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Thread: direct wire

  1. #1
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    direct wire

    ok I just 1 more question as you guys been there done that

    can you direct wire your lift meaning up down don/t work unless on overdrive

    so why can we not kinda hot wire it I know not the clearest but u guys know what I mean

    looked at used lift but scared to death I just screw up motr than I already have

  2. #2
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    Are you talking about the pump on a van lift? If you are, yeah you can if you are testing the pump. You just connect to the leads coming out of the motor. Make sure the polarity is correct.

  3. #3
    I'm guessing too. I have done toggle switches on a van. One open/closed the door, one lowered/raised the van, third one lowered raised the lift. Is that what you mean.

  4. #4
    Yes, you certainly can bypass and connect right to the motor, but for someone that's familiar with these type of systems it's usually not necessary.

  5. #5
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    no open and close door work great floding up and down great only way down and up work is hit the over driver emercency swith then use the toggle specifyly for down up and it will work

    then you shut emerecency switch off go to other switches to raise flod and close dr

  6. #6
    Sounds like what you are describing is a limit switch failure. They disable functions to enable "safety". But when they fail, they don't make it any safer. They just make it fail. Like RustyJames says, you don't need them if you know what you are doing. You can bypass them.

    Having said that, even the most competent people are still capable of operator error. Hence, I use all limit switches except the "door fully open" limit switch because I cannot access it to adjust it. It is there to prevent the lift from being deployed in case the "lift down" button goes on while the door is not fully open. You could crack a window that way. Fortunately, in my van, if the lift is deployed while the door is not fully open, the lift hits the door not the window. Hence, it's no problem to bypass IN MY VAN. It could be a problem to bypass IN YOUR VAN. Use your judgement which ones to bypass.

  7. #7
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    Quote Originally Posted by August West View Post
    Having said that, even the most competent people are still capable of operator error.
    And, don't forget that you may not be the ONLY person who twiddles with the switches! Someone "trying to be helpful" can end up leaving you with a mess ("I'm sorry! I didn't KNOW that I shouldn't have done that!")

    It is there to prevent the lift from being deployed in case the "lift down" button goes on while the door is not fully open.
    A smarter design would place the switch on the "underside" of the lift so that as IT (almost) hits the not-completely-opened door, it interrupts the power. That more directly detects the "problem" against which they are trying to protect. It also will tend to put the switch/detector somewhere that is probably more accessible (for repair/adjustment).

    It's like an obstacle detector for a garage door opener... if you shoot a beam of light across the door opening (typical for most sensors) and use that to determine when an obstacle is present, all you know is that "something is (or is not) in the beam of light". Instead, if you had a "tactile" switch/sensor on the underside of the door that noted when it HIT something, you'd get a more direct indication of an obstacle (because the door actually tried to hit it).

    [Imagine having the nose of your car pulled into the garage just enough to place it in the way of the closing garage door -- but, being up so high off the ground, the light beam sensor passes completely under it and indicates "nothing in the way"!]
    Last edited by automation; 09-28-2018 at 02:11 PM.

  8. #8
    Quote Originally Posted by automation View Post
    A smarter design would place the switch on the "underside" of the lift so that as IT (almost) hits the not-completely-opened door, it interrupts the power. That more directly detects the "problem" against which they are trying to protect. It also will tend to put the switch/detector somewhere that is probably more accessible (for repair/adjustment).
    If a safety device fails, the failure mode must be power off.

    For example, by placing a normally open limit switch - that is in series with the lift motor - at the end of the door track, power to the lift is normally off. Once the door reaches its fully open position, the limit switch will toggle to the closed position in order to enable power to the lift motor. In case the limit switch fails to toggle, power to the lift motor remains off, which is a safe mode of failure.

    Consider the second scenario. By placing a normally closed limit switch - that is in series with the lift motor - at the bottom of the lift, power to the lift is normally on. Once the lift touches something (the door if it is not fully open), the limit switch will toggle to the open position in order to switch off power to the lift motor. In case the limit switch fails to toggle, power to the lift motor remains on, which is not a safe mode of failure.

    The limit switch is much more convenient at the bottom of the lift. But it's safer to put it at the end of the door track. Safety and convenience tend to work against each other.

  9. #9
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    Quote Originally Posted by August West View Post
    If a safety device fails, the failure mode must be power off.

    For example, by placing a normally open limit switch - that is in series with the lift motor - at the end of the door track, power to the lift is normally off. Once the door reaches its fully open position, the limit switch will toggle to the closed position in order to enable power to the lift motor. In case the limit switch fails to toggle, power to the lift motor remains off, which is a safe mode of failure.
    You've only considered one possible failure mode.

