Contactor + Switch vs. High Amperage Switch

After spending more hours than I'd like to admit reading some threads on here, I've come to the conclusion that the common recommendation here is to combine an SSR with an actual switch (double pole) that truly and fully cuts off the power when desired for two reasons:

1. SSRs even in their "off" state still leak voltage.

2. When an SSR fails it fails in a state in which power continues to flow through it (counter-intuitively referred to by the electrical nerds as "open") which could introduce the dangerous situation where you expect the element to be off but it's actually on. -It could also lead to accidental dry firing an element.


After searching for a few DPST switches I initially assumed that the typical Kal-style DPST switches could actually switch the two 120v legs but it appears that high amp switches aren't made??? (question) because everyone is instead recommending to combine the SSRs with a contactor. -Correct?

I've purchased this contactor http://www.amazon.com/gp/product/B003U7Z8Q6/?tag=skimlinks_replacement-20 and my understanding is that the contactor is the equivalent of a traditional electrical switch with some extra tech to prevent the contacts from wearing out under larger loads and that it also enable it to be controlled via a remote switch wired to the "coil". Based upon the discussions on the board it sounds like there's an extra safety benefit to going with a contactor that has a low voltage coil (there's only 24volts actually going to the switch on the outside of the panel).


What did I get right vs. wrong?

What sort of switch should I use with the contactor linked to above?


Thanks for entertaining my newbie questions.

Adam

Any switch will work. spst is preferable. Unless your build is using 24v elsewhere I'd toss the 24v coil contactor and either get a 120 or 240v one as those are the voltages which are common to your system. stuffing a 24v stepdown xformer in a control panel just to power your contractors is not necessary.

Get this one: amazon.com Packard 2-Pole Contactor - 120V coil

Or this: amazon.com Packard 2-Pole-Contactor - 240V coil

Dang... Already purchased the 24v contactor; oh well I'll just sell it back...

Not sure whether I should use the 120v coil contactor or the 240v coil contactor? -What are the pros vs. cons?


Adam

I'll throw one more dumb question on here so the Electric Brewing forum isn't filled up with dumb questions from me.

Are DIN Rails simply used as easy mounting rails or do they actually control current? -I have the same question for the rails that breakers snap into in an electrical box do the rails that the breakers snap onto actually have current running through them or are they just used for organization purposes?



Adam

biertourist said:

2. When an SSR fails it fails in a state in which power continues to flow through it (counter-intuitively referred to by the electrical nerds as "open") which could introduce the dangerous situation where you expect the element to be off but it's actually on. -It could also lead to accidental dry firing an element.
Adam

Click to expand...

Actually, open means no power, closed means power, which is counterintuitive to me but the reverse of what you stated. Closing a switch allows power to flow, and SSRs can fail closed.

Din rail is an industry standard mounting style.

Your buss bars in your breaker panel supply the power to your breakers.

I like the idea of the contactor (vs switch) so that an E-Stop can be used to disconnect the contactor coil(s) and cut off all high voltage within the control panel.

Maxkling said:

Din rail is an industry standard mounting style.

Your buss bars in your breaker panel supply the power to your breakers.

Click to expand...

So no power is transferred through the din rail?


Adam

Correct. No power is transmitted via the DIN rail.

If you want to transmit power, you normally use DIN mounted terminal blocks to allow interconnects between your breakers/components.

MOSTLY correct...

You can buy grounding DIN contacts that actually make an electrical bond with the DIN rail (and thus the grounded chassis)

grandequeso said:

Any switch will work. spst is preferable. Unless your build is using 24v elsewhere I'd toss the 24v coil contactor and either get a 120 or 240v one as those are the voltages which are common to your system. stuffing a 24v stepdown xformer in a control panel just to power your contractors is not necessary.

Click to expand...

there is an exception that comes to mind (as in I am using 24V elsewhere). I am planning on using a 240V heating element for my HLT, but I would also like to use a bulkhead mounted stainless steel float switch as protection for my heating element if the water level gets too low. My intention is to install the float switch in series between a Ranco temp controller power out and the coil of the contactor (with a lamp to indicate power on)
These switches are readily available quite inexpensively on ebay, but they cannot handle 120V AC and higher so a 24VDC power source would be ideal.

great idea schroeder. mind if I incorporate the float concept to my kettle and hlt? :rockin:

Sure. I had this in mind...

http://www.ebay.com/itm/CR-Horizont...869?pt=LH_DefaultDomain_0&hash=item416dcdfacd

... or this...

http://www.ebay.com/itm/Sus304-Stai...961?pt=LH_DefaultDomain_0&hash=item3ccae29df1

I think I would go with the first one myself. Like the simple design of it.

And with a second float switch positioned higher in you HLT you could wire up a circuit through an icecube relay or similar connected to a water solenoid valve (flip the float switch over so that it breaks the circuit when it lifts).

push a button on a momentary switch to initiate a fill cycle, and when the vessel is full the float rises, cuts power to the relay coil and stops filling your HLT (no - I don't have the schematic planned, but I know it's possible)... that would be worth a few geek points!