Wiring up 3-way 240/120V switch

[KJB5200]

Hi Everyone,

I'm working on a RIMS build based off of Kal's 30A electric setup but I'd like to have 3 elements instead of 1, each capable of running 120 or 240V with the switch of a hand. Ideally I'd like to use 3-way switches in an [ON - OFF - ON] setup to manually switch any given element from a 120 to 240V input supply. Kal's setup shows how to wire a 3-way switch with two 30A 240 DPDT 120 VAC Coil Relays (to switch from one element to another) but I'm a bit fuzzy on how to wire this up for the application I need.

Can anyone point me in the right direction for wiring up a 120/240 3-way switch to a single element outlet?

Thanks,
Kyle

 

[hustlebird]

You're going to be using a 120v source and a 240v source simulatenously? Or are you just wanting to drop the watts coming out of your element at a given time? I wouldn't recommend using a 120v and 240v source at the same time.

 

[zeus53219]

I guess I don't understand why you would want to run 3 elements at multi-voltage(120/240). But it can be done, you could use 6 contactors, 2 for each element, 1 for 120v 1 for 240v and a 3 position switch. But you would need auxiliary contacts, or dual non-reversing contactors to prevent more than one element being on at any given time. What size elements? And a little more info would help?

 

[KJB5200]

hustlebird - I'm looking just to run any given element at 120 OR 240, not both at any given time.

zeus - sometimes a comment as simple as "what the hell are you even trying to do" is all you need! I realized after thinking a little more about my proposed brewing process that I don't have very good reasons for wanting to run any given element in 120 or 240 mode. I was planning on 4500W/240V elements (HLT & RIMS) and a 5500W/240V for the BK, which makes it very tricky to run multiple elements on a 30A system but I realize now the only time I'd need multiple elements running would be while heating my sparge water during the mash - that's what happens when you take WAY too long to design a system and forget the basic process

I think instead I'll plan to use my leftover 2000W/120V HLT element since I could run that and the 4500W/240V RIMS element (in 120 mode) at the same time on a 30A circuit. Now I just have to figure out whether using the BCS-462 to adjust the voltage is best or whether I should include another relay to manually switch voltages for the RIMS element.

 

[zeus53219]

"what the hell are you even trying to do"

Still not going to have enough juice if you are running this off the same circuit. 2000w @120v =16.66a. 4500w @240v=18.75a Total 35.41a. Even if you were to run the 4500w @120 it would still pull the same amperage. 2250w @120v=18.75.

You could always run a dedicated 120v circuit to a separate RIMS control panel. This is what I do when I'm doing back to back batches. I use the RIMS to bring HLT up to temp during the boil, then after the boil I recirculate through the HERMS as normal with HLT element on. I regret not going with a 50a set-up, I rarely do back to back, but would have been nice to have the power if I wanted to.

 

[hustlebird]

If he's running a 30a-240v circuit, isn't it 30 amps @ 120v on each line (60amps @ 120v total capable)? So if he had the 4500w element using 1 line and neutral, and the 2000w element using the other he'd be in the clear?

 

[KJB5200]

Damn, hearing you say you regret not going 50a is making me regret buying so much equipment without a clearer design in my head...

Wouldn't the 4500/240 element running at 120V only pull 9.375amps since the wattage would be reduced to 1/4 of its 240 capability? Or do 240 elements run at 120 still pull half the amps they would at 240, instead of 1/4?

 

[hustlebird]

Alright, I decided to look it up. Current (Amps) = Power (Watt)/Voltage (V) and Resistance = Volts / Current (and inversly, volts/resistance=current) so:

4500w/240v = 18.75amps
240v/18.75a = 12.8ohms
120v/12.8ohms = 9.375amps
9.375a*120v = 1125watts

So - your 4500watt element will run at 1125 watts and draw 9.375amps when you've hooked it to a 120v source (like you said).

 

[jeffmeh]

To the original question, I believe this would work: 3-way switch wired to the coil of a SPDT contactor, with both H2 and N running through the contactor, and both wired to the H2 pole on the element. I would probably also want to run H1 and H2 through a DPST contactor before the SPDT contactor. So on the 3-way switch: 120v closes the DPST contactor and closes N on the SPDT contactor (H1 and N are powering element); Off opens both contactors, so no power to the element; 240v closes the DPST contactor and closes H2 on the SPDT contactor (H1 and H2 are powering element). The ground runs to the element in all scenarios.

 

[zeus53219]

My fault. You are correct, constant resistive load. It would be 12.8 ohm. I = V/R = 240/12.8 = 18.75a, 120/12.8 = 9.375a.

Go 50a if it is not to late. I am soon, have the components to but haven't gotten around to it yet. It's just going to get harder with the nicer weather coming up.

 

[mrwizard0]

If you have a switch that is rated to the highest amp of the element, which would be the 240 line, you could always switch what goes into your contactor. Then hot and neutral go to the switch and only one of them continue to your contactor. I don't think you would even want an on-off-on switch. An on-on switch would ensure you always have power available to the contactor.