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Thread: Suitable relay for three wire control on a VFD

  1. #31
    Join Date
    Jun 2017
    Landenberg, Pa
    I may have solution worked out, I had the same issue. It involves a $10 circuit I bought from amazon (intended for guitar amps, but it has the appropriate relay and it is cheaper than the constituent parts). Stay tuned. It works on my bench, just have to get it on the switch and VFD this evening. If it works, I'll post the details.

    Quote Originally Posted by Tom Trees View Post
    Hello folks
    I have been walking through the steps with another forum member on setting up a VFD for his saw.
    Unfortunately the VFD does not have a relay OR COMMON for three wire control/push button station.
    Can any of you guys point me in the right direction to find a suitable relay for him?

    Any help would be much appreciated.

    Many thanks in advance.

  2. #32
    Join Date
    Jun 2017
    Landenberg, Pa
    Ok - my VFD is a cheaper model, Isacon or Askpower. The trigger to turn the motor on and off is a simple matter of closing a circuit between a lug marked GND and a lug marked FWD. One can also close the circuit to a lug marked REV to run in reverse. The control lugs on my VFD have a +12V source and a +5V source. No options for three wire control. I offer the following solution if your VFD is similar.

    Here's the solution, and maybe this will work for those that have a cheap VFD like mine without three wire control built in.
    I bought a small relay assembly really meant for guitar amps, etc, with multiple headphone connections (or so my friend says). Click link for a source to buy it. Cheap, $13 to my door.

    Here are the wiring diagrams for the relay board.

    Check out the image on the purchase site. You'll see the board features two resistors, a transistor, and two more resistors.
    We unsoldered the transistor, simply jumped that connection on the top of the board, and removed the bottom two resistors, effectively deleting everything from BC517 on down (see wiring diagram). The resistors really can stay, but they were in the way of manipulating the resistor so we took them off.

    From there, here's what you do:

    I identified the start/stop/common wires on the saw nose button switches with my multimeter. This is best with a second set of hands - one must identify the start wire, and then to identify the common, you need to be able to press both buttons at once while interrogating with the multimeter.
    Connect the +12V output from the VFD to the switch common wire.
    Connect the start button wire to the VCC connection on the board.
    Connect the stop button to COM1 on the board.
    Connect COM2 to the VFD GND lug on the VFD control lugs, and also bridge COM2 to the GND on the board.
    Bridge NO1 on the board to VCC on the board.
    Connect NO2 on the board to the VFD FWD control lug.
    I set the VFD to accept the buttons for start/stop - on my VFD, it was parameter Pn04 = 2, and reverse is disabled - on my VFD, it was parameter Pn05 = 1.
    And - BINGO. Start starts the saw, stop stops the saw. Yay. The relay on the little board takes the input from the start button and closes the link between GND and FWD. The relay opens again when you hit the stop button. Exactly as one would get from the three wire control on the magnetic starter.


    Quote Originally Posted by William Chain View Post
    I may have solution worked out, I had the same issue. It involves a $10 circuit I bought from amazon (intended for guitar amps, but it has the appropriate relay and it is cheaper than the constituent parts). Stay tuned. It works on my bench, just have to get it on the switch and VFD this evening. If it works, I'll post the details.

  3. #33


    Sorry, I'm so late to reply back guys, this has been a very interesting read.
    I wanted to do a wee bit of research on this before replying back to you knowledgeable folks, but couldn't get the time.

    David Buchauser,
    I have the wiring done as in the picture, I used to have the Huanyang VFD mounted onto the bandsaw,
    I actually had two on the bandsaw, the first I let the magic smoke out of bogging down the saw salvaging window frames cutting putty with a 1 TPI blade.
    my supplier of previous bandsaw blades were wandering on the tired old tires, so probably not the best idea to try cut next to putty, destroy the set and fight the drift.
    The motor got quite warm so it coulda been worse.

    I have an Isacon VFD on it now, as it has the auto shutoff cooling fan, and sometimes I use the bandsaw frequently throughout the day,
    so it's nice to have the peace...
    Absolute guess, but I'm under the assumption that it's good to have/leave it powered up and to treat the capacitors like rechargeable batteries.
    as I've read that some are left on 24/7, so the Isacon seems like a good choice to me.

    It was a mystery why the common/reset failed on my inverter because it was new, got no neglect and was just moved to the tablesaw a few feet away.
    I always wait for these units to thoroughly drain the charge from the capacitors before going near the input/output.

    My friend is talking with the supplier to try and sort out what's wrong.
    He has sent a video to the seller, but it's not very clear, and I think he's going to make another demonstrating the failed common/reset/relay
    using short wire to fit in video frame/eliminate variables like switches, and do so in the configuration and sequence that I have said..

