PWM..Show us How

[Homercidal]

"C1 is between the ground post and the Pot! C2 is next to the 555 Chip"

I think you need to mind the polarity of the replacement cap if it's an electrolytic.

 

[Dirty]

Homercidal

Thank

The polarity of the Capacitor it noted by a (+) correct?


Rock Chalk
Chris

 

[Homercidal]

The cap will have a (-) on one side I think, and one of the leads will be longer as well. I can't remember which one was longer. Plus the board may not be marked for polarity, since the original cap probably didn't need it (I think). They give a schematic, so you should be able to tell which goes where by reading that.

 

[Dirty]

Thanks

If i have any questions when i get the cap ill post a pic. Thanks again.

Rock Chalk

Chris

 

[FrFtr28]

Is there any place besides Bakatronics to get that pwm board? Shipping doubles the price and I have looked on ebay and found quite a few, but I'm not sure if any would work.

BTW, I am looking for a completely assembled board.

 

[Homercidal]

I've seen the same circuit other places. The cost is still about the same though.

I'm currently (kinda) working on building them at home by buying lots of components cheap on ebay and etching my own boards. Reminds me I need to try the layout transfer again tonight after racking my barleywine into secondary. Actually, I think the Christmas Ale is ready for secondary (keg) too. Also reminds me I wanted to grab a piece of aluminum for pressing the transfer. Gotta run out back. See ya!

 

[Walker]

Homer: have you looked at mouser.com for ordering parts? I can't imagine things being too much cheaper on ebay than from mouser. 555 timers are like $0.18, diodes are $0.09, resistors and capacitors are a couple of pennies.

Here's the total bill of components for the PWMs like I have built , $2.05 per build.

http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=42dabdadd1

 

[lschiavo]

barleywine!

Save me one. The one you gave me at Yoopers brewday was awesome

 

[FrFtr28]

I've seen the same circuit other places. The cost is still about the same though.

I'm currently (kinda) working on building them at home by buying lots of components cheap on ebay and etching my own boards. Reminds me I need to try the layout transfer again tonight after racking my barleywine into secondary. Actually, I think the Christmas Ale is ready for secondary (keg) too. Also reminds me I wanted to grab a piece of aluminum for pressing the transfer. Gotta run out back. See ya!

If you, or anybody on here for that matter, are building these to sell I would be interested in buying one. I don't have any experience when it comes to soldering circuit boards and I would feel a lot more comfortable with somebody else doing it.

 

[Homercidal]

Homer: have you looked at mouser.com for ordering parts? I can't imagine things being too much cheaper on ebay than from mouser. 555 timers are like $0.18, diodes are $0.09, resistors and capacitors are a couple of pennies.

Here's the total bill of components for the PWMs like I have built , $2.05 per build.

http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=42dabdadd1

I don't think I have. That's pretty cheap for a 555. Unfortunately I've got all of the "odd" stuff and only have a few components left to buy.

Save me one. The one you gave me at Yoopers brewday was awesome

Thanks. this one will be a bit different. I wanted a "lighter" color. More like a IIPA/barleywine like I've had a beer festival. We'll see. I think I put too much hops in. Might be best after 9 months or so (I hope). My autosiphon is missing the tubing so it will have to wait until tomorrow.

If you, or anybody on here for that matter, are building these to sell I would be interested in buying one. I don't have any experience when it comes to soldering circuit boards and I would feel a lot more comfortable with somebody else doing it.

I had hoped to make them cheap enough that I don't feel ripped off for selling them on here. We'll see. It's hard to be the cheap online deals, but honestly, they don't seem too hard to make. I still have to find 100K pots or modify the circuit to handle 500K.

Gotta go make some etching solution!

 

[Walker]

Homer: I considered making and selling them too but I don't think it would be possible to cover the vendor fees with a small margin on a PWM.

 

[stamandster]

Walker, which schematic is the one that will work with the parts you listed for mouser? I'm really keen on making one now that a parts list is readily available. Maybe even two!

 

[Walker]

Walker, which schematic is the one that will work with the parts you listed for mouser? I'm really keen on making one now that a parts list is readily available. Maybe even two!

This is how I build them:

The parts list I gave is not 100% complete in the sense that it does not include a board to put all of the parts on. The one in my panel was built by soldering all of that stuff down to one of these:

Dual General-Purpose IC PC Board - RadioShack.com

But that honestly was a bit of a pain. Tiny connections and wires. I have built several more since then, and I went the cheater route and used a

solderless breadboard to assemble them, which is really handy. (If that link is dead, just search ebay for "solderless breadboard" and you will find more.)

The solderless breadboard allows you to quickly assemble them and you can just cut off a short piece of that board since the circuit only needs a few rows of the thing. You can quickly switch components out if you want/need to.

