Treadmill safety. Full speed when switched on.

Discussion in 'General Electronics Chat' started by zariq, Jun 28, 2016.

  1. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Hello.

    About three months ago my treadmill started blowing fuses as soon as it was switched on.
    I replaced a few components and got going. The link to the thread is at end.

    A few days a go the treadmill was being used by my wife at a steady walking pace and suddenly
    it went full speed. The top speed is about 12 mph. If you have seen videos of people getting
    thrown across the room by treadmills then you know how dangerous falling on a treadmill can be.
    The only reason she didn't fall off is because she had her both hands on the hand rails.

    What I would like to ask is do treadmills have some safety feature to prevent this happening?
    If they don't then how are they allowed to sell something that could injure or even kill. Thanks.

    http://forum.allaboutcircuits.com/threads/treadmill-motor-control-board-keeps-blowing-fuse.122671/
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It could be detected using a small micro as most have some form of rpm feedback, but that fact that it has happened on more than a few of occasions seems to indicate not all manuf. build this in.
    Max.
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,778
    1,205
    Which components did you replace? -- It seems reasonable to conclude that the described power-up over-current condition owed to excessive inrush secondary to abrupt full excitation of the motor? - Were your findings consistent with said assumption?

    FWIW (assuming the 'tread motor' is of the 'brush commutated' topology) I've observed similar malfunction in an automated lathe -- upon examination, the difficulty was traced to failures in the bridge owed to 'commutation spikes' (inasmuch as surge absorbers placed in shunt with the motor solved the problem)...

    In general yes - Howbeit said features have their limits - as, for instance, when all control of the motor is lost owing to failed (shorted) switching device{s} (which being, for obvious reasons, most common in 'half-bridge' arrangements) - Good safety practice will implement over-speed protection via redundant AV detection in conjunction with a dedicated mechanical interrupter (e.g. an EM rely, etc) in the motor circuit -- Sadly, such 'conscientiousness' is seldom seen in consumer-grade products:mad::(

    Best regards
    HP
     
  4. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1

    Thank You Max. would think they would build it in for the sake of users safety and to protect themselves from lawsuits. Most people would
    pay extra if it was available as an option. I'm surprised the health and safety regulations don't require it.

    This particular fault seems to be same as the previous one. The first time the fuse was blowing before the belt had time to move
    but this time the fuse didn't blow and let the full power through to the motor.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    In the case of a failed/shorted semi, it takes the fuse out before any power to the motor, but if you have a full-on condition at switch on then the motor is going to take off.
    Fusing it a bit tighter might work as then the inrush may take the fuse out.
    Max.
     
  6. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,778
    1,205
    --Emphasis added--

    Re: the latter failure; the motor was already operating (albeit it at a lower AV) and, hence, generating 'back EMF' - thus reducing inrush attendant to acceleration...

    A properly designed over-speed /over acceleration fail-safe does not rely upon OCP devices alone!

    Best regards
    HP:cool:
     
  7. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Thanks for your comment. I replied to Max before I saw your comment. Yes it is sad. If given a choice, then the cheapest or most profitable solution will be chosen. Where public safety is concerned, it shouldn't be left to choice. I changed the bridge, mosfet, current limiter and a diode next to the mosfet. Not all needed changing but I did anyway. If you take a peek at the original thread from April, you will understand why the rest of your post flew over my head.
     
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  8. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
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    By tighter do you mean lower value?
     
  9. ISB123

    Well-Known Member

    May 21, 2014
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    Yes he does.
     
  10. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Thank you.

    When my wife managed to get off the treadmill in one piece, she took out the safety key and unplugged it. Later I
    plugged in the wall socket and when I put the safety key in the thing jumped straight to full speed. It kept running for about
    three seconds then I saw a flash from the motor compartment. When I saw the flash I pulled the safety key out straight away.
    There also was a burning smell coming from it. I have had look at the motor control board and the fuse is black and seem
    cracked, so is likely blown.

    Lowering the fuse would most likely stop it going full speed, but as things are I would needs to change some of the components
    I changed three months and about 15 hours of running time before. I believe that even if I got it going, the fault which is causing
    this to happen would still be there. The reason I decided the repair it in April and not buy a used motor control from Ebay was
    that I saw it as a good learning opportunity. Learning opportunities are good but not worth a visit to the hospital. The reason for
    this thread was to highlight the safety aspect of treadmills and I thank you all for your comments. I have another couple have
    questions that I will ask once I work out what to write.

    Thank you.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It may also blow before it takes out any more S.S. components, as a safety precaution you could start with fast-blo fuses if slow-blo are used presently.
    Max.
     
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  12. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Missing speed feedback can cause this, shorted FET/Kickback set, bad storage caps can allow control voltages to become erratic so comparisons also become invalid, speeds, checks, .. If this is the same board as in the listed post, have those large capacitors been replaced?
    Also, not sure who may have mentioned lowering a fuse rating may lower your motor spin, not much on that idea, as either will blow.
    You can check D2 (Surge Supressor near the Bridge) for burns or issues, but this too, will short when fired to save further circuits. If this D2 shorts you will rip fuses each time the safety relay engages. This controller should be replaced with a newer style of control board similar to the JDY02 series. If the PIC chip on the little daughter board takes a dump, that board also becomes junk ;o( The PIC chip was usually potted, or covered with hard black glue or epoxy.
    Good Luck!
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    The OP himself!
    Max.
     
