geoffey
Well-Known Member
Guys, (and gals too) I'm looking for some feedback on an electric rig I'm planning on setting up. It is inspired by Kal's system at theelectricbrewery, but differs in one important respect: I plan on using lighting relays instead of SSR's. There are a couple important reasons I'm going in that direction, which it isn't really important to me to discuss at this point. Suffice it to say I plan on using lighting relays to control my 240v heating elements, relays which I am very certain can handle the switching cycle of my brewing system for at least 5 years.
In order to use relays in a system with PIDs I would use a PID with a relay output control. The one I'm looking at is Auber SYL-2342, which is the exact model Kal's system uses with the exception that it has a relay contact output instead of a 12vdc SSR output. The hitch here is that the timing cycle needs to be set at a minimum of 20 seconds since relays are not designed to switch as quickly or as often as SSRs. (that's the whole reason he designed his system with them). This is an important issue to point out: the timing cycle in an SSR PID set up is 2 seconds by default. This means if the PID requires the system to fire the heating element 10% of the time it will turn it on for .2 seconds and off for 1.8 seconds. If the timing cycle were set at 100 seconds then under the same scenario it would turn on for 10 seconds and off for 90 seconds. In my setup the least I could set it for would be 20seconds. This would mean my relay would cycle on/off a maximum of 3 times per minute. And let me repeat: I have chosen relays which can handle this switching cycle.
My dilemma is that I will lose precision of temperature control under my planned scenario. I just don't know how much precision I will lose. 2-3 degrees I could tolerate. 10-12 degrees I could not, for reasons I would think are fairly clear. So I'm wondering if anyone else out there has tried this before and could give any feedback. OR if anyone with an existing PID SSR setup would be willing to set up a simple test: change your default timing cycle from 2 seconds to 20, 40 or 60 seconds and see if you can hold 5 gallons of water at 150 degrees for 60 minutes. If not, how much temperature drift did you get? This will give me a very good idea of the performance I can expect from my planned system.
Please note: I am not asking anyone to mess with their default PID settings unless you are confident you understand what you are doing and know how to make this change and then return it back to your previous setting.
Also, please consider the fact that I am not currently looking for advice on whether or not to use relays in place of SSRs. "Just use SSRs" isn't really the feedback I'm looking for. I have good reasons to be exploring the option of building my system this way, but I'm hoping to get a little help/feedback on the possible temperature drift before I start putting money into it.
Thanks in advance for any help you can give!
In order to use relays in a system with PIDs I would use a PID with a relay output control. The one I'm looking at is Auber SYL-2342, which is the exact model Kal's system uses with the exception that it has a relay contact output instead of a 12vdc SSR output. The hitch here is that the timing cycle needs to be set at a minimum of 20 seconds since relays are not designed to switch as quickly or as often as SSRs. (that's the whole reason he designed his system with them). This is an important issue to point out: the timing cycle in an SSR PID set up is 2 seconds by default. This means if the PID requires the system to fire the heating element 10% of the time it will turn it on for .2 seconds and off for 1.8 seconds. If the timing cycle were set at 100 seconds then under the same scenario it would turn on for 10 seconds and off for 90 seconds. In my setup the least I could set it for would be 20seconds. This would mean my relay would cycle on/off a maximum of 3 times per minute. And let me repeat: I have chosen relays which can handle this switching cycle.
My dilemma is that I will lose precision of temperature control under my planned scenario. I just don't know how much precision I will lose. 2-3 degrees I could tolerate. 10-12 degrees I could not, for reasons I would think are fairly clear. So I'm wondering if anyone else out there has tried this before and could give any feedback. OR if anyone with an existing PID SSR setup would be willing to set up a simple test: change your default timing cycle from 2 seconds to 20, 40 or 60 seconds and see if you can hold 5 gallons of water at 150 degrees for 60 minutes. If not, how much temperature drift did you get? This will give me a very good idea of the performance I can expect from my planned system.
Please note: I am not asking anyone to mess with their default PID settings unless you are confident you understand what you are doing and know how to make this change and then return it back to your previous setting.
Also, please consider the fact that I am not currently looking for advice on whether or not to use relays in place of SSRs. "Just use SSRs" isn't really the feedback I'm looking for. I have good reasons to be exploring the option of building my system this way, but I'm hoping to get a little help/feedback on the possible temperature drift before I start putting money into it.
Thanks in advance for any help you can give!