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DPDT to SSR setup

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QldKev

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I want to wire up a circuit so that one power feed is shared between two heating elements, controlled by 2 separate pids.

IF OUT1 wants power
OUT1 ON
OUT2 OFF
ELSE IF OUT2 wants power
OUT1 OFF
OUT2 ON
ELSE
OUT1 OFF
OUT2 OFF
ENDIF

Using old manual relays, it would be pretty easy.
wiring_relay.gif


But I want to do this using SSR's to allow the speed of them, and gain the benefits of using a pid and <1 sec possible contact times.

Is there a NC SSR? How would I/my electrician wire this up?


QldKev
 

newguy

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Using a microcontroller or something like that, this would literally be a few lines of code which you've outlined already. If you're after a wired solution, there's a pretty easy way to do this.

The logic you need is as follows. The SSR_A activation signal and the SSR_B activation signals depend on each other and I've interpreted what you want as:

SSR_A activation state SSR_B activation state SSR_A output state SSR_B output state
OFF OFF OFF OFF
ON OFF ON OFF
OFF ON OFF ON
ON ON OFF OFF

For both SSRs you'll need a "wired AND" circuit BUT you'll also need a single "inverter" prior to the AND. SSR A's drive circuit will consist of the SSR_A activation state signal going straight to the AND, but the SSR_B activation state signal must first go through an inverter before it gets to the AND. The output of the AND then drives the SSR.

For SSR_B, the situation is reversed. SSR_A activation state goes to an inverter, then to the AND while SSR_B activation state signal is fed directly to the AND.

Wired AND: http://en.wikipedia.org/wiki/Wired_logic_connection
BJT inverter: http://courseware.ee.calpoly.edu/~dbraun/courses/ee307/f03/13/02_13_philippegonzaga.html

You'll also need a DC voltage equal to the SSR's activation voltage, probably 5V but in reality can be almost anything. Give me more information and I can get you a more detailed schematic.
 

jonw

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Wouldn't that be:-


SSR_A activation state SSR_B activation state SSR_A output state SSR_B output state
OFF OFF OFF OFF
ON OFF ON OFF
OFF ON OFF ON
ON ON ON OFF

I've done this on my Arduino based controller, but I've got no idea for hard wired stuff.
 

newguy

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jonw said:
Wouldn't that be:-


SSR_A activation state SSR_B activation state SSR_A output state SSR_B output state
OFF OFF OFF OFF
ON OFF ON OFF
OFF ON OFF ON
ON ON ON OFF

I've done this on my Arduino based controller, but I've got no idea for hard wired stuff.
Could be - need QldKev to confirm how he wants it to behave and I can massage the schematic accordingly.
 

QldKev

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I'm after

SSR_A activation state SSR_B activation state SSR_A output state SSR_B output state
OFF OFF OFF OFF
ON OFF ON OFF
OFF ON OFF ON
ON ON ON OFF


I'm really chasing doing this without needing a micro-controller. I do have a Arduino I was going to use for the main logic and software development is my profession, but I'm trying to simplify it using a hard wired setup and avoid the Arduino altogether. So a hard wired system.

It's use will be; I have one 240vac 10amp feed that will control 2 heating elements.
Element_A is in the heat exchanger and needs the priority.
Element_B is in the HLT, and is used to help ramp it faster if the power is not being consumed by element A.

I'm happy to use 5vdc, 12vdc or 240vac input to the SSRs, I will need to buy at least one more anyway.

Not sure if you can see the pic in the first post, it shows what I would have done with mechanical relays; but I have labelled NO and NC backwards, doh!


I already have a couple of other 10amp elements in use, so I cannot just pull another 10amp feed.

This is an idea of the entire system; with the OR box being what we are looking at here.

-----------------
wiring_full.gif
------------------

man.. attached pics are shite at the moment...
 

mxd

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I thought mine did ?

