PWM..Show us How

[clearwaterbrewer]

A lot of us use a PID that has a manual control mode that simply allows you to hit a button on the PID to switch to manual mode.

I have not noticed very many of the affordable PID's to have this manual mode, other than the Auber one... and it is hard to tell on the ones on eBay and such, so I assume they do not... even fewer of the 1/32 DIN units have this control from what I have seen, and 1/16 DIN takes up a lot of room for a simple PWM boil power control...

Additionally, stopping a boilover or just adjusting the percent power is really easy for *anyone* nearby with a knob, but can be an exercise in memory and button pressing with a PID...

From the OMRON manual:
press and hold < and > for 3 seconds..
select the 'level' parameter
select level 2 parameters
select hand parameter..
adjust < or >

it may stay in this mode just fine, and you can use the < and > buttons to adjust up and down throughout the boil, but if it is like the one on my espresso machine, it goes back to the main menu after a timeout..

 

[jsguitar]

Yeah, I and a number of others on the board use the one's from Auber. All you have to do is hit the manual mode button when you're ready to boil (and it stays in that mode) and down or up arrow until you're happy on mine (2352). For me, I just set it at 60% and forget about it. If I'm in a hurry I set it to 100% and then dial it down by hitting the down arrow. It doesn't require any other fussing with it at all. Nothing wrong with a knob but it's really not much more difficult to hit the down arrow on this particular PID.

 

[lschiavo]

Hm... I didn't think I was feisty, just stating some facts and opinions. It was clear in my head that if you wanted to use buttons to adjust the element that would work. Personally, for the simplicity and cost of the circuit, I'd rather have a knob.

Maybe that's not what the post sounds like to others? I certainly meant no insult or anything. Just trying to hold a useful conversation.

But while we're on the subject, I'd like to point out that a PID is great for a recirc system, but if you're just heating up some water to mash with, or to boil with, that simple PWM circuit would suffice by itself. Just something to think about.

I meant that with sarcasm. I totally agree with you. And if I didn't, I would just shut up and let you have your own opinion. I am on the "DONE" list too

 

[passedpawn]

I have not noticed very many of the affordable PID's to have this manual mode, other than the Auber one... and it is hard to tell on the ones on eBay and such, so I assume they do not... even fewer of the 1/32 DIN units have this control from what I have seen, and 1/16 DIN takes up a lot of room for a simple PWM boil power control...

Additionally, stopping a boilover or just adjusting the percent power is really easy for *anyone* nearby with a knob, but can be an exercise in memory and button pressing with a PID...

From the OMRON manual:
press and hold < and > for 3 seconds..
select the 'level' parameter
select level 2 parameters
select hand parameter..
adjust < or >

it may stay in this mode just fine, and you can use the < and > buttons to adjust up and down throughout the boil, but if it is like the one on my espresso machine, it goes back to the main menu after a timeout..

The auber PIDs have a dedicated button to switch from auto to manual mode. There is a corresponding red LED indicator too. It could be clearer, but it's certainly not difficult.

I love the idea of setting the PWM duty with something other than the PID. I'd do something digital so I could set it the same every time.

One thing that I don't think was mentioned here: the PID has a temp sensor input will show the temp of the boil pot. If you chill in your pot, say with an IC or recirculating CFC, that's a nice feature.

 

[ekjohns]

Here's a diagram I made. I tried to keep it simple. Hopefully it's enough to get you going. It's easier to understand once you get your hands on this stuff and start piecing it together.

Would wiring it this way cause the element to be always on (but only using 120V) when the system is hot and the PWM only controls one leg of the 240V. Would you need 2 SSRs to control both 120V legs?

 

[shortyjacobs]

Would wiring it this way cause the element to be always on (but only using 120V) when the system is hot and the PWM only controls one leg of the 240V. Would you need 2 SSRs to control both 120V legs?

