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

[kjparker]

am trying to work out what my current draw is going to be with my proposed setup for my brewery.

At present all I have available to me is a 16amp circuit.

Loads that I would like to have running concurrently:

*HLT - with a 2200w element, PID controlled
*Herms unit with a 2200w element, PID Controlled

Now I know that the total loads on those two elements exceeds my total number of amps, however the HLT until it reaches temperature, will be the only load running, so will be fine.

Once the water is at temperature, would the pid be supplying / drawing a full 10 amps full time to keep the water at set temps, or is it likely to be somewhat reduced, allowing me to have the hlt maintaining the water temp, so my sparge water will be ready for when I want it, and the herms unit maintaining the temp I have it set to?

I was going to use a simple on / off controller like an stc1000for the hlt but am investigating PID's to try and get my current draw down.

Am I on the right track, or am I completely way off base?

 

[QldKev]

Why don't you stick 2 elements in the HLT

The 2200w element you already have, and another <=1000w element.

Warming the HLT up you use the 2200w element. (you could also use the 1000w HLT element for faster ramp times)

Once the HLT is to temp, unplug the 2200w and plug in the 1000w to maintain the temp.

Then you can use the HERMS 2200w + HLT 1000w + <10w PIDS all at once and be ok on 16amp


edit: A lot of kettle elements are only 1800w


QldKev

 

[kjparker]

Why don't you stick 2 elements in the HLT

The 2200w element you already have, and another <=1000w element.

Warming the HLT up you use the 2200w element. (you could also use the 1000w HLT element for faster ramp times)

Once the HLT is to temp, unplug the 2200w and plug in the 1000w to maintain the temp.

Then you can use the HERMS 2200w + HLT 1000w + <10w PIDS all at once and be ok on 16amp


edit: A lot of kettle elements are only 1800w


QldKev

Yep had considered that, and will do that if I have to, but I'm trying to keep it relatively simple.

Google doesnt even seem to know, or at least it doesnt want to tell me!

 

[QldKev]

I think it would be fairly simple, just yank out the main HLT element and plug in the HERMS.

Look up Pulse Width Modulation, I think that is where you are going with the PIDs and using SSRs, but using PWM you still may exceed your threshold.

The only other way I'm thinking is if you use a relay setup on the outputs to switch between them. You would give the HERMS the priority on the power, and if it doesn't want it, then you allow the HLT to have it. I've seen it done at a mill, between loads, but don't ask me how it was wired to do it.

QldKev

 

[black_labb]

The pid will be switching the element on and off to keep the temp, so it will draw nothing then the full 10A until it gets back to temp then nothing. It doesn't turn the element down. If you have something drawing any meaningful current and the 10A turns on you will blow the 10A fuse assuming they are plugged into the same 10A circuit.

You could plug things into different circuits (not neccesarily just different plugs) or plug into a higher current circuit (laundry circuits are often rated for higher current or you could have a sparky put one in).

 

[kjparker]

I think it would be fairly simple, just yank out the main HLT element and plug in the HERMS.

Look up Pulse Width Modulation, I think that is where you are going with the PIDs and using SSRs, but using PWM you still may exceed your threshold.

The only other way I'm thinking is if you use a relay setup on the outputs to switch between them. You would give the HERMS the priority on the power, and if it doesn't want it, then you allow the HLT to have it. I've seen it done at a mill, between loads, but don't ask me how it was wired to do it.

QldKev

Yep, using PWM is where my head was at.

I'd be more inclined to have both elements in the hlt running, through ssr's and once at temp (preferably automaticaly) cut power to the larger element. not sure how yet though

I guess I could try it. I have a watt meter that I got from Jaycar. If I were to plug the HLT into it, connected to the pid, with the pid through the watt meter, and see what happens when the temp reaches set point.

I intend to insulate the hlt so that there is minimal heat loss, which I presume would help. The more I think about it, the more I think I should just give it a crack!

 

[black_labb]

The only other way I'm thinking is if you use a relay setup on the outputs to switch between them. You would give the HERMS the priority on the power, and if it doesn't want it, then you allow the HLT to have it. I've seen it done at a mill, between loads, but don't ask me how it was wired to do it.

QldKev

I would imagine that a NC (normally closed) relay could run from the dc supply that runs the herms relay running the HLT. This way when the herms relay is switched on the power is cut to the HLT.

Never seen an NC relay but I've barely done anything with relays so that's probably just me.

