Heater Circuit for a Chlorate Cell

[WSM]

Rather than use an aquarium heater (which is limited because of other circuitry in it) to heat a portion of a chlorate cell (a small heat well in the crystallizer to prevent crystal fouling of the pump intake port), at the encouraging of a friend, I'm building a heater using a 10W resistor in a test tube. I plan to surround the resistor with silica sand to protect the components and diffuse the heat gently. The challenge is figuring out which ohm rating (how many ohms?) to use with a 12Vdc power supply. I have an idea but I want to hear what others think...

 

Please let me know. Thanks.

 

WSM

Edited October 13, 2011 by WSM

[Verge]

Rather than use an aquarium heater (which is limited because of other circuitry in it) to heat a portion of a chlorate cell (a small heat well in the crystallizer to prevent crystal fouling of the pump intake port), at the encouraging of a friend, I'm building a heater using a 10W resistor in a test tube. I plan to surround the resistor with silica sand to protect the components and diffuse the heat gently. The challenge is figuring out which ohm rating (how many ohms?) to use with a 12Vdc power supply. I have an idea but I want to hear what others think...

 

Please let me know. Thanks.

 

WSM

 

Wait.What?Whats the purpose of this?

[WSM]

Wait.What?Whats the purpose of this?

 

To heat a small semi-enclosed tank area (in the crystallizer tank) near the pump inlet so crystals don't form there, but stay in solution. If the pump inlet is at (the lower) crystallizer temperatures, it'll clog up with chlorate crystals. The problem with the aquarium heaters I have is the limited temperature range and the thermal cutoff built in. To solve the problem, I'm determined to build my own glass heater to prevent the problems I mentioned.

 

Understand the rest of the crystallizer is designed to be at a temperature low enough to encourage chlorate crystals to drop out of solution, just not this little chamber near the pump inlet. The pump is returning depleated fluid back to the reaction chamber (which is hotter than the crystallizer chamber) for salt replenishment and further development of chlorate crystals. If the returning liquid is cool, the crystals drop out in the reaction chamber (which is undesireable).

 

I hope I answered the question.

 

WSM

[mike_au]

Power = Voltage * Current

 

You want to dissipate 10W at 12V so

 

P=VI

I=P/V

I= 10/12 = 0.83333....

So you want to draw about 0.8A

 

Current = Voltage / Resistance

 

I=V/R

R=V/I

R= 12/0.833 = 14.4

 

So you want a minimum resistance of 14.4Ohms. Maybe call it 15-16 just in case.

Edited October 13, 2011 by mike_au

[Arthur]

As Mike says Power = V x I and E=IR so the values are easily calculatable. However get the biggest wattage resistor that will fit in the space available so that heat concentration is reduced or localised cracking will result.

 

Be very sure that the bung (rubber or soft PVC) and the cable (likely soft PVC) will withstand the chemical liquid and fumes. Maybe it's time to look for a Titanium clad process heater (Search "stud heater") and look for something with corrosion resistant leads long enough to get them into a project box.

 

Alternatively see whether you can heat the hot well with heat from the main electrode chamber (glue them together?!?).

 

Added;

It would perhaps be simpler to put the pump in the hot flow TO the crystaliser where crystals would not form. While it's a closed loop then the location of the pump doesn't matter it will still circulate the liquid

Edited October 13, 2011 by Arthur

[WSM]

Power = Voltage * Current

You want to dissipate 10W at 12V so

P=VI

I=P/V

I= 10/12 = 0.83333....

So you want to draw about 0.8A

Current = Voltage / Resistance

I=V/R

R=V/I

R= 12/0.833 = 14.4

So you want a minimum resistance of 14.4Ohms. Maybe call it 15-16 just in case.

 

Thanks mike_au, that's exactly what I figured !

 

I bought the 15 ohm, 10 watt resisters. I need to assemble the heater and test it. I'm planning to put it in a Pyrex test tube which ought to withstand the temperature and transfer heat to the liquid in the heat well. I think putting silica sand around the resistor should soften the effect on the glass envelope.

 

Thanks again for the confirmation.

 

WSM

[WSM]

As Mike says Power = V x I and E=IR so the values are easily calculatable. However get the biggest wattage resistor that will fit in the space available so that heat concentration is reduced or localised cracking will result.

Be very sure that the bung (rubber or soft PVC) and the cable (likely soft PVC) will withstand the chemical liquid and fumes. Maybe it's time to look for a Titanium clad process heater (Search "stud heater") and look for something with corrosion resistant leads long enough to get them into a project box.

