how to calculate heat transfer rate through a heat pipe ?

Objective: maintain a temperature of water feed into an equipment to be ( 0C-20C). he surrounding temp is about -15 C in Winter and 40 C in summer. I would consider the soil as a heat sync. Any equation to calculate the amount of heat the heat pipe can transfer or  be dissipated  ? Thanks !!

Question by sultan86 5 years ago  |  last reply 5 years ago


Home/Lab made heating element?

I am trying to construct a heating element, preferably out of nichrome, for heating a small box (24 * 40 * 13 cc). The box is covered on all sides, so the heat dissipation from the box will be very low, as per estimate. I think a 12V supply would suffice for the nichrome wire. The only thing is, I need to maintain the box at an ambient temperature of about 38 degrees. Any thoughts on how I could go about constructing the heating element?

Question by Psyclops 8 years ago  |  last reply 8 years ago


wiring of L.E.D. bulbs for constant "on" and reduced heat ?

Self-confessed "tinkerer" with little/no electronics knowledge OR understanding....In need of guidance/expertise ? I have a project; requires constant 5V (from USB) to power/light several L.E.D.'s (either cool white or bright white) in a straight line(s) to illuminate an area approx. 1/2" (W)x 6.0"(L) x 1" (H)... Not knowing the power requirements of various L.E.D.'s ....some LED's require 12V and additional equipment. And the expected period of use being 6-8 hrs (max.) - I'm afraid of problems regarding heat dissipation and poor LED longevity ? With these constraints, I'm unsure if this is feasible or not ? Any help or suggestions ?  Have "tinkered with a string of LED's powered by (3) AA batteries = 4.5 volts x 30 LED bulbs. Didn't seem to get hot using the batteries. After cutting these bulbs from string and "bundling " positive (+) and negative (-) ends and connecting to 5V from USB ...got very warm-hot ? Reading various online posts that seem to agree that the output from batteries is NOT constant...is this the problem OR maybe not using "resistors" and not knowing what type or how many would be needed ?

Topic by callhow 3 years ago  |  last reply 3 years ago


Is someone willing to give me a good amount of technical advice concerning heat dissipation using a Peltier device ?

Ok, I have a laptop that I use to play many videogames with, and as you can imagine, it has an overheating is a problem. I have software that monitors the GPU and CPU temperatures while I play. The GPU and CPU are rated at a 100c max temperature. Now that the summer season has started, my laptop gets hotter and hotter as I play. I am usually forced to Under-volt my computer so that it stays below safe temperatures. Now, I was digging around online and came across something called a "Peltier device". It is a small ceramic plate (with electrical nodes inside) that when electrified, transfers the heat from one side to the other. The peltier I got is rated at 545 watts, 32 amps, and 18vdc, and gets as cold as -60c, 150c. I ordered a desktop power supply online, along with 2 CPU cooling systems. (I.E.  2x Professional grade heat-sink, and 2x 120mm fan) The Power supply outputs 430watts, 28 amps, and 12vdc. I planned on taking these parts and simply sandwiching the peltier between 2 heatsinks, having 1 hot heatsink+fan and 1 cold heatsink+fan. I planned on pumping the cold air into the air intake on the bottom of my laptop, and just pump the hot air into the room.  Unfortunately, the problem I face (and this is a really stupid mistake) was that I did not measure out this whole assembly. It turns out, the peltier face plates are roughly 2.5" x 2.5", whereas the heat-transfer faceplate of the heatsinks are only about 1.5" x 1.5". Now, I wired this all up, and put it all together, ignoring the parts of the peltier that were hanging off and lo' and behold, the peltier worked as designed, one side got extremely cold, and the other got hot. The only problem is, over time, since nothing was drawing the heat away from the edges of the hot side, it transferred over to the cold side, thus warming it up to about room temperature, negating the entire purpose of the contraption.  This is the part that I need help on, would simply taking some aluminum plates that are large enough to cover the entire surface of the peltier, smother both sides in my remaining thermal compound, and then connect this aluminum (with more thermal compound) to the heatsink? This contraption is essentially meant to be a laptop cooling pad. Mounted inside of an old computer case. So it needs to be mobile (IE, liquid cooling is not an option). Can anyone think of a better solution to this? 

Question by schwerlin 6 years ago  |  last reply 6 years ago


How do i go about choosing LEDs for a project? Answered

So i'm planning on building a battery bank to charge my phone and other usb devices . I wanted to also use it as a flashlight, My size is limited, since i was planning on using an altoids tin, and i'm already stuffing two 18650 batteries inside. What i want to know is what is the brightest led i can use that wont need a heat sink? or at least one that will dissipate enough heat into the tin alone.

