PWM for Boil Kettle Control

When I was starting the design of my brew rig, I went looking for a way to control my electric boil kettle without buying another PID. I came across this website.

http://home.highertech.net/~cdp/boilnew/boilnew.htm

I thought to myself. This should be easy. I have built PWM circuits before and I probably have enough spare parts laying around to make it. So that is what I did.

Well yesterday i finally got around to testing the circuit properly. So Plugged a DC motor into the SSR output and turned on the power. I started turning the potentiometer knob expecting to see the speed slow down. Nothing.......... Well that is strange. I tried a few combinations of wiring on the knob. Nothing. It just turns the motor off at certain spots when you turn it down. So now what?

I get out my volt meter and connect it. 12v when turned all the way up. Fine. Start turning the knob "down", and still 12v. I hesitate for a moment and the power goes off. I wait a few more seconds and the power goes back on. So i keep turning the knob and counting the second between on and off. Sure enough it changes when I turn the knob.

This is the first time I have come across a PWM circuit like this. It turns the output full on, or full off for set amounts of time. No variance in voltage and no quicker or slower pulsing that I am used to.

So I guess my question to all of you is and others who may go this route. Would a normal PWM still work? I am thinking that a normal PWM circuit might kill a SSR if it pulsed on/off too fast.

Also if anyone is interested in one of these circuits. I have an extra one that I built. I can also make more boards pretty easy. I could make them in two different configurations. All in a box complete with dial and inputs, or just the board and terminal blocks like the picture below.

I used a PWM kit from Bakatronics #FK804, cost $8, and swapped a capacitor to reduce the cycle time to 1Hz (also calculated the cap value for 1/2 Hz but deemed it unnecessarily slow). Hooked the output directly to the SSR and it worked great in my new 5500W brew kettle.

My understanding of SSRs is that the faster you cycle them, the hotter they run. That and how much current they're handling.

That makes sense to me. My only experience with PWM has been with motor controls and light controls. I guess I was expecting the same results.

did you figure out what was going on with the controller?
I am thinking to build it from CD's schematics...

Any feedback/recommendations?

The circuit works great. It just was not what I had thought when I started building it. I thought the pulses were going to be faster. Like the speed controllers I have used in the past. I love the way it works for me.

I say go for it. I am using a 5500w element with an SSD. I use a pot to control it and also put an status LED on my panel so I know when it is on and off.

Freddyb, What value capacitor did you settle on? I'm looking at buying that same kit, but am not sure how to calculate the cycle time.

Thanks.

I used the following equeations to calculate charging and discharge times along with frequency with the following equations:

Charging Time - T1 = 0.693(Ra+Rb1)C
Discharge Time - T2 = 0.693(Rb2)C
Frequency - f = 1/(T1+T2)

If you're using the circuit above, Ra and Rb are both 1k ohm resistors.

Rb1 = 1k + one side of 1M pot depending on where it's position is
Rb2 = 1k + other side of 1M pot depending on where it's position is

Pot all the way to one side: Rb1 - 1k ohm and Rb2 - 1M ohm
Pot in the middle: Rb1 - 501k ohm and Rb2 - 501k ohm

If you use the 4.7uF cap you'll get a frequency around 0.31. If you use a 1uF cap you'll get a frequency around 1.44.

Hope that helps.

I use a 2.2uF cap and it works great, around 1 second cycle time. I recall finding an error (or typo) with the calculations provided with the kit but I don't recall exactly what it was.

I've done quite a few batches using this system and I absolutely love it. Very "responsive" with my 5.5kW element, even with a full 13.5 gallons in the BK. I can go from rolling boil to gentle boil and back to rolling in a few seconds by adjusting the potentiometer. I put a big knob on there so it looks sweet too.

Thanks to the both of you for your info. I'll be building on very soon.

Send me some photo's and steps for dummy's I just bought components and would like some kind of photo's of PWM controller
Cheers

still offering to make these? how much for one with dial? i plan on getting a 20 gal pot and running a 5500 w element

Brewmoor said:

Also if anyone is interested in one of these circuits. I have an extra one that I built. I can also make more boards pretty easy. I could make them in two different configurations. All in a box complete with dial and inputs, or just the board and terminal blocks like the picture below.

Click to expand...

I would like the all in one version, with potentiometer to control a 5500w element!! I have an SSR just need the actual controller!! I also have my own box to put circuit in!! What's the price?

ErinWhite said:

I would like the all in one version, with potentiometer to control a 5500w element!! I have an SSR just need the actual controller!! I also have my own box to put circuit in!! What's the price?

Click to expand...

X2

freddyb said:

I used a PWM kit from Bakatronics #FK804, cost $8, and swapped a capacitor to reduce the cycle time to 1Hz (also calculated the cap value for 1/2 Hz but deemed it unnecessarily slow). ....

Click to expand...

I am a little confused by the cycle time. I thought the PWM adjusted cycle time? Or does the adjustment change the amount of time between cycles?

PWM changes the percentage of the cycle that the output is high vs low (duty cycle) the frequency (time between pulse leading edges) is fixed by the circuit design usually.

