Hello Guest it is December 07, 2021, 07:27:30 AM

Author Topic: Setting up Spindle/VFD control Issues  (Read 2522 times)

0 Members and 1 Guest are viewing this topic.

Re: Setting up Spindle/VFD control Issues
« Reply #20 on: February 15, 2019, 07:11:32 PM »
Hi,

Quote
Just for my understanding and curiosity is it working by the zener diode "bleeding" off any voltage it "see's" above its set value to ground (in this case 10v)
Yes, in fact that is a very good description as to what exactly a Zener diode does.

Quote
What I don't understand is how this does not create a short circuit and overload the amp capacity of the VFD 12v output?

Also can you explain what the resistor does for this setup please.
The resistor is between the VFD 12V output and the Zener. In absence of the resistor the Zener would 'short out'
the output and the VFD might not like it.

You are correct, but the 'short' is not quite the normal sense of it. Normally you would short a circuit and force the output
voltage to zero. In this instance you would 'short' it to not 0V but 9.1V (or whatever value Zener you used).
In engineering parlance that is called a 'differential short circuit'.

The resistor is to limit the current in the differential short and drop some voltage, in this case 13.2V-9.1V=4.1V.
It is entirely likely that the manufacturer of the VFD put some current limit resistor or other circuit within the VFD
to protect the output in case of a short circuit. Quality designed and built US, Japanese and European brands
will almost certainly have protection built in. Who knows with Chinese brands? Some are actually very good indeed,
anything made by Delta for instance I rate as good or better than any US, Japanese, European stuff but other Chinese
stuff I wouldn't 'cross the road to piss on'.

Craig
My wife left with my best friend...
     and I miss him!
Re: Setting up Spindle/VFD control Issues
« Reply #21 on: February 15, 2019, 08:32:08 PM »
Thanks Craig, all makes sense.

My next problem is setting up Mach4 control of the mist coolant sprayer. I plan to use the spare gecko output which is rated at 1amp 50vdc max

I have a pneumatic valve which has a 12V 4.12W Solenoid on it which I believe equates to 0.343Amps / 343milliamps

Problem is I do not have a suitable 12v power supply.

Current voltage sources are
-48V 7.3amp switching power supply (main supply running geckog540)
-5v 3amp switch mode supply (running Ethernet smooth stepper)
-Gecko chiller has a 12V 200milliamp output (currently running a box fan)
-VFD has the 12-14v output but says limited to 20ma

Could I use the same trick with the Zener Diode's and the 48v supply or is it too much of a drop from 48-12v? if its ok what value resistor would you use (and out of curiosity how do you calculate that value)

Or since its likely going to be a constant load? could I just use a Voltage divider circuit with resistors or is this once again too much of a differential between 48-12volt and resistors would get very hot?

Other possible option is I think I can get a 24v solenoid for this valve which might help? but I know there is no 48v one. 

Re: Setting up Spindle/VFD control Issues
« Reply #22 on: February 15, 2019, 08:47:31 PM »
Hi,

Quote
Could I use the same trick with the Zener Diode's and the 48v supply or is it too much of a drop from 48-12v? if its ok what value resistor would you use (and out of curiosity how do you calculate that value)

NO! the Zener and resistor will fry up BIGTIME.

A 12V 1W zener will get to limiting heat at 1/12=83mA. If at 83mA you had to drop (48-12)=36V then the resistor
would be 36/0.083=432 Ohm. The dropper resistor would dissipate 36 x 0.083=2.988W.

Either way such a setup wont deliver anything like your required 450mA to a load.

I will give it some thought and make a few suggestions.

Craig
My wife left with my best friend...
     and I miss him!

Offline MN300

*
  •  251 251
    • View Profile
Re: Setting up Spindle/VFD control Issues
« Reply #24 on: February 15, 2019, 09:48:32 PM »
Viperx85,  Your last post came in whilst I was writing this.

A 100 ohm in series with the valve you describe would let you use 48V. However it would be dissipating 12 watts, not very practical.
A 24V valve with the same wattage could use a 33 ohm resistor and waste 4.1 watts. It would draw half the current but that's still not ideal.
There are 48V valves but they are less common, probably more expensive.

12V 1.0A power supplies are cheap on eBay or other sources. The extra current is good in case you want to add something later. I think this is your best option.
Example:
https://www.ebay.com.au/itm/Switching-Power-Adapter-Charger-ADS-12FB-12-12012GPSA-12V-1-0A/263731008662?hash=item3d6797d496:g:U~4AAOSwW8RbEgct:rk:2:pf:0

Another option would be to use a solid state relay and a mains powered valve. Common SSRs are 32VDC input max so a small resistor would be needed in series. This method can control small motors too like a coolant pump.
Re: Setting up Spindle/VFD control Issues
« Reply #25 on: February 15, 2019, 09:59:30 PM »
Hi,
yes that would be simplest and probably cheapest.

48V to 12V is a bit outside the normal realm of linear regulators so you would have to augment the pass transitior
with an external transistor, doable but depending on your electronic skills fiddly.

Another possibility is a switching buck regulator but would require an IC, a Mosfet and an inductor with maybe a few
other smaller components to 'glue' it all together on a circuit board. Again doable but fiddly.

Yet another alternative is a DC-DC converter. This a typical example:

https://nz.element14.com/recom-power/r-78hb12-0-5-w/dc-dc-converter-12v-0-5a/dp/2774032

Useful, elegant and tidy solution for $27NZD plus GST and freight.

Craig
My wife left with my best friend...
     and I miss him!

Offline MN300

*
  •  251 251
    • View Profile
Re: Setting up Spindle/VFD control Issues
« Reply #26 on: February 15, 2019, 10:26:07 PM »
When a relay is switched off the falling current generates a voltage spike, often several times the supply voltage. The traditional way to protect the driving circuit is by placing a diode across the relay coil. A 1N4001 or other higher voltage rated diode in the 1N400x series would do. The cathode would be connected to the end of the coil going to the +12V supply.

The 50V output may not need protection but for a few pennies better safe than sorry.