Is there the option on the PID ?
 

newguy

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The circuitry is pretty easy then. SSR_A activation state (the command signal, +12V for ON and 0V for OFF) is routed directly to SSR A's "activate" input.

SSR_B activation state is identical to what I already spec'd: B goes to a wired AND circuit and the other input of the wired AND is driven by an inverter, which in turn is driven by the SSR_A activation signal.

PM me for the schematic. Can't figure out how to attach a pdf since the site upgrade. Shoot me your email address in the message.

You can't use a mechanical relay for this because a PID will rapidly cycle the control signal to switch the SSR on/off many times per minute. A mechanical relay will fail very quickly. The other consideration is that since you're bypassing the PID, don't expect it to hit your target temperatures reliably. It may oscillate very badly or suffer from severe "undershoot", all on the same day.
 

mxd

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QldKev said:
I'm playing with a Sestos, and the D1S-VR being the SSR version doesn't. The D1S-2R mechanical relay version does have both NO and NC.
http://www.sestos-hk.com/english/product_show.asp?id=495

I may go and read up on the Auber ones.
I'm sure when I was looking at doing a single power point I was going to use 2 pids with 1 priorityto MLT and the other HLT, so I assume my PID allows it.
 

QldKev

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Edak said:
You are going to need logic to get around this problem. Either you can over-engineer and use an Arduino or you could get away with a 74F00 quad NAND gate (or equivalent).

See attached diagram

EDIT:

Links
http://www.jaycar.com.au/productView.asp?ID=ZS5001 (for 5V system)
http://www.jaycar.com.au/productView.asp?ID=ZC4011 (for 12V system)
How does that diagram translate into wiring of the 4011 Quad 2-in NAND Gate CMOS IC

Do I just follow the diagram
Jump 12 and 13 together, and connect SSR_A activation to either, and also SSR_A_OUT
Jump 11 to 9
connect SSR_A activation to 8
Jump 5 and 6 together and join 10 to them
Join 4 to SSR_B_OUT

If so I don't get how that causes a "not A" condition for SSR_B_OUT

Also what would I do with Vdd and Vss

QldKev
 

QldKev

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I was also thinking this morning :blink: Could we just use a NPN transistor to complete this?
npn1.gif

edit: But I guess that's what newguy was referring to? if I included a wired AND circuit I could get rid of the extra SSR.
I may go google more on wired AND circuits

QldKev
 

stux

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In a NAND circuit the output of the AND is NOTed

So if you tie the two inputs together you get a NOT circuit
 

QldKev

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Stux said:
In a NAND circuit the output of the AND is NOTed

So if you tie the two inputs together you get a NOT circuit
Ahh, now I get it, NAND is "NOT AND"... a bit like an XOR. So in this case I think my wiring as above would be safe, just got to work out Vdd and Vss means
 

mxd

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QldKev said:
Ahh, now I get it, NAND is "NOT AND"... a bit like an XOR. So in this case I think my wiring as above would be safe, just got to work out Vdd and Vss means
can't you just AND your NO from PID A with the NC from PID B and only use 2 SSR's

so when PID A is asserting on the NO and PID B then asserts on the NC SSR B will get power.

unless your PID doesn't have the NO and NC, but the pics you sent looked like it did ?
 

QldKev

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mxd said:
can't you just AND your NO from PID A with the NC from PID B and only use 2 SSR's

so when PID A is asserting on the NO and PID B then asserts on the NC SSR B will get power.

unless your PID doesn't have the NO and NC, but the pics you sent looked like it did ?
On the D1S-VR, the SSR output is at terminals 6 and 8. The terminals 1 and 11 with NO and NC are only alarm outputs used with terminal 12.

How do you "AND" two outputs?

Then we could use this

npn1.gif

Which I think is what newguy was referring to.
 

mxd

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yep that's what newguy has described, I didn't read his fully whoops

and edak has given you the parts as well (I thinkj) :)
 

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