  14. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Hello everyone.

    Sorry to revive an oldish thread. Since it has been a while, I will mention some of the main points.

    In April my treadmill started blowing the internal 10 amp fuse when turned on .
    After replacing the bridge recifier, the inrush limiter, the mosfet and diode, it started working again.
    After two months, while it was in use, it jumped from 5 mph to full speed instantaneously. The person using
    it managed to stay on it and stopped it by pulling the safety key. When I put the key back in, it ran at full
    speed for a few seconds before blowing the fuse. Once it starts blowing fuses, then it will keep on blowing
    fuses when switched on.


    I changed the mosfet again in August and it is working fine. Since then, I have switched it on a few times
    to verify it is still working, but it hasn't been used. I can't bring myself to let
    anybody use it, and since it is working, I would rather not pay someone to take it away.

    before disposing of it, I would like to ask if there are any other options. At the moment the only way I could
    see the machine getting used would be if it was unable to go faster than about 6 mph under most circumstances.


    Would a 80 or 90 volt pwm controller from ebay or similar do the job? My thinking is that if the treadmill is run with
    reduced voltage then, in case of full speed type failure, the tredmill wouldn't have enough power available to attain dangerous
    speed. These motors do run on reduced voltage, but would it run long term without being damaged? I suppose choosing the voltage
    would be a guess and the transformer for the dc power would be quite expensive.

    Motor details.

    DC Motor
    Greenmaster GMD82-06-2B
    1.75 HP continous duty
    180 DC max input
    4800 rpm

    Thanks.
     
  15. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Hi There...you didn't mention the manufacturer of the treadmill, greenmaster may make me think UK? There could be a positive reason for the HexFET blowing again, and I wonder ...did you find the exact replacement parts when you replaced them the first time? The UK would mean 400v Storage Capacitor(s) on that control board, were they also replaced? How about what might that motor control board look like?
    The Large Capacitors you see on the motor control boards are the main storage capacitors for the motor power rail. These caps are worked very hard in most control boards due to the costing and meeting "price points" against competing brands. It's a truly ruthless world in some manufacturing sectors, fitness being one of them. Back to these caps, these fail often. They degrade heavily and loose capacitance as they age. The loss of capacitance on that high-power motor rail will cause the FET and motor power rail parts to see much higher currents at peak and hot use, and will exceed breakdowns, overheat and struggle to deliver motor drive current without reaching/latching into a current-limit situation, which never happens in your case and the tread takes off at dangerous speeds. As a rule, if you service electronics, you will pay very close attention to most electrolytic capacitors, as they "hold up" a lot of power-points in circuits, they do degrade, it pays to replace them with high-temp/high-hour caps instead of general purpose caps.
    To answer the question of using a different controller, the thought is right on track, although the voltage needed to get that motor turning is not much at all, it is the issue of "pushing" that walking belt as the human foot hits the tread, then, expanding the PWM to increase motor current during the foot-to-deck period, then a tiny period of lighter force and the next foot centers on the tread, pushing the tread onto the deck, relying on the lubricant under the tread to "slide" to produce a walking-tread. Yes, you could control incoming AC via a large variac or rheostat, then rectify this, and pass it onto the motor, but you would still need hold-up capacitance on the power to that motor due to the increased drag when someone walks on the deck, that motor current jumps to push the foot, and also "watches" the front roller for tread-speed, via a reed-switch mounted near the roller and a magnet in the drive puller on the roller. this also adjusts the pwm to maintain speeds.
    Post a pic and someone may know the board? Have a great one!
     
  16. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Thank you lamJatinah

    Yes I am in the UK. The treadmill is a Reebok Edge. The board has 1 large 390 microfarad 400 volt capacitor for the high voltage
    side and some smaller ones for the board power. I didn't replace the large capacitor because I couldn't find one like it at the time.
    The original mosfet and diode are obsolete and were replaced with manufacturer recommended replacements for those parts.
    the replaced the 3.3 ohm inrush limiter with a 4.5 ohm.

    At this moment in time, I don't see a benefit in replacing the capacitors or anything else, as it would not achieve anything.
    the board is working as it is, and it would still be working after replacing some components. I think replacing components would
    not remove the thought that it could fail at any time.


    I understand the bit about maintaing speed under varying load,and it would be a problem if running. I am happy to accept a decent paced
    walking speed. Would varying speed still be a problem under those circumstances. Since at least one foot is always in contact with
    the belt, then the weight on the belt shouldn't vary by much. When walking, different parts of the belt will have different amount of load
    on it, but the total shoul be roughly the same or is that not the case?

    My preference would be to find a basic circuit and build it as a learning excercise. Most I found online are 12 or 24 volt output.
    I'm not sure if such a big difference between the motor voltage and controller voltage would have the desired result.


    20160403_180907.jpg
    20160403_181036.jpg
     
  17. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    1,099
    It may be a trick of the light, but that dark-coloured disc (surge suppressor?) at top right of the first pic looks damaged?
     
  18. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    No, It's not a trick. That photo is from the first incident. The fuse kept blowing and I kept on replacing it in hope. Third
    attempt took a big piece of material out of it. Since then I replaced it with a new one. I should have uploaded a new photo,
    but it was very late in the night.
     
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    You will be OK if the part you replaced with are genuine.
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Appears to be a NTC rather than a MOV, wired in series with the load to take power inrush surges.
    Max.
     
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