Heat Blanket
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
after extensive research i think i have it figured out. these controllers come with one of three output types (some come with multiple types). these are relay output, voltage output, and current output. despite what might sound right, for ssr's we want voltage output (12 VDC, 20mA). relay output is not an output at all, it is merely a dead switch. it IS a relay, its not FOR a relay. so now i have to buy a new controller. learn from my mistake, if you have an ssr, you want voltage output on your controller.
mattman,
Good work. Sorry that you have to get a new controller, though. Sharing what you have learned will definately be helpful to others.
So, if I understand your last post correctly, in addition to being a PID controller, your present unit also has a built-in relay switch (just as Kelvin suggested a couple of posts back). I'm assuming that the 3A/250V rating means that the maximun load that you can run through that switch is 3 amps. I'm running 8 amps on my heater system, so 3 amps wouldn't run much of a heater, would it. Oh, well. Onward and upward...
G-man
Good work. Sorry that you have to get a new controller, though. Sharing what you have learned will definately be helpful to others.
So, if I understand your last post correctly, in addition to being a PID controller, your present unit also has a built-in relay switch (just as Kelvin suggested a couple of posts back). I'm assuming that the 3A/250V rating means that the maximun load that you can run through that switch is 3 amps. I'm running 8 amps on my heater system, so 3 amps wouldn't run much of a heater, would it. Oh, well. Onward and upward...
G-man
Yes, relay output is just a switch, but you can use is to control another relay.
Instead of getting a new controller, you can get this or similar:
mcmaster part # 7384k15 (mechanical relay) or 7456k13 (SSR)
They are both spst-no relay that take 100-240vac inputs with 25-30amp outputs.
here is a circuit diagram on how to connect them. The manual says to not run it faster than 5 second cycle time, which should work. But I think that if you ran it faster, it'll probably be fine too. There is very little current going through the internal relay and they are rated for millions of cycles at full rating.
-kelvin
Instead of getting a new controller, you can get this or similar:
mcmaster part # 7384k15 (mechanical relay) or 7456k13 (SSR)
They are both spst-no relay that take 100-240vac inputs with 25-30amp outputs.
here is a circuit diagram on how to connect them. The manual says to not run it faster than 5 second cycle time, which should work. But I think that if you ran it faster, it'll probably be fine too. There is very little current going through the internal relay and they are rated for millions of cycles at full rating.
-kelvin
Very slick Kelvin. I had to stare at it awhile before I got it, though. I guess I shouldn't have quit school during the second grade to help with the family cotton pickin'. I see now that, in reality, most PID controllers (if not all of them) are just very elaborate low votage relays... a small, but very smart switch, that sends (relays) orders to a bigger, not so smart switch. Mattman's PID output just happened to be large enough that he could have run a small heating load from it, but it wasn't enough to run a ski press heater. Thanks again, Kelvin, for your expertise.
I hope that mattman sees your post before he orders a new controller. Man, what a wild ride this thread has been.
G-man
I hope that mattman sees your post before he orders a new controller. Man, what a wild ride this thread has been.
G-man
kelvin, great idea for a circuit. i also thought of just wiring a 9V battery in series with the controller and my ssr. this should provide an ample signal to the ssr and be able to be switched by the controller. my only concern is the short life of a battery (it would be unfortunate if it died mid-press). i just hate to add another major part (like an additional relay) when right now i MIGHT be able to return my controller and get the correct kind for $45 on ebay. of course if i thought the 9V battery method were reliable i might just do that to save the hassle and the waste of money on shipping.
mattman,
After reading your last post, I realized that I STILL didn't really get it. So, I went back and read over everything on the thread. I just wasn't getting it through my cotton pickin' head that your controller simply doesn't have an actual electical output, and, as you guys have been saying, it just functions as a switch for a curcuit that has it's own power source... hence your idea about the 9v battery wired in series into your DC SSR input curcuit (very clever, by the way). I know that you are concerned about the possibility that the battery could go dead mid-pressing, but, if you were watching your temperature reading on your PID read-out, you could see that your press temperature was dropping, and you could just quickly change batteries. These controllers normally keep the temperature within a couple of degrees, so you'd know pretty quickly if your battery went south. Just a thought.
Okay, back to cotton pickin'.