    Consider: Armature on NO switch at end of track gets mashed by door closing hard on it (e.g., spring in switch fails). Or, some part of mechanism involved manages to hold switch "actuated" (i.e., circuit completed). Or, some DIYer bypasses the switch because its been "acting up" and inconveniencing him. Switch mistakenly (and continuously) indicates door is fully open -- even after door has been closed. Nothing tells the user that the switch is still supplying power to the lift motor because the lift motor has stopped at its end-of-travel (up). User mistakenly activates control some time later, lift gladly attempts to open into closed door.

    Designing safety mechanisms is difficult as one has to consider how a device is likely to fail, how it can possibly fail, how it can be subverted and the probabilities of each of these events. Then, determine the costs associated with each such failure (for an "expected value" analysis).

    I design commercial process control equipment as well as consumer kit -- each of which can expose the user to conditions that can injure or kill (and, the manufacturer to lawsuits). You not only have to consider what can likely happen but what could potentially happen, esp given "human nature".

    [I once cinched a job interview by bypassing a key security feature of a device (whose primary role was security) while the client was demonstrating it to me. "Hey, you're not supposed to unplug that cable!" "Then, why did your design LET ME?? Or, more importantly, why did your security rely on the cable being plugged in?"]

    E.g., one reason smoke detectors are often prohibited, by Code, in kitchens is because of the number of false alarms that tend to arise ("Dinner will be served at the sound of the smoke detector"). False/nuisance alarms lead to users, being "human", removing the batteries from the detector. Now, they have the appearance of protection (the detector is still up there on the ceiling) but without any actual protection!

    You can also have instances where things are improperly repaired or installed -- and the fault not immediately apparent. This is particularly an issue in cases where a DIYer can opt to tinker with things (to avoid the cost/inconvenience of a service call).
    "Damn, this switch is broken and I can't get into my van! Let me just BYPASS it so I can go to the store, NOW..."
    Thereafter, there is nothing to remind the user that he is operating in an unsafe condition -- because most mechanisms aren't smart enough to notice their own dynamics:
    "I would expect the switch to open at some point, yet it hasn't in 27 door open/close cycles!"

    For a van lift, you have several mechanism states to consider:
    • door fully open
    • door fully closed
    • door somewhere-in-between
    • lift fully retracted (up)
    • lift fully deployed (down)
    • lift somewhere-in-between
    • user control calling for up, down or neither


    The "controller" also knows whether or not it is commanding the lift up or down or neither. A trivial set of rules for its operation would include:

    • Do not allow the lift to be commanded down (deployed) unless the door is fully open.
    • Stop the "deploy" motion when "lift fully deployed" has been sensed.
    • Stop the "retract" motion when "lift fully retracted" has been sensed.


    [A "paranoid" controller may not allow any lift motion while the vehicle is "not in park"/stopped. And, could also potentially prevent the vehicle from being moved while the door is open -- which may or may not coincide with the lift being deployed. This level of paranoia is often not desired as it leads to the "smoke detector" syndrome: "Crap, I can never move the van to better align the lift with the cut it the sidewalk after the lift has started to deploy! I'll have to fix that!"]

    A smarter controller goes farther than this simple "static" set of rules. It knows that the "fully retracted" switch should "release" (unassert) shortly after the controller commands the "deployment" mechanism to reflect the "lift somewhere-in-between" condition. It also knows that this should occur before the "lift fully deployed" sensor signals (asserts). The reverse series of events occurs when a deployed lift is retracting.

    Failing to detect the proper SEQUENCING of these signals should cause the controller to fault: "The information received from these sensors is not consistent with the mechanical design of this lift mechanism!"

    Additionally, it should be able to determine WHEN each of these events are likely to occur -- because it has watched the mechanism go up and down for the last umpteen cycles and can time these events: "Deploy mechanism has been engaged for 15 seconds and the mechanism still hasn't signaled "no longer fully retracted" -- which, normally, it does after 8 seconds of motion. Stop the mechanism as it is likely being damaged by this action. (something is bound up)"

    Or, "deploy mechanism has been engaged for 45 seconds. Not fully retracted sensed at 10 seconds. But, fully deployed has not yet been signaled and it normally asserts at 30 seconds! Stop the mechanism as something is wonky!"

    Note how this sort of smarts avoids the failure mode I presented: "Door has claimed to be fully open for 45 days! Hard to believe that to be true! Lift has been deployed and retracted 93 times in that interval..."

    We're no longer living in the days of hardwired switches, limit switches and motors. "Smarts" are often the cheapest and safest (overall) solution.

    [Of course, DIYers grumble because they can no longer work-around a failed controller! But, you can't work around a failed power module in your chair, either!]

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