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Old 08-14-2012, 01:46 PM   #1
RichBenn
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Default SSRs, PID loops, and scortching questions

The more I read and think about it, the more questions I have (sound familiar?). Anyway, here are a few questions for those of you who have been there.

1. I notice everyone using 40 amp SSRs even on 110V 20 amp circuits. (Say, like a 2000 watt element. Why not a 25 amp SSR? These things are supposed to be built with safety factors (headroom) built in already, and the breaker would go at 20 amps(15 for some) so it would seem to be overkill. Did I miss something?
2. I'm going to use a RIMs tube to heat up the HLT, then switch the valves and use it to recirc (and likely mashout) the MLT. If I autotune the PID for the HLT, will it work correctly for the recirc? Seems like the flow rates could be quite different, meaning less work to raise temperature. So is the "tune" needed different as well? Should I use two different PIDs? (Newbie to PID controllers here).
3. When one first starts recirculating, there will be some grain particles going through the RIMs tube. Are there any issues with scorching to be addressed?

More questions, but they probably belong in the automation section. There seems to be some overlap with DIY, automation, and electric brewing, so I never know where to ask.
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Old 08-14-2012, 01:55 PM   #2
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1. People use 40 amp SSR's since they are cheap, available and overbuilt.

2. Your autotune function will indeed be different due to the gravity of the fluid going through it at the time. I would tune it for wort, and use that tune for heating the water as well. It won't be as big a deal to run the other tune on the water as it doesn't have to be as precise.

If that makes sense.
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Old 08-14-2012, 02:00 PM   #3
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1. Higher wattage SSRs are "better" because 1) the price difference is not that much, 2) the higher rating will allow you to upgrade in the near future without having to replace anything and 3) will not heat up as much/fast since they can handle the power

I don't have a rims/herms setup yet, but...

2. The way I understand you is that you're going to "share" the rims between HLT and M/T, is that correct? If so, I believe you want to auto tune it for M/T recirc and run it in manual to heat up the HLT, since you want to heat that up fast as possible.

3. Not a problem. Scorching has been debunked in a lot of other threads.
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Old 08-14-2012, 04:20 PM   #4
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Quote:
Originally Posted by onthekeg View Post
2. Your autotune function will indeed be different due to the gravity of the fluid going through it at the time. I would tune it for wort, and use that tune for heating the water as well. It won't be as big a deal to run the other tune on the water as it doesn't have to be as precise.

If that makes sense.
I don't think the difference is S.G. will make nearly as much difference as the speed of the liquid. In a HERMS or normal heating operation, there is this huge thermal mass, meaning the measured temperature doesn't change that fast. I image the tune for that is way different.

But in the RIMs tube, I'm speculating that when the liquid temperature needs to be changed:
1. A fast flow will show a big differential between target and actual.
2. A slow flow(sparge, for example) will have a much smaller differential, thus more time may be spent pulsing the heating element since the measured temp is almost "there". Will that cause overshoot, slow heating or some funny stuff if I leave the pump valve during HLT operation wide open?

For it to work right for mashing, supposedly I should auto-tune for the flow rate and amount thermal mass (liquid, mash tun & grain) I'd be using most offten, and that's probably what I'll do. Just wondering what that means for the HLT. I'd like to set and forget on the HLT twice, without overshoot:
1. Once to get to strike temp, and
2. Raise what's left to sparge temp.

I'm using a cooler for the HLT, so holding the HLT temp once I move to MLT recirc is no problem.

I suppose I could just solve this by keeping the outlet valve on the pump pretty much the same as on the MLT during sparge, that is, partially open.

Quote:
Originally Posted by mendesm View Post

2. The way I understand you is that you're going to "share" the rims between HLT and M/T, is that correct? If so, I believe you want to auto tune it for M/T recirc and run it in manual to heat up the HLT, since you want to heat that up fast as possible.

3. Not a problem. Scorching has been debunked in a lot of other threads.
2. I was looking for set and forget on the HLT without overshoot. I'd like to do other stuff(grind grains, measure water salts, etc) while it's heating. If that means I'll need another PID or use a software programmable PID like Arduino (and change profiles), so be it. Just kinda hard to buy the right size box or do panel design if I don't know what I"m doing, !

Maybe I need to just get one and do a breadboard trial run....
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Old 08-14-2012, 04:36 PM   #5
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You're over thinking the situation. Set it first during a water brew then do it again during a real brew. Setting it first with a water brew will get you in the ball park without causing scorching and overshoot that you could potentially get if you autotuned the first time with wort. Of course, you could always autotune 10*F lower than your target temp then ramp it up.
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Old 08-14-2012, 04:43 PM   #6
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RichBenn,
there will be different thermal properties of the fluid at the same flow rates. That is what I was trying to elaborate. If he is trying to just heat up water as efficiently as possible, you would want to throttle the valve to the point that the element does NOT turn off.
If using as a RIMS, you would want it to be adjusted where it maintains the temp but would cycle some. This would be by throttling the valve differently as you would not be wanting a controlled rise in temp.

I would autotune in the RIMS range, and probably have the element at 100% power manually on the heat up of the strike water.
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Old 08-14-2012, 06:05 PM   #7
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Quote:
Originally Posted by onthekeg View Post
RichBenn,
there will be different thermal properties of the fluid at the same flow rates. That is what I was trying to elaborate.
Yes, of course I understand S.G. and different thermal properties. However, like I said, it's not going to be that significant, IMHO. Density of distilled water gives 8.34 lbs/gallon; for 1.040 s.g. it's 8.68 lbs./gallon. How much of a difference in PID applied heating is that going to be vs. different flow rates?(a flick of the wrist on the pump valve?) Might be important if I was doing code to directly control using the S.G. of the batch, accurate valve positioning, etc. vs. using a PID that gets control "close enough" doing an autotune. Most other recommendations I've read here say to just use water, as autotuning screws the batch.

Quote:
Originally Posted by onthekeg View Post
If he is trying to just heat up water as efficiently as possible, you would want to throttle the valve to the point that the element does NOT turn off.
If using as a RIMS, you would want it to be adjusted where it maintains the temp but would cycle some. This would be by throttling the valve differently as you would not be wanting a controlled rise in temp.

I would autotune in the RIMS range, and probably have the element at 100% power manually on the heat up of the strike water.
Yes, I understand this quite well. But as I said above, I want set and forget. I see a bunch of threads where people actually do more hands on with automation vs. when they were not automated. That's fine for some, but that's not where I am headed. Like I said before, if it requires another PID and heating element to get a better solution, I'll go there.
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