# Fog machine Heater resistance



## jdsteel82 (Aug 27, 2010)

Trying to make a killer fog machine with a pic controlled PID heater. Need some base line figures for what the real wattage of these fog machines are. So I was wondering if anybody has measured the resistance of the heater element of their fog machines.

Thanks


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## Otaku (Dec 3, 2004)

I've wanted to do this for a long time. It would be pretty easy to remove the bi-metallic thermostat from a fogger and cut in a PID controller with a TC feedback loop. I have a Watlow 925 heater controller that would work perfectly for converting a standard fogger into a continuous-running machine.
I have a Lite FX 1741 with the U-shaped heating element - I'll try to get a number for you in a day or two (busy schedule these days). I have measured the wattage draw for this fogger. It's rated at 700W and my Kill-A-Watt says it pulls ~690W; pretty close to spec.


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## Thisaintmayberry (Aug 23, 2010)

Interesting. So would the TC loop feed a temp to the controller, which would then control the on/off cycle of the heater? The idea I presume is to increase the envelope of "on" time performance?


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## Otaku (Dec 3, 2004)

Yes. The TC would monitor the heater temp and the controller would maintain the setpoint temp. Instead of the heater either getting a reduced wattage or cutting out altogether when the pump is running the controller would ramp the power to the heater element, maintaining a constant temp. The PID settings would be adjusted to prevent temp overshoots when the pump stops. I haven't yet used a remote TC readout to check the temp at which the system decides it's ready to start fogging.
I'm not sure if an off-the-rack fogger timer could be used under this system. For better control, a simple 2-stage 556 timing circuit could be built to turn the pump on and off. I'd want to monitor the heater temp drop when the pump is running to be sure the controller could keep up with the wattage demand. Once the PID settings are optimized, one should be able to get fog on demand. This would simplify the issues around props that need to have a fog burst when the prop is activated.
Cost may an issue here. too. Watlow controllers and the SSR's aren't cheap.


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## Thisaintmayberry (Aug 23, 2010)

I think you're on to something here. Most of the foggers we haunters use are made as cheaply as possible, thus the limited amount of "controllability." No doubt a huge safety margin is built into the design using thermostats with low settings. My experience in trying to hack around the heat delay has been unsuccessful and frustrating (and expensive ).

Since it seems that the higher output foggers have longer fog times and faster recovery rates, would it be reasonable to assume that a bigger fogger has a higher heating/cooling "tripping" point? If so, shouldn't it be possible to "fool" any heater into thinking the tripping point hasn't been reached - and thus extend the run time - by removing the super safety thermostat and replacing it with a programmed switch? Once you knew the parameters of the heater, i.e. the tripping point, you could manipulate power to the heater to keep it in a constant state of readiness, yes?. This was my line of thinking which has so far failed to work. I couldn't figure out how to get the temp info from the heater to the relay controller.

I have a Chauvet POS fogger I'd be more than willing to donate as a mule for testing. I'm not familiar with Watlow controllers. 

AND, I'm not far from you (Livermore).


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## Thisaintmayberry (Aug 23, 2010)

Apologies to JDsteel82, I didn't mean to jump your thread. This is just something I've been chewing on for awhile.


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## jdsteel82 (Aug 27, 2010)

No worries! I love good brain storming!
Now one thing I don't know right now is if the element is like a solid hot water heater style or a wound NiCrA wire around the block?

Want to build(mill) my own block, and install my own element...1300W is realistic for 120VAC 

It will be fun building and calibrating this Pid library!


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## spinman1949 (Jun 29, 2009)

Otaku,

From my understanding of foggers, I was under the impression that the bi-metal switch controls the pump cycle. I have always been under the impression that a fogger cycles because as the fog juice expands through the heater it of course transfers heat from the heating element into the fluid. Are you saying that the circuit to the heater is cut as well? I know the heater has a thermistor to prevent overheating, but I always thought it was the rapid cooling of the heater element that brought the thermal circuit breaker down in temp and thus shut off the pump circuit. I think the way to have a continuous fog machine is to have a high wattage heater and a controlled volume of fog fluid. Thus allowing the heater to maintain it's required temperature. Am I incorrect in this?


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## Otaku (Dec 3, 2004)

You are correct, the thermostat does control the pump - my bad. When the heat reaches the setpoint the pump is enabled. So if you are using a timer control, the fogger can now start up.
It was discovered a couple of years ago with Chauvet F1250 foggers that the heater drew higher wattage during the initial heating cycle, say, 700 - 800W. But when the temp setpoint was reached, the wattage was cut to practically zero, and when the fogger went into the re-heat cycle (pump disabled) the wattage was ~25W. The low re-heat wattage is likely used to prevent temp overshooting, but it means that it takes a while to get back to operating temp. The cutoff of the power to the heater when the pump starts running causes the block to cool rapidly until the fogger goes into the re-heat cycle.
If you use a PID controller, as soon as the temp varies a bit from the setpoint (and this window is programmed into the controller) the controller will start ramping power to the heater. As the temp gets closer to the low end of the setpoint window, more power is sent to the heater, and at a faster pulse rate. When the pump cuts off, the TC will sense the increase in the block temp and the controller cuts the power based on the speed of the temp rise. The Watlow controller I mentioned samples the TC reading every 0.1 secs, and responds by varying it's output at the same rate. I use these controllers on hot-die plastic welders; they hold the temp to ± 2 °F even when the welders are joining parts.
So, based on this it would appear that the only things needed to achieve the goal would be the Watlow (or other) controller, the proper TC (mounted to the heater block) and a SSR. The wires that go to the actual heating element would be attached to the Watlow outputs via the SSR. You'd need to know the actual operating temp of the particular fogger to program the setpoint, so a remote TC readout would be needed. The controller can do this job very accurately as long as you tell it which type of TC you're using.
This can be done, but as I said there's some $$ involved. I wouldn't spend the money on a low-end machine, but it might be cost effective to convert a mid-range fogger. If the system can hold the heater within the operating temp window as read at the bi-metallic thermostat, you'd have a continuous, fog-on-demand machine.