Question by Tomahawk92 4 years ago  |  last reply 4 years ago


over 90W of flyback (back EMF) energy? how to dissipate it? Answered

Continuing my work on the flyback driver, I am investigating methods and practices to protect my MOSFETs from overvoltage conditions. I have measured peaks of as much as 350V across a 250V MOSFET while drawing an arc, and it does not matter what I do it seems like I simply cannot limit the back EMF transients to <250V. I am really impressed by the rugged nature of these MOSFETs, although I have popped quite a few of them. Seeing that they are being bombarded with almost 400V transients, it is a wonder they survive as long as they do. When I added a medium sized reverse biased zener diode in series with a 10 ohm 1 watt resistor, both went up in smoke, especially the resistor! The zener diode survived. I also tried a much larger screw mounted 30V zener diode w/o the resistor and it reached much over 100 degrees C after only a few seconds and I had very little output on the secondary. Judging by how quickly a 10 watt resistor heats up I assume that the back EMF very low impedance and has to be over 90W average!!! I'll need to try to use the integration feature on my scope to measure the average power dissipation accurately. In none of the configurations involving a resistor did I see the voltage clamped any lower than before. :(

Question by -max- 2 years ago  |  last reply 2 years ago


Arduino DC-DC converter? Answered

I have an Arduino project which drives a set of 12V LEDs using NPN transistors, I had been using the linear regulator on the Arduino to convert 12V to 5V for the Arduino and Ethernet shield, however I have some IL1205 DC-DC converters which could also be used, personally I think the IL1205s are the better option as they seem to dissipate less heat then the regulator on the board. Are there any other solutions to this, It would be ideal of I could power the entire project from a single 12V power supply, it also has to run continuously so must either produce little heat or be easy to dissipate the heat away from. Also because of the circuit I have to bridge the -Vin and -Vout terminals of the converter (for the transistors to work properly) I assume there is no problem in doing so. Any help is greatly appreciated. Thanks, Dan

Question by DanNixon 6 years ago  |  last reply 6 years ago


How to repair a broken left hinge on a HP Pavillion dv9008nr laptop computer?

I can not close the lid of the laptop because the left hinge has seperated from the plastic that frames the viewing screen and back of the lid. Is there a video or illustrated description of how to repair the broken hinge? I was told that the design placed a heat dissipator device too close to the left hinge and the heat caused the plastic to fail. Is this true?

Question by 9 years ago  |  last reply 9 years ago


Mini heater plan , what electronic componenet is better for the job? Answered

I have free energy coming from a wind gen and I like to heat the house with it. What do I place inside a metal box with a fan to blow out in to the room...24/7 a: resisters in correct wattage b: 12v heating elements for a car c: 20 voltage regulator can dissipate good amount of heat d: a peltier e: just simple car light bulbs what say you, need this by asap, it's cold here and I am anemic thanks

Question by celalboz 9 years ago  |  last reply 9 years ago


Stator casting and best casting resins ?

I am curious which would be best for casting my 9 coil 3 phase stator ,Cyanate ester resin ,or Polyester resin?I also curious if it would be best to cast all coils together as a whole or would individual castings work better for heat dissipation? The individual picture just for example. Thanks for taking time to help :)

Question by 1RaceFTW 9 years ago  |  last reply 9 years ago


Can I fit a 10W heatsink in a zippo? Answered

I want to put a cree XM-L LED in an old zippo, and I want to know if anyone knows how to fit a big heatsink in the top part of a zippo lighter, not in the base, and preferably able to buy everything from a hardware store, not ordered online.  Also, does anyone know how to anodize aluminum for added heat dissipation?

Question by jduffy54 6 years ago  |  last reply 6 years ago


Thermal epoxy or Thermal grease and bolts?

I am mounting 15 Cree LEDs to get an old overhead projector to work as a video projector. the only thing I am wondering is whether thermal epoxy is better to use than thermal grease with bolts and nuts attached to a heatsink. Do both have the same heat dissipation? What I am trying to do is still use the LEDs for use with other projects in case i need them for something else.

Topic by KT Gadget 9 years ago  |  last reply 9 years ago


Does Increased resistor wattage effect peak amperage output?

Hello, I am in the process of building a 900W+ (60v  ~14a)  RC EDM generator. I am using a heavily modified hairdryer heating coil at  4 Ohms resistance at about 1200 watts. According to my calculations (derate transformer output wattage 20% in order to obtain minimum wattage required), I needed a minimum of 720 watts of dissipation on the resistor. Would it be okay to use a higher wattage resistor without any amperage drop on the circuit while it is operating?

Question by abadon 6 years ago  |  last reply 6 years ago


Wall outlet current draw

I have built a transformer, that will take 120v, and step it down to 2.5v. I used all the right parts, and the correct rated wire for this. My only issue, is that when i connect the primary coil, to a call outlet, at 120v, it draws more current then my 5A fuse can handle, and the power goes out in my home. I need to get 1.5 amps, @120v going through my primary coil, in order to get the desired output on the secondary. I was wondering, how things "draw" current from the wall, as well as if i where to use a resistor, wouldn't it still draw too much amperage, and just dissipate it in heat, to give the desired output (i cannot use, because it draws more than 5 amps). i could not find a resistor out their, that could handle over 100 watts, so i was also wondering how things like vacuum cleaners only draw a small amount of current. Would i need some sort of current regulator (if that's even a thing)? if you had a light-bulb, and a battery, would the circuit the light-bulb is attached to drain less current, if their was a resistor, and thus having the battery last longer, or would it draw the same amount, and just dissipate energy through the resistor in the form of heat, to give the light-bulb its self less current?

