Change BOB PWM signal to 0-10 V signal

[Sterob]

I continued trying to get my PWM to 0~ 10V converter working today and eventually gave up. I can't get any output from the converter and I assume that is why my VSD now won't start now. ( it has to see a 'on' command AND a speed voltage? )
I can detect millivolt changes on the input to the converter ,with my Fluke, so that seems to be working, but as I don't have a CRO I can't prove it.

I'm aware the input voltage range can be selected via the yellow jumper. The pot is for calibration of the output.
The vague chinese instructions infer that one can select 0-5V OR 0-10V output but don't say how. There are 2 unused pads on the PCB so I'm wondering if they need to be shorted...dunno. reluctant to short them out in case I do damage.

Has anyone used this particular converter?

In case its a dud, I've ordered another one...and a different one....

Steve



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[john-100]

what breakout board or controller are you connecting the PWM converter to ???

I have not found the instructions for the board but going by this photo found on the net

the yellow jumper selects one of two resistors to limit the opto-isolators LED current

330 ohms for a 5V PWM input which will be correct for most Mach3 breakout boards sold
or
2700 ohms for a 24V PWM input used by industrial PLC controls for example

with no other controls I can only assume the potentiometer has enough range to adjust the output to either 5V or 10V
with the PWM signal on nearly 100% of the time


seeing the 78M12 12V regulator on the board
I would expect the minimum input voltage should be 14V not 12V as printed on the board -

usually the "78xx" and "79xx" regulator require the input voltage to be a minimum of 2V more than the designed output voltage to work correctly


John

PS
I expect the unused pcb pads to for an ceramic capacitor that has not been fitted

[Sterob]

Thanks John,

My break out board is a AKZ250. It came in a X61500GT CNC Router. Info on that is scarce/vague as well, but that board's PWM output is 5 V. I tried the 24V jumper setting anyway...

Info suggests the pot will calibrate the output , as you say.

I *was* only using a 12V to power it intially, but then tried an external 24V supply, just in case that was the problem. Same result.....I just get a nice blue LED.

Unused pads: yes, that makes sense.

I think I'll have to assume that its a DOA and wait for the other 2 to arrive. I guess I will know once I get working....lol

Steve

[john-100]

Hi Steve

just had a look at the AKZ250 motion controllers manual and see the PWM outputs are the open collector output of a 6N137 opto-isolator

have you connected the VFD to analogue converters positive input to the AKZ250 +5V output
and the converters negative input to the AKZ250 open collector output ?

the AKZ250's yellow jumper needs to be on the 5V position

John

[Sterob]

While looking for a pic of the AKZ250 to draw what I did, I found this!:

CNC-Steuerung f

It translates to English with Google. No time to read it now as its 0130 in the Morning. ( I can't sleep...)
What I can say is that I wasn't using a 1k resistor on the AKZ250.....( pull up resistor??) Maybe that is the key?

Will be away for a few days now so will dive in again. soon.

Steve

[john-100]

the pull up resistor would be needed if you was connecting the output to the input of a logic IC ( especially if its a CMOS IC )

but will not be needed when connected to the opto-isolator input of the PWM to 0~ 10V board

John

PS

[Sterob]

Hi Steve

just had a look at the AKZ250 motion controllers manual and see the PWM outputs are the open collector output of a 6N137 opto-isolator

have you connected the VFD to analogue converters positive input to the AKZ250 +5V output
and the converters negative input to the AKZ250 open collector output ?

the AKZ250's yellow jumper needs to be on the 5V position

John

Hi John,
Back from the break....

This how I wired up the Converter board. I thought the PWM signal would already be at 5V and just needed to connect the Gnd to -ve input to converter.
I have the yellow jumper in the 5V position, although I did try the 24V position to see if that made any difference....


Andre, on the RC-network.de forum has wired in a 1k pull up resistor:


I will give this a go tomorrow. It might be my missing link......