Here's one that is 90% assembled on a solderless breadboard. The only thing not attached is the pot and DC power source which is 5 more wires that need to plug into the board.

edit: if you are looking at this pic to build your own, I had the black capacitor in backwards. There is a grey stripe on the thing to denote which side is the 'negative' side. I have that side pointing up in this above photo, and it should be pointed down. The circuit will NOT work properly if you assemble it like I did here. Turn the large cap around so that the grey stripe is pointing down.

Almost forgot. I drew this pic to help someone assemble one of their own on a solderless breadboard:

The little circles represent the holes in the breadboard and that diagram shows everything connected (power source, pot, all components). It's basically the exact thing I show built above on the breadboard, just with different colored wires.

One thing you may want to add to this is a LED that you can install next to the knob on the panel face. Connect it to the same points that the SSR control signals are connected to. The LED will serve as a visual indicator of the pulse you are generating.

The comment about the fan is on there because the guy I drew this for wanted to add a small CPU cooling fan to his control panel to blow air across his SSR's heatsink, so I was just instructing him to tap the fan into this same DC power source (make sure you use a DC power source that matches the fan in that case.... most cell phone chargers these days are 5V but the CPU cooling fans are often 12V. It'll spin with 5V, but not very fast and won't push enough air to cool well.)

 

[birvine]

Wow - I was just perusing that schematic online last night and here it is. This is getting easier all the time!

B

 

[stamandster]

...
The parts list I gave is not 100% complete in the sense that it does not include a board to put all of the parts on. ...

But that honestly was a bit of a pain. Tiny connections and wires. I have built several more since then, and I went the cheater route and used a

solderless breadboard to assemble them, which is really handy. (If that link is dead, just search ebay for "solderless breadboard" and you will find more.)

Awesome thanks so much Walker! I have a solderless breadboard that i bought for another project (some USB hacking ) that I could use for testing.

 

[Homercidal]

Homer: I considered making and selling them too but I don't think it would be possible to cover the vendor fees with a small margin on a PWM.

Yes, that is true. I was not planning on joining as a vendor, but to offer them to friends on the site at no profit.

Of course, I wouldn't want to take sales away from any stirplate vendor on here.

With the few people I know IRL it was worth it to make them myself anyway, and for Pete's sake just BUILDING them is a lot of fun.

Etched a board last night and it worked SWEET! But I did find out I have to massage the layout some more and I found some VERY small "noise" in the print, which came out as small flecks of copper on the board where they shouldn't be, so I'll have to clean up the image I used while I'm tweaking the traces.

I was very surprised at how fine the etching process could make traces.

 

[FrFtr28]

... Here's the total bill of components for the PWMs like I have built , $2.05 per build.

http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=42dabdadd1

... But that honestly was a bit of a pain. Tiny connections and wires. I have built several more since then, and I went the cheater route and used a

solderless breadboard to assemble them, which is really handy. (If that link is dead, just search ebay for "solderless breadboard" and you will find more.)

This definitely seems more up my alley since there is no soldering to be done.

Just to make sure I understand this right, if I order Walker's project from Mouser and a solderless breadboard, that is all I need to build this board? After that, all I would need is a DC power source and SSR and that would control the heating element?

 

[stamandster]

Homer, did you post your process for etching the boards already?

Walker, I ordered 4 kits Just because it makes more sense with shipping.

 

[Walker]

This definitely seems more up my alley since there is no soldering to be done.

Well.... there is still some soldering. The potentiometer looks sort of like this:

So you need to solder wires onto those little lugs. (And actually.... the pot on my parts list has FIVE lugs... two of them act as a power switch, but you don't need to use that .... see next post if you want to use the power switch part of the pot).

Just to make sure I understand this right, if I order Walker's project from Mouser and a solderless breadboard, that is all I need to build this board? After that, all I would need is a DC power source and SSR and that would control the heating element?

The solderless breadboard, the components on that mouser 'project' I linked to, a DC power supply, and an SSR. Those things gives you the ability to adjust the amount of on/off time of a heating element.

There's a lot more to complete a full project: a box to put it all in, power cables, heating element, mounting kit for an element, etc, etc.... but the board, mouser components, SSR and DC power are all you need to build a basic control circuit.

 

[Walker]

here's a re-draw showing how the exact poteniometer I used can be wired in and make use of the built in power-switch on the pot:

That one in my project at mouser will "click" when you turn it all the way down, and that will cut off the DC power source (+) wire. It basically diconnects the blue wire and the red wire. The circuit powers down and no voltage can reach the SSR control.

It's optional. You can totally ignore the built in power switch on the potentiometer, but it was there, so I used it.