Topic by merlinj 3 years ago  |  last reply 3 years ago


Flyback Driver and Plasma Speaker Driver Question?

I was looking for a good way to drive a flyback, and a circuit to make a Plasma Speaker.  What I came up with, can you use an MC12061 running at 3.8MHz through an IRF540 MOSFET to drive it?  If that works, could you make a summing amplifier with an Op Amp to sum the output of the MC12061 and the Audio (Maybe amplify the audio a bit before the summing amp?) before driving the MOSFET?  Would this work?  Would there be significant problems like heat dissipation from the MOSFET, distorted sound, etc? Thanks

Question by Electric Spectre1 6 years ago  |  last reply 6 years ago


Limit DC current from LiPo battery?

Dear Colleagues,  could you please advise if there is a way to limit DC current from LiPo battery?  I need to push the high current (80A) through very low resistance circuit, but do not want to fry LiPo. So need to limit the current at 80A I am not an electronic professional, and all solutions coming to my mind are based on increasing resistance of circuit (by adding resistance manually, or constructing something like FET-regulated limiter). The problem here is that I will generate lots of heat, and need too much space for its dissipation.

Question by SergeyD15 2 years ago  |  last reply 2 years ago


Finding an appropriate heatsink for 5V 3W LED? Answered

Hello, I have bought some 3W 5V leds, and now I have to dissipate the heat they produce. I am thinking of using an xbox 360 GPU heatsink i have laying around ( https://s3.amazonaws.com/assets.overclock.net/7/7b/7bb1229a_vbattach111891.jpeg ), cut in apprpriate size. Then I would glue the led with thermal epoxy to it.  Can somebody suggest an adequate size for the heatsink? I can't find any info around. I have other heatsinks as well, I would rather not buying a LED heatsink if that's not mandatory. Thanks in advance :) Picture of the leds attached, they have no board to screw them with.

Question by en_rov 4 years ago  |  last reply 4 years ago


Joule Thief in between Peltier/TEG and DC Motor?

As per the title I've got a Peltier cooler chip sandwiched between 2 heat sinks acting as a Thermoelectric generator (TEG) which when sat on my wood burning stove generates about .5V (which is a bit disappointing).  The idea was to cheaply recreate one of the EcoFans, so the plan was to connect the TEG to a low voltage DC motor.  The obvious issue is the low output from the TEG itself - I need to maximise the heat dissipation from the top heatsink to create the temperature difference, but even solving that I'm going to struggle to consistently get more the 1V from the TEG. Before I go to the hassle of sourcing and making a Joule Thief (like the 1up instructable) is there something fundamental I've missed that means either the TEG won't work with the JT, or a 1.5V - 3V DC motor won't work with the JT? Appreciate any help is establishing the feasibility of this idea, or suggestions to an alternative solution :-)

Topic by thankyousam 7 years ago  |  last reply 7 years ago


How do I power my LED's?

I posted before with unknown specs on the lights, but I now have the specs. I have 50 Red LED's and 20 Blue LED's that I would like to make in an array for a grow light. I was thinking about gluing them with thermal glue on flat aluminum bars that are 2 inches wide in a rectangle with about 1 inch spaces around them because I don't have heat sinks. I think they would be able to dissipate enough heat if I use them in conjunction with a fan. Here are the specs for the red lights (50): 2.4mV forward current 700mA blue lights (20): 3.2mV forward current 700mA If I'm correct, I need 84 watts for the Red LED's altogether; 44.8 watts for the Blue LED's altogether: combined wattage of 128.8 watts. Previously, I stated that these lights were 3w, each. But I would rather save life on the diodes and run them at this lower power because they still give off a great amount of lumens. Can anyone give me some directions on how I would construct this array? (what drivers to use, how to wire the LED's together, and how I could make the system plug into my wall outlet (standard USA socket)). THANKS!

Question by ammakrom 8 years ago  |  last reply 8 years ago


Could you weld with an induction cooker? Answered

Having seen the microwave transformer welding kit and similar projects I started wondering about this one... Induction cookers are basically one side of a transformer and usually just dissipate current in to the pot to heat up the pot. But they've a high number of coils and I've seen them rated at 3000 watts, so if you made a coil that was a few turns of thick wire to be the other side of the transformer you'd possibly be able to have a huge current low voltage supply similar to the microwave oven welder. I imagine there'd be safety devices that may need disabled but the idea of your oven being a welder seems cool to me, especially if someone had a need to weld often and their kitchen was through to their garage.

Question by killerjackalope 9 years ago  |  last reply 9 years ago


How inefficient are resistors? Answered

I know how to calculate resistive losses, but do different types of resistors have different amounts of losses (power in vs power-out, in watts) From my own observations, connecting a 10 ohm resistor across a barrey will cause significant heating in both the resistor and battery, and cause the wires to get warm. All of this is resistive loss, but when I exchange the resistor for a 10k resistor, there is virtually no heating at all. What if I use a 0 ohm resistor (direct short). The only thing getting hot would be the power supply, due to internal resistance. Does this mean higher resistance is less lossy and by definition, more efficient, or is this simply due to the fact that there is less current flow, and less power loss, and efficiency (% of power loss)  With an ideal constant current source, will the losses though any resistive load be equal? ( X amount of watts lost/dissipated @ 1A) Is it possible to limit current like a resistor without losses? (I know PWM techniques are more efficient, but I want actual resistance rather than chopping current flow and filtering with an inductor/capacitor RC filter)

Question by -max- 5 years ago  |  last reply 5 years ago


Are high power resistors really neccessary on a benchtop PSU conversion?