 

[QldKev]

Where's matho and those electronic people when we need them :huh:

Just be careful if it does regulate out to a small draw, then someone tops up the HLT for sparge / cleaning water and bang, back to 100% load.

I've got one of those light dimmers on steroids. I wonder if you could mark one at the correct point to maximise load potential to 1000w.

Silly question, can you run a 25m extension cord to the house to find more power?


QldKev

 

[kjparker]

The pid will be switching the element on and off to keep the temp, so it will draw nothing then the full 10A until it gets back to temp then nothing. It doesn't turn the element down. If you have something drawing any meaningful current and the 10A turns on you will blow the 10A fuse assuming they are plugged into the same 10A circuit.

You could plug things into different circuits (not neccesarily just different plugs) or plug into a higher current circuit (laundry circuits are often rated for higher current or you could have a sparky put one in).

I brew in my garden shed, and only have a 16amp main breaker for it.

my understanding of PWM, was that it wasnt simply on/off, it had some sort of algorithm of how much current to provide to the element so as not to overshoot.

The only two loads at mash time would be the herms and the HLT, both PId controlled, so hopefully, neither is drawing any meaningfull current for any extended period of time.

But I am certainly open to suggestions, and more than happy to be corrected!

Where's matho and those electronic people when we need them :huh:

Just be careful if it does regulate out to a small draw, then someone tops up the HLT for sparge / cleaning water and bang, back to 100% load.

I've got one of those light dimmers on steroids. I wonder if you could mark one at the correct point to maximise load potential to 1000w.

Silly question, can you run a 25m extension cord to the house to find more power?


QldKev

Sure can with regards to the extension lead, and that was how I was powering my kettle. I have a kegking element, plus a 1500w element in it. I was going to do away with the 1500w and use only the kegking one. I really want to stay under the 16amp ceiling, as when we move (which will probably be in the next 18 months) I would really like to be able to just get a 15amp circuit installed and be done with it!

 

[kjparker]

Found this 500w element, but I wonder if this would be enough to keep it at temp...

http://www.uxcell.com/220v-500w-7mm-dia-ba...t-p-190448.html

 

[black_labb]

The PID you have controls the element using PWM? If so then you would be running less current, though I'm under the impression that most PID's run off a simple SSR turning the element on and off when neccesary.

 

[booargy]

You need at least a SPDT (single pole double throw) relay.
This is a DPDT (double pole double throw) relay. SPDT only has 3 power terminals

This is the circuit diagram on the relay.

Terminals 0 and 1 are for the relay coil
terminals 2 4 3 are one pole
terminals 6 8 7 are the other pole
8 is common
6 is N/O
7 is N/C

Not sure if this will help or hinder. but here is the basic control circuit.

 

[black_labb]

Didn't realise they had double throw relays. I've spent too much time playing around with valve amplifiers and not enough with brewing related electronics.

*blows element trying to run it on 750vdc*

 

[mILLrAT]

Didn't realise they had double throw relays. I've spent too much time playing around with valve amplifiers and not enough with brewing related electronics.

*blows element trying to run it on 750vdc*

I use solid state relays, cheaper and more reliable than mechanical relays. Try these units on ebay
http://www.ebay.com.au/itm/SSR-25A-Solid-S...=item3374d92225
Less than $5 delivered for a 25amp controller. The solid state relays are also suitable for proportional control via a PID loop. The solid state relay can be turned on & off using a digital output from the arduino.

The PWM (pulse width modulation) pins on an arduino are digital pins that can create a psuedo variable voltage output on that pin. Typically 100% output = 5 volts, 50% output 2.5 volts etc. You cant use PWM to control a solid state relay (SSR). Send a SSR a signal between about 3 and 30 volts and it switches on and stays on until the voltage turns off. You can control the SSRby adjusting how long the relay is turned on for over a given time period. If your time period is 60 seconds, then at 100% output the relay is turned on for 60 seconds in every 60 seconds. At 50% output the relay is turned on for 30 seconds in every 60 seconds and so on. This style of output would be suitable for a PID loop

 

[kjparker]

Well I have a second pid and ssr on the way to me.

I can now start working out the layout for my control panel and other bits.

Has anyone put a plug on their pt100 probes to make it easier to remove for cleaning vessels etc?

 

[seravitae]

The PID you have controls the element using PWM? If so then you would be running less current, though I'm under the impression that most PID's run off a simple SSR turning the element on and off when neccesary.