The element runs with current running through one leg and out the other... No neutral. Switching one leg will turn the entire element on (240v) and off (0v). Only one ssr is required for full control.

 

[ekjohns]

The element runs with current running through one leg and out the other...

that wrinkles my brain!

edit: after a quick google search I found this "+120V - (-120V) = 240V" cause of AC...correct?

 

[shortyjacobs]

that wrinkles my brain!

Think of electricity like a waterfall. The farther the water falls, the more power it has. In 120V service, your waterfall is 120 feet high, and falls from 120 to 0, (with 0 being the neutral line) giving you 120 volts. In 240 volt service, both legs are 120V, but one is +120V, and the other is -120V with respect to the first, (the wave function is reversed 180 degrees). So, going back to the waterfall, imagine digging a hole 120 feet into the ground at the base of the waterfall. Water now falls from 120 feet up (+120V), to 120 below ground (-120V), giving a total fall of 240 feet, or 240V.

Put more simply, 240 volt service is NOT equivalent to 2x 120 foot waterfalls next to each other, (both hitting the ground at 0 feet), but equivalent to ONE 120 foot waterfall falling into a hole 120 feet deep, making the total height of the fall 240 feet.

There is no neutral line in this setup....the electricity in the +120 leg falls from a potential of 120V, right past 0, and to a potential of -120V. The circuit is ONLY between the +120V and -120V, so by switching one leg, you break the circuit. Even though the other leg is still at -120V, there's nowhere for current to flow - no circuit, no loop - so the element is switched entirely off. When the SSR fires, there's a circuit again, and you get 240V flowing through the element.

 

[passedpawn]

that wrinkles my brain!

The legs are always 180° out of phase. When one leg is high (120VAC), the other is -120VAC. Then they gradually switch polarites, and repeat 120 times a second. The difference between them is 240VAC.

Imagine a marble sitting on a teeter totter. Marble rolls one way, then the other. The current does the same thing as the marble.

 

[clearwaterbrewer]

The legs are always 180° out of phase. When one leg is high (120VAC), the other is -120VAC. Then they gradually switch polarites, and repeat 120 times a second. The difference between them is 240VAC.

Imagine a marble sitting on a teeter totter. Marble rolls one way, then the other. The current does the same thing as the marble.

wow, his brain is REALLY wrinkled now!

 

[passedpawn]

wow, his brain is REALLY wrinkled now!

It's like quicksand... the more I talk, the worse it gets. There's only one clear solution...

....

 

[mrbippers]

If one were to go the PID route (SYL-2352), does that come with the temperature probe or is that something that has to be purchased separate?

 

[passedpawn]

If one were to go the PID route (SYL-2352), does that come with the temperature probe or is that something that has to be purchased separate?

separate. Auber sells these also, lots of choices.

 

[ezzieyguywuf]

Question about the power supply you guys are using here, either with the Baktronics board or with Clearwaterbrewer's setup: I got a bunch of old phone chargers that output 5V at ~1 amp, I got one outputting at 0.7 amps. Looking at the LM555 datasheet, however, it looks like it has an upper input current limit of 6 mA at 5V and 15 mA at 15V: am I missing something here, or is a phone charger just not going to cut it? Where might I scavenge an appropriate power supply if this won't work? I suppose I could put a resistor in-line with my power-supply output, but I haven't heard anyone mention doing this yet.

Thanks.

Edit: Pretty sure the resistor would just drop the voltage, not the current. I think I'd have to place the resistor in parallel to the LM555. Either way, this seems like a valid solution.

 

[nate456789]

Question about the power supply you guys are using here, either with the Baktronics board or with Clearwaterbrewer's setup: I got a bunch of old phone chargers that output 5V at ~1 amp, I got one outputting at 0.7 amps. Looking at the LM555 datasheet, however, it looks like it has an upper input current limit of 6 mA at 5V and 15 mA at 15V: am I missing something here, or is a phone charger just not going to cut it? Where might I scavenge an appropriate power supply if this won't work? I suppose I could put a resistor in-line with my power-supply output, but I haven't heard anyone mention doing this yet.