 

[FrFtr28]

Well.... there is still some soldering. The potentiometer looks sort of like this:

...

So you need to solder wires onto those little lugs. (And actually.... the pot on my parts list has FIVE lugs... two of them act as a power switch, but you don't need to use that).



The solderless breadboard, the components on that mouser 'project' I linked to, a DC power supply, and an SSR. Those things gives you the ability to adjust the amount of on/off time of a heating element.

There's a lot more to complete a full project: a box to put it all in, power cables, heating element, mounting kit for an element, etc, etc.... but the board, mouser components, SSR and DC power are all you need to build a basic control circuit.

I can handle that soldering, it's the soldering on circuit boards I seem to fail at.

I've been trying to figure out how I want my setup since my situation is a little unique. We just moved into a new house in October and I want to make the switch to electric but don't have the funds to go all out right now, that is why I am trying to go as simple as I can right now and then slowly gather the parts to go all out. I plan on using the spa panel from HD to house all the electronics, a 5500w element from HD as well and getting my power from a stove outlet.

I pretty much have everything figured out. Controlling the element was the biggest hurdle, but that's no longer a problem.

BTW, those faucets and shanks you sold me are still working great!

 

[Walker]

I can handle that soldering, it's the soldering on circuit boards I seem to fail at.

I've been trying to figure out how I want my setup since my situation is a little unique. We just moved into a new house in October and I want to make the switch to electric but don't have the funds to go all out right now, that is why I am trying to go as simple as I can right now and then slowly gather the parts to go all out. I plan on using the spa panel from HD to house all the electronics, a 5500w element from HD as well and getting my power from a stove outlet.

I pretty much have everything figured out. Controlling the element was the biggest hurdle, but that's no longer a problem.

One bit of advice.

Before you go ordering anything from mouser.com plan your whole system out on paper and see if there is anything else you want/need from mouser. The PWM parts only cost $2, but you will get hit with probably $5 in shipping charges if you just order that stuff. I ordered like $40 worth of stuff from mouser.com in one shot, so my $7 shipping charges were not that big of a deal (and I bought extra parts for spares).

A couple other things I think you will want to add to your system:
- a manual "kill" switch to absolutely positively kill the power to your heating element.
- a small fan to blow air around and keep the SSR cool. They tend to generate a lot of heat.
- some thermal grease to put between the SSR and it's heatsink (helps transfer heat)
- small panel mount circuit breakers to drop that 50A service you have down to 25A or 30A (whatever your heating element needs).

You can probably get those things from mouser, too. That place pretty much sells everything in the world related to electronics. I know the thermal grease and breakers are available.

BTW, those faucets and shanks you sold me are still working great!

LOL. I honestly didn't realize that you were the same person, though your screen name did seem vaguely familiar. I just couldn't place it.

 

[FrFtr28]

One bit of advice.

Before you go ordering anything from mouser.com...

A couple other things I think you will want to add to your system:
- a manual "kill" switch to absolutely positively kill the power to your heating element.
- a small fan to blow air around and keep the SSR cool. They tend to generate a lot of heat.
- some thermal grease to put between the SSR and it's heatsink (helps transfer heat)
- small panel mount circuit breakers to drop that 50A service you have down to 25A or 30A (whatever your heating element needs).

Too late, I already placed the order for two sets of your project. I already have a fan I got out of a dead copier so I was thinking of using that to keep things cool. I'll be using a 40 amp SSR so that should run a little cooler than a 25 also. I ordered the solderless board, SSR and heat sink from Ebay and everything else I need I should be able to pick up locally.

One other question I had. What gauge of wire should I get for assembling the board?

 

[Walker]

There's very little current flowing through those wires on the pwm circuit. I think I built mine out of wires that I harvested from a piece of Ethernet cable.

That stuff is like 22 gauge or 24 gauge. Small small stuff.

 

[stamandster]

Thanks Walker that diagram is what I'll be using to use the potentiometer to control the power completely. Might as well, right?

 

[Walker]

Thanks Walker that diagram is what I'll be using to use the potentiometer to control the power completely. Might as well, right?

Might as well... but you still want a manual kill switch to interrupt the hot lines going to the element.. Don't rely on the SSR to kill power. They can fail in a mode where that will not shut off and the power just goes through them regardless of what the PWM is telling it to do (this has happened to me personally.)

 

[Clementine]

I was going to put on here that you could use a 555 ic as an oscillator with a pot to skew the duty cycle and make your own PWM but after looking at how cheap those bakatronics PWM controllers are I say that is gold.

Clem

 

[Walker]

I have never looked closely at the bakatronics one, but I think I have seen it mentioned that you have to modify them because they use too high a frequency (they are intended for DC motor speed control and not lazily pulsing AC heating elements).

