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  1. #21

    Anyways, I disconnected the BOB from the VFD and I can get sensible measurements from 0 - 10v so it seems the BOB is fine, the output is not linear though.

    When connected to the VFD, no voltage again and the motor stops as soon as the meter is connected.

    Very odd.

    I did make a lookup table of speeds so I can easily set what i really want even though its not what it displays.

  2. #22
    If you only use a few speeds to cover your jobs I wonder if a relay module board with each relay connected to a trim pot and resistor pair from a 10v supply (each of which was fine tuned to give the right volts for that speed) could be used?
    I guess you would need a gcode command in the code to switch the right relay on instead of the speed command. Just a different take on it.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #23
    I have done a similar thing at work with an awkward interface for a temperature controller - works well.
    It used a 10 channel bargraph chip to take a 0-10v signal and convert to 10 adjustable resistance outputs using 10 miniature relays and 10 trim-pots - the relays were needed to give isolation.

    trouble with using Mach it would need multiple outputs to do it directly and thats not so easy.

    The bargraph / relay / pot system would work though - it just converts 0-10v variable into 0-10v stepped signals.

    I think the lookup table will work for now until a proper fix comes up.

    I see we have 15 spindle pulleys - could they be set up to do this?
    I'm not sure the ratio does anything when using PWM though.
    Last edited by Davek0974; 28-03-2016 at 08:37 AM.

  4. #24
    Having just come in from the shed doing very much the same thing:

    BOBs, or cheap ones at least, may not have a linear output from the PWM drive. I had very much the same experience as the OP.

    You absolutely should be able to measure the voltage at the VFD with a DVM/DMM/etc. If you can't, then I'd look for possible dry-joints (as you prod the terminals with the meter leads it may crack the joint open). Try prodding each terminal in turn with a single lead to rule out mechanical play. Other than that - hand-held or bench meter? (I'm wondering if a bench meter if you've got a grounded common line... unlikely, but I can't think of any explanation why, having confirmed not on current-input on meter, why you couldn't read the voltage at the analogue input to the VFD).

    What I can recommend as a very cheap alternative solution is one of the 2-pin USB/RS485 adapters (I picked up 3 for less than a tenner, UK) - use one to control the spindle (direction, speed, on/off) digitally, using the Mach3 plugin. (assuming HuanYang VFD).

    Or, google mach3 linearity.dat
    Last edited by Doddy; 28-03-2016 at 03:50 PM.

  5. #25
    It seems i can measure the 0-10v ok but only if the vfd is not connected?

    I now have a list of voltages to speeds and also a list of actual s commands to speeds

    I tried googling linearity.dat but all i can find is that you can delete it :)

  6. #26
    I had a mail back from CNC4YOU today, they supplied the BOB but not the VFD - I presumed my VFD was identical as they are both (supposedly) the standard Huyanyang 2.2kw items.

    Their tests revealed that voltage should definitely be measurable when the BOB is connected to the VFD, they even loaded it up a little with a 4k7 resistor and still got the 0-10v ok.

    So this issue points to my VFD being a bit iffy - it came from the usual guy on Aliexpress with all my other bits.

    Most odd, hopefully it won't damage my BOB?
    Last edited by Davek0974; 29-03-2016 at 12:06 PM.

  7. #27
    Lets have look at the VFD front Dave because some of the VFD look like Huanyang and use same shell but are not. Can tell at glance.

    Also you sure your using VI not AI. It's usualy 3rd terminal from right on bottom row.

  8. #28
    Hi JAZZ,

    Just got off the blower to my preferred UK inverter supplier, use them a lot in the day job, well used to anyway ;)

    Lengthy chat, helpful as always. Explained exactly what I was seeing and they had never seen that behaviour before!

    The fact that I can see 0-10v when disconnected indicates my control is working fine, the big question mark comes from the fact that as soon as you connect the signal to VFD and put a volt meter across it the motor stops as if the 0-10v was being shorted out - no volts are read. This was tested with two meters - a new(ish) Fluke DMM and a 1960's vintage Avo Mark8 - same results both times.

    A bit more chat with the VFD guy and as it was not behaving as expected, I decided to bin the Huanyang probably to eBay and ordered a new Schneider Altivar 12 sensorless vector drive for 115.

    My main concern was that something clearly was wrong in that VFD and knowing my luck it would end up in fried BOB and possibly more, usually on a Friday afternoon;)

    Should be here tomorrow and slot straight in hopefully.

    I can't relax when things just don't play together. Possibly the VFD is a clone, or has some minor parts missing from the inputs, expecting everyone to use the front panel pot for speed maybe, who knows.
    Last edited by Davek0974; 29-03-2016 at 02:15 PM.

  9. #29
    Messing with numbers...

    Seems pretty linear, no dips or bumps...

    Click image for larger version. 

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    Not centred at 5v / 12000rpm though - bit lower in the middle.

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