Was looking through the site and I was just wondering--why all the huge resistors on the bench-top power supply conversions of PC Power supplies? From personal experience this seems like a waste of perfectly good electricity.I know that they require some current to just stay on however in designing a project for my school's Engineering Technology department I found that the heat generated by such a small resistance (Around 10 ohms) was unacceptably high. Originally I was looking at Instructables and this sitethis site for inspiration but all the cooling measures taken to prevent the high power resistor from becoming a hazard seemed rather silly. A few calculations and experiments later with the 250 watt power supply and I determined that 160 ohm1 watt resistors and 1K 1/2 watt resistors were perfectly acceptable for the purpose of keeping the PSU awake and functioning. I connected one of each between each voltage and ground. According to calculations I can get away with dissipating a grand total of two watts or less spread across multiple resistors.The current divider rule dictates that if you add resistances in parallel, the resulting resistance will be smaller meaning more current will flow through the overall circuit. However this increased current will divide itself across the parallel resistances according to the rule Ix= RtIT/(Rx+Rt). The current through and power dissipated by the resistor you've soldered into the PSU will not change enough to be significant no matter how large or small a resistance you attach in parallel with it--with the exception of an effective short and what in God's name are you doing intentionally shorting the terminals of your bench-top PSU? Now several months later, the PSU is still operating happily and powering multiple micro-controller projects on a display board. Therefore I can reliably conclude that the high-power 10 ohm resistors in many computer power supply conversions are probably a gratuitous waste of wattage. You can get away with using a higher resistance and a resistor that dissipates much less current.

Topic by Psickattus 11 years ago  |  last reply 11 years ago


BJT vs MOSFET? Answered

-- background: In my perpetual pursuit for designing the best, cheapest, & best performing flyback (line transformer) driver, I've decided to try out some big BJTs, which appear to have higher voltage & current ratings @ considerably lower cost. In the past, I have tried MJE3055's, which work OK, and allow the generation of thin blue arcs from a 12V supply for a few minutes until the transistor dies due to high voltage kickback or overheating. The FDP33N25 gives good results but is somewhat unreliable at 24V. So I decided to give these alluring "PHE13009" 400V 12A rated NPN BJT's a try. However driving the transistor adequately seems to be the problem. (I didn't realize these transistors would require like 5A base current w/ only HFe of 2!) It seems like almost all the "good" driver schematics utilize large $$$ FETs or even IGBTs, but almost every CRT, plasma globe, and ballast (SMPS) I took apart seem to prefer high power BJTs probably due to this exact cost difference. I was only able to get simalar performance to my 33N25 MOSFET when I stuck an additional TIP120 in as an additional darlington stage, which worked very nicely (white hot arcs) for about 1 second, then it popped! :( Since the collectors are tied together they are all exposed to >200V transients, I am sure that's what killed it. I substituted that transistor for another PHE13009 to see what would happen and with a third driving stage (2N2222) I could get somewhat acceptable results but I know I can do better. >:) - My actual questions:  * The GDP of this transistor is 40MHz, seems fast to me. (certainly faster than the 2MHz GDP of the 2N3055 which works well in my slayer exciter.) and MOSFETs have significant gate charge. ECE2630 glossed over transistors mentioning BJTs are faster, (small signal ones, anyway :P ) and some internet sources agree, but I am finding lots of sources saying the opposite! What's the deal? Which one "faster?"  * How to traditional BJTs compare to IBGTs? Which are faster/better? The datasheet for this transistor explicitly mentions its use for "high frequency ballast and switch mode applications" which implies that it is well suited for my needs. It also includes a several inductor test circuits, but other than that the datasheet is pretty bare-bones.  I'm actually a little disappointed the HFe is so low (around 2-3) @ >10A. I may require more windings on my primary and a 48v supply. (not ideal) * I know I will dissipate a little more heat due to the base current, and something I didn't consider was heat dissipated in the resistor biasing/controlling the base. (like 12V at several amps just to drive the damn thing!!) so it is worth the cost benefit of $0.5? Is there a configuration I could use that makes driving the transistor easier?

Question by -max- 2 years ago  |  last reply 2 years ago


Voltage regulator Design Problem?

