240v heating element question

[Walker]

Please note the comments below the image:

The two components in blue (one capacitor and the potentiometer/rheostat) are where you can make changes to control the frequency of this thing.

The frequency will be:

1.44/(C * R)

So, in this example, the circuit will have a frequency of

1.44/(0.000020 * 100000) = 0.72Hz

It will go through one timing cycle every 1.38 seconds.

By turning the knob on the potentiometer, you can adjust how much time out of that 1.38 seconds the pulse will be ON vs OFF. Turn the knob all the way one direction and the element will basically be on 100% of the time. Turn the knob all the way the other direction and the element will basically be on 0% of the time.

You will need to supply the circuit with a DC voltage source. If you have an old cell phone charger or other old power adapter lying around, you can use that for the DC source.

The end result is that the "dis" (discharge) pin of the 555 timer chip will periodically drain current (as controlled by your knob setting). When the discharge pin is sinking current, you will get a voltage difference between the + and - wires that are marked as "relay control voltage", and the relay will allow your 220V to pass through. When the discharge pin is not sinking current, there will be no voltage drop across the relay control and the relay will not allow the voltage through.

THIS IS NOT NECESSARILY A COMPLETE CIRCUIT. YOU MAY HAVE TO TWEAK THINGS BY ADDING A RESISTOR BETWEEN THE "DIS" PIN AND THE RELAY TO LIMIT THE AMOUNT OF CURRENT THAT WILL BE PULLED THROUGH THE RELAY. THIS IS GOING TO DEPEND ON THE SPECIFIC SSRs YOU BUY.

Also note that many people use two relays to turn on and off both hot wires of the 220V power feed. You will be able to adjust the power with just a single relay on one of the hot lines, but note that this means that the other hot line (the one not passing through the relay) will have a live 110V on it as long as it is plugged in.

 

[Walker]

FYI: am about to build a couple of these for my HERMS and I am ordering from mouser.com.

The total cost of parts from mouser.com (555 timer chip, potentiometer with knob, large capacitor, small capacitor, and two diodes) came in at under $1.50. I already have circui boards laying around to solder everything to, so I don't know the price of those.

Shipping is about $6 for a minimal order from mouser, but I had a bunch of other stuff to get from there anyway.

I did not price everything at Radio Shack, but I looked in there the other day and found that the price of the 555 timer alone was about $1.75 (it's $0.28 from mouser).

I'm thinking about starting to build these things and sell them. They are super easy to make, cost next to nothing, and could be sold easily for a small profit.

 

[Bjornbrewer]

Wasting power? How does an SSR waste power?

They get hot right? that's dissapated power that isn't going towards any work...it's waste. You waste about 1-1.5W/amp through an SSR.

I mean, with 4 elements on the brew rig, I dont want (4) live wires running around it when the system is powered down. It was $30 to get the SSR and heatsinks to power down each element, so it wasnt bad IMHO

I guess it depends on the system and it's funcitonality, but only one is required. That should be made clear to the OP...he was told he NEEDS two.

 

[The Pol]

They get hot right? that's dissapated power that isn't going towards any work...it's waste. You waste about 1-1.5W/amp through an SSR.

I think I am okay with a 9000W kettle and 9000W RIMS, I can afford it. It was a safety thing, I dont want (4) live 120VAC lines when the system is powered down. To each thier own.

I know that one is required, my previous rig had one, but a DPST switch to kill power to the whole thing when it was powered down, just for safety reasons. Just trying to err. on the side of safety and conservative advice.

 

[Walker]

I would also suggest considering a definite purpose contactor, not in place of the SSRs, but rather as a cheaper option to using two SSRs and waterproof DPST 30A switch. These are basically inexpensive mechanical relays designed for high power.

I am not familiar with contactors, but I would actually caution AGAINST any kind of mechanical device, especially for something like pulse-width modulation (or the "manual" mode of the auber PIDS). You are going to be turning on and off the power many many many times during a brew, and a mechanical device is going to wear out.

