Pulse Relay to activate blower shutdown?

[Waxman]

Hi all. Will soon be installing an air switch (Kleen Rite, Normally Open) to shutdown blowers if customer 'blows thru' too fast (haha).

Electrician is on it, but wanted me to research the air switch. I have, somewhat, and it seems I'll need to install a pulse relay as well to send the shutoff signal after the second pulse of the air switch.

Sound right or do I need to research further?

 

[MEP001]

I'm sure I've said this before, but I would use a PLC. The air switches don't always send just one pulse when you drive over them, so if you use a relay that will indiscriminately shut off the dryer when it receives two pulses, it may be shutting off after their front tires cross it. A PLC can be programmed to ignore pulses too close together to make sure that the front tires don't shut it down. You might even use two air switches a foot or so apart and a PLC so the first and second switches must be triggered in sequence twice to kill the dryer.

Do customers pull through the dryer and sometimes back up to get a better drying? That could also cause problems with an air switch shut-off.

 

[Waxman]

What does a PLC for this purpose cost?


Yes, sometimes cars 'disco' back and forth under the blowers.

 

[MEP001]

PLCs or programmable relays start at around $100. The downside is that for some you have to buy software and a cable or program chip. The upside is that (especially with models with a display) they are field adjustable.

 

[Waxman]

I'm confused; do I need a plc or programmable relay? are they different?

 

[MEP001]

A PLC is a programmable logic control; a programmable relay can do many switching and timed actions, but has no logic. What you want to do is very simple and shouldn't require anything smart such as accumulating coins or self-adjusting time as a bonus timer, so either will work.

 

[Waxman]

I looked at the dryer schematic and found a blower shutdown photo eye, optional.

Calling the company to ask where to wire in photo eye, cause it really doesn't say.

I was reluctant to use eyes, but if this is the way the MFG has it set up I guess it's worth a shot.

 

[MEP001]

I think it's a better idea - you could use a loop with the same results, but you're the least likely to get a "false" shutoff with eyes. If you buy the components and build your own mounting, the cost won't be much more. Just make sure you stagger them both horizontally and vertically by at least 5 degrees so they can't see through fender wells and gaps between truck beds/bodies.

 

[Waxman]

Blower Shutdown Update

I had a false start implementing this. I now know and understand what needs to be done and have found the right electrician.

The conduit is run and the electrician is creating a program for the relay to control the photo eyes.

It will be more expensive than I originally thought, but soon I will be saving money and operating more efficiently!

 

[I.B. Washincars]

I saved a lot of money when I used a $30 air switch and had the blower shut down 10 seconds after the 2nd pulse (back tire).