Motor Question...

[4-20mA]

We have a tank that we suck in a power through a vacuum powder charge system. The vac consumes volatile vapors during this time, so we now have a vac pump that has a purge on it. We want to air purge for the vac for 15 min while running after the charge. We came up with a way to do it with an On/Off switch that when turned off triggers a timer relay to purge(and run) for the set amount of time. Bench tests looks like this will work, but one of my concerns are the motor when quickly switched from "run" to "off- but after the alloted time. Is there major issues with on-off-on'ing a motor that quicky? Anyone have a better idea or route? This is all done locally in the field, no plc or dcs control.

 

[tom baker]

You could use an air eductor vacuum and then no issues with a motor, etc

 

[Strathead]

What do you mean by on-offing? You are just turning the switch off, right? I don't see anything on the plate about thermal protection either. Do you need a starter?

 

[4-20mA]

You could use an air eductor vacuum and then no issues with a motor, etc

I'll have to Google that.. ha

 

[4-20mA]

What do you mean by on-offing? You are just turning the switch off, right? I don't see anything on the plate about thermal protection either. Do you need a starter?

Yes it's an on off switch, but when switched to off, there is a second where the contacts open and then close again - operating the starter - so will the starter be able to be quicky off'd then back on likely while still running full speed is what I'm thinking...

 

[tom baker]

I'll have to Google that.. ha

When I was in the Naval shipyard in Bremerton, there was an air eductor vacuum that sat on top of a 55 gallon drum. We used to clean the bilges. It would suck up everything including nuts and bolts.

 

[don_resqcapt19]

Wire it with an off delay in the control circuit. The off delay timer will pull in the starter when you start the machine, but when you push stop, it will continue to run for the set amount of time. Depending on the equipment, this may require an emergency stop that will stop the motor no matter what the timer is saying.

 

[Joethemechanic]

Yes it's an on off switch, but when switched to off, there is a second where the contacts open and then close again - operating the starter - so will the starter be able to be quicky off'd then back on likely while still running full speed is what I'm thinking...

So more or less it would be the same as "jogging"?

 

[LarryFine]

Use a timer that can be programmed to be on the whole time the fan is running, and then time down the 15 minutes after turning off, so there's no drop-out.

 

[4-20mA]

You could use an air eductor vacuum and then no issues with a motor, etc

We're pulling in several pounds of powder into a chamber, I doubt inducted vacuum could withstand the demand


Just saw your other reply. I'll look further into those but not sure they're what we need.

 

[4-20mA]

Use a timer that can be programmed to be on the whole time the fan is running, and then time down the 15 minutes after turning off, so there's no drop-out.

There's no set time to charge. Totally random.

 

[4-20mA]

So more or less it would be the same as "jogging"?

Yes, more or less. Good point

 

[4-20mA]

Wire it with an off delay in the control circuit. The off delay timer will pull in the starter when you start the machine, but when you push stop, it will continue to run for the set amount of time. Depending on the equipment, this may require an emergency stop that will stop the motor no matter what the timer is saying.

Great point bringing up an E Stop also

 

[don_resqcapt19]

There's no set time to charge. Totally random.

It doesn't matter...the time starts its timing function when you push the stop button and lets the motor run for the time setting on the timer.

 

[4-20mA]

It doesn't matter...the time starts its timing function when you push the stop button and lets the motor run for the time setting on the timer.

I see what you mean on your first post now. That relay may be able to do that as well, thanks! Gonna look at that shortly

 

[zbang]

off delay timer

For the OP- also called "delay-on-release", you'll see that sometimes.

 

[don_resqcapt19]

I see what you mean on your first post now. That relay may be able to do that as well, thanks! Gonna look at that shortly

Yes, some are multi-function ones. When I was working I always kept this one on hand because it can do most any time function that you want to do.

 

[LarryFine]

Do

I see what you mean on your first post now. That relay may be able to do that as well, thanks! Gonna look at that shortly

Does your timer have separate power and trigger terminals?

 

[4-20mA]

Do

Does your timer have separate power and trigger terminals?

Yes, the relay uses dry contacts for the trigger. Going to mess with it some today after I work on this temperature transmitter that's pegged out.