Thanks.

Edit: Pretty sure the resistor would just drop the voltage, not the current. I think I'd have to place the resistor in parallel to the LM555. Either way, this seems like a valid solution.

Those are plenty powerful enough. You can run this circuit from a 9v battery if you had to.

 

[ezzieyguywuf]

Those are plenty powerful enough. You can run this circuit from a 9v battery if you had to.

I was more worried about my phone charger providing too much current, but I realize now that the 0.7 Amps (700 mA) is the maximum amount of current that the PS can supply. The max amp specs on the LM555 datasheet are telling me how much I can expect the IC to draw, which is will within the capabilities of my phone charger. Sweet!

 

[clearwaterbrewer]

Question about the power supply you guys are using here, either with the Baktronics board or with Clearwaterbrewer's setup: I got a bunch of old phone chargers that output 5V at ~1 amp, I got one outputting at 0.7 amps. Looking at the LM555 datasheet, however, it looks like it has an upper input current limit of 6 mA at 5V and 15 mA at 15V: am I missing something here, or is a phone charger just not going to cut it? Where might I scavenge an appropriate power supply if this won't work? I suppose I could put a resistor in-line with my power-supply output, but I haven't heard anyone mention doing this yet.

Thanks.

Edit: Pretty sure the resistor would just drop the voltage, not the current. I think I'd have to place the resistor in parallel to the LM555. Either way, this seems like a valid solution.

No resistor required, connect straight to the charger. The current output of the charger is what it 'can' do, not what it 'will always' put out... The PWM circuit will only draw .020 A or so, half of that is turning on the SSR... Use whatever one is most convenient... I prefer ones with cords vs ones that plug in, myself..

 

[ezzieyguywuf]

I don't see the distinction between the types of phone chargers your talking about, but that's ok. Here is my next question: why did you leave the .01uF capacitor out in your original circuit? I've read through a good portion of this thread and don't think I see an explanation for that anywhere. Also, did you ever hook up your circuit to some sort of signal analyzer (I dunno what those things are called) the kind that show you the waveform of your signal? I'm wondering if the blinking light on the SSR isn't showing you what is actually going on, and that really your circuit _is_ able to vary for the whole range of the Pot and not just the first 80%.

Thanks!

 

[Walker]

One thing that I don't think was mentioned here: the PID has a temp sensor input will show the temp of the boil pot. If you chill in your pot, say with an IC or recirculating CFC, that's a nice feature.

Another thing that may or may not have been mentioned here: If you are using a PID, even if it's for manual mode where the temperature is irrelevant, you must have a temp probe connected to it or the PID will not function.

You can just fake it with a 100 Ohm resistor across the terminals for the temp probe, but it's something be aware of.

 

[clearwaterbrewer]

I don't see the distinction between the types of phone chargers your talking about, but that's ok. Here is my next question: why did you leave the .01uF capacitor out in your original circuit? I've read through a good portion of this thread and don't think I see an explanation for that anywhere. Also, did you ever hook up your circuit to some sort of signal analyzer (I dunno what those things are called) the kind that show you the waveform of your signal? I'm wondering if the blinking light on the SSR isn't showing you what is actually going on, and that really your circuit _is_ able to vary for the whole range of the Pot and not just the first 80%.

Thanks!

I like ones that can have the end of the cord cut off, stripped, and put into t terminal block in the control panel... then velcro the unit to the inside of the control panel, out of the way. The kind that are a 'brick', and plug right into an outlet are more difficult to do this to. (I uses an old digital camera charger that had a removable cord.)

I left off the .01uF cap because the wiki (referenced earlier) did not have it, and I wanted simple... I think I added it back in when I added the diode to get the last 20%..

You could hook up to an oscilloscope, but you would have to change the cap to make the PWM fast for testing...

