Heating Element Controlled By A Pid - Current Draw Once At Temp

[JPAT]

That would be peak though. I think OP was hoping that the PID throttled the element, or somehow ran it at 500W or whatever to hold temp when it actually turns the element on full for a second, then off for a second (or whatever the actual timing is) so the average might be 500W but it's not a constant wattage.

What type/model PID controller are you using?

 

[Parks]

What type/model PID controller are you using?

I'm not yet, just my understanding of PWM.

Feel free to correct me if I'm wrong.

(I will be using an Arduino once I've finished building it)

 

[JPAT]

I'm not yet, just my understanding of PWM.

Feel free to correct me if I'm wrong.

(I will be using an Arduino once I've finished building it)
[/quote

PWM will throttle back current but it would probably be a good idea to use a relay so both elements are never on together

 

[Parks]

PWM will throttle back current but it would probably be a good idea to use a relay so both elements are never on together

PWM doesn't actually throttle or reduce the current. It turns the signal on and off repeatedly so the average appears to be throttled.

I am coming from the point of view that this will be going through an SSR.

eg, if it's a 2400W element, 240V @ 10 amps and your PID wants to run it at 1200W then it will constantly turn the SSR on and off (how ever many times per second) to achieve this. The element still draws 2400W when it's on, but it also draws 0W when it's off.

 

[MastersBrewery]

It's this one. Works a treat :icon_cheers:

you could always use a dimmer switch as above to limit max power and PID to control temp by switching on off. would take a bit of trial and error to find the best setting on the dimmer for mashing, but for boil just max it, or switch so the dimmer is no longer in circuit. I've now prolly confused everyone..... including me :blink:

 

[Parks]

you could always use a dimmer switch as above to limit max power and PID to control temp by switching on off. would take a bit of trial and error to find the best setting on the dimmer for mashing, but for boil just max it, or switch so the dimmer is no longer in circuit. I've now prolly confused everyone..... including me :blink:

That makes sense to me.

The dimmer will reduce the voltage to the element and thus wattage.

-- assuming that elements will be OK with it, I don't see why they wouldn't be --

 

[JPAT]

PWM doesn't actually throttle or reduce the current. It turns the signal on and off repeatedly so the average appears to be throttled.

I am coming from the point of view that this will be going through an SSR.

eg, if it's a 2400W element, 240V @ 10 amps and your PID wants to run it at 1200W then it will constantly turn the SSR on and off (how ever many times per second) to achieve this. The element still draws 2400W when it's on, but it also draws 0W when it's off.

When the PWM turns on and off faster than one cycle it cuts the wave meaning it reduces the voltage which reduces the watts which reduces the current. One cycle is 20mS long.

 

[kjparker]

you could always use a dimmer switch as above to limit max power and PID to control temp by switching on off. would take a bit of trial and error to find the best setting on the dimmer for mashing, but for boil just max it, or switch so the dimmer is no longer in circuit. I've now prolly confused everyone..... including me :blink:

Except that would probably muck up any self tuning the pid has done....

 

[Parks]

When the PWM turns on and off faster than one cycle it cuts the wave meaning it reduces the voltage which reduces the watts which reduces the current. One cycle is 20mS long.

That doesn't sound right - got any info sources?

 

[MastersBrewery]

Except that would probably muck up any self tuning the pid has done....

yes it would.


perhaps using the dimmer directly in line and removing pid control from the boil, thus the pid would self tune to always switching the lower (dimmed) wattage.

 

[JPAT]

You cant use PWM to control a solid state relay (SSR).

We use PWM over SSRs to control heaters varies voltage 50-230

 

[QldKev]

What if you put the dimmer on the HLT circuit.
Initially allow 100% load to get up to temp.
BEFORE you mash in, turn the dimmer to 50% ie 1100w
The PID on the Heat exchanger will always have the full 2200w element behind it.
....
maybe a bit dangerous if you forget to set the dimmer.




I like booargy's way with the relay.
Initially the HLT gets the 2200w until you mash in
When you enable the Heat exchanger the PID controlls it with the full power.
When the PID isn't using the power, the HLT can have it, if the controller wants it.

As long as the HX doesn't steal too much time on the power and the HLT gets enough time to get the water hot enough by the end of mashing.



the only other alternative I can think off is the way method I said initially
have a 2200w and a 1000w element in the HLT.
Run the HLT controller on the 2200w to get to temp, and then swap it over for the smaller element.
OR
Run the HLT controller on the 1000w element, and use the 2200w without the controller to get you close to the temp, then swap over the power from the 2200w to the HX.

Then the PID has the full 2200w for the HX,
and the HLT can use the 1000w to play at 100% of the time.



QldKev

 

[JaseH]

Its probably too obvious to not have considered it already, but do you have a standard 10amp outlet available as well as your 15amp? I run my rig off 2 circuits a 10 and 15 to get around overloading a single circuit.

 

[kjparker]

Its probably too obvious to not have considered it already, but do you have a standard 10amp outlet available as well as your 15amp? I run my rig off 2 circuits a 10 and 15 to get around overloading a single circuit.

Unfortunately not.

In my shed, the einstein who wired it up used a 16amp main breaker for it.

I had considered having the breakers upgraded, as the cable is 4mm so upping to to 25a would be perfectly safe.... but for now I got to work with what I have....

yes it would.


perhaps using the dimmer directly in line and removing pid control from the boil, thus the pid would self tune to always switching the lower (dimmed) wattage.

PID wont have anything to do with the boil, the boil wont be happening in any of these vessels either! Once the mash is done, it will be moved to the kettle for the boil, which will end up with a 15amp element in it.

 

[QldKev]

I still don't get why you don't want to swap over plugs during the brewday?

Use the houses 10amp for the HERMS

Use the 16amp to run the HLT, and swap over the cable to the kettle when needed.

 

[kjparker]

I still don't get why you don't want to swap over plugs during the brewday?

Use the houses 10amp for the HERMS

Use the 16amp to run the HLT, and swap over the cable to the kettle when needed.

In a word.. Convenience.

If I can get away with not running the monster extension lead from the house to the shed I will.....

 

[mILLrAT]

We use PWM over SSRs to control heaters varies voltage 50-230

Another day and I have learn't something new, thanks for that. I hooked up a SSR this morning and plugged in the multimeter, changing pins to a PWM pin helped and as advertised it gave a proportional control.

I still think a software implementation that uses one or two seconds as the cycle time will have fewer on/offs for the SSR than using PWM, the more on/offs the more heat to be dissipated. But if it works then it works!

 

[kjparker]

Another day and I have learn't something new, thanks for that. I hooked up a SSR this morning and plugged in the multimeter, changing pins to a PWM pin helped and as advertised it gave a proportional control.

I still think a software implementation that uses one or two seconds as the cycle time will have fewer on/offs for the SSR than using PWM, the more on/offs the more heat to be dissipated. But if it works then it works!

What pid were you using?

 

[mILLrAT]

What pid were you using?

I was playing with a PID loop hooked up to a paint stripper heat gun controlled using a thermocouple used for roasting coffee beans, the following link has code and references etc

http://www.arduino.cc/playground/Code/PIDLibrary