Alternatively see whether you can heat the hot well with heat from the main electrode chamber (glue them together?!?).

Added;

It would perhaps be simpler to put the pump in the hot flow TO the crystaliser where crystals would not form. While it's a closed loop then the location of the pump doesn't matter it will still circulate the liquid

 

Hi Arthur,

 

Thanks. I'm leaning toward using silicone or Viton for a seal. I could put the resistor in a titanium tube but I think cathodic protection would be required (not difficult, just a different direction than I intended) to keep the titanium from being affected.

 

I moved away from pumping from the RC to the CC to simplify the process. If you pump from the RC you still need heating so the crystals don't form till the liquid is in the CC. Any cooling before the CC is reached will help cause the crystals to form where they're not wanted and jam the system badly (remember what happened to Swede's two tank system?)! I'm planning on heating the small plastic heat well (in the CC) where the pump and the float switches are, so that small area in the CC will be free of crystals and problems caused by crystal jamming.

 

Thanks for confirming the resistor size, too.

 

WSM

[WSM]

If anyone is interested, I posted a simple circuit I made to act as a fluid level controller for the chlorate crystallizer tank. It's in the chemistry section in the (per)chlorate production posts.

 

The whole idea is to make a continuous chlorate system, rather than a batch system. I run the reaction chamber (RC) and let the chlorate filled solution gravity feed to a crystallization chamber (CC) where the chlorate crystals drop out of solution and collect. I then pump the depleated solution back to the RC where more salt solution is added when the level in the CC gets low enough to actuate the fluid level controller. The circuit latches on when a float switch is actuated, turning on the pump which fills the CC by pumping replacement salt solution into the RC, till the high limit float switch in the CC is actuated, opening the control circuit and stopping the pump.

 

Any thoughts or suggestions? Thanks.

 

WSM

[WSM]

I built a power supply box to house a 12Vdc wall wart and make testing circuits easier. The PVC electrical box (2" x 4" x 4") has a fused receptical for a computer power cord, an on-off toggle switch and two polarized banana sockets that I plug colored test leads into and that have hooking leads on the other ends. With his power set up I clipped the 10W 15 Ohm resister on the leads and powered it up.

 

Nothing happened immediately but after a minute or two the resistor started to heat up. I was monitoring the temperature with a digital IR scanner and got nervous when it was on a steady climb getting closer to 90^oC, so I pulled the plug on this experiment. As I see it, I have two options here; 1) I can add a temperature controller of some sort, or 2) I can experiment with different set ups till I find a combination that heats to a set temperature and stays there without external controls.

 

Is there a resistance value I should consider that would self regulate, or am I kidding myself and just resort to using a temperature controller with the resistor/heater?

 

Ideally, I'd like to heat the liquid in the heat well to no more than 40^oC.

 

Any thoughts?

 

WSM

[Arthur]

The casing will be very important. Resistor in test tube with some (silicone ) oil to spread the heat to the test tube walls and this could be a reasonable heat input to hold 40c.

 

You will have to try this accurately.

[WSM]

The casing will be very important. Resistor in test tube with some (silicone ) oil to spread the heat to the test tube walls and this could be a reasonable heat input to hold 40c.

You will have to try this accurately.

 

Do you think a thick or thin silicone oil would be better (I have both, if you mean polydimethylsiloxane)? Thanks.

 

WSM

[mike_au]

Is there a resistance value I should consider that would self regulate, or am I kidding myself and just resort to using a temperature controller with the resistor/heater?

 

Depends how accurate you want to be. If you only need +/- 10degC and you don't have to worry about outside temperature swings then I suspect you could make a reasonably OK heater without any smarts, if you want +/-1degC then you will need a controller of some sort.

[Arthur]

At low volts you could probably use vegetable oil or motor oil! Basically the resistor will be hot and touch the cool glass test tube in small places. commercial stud heaters use silica sand to insulate and separate the element from the enclosure.

[WSM]

Depends how accurate you want to be. If you only need +/- 10degC and you don't have to worry about outside temperature swings then I suspect you could make a reasonably OK heater without any smarts, if you want +/-1degC then you will need a controller of some sort.

 

Give or take 10% is close enough. I just don't want a runnaway situation where the temperature rises to a failure of the circuit . Thanks for the input.

 

WSM

[WSM]

At low volts you could probably use vegetable oil or motor oil! Basically the resistor will be hot and touch the cool glass test tube in small places. commercial stud heaters use silica sand to insulate and separate the element from the enclosure.