The solid state relays can be switched on and off as much as you want and won't wear out.

 

[MrH]

I am not familiar with contactors, but I would actually caution AGAINST any kind of mechanical device, especially for something like pulse-width modulation (or the "manual" mode of the auber PIDS). You are going to be turning on and off the power many many many times during a brew, and a mechanical device is going to wear out.

The solid state relays can be switched on and off as much as you want and won't wear out.

You're misunderstanding what I said. I do not use the contactor in place of the SSR, but instead of using TWO SSRs as a way to disconnect BOTH hot legs to the element. Contactors are really little more than very robust high current relays. Most common are Double Pole, and can be used (in my case) as a mains disconnect. I still use a SSR driven by a PID to cycle my elements, but the contactor feeds the SSR, so when the switch for my HLT is off on my CP, I know that the element is not receiving power, regardless of what the SSR is doing. It's an extra measure of safety, and gives me an easy way to kill the element if the SSR fails and fuses on without having to turn off the whole system. (It's generally accepted that if an SSR fails it tends to stick ON - I could be wrong but that's my understanding).

Contactors are very good at what they do, and I am using them as they are designed to be used, but you're right that they shouldn't be used where rapid switching is required. If I had a single 240V 4-wire feed to my CP, I might have used a Triple Pole contactor and used it as a master disconnect for the whole CP, but since I have separate 240V and 120V feeds, I use two DP contactors.

MrH

 

[Walker]

You're right... I did misunderstand what you were talking about. You're using the contactor as a kill switch and I thought you were using it as the pid controlled switch.

How much are the contactors? I found a DPST toggle with a rubber water resistant boot for $7 that I was going to use for the kill switch, but if the contactors are cheaper, maybe I'll go that way.

 

[passedpawn]

if you're building two, you could save a few pins by using a 556.

 

[Walker]

I wasn't clear before. One is for my kettle. The other is for my buddy's kettle.

 

[passedpawn]

10A running through an AC SSR will "waste" about 16W. Scale that to your current and number of legs. Not a big deal, really, just putting some numbers out there.

 

[MrH]

You're right... I did misunderstand what you were talking about. You're using the contactor as a kill switch and I thought you were using it as the pid controlled switch.

How much are the contactors? I found a DPST toggle with a rubber water resistant boot for $7 that I was going to use for the kill switch, but if the contactors are cheaper, maybe I'll go that way.

A bit more than the switch you mention, but a more elegant and safer solution imo, since there's almost no chance of high amperage anywhere near where you'll be touching your CP. (3rd and 4th item listed)

MrH

 

[Walker]

Thanks, MrH.

I found a deal on ebay for some contactors for just over $8 shipped, so I'll only be spending an extra couple of bucks to go that way instead of a heavy-duty toggle.

 

[carcinogen]

Walker,
I built the circuit according to your diagram above, and after correcting a few botched solders, I managed to get it to work. Thing is, it doesn't seem to provide a duty cycle of less than about 50%; below this it switches off completely.
I am using two power supplies: a PID (without manual setting) providing 12v, and a 9v/500ma power supply, with both grounds on a SPDT switch to the circuit. Should I switch to a DPDT switch instead? I disconnected the PID supply completely, and it didn't seem to change the running state...
One more thing: I had to sub a 22uF cap in place of where your plans call for a 20uF. According to my circuit simulator, it should function similarly, but reality is not panning out as planned. Any thoughts?

 

[Walker]

Hmmm... That really doesn't make much sense to me. I've built two of these in the past couple of weeks and they work just fine.

The exact size of the capacitor isn't critical, it will just affect the frequency of the thing a little. I actually used 33uF caps on mine for a lower overall frequency.

How are you making your observations about the duty cycle? Do you have a LED hooked up to give you a visual indicator or something?

I can absolutely dial mine down to things below 50% duty cycle.

All I an suggest is to look closely look at you connections again. Shorts or miswirings can cause really weird stuff to happen.

 

[Walker]

Hang on... I am confused by your mentioning of the switches and multiple power supplies now that I re-read your message.

