What setup would you recommend?

[Kanefire]

I have a floatation tank (aka sensory deprivation)

I am looking to replace the heating system. The heater I am using is a waterbed heater@ 350w, 110v, 3amp. I would like a controller that can keep the temperature differential to .5 degrees of 93.7 degrees farenheit with sensor accuracy to .1 of a degree and running off 110v. I would also like a thermocoupler about 1" with insulated 4' extension. The tip needs to be rounded as it will be under a liner.

Would be grateful for some "more expert than myself" advice here for a proper setup.

[Tech_Marco]

I'll suggestion the following item:

PID temperature controller JLD612
http://www.lightobject.com/JLD612-Dual- ... r-P43.aspx

25A SSR:
http://www.lightobject.com/25A-Solid-St ... t-P61.aspx

Stainless steel PT100 probe
http://www.lightobject.com/Premium-Stai ... -P657.aspx
or
http://www.lightobject.com/Water-resist ... -P592.aspx


Marco

[richiem]

I second Marco's recs -- my controller keeps my 250 gallon hot tub, located outdoors, within 0.2 deg F as long as the cover is on, despite weather conditions -- right now, it's 30 deg out, and it was 25 overnight, but when I got in the tub this morning it was 0.1 deg off setpoint -- which just could be measurement "wobble."

Your tank is closed except for the brief time when you get in or get out, and I believe your setup will hold within 0.2 deg F. The only caveat is that you are perhaps a little short on heater power for the volume of water. Further insulating the external shell of your tank with closed-cell foam may yield big dividends in stability.

[Kanefire]

Thanks Marco... I'm shocked (pun). This is a commercial setup (so it is insulated Richie) and I have recently ordered the identical temperature controller system that it came with (Watlow) and it cost me about $250. This setup will cost a fraction of that.

I have a question. In reading up on what you recommended, I am curious to know about the SSR. The SSR description states DC in AC out, but the controller will use AC and the heater is AC. Could you briefly explain the setup so that I can understand why you recommend this device?

Also any recommendations for a plastic enclosure would be appreciated.

Thanks in advance.

[Tech_Marco]

Technically speaking, there are four different types of SSR (Solid State Relay)

1) DC in, AC out
2) DC in, DC out
3) AC in, AC out
4) AC in, AC out

The "in" means the input voltage it also means the controlling voltage. The "out" means the type of voltage it can pass through the SSR. Remember that a SSR is just like a "switch". It works On (closed circuit) and Off (open circuit). Take our 25A DC in DC out SSR as an example, it means that the controlling voltage is DC 3V~32V and the output (the max voltage it can control On and Off) is 380V AC.

The signal output from a temperature controller in general is "DC" type. It depends the brand and our controller output is running about 8V dc with up to 40mA current. To drive a SSR, 10~20mA is good enough as it's merely a "LED" circuitry inside of the SSR. If you're planning to drive a load that is running on DC voltage say a 48V 1000W electric heater. Then you must use DC in and DC out SSR. If you use DC in, AC out, the chance is that you will get about half (50%) power.

It depends on the load you're trying to drive it. For small power load, say 300Watt or less, A plastic box with air hole should work but I will suggest a heat sink to be used in all time. Or, at least to use a metal box so that heat generated from the SSR can be divese to the box. Remember that a SSR will take some 'hit' when conducting current. Once it is getting hot, the efficiency of a SSR dropped expotentially. I'll suggest you use 50% of the rated current when selecting a SSR. Say the load is 1000W AC 110V. Then the current it take is about 10A. So, I'll go for 25A. But if the load is 5000Watt, then the current is about 45A. Instead of using 60A, I'll go for 90A. Remebmer, you need to use proper heat-sink for the SSR and better installed outside of a container. If you must installed inside a container, I'll suggest you to install a small DC cooling fan In Additional to the heat-sink alone. Please take it serious rather than regret.

Hopefully you can follow me and get some idea what is a SSR and how to pick one.


Marco

[Kanefire]

right on Marco, thanks a bunch.

To reiterate what I have just learned, I have a PID controller that connects to a 110 volts AC power supply. The controller puts out a DC current. I then use a 25a SSR DC in AC out which will be sufficient to power a 350 watt AC heating element.

Due to the wet environment, I will be required to enclose the controller and SSR. You recommend both a heat sink as well as a cooling fan. I will assume that the fan should only activate when the controller activates the heater. How would you recommend I set up the fan to accomplish this?