 Ah, voltage regulators. Easy Right! Not this one. I am making a voltage regulator like for an automobile regulator for a DC generator. (I'm replacing the old DC generator regulator on Pre 60's cars) A battery is charged from a winding on a Generator  (20V @ 60 Amps) A voltage sensor on the battery voltage turns on and off a switch driving the Field winding. The Field winding basically "turns on and off" the generator output. The battery is connected directly to the generator. (Why  and Why not is coming up) But when the Genrator's output is lower than the Battery voltage, current will flow back from the battery to the generator winding and discharge the Battery. So I need some isolation between the generator output and the battery. Alternators are easy since it has a bridge onthe output keeping the current from flowing backwards. Old regulators used a relay which burned out sooner or later. So easy, use a diode right? Just put a diode inseries with the generator to the batery. By the way, the "open circuit" voltage on a generator is about 200VDC No! The best diode I can find has a .7V drop at 60 Amps which is 42 Watts of heat to dissipate. Ahhh, so use a FET, They can get down into the milliOhms right? Except for the reverse polarity (and ESD) protecton diode always across the FETs defeat the purpose of a reverse polarity switch. So who out there is smarter than me? What goes inthe box marked ?? Any solutions accepted. Ungefahrt (now neither young or fast)

Question by ungefahrt 6 years ago  |  last reply 6 years ago


10 Watt LED Circuit

I am a software developer by trade and have little or no experience regarding LED and/or electronic designs. I am hoping someone here can help with a project I am working on using high brightness LEDs. I have studied several 'instructables' and specifically dan's "Circuits for using High Power LED's." My project consists of a few high brightness LEDs that will be placed in a high ceiling room with the brightness controlled by a microcontroller based on the light in the room (time of day, sun in window, etc). The microcontroller will use photocells to determine the brightness in the room and then adjust the LED using PWM pins. The LED is 10 watt and approximately 450 lumens. Attached is a circuit I drew as a starting point and would like help in determining if it will work, I am close or does it need to be trashed. I am not sure what the value for the resistor should be. Below are some calculations but not sure if I am on the right track or not. No need to be kind, I am more interested in getting it right and not losing any 'magic puffs of smoke' from any of the components. Here are the specs: LED IF: 1.6 A Peak Forward Current: 1.7 A Forward Voltage: 8 V LM350 (heavy duty version of LM317 IO_MAX: 4.5 A 1.2 - 25 V adjustable regulator BC337-40 Collection Current - Continuous: 800 mA dc Total Device Dissipation: 625 mW Resistor: 5W or 10W Voltage Amp Ohms Watt 8 1.60 5.0 12.8 8 0.80 10.0 10.0 8 1.10 7.5 8.5 Note: LED and components will have adequate heat sinks.

Topic by desnotes 9 years ago  |  last reply 6 months ago


water-based kinetic LED lamp

I want to mak a kinetic light using high-powered LEDs to produce glitter line through a thin layer of agitated turbulent water in a wall mounted shelf. So, this gives me a few questions, but let me start with the idea I've got. I want to seperate a shelving unit (preferably solid wood not particleboard with some decent HxDxW) into two compartments. A glass sheet would be slid into grooves onto the side supports. The upper portion of the shelving unit would then be wood, waterproofed with some thin styrene plastic sheets. The bottom would then be composed of a large aluminum sheet (recessed slightly upwards for astheatics) which would house several LEDs in addition to the power adapter and voltage regulator. This would likely follow the "powering high powered LED" tutorial's alternate power source to the pucks. At this point a small pump would be placed into the upper compartment along with just enough water to submerge the pump to a safe level. Perhaps a small recess would be included in the top to allow instant colour shifts by using stained clear plastic sheets (this would reduce total illumination, but these are to be mood/ambient accents not primary lighting source) to avoid any of the more expensive/complex colour shifting lamps. The big question I have at this point is how thermally safe this would be, and how much LED I would actually need to achieve decent brightness. Also, I would prefer if the bottom was modular enough I could remove and work on it without dissasembling the entire assembly, but this may not be possible. Finally, I was wondering if I could run the heatsink material up the ront of the shelf, past the glass, and into the water (this should give great heat dissipation) and have a SAFE and STABLE waterproof join between a flush glass-metal joint with possible use of epoxy and/or silicone caulking. Anything not specified in here I'm uncertain of how to do exactly. So! If anyone has any ideas, suggestions, or awareness that this is pure madness (or has a better way t oget those glitter lines i lust for) please let me know.

Topic by JRGumby 11 years ago  |  last reply 11 years ago


Changing DC voltage and amperage?

I've been looking into HHO units and the most efficient voltage is 1.5 VDC but the units pull 30 Amps.  All the converters and modules seem wasteful while I feel there is a direct way to create this supply with minimal loss from battery supply.  Resistors seem to be the most efficient but what resistor can turn 12V into 1.5V while delivering 30 Amps without burning something out.  I'm contemplating a bank of resistors all on separate leads and tied together in a parallel combination so the 30 Amps are split along many lower amp rated resistors.  I just don't know enough about DC conversion to know if amps will become volts or just get lost to heat dissipation.  An HHO unit relies on the highest efficiency current supply to perform correctly and save my gas.  The units are out there but not this fine tuned system I want to build because 1.5V at a 30 A draw from a 12V car battery is hard to do without wasting the gas in just converting the ideal power supply.  I've heard talk of using diodes as well.  Is a diode or resistor setup more efficient than a PWM?  Could I combine diodes and resistors for better efficiency?  I've been searching the web for info but it just confused me more as nothing I've read comes anywhere close to what I'm trying to do.  Those I've read about that try to build the most efficient power supply end up burning up their components by pushing them too hard while instructing others to do the same.  There has to be an efficient way to create that ideal supply current without much loss.  Could it be run straight off my alternator since it produces AC before the voltage regulator converts it to DC or would a second regulator just waste more current than resistors and diodes from the 12V battery?  Any advice or info would be greatly appreciated.    