 

I'll use the silicone oil if I use oil at all. My original idea was to use silica sand, and I didn't even know it was used commercially ( I must be intuitive* ) ! I prefer to avoid a contamination problem (with the oil) should the glass envelope rupture.

 

*What do you know, getting old is good for something!

 

WSM

[WSM]

I'll use the silicone oil if I use oil at all. My original idea was to use silica sand, and I didn't even know it was used commercially ( I must be intuitive* ) ! I prefer to avoid a contamination problem (with the oil) should the glass envelope rupture.

*What do you know, getting old is good for something!

WSM

 

I went to the local "big box home center" and see they carry a 100lb sack of silica sand for ~$7. I need about 1/2lb maximum and the rest would be a waste. Would another material work? I have fine alumina or glass beads (sand blasting media) I could use, or 40 mesh Kyanite mineral (ceramics grade) as well as a host of various powdered fireclay materials or other refractories.

 

What do you think?

 

WSM

[WSM]

I went to the local "big box home center" and see they carry a 100lb sack of silica sand for ~$7. I need about 1/2lb maximum and the rest would be a waste. Would another material work? I have fine alumina or glass beads (sand blasting media) I could use, or 40 mesh Kyanite mineral (ceramics grade) as well as a host of various powdered fireclay materials or other refractories.

What do you think?

WSM

 

I dug out my tub of alumina powder and filled the test tube "aquarium" heater about 3/4 full. I took the photo below before filling the tube:

 

 

Shown is the 10 Watt 15 Ohm resistor soldered to 18 AWG solid wire and the black Viton tube used for insulation on the wire; all inside a Pyrex brand borosilicate glass test tube (~16mm OD X 150mm Long). The looks of the tube after filling is a test tube full of fine white crystals with black wires coming out, not worth a photo. I'll show the test when I set it up and share the results.

 

WSM

[WSM]

Hello! I'm relatively new on this board but I can say I know some about controls and electronics. If you want a cheap control, using a thermal snap switch may work. You said 40°C which is 104°F.

This switch closes at 110°F. You'd need a 110V relay and wire it with the switch to turn OFF the heater at 110°F but it is easy enough to do...

Amazon has a switch here

Anything more precise and you'd need a temperature controller.

Hope this helps!

May the FORCE be with you and have a magical day!

MagicBill

 

Wow! This was posted on June 6th, and I just noticed it today.

 

Thanks, Bill.

 

Actually, since I discovered affordable teflon coated PT100 sensors on eBay (and acquired a few), I've decided to make the leap and use a temperature controller. I plan to use an inexpensive PID controller which will fire a solid state relay. Since the SSR controls 24-380 VAC, I'll have the control circuit power a 120Vac outlet on my project box. I'll simply plug a 12Vdc wall wart into the AC outlet to supply power to the glass heater I made. My controller will be usable for many other projects so I decided to make it more universal. Total cost, roughly $50 US.

 

I'll post a photo of the controller box when it's more than a collection of bits and sketches.

 

WSM

[WSM]

Actually, since I discovered affordable teflon coated PT100 sensors on eBay (and acquired a few), I've decided to make the leap and use a temperature controller. I plan to use an inexpensive PID controller which will fire a solid state relay. Since the SSR controls 24-380 VAC, I'll have the control circuit power a 120Vac outlet on my project box. I'll simply plug a 12Vdc wall wart into the AC outlet to supply power to the glass heater I made. My controller will be usable for many other projects so I decided to make it more universal. Total cost, roughly $50 US.

I'll post a photo of the controller box when it's more than a collection of bits and sketches.

WSM

 

I'll have to post a photo of the temperature controller when I modify it because I'm not satisfied with it yet (though it's nearly done).

 

I've been experimenting with the heater (10W resistor in a test tube) and discovered it self-regulates when filled with alumina powder and is in a pan of water. In fact, the water hardly gets to about 30^oC . I figured the voltage and current of the wall warts I was using weren't getting the job done when a couple of them died trying.

 

I bought a 15Vdc, 5A power supply and hooked it up and it performed well and the water in the system got up to 36^oC (definately a step in the right dirrection)! I think a 24Vdc power supply would do a better job if it delivers adequate current. If the resulting heat is upwards of 50^oC, I can use the temperature controller to effectively set and keep the heat well at a temperature roughly equal to the RC (which ought to prevent crystal fouling of the components in the heat well).