Steve

[john-100]

Hi Steve

the first connection in the first diagram can not work as the AKZ250 has an open collector output
that can only sink current to GND and not source current from the +5V supply

the second diagram with the pull up resistor may work depending on the minimum current needed to operate the PWM boards input opto-isolator when the jumper is set to 5V

using my guess of what the PWM to ANALOGUE boards circuit will be like

this is how the AKZ250 output needs to be connected





note
if the PWM to ANALOGUE circuit is DC coupled as I have drawn

the AKZ250 must be configured so the average output is High at minimum speed
(output ON most of the time)

this switches on the PWM to Analogue boards opto isolator's NPN transistor

and grounds the junction of the 10K & 2K2 resistors so the 22uf capacitor is discharged

the DC voltage across this capacitor times the LM358 op-amps gain is the control voltage output

if the control works the wrong way and runs at maximum speed instead of minimum & vise versa
the outputs active high / low setting will need changing in your control software



John

[Sterob]

Thanks John,
That makes sense.
I will have a play and see how I go.

Steve

[Sterob]

Hi John,
I've had some success today. I used your wiring, and had to change the output high/low setting in Mach 3 as you said.
Its working but its not very accurate. I can get *one* point accurate but not *all* of them. I do not seem to be able to get the full 10v output as well. Not sure whats going on yet. Maybe I'm not getting the full 5V for the PWM signal. I'll check tomorrow.
It all suggests the VSD is outputing what it is being asked to. Voltage is low so the output speed is low.

I've tired calibrating the output at mid scale as well as full scale but that does not work. it shifts the error but doesn't fix it either. I wonder if I can use the 10V output from the VSD to step down to 5V for the input?
The AKZ250 getting is power from the USB port so maybe I am drawing too much current...dunno,
The AKZ250 documents say the board can be externally powered but does not say where form. I assume via the 5V & Ground terminals adjacent to my speed signals come from.
Will do some more testing tomorrow.
Steve


Steve

[john-100]

if the 6.65V is the maximum you can get at full speed with the blue 10K multiturn potentiometer adjusted for the maximum output

can you use the potentiometer to adjust the output down to 5V ???

the potentiometer looks like a Bourns 25 turn potentiometer (or a copy)
once you reach an end stop you should hear a click click as a spring dis-enguages

if you can , set your VFD for a 0 to 5V analogue control

what speed range do you have now ?

John

[Sterob]

I've been playing with this all day.I can't get any consistent linear results.
I've tried your wiring and Andre's wiring...both work, but I cannot get linear output from the converter. I can't measure the input waveform as I don't have DSO. ( I may have to buy one )
If I set the pot at low speed the top speed is way out and vise versa....
I'm an Instrument fitter, by trade and its still baffling me...lol Its not right!
I'm used to having 2 calibration pots....zero and span. At least with two adjustments , one can compensate for non linearity. to a certain degree.
I've tried starting at zero rpm....tried starting at 6000 rpm. I've tried different voltage ranges on the converter AND the VSD.
Nothing seems to work. It can't be this hard...lol

I don't know what the carrier frequency of the converter is. Mach 3 keeps on changing it to 4166 , if I make it higher than that.
I've tried several lower figures. Instructions say its between 1- 3k (? ) Shouldn't it be constant?
Used a separate supply for the converter again, but no difference.
My head is spinning....going to leave it for a day or so.....Maybe the unit is faulty...maybe I've damaged it....

Steve

[Sterob]

You won't believe it, but I have found the missing piece of the puzzle.
Even though I said I was going to leave it, I kept on looking.( I couldn't help it....)
I saw a fleeting screen on this video:

It shows the PWM Base freq set to 250. I have no idea why yet. The Chinese instructions mention between 1-3k (?)I have been using 5000 ( as that is what I seen to do many different times on the Internet, and Mach3 changes it to 4166. I had tried other figures as well, but none CLOSE to 250.
I did that and now the voltage outputs are very linear and very close. I will document the figures tomorrow