. That's why I don't believe this will work effectively unless the motor will be driving a constant load.
    Chris

  11. #11
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    Thumbs up Motor Speed controller !

    Hi Guys, Happy New Year to all.

    I'll try to cover the points made in these posts.

    I said earlier.

    Both Triac's and Thyristors chop the sine wave such that only the power under the curve is made available at the output, the difference between the two is the Triac chops both halves of the sine wave."
    Whilst this is strictly correct, the output voltage is DC ! It is however a voltage that is falling from the point that the device switches on. In the case of a thyristor, the negative half of the sine wave is completely chopped off. In other words 'it is a rectifier' that is only switched on for part of the positive going sine wave input. In the case of a triac, it can be visualised as a pair of thyristors in parallel, in opposite directions. Each one only able to control one half of the sine wave.

    Familguy: Said quite correctly "I'm no solid state electronics expert but that circuit looks suspiciously like a universal (AC/DC) brush motor speed controller, this type of motor is commonly found in mains powered hand tools - drills, angle grinders etc."
    And I agree ! However, treadmill motors are brush motors. The primary difference is that they have magnets rather than field coils in them to provide a static magnetic field that the armature field pushes against in order for it to rotate. The second difference is that you only have to reverse the voltage polarity to reverse motor rotation direction. Hence the need to use a bridge rectifier from the output of a triac based controller to ensure that the correct polarity is fed to the motor depending upon the direction you wish it to rotate.

    Replacing the triac in the circuit I posted with a thyristor, would provide the treadmill motor with a variable DC voltage of one polarity. Indeed that voltage could be smoothed with a suitable capacitor.

    J3dprints: I'm an engineer, I hold various qualifications in electrical and mechanical engineering. Latterly a Bsc in Computing Technologies with PG. Software Engineering. Before anyone comments, yes I can program, but it is not something that I like to do, in fact I hated the rigidity of the methodology.
    I did specifically point out that there was no feedback mechanism in the circuit that I posted. However it could be added.
    You would need to be able to detect the effect of the load on the motor and there are a number of ways that this could be done, both mechanically and electrically. Strictly speaking there is some effect from the changing voltage across the potentiometer compensating for changes in motor load, but nowhere near enough to call useful.

    Familyguy, correctly identified the "back EMF" that I referred to above, as "changing voltage across the potentiometer".

    Chris, pointed out that the circuit would need to be much more complex to achieve load/speed stabilisation, and I agree ! The only problem is then it takes it further away from being a hobbyist project.

    I think I've covered the points made in this thread. I'm happy to clarify if needed.

    Thanks Guys.
    Best Regards:
    Baron J.

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