The LED on the SSR is a good indicator of the output, and if it were not, the 120V LED I have in my H-O-A switch that runs from neutral to the output of one of the SSR's would be, but they both act the exact same..

The circuit works good, I have three of them on my panel...

 

[ezzieyguywuf]

The circuit works good, I have three of them on my panel...

Yea I'm not questioning the 'goodness' of the circuit, just exercising my engineering curiosity is all. A few more questions for the group in general:

1) I'm only able to find 0.011uF capacitors on Digikey (am I not looking in the right place?): is it safe to assume that such a small deviation in the capacitance will not affect the function (whatever it may be, it's beyond me) of this already small capacitor in the circuit?

2) It looks to me like there is a 50% maximum possible duty-cycle using a Pot to represent both resistors. I'm basing this on the equation for the duty cycle from the datasheet for the LM555, namely D = Rb / (Ra + 2Rb). I used Ra + Rb = 500,000 (for a 500K pot) and subbed in for Ra and got: D = Rb / (500,000 + Rb), from which I got the 50% max. Feel free to check my math here: is this 50% max duty cycle unnecessarily restricting the output of our heating element?

I should note that the frequency at this duty cycle with the 2.2uF capacitor is approx 0.654 Hz, or a period of 1.53 seconds. I could be wrong, but it seems to be that turning the element on/off every 0.77 seconds would in reduce the output to less than the maximum.


Edit: I see now that by connecting the + of your load to your Vcc instead of Ground, your signal is 'Normally On' as specified on the data sheet, as opposed to 'Normally Off'. I take this to mean that you can effectively vary your duty cycle from 100% to 50% as opposed to 0% to 50%. I also see the section of the Wikipedia page that mentions using a diode to achieve this <50% duty cycle, though I'm not exactly comprehending how that works. I'll go take a look at the data sheet some more to see if I can understand the reasoning behind this.

 

[clearwaterbrewer]

Yea I'm not questioning the 'goodness' of the circuit, just exercising my engineering curiosity is all. A few more questions for the group in general:

1) I'm only able to find 0.011uF capacitors on Digikey (am I not looking in the right place?): is it safe to assume that such a small deviation in the capacitance will not affect the function (whatever it may be, it's beyond me) of this already small capacitor in the circuit?

2) It looks to me like there is a 50% maximum possible duty-cycle using a Pot to represent both resistors. I'm basing this on the equation for the duty cycle from the datasheet for the LM555, namely D = Rb / (Ra + 2Rb). I used Ra + Rb = 500,000 (for a 500K pot) and subbed in for Ra and got: D = Rb / (500,000 + Rb), from which I got the 50% max. Feel free to check my math here: is this 50% max duty cycle unnecessarily restricting the output of our heating element?

I should note that the frequency at this duty cycle with the 2.2uF capacitor is approx 0.654 Hz, or a period of 1.53 seconds. I could be wrong, but it seems to be that turning the element on/off every 0.77 seconds would in reduce the output to less than the maximum.


Edit: I see now that by connecting the + of your load to your Vcc instead of Ground, your signal is 'Normally On' as specified on the data sheet, as opposed to 'Normally Off'. I take this to mean that you can effectively vary your duty cycle from 100% to 50% as opposed to 0% to 50%. I also see the section of the Wikipedia page that mentions using a diode to achieve this <50% duty cycle, though I'm not exactly comprehending how that works. I'll go take a look at the data sheet some more to see if I can understand the reasoning behind this.

1 - http://www.radioshack.com/product/index.jsp?productId=2103628

I am sure that digi-key has them, their search leaves something to be desired.. .011 is close enough though..

