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Old 09-19-2006, 03:05 AM   #1
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Default PID help for an electronics dummy

I'm stupid when it comes to electronics, but I can at least follow directions. I'm buying a PID controller to build a HERMS system, and I see that most of them come with contacts for a regular relay and a SSR. Does anyone know what the difference is between the two, and which I would want to use to power my heating element (probably will be a 120 volt water heater element) for my heat exchanger?

I have a friend who's very good at this stuff, but I wanted to do it on my own (as far as he knows). Although I could sure enlist his help - he drinks enough of my beer.

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Old 10-04-2006, 04:44 AM   #2
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I can help you with a PID setup, but I'd need to know more about the system you're wanting to design. SSR is just a solid state relay, as opposed to a mechanical relay with a coil and springs and contacts and such.

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Old 10-04-2006, 04:46 AM   #3
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Nice.

Dont know much about that alemonkey but would like to see the setup when finished.

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Old 10-05-2006, 09:42 PM   #4
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The relay output doesn't drive a relay, it is a relay. When the output is "on" the contacts are effectively a short circuit and I doubt it's capable of driving a heating element. The SSR output provides a voltage suitable for triggering a solid state relay. This is the output you want to use in conjunction with an SSR.

/Phil.

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Old 10-06-2006, 12:35 AM   #5
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Gotcha, that makes sense.

I'll make sure to post pics when I'm done - one of these day's when I join the Lincoln Lagers I'll have to bring it to a brew day.

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Old 10-06-2006, 05:35 PM   #6
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Quote:
Originally Posted by Seveneer
The relay output doesn't drive a relay, it is a relay. When the output is "on" the contacts are effectively a short circuit and I doubt it's capable of driving a heating element. The SSR output provides a voltage suitable for triggering a solid state relay. This is the output you want to use in conjunction with an SSR.

/Phil.
RIght, and since the relay output likely doesn't have the current capacity to run a heater element, you WOULD in fact have to use it to drive a larger external relay. Either output should work. However, if you're going to be using this as a pulse width modulator (rapidly switching the heater on and off, with the ratio of on to off time modulated to control heat) you really don't want to drive a mechnical relay, it'll wear out REAL fast. SSR is the way to go. Another option would be to get a controller with a true analog output, although that's probably cost prohibitive.
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Old 10-08-2006, 02:58 PM   #7
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Ok, one more dumb question. I found an SSR really cheap on ebay and bought it (should have thought a little more about it first). It can handle up to 220 volts and 70 amps, so the output side should be fine. The input side says it requires from 30 to 240 volts (or something similar).

On my PID, the SSR output only puts out 10 volts, so I'm assuming it won't be sufficient to turn on the SSR. However, the relay output should put out 110-220 volts, depending on what I'm powering the PID with (it handles from 20 to 260 volts), so could I run the SSR off the regular relay output? Or is there something I'm missing here?

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Old 10-08-2006, 11:51 PM   #8
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At this point I'd want to just look at the documentation for the PID and see what sort of circuits are used. I don't want to give you any advice that will result in your equipment burning up....

While things can be jerry-rigged sometimes, it's usually much easier and cheaper in the long run just to do things the way they're intended

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Old 10-09-2006, 01:04 AM   #9
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Well, I have pdf copy of the manual, if you'd like to see it.

I'll probably end up buying a compatible SSR, though.

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Old 10-10-2006, 08:27 AM   #10
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Sure, why not. I'm sure though that it's available online, if you want to just post the model controller you're using.

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