I also have an ancillary question. I was interested in developing a heating system that utilizes a DC heating element. I was informed by the representative of watlow that a DC heating element would be inefficient to the point of recommending against using one. I am inferring from your reply that this isn't the case. Would you know an equivalent heat output of a 350w 110v AC heating element? And would I use a similar setup, replacing the dc/ac SSR with a dc/dc SSR?

[Tech_Marco]

If you know electronics then it's easy to set the fan On while temperature reach certain temperature. In this case, I'll suggest a simple solution: let it on once heater is on. A small DC cooling fan won't take too much power. Possible 4~5Watt only.

If you have a DC heating element of having the same power rating, I don't see why won't it work. If the AC heating element is 350W RMS (note: RMS rating of AC device = dc rating), then a dc 350W heating element should provide the same heating power. But you need to be caution when dealing with high power DC heating element of such high power rating, especially for low voltage but high current. When you mentioned DC, I'm not sure what would be voltage you're going to use, 12V , 24V, 50V, or 100V dc?? For AC 110v 350W, the current the heating element will take is 3.2A. But if you use dc element of same power rating but let it say DC12V , then we're dealing with 29A! A big gauge cable is required and heat lost a lot (I^2 * R). If power by DC50V, then the current dropped to 7A and has 17times less power lost on the cable.

FYI, I do have a DC type temperature controller with from DC12V~32V just in case you need to swap AC for DC.

Marco

[richiem]

Marco ID'ed the trouble with using DC for the heater -- typically, low voltage and high current. So, not sure why you would be interested in DC heating. As to the fan control, just wire the 120VAC fan motor in parallel with the 120VAC heater. The fan can be small -- not much bigger than the heat sink -- it doesn't take a lot of air movement at human tolerable ambient temps to really make a difference in the efficiency of the heat sink. The fan will come on when the heater comes on.

[Kanefire]

Thanks a bunch Richie and Marco, you have helped me considerably. I found a 60mm 110v ac fan. I should be able to wire that parallel to the heating element and not worry about overloading it? My concern is that it might be too noisy for my specific use, I'd have to test it out.

If I were to find a small DC fan, how would it be connected? It obviously couldn't be connected parellel with the ac heater. And, am I correct in thinking the controller doesn't have enough power to run it?

About the DC heating element. I am looking to create an EMF free environment for floating. At an unrelated business meeting I was speaking with an electrical engineer who told me that DC will not produce EMFs. It was this statement that has led me on the path of testing DC heating elements.

Marco, when you write

But you need to be caution when dealing with high power DC heating element of such high power rating, especially for low voltage but high current.

What is the concern?

For this fork in the project, I'd be looking for heating cable to be placed between the walls of a doubled walled device so it would be shielded entirely from human contact. I have currently found 12v DC heating cable that has a rating of 9 watts per foot and would require approximately 35' (about 320w)... ≃ 27a.

But you suggest going with higher voltage to bring down the amps and also increase the efficiency. There is another heating cable I found that runs 24v DC, but it drops to 5 watts per foot and I'd require approximately 65' to reach 320w at 13a.

This nearly doubles the cost. Is this what you would recommend? Why?

[richiem]

Your issue is not EMF (electromotive force), it is EMI -- electro-magnetic interference. DC current does in fact generate an electric field that switches on and off as the current flow turns on and off; this is low-frequency, but it is still a strong field at high currents.

Part of the problem with using DC for high power is that you need to convert AC to DC at the right voltage -- high current requires a big transformer, which raises the cost substantially, and then you need to rectify and filter the AC from the transformer to get DC that does not have pulses of current (unfiltered rectification "ripple") that generate EMI, and that also raises the cost significantly -- so if cost is an issue for you, then DC, whatever benefits it have have for you, is going to be expensive. Cost is the main reason that household AC supplies are used for high power heating -- cheap, readily available and controllable, and all the heavy lifting on design and control has been done for you.

If you want to go forward with DC, then I recommend getting professional help. At your level of knowledge -- no criticism intended -- you will need someone who really gets it about the design and build/buy issues you face.

[Kanefire]

What if my concern was "Electro-Magnetic Field" the field that creates electrical currents in uninsulated conduits. Does your recommendation still apply? It is my understanding that DC does produce a field (an example is the Earth's field), but that the field interacts with the body differently.

Back to the fan, you recommended an AC fan in parallel to the heating element, but what about a 9v DC fan, how would this be connected?

BTW, no offense taken. I am trying to gather as much information as possible in this discovery phase.

[richiem]

The fan noise will depend pretty much on how fast it turns, not on its operating voltage. Larger fans are generally quieter.

You can use a DC fan powered from a DC power supply and controlled by one of the relays in the JLD612 that can be set to work in concert with the main control output. You can vary the DC voltage to the fan to control its speed, so that you can get adequate cooling with low noise.

