watering system- relay problem

Using Arduino Motors, Mechanics, Power and CNC
1

Hello, I'm using the arduino to control a relay (crydom EZ240D18) that turns a water pump on and off at a given time each day. To save water, I've been testing the setup with a box fan instead of the water pump. Everything was working fine.

After testing was successful with the stand-in fan, I plugged in the water pump and the relay turns it on, but not off!.

I think it may have something to do with the fact that the box fan did not have a ground pin on it's electrical cord. The water pump does have the third, ground pin.

And here's a description of my project with pictures: http://cameronzotter.com/watering-system/
Here's a picture of the relay: 061/365 March 01 2012 | 061/365 A Relay. | Command Z | Flickr

Any ideas? Thanks!!!

Thanks.

2

More likely your problem is the higher inductive load that your motor has over the fan you tested with. Solid-state relays based on triacs and SCRs are subject to turn on and turn off problems due to fact that their reactance causes the voltage and current to go out of phase with each other and because such devices can only be turned off when current crosses zero. Here is a link that discusses the subject and possible solutions called snubber components.

http://nuwaveproducts.com/blog/2012/01/19/lets-talk-about-thyristor-scr-triac-and-ssr-snubbers/

Lefty

3

Thank you. I can't find any good tutorials on how to build the snubber circuit. I wonder if I could just purchase another relay?

http://www.sparkfun.com/tutorials/119

Thanks for your help

4

I just had a crazy Idea. I could use the current relay setup to control another power strip that the water pump is then plugged into. Do you think that would work?

5

command_z:
I just had a crazy Idea. I could use the current relay setup to control another power strip that the water pump is then plugged into. Do you think that would work?

Nope. All that does is (essentially) add a few extra feet of wire.

FYI the "third" wire on your pump, the ground, will only carry current when the pump shorts out internally. As a safety measure it should be connected directly to the ground on your outlet.

6

I suppose I could use a plug-in timer an eliminate the arduino and relay altogether.

Do you think my water pump would have a similar problem working with this:

http://www.walmart.com/ip/NSI-Industries-7-Days-Digital-Plug-In-Timer/19290452

7

command_z:
Thank you. I can't find any good tutorials on how to build the snubber circuit. I wonder if I could just purchase another relay?

Controllable Power Outlet - SparkFun Electronics

Thanks for your help

Yes, that being a standard electromechanical relay would not suffer from the same problems that SSR relays have with inductive loads. Just be sure the relay contacts are rated (current and voltage) well above that required for your motor.

Lefty

8

Thanks for your help. I've found two relays. They will both handle the voltage of my water pump, but I'm unsure which one is best. Can you suggest one of the kits below? Thanks!

The water pump I want to control: Water Pump: 120 volts, 60 Hz, .14 A

$7.95 Beefcake Relay Control Kit SPST-NO 20A Relay (max: 220 VAC @ 20 Amps )

$19.95 Solid State Relay Kit (max: 125VAC @ 8A)

9

That cheaper one should work just fine.

Lefty

10

oh good. Thanks so much for your help. I really appreciate it. I'll pass it on.

Enjoy the weekend.