 

WSM

Edited July 14, 2012 by WSM

[pyrojig]

Oh boy, this topic is just starting to get juicy.

The use of a larger heating unit may be a idea. The 50C mark is a good one, but 30 may do the job. I like the input that these fellows have been contributing . Its nice to put our heads together and build something great !! It would be nice to find a passive source of heat your could transfer over to the heat well. Could you make use of the reaction chamber ( take a radiator effect ) and circulate a hot tube through the heat well. Or use the PS , or other hot running electronics to do the work. I like making best use of the energy if possible, even recycling some of it .

[WSM]

Oh boy, this topic is just starting to get juicy.

The use of a larger heating unit may be a idea. The 50C mark is a good one, but 30 may do the job. I like the input that these fellows have been contributing . Its nice to put our heads together and build something great !! It would be nice to find a passive source of heat your could transfer over to the heat well. Could you make use of the reaction chamber ( take a radiator effect ) and circulate a hot tube through the heat well. Or use the PS , or other hot running electronics to do the work. I like making best use of the energy if possible, even recycling some of it .

 

Hi pyrojig,

 

It would be nice, BUT, before the RC liquids would heat the "heat well" the cooler temperatures of the crystallizer would probably cause the dissolved chlorate in the tubing to drop out of solution, making the tubing jam tight with crystals. The only reason the RC keeps the chlorate in solution is because of the heat there. Once it cools, the chlorate drops out of solution. The trick is to get the liquor to the crystallizer before the crystals form (by whatever means you can do it)!

 

I think the reason Swede had trouble with his two tank cell (described in his blogs) is because of the temperature differential of the various parts of the system. If the liquor cooled, that section jammed tight with crystals. If you can keep everything hot till it gets to the CC, it's all happiness !!!

 

Don't stop thinking of ways to make the various parts work. Some great notions have come up and may find application here. An idea from someone may open a path to overcome a sticky problem holding up the progress of a fellow experimenter. Keep 'em coming!!!

 

WSM

Edited July 15, 2012 by WSM

[WSM]

Oh boy, this topic is just starting to get juicy.

The use of a larger heating unit may be a idea. The 50C mark is a good one, but 30 may do the job. I like the input that these fellows have been contributing . Its nice to put our heads together and build something great !! It would be nice to find a passive source of heat your could transfer over to the heat well. Could you make use of the reaction chamber ( take a radiator effect ) and circulate a hot tube through the heat well. Or use the PS , or other hot running electronics to do the work. I like making best use of the energy if possible, even recycling some of it .

 

Another thought, If you can get the heater to work well on 12Vdc and you're using the 5Vdc output of a computer power supply for your cell electrodes; use the 12Vdc leads to power the other components. Most of the meters and other attendant electronics I use need a 12Vdc source. It fits well if a computer supply is your power source.

 

I like consolidating my resources and getting the most efficient use, too. Thanks for sharing.

 

WSM

[WSM]

I'll have to post a photo of the temperature controller when I modify it because I'm not satisfied with it yet (though it's nearly done).

I've been experimenting with the heater (10W resistor in a test tube) and discovered it self-regulates when filled with alumina powder and is in a pan of water. In fact, the water hardly gets to about 30^oC . I figured the voltage and current of the wall warts I was using weren't getting the job done when a couple of them died trying.

I bought a 15Vdc, 5A power supply and hooked it up and it performed well and the water in the system got up to 36^oC (definately a step in the right dirrection)! I think a 24Vdc power supply would do a better job if it delivers adequate current. If the resulting heat is upwards of 50^oC, I can use the temperature controller to effectively set and keep the heat well at a temperature roughly equal to the RC (which ought to prevent crystal fouling of the components in the heat well).

WSM

 

SUCCESS!!!

 

I took the same setup and changed the resister from a 10W/15 Ohm, to a 10W/10 Ohm. I put the test tube with resistor and alumina sand in a ceramic mug filled with water and applied the 15Vdc power. I also dropped in the waterproof thermal sensor connected to a digital panel meter (LCD with blue LED illumination). After roughly an hour, it's risen to 54.8^oC and is still rising very slowly.

 

Whether I use this setup or switch to a small cartridge heater in a sealed titanium tube, as Swede recommended; at least I know the resistor in a test tube will work. Also, I'm convinced using a temperature controller will be the best way to maintain the proper temperature in my heat well.

 

Thanks for your support and assistance with my efforts.

 

WSM