5 of my first 6, Posts have been about PWM controllers. Seems i got a better chance of getting a lap dance from Barbara Bush then get a " How to " for PWM.
Well i allways got Kal's E-BREW to rub one off too.

Sorry Folks. My life has change a great deal over the last few months. Some of you know I was starting a commercial taproom. Well we have been open for over two months and it is going very well. I do not have any time to make these controllers. Some of you have PM'd me and i will send the files I have soon. It has been a very crazy two weeks for me.

We were invited to do a beer tasting at the Winter X-Games for ESPN and their sponsers. We had our grand opening the following day too. We went through so much beer I have been frantically trying to make more. I will try my best to get my stuff together and email everyone that has asked.

Double-R said:

5 of my first 6, Posts have been about PWM controllers. Seems i got a better chance of getting a lap dance from Barbara Bush then get a " How to " for PWM.
Well i allways got Kal's E-BREW to rub one off too.

Click to expand...

got this info from freddyb

freddyb said:

Buy this: http://www.bakatronics.com/shop/item.aspx?itemid=383
Replace C1 with a 2.2uF capacitor to lower the frequency.
Use a 12V wall wart as a power supply to the PWM board.
Connect the output of the PWM board to a SSR to control your boil.

This is how I did it and I'm very happy. Cheap, easy, responsive control.

Click to expand...

atoyot said:

got this info from freddyb

Click to expand...

that looks like a pretty easy and economical way to go. can't be sure since the picture is kind of blurry but it looks like a standard NE555 timer based circuit. They work great, and are easy to configure.

atoyot,

Thanks for providing the info, I was originally looking at using an infinite switch to control BK as I didn't want to invest in another PID. This solution looks much easier and will fit nicely in a small control panel.

I would recommend one uses a numbered dial, so once you determine the cycle needed to maintain a boil you can mark some how and go from there.

Thank again!

*Just want to confirm, once constructed (switching the cap) one would run 12vdc to the speed control, and it's output would run to a dc controlled SSR? *

Also anyone whom purchases want to post the parts list. Shipping cost more then the unit itself

bump.

Looking for an answer above before I place an order

I don't have that board, but yes the low voltage goes to the board and chopped control signal goes to the CTRL input of SSR. Make sure the SSR has a 5-12VDC input and you should be good to go. I bought one off e-bay for next to nothing.

Squeeky said:

*Just want to confirm, once constructed (switching the cap) one would run 12vdc to the speed control, and it's output would run to a dc controlled SSR? *

Click to expand...

correct

Squeeky said:

atoyot,

Thanks for providing the info, I was originally looking at using an infinite switch to control BK as I didn't want to invest in another PID. This solution looks much easier and will fit nicely in a small control panel.

I would recommend one uses a numbered dial, so once you determine the cycle needed to maintain a boil you can mark some how and go from there.

Thank again!

*Just want to confirm, once constructed (switching the cap) one would run 12vdc to the speed control, and it's output would run to a dc controlled SSR? *

Also anyone whom purchases want to post the parts list. Shipping cost more then the unit itself

Click to expand...

That's how I am doing it and it works great. Get a 40A SSR and make sure you use a heatsink.

Thanks everyone, now to find a cheap PWM on ebay or order the one listed above.

Also it might be worth mentioning that the power supply for PWM circuit doesn't have to be 12v necessarily. I believe mine operates from 3-12v. I had a 5v phone charger I didn't need so I just used the circuit from that.

I build that exact PWM for my BK and it works great. The point is to turn the power completely off and on. It basically gives you a square wave on an oscilloscope. Anyway, it controls my 4500w element just fine. It has some pretty good fine tuning too.

I would imagine an infinity switch might create a lot more heat as you start dialing it down. That's a lot of lost energy... no?

I think I'll be moving forward with this design, since the potentiometer used can completely cut power. I think I'll use a 9v battery to power the circuit. I read on an old HBD post that the 9v battery had been going strong for over 10 brews. It's extremely simple circuit so I would assume the battery would last a long time. That way I could have everything in a small project box.

I also sent a PM to walker, and he mentioned if he had to make it all over again he would use a 15uf or 22uf cap, instead of the 33uf to decrease the amount of time between cycles. It's just food for thought.

This is exactly the post I was looking for. I started buying parts before completely planning out my brewery (first mistake). I ended up settling on a single-keggle electric BIAB design, but had bought a PID that does not have a manual mode (JLD612) so it wouldn't work for the boil. According to SWMBO, I have blown my build budget for the time being, but can certainly spring for an $8 PWM and scrounge a 12V supply from my closet. Now all I have to do is figure out the switching from PID-control to PWM-control of the SSR. The biggest problem I see is that my control box is about to get a lot more crowded.

freddyb said:

I used a PWM kit from Bakatronics #FK804, cost $8, and swapped a capacitor to reduce the cycle time to 1Hz (also calculated the cap value for 1/2 Hz but deemed it unnecessarily slow). Hooked the output directly to the SSR and it worked great in my new 5500W brew kettle.

My understanding of SSRs is that the faster you cycle them, the hotter they run. That and how much current they're handling.

Click to expand...

