50A, 3 elements - Interlock two of them?

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angrybits

Mountain Medicine Brewery
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I am beginning to draw up my plans for a half barrel, 3 vessel, electric RIMS brewhouse. My thinking is that I would have 3 4500w elements in the system, one each in the HLT, BK, and RIMS tube. I would probably want to interlock two of them to prevent firing all three at the same time and tripping the breaker. If I were to do that, my thinking is that I would not be firing the RIMS tube and BK at the same time, so I could wire them up to be exclusive using a 3-way switch (like in Kal's controller).

The other choice is maybe have a simple MCU programmed to allow me to arbitrarily choose two elements to fire. So in that instance I could even have two in the BK and HLT with the option to fire one or both. As long as I only fire two at a time I should be golden. I don't think the firmware would be difficult for something like that.

Interested in thoughts on either approach. I realize the latter would be a bit more complicated, but the majority of the controller would indistinguishable from Kal's. It's just some additional switching.
 
Should be simple enough to do with a couple of relays each with 2 NO and 2 NC contacts per the diagram below. The NO contact not shown for each is used to operate the contactor or relay that controls the load. If you can find a contactor with 4 auxiliary contacts of course the relays are not needed.

Push Start 1 and K1 latches through K2 and K3's NC contacts. The K1 NC contacts are now held open in leg 2 and leg 3 but there is still continuity to the K2 and K3 coils through the K2 and K3 NC contacts. Push Start 2 and K2 latches through the K3 NC contact. This opens the K2 NC contact and you cannot, therefore, start the 3rd load. Similar reasoning applies if you press Start 3 after pressing Start 1. You will not, in that case, be able to start Load 2.

Two_of_3.jpg
 
Should be simple enough to do with a couple of relays each with 2 NO and 2 NC contacts per the diagram below.

That is a neat trick, sir, thank you for sharing. Looks like you could put the NC contacts in series to make the whole thing mutually exclusive?

Hypothetically speaking, if you were going to have four elements but still with the 2-at-a-time rule, how would that look? (Now I'm just begging for some free engineering training, so if you don't have time to mess with it, it's cool.)

Cheers! :mug:
 
Whoa... ajdelange is arguably the best scientist/engineer on this forum... but this seems overkill to me. Easy to draw, lots of work to wire.

I would just put a SPDT relay or switch in front of the two contactors that supply the RIMS SSR and the BK SSR (aka Kal's and other designs). This would prevent both from being powered simultaneously. If you wanted to be extra careful, you could make that a DPDT relay or switch and run the SSR switching power through it also. If you wanted the freedom of firing two in a different order, run another switch/relay in series.

-BD
 
Easy to draw, lots of work to wire.
Wow!!! This is about as simple as it gets and is based on the standard Start/Stop pushbuttonb station. Not hard to wire at all.
1)Control power + bus to Start PB
2)Start PB to Stop PB
3)Stop PB to K1 NC
4)K2 NC to relay coil
5)Relay coil to control power - bus
5)K3 NC in parallel w/ K1 NC coil (2 wires)
6)K1 NO in parallel w/ Start PB (2 wires).
7)Repeat twice for other two loads

Total of 24 wires. Looks pretty simple to me and allows selection of any two of three loads. I've certainly wired more complex control circuits than this but I will admit that in the usual case I drew it and some one else wired it.

Of course there are lots of other ways to do it. One could buy three panel switches with 1 NO contacts and 2 NC and wire them with the NO contact on S1 in series with the paralleled NC contacts on S2 and S3 (and similarly for the other two) thus eliminating the relays. If the switches are hefty enough the load can be wired directly to them. O/W a control signal for contactor or SSR would be connected.


Now if you want to expand this to any two out of 4 things become much more complex. You would need, for each load, a series connection of a normally open contact which closes when you select a load and three normally closed contacts each of which opens if a pair of other loads is selected. Here is a matrix of all the possible ways to pair the numbers 1 through 4

11 12 13 14
21 22 23 24
31 32 33 34
41 42 43 44

You cannot select any pair along the diagonal (the same load twice isn't a pair) and the pair 23 is the same as the pair 32. Thus the pairs that must be considered are

xx 12 13 14
xx xx 23 24
xx xx xx 34
xx xx xx xx

For the first load, L1, you need a series NC contact for each pairing in the reduced matrix that doesn't contain a 1. For L2 you need a series NC contact that doesn't contain a 2 etc. so the four load circuits need the following:

L1: 23, 24, 34
L2: 13, 14, 34
L3: 12, 14, 23
L4: 12, 13, 23

To develop the 6 pair NC contacts you would need 6 additional relays with an NC contact. The coil of the 23 relay, for example, would be fed by a series connection of NO contacts on the load relays for L2 and L3 and so on. As each of the numbers 1, 2, 3 and 4 appears 3 times in the attenuated matrix it is clear that 3 additional NO contacts would be required on each load relay. It's also pretty clear at this point that some type of transistor logic should be considered.

It should also be clear that the basic idea here can be extended to any 2 out of N for any N including 2 out of 3
 
I have 3 elements on my 30A system (two 4500w) and one 1800w.... I can run either 4500w along with the 1800w element simultaneously .
I simply put my rims on its own switched relay and the other two elements are setup on a three position on-off-on switch so only one can be on at a time.... I have no need to ever have my HLT heating at the same time as my BK so this works perfectly. something you can do also unless you feel you need to heat both kettles at once.

I also added a float switch in my HLT to kill the element if the sparging process uses enough water to were the element is going to be exposed to air.
I have a flow switch in my rims tube to prevent heating during a stuck flow or no flow situation.
 
Why not use CMOS logic to do this?

If PID.BOIL.HEAT THEN SSR.BOIL.HEAT
IF PID.HLT.HEAT THEN SSR.HLT.HEAT
IF PID.RIMS.HEAT AND NOT (PID.HLT.HEAT AND PID.BOIL.HEAT) THEN SSR.RIMS.HEAT

1. IF ANY SINGLE PID ASSERTS HEAT, THEN ITS SSR WILL TRIGGER.
2. IF ANY TWO PIDS ASSERT HEAT, THEIR SSRS WILL TRIGGER.
3. IF ALL THREE PIDS ASSERT HEAT, BOIL AND HLT SSRS WILL TRIGGER, AND RIMS_HEAT WILL BE INHIBITED.

LOOKS LIKE YOU WOULD NEED 2 AND GATES AND 2 NOT(INVERTER) GATES.
 
Hi, thanks for the suggestion. I am now thinking I will have 2 x HLT elements, 2 x BK elements, 1 x RIMS tube elements. With this many, I think using hardware logic is going to get a bit unruly, so I plan to just use a microcontroller with a small LCD character display and a few buttons to allow me to choose from the handful of combinations that I care about. Will make a thread about it when I get the prototype up and running, I have about half the firmware written and am waiting on parts from China still.

Cheers!
 
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