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## spinman1949 (Jun 29, 2009)

Otaku,

Now I get how you are controlling the heater. I was not aware there was a re-heat circuit. Is that contained on the mail control board? And it seems to me that with your controller you should be able to bypass the bi-metal relay. That device is relatively slow acting. Could the controller trigger a SSR?


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## Otaku (Dec 3, 2004)

I'm not sure you'd need to cut out the bi-metal device. As long as the heater stays in the operating range it'll supply power on-demand to the pump. Essentially, it'll be in an always-on mode.
The Watlow does use a SSR to switch current to the heater element(s) it's controlling. It also has an internal switched DC relay to control alarm relays and such. I find that the 925/935 series controllers are being phased out, which is OK. The price on them is $237.50. The replacement series is much less, relatively. The new SD series, same features, go for ~$145.00. The required SSR is $37.00. As I said, it's some $$ to do this thing.


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## spinman1949 (Jun 29, 2009)

Otaku,

So you say a DC relay? Would this relay be able to be triggered to stay active one heater temp was achieved? That would be ideal. Might have to put a restrictor in the pump line. Maybe use a bleed valve to divert some of the flow back to the tank. Could be an easy way to control output. What do you think? Not sure how the pump will respond to increased back pressure. Maybe just an small ball valve would suffice.


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## Otaku (Dec 3, 2004)

I don't know what could be done with the relay but I think you could keep it active if you set an alarm condition that's always going to be outside of the temp window. It's typically used for alarm systems in the case of over/under temp conditions. I use a different monitoring system that locks out the welders if they're not in the process window. I'd need to go through the book to see how the DC relay could be used in a fogger application, as well as what happens when the relay goes active.

What do you have in mind?


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## jdsteel82 (Aug 27, 2010)

Agh! wow those controllers are expensive! I was planning on building my own with a Picaxe 08m and use a Omron G3NA SSR. Along with Zero Cross detection for all around $40 or less. when I do this I might sell the PCB's if successful. And do a write up of course.


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## jdsteel82 (Aug 27, 2010)

http://www.hauntforum.com/showthread.php?t=14096

looket what I found! Hmmm...vast amount of room to improve upon on just the heating element!
2 goals
1, Tons of continuous fog
2, Don't burn the house down (will build in plenty of overload protection!)


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## Otaku (Dec 3, 2004)

That block looks similar to the one in my Lite FX fogger:










I tore it apart last month to clear out a clog in the heater. A succesful operation.


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## Thisaintmayberry (Aug 23, 2010)

Well the science sounds good, now to work on the cost. Any idea how much current would get pulled through the relay? Otaku - are you talking about something specific to the Watlow? (I've got to get educated on those). 

jdsteel82- What is your line of thinking on the block mod? More juice through at the steady hot (or hotter) temp Otaku proposes = more fog?


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## jdsteel82 (Aug 27, 2010)

here is the plan and thinking as is now. 
08M with a T type thermocouple input.
set up PID library and calibrate (this will be the most difficult part for me)
will use zero cross detection circuit to tell 08m to not count 0vAC times in the PID table.
PID output table will drive the output of the 08M to drive a Omron G3NA SSR (5v trigger)(opto isolated). that will then power the AC side to the heater element. 

2 options for heater right now. both will eventually involve a custom heater block with fluid passage.

Use a 120vAC water heater element around 1200W (12 ohm @ 10A), but I can only find a 1440W(10 ohm @ 12A) heater at the lowest (Google shopping search).

option2: custom wind my own element with NiCr60 wire at 16awg...still working on the idea in my head on this one...would most definitely have to make my own custom block (inner fog juice passage tube of aluminum wrapped in NiCr60 wire with heavy outer steel tube as a thermal mass block?).

My big concern is safety and the capacity for my house electrical. will have to see how much the avg pump draws in current...maybe even see if I can find a DC diaphragm pump that can do 30PSI that can be PWM driven without chatter.

You guys think I am being realistic? I think I am, but I am known for being a dreamer. Right now its not the cost...its the challenge and quality (which I feel the OTS foggers don't have).


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## Thisaintmayberry (Aug 23, 2010)

Barney left the building on your first paragraph. I think I'm just along for the ride at this point.

This site http://www.lockeplumbing.com/catalog.asp?c=Water Heater Parts advertising a 1200 watt 120V screw in-type element for $10.36. If you went this route couldn't you also use a standard thermo-disk style water heater thermostat attached to the heater block to control overheat?


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## Otaku (Dec 3, 2004)

Agreed on the challenge part, jd. I'm not sure that designing a heater block is the way to go, though. To test the theory and your new circuit, I'd go with a cheap after-Halloween-sale fogger. No need to re-invent any wheels at this stage.


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## jdsteel82 (Aug 27, 2010)

Otaku said:


> Agreed on the challenge part, jd. I'm not sure that designing a heater block is the way to go, though. To test the theory and your new circuit, I'd go with a cheap after-Halloween-sale fogger. No need to re-invent any wheels at this stage.


I agree, I really need to understand the mechanical aspect fully before I make heater blocks. Can still work on all the electrical and PID.


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## jdsteel82 (Aug 27, 2010)

I couldn't find any results for this question other than a vague 400f. Anybody measure the temps of our standard H2O based fluid fog machines? I know I will end up with wet fog or no fog if too low, but I NEED to know the max to have a safe margin before thermal breakdown of the fluids.


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