Mechanical relay cost

[mofox1]

Hi folks,

Events conspire to accelerate my control panel build (or am I just looking for excuses!), this time it's the ebay 15% sale.

Question on mechanical relay cost... the best price I can find for at >= 30A relays is ~$30 or so. Is that reasonable?

These are two that I've found so far (counter intuitively getting cheaper for more amps):
50A contact: http://www.ebay.com.au/itm/271556167165
80A contact: www.ebay.com.au/itm/JQX-62F-2Z-220V-Coil-80A-High-Power-Relay-DPDT-2-NO-2-NC-/191216537889

Need three of these... if these are pretty much what they should cost, then it would be a good time to buy them now.

 

[seamad]

Is there a reason for using mechanical relays ? Most builds use SSRs I think ( including mine) as they are quieter and last longer ?

 

[sponge]

Go SSR.. they're made for repeated switching of larger loads. You'll probably wear a mech relay out pretty quickly with a PID controller.


EDIT: Also grab yourself a heat sink when using an SSR.

 

[mofox1]

Using both.

SSR's for the repeated switching, mechanical for the element select.

Electric brewery setup: Three pos switch for kettle-off-hlt control. Temp controllers to SSR's which can only complete the circuit if the mechanical relay is switched for that circuit.

It's not compete overkill, a double pole relay ensures the element is completely off (not one hot leg) when the mechanical relay is switched off. It also has some protection from the SSR's failing "on".

EDIT: Linky - middle of this page describes the setup: http://www.theelectricbrewery.com/control-panel-part-2?page=11

 

[bazfletch3]

Hey mate

Jaycar have what u need for about $16 each. My phone is playing games at the moment and I can't find a linky, but that's what I used.

Being picky, they have push on spade connectors which I don't think is ideal, but they do the job.

Cheers

Baz

Edit - found the link

http://www.jaycar.com.au/productView.asp?ID=SY4044

 

[mofox1]

Hey mate

Jaycar have what u need for about $16 each. My phone is playing games at the moment and I can't find a linky, but that's what I used.

Being picky, they have push on spade connectors which I don't think is ideal, but they do the job.

Cheers

Baz

Edit - found the link

http://www.jaycar.com.au/productView.asp?ID=SY4044

Bummer - I had just purchased 3 of the 80A ones. Only $23 for those, so not too bad - and they're not spade connections.

Kind'a sad state of affairs when I didn't even think of checking local retailers for electrical bits. Never asssumed they would come close to competing!

Lesson learned, will check next time.

 

[bazfletch3]

Im the same mate, first thing I do is start googling things and checking Ebay. Only in this case I actualy couldnt find anything anywhere else; unless I ended up on Aliexpress or somewhere else slightly out of the ordinary (I must not have been searching for Ebay US).

I actualy had similar with the heat sink I ended up buying for my control panel build; I had a specific size I was looking for and ended up finding one at RS components for $10, I walked into the shop in West Sunshine and picked it up - I had always thought that they were just another overpriced wholesaler!

Good luck with the build.

Cheers

Baz

 

[Ducatiboy stu]

It's not compete overkill, a double pole relay ensures the element is completely off (not one hot leg)

Whats the issue with only one leg (active) being switched ?

 

[O-beer-wan-kenobi]

Using both.

SSR's for the repeated switching, mechanical for the element select.

Electric brewery setup: Three pos switch for kettle-off-hlt control. Temp controllers to SSR's which can only complete the circuit if the mechanical relay is switched for that circuit.

It's not compete overkill, a double pole relay ensures the element is completely off (not one hot leg) when the mechanical relay is switched off. It also has some protection from the SSR's failing "on".

EDIT: Linky - middle of this page describes the setup: http://www.theelectricbrewery.com/control-panel-part-2?page=11

Are you using two SSR's - one for the Kettle and one for the HLT? or one SSR to be switched between the two?

 

[bazfletch3]

Whats the issue with only one leg (active) being switched ?

Could this be a throw back from the original Electric Brewery - given thats based on the 120V North American system, doubling up both "active-hots" to give 240V?

Im only taking a stab on this, as im only a pretend sparky - you're a proper one arnt you Stu?



Baz

 

[TheWiggman]

I haven't gone through AS3000, but there are applications where double-pole switching is required. It mainly eliminates the risk of shock/electrocution if the electrician (...) gets the active and neutral mixed up. It would be required in the US where the unearthed plugs can be flipped over, meaning either side could end up being active.
Not so much of a risk in Australia or for an earthed system, but could become one if someone decides to improperly replace a plug.

 

[Ducatiboy stu]

I haven't gone through AS3000,

Maybe you should

 

[Ducatiboy stu]

Could this be a throw back from the original Electric Brewery - given thats based on the 120V North American system, doubling up both "active-hots" to give 240V?

Irrelevant in Australia as we use 240v.

And why would/are you buying 110v elements...

 

[billygoat]

I haven't gone through AS3000, but there are applications where double-pole switching is required.

Caravans are one application as they are supplied by an extension lead.

 

[QldKev]

You could have used a circuit breaker too, it would double as an overload protection and a manual switch. Also a lot cheaper. Even for the $ you could have looked at an RCD safety switch. Just some too late ideas.

 

[Ducatiboy stu]

You could have used a circuit breaker too, it would double as an overload protection and a manual switch. Also a lot cheaper. Even for the $ you could have looked at an RCD safety switch. Just some too late ideas.

As long as you can get DIN rail to mount them on...but they are not controllable

 

[mofox1]

Whats the issue with only one leg (active) being switched ?

I'd prefer to have my kettle and HLT to be electrically isolated when I set my "element select" switch to "off".

Edit: I should point out that I don't bother with this for the pumps... They are just switched on the active leg.

 

[mofox1]

Are you using two SSR's - one for the Kettle and one for the HLT? or one SSR to be switched between the two?

Two SSR's. The mechanical relays connect one SSR to its element courtesy of a 3 pos switch on the front panel.

 

[dent]

Relays have the main benefit of not generating lots of heat under load like SSRs will.

A relay isn't appropriate for isolating a circuit if that is the intent. An SSR even less so. Though I use the term isolation in a manner that you may not.

Both relays and SSRs can fail ON.

AS3000 does not require switching neutral for "Functional switching". Switching neutral is generally not required.

 

[mofox1]

You could have used a circuit breaker too, it would double as an overload protection and a manual switch. Also a lot cheaper. Even for the $ you could have looked at an RCD safety switch. Just some too late ideas.

Ummm, I want a nice front panel switch to switch between elements. As a switch. On the front.

Defiantly not to late for an RCD, and a couple of those circuit breakers too.

As long as you can get DIN rail to mount them on...but they are not controllable

Yeah, that.