Question by bmac30 7 years ago  |  last reply 7 years ago


Technology Makes Cheap Drinking Water from Air

INTRODUCTION:   How can we best apply basic technology to help the underprivileged and/or disaster-hit countries like Haiti? Daily hygiene and nourishment are among the top needs for disaster ridden regions!  Simply put, no water means no hygiene. The Romans understood that over two millennia ago and created their complexly beautiful aqueduct networks for handling both fresh and wastewater! Other ingenious water systems like “air wells” have been found in the city of Theodosia (cf: discovered in 1900 by Zibold, see Zibold’s Collectors/Dehumidifiers) dating back to Greco-Roman times during the Byzantine Empire. These were strictly passive systems that naturally dehumidified air, collecting its potable water in underground basins. All air, even in relatively dry desert regions, will precipitate or release its natural water content (initially in the form of vapor) through condensation when it hits its dew-point temperature and below. That means you “chill” it to an appropriate level that is anywhere from 5F to 50F below its current air temperature, depending upon how much water content (relative humidity) it has locally absorbed. The condensation of the water vapor releases its internal latent heat (reheating the cooled air) which must be constantly dissipated (absorbed by something) in order for water formation to steadily continue. So how do we dissipate this resultant vapor-heat and chill our air without any infrastructure or electricity, in an underprivileged or disaster-ridden region? We simply bury a long cast-iron or any metallic drain-pipe sufficiently underground where the temperature of the earth is naturally held to a constant at around 45F to 55F. That’s our “free” chiller gift from nature. One end of the pipe, Figure-1,  sticks out of the ground to suck-in local outside hot air, and the other end dumps cooled dry air and water into an underground cistern where it gets collected and is piped to the surface to both exhaust the cooled dry air and connect to a water pump. We need a hand operated water pump to lift up the water above ground, and we need an electric fan to constantly pump air through the ground-chilled piping system. We can even force the cooled piped air to exhaust into a tent-like structure where it provides air conditioning as an added bonus, but this adds the penalty of both power and the increased fan size necessary to drive our required airflow further into an enclosure! While this concept is not “passive” (requiring electricity to work) like those clever Byzantine air-wells, it will produce much more potable water and within a smaller volume than those elegantly passive historic devices. The electricity for our fan power requirements can be produced by any one of four ways using either “active” or “passive” techniques: 1) An active playground or bike-pedaling-person or oxen-driven mechanism-generator, 2) A passive windmill generator, 3) A passive solar energy collection system that directly generates electricity, or 4) A passive thermo-electric system that directly generates electricity using the Peltier effect, operating solely on temperature differences between the cell’s top and bottom surface (we jury-rig the cool pipe and hot ambient air to contact separate sides of the cell). Depending upon how much water is needed, the required air volume plus pipe length and diameter, together with the fan will be sized accordingly. We can also configure groups of parallel fan-driven air pipes that are radially fed into the cistern. The sizing of this underground network depends upon the ambient air’s local average temperature and relative humidity (how much water gets absorbed into the air) plus buried pipe depth and effective underground temperatures achieved. The basic concept is one where we “wring” water from air at some given humidity content. The higher its relative humidity the more water is recovered from the air. The air-wringing process simply chills the air as it scrubs along the cooled internal pipe surface until it starts to rain inside the pipe from condensation onto its surface. The condensation is like the dew that forms on car windows, grass or any cooled surface in the early morning, before the sun comes out and evaporates the dew back into the heating air. A further bonus is that our dew-formed water is naturally distilled and very clean. It is potable water ready to drink without the need for additional sterilizing agents. Of course, we must make sure that the interior piping and cistern network is biologically cleansed before burying it underground. The hand pump with its 10 to 15 foot extended piping to reach the underground cistern must also be cleansed. The beauty of this constantly replenishable water supply is its convenient underground installation anywhere! After the in-ground installation, we have a virtual, partially passive, no moving parts, non-breakdown system containing above ground total access to all moving parts that could breakdown, namely the water pump and electric fan. Also, it is easily maintained, with few moving parts (water hand-pump and electric fan) and basically lacking any technical complexity which makes it ideal for technologically backward regions. The example below uses a relatively small industrial fan moving air at 1500 CFM (Cubic Feet per Minute) with a DC motor rated at 1kW. This fan together with our underground piping system will conservatively generate 12 GPH (Gallons Per Hour) of potable drinking water without need for any purification chemistry. Based on an average electrical cost of 14-cents per kWh (kilo-Watt hour), the typical commercial distillation of one gallon of drinking water costs roughly 35-cents as compared