Minimum Run Time Switch for CVMAX

[Rushton]

The community wood workshop we're upgrading will have a Clear Vue CVMAX cyclone dust collector installed. As I recall, the recommendation is not more on/off cycles than about 5 per hour, so 12 minutes minimum run time.

Because this is a shared use shop, I'm concerned we won't be able to educate users to "keep the cyclone running!" So many people have never worked with a machine like this. And, being used to working with their shop vacs or some small dust collector, I'm concerned they will default to turning the big cyclone on and off like a shop vac.

Which leads me to wonder if the power relay for the cyclone's motor can be connected to some sort of minimum run time switch that can be adjusted to that minimum 12-15 minutes the motor should see. I'll be installing the standard Clear Vue power control kit and adding the dust bin full warning kit.

Edit: I've learned that what I'm asking about is called an "off-delay relay".

Thoughts? What materials would you use and how would you wire it up?

 

[McRabbet]

Rush, I posted the following on the NCWoodworker.net forum:

I think your goal of maintaining fewer start/stop sequences to avoid motor overheating is good, but the strategy of forcing an artificial duration of 1/5 of an hour to keep the cyclone running regardless of actual demand is flawed for some key reasons. I'll outline some examples.

First example, a user wants to use one or two of the connected tools (e.g. the jointer followed by the planer) to mill some lumber. It takes him ten minutes to accomplish his tasks, so he doesn't care if the cyclone runs for another 2 minutes and then shuts off. Meanwhile, another user wants to use the planer and waits for his colleague to finish before he starts his runs of five boards -- unbeknownst to him (or her), the cyclone is on a countdown timer and it stops the cyclone while his stock is just a short way into the planer and he has taken a hefty pass that ends up clogging the machine and damages his stock.

Second example has a user that has more than 12 minutes of work planned and the cyclone doesn't give him enough time to complete his tasks, so he restarts the cyclone as soon as it shuts down, potentially overheating the motor. Does he need to wait for a cooldown period?

The issue at hand is motor overload due to heat buildup created by repeated start and stop sequences. The 5 HP Leeson motor is designed for continuous operation and if you monitor the amperage draw, you'll quickly realize that startup causes the peak demand and produces the majority of the heat generation. Once running with one or more gates open, the motor will draw less than half the amperage than at startup and it can run for hours without overheating. Start the cyclone up when the shop is opened (use a key switch next to the entrance or next to the cyclone closet) and shut it down when the last user leaves the shop. Letting it run won't harm it and the electric bill won't be that drastic. The only downside of this strategy is when nobody needs dust collection and it runs without need.

 

[Rushton]

Rob, your example scenarios were very helpful to me envisioning how such a delay timer might adversely impact people in the shop.

We will plan to move forward without a delay timer and instead rely on forcing people to walk to a switch at the cyclone to power it on and off. As suggested in the NCWoodworker.net forum, we'll apply a little social engineering to the solution.

 

[L. Olsen]

Hi. I have somewhat of the same problem to solve. I am thinking of putting a VFD on the motor and letting it run idle with mayby an automated blastgate that opens when you start your machines and the VFD will speed up the motor. That way you won't have the startup current running so high and you will have ambient cooling at all times.

 

[Curly1]

The VFD will only work if you have/get the 3 phase motor. You wouldn't need to run the 3 phase motor all the time since it doesn't build up the heat like a single phase does when starting. The VFD can be set to ramp up the motor to speed over a few seconds letting you start and stop as much as you like. Running the motor too slow, idling as you put it, may make it get hot because their isn't enough airflow to cool the motor. The other upside to the 3 phase is being able, within reason, to run the motor faster (66hertz/cycle) for a little more airflow when needed.

Pete

I'll add the Aussies sell their Clear Vue cyclones with 3 phase motors and a Powtran VFD from China to speed them up from their 50 hertz/cycle power to get the airflows we enjoy with our 60 hertz/cycle. They even have a programming guide for the VFD on their site.

 

[L. Olsen]

Thank you. That’s a very good point. I hadn’t thought of the cooling going down as well. As I live in Denmark, Europe, I have the same 50hz problem and a soft start solution is easy if you have the vfd already.

 

[Darren]

It sounds to me like the proper solution is a minimum runtime timer in the circuit. If it hasn't run for 12 minutes and someone attempts to shut off then keep running until 12 minutes has elapsed else, shut off. This introduces a safety concern where it would need to be shut off regardless of run time due to a hazard or emergency. Provisions would have to be made for an easily accessible "shut off anyway" button on the same remote or same location. IE: E-Stop.

 

[Rushton]

It sounds to me like the proper solution is a minimum runtime timer in the circuit...

Thanks, Darren. I've abandoned the thought of some "minimum runtime" in light of the considerations McRabbet shared. Your further safety consideration for an override shutdown is yet another good reason to avoid this. We'll do "user education" coupled with a walk to the shutoff as the means for treating the cyclone's motor gently.

 

[Darren]

Might be a fun project to put a timer above the cyclone with the current run time on it. Would be a good reminder. It would reset each time the power was cut off.