Speed reference for drives.

Mr_lee · Apr 28, 2017

Hey guys
I got a machine that has proprietary plc the analog output went out. I'm using my test bed power supply now for the two drives it has for belt speed. The new comp. is really expensive I'm thinking I'll just put a power supply in and a pot and a voltage readout on the panel for belt speed. Could anyone recommend a power supply for this setup or have a better idea?

rdrast · Apr 28, 2017

The best idea I have, is suck it up, replace the broken part. No matter the cost.

Patching around things that break is not a good habit to get into.

jaden · Apr 28, 2017

What kind of drive? You may be able to just change the speed reference parameter and use a pot, no power supply.

Mr_lee · Apr 28, 2017

jaden said:
What kind of drive? You may be able to just change the speed reference parameter and use a pot, no power supply.

Here's a picture of the two drive's

jraef · Apr 28, 2017

You need to read and understand the manual specific to that drive. In some drives, you do NIT want to use an external supply for the Potentiometer because the drive includes their own and all it is looking for is the change in resistance. On others you wire your external pot signal as a D.C. Voltage input, usually 0-10VDC, but even then the drive may give you its own power supply for that because the input is not isolated. Acting without knowing is inviting trouble.

cardosocea · Apr 28, 2017

rdrast said:
The best idea I have, is suck it up, replace the broken part. No matter the cost.

Patching around things that break is not a good habit to get into.

+1

This is a slippery slope that you don't want to get caught into... plus, when your temporary fix fails you'll be guilty of coming up with a falible solution, not repairing equipment and most likely being taken out of bed because of it.

gbradley · Apr 28, 2017

Mr_lee said:
...The new comp. is really expensive...

I'm not a big fan of Ebay, but sometimes you gotta get the part where you can.
Good Luck!

Mr_lee · Apr 28, 2017

jraef said:
You need to read and understand the manual specific to that drive. In some drives, you do NIT want to use an external supply for the Potentiometer because the drive includes their own and all it is looking for is the change in resistance. On others you wire your external pot signal as a D.C. Voltage input, usually 0-10VDC, but even then the drive may give you its own power supply for that because the input is not isolated. Acting without knowing is inviting trouble.

The machine manufacturer recommended the fix while I waited on the part so I thought why pay 5 grand for the part when I can run it like this.

Steve Bailey · Apr 28, 2017

The machine manufacturer recommended the fix while I waited on the part so I thought why pay 5 grand for the part when I can run it like this.

This attitude and the fact that temporary patches tend to become permanent is behind rdrast's comment.

Pete.S. · Apr 28, 2017

Mr_lee said:
The machine manufacturer recommended the fix while I waited on the part so I thought why pay 5 grand for the part when I can run it like this.

If the PLC/analog out is broken what makes you think that other parts are not going to break soon as well?

I assume you control the speed some other way when everything is working? What happens if someone accidentally bumps the voltage on your power supply, can somebody get hurt? What do you think happens to the drives if you put 30 Volts in by mistake?

You pay 5 grand to put it back into it's original state and have the machine manufacturer be liable. Does the money come out of your own pocket? How much did the machine cost? Did you really expect it to work forever at no cost?

Mr_lee · Apr 28, 2017

Pete.S. said:
If the PLC/analog out is broken what makes you think that other parts are not going to break soon as well?

I assume you control the speed some other way when everything is working? What happens if someone accidentally bumps the voltage on your power supply, can somebody get hurt? What do you think happens to the drives if you put 30 Volts in by mistake?

You pay 5 grand to put it back into it's original state and have the machine manufacturer be liable. Does the money come out of your own pocket? How much did the machine cost? Did you really expect it to work forever at no cost?

They is a keypad where you put in the speed you want. It's all caged off so no danger. I told them that if this went bad probably just a matter of time before more goes bad on it. Ill tell them I talked to a group of tech's and they all agreed with this maybe they'll give me the go ahead to order the comp. You guys are a very active fourm I appreciate the reply's ill probably be hitting you all up with more questions soon thanks

Pete.S. · Apr 28, 2017

Mr_lee said:
They is a keypad where you put in the speed you want. It's all caged off so no danger. I told them that if this went bad probably just a matter of time before more goes bad on it. Ill tell them I talked to a group of tech's and they all agreed with this maybe they'll give me the go ahead to order the comp. You guys are a very active fourm I appreciate the reply's ill probably be hitting you all up with more questions soon thanks

Sounds good.

I make it a point to make every temporary fix look VERY temporary. No neat cable installations, no proper mounting etc. I'll just do the minimum it takes to make it work without any danger, until a proper job can be done a couple of days or weeks later with the right components.

It's important from a psychological perspective - more so than from a technical perspective. It's a reminder for everybody that walks by that it's only temporary and that it can't stay that way.

.

Mr_lee · Apr 28, 2017

Pete.S. said:
Sounds good.

I make it a point to make every temporary fix look VERY temporary. No neat cable installations, no proper mounting etc. I'll just do the minimum it takes to make it work without any danger, until a proper job can be done a couple of days or weeks later with the right components.

More good information I'm learning and you guys are helping and I appreciate it a lot.

jraef · Apr 28, 2017

So... that low cost proprietary PLC isn't so low cost any more, is it? This is the argument I get into constantly when I propose using a commercial off-the-shelf PLC and get compared to someone making a custom "green board" controller. I realize you are not the one who likely specified it or allowed it, I just had to vent my spleen a little. I just lost an OEM project where I proposed using a small standard PLC and standard VFDs but lost to someone green boarding a control box and custom open board style inverter system for 1/2 the price. The OEM seems unfazed by the likely ill will this will cause with their end users in the future when something dies and there are no resources available.

DickDV · Apr 28, 2017

if you have two digital outputs spare in your existing PLC, why not convert the speed reference to MOP (sometimes called Floating Point). Read about it in the drive Instruction Manual. No analog card required.

Speed reference for drives.

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