to our cost of only 1.2-cents. Furthermore, if we decide to go green and use solar energy for generating our water, it would effectively cost us nothing beyond the initial installation! USING A PSYCHROMETRIC CHART TO SIZE OUR WATER SUPPLY: The following gets a little technical and is only provided for those die-hards who are truly interested in how the science works. Those non-technically schooled may skip this part and not miss the basic concept. Figure-2 shows a Psychrometric Chart for air. This chart summarizes some of the basic thermodynamic properties of air throughout its typical range of operating temperature. The chart uses six basic air properties that defines the physical chemistry of water evaporation into air:  (1) the enthalpy or total energy contained within a unit of air which is a combination of its internal and external energy, expressed as the amount of BTU-energy per unit mass of reference dry-air, (2) the specific volume or the ratio of a unit volume of local air to its mass of reference dry-air, (3) the humidity ratio or the amount (mass) of moisture in a local unit of air divided by its reference mass of dry-air, (4) the percent relative humidity per unit of local air, or the mass ratio (expressed in percentage form) of the partial pressure of water vapor in the air-water mixture to the saturated vapor pressure of water at those conditions (the relative humidity depends not only on air temperature but also on the pressure of the system of interest),  (5) the dry-bulb temperature or the locally measured air temperature, and (6) the wet-bulb temperature or saturation temperature which is the local air temperature experienced during constant water evaporation (a wet-bulb thermometer is typically used:   a thermometer that measures resultant temperature while wrapped in a water wet-gauze and spun to generate local air movement and max-evaporation)  1.0   The Process and A Sample Calculation Our Psychrometric Chart uses six thermodynamic properties that help to determine the amount of water available for extraction from the local ambient air as a function of its temperature, pressure and relative humidity.  Let’s assume the following local ambient conditions for the region we plan to construct our water system at:  (1) Typical daily air temperature Td = 106F and one atmosphere pressure assumed at sea-level, (2) Relative Humidity, RH = 55%, and (3) Typical underground temperature down at six feet is measured at Tu=55F (at 12ft. it drops to ~45F). This yields the following calculated results for obtaining a steady-state supply (changes at night) of water to fill the cistern:      1)      In our example, the “local” air (dry-bulb) temperature is Td=106F, at a relative humidity of RH= 55%.  Fig-2 indicates that the resultant Humidity Ratio is HR= 0.0253 Lbs-water/Lb-Dry-Air (intersection of Td=106F line and RH=55% line, then horizontal to HR value).  We then determine the “gulp” of air volume containing the HR Lbs-water which corresponds to the point of intersection of Td and RH. Interpolating on specific volume “mv” yields mv=14.7 ft3/Lb-Dry-Air (this value sets the optimum unit airflow for our given ambient conditions, and creates a ballpark pipe length to diameter ratio needed later). It represents the basic unit of air volume that will enter our underground pipe per given time, and ultimately defines the size of our fan and piping network. For increased water creation, multiples of this unit volume will scale up the additional amounts of water that can be collected. 2)      As the inlet air cools down to a temperature of Tu=55F, from contact with the relatively cold underground pipe, we follow the constant enthalpy line (red upward left-diagonal) from the intersection of Td and RH to its saturated air temperature condition of Ts= ~88F, which is its dew-point temperature where the corresponding local RH=100%.  At this temperature or under, the air precipitates and releases its moisture content, resulting in water condensation onto the pipe walls.  Since our air will chill to a final pipe temperature of Tu=~55F, we follow the RH=100% saturated curve (green) down to yield an HR=~0.009 Lbs-water/Lb-Dry-Air. This is how much water is left in the air when it gets to 55F.  Therefore for every pound of local outside air that enters the pipe, mw=0.0253 – 0.009 = 0.0163 pounds of absolute pure, distilled potable water precipitates onto the inside pipe wall (per pound of dry air that is cooled and dehydrated) to gravity-flow out the pipe exit and into the cistern. 3)      We now convert pounds of air per unit time into a unitized volumetric airflow that yields gallons of hygienically pure potable water production per unit time. For every Va=100 ft3 of local volumetric air movement per minute (CFM) through the pipe, which translates into ma=Va/mv= 100/14.7 = 6.8 lbs. of dry air per minute or 6.8 * 60 = 408 lbs. per hour (PPH), to yield a water-flow of mwf=ma * mw = 408 * 0.0163 = 6.65 PPH or 6.65/8.345 = 0.8 GPH of water.  An industrial fan rated at 1kW DC will typically move 1500 CFM at a pressure of 8-iwc, to continuously produce 15 * 0.8 = 12 GPH of pristine potable water. 4)      Not shown here are the design details of sizing our pipe, fan and solar collection system for electric power requirements using heat transfer principles coupled with a thermodynamic heat balance, and aerodynamic fan performance assessment. These details help to size the electric power generation requirements plus margin used to properly size a solar collector containing further margins for overcast days. The engineering involved here is straight forward but beyond the scope of the current project.

Topic by RT-101 6 years ago  |  last reply 1 year ago


PSU design (major revisions): Transformer calculations help?