And no need to mention the 555 timer. that's what most of the thread is about.

 

[stamandster]

I was going to put on here that you could use a 555 ic as an oscillator with a pot to skew the duty cycle and make your own PWM but after looking at how cheap those bakatronics PWM controllers are I say that is gold.

Clem

The problem is that the shipping doubles the price. I can get four kits for less than one total at Baka.

 

[Csuho]

12V-40V 10A PWM DC Motor Speed Controller w/ Knob - Free Shipping

what does every1 think of this controller? It looks beefy and cheaper than the bakatronic controller and its put together.

 

[Walker]

Definitely looks beefier. But beefy is not something you need. The only thing you will be driving with pwm is a solid state relay and that does it need a very beefy circuit.

The price is good considering that it's completely assembled. But you will still need to modify it. A pwm that does dc motor speed control will be cycling too fast for a solid state relay.

 

[passedpawn]

I don't think the AC SSR consumes much more current when switching since it does that at zero crossing (unlike DC FET control). Since there are 120 crossings per second, you probably could go ahead and switch fairly fast without much problem. You'd want to drive the optical input of the SSR with a very compliant source (bulk caps good here). I don't think an AC SSR will heat much more if pulsed at a high rate (i.e, 50 pps).

All this is guessing. I'm with Walker, if you can pulse it slower there's no downside.

 

[Walker]

To make the math easier, assume you tried a 60Hz frequency for the PWM.

Like you said, there are 120 zero-crossings per second with an AC SSR. But in terms of zero crossings per PWM cycle you only see two crossings.

A 60Hz PWM would only be able to hit 3 settings: 0%, 50%, or 100%. No finer granularity would be possible.

And don't forget that the PWM does not switch instantaneously. I think the one I use has a 25ms switching time. If you cycle the PWM too fast the SSR will never even be able to actually switch on and pass current through.

 

[passedpawn]

To make the math easier, assume you tried a 60Hz frequency for the PWM.

Like you said, there are 120 zero-crossings per second with an AC SSR. But in terms of zero crossings per PWM cycle you only see two crossings.

A 60Hz PWM would only be able to hit 3 settings: 0%, 50%, or 100%. No finer granularity would be possible.

And don't forget that the PWM does not switch instantaneously. I think the one I use has a 25ms switching time. If you cycle the PWM too fast the SSR will never even be able to actually switch on and pass current through.

Ah, right! I was "quick-posting", which is traditionally done with the brain in neutral. I forgot we were talking about changing the duty cycle.

So, to get 1% resolution on the duty cycle, you wouldn't want the switching period to be any faster than about 1 second (1 Hz).

Thanks for correcting me so quickly there.

 

[Jbt]

Any local sources for a 500k pot?? I have a circuit built and blinking away with resistors on it but ratshack only has up to 100k. I don't really want to pay $8 in shipping to get a .80 pot from mouser.

I already looked for a guitar repair place in the area but nothing.

 

[Walker]

what schematic are you using? You can probably use the smaller pot if you use a smaller controlling capacitor.

 

[Jbt]

what schematic are you using? You can probably use the smaller pot if you use a smaller controlling capacitor.

I used the 3 component schematic. With the 2.2 cap

 

[Walker]

I used the 3 component schematic. With the 2.2 cap

If the pot you have available is 1/5th the size as the one in the schematic, then you can probably just use a capacitor that is 5 times the size of the one in the schematic and maintain the same timing behavior.

So... 11uF in this case.

But, you could even go larger and still get a reasonable frequency for the PWM. If I am reading/understanding it right, the circuit with the 2.2uF cap and the 500kOhm pot is actually cycling a little too fast (about 1.3Hz).

If I am correct on my calculations, I'd probably throw a 22uF cap in that with the 100KOhm pot and get a frequency of 0.65Hz.

 

[Jbt]

If the pot you have available is 1/5th the size as the one in the schematic, then you can probably just use a capacitor that is 5 times the size of the one in the schematic and maintain the same timing behavior.

So... 11uF in this case.

But, you could even go larger and still get a reasonable frequency for the PWM. If I am reading/understanding it right, the circuit with the 2.2uF cap and the 500kOhm pot is actually cycling a little too fast (about 1.3Hz).

If I am correct on my calculations, I'd probably throw a 22uF cap in that with the 100KOhm pot and get a frequency of 0.65Hz.

Awesome thanks..
Should I add the .01 cap to control and diodes on the pot right away?? I was just looking at your most current schematic

 

[Walker]

Not sure what you mean with the 'right away' part of that. The diode is absolutely necessary for the circuit to work.

The tiny cap on the control pin of the 555.... I've seen a few folks claim its not needed, but I always put it there.