Buildbotics Forum

Can you guys recommend a "known to work" PWM adapter? My VFD only uses 0-10V.

edit: Here is a link to the spindle I am using: https://www.amazon.com/gp/product/B01LNBOCDA

Is this what I need?

https://www.amazon.com/Studyset-Voltage ... B07Z7JZ3H5

What is the voltage and frequency of the PWM output?

This is the first time I've seen the particular spindle and power supply that you are using.

The PWM to 0-10V converter that you referenced will probably work, but the information provided is a little unclear.

The Buildbotics Controller puts out a 3.3V PWM signal. The PWM output frequency from the BB Controller is configurable. I do not know the maximum frequency that it will support, but it will not be a limiting factor. I'd go with one that clearly states that it works with 3.3V PWM signals, like this:

https://www.amazon.com/gp/product/B079B ... LEZQ&psc=1

or this one, which is enclosed and is made so you can screw it down to some surface:

https://www.ebay.com/itm/173834358106

I suspect that the enclosed one uses the exact same circuit board as the other one. The problem that I see with both of these devices is that they require a 15-30 volt power supply. If the power supply you are using for the Buildbotics Controller is in this range, you can just tap off of that power supply. If not, you will need another power supply or a DC/DC converter that can step down to the level that you need.

If your BB power supply is 36V, something like this would probably do the job:

https://www.amazon.com/SMAKN-Voltage-St ... ics&sr=1-5

I am going to purchase one of these step down converters and the 3.3V PWM to 0-10V converter from Amazon and should have them in a few days. I will report my results soon after.

OK, My KNARCO 3.3P-10V 3.3V PWM to 0-10 Volt adapter came in and I gave it a try. Here's a link to the unit that I bought.
https://www.amazon.com/gp/product/B079B ... UTF8&psc=1

It does work, but is not particularly accurate. I set it up on my machine. I set the max-spin to 24000 and the min-spin to 8000 and the pwm-min-duty to 0% and the pwm-max-duty to 100%. With these settings, I told the spindle to turn at 8000 RPM. The output of the adapter should have been 3.3V, but it was actually 3.7V and the spindle turned at about 9200 RPM.

I tried messing with pwm-max-duty and found that I could get a fairly accurate speed from the spindle if I change its value to 87%, but then the spindle would only turn at about 21,700 when I told it to go at 24000RPM.

In summary, this device works with about 10-15% accuracy. If you need better accuracy, you can play around with the duty cycle to get it to be more accurate, but only in the range of where you expect to operate. If the speed at which you expect operate varies widely, then you're stuck.

This type of interface is inferior to an RS-485/MODBUS interface. Using the Modbus interface on the same VFD and spindle, the actual speed is always within 1% of the value that is requested. Nevertheless, accuracy of 10-15% is probably OK for most application.

Hope this helps

I bought a couple of those (in case I destroy one). I am in the process of building the system today. What supply voltage are you using? I got a separate 12Vx5A supply to run peripherals like case fans and the converter. Putting everything into a metal case with the controller sitting on the top. I will post some pics when I have it working.

My Buildbotics Controller runs on 36VDC. I have a 36V to 24V step down converter to supply the KNARCO 3.3VPWM to 0-10V converter. The limited documentation says that it requires a 15-30 VDC supply. I just connect the input of the step down converter to the power supply and the output to the PWM converter power input pins.