No this is not true in all but a very few cases


a PID using relays will draw the same amount of current when the relay has completed the circuit. The cumulative amount of energy used will be less than if it is fully switched on given a period of time, but the current will always be a factor of voltage and resistance.

with a PWM circuit using a solid state relay this is usually the same, unless the period of the full PWM cycle is much more frequent than the period of whatever timescale you are measuring the current on. Usually in the brewers case this is the RCD/breakers. You can drive solid state systems with such a fast period that the average current as 'sensed' by your breakers/rcd/whatever is the "average current".

AFAIK.

also: no standard SSRs have zero-crossing detection for synchronisation to microcontrollers. they do have internal ZCD which simply stops DC-ofsetting when switching on and off AC loads. However you do not know where or when this zero crossing is so you cannot synchronise with it. so very fast PWM cycles ( ie greater than 50/60hz ) is impossible with standard SSRs.
further note: the above is not really an issue with brewing since the large thermal/energy sink (20L+ of water) means that your PID is usually cycling on and off on the second-to-minute scale, not subsecond)

 

[Thirsty Boy]

i run my brewery on a single 10amp circuit. 2200w rims and 2400w hlt.

two channel mechanical relay - the RIMS pid drives the mech relay (via 12V control loop) and the other side of the mech relay runs to the HLT (which is an urn so has its own built in thermostat)

HLT is filled and brought up to mash temp - at this point the rims is not running so the HLT gets full time power.
Mash in and rims goes on, taking primary control of the power. HLT is turned up to sparge temp.
The rims just cycles in and out while its "maintaining" temp, still more time with the HLT getting power than without - when i do a step, then the HLT essentially gets nothing.

Basically it all works out nicely, the power the HLT gets is more than enough to bring it to sparge temp during the hour or so of mash time. And i never use more than the 10A i have available.

Kettle is boiled using a 2400W over the side element, but by the time I am using that, everything else is switched off.

As for SSRs being more reliable than mechanical relays... well, I'm sure they are and everything, but I have managed to fritz exactly one mech relay in the last 7 years of brewing on a rims/herms. And they aren't even tough industrial jobbies either.... just dick smith numbers. So less reliable is still pretty damn reliable in my opinion.

Edit - the PIDs I have, which are the cheapies off ebay & i think they are mostly all the same, dont do PWM as far as i know. They just do the on/off thing. They dont even drive the system fast as I think the minimum control period is 2seconds. Fancier PIDs required for the fancier stuff near as I can tell. Mind you, I might just not know how to drive it properly.....

 

[QldKev]

I use solid state relays, cheaper and more reliable than mechanical relays. Try these units on ebay
http://www.ebay.com.au/itm/SSR-25A-Solid-S...=item3374d92225
Less than $5 delivered for a 25amp controller. The solid state relays are also suitable for proportional control via a PID loop. The solid state relay can be turned on & off using a digital output from the arduino.

The PWM (pulse width modulation) pins on an arduino are digital pins that can create a psuedo variable voltage output on that pin. Typically 100% output = 5 volts, 50% output 2.5 volts etc. You cant use PWM to control a solid state relay (SSR). Send a SSR a signal between about 3 and 30 volts and it switches on and stays on until the voltage turns off. You can control the SSRby adjusting how long the relay is turned on for over a given time period. If your time period is 60 seconds, then at 100% output the relay is turned on for 60 seconds in every 60 seconds. At 50% output the relay is turned on for 30 seconds in every 60 seconds and so on. This style of output would be suitable for a PID loop

With that 25amp relay, running a 10amp load would you still need a heat sink?


QldKev

 

[kjparker]

I've seen divided opinions on that. Some say yes, some say no. Some say just make sure it's bolted to something metal. I bought a heatsink originaly for the first ssr I bought, but I didnt this time round. I will be bolting it to the metal box I'm builing my panel out of. if it gets hot, I'll get a heatsink for it. the last one was only $5....

 

[matho]

hey kev its hard say because the data sheet doesn't tell me the thermal rating of the case to air but if you look at the data sheet is says the voltage drop of 1.6v across the ssr (I think it drops as the temperature increases but I can't remember) that means the power dissipated id about 16 watts at 10 amps, maximum operating temperature is 80 deg that means at an ambient temp of 30 deg you are allowed a 50 deg rise. At 16w you will need to have a "heatsink" with a thermal rating of 3.125 deg/watt and I doubt that the thermal resistance of the case to air would be that.

View attachment SSR.pdf

cheers steve