Is your goal to have the ability to flip a switch so that either the PID or the modulator is the thing in control of your element?

You will want to switch both lines that feed to the relay. Don't assume that "ground" is the same on the the PID and your modulator. It's better to think of DC as having a "high" voltage and a "low" voltage line.

Regardless, I don't think the switched have anything to do with your problem since you took the PID out of the equation while debugging.

I do suspect a wiring problem on your modulator.

 

[carcinogen]

Thanks Walker. The solder I had was a little thick for the Radio Shack breadboard, and I had to clean up a few pins. I might desolder the whole thing and start over again. I tested voltage at the SSR and found it was only reading 3-4V while the output at the PID was at least 12. Must be a continuity problem somewhere. I probably need smaller gauge jumper wires (just used what I had lying around and my iron is not a very hot model)
BTW, my SSR from Auber Ins. has an indicator LED.

 

[Walker]

If you are only seeing 3-4V at the SSR then something is WAY wrong. It should be exactly the same voltage that you are getting from the power supply!

I mentioned putting a resistor in to limit the current through the relay in one of my posts. Did you do that? If so, remove it.

 

[willynilly]

I dont know that the wire ga. will matter that much on the signal wire... I mean I have used 16ga and 22ga and still read 5v at the SSR and the BCS

 

[Walker]

the wire gauge won't matter.

unless, of course, you are running the wire hundreds of feet.

 

[Walker]

BTW, my SSR from Auber Ins. has an indicator LED.

The thing about that LED on the SSR itself is that it is only going to light up when you have enough voltage dropping across the SSR to cause it to switch.

However, given all of the information you have provided, I would say that you have some mis-wiring problem that is causing the relay control voltage to change when you twist your knob. When you dial your knob low enough, the voltage agross the regulator isn't high enough to switch the relay, so that SSR LED never lights up. This should not be happening. When the modulator is in the "ON" state, the voltage across the relay control lines should be the same as what is coming from the power supply.

Measure the voltage with your knob turned all the way ON vs all the way OFF and and make sure they are the same. That would be a good starting point in getting this thing corrected.

 

[willynilly]

My SSR lights up even with no voltage across it... just the signal

 

[Walker]

My SSR lights up even with no voltage across it... just the signal

I'm not talking about the "load" side. I am only talking about the "control" side. If you don't put enough voltage across the control terminals, the relay won't switch and the LED won't come on.

My SSRs require a minimun of 4V to cause it to switch (and can handle a max of something like 24V). If I put less than 4V, the relay doesn't close and the LED doesn't come on.

 

[willynilly]

I'm not talking about the "load" side. I am only talking about the "control" side. If you don't put enough voltage across the control terminals, the relay won't switch and the LED won't come on.

My SSRs require a minimun of 4V to cause it to switch (and can handle a max of something like 24V). If I put less than 4V, the relay doesn't close and the LED doesn't come on.

Thanks for clearing that up

 

[Walker]

Packaged up a modulator today. (Sorry about crappy video quality... I took it with my phone.)

 

[wirewiggler]

Just to be sure I understand this Evan if you have 2 ssr they are current devices and still have voltage output when shut off, so for safety sake a contactor upstream or mechanical disconnect would be required to safely service the heater.

 

[Walker]

a contactor upstream or mechanical disconnect would be required to safely service the heater.

or you just unplug the thing....

 

[Islandboy85]

How has that pulse width modulator been holding up for you? I think I may make some of my equipment electric. I like the idea of it being way cheaper than a PID.

 

[dallasdb]

Subscribed (for future eBIAB build)

Thanks for the input Gents!

 

[Walker]

How has that pulse width modulator been holding up for you? I think I may make some of my equipment electric. I like the idea of it being way cheaper than a PID.

works great. I have never had an issue.

I have built two others for people to use in their systems, too. But I cheated on those and bought solderless breadboards off ebay for next to nothing. That allows you to just plug the components in and not solder anything except the wires that attach to the pot.