# Reliance VTAC9 Analog Bipolar operation



## althecontrolguy (Aug 17, 2013)

I have a VTAC 9 VFD, that I need to be able to run in both directions. Unfortunately, there are no extra wires available, nor a chance to get more to the drive. What I'm wondering is, is it possible to give the drive a 0-10 volt signal, for forward running, and a (negative)0-10, for reverse running? If so what parameters do I need to change? I have changed parameter 190 from "Reverse Disabled" to "Bipolar". Do I need to set parameter 92 to -60Hz, to get the drive to reverse?


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## emtnut (Mar 1, 2015)

althecontrolguy said:


> I have a VTAC 9 VFD, that I need to be able to run in both directions. Unfortunately, there are no extra wires available, nor a chance to get more to the drive. What I'm wondering is, is it possible to give the drive a 0-10 volt signal, for forward running, and a (negative)0-10, for reverse running? If so what parameters do I need to change? I have changed parameter 190 from "Reverse Disabled" to "Bipolar". Do I need to set parameter 92 to -60Hz, to get the drive to reverse?


Looks like it ... 91 to 60hz and 92 to -60hz
Take a look at parm 124 bit 4 as well, the way I read it the zero clamp should be disabled


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## JRaef (Mar 23, 2009)

emtnut said:


> Looks like it ... 91 to 60hz and 92 to -60hz
> Take a look at parm 124 bit 4 as well, the way I read it the zero clamp should be disabled


Looks that way to me too.


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## althecontrolguy (Aug 17, 2013)

Thanks guys, got it running. Needed to reverse the fans on the customers cooling towers, for de-icing. I'm using a DPDT relay, to invert the 0 - 10 volts, so the drive thinks it is seeing a -10 - 0 volts. I set parameter to 92, to a -30Hz, to limit the speed of the fan when running in reverse, per the manufacturer.


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## emtnut (Mar 1, 2015)

althecontrolguy said:


> Thanks guys, got it running. Needed to reverse the fans on the customers cooling towers, for de-icing. I'm using a DPDT relay, to invert the 0 - 10 volts, so the drive thinks it is seeing a -10 - 0 volts. I set parameter to 92, to a -30Hz, to limit the speed of the fan when running in reverse, per the manufacturer.


Good to hear it worked ! ... and clever idea using the relay to invert your signal :thumbsup:


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## JRaef (Mar 23, 2009)

Nice.
If you didn't use some type of relay designed for use with low energy signals, expect that the speed signal will deteriorate over time. It will be fine for a while, but eventually the contact resistance will increase which will drop the voltage signal. For standard relays to avoid that happening, the arcing of the current through them actually burns off any oxides that form on the surfaces. When the voltage is so low like that, this doesn't take place and over time, a resistive film builds up on the contact pole faces. 

If you didn't use anything special, I suggest swapping that relay out when you get a chance. You will need either a reed relay, bifurcated contacts, gold flashed contacts, something like that. They won't be off the shelf in many places so you may have to wait, but it's not an immediate problem.


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## wendon (Sep 27, 2010)

JRaef said:


> Nice.
> If you didn't use some type of relay designed for use with low energy signals, expect that the speed signal will deteriorate over time. It will be fine for a while, but eventually the contact resistance will increase which will drop the voltage signal. For standard relays to avoid that happening, the arcing of the current through them actually burns off any oxides that form on the surfaces. When the voltage is so low like that, this doesn't take place and over time, a resistive film builds up on the contact pole faces.
> 
> If you didn't use anything special, I suggest swapping that relay out when you get a chance. You will need either a reed relay, bifurcated contacts, gold flashed contacts, something like that. They won't be off the shelf in many places so you may have to wait, but it's not an immediate problem.


Any links to those type of relays? I've had trouble with that before and it's very annoying as it can be intermittent.


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## JRaef (Mar 23, 2009)

Most relay mfrs offer some sort of low energy contact option. It can be tricky to figure out what you are looking at if you are not familiar with the issue though.

Look on page 15 of this pdf:
http://literature.rockwellautomation.com/idc/groups/literature/documents/td/700-td552_-en-p.pdf

If you look under the spec section called "Min. Low Energy Permissible Load", you see that it is 100mW for silver contacts, which is pretty much the same for all the others, but if you order the gold contacts, it is 50mW. So at 10VDC, that's the difference between 10mA or 5mA of minimum current.


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## emtnut (Mar 1, 2015)

JRaef said:


> Nice.
> If you didn't use some type of relay designed for use with low energy signals, expect that the speed signal will deteriorate over time. It will be fine for a while, but eventually the contact resistance will increase which will drop the voltage signal.


Ran into that in the water plants a lot. Hi humidity seemed to speed up that process.
We ran sealing currents on the data lines, and used these P&B relays http://www.google.ca/url?q=http://w...ggTMAA&usg=AFQjCNHE-BsbXl8Trfxr6HEa0C7LcP7S1Q
They are rated for dry contact.


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