how many dpdt switches will i need?

[bagpiperjosh]

id like to make a 2 element e herms system.. i only plan to use 1 element at a time.. do i need 2 dpdt relays? or will 1 be fine? im planning to eventually build a cal clone, but im just doin the neccessities now. i noticed his system has 3. one for the input power, and one for each element.

 

[HopDr]

I am certainly no electrical expert, but you pretty much need 2 for the elements and one for the power switch if you are planning on having them switched I think. How would you wire it with one?

On the other hand, you could forego the switching to select the element that you want on- leave the switch and DPDTs out and wire directly to the SSRs. The relays are redundant, they are there for safety so that you don't fire both elements at the same time since firing both elements at the same time would draw almost 50A (assuming you are using the 5500 w elements). That seems unwise, but certainly doable.

 

[bagpiperjosh]

I am certainly no electrical expert, but you pretty much need 2 for the elements and one for the power switch if you are planning on having them switched I think. How would you wire it with one?

On the other hand, you could forego the switching to select the element that you want on- leave the switch and DPDTs out and wire directly to the SSRs. The relays are redundant, they are there for safety so that you don't fire both elements at the same time since firing both elements at the same time would draw almost 50A (assuming you are using the 5500 w elements). That seems unwise, but certainly doable.

thats why id like to hook them up to a 3 pos switch with center off like the kals design. so theres no chance of firing both up

 

[l3asturd]

I am certainly no electrical expert, but you pretty much need 2 for the elements and one for the power switch if you are planning on having them switched I think. How would you wire it with one?

On the other hand, you could forego the switching to select the element that you want on- leave the switch and DPDTs out and wire directly to the SSRs. The relays are redundant, they are there for safety so that you don't fire both elements at the same time since firing both elements at the same time would draw almost 50A (assuming you are using the 5500 w elements). That seems unwise, but certainly doable.

Actually the relays are used to cut BOTH legs of the 240V required for the elements. If you only use an SSR (not a SSRD) then only one leg is cut, meaning the element won't heat, but potential will still be at one of the element lugs. The double pole relays (or the rarer SSRD's) cut both legs so no heat OR voltage are at the element when the switch is in the off position.

You're right though, typically three relays are used, one for each element and one to cut all power to the panel when your power switch is turned off.

 

[bagpiperjosh]

if only those darn relays werent so expensive. Dont get me wrong, they are a worthy investment. But they dont come cheap

 

[kevin509]

If one uses SSRs and only one leg is cut then a spst switch would be all that is needed to kill power to element? SSR last longer than relays if the circuit cycles a lot but leak current and switches that can handle 20-25A are hard to find that aren't huge. Contactor would work but more big stuff to cram in the panel. It's frustrating.

 

[l3asturd]

Ya you'd still want to use SSR's for the element control for their longevity. The relays are used to remove both legs of power when the switch is in the center off position. A contactor would work in place of a relay.