    I have advised him to find some thin wire to make up four strands, a pair of these are squeezed into the common/reset/relay terminal.
    Demonstrating FOR to DCM exhibiting his saw working, ala... two wire control.
    Afterwards hooking/twisting the DCM(stop) to the common/reset.

    And then to start his saw strike the FOR (like a match) against the other thin common/reset wire, and keep it separated from the other wires.
    To stop the saw, pull apart the common/reset, and the DCM stop apart.

    I also said it would be a good idea to show that, Pd046 common terminal parameter was set to 14 (default).

    He has yet to get back to me on this.

    David L Morse
    That is genius!
    I thought had all those parameters sorted and never thought about the manual would have more interesting stuff in it.
    It seems even if the common failed, one could change the function of the terminal.

    FOR, REV, RST(common) terminals...and three other spindle terminals.
    I said to my mate it might be worth seeing if he could swap the FOR and RST terminals over, or if he was to be safer in regards to possibly damaging
    a terminal, to choose the REV terminal as the common.
    Maybe making sure the other reverse parameter elsewhere in the book would be disabled, might be a good idea.

    I responded or bumped my mates thread on a UK forum, and got a reply stating that a relay needs power to work and won't work independently.
    That must be why David Buchauser wanted to see my setup as he was going to draw a schematic for me. , thanks BTW : )

    Would these other ports have the capacity to power the relay/common/reset?

    Another thing is I must have a mooch around my inverters to see another source of a low voltage supply for this kind of thing.
    My saw is buried under stuff and I can't get to it to have a look.

    That sounds really interesting as I was thinking about getting another of the Isacon/Askpower drives of the same size and dimentions
    if I could get this niggle sorted out, It would be no contest, as who want's a noisy fan running? : )

    David L Morse's reply looked really promising, hopefully a common/reset/relay function can be allocated via parameters
    I am eager to find the manual for the Isacon/Askpower now.
    If that sounds all too much like wishful thinking, then your device sounds clever.

    Thanks for posting, I am eager to see how things pan out.
    Cheers folks

    Last edited by Tom Trees; 10-17-2019 at 3:13 AM.

  4. #34
    Join Date
    Feb 2013
    Tippecanoe County, IN
    Tom, look at the manual excerpt I posted. It shows exactly the three wire control you are trying to accomplish. PD0046 must be set to 04, not 14, for this to work.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  5. #35
    Thank you David
    I can't exactly understand why PD046 would be changed to stop instead of default reset, nor am I asking for an explanation,
    but if you say this is how it should work, that's music to my ears

    I will report back afterwards to see how it goes for him, after I give my mate an e-mail in a few minutes.

    I don't have access to pictures of the setup David, but have the manual from the newish Huanyang I bought, so will seek to find if I am missing something.
    Looking for the diagram of the control circuit terminals on page 11 and 12, and noticed that DCM is titled as ground in brackets, whilst RST is reset.
    I thought the RST Reset would have the ground in brackets. and obviously FOR is what it is.

    What's interesting is that ACM also has ground in brackets, with the description as common terminals of analog and control signals.

    Just for what its worth the picture I posted here and sent to my friend was confirmed that it was correct.
    That's not to say it means the only way to do it though from what you are saying.
    I just followed some instruction and have stuck to it since, so will look it up.

    Oops, I forgot to say to the other David
    I will suggest the latching push button switch for consideration , if any of this does not work or turns out to get complicated.

    Thanks again folks

  6. #36


    Great news! my friend had got his push buttons working.
    He swapped the function of the REV terminal to act as the RST/relay/common
    Changing Pd 045 to 4.
    Many thanks to you guys.

    This might be worth looking into on the Isacon/Askpower units.
    I was favouring these because of the fan shutoff control, if it can be programmed for three wire control it would be the winner.
    Although the Huanyang mod for the fan looks simple enough and cheap.

    I haven't found my Isacon manual to check out the parameters for three wire control

    Cheers for the help folks

  7. #37
    Join Date
    Apr 2017
    Tucson, Arizona
    Quote Originally Posted by Tom Trees View Post
    Great news! my friend had got his push buttons working.
    He swapped the function of the REV terminal to act as the RST/relay/common
    Changing Pd 045 to 4.
    Many thanks to you guys.
    Glad to hear you've got it working. I suppose that it sometimes pays to read the manual (when all else fails).

  8. #38
    Reading it is one thing, understanding what you have read is another matter
    I attempted to on numerous occasions, and got an instant glazing over look in my eyes.
    Somethings only make sense when you are knee deep in the trenches, so I suppose I shoulda had another look beyond the troubleshooting section.
    Easy to get tunnel vision by following the same instructions without question and never differing from what is the norm, as these things are complicated.

    I have posted this info in the comments on a few of the Huanyang videos on YT, so hopefully anyone who has the same issue will know what can be done.
    Thanks for the help David


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