2 - Please read the entire thread, there is good stuff in here... especially talking about the diode (also talked about in 555 Wiki mentioned in this thread)
"To achieve a duty cycle of less than 50% a diode can be added in parallel with R2 towards the capacitor. This bypasses R2 during the high part of the cycle so that the high interval depends only on R1 and C."


again, please read the entire thread

 

[Dirty]

Can anyone else post how they have there control panel set up. im thinking of going similar to the High Gravity set up with the a 6x6 box next to my spa panel with the pwm and ssr inside.


Thank God its Basketball Season

Rock Chalk

Chris

 

[mrbippers]

So if I wanted to go with a PID, I need to have either a 4 wire incoming 240V supply with neutral or 3 wire 240V and a separate 120V to power to PID right? I picked up a 30 amp 240V GFCI line cord on ebay cheaply instead of the spa panel route since I plan on moving in a year, but it's for 3 wire outlets. I like the idea of being able to program in a specific temperature with the PID, but if it's a matter of bringing in a second 120V line to power it the cheaper/easier PWM will probably win out.

Edit: Whoops. Looks like I need the neutral for the PWM power supply too unless I run it off batteries.

 

[clearwaterbrewer]

Theoretically, you could make a complete 240V system, All PID's I have seen are 120-240VAC input... ( I am sure there are old 120V only ones) if you had a 240V pump and 240V (or 12V or 24V) indicators, no neutral, one less wire, and a GFCI'd 3-prong dryer outlet is all you need... PWM can run off any 5-12v cell-phone/digital camera charger, etc brick, most new ones are 120V-240V also...

 

[nate456789]

I tried running my PWM circuit from the 240v line using one leg of it to power my power supply for the circuit and it kept tripping my GFCI for the 240V.
I had to break it out to a different 120v circuit that runs my pump.
Obviously I did something wrong because it looks like you guys are running most of your panel items from the 240v. I think I read that somewhere.
I would love to just have one 240v line feeding everything.
Any pointers would be appreciated.

 

[clearwaterbrewer]

One leg is not 240V... One leg is 120V, if it was tripping the 240V GFCI, then it was likely not to a neutral, but ground..

If you did not have a neutral on your 240V setup, and did not want it to trip the GFCI, you wold have to connect it to both legs ( it would have to be a 240V capable power supply, saying something like: "INPUT: 100-240V 50/60Hz 0.5A")

If you have a 120V circuit for your pump, then yes, you can hook the PWM to that, but you would want a GFCI on that also.....

To go all 240V, get a 240V March pump, I think they are the same cost...

 

[Homercidal]

Quick Question:

This PWM for BK circuit would work equally well for an electric hotplate, yes? I have need to use an electric hotplate for heating a small vessel containing fermented stuff, where an open flame would not be as safe...

 

[clearwaterbrewer]

PWM will work for heating, but needs to be controlled, so really not the best choice when comparing to a PID... that is why PID is used for mash(temp control), and PWM is used for boil(power control)... I personally would find a cheap heated stirplate on eBay if I were you...

 

[Henrythe9th]

Has anyone made a PWM board that could be powered by the output form a PID?
Thinking about having a PWM between the PID and the SSR for a RIMs set up and what about using a PWM computer fan contoller
If so a diagram would be helpfull as a parts list also
Thanks

 

[wyzazz]

Has anyone made a PWM board that could be powered by the output form a PID?

My first question would be why?

 

[clearwaterbrewer]

Has anyone made a PWM board that could be powered by the output form a PID?
Thinking about having a PWM between the PID and the SSR for a RIMs set up and what about using a PWM computer fan contoller
If so a diagram would be helpfull as a parts list also
Thanks

PWM is DC, so you will need a rectifier, 120v has to be stepped down, via a transformer or fairly custom silicon...

PWM computer fan controller uses 12VDC from the computer power supply...

Why reinvent the wheel? I don't know anyone that does NOT have a 5-12v power supply from something laying around....

Hmmmm... come to think about it, you know what PWM controller will work off of 120V AC line voltage?
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A PID Controller that does manual mode...
(I think I just kicked you to the other side of this thread! LOL... )

 

[Walker]

This was discussed on this forum in a threat several months ago. The main advantage to it is that you do not need a separate d c power source for the p w m. And you don't need any sort of switch to flip control between the 2 devices.

