hdbb2 bob vfd control

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hdbb2 bob vfd control

Postby thegreatwaldo » Fri Nov 24, 2017 9:56 am

Hi Balasz.
I have just ordered a hdbb2 bob can you tell if I can control my hitachi vfd from it. I think the vfd needs 0-10 v for control. Thanks in advance.
Andrew
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Re: hdbb2 bob vfd control

Postby Derek » Fri Nov 24, 2017 6:53 pm

The HDBB2 only outputs 0-5v from what I understand. If you are using a UC-300 you can get 0-10V from that. That's how I control my Hitachi VFD.
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Re: hdbb2 bob vfd control

Postby cncdrive » Fri Nov 24, 2017 10:15 pm

How you can get an isolated 10Volts from the HDBB2 is you could use any of the Open-drain outputs and connect them to 10Volts or 12Volts via an external pullup resistor.
What we use when we make a connection like that is the 12Volts which we already have, because that is what powers the HDBB2's output circuitry, so it is a power which is already isolated from the UCxxx motion controller connected to the HDBB2, so using that PSU voltage is absolutely safe.

So, if you configure the spindle PWM to that output then you will see a 12V amplitude PWM signal.
Most VFDs will smooth the signal out with their internal low pass filter on the analog input.
Some VFDs even have a parameter to adjust the low pass filter's time constant, so you could even optimise to the required fastest signal change and the PWM frequency.
So, the VFD reads the PWM as an analog signal and with the low pass filtering the amplitude of the signal will be the duty cycle of the PWM.
For example 50% duty cycle PWM gives an avarage of 12V * 50% = 6Volts.

The 12Volts is not a problem, I mean that it is not 10Volts but 12V is not a problem, because VFDs have protection circuitry (protection diodes on the analog input) and also the signal is mostly scaled down more inside before it is sampled by the ADC, so some overvoltage will not cause any problems for the inputs.

And the UCCNC is intelligent about the spindle PWM, I mean you can fine-tune the PWM to fit the 0-10V range using the PWM min. and max. duty cycle settings,
because the UCCNC automatically scales the PWM duty cycle min. and max. range into the S speed min. and S max. range.
So, eventhough the max. output voltage will be 12Volts, but you can tune that down to 10V max. with lowering the max. spindle PWM duty cycle value in the UCCNC settings.
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