Relay switch on a vacuum pump (veneer press)

[David Kenagy]

Joewoodworker.com gives advice on making a vacuum system for a veneer press. Some folks have made YouTube videos on their builds (of his plans and pumps). One of these guys said the 5A pump can draw up to 15A at start-up. (Will probably flip the circuit breaker I wanted to use)

The fellow added a "relay" and said that would slow the draw, reducing the max.

If this makes sense, then with all the "relays" I find online, what model (or specs) will meet this purpose? Where can I learn more about this?

[Brice Rogers]

It is hard to understand exactly how adding a relay would do much without knowing how the relay was hooked up and the other components.

I have a Thomas vacuum pump that can move about 3.5 cubic feet of air a minute that I use with a vacuum chuck. It is similar to ones used for veneering. It is on a 15 amp breaker and works fine. It doesn't dim the lights (that already have 3 or 4 amps of lighting hooked up to it) on start up. It is actually a fairly low current device. If the vacuum pump is turned on without a vacuum yet established, it'll draw less current on start up. How big of a vacuum pump are you running and are you starting it with a full or nearly full vacuum already established? Or more specifically, what vacuum pump are you contemplating buying?

I suppose that if the relay was connected to an air solenoid and there was some delay circuit in between that it could help.

[David Kenagy]

I was planning to use the 5 cfm pump.

Looking back at his site, Joewoodworker says he's stocking pumps from a different source, lately. The 5cfm pump now on the site draws 3.7A, but 7.5A at start-up. Maybe the YouTube guy was using a bigger (or discontinued) pump.

[Lee Schierer]

You need to look at the name plate on the motor and see what it says for amps. Adding a relay will not alter how many amps the motor pulls on start up. A time delay relay can sometimes be used when starting multiple devices at the same time on a single circuit to eliminate breaker tripping, but it does not change the individual draw of any device. Our original heating system had two blower motors and a compressor that would all start at the same time, causing the lights to blink every time the unit started. By adding a time delay relay on one of the fan motors we were able to stagger the sudden demand slightly and thereby eliminate the blink.

If you wire the circuit with #12 wire and put in a 20 amp breaker, you should be good to go even if the motor pulls 15 amps on start up. Your motor will still be protected on a 20 amp breaker. The motor should have its own internal protection. Most outlets are wired with #12 wire, but you would need to check your wiring to insure it was done properly.

[Paul F Franklin]

Circuit breakers don't trip on a short, slight overload. Chances are you will be fine even on a 15 amp circuit.