G-man
After reading your last post, I realized that I STILL didn't really get it. So, I went back and read over everything on the thread. I just wasn't getting it through my cotton pickin' head that your controller simply doesn't have an actual electical output, and, as you guys have been saying, it just functions as a switch for a curcuit that has it's own power source... hence your idea about the 9v battery wired in series into your DC SSR input curcuit (very clever, by the way). I know that you are concerned about the possibility that the battery could go dead mid-pressing, but, if you were watching your temperature reading on your PID read-out, you could see that your press temperature was dropping, and you could just quickly change batteries. These controllers normally keep the temperature within a couple of degrees, so you'd know pretty quickly if your battery went south. Just a thought.
Okay, back to cotton pickin'.
G-man
I thought about that, but the internal relay is an ac relay and ac relays do not always work with dc. You would think it should work since it is just a piece of metal that goes open and closed, but I believe that the ac relays rely on the fact that there is a time in the cycle with 0 current and that is when it breaks the connection, with dc you don't have that. However, it may work and one way to test is to connect a multimeter to the relay outputs and see if it closes and opens. (be careful what you touch, since everything will be live)
Instead of using a battery, get a cheap power supply or a wall wart transformer. Either get 120v in your box, or find a power supply that works with 240v. Radio shack sells them or scrounge around for an old laptop adapter, usually they can take 240v.
-kelvin
Instead of using a battery, get a cheap power supply or a wall wart transformer. Either get 120v in your box, or find a power supply that works with 240v. Radio shack sells them or scrounge around for an old laptop adapter, usually they can take 240v.
-kelvin
i like the transformer idea since that would allow me to plug the 120V line into a household timer in the future (set it for 2 hours and it will turn off the blanket on its own). my only concern is that since the external relay is 3-32DC, will the ac voltage be a problem? also, in using a transformer, what determines the current reaching the controller (only rated to 3amps)? a doorbell transformer reads "16v, 10VA" on the back, would this mean that .625 amps is always the current? the only load seems to be the LED inside the control side of the external relay.
I just took a look at the transformer that powers my DSL box. It says 120VAC/20Watts in, 12VDC/1000mA out. So, the output on this transformer is 12 volts DC. In fact, all of the transformers that I looked at this morning have DC outputs. Are you saying that your doorbell transformer has an AC output? As Kelvin suggested, even if you use a transformer with DC output, there is still the question of how the internal relay will react to DC current.
Also, for my DSL transformer, the 12VDC x 1A = 12 watts. Does the "10VA" designation on your doorbell transformer mean the same as 10 watts (V times A = watts)?.. and that's how you came up with the .625 amp figure? I've just never seen watt ratings designated that way. Anyway, based on the formula, it seems that the actual amperage that the internal relay is going to 'see' is going to vary with the watts of power that the curcuit is drawing. If the LED on the SSR only draws 4 watts of power at 16V, that's just going to be .25 amps. If I have this incorrect, please feel free to clarify.
G-man
Also, for my DSL transformer, the 12VDC x 1A = 12 watts. Does the "10VA" designation on your doorbell transformer mean the same as 10 watts (V times A = watts)?.. and that's how you came up with the .625 amp figure? I've just never seen watt ratings designated that way. Anyway, based on the formula, it seems that the actual amperage that the internal relay is going to 'see' is going to vary with the watts of power that the curcuit is drawing. If the LED on the SSR only draws 4 watts of power at 16V, that's just going to be .25 amps. If I have this incorrect, please feel free to clarify.
G-man
Sorry, a true transformer changes ac voltage to another ac voltage, like mattman's doorbell transformer. When I said 'transformer' before, I meant the cubes that you plug into the wall. Some of them give ac output, but most have additional circuitry to convert to dc output.
Here is something that would work:
http://www.radioshack.com/product/index ... age=family
Your relay will have some internal resistance and will only use as much current as neccessary. The 10VA rating is the maximum power that the transformer can produce, while maintaining 16v. It will only output the current that your load uses. You can look on specs sheets for the power requirements (~5-10ma for a dc ssr) for your relay.
VA (volt amps) is a measure of power used for AC circuits. It is V x I, but it uses the RMS (root mean square) values for V and I. For resistive loads (lights, heaters...) and small motors, you can assume VA = watts. You start running into difference in huge motors where the inductive load is large. For dc circuits, VA=watts, but normally people use watts for dc.