4 temperature controlled you just sent to pwm 2 full power. P I d control passes through it to the s s r.

When you want to control the boil strength You set the p I d to some temperature over boiling And then you adjust the pwm knob.

The only concern that came up when we discussed it before.. was whether you might potentially damaged p I d doing this.

Nobody really knows if there's any kind of inrush current when the 555 timer circuits starts up. The pid would have to handle that inrush current when the PWM was in passthrough mode for temp control.

 

[wyzazz]

I just don't see the advantage of a PWM controlled by the output of a PID, when you could just use a PID with manual mode. Or use a PID for temp control then have a switch to flip over to the PWM circuit to control your boil. Chaining the two together seems unnecessary and overly-complicated.

 

[clearwaterbrewer]

I just don't see the advantage of a PWM controlled by the output of a PID, when you could just use a PID with manual mode. Or use a PID for temp control then have a switch to flip over to the PWM circuit to control your boil. Chaining the two together seems unnecessary and overly-complicated.

agreed 100%... maybe the OP does not understand that you can set the max duty cycle of a PID so that even when it is in auto, when it is 'on', it is really just PWM..

 

[Walker]

I think the question stems from people trying to save as much money as possible, which I am generally a fan of. You can get basic PID (no manual mode) and build a PWM for half the price of buying a PID with manual mode support.

Another motivation might be control panel size. You need a DC power source and that switch to be able to flip between a PID and a PWM. Making use of the PID's SSR output *as* a DC power source, and avoiding the switch since the PWM sits in line on the SSR control lines would save some space.

I wouldn't call it "overly-complicated" at all. It uses less components and the idea is pretty straight-forward.

Would it work? No idea. Is it absolutely a worse idea than a PID with manual mode? No. That all depends on the individual's users situation.

 

[Henrythe9th]

What I was thinking was that if you had a PWM wired after the PID you could control the amount of heat being made by the elements for a RIMs set up,
when you set a PID in auto to say 80/20% when it comes on its at full power then completely off
I'm looking for a easy way to control the amount of heat/current that is going to the elements
I was planing on using a Ramp/ soak timer with PWM control for mashing with 2 2000w elements mounted into the grant for recirc mashing and mash out.
something like set the ramp PID to 151f for 45 min recirc, and ramp up to 185 for mash out, but with out any scorching possible, this is for a 5bbl sys

 

[shortyjacobs]

What I was thinking was that if you had a PWM wired after the PID you could control the amount of heat being made by the elements for a RIMs set up,
when you set a PID in auto to say 80/20% when it comes on its at full power then completely off
I'm looking for a easy way to control the amount of heat/current that is going to the elements
I was planing on using a Ramp/ soak timer with PWM control for mashing with 2 2000w elements mounted into the grant for recirc mashing and mash out.
something like set the ramp PID to 151f for 45 min recirc, and ramp up to 185 for mash out, but with out any scorching possible, this is for a 5bbl sys

A PWM works the same as a PID in terms of "on off" cycles. A PWM set at 60% will provide 100% power 60% of the time, and 0% power 40% of the time. A PID running in auto mode will cycle between 100 and 0% power as well.

A PWM is not a variable resistor, that would limit the max current going through an element. It's a variable duty cycle, but it's still binary, providing only "100% ON" and "OFF" states.

 

[Walker]

shorty has it right. a PWM does not limit the current. It causes 100% on/off cycling.

 

[Dirty]

OK. Ive got my board and my SSR.
Only questions are: According to what ive read he Capacitors and the Resistors dont have to be soldered in and specific direction. Is this correct?

And which capacitor is C1 which im supposed to swap out? If the POT faces you is it the upper or lower on?

Thanks

Rock Chalk

Chris