Recently I have attempting to design a proper dual-rail power supply that will allow me to set a voltage as low as +-1V up to +-30V in 0.1V increments at (hopefully) 3 significant digits (at least for the lower voltage settings). Anyway, this supply is also going to be current limited to up to 5A,again, it can be set to just about anything. I plan on using an Arduino micro-controller to set the output. In order to do this, I plan on using the analogWrite functions, or better yet, a legit DAC. There will be 4 outputs from the Arduino that will set the power supply output by applying a 0-5V voltage on the input of the 2 current limits and 2 voltage sets. (one for the negative rail, one for the positive). However, I have kept running into the same problem: how do I plan on driving this linear power supply with up to 200W*? My first idea was to use a a MOT, due to their high-power capabilities, and re wind the secondary with the right number of turns to achieve this output. However, I have heard that these transformers are not optimal for continuous running due to their poor and cheap design. (losses are very high). My second idea was to search around for a 250VA transformer. However, even until now, the VA rating confuses me. How does VA compare to W? I know this has something to due with reactive power, real power, and apparent power. However, I have no intuition of any of these 'powers.' How would I go about calculating the correct size transformer for the job, also, I am going to assume this linear power supply has the properties of a resistive load, since it is rectified and smoothed with a filter capacitor, so practically nothing should react with the AC power. (unless there is something more to the full-bridge rectifier setup I am considering.) This is when I came across unwound toroidal cores found on eBay for $25, the perfect price range! However, this has raised more questions! to start off, beyond turns ratio, I do not know now many turns I need for the AC side of things. I know intuitively and from experience, mains-frequency transformers do not work with only one (or even few) winding(s). I think this has to do with saturation, but I'm no expert by any means. and the inductive reactance of the transformer's primary. How do I calculate losses, inductance, and other important parameters of a homemade transformer like this? Things get very nasty when I look back at rewinding an old transformer. Now I have all these questions about inductive reactance, power, currents, magnetic flux and saturation, but also, about determining the original power rating of something like a very old small welding transformer or one from a large 10A car-battery charger. Is it possible to approximate the power by measuring the dimensions of the core? How close will this approximation be?  After getting frustrated with this, I considered alternative approaches. What if I purchased 2 ~20V ~6A SMPS (switch mode power supplies) connected them in series, and connect the center tap of my linear supply to the joining point between the 2 SWPS's? Would this be unstable and be bad for the SMPS if a load was connected between the 'outputs' of this new center tapped supply? Would any sort of balancing be required? Also, a bigger problem includes how this will be connected to my linear PSU design. With a low voltage @ high currents, I would be wasting a LOT of power, power that has to be dissipated away from the transistors. This heat can approach 200W, which is company unreasonable! Anyway, I would them have to either a switching preregulator, or modify the SMPS's so the voltage can be controlled easily and varied between, say, 3V to 20V. absolute accuracy is not required, close enough, and rest of my PSU should handle it. This becomes seemingly impractical too, and many other considerations need to be made. What should I do? what are the calculations and factors I need to know? i do not have an LCR meter to measure inductance, so trial and error is out. Does anyone here have experience at this? Help would be greatly appreciated! *The 200W figure was calculated by taking 40V, (What I believe would be a safe to allow some slack for +-5V voltage drop across my 2 shunts and transistors) and multiplying it to 5A of current for the maximum power output. ------------------------------------------------------------------------------------------------------------------- I have added an image of my current design, and I have modularized it the best I could. The YELLOW is all my current power-management circuitry. Currently just a transformer with many taps, going to a currently-undesigned switch box that will change the voltage on the output, which is then rectified and enters a filtering capacitor, finally entering the circuit.  The GREEN field is the voltage set. It is the most major part of the PID feedback loop, along with the ORANGE field. It works simply by feeding a voltage to the positive of a op amp configured as a comparator, and with negative feedback from the output. It then outputs a signal to the transistor, turning it either more ON, or more OFF depending on how the output voltage compares to the +Vset. The negative portion is largely the same, but the input voltage needs to be inverted so the output voltage is set negative properly. I was not able to use less than 2 op amps for this portion, unfortunately. The ORANGE field is current set. It works by measuring the voltage drop across the shunt resistor, and outputting a unity voltage that is referenced to ground, instead of to the positive rail. (It took me forever to finalize and perfect that!!!) Anyway, this voltage is then fed into a op-amp configured as a comparator to drive the transistor. The BLUE field is my switching regulation topology, which is controlled by both the ORANGE and GREEN fields. Do you like my use of diodes as a super-simple voltage or current selection switch? the op amp that outputs a lower voltage is the one that gets 'listened to' by the transistors. This way, current and voltage mode enable properly. This does add a small problem when it comes to powering the op amps, all of them have to be powered off of slightly higher voltages to swing the full range due to the voltage drops of those diodes. In the PINK field is simply a single-transistor solution to a constant current load. This allows the regulator to be regulated even at very low voltage set levels. This is why I am able to achieve a +-0.5V on the output (at least within LTspice) Finally, and most unimportantly, the light PURPLE fields have a simple ultra high-gain difference amplifiers that will detect if the output current and current set are the same, and turn On or OFF the respective LEDs. The green LEDs are voltage-mode indicators, and the red LEDs are to show when current-limiting mode comes on.

Question by -max- 5 years ago  |  last reply 5 years ago