what happens when a relay's wired like this?

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reax222

Copper - Posts: 220

Joined: March 11, 2006

Location: United States

Posted: August 25, 2008 at 12:13 AM / IP Logged

I don't have a relay to blow up and I am curious after an instructor told me about it.

85 to ground

86 to 87a

30 to power.

I realize that it will switch constantly, but the instructor briefly mentioned this when he said that 12v will not create a spark. I believe the idea is that a very large charge will build up since the coil will be constantly energizing and deenergizing.

Will it glow, will it send sparks, will it explode?

KPierson

Platinum - Posts: 3,527

This member consistently provides reliable information

Joined: April 14, 2005

Location: Ohio, United States

Posted: August 25, 2008 at 8:02 AM / IP Logged

No, not like that, and no.

It won't glow, the coil is a current limiting load - and therefore will never pull more current then it is designed to. The only way it would glow is if you ran more current through it then it could dissipate.

It won't spark at all because there isn't enough load for the current to jump across the contacts. Put a 30A load across the contacts and switch it on and off that fast and it will creat some internal sparks.

I've never seen a relay explode - neither in cars nor in industrial applications.

Kevin Pierson

reax222

Copper - Posts: 220

Joined: March 11, 2006

Location: United States

Posted: August 25, 2008 at 8:06 AM / IP Logged

It wasn't supposed to be an amperage issue, it was supposed to have something to do with cumulative voltage spikes.

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: August 25, 2008 at 9:41 AM / IP Logged

The reverse voltage created by the collapse of the magnetic field can damage transistors and other solid state devices that are used to drive relays if a diode isn't placed across the coil, but I've never heard of it harming the relay in any way. If I get a chance later today I'll hook one up and let it cycle for a few hours.

Kevin Pierson

i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: August 28, 2008 at 5:08 PM / IP Logged

I thought it would chatter when wired as above. It does not chatter, but it does whine a bit. It produces about a 1K noise that seems as though it does not like it. But as stated above, it will not damage the relay. I left it like that for about 5 minutes, still making the noise and no heat at all.

hotwaterwizard

Silver - Posts: 1,350

Joined: December 11, 2003

Location: California, United States

Posted: August 29, 2008 at 1:26 AM / IP Logged

Looks like you just created yourself a Buzzer. LOL

Want sparks hook it up to 120 vac cord and watch it smoke.

John DeRosa (Hotwaterwizard)

Stockton California

When in doubt, try it out !

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reax222

Copper - Posts: 220

Joined: March 11, 2006

Location: United States

Posted: August 29, 2008 at 8:26 AM / IP Logged

Well that's a little disappointing.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: August 29, 2008 at 9:57 PM / IP Logged

Put an AM radio next to your EMI generator and see what it sounds like-

i am an idiot

Platinum - Posts: 13,667

Joined: September 21, 2006

Location: Louisiana, United States

Posted: August 29, 2008 at 10:10 PM / IP Logged

It even interferes with FM stations.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: August 29, 2008 at 10:44 PM / IP Logged

Pretty much puts out every frequency across the board- try different length wires connected and seeing what it does to your TV reception.

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