Opinions on the effects on humans of low-frequency electric fields are mixed -- but Nikola Tesla was the first to stick his head into the field coil of a large AC motor being tested, and notice that lights he could see through the open end of the motor were shimmering at 60Hz -- and they weren't shimmering when he took his head out of the field. He lived for a very long time even though he constantly immersed himself in LF and RF fields of very high intensity. It is very hard to get away from 60Hz AC fields -- they are EVEYWHERE. So it may be that field strength is the issue. There are fairly expensive EMI-RFI-field strength meters available that are quite sensitive and may help you find a place to put your stuff that is relatively free from electric fields.

[Kanefire]

Thanks for the reply Richie.

I am simply using the decibel rating for the only fan I could find that is AC and 60mm. In the environment of a floatation tank, one is not processing sight, sound, temperature, and even specific gravity, this means that any noise will be amplified as the subject floating becomes highly attuned.

As I look into using a DC fan, taking what you have already shared, It seems that I will be required to find a power supply different from the controller. Is that accurate? Then the power supply would feed into the controller and the controller would feed it to the fan.

So I found a 110v AC to 9V DC transformer for a decent price. Can I simply wire this parallel to the AC heating element coming off the SSR or would you recommend plugging it in to its own power source and passing it through the controller?

As far as the AC EMF, I do understand this is not a settled debate. There seems to be evidence on both sides. I would like to continue to explore this path for a number of reasons. For my personal use, and this may seem odd, but given what I mentioned above about becoming highly attuned when floating, I move into incredible states of consciousness. I know immediately when the heating element kicks on because my conscious experience gets "static". I don't know how else to describe it. I have come to realize it was the heating element because when this happened I would place my hand over the heater and within a minute it would heat up. This was tested numerous times. I recognize this is only anecdotal evidence, and it is hard to relate to what one experiences while floating, but I'd be willing to explore it to, hopefully, create the purest space available.

[Tech_Marco]

Rich, sorry to interruption.

Kan (I don't know your name), why not just make it simple by getting a small DC12V fan and install it on the enclosure and let it run all time. You can get a DC12V 1A ac adapter and it wont' cost you too much. The main thing is to keep the SSR cool and it will make it happy to work for you.

Regarding the EMI, Rich was correct. Even a DC will generate EMI when you turn On and Off of the power. There is not much different to the AC which is coming with Positive and Negative cycle. EMI generate when there is current movement. So, when DC On and Off, it generate a "pulse" type current and believe it not, it will generate electromagnetic field.

If you have a small transformer say 12V secondary and 110V primary. If you apply DC (don't care 6v, 9v, 12V) on the secondary, the moment you "closed" loop the DC power and the secondary coil, there will be a pulse voltage as high as 110V (should be higher) appear on the primary side. But, the pulse gone if the DC stay closed loop (ON) as no movement (like an acceleration of a car). But when you break the loop (switch it off), a quick pulse voltage appear again in a fraction of second (enough to give you a shock)!

Once you have a DC current passing through a copper wire, the wire generate electromagnetic field (pulse in less than 1/10th second).
If you need something precise for your experiment, make sure the device stay away from the power line, regardless AC or DC

Sorry my English is not very good. Hopefully you understand me to some extend.


Marco

[Kanefire]

Thanks for the info Marco, I can understand your english well enough.

I have found a decent DC fan and AC to 12v DC adapter. You would recommend constant activation over intermittent to run with the heater?

I also came across this at usinspect.com and am curious to your thoughts

How do static fields differ from time-varying fields?
A static field does not vary over time. A direct current (DC) is an electric current flowing in one direction only. In any battery-powered appliance the current flows from the battery to the appliance and then back to the battery. It will create a static magnetic field. The earth's magnetic field is also a static field. So is the magnetic field around a bar magnet which can be visualized by observing the pattern that is formed when iron filings are sprinkled around it.

In contrast, time-varying electromagnetic fields are produced by alternating currents (AC). Alternating currents reverse their direction at regular intervals. In most European countries electricity changes direction with a frequency of 50 cycles per second or 50 Hertz. Equally, the associated electromagnetic field changes its orientation 50 times every second. North American electricity has a frequency of 60 Hertz.

I also came across this description

If DC ("direct current") is chosen, current flows one way from the batteries to the appliance. AC fields induce weak electric currents in conducting objects, including humans; DC fields do not, unless the DC field changes in space or time relative to the person in the field. In most practical situations, a battery-operated appliance is unlikely to induce electric current in the person using the appliance. Induced currents from AC fields have been a focus for research on how EMFs could affect human health.