In this kit, the capacitor I want to swap out is C1, correct?

wrench said:

In this kit, the capacitor I want to swap out is C1, correct?

Click to expand...

Correct.

This may be a dumb question, but if you used this unit, it appears you can adjust the frequency without changing capacitors, correct? Would this be a better unit than the 7.99 one from Bakatronics? I suppose no one uses it since we are getting close to the PID price from Auber though..
http://www.bakatronics.com/shop/item.aspx?itemid=444

onthekeg said:

This may be a dumb question, but if you used this unit, it appears you can adjust the frequency without changing capacitors, correct? Would this be a better unit than the 7.99 one from Bakatronics? I suppose no one uses it since we are getting close to the PID price from Auber though..
http://www.bakatronics.com/shop/item.aspx?itemid=444

Click to expand...

The frequency of this part is listed as 100Hz. The frequency adjust kit which is purchased separately let's you adjust between 100Hz and 15KHz. We want ~1Hz, so it's not what we need.

I have been really happy with the $8 unit from Bakatronics. Since I ordered it as a kit and had to build it anyway, using a different capacitor wasn't an issue and the calculations were simple. I love the analog knob PWM control vs. the push-button manual control on the PID. The system is very responsive.

I'm still interested to know what other kit or pre-assembled options exist for "really slow PWM controllers."

Ok, I have to ask this: Why bother with PWM control on your BK? I have a 5500 watt element in my keggle running with no control. Works great and have not had a boil over yet. Maybe because of my water profile?

I have had boil overs with propane on occasion. But I was using smaller pots back then.

Pick said:

Ok, I have to ask this: Why bother with PWM control on your BK? I have a 5500 watt element in my keggle running with no control. Works great and have not had a boil over yet. Maybe because of my water profile?

I have had boil overs with propane on occasion. But I was using smaller pots back then.

Click to expand...

I get boilovers easily if I don't turn the power down to about 75%. Even with foam control (although that helps a LOT). I use a PID for PWM.

Pick said:

Ok, I have to ask this: Why bother with PWM control on your BK? I have a 5500 watt element in my keggle running with no control. Works great and have not had a boil over yet. Maybe because of my water profile?

I have had boil overs with propane on occasion. But I was using smaller pots back then.

Click to expand...

If you want to do a 5 gallon batch instead of a 10 in an eKeggle for example. Or, if you want to "over power" the system to get a faster boil and then dial it back for a nice rolling boil. If you fly sparge (like I do) you'd probably want to turn on the element as soon as it is covered by wort and don't want to run it full blast. Controlling the heating element is also a good way to tinker with your evaporation losses to hit your final volume. I used my boil kettle to heat my strike water before mashing in and I like to dial it back to a very low setting to maintain the temp until I'm ready for the water.

As-is, I run my 5500W element at about 65-70% power for 10 gallon batches in my eKeggle (my guess based on the dial position.) Much higher and the boil is too hard and I would get a boil over.

Unless your heating element, boil kettle, batch size, etc...are all nicely matched, there are plenty of reasons you'd want some control over the heating element.

freddyb said:

The frequency of this part is listed as 100Hz. The frequency adjust kit which is purchased separately let's you adjust between 100Hz and 15KHz. We want ~1Hz, so it's not what we need.

I have been really happy with the $8 unit from Bakatronics. Since I ordered it as a kit and had to build it anyway, using a different capacitor wasn't an issue and the calculations were simple. I love the analog knob PWM control vs. the push-button manual control on the PID. The system is very responsive.

I'm still interested to know what other kit or pre-assembled options exist for "really slow PWM controllers."

Click to expand...

Freddy,
I ended up ordering the PWM kit factory assembled, the one originally mentioned in the thread, so I have to remove a capacitor and replace it. Do you happen to know the number of the one needed? I suppose I can get that at Radio Shack? Looking at the unit as pictured on their site, it would be the one nearest the timer (555) or the other one? From the crappy documentation sent with it I am assuming its the one furthest from the timer.

I went ahead and replaced C1 with a 10uf capacitor from radio shack. Now when I test it with my little dc motor there isn't any speed control. Will my SSR function properly? I suppose there is only one way to find out! Once they get here from China I will have this little project done I hope!

onthekeg said:

I went ahead and replaced C1 with a 10uf capacitor from radio shack. Now when I test it with my little dc motor there isn't any speed control. Will my SSR function properly? I suppose there is only one way to find out! Once they get here from China I will have this little project done I hope!

Click to expand...

The amount of time between pulses is too wide now for a fan I think. The fan's capacitor would be too narrow for a heating element.

onthekeg said:

I went ahead and replaced C1 with a 10uf capacitor from radio shack. Now when I test it with my little dc motor there isn't any speed control. Will my SSR function properly? I suppose there is only one way to find out! Once they get here from China I will have this little project done I hope!

Click to expand...

I used the suggested 2.2uf to replace c1 and it seems to work great with a lamp for testing. Haven't had a chance to boil yet. My local Radio Shack stocks this http://www.radioshack.com/product/index.jsp?productId=2102479&filterName=Type&filterValue=Electrolytic+capacitors