-kelvin
Here is something that would work:
http://www.radioshack.com/product/index ... age=family
Your relay will have some internal resistance and will only use as much current as neccessary. The 10VA rating is the maximum power that the transformer can produce, while maintaining 16v. It will only output the current that your load uses. You can look on specs sheets for the power requirements (~5-10ma for a dc ssr) for your relay.
VA (volt amps) is a measure of power used for AC circuits. It is V x I, but it uses the RMS (root mean square) values for V and I. For resistive loads (lights, heaters...) and small motors, you can assume VA = watts. You start running into difference in huge motors where the inductive load is large. For dc circuits, VA=watts, but normally people use watts for dc.
-kelvin
hey, i just did a college lab on rms values! anyway, i called the manufacturer of the controller (omron) and they said that dc current would work fine with the internal relay. I also called the ssr manufacturer and they said ac current would cause major problems on the control side. So it looks like i am using a plug-in 120AC to 9DC transformer. I am sure i have one a can scrap from old cd players. but this also means that the 9V battery method would work fine too right? I might start with that just to cut down on all the plugs coming out of this thing. do you know what 9V batteries can supply for current? should be enough for the ssr (10mA is pretty miniscule). thanks for all the help guys, this has been a rapidly changing project!!!
Thanks Kelvin for the additional explanation. Obviously, I'm not able to keep up with you guys, but it's sure great to be learning more about this stuff. So, regarding the plug in units, if they're not truely transformers, what is their proper designation? adaptors? converters?
Well, mattman, it really does look like you're getting close. Have you figured out the programming on your controller yet? That was one of the toughest parts for me. The user instructions were not very clear at all. When I set up my heating unit, a friend was staying with us who retired at 40 years old because he was the guy who designed and built the first machines that made computer chips. He still gets called back by the manufacturers for a few weeks every year to update the machines. Anyway, even he had a bit of difficulty going from the instructions to the actual operational programming. I would have been lost without him. I hope that your instructions are written better than mine are.
Looking forward to the report that all is working.
G-man
Well, mattman, it really does look like you're getting close. Have you figured out the programming on your controller yet? That was one of the toughest parts for me. The user instructions were not very clear at all. When I set up my heating unit, a friend was staying with us who retired at 40 years old because he was the guy who designed and built the first machines that made computer chips. He still gets called back by the manufacturers for a few weeks every year to update the machines. Anyway, even he had a bit of difficulty going from the instructions to the actual operational programming. I would have been lost without him. I hope that your instructions are written better than mine are.
Looking forward to the report that all is working.
G-man
my instructions are all german (damn ebay) so it sounds like the programming will be another feat. i imagine that having only one output type will help though. any pointers on programming it? i am not even sure what i need to tell it to do...i figured you just plug in the themocouple, tell it what temp you want and GO! i should have known it wouldnt be that simple. oh and as far as the actual name, i have seen "ac adapter" and "power supply" as the most popular, adapter seems most fitting. i believe transformers convert current between two electromagnetic coils, whereas adapters use some series of diodes to switch from ac to dc. thats my vague understanding thusfar.
Yikes!! German? Maybe you will be able to figure the programming out without a manual. Since you are now in college, you are a whole lot younger than I am, and you grew up with computers and other gadgets that need to be programmed, so it may come much easier to you. I have a PDF version of my instructions, but no on-line address to copy and paste to you. If worse comes to worse, I can mail you a hard copy, although I'm not sure how helpful it might be. On the other hand, all of these controllers look like they came out of the same factory and just have different names on them, so programming may similar.
These PID controllers go through an initial process where they actually learn how much mass they are heating up (by how long it takes to increase the temp a certain amount over a given time), and how quickly heat is lost once the desired temp is reached. Then, the unit programs itself in such a way that it knows how often to close the heater curcuit and how long to keep it closed in order to maintain the temp within 1 or 2 degrees of the desired end temperature. So, there is quite a number of parameters that need to be input and it's kind of tricky to get around in the menu. Good luck.
G-man
These PID controllers go through an initial process where they actually learn how much mass they are heating up (by how long it takes to increase the temp a certain amount over a given time), and how quickly heat is lost once the desired temp is reached. Then, the unit programs itself in such a way that it knows how often to close the heater curcuit and how long to keep it closed in order to maintain the temp within 1 or 2 degrees of the desired end temperature. So, there is quite a number of parameters that need to be input and it's kind of tricky to get around in the menu. Good luck.
G-man