Potentiometer for 20v??

Hello! I am trying to build a bench power supply from a laptop power supply and i need a potentiometer capable to handle 0-20v. I have tried many times with different potentiometers but they all start smoking and later starts burning :( i don't know that much about elektroniks circuits so be gentle :) Please help me!

Topic by WaNa_Cookie   |  last reply


Voltage Control: 20v DC

I am trying to find an electronic part that will take in anywhere between 12-36v and put out a consistent 20v. What could do this? And how can I get one? If amperage matters, I'll probably be putting between 1 and 4 amps through it.

Topic by V-Man737   |  last reply


Bench power supply potentiometer for 20v?

Hello! I am trying to build a bench power supply from a laptop power supply and i need a potentiometer capable to handle 0-20v. I have tried many times with different potentiometers but they all start smoking and later starts burning :( i don't know that much about elektroniks circuits so be gentle :) Please help me!

Question by WaNa_Cookie   |  last reply


Powering a Salvaged Window Motor with 20v Battery (HELP!!!)

So earlier this month, I replaced the window regulator in my Honda Accord so I can sell it later on. After looking at the old regulator to see what was broken, I saw the motor component was perfectly fine, so I salvaged it for a future project! I do have a few ideas for what to do with this, but my main conundrum is how to power it when I have no 12V batteries lying around.I do have a Black & Decker Cordless Drill that uses 20v Li-Ion rechargeable batteries, and the shape of the battery is pretty compact. Its got 2 POS and NEG leads which you slide the contacts inbetween, and I can 3D print something to hold the battery in place for the project I intend to make with it. However, 20V is clearly overkill for this motor and that means I need to convert 20V to 12V. Does anyone have any ideas how to achieve this?

Question by EngineerJakit   |  last reply


Can i use a laptop charger whose input and output ampers are higher than my original charger?

My original laptop charger is not working can i use New charger whose input is 100-240v-2.4a (2.4a) 50-60hz and output 20v(20v)== 4.5a(4.5a) insted of my original cahrger whose input was 100-240v~1.7a 50-60hz and output was 20v(20v) == 3.24a(3.24a). As you see there is difference in input and output ampers

Question by AbdulR138   |  last reply



Transistor Voltage Inverter

I am a newbie and was hoping someone could assist me. Given the following schematic which takes a voltage of 12v and considers it off and a voltage of 2 volts and considers it on can someone tell me what changes would need to take place regarding capacitors and resistors (if any) to account for 20v instead of 12v? Meaning that when 20v is considered off and 2v is considered on.

Topic by TimothyE2   |  last reply


Transistor Voltage Inverter?

I am a newbie and was hoping someone could assist me. Given the following schematic which takes a voltage of 12v and considers it off and a voltage of 2 volts and considers it on can someone tell me what changes would need to take place regarding capacitors and resistors (if any) to account for 20v instead of 12v? Meaning that when 20v is considered off and 2v is considered on.

Question by TimothyE2   |  last reply



Solar charging

Hi, pls suggest me for the following A 20Watt ( 20V , 1000 ma) solar panel is connected to charge a 12V, 80AH battery . What is the value and wattage of a Current limiting resistor to be added?

Topic by khhrao   |  last reply


How can I convert a 17vinDC to 20vout DC?

Hi Fella's I was wondering again if there is any schematics here that I can use to convert a 17in to 20v out DC-DC converter? Kindly send me a link please. TiA

Question by mitchiko   |  last reply


external battery charging option for Asus EP121 tablet pc

Hello all, A friend posed me with a problem as to how to extend his field time with his Asus EP121 tablet pc. It does not have removable batteries so the option appeared to be to come up with an external battery pack to power the tablet when the internal battery got low on charge. The output of the DC charger is listed as 19.5 V DC / 3.08A. A suitable option to me appears to be a Dewalt cordless tool battery pack. The unit in particular is the DCB200 20V MAX lithium ion battery pack, spec'd at 20V at 3.0AH. Aside from having to come up with an interface between the connector on the battery pack to the jack on the tablet, is this idea advisable or viable? Thanks, Gutbucket gutbucket@bell.net

Topic by gutbucket 


Laptop powerbank 12v to 20v and upto 5A output using 18650 batteries with USB 5v added

Hello ladies and gentlemen.  Im looking into buying a laptop powerbank charger for my Lenovo X1 carbon that charges at 20v 4.5A 90w fast charge with upto 80% charge in 1hr. But it will also charge at 65w and maybe 45w I've read. But this will not give me the full power of the processors and gpu etc. Unless I charge at 90w 4.53A  there are are some powerbank that are around £100-170 for sale but these don't give full 4.5A. Mainly around 2-3.5A so will maybe or maybe not charge she give me full power of the laptop   so I'm thinking about making me own using 18650 batteries. Good Samsung or LG 2500maH plus cells. Prob around 3000mah.  Im thinking I could either use a buck down or step up and use the batteries on series from 3S to 8S and then 3-4P to give me around 10000mah. I'm looking for the best efficient output so I'm not sure whether to use higher input or lower input to give me 20v.  Or or maybe I could go the inveter route using a 12-24v 150w inverter?? Efficiency is the main thing here. What is the best option do you think. Should I use 12v or 24v for max effecient conversion.  Ive searched the instructables for such devices but cannot seem to find anything like this. Or would I be better to buy one??? I would want to add USB and USB c also. Defo USB 2.0.  Could you you please help me choose and find the answers please?  I fancy the DIY route because I'm looking into solar and battery power storage and also boost my range wifi range through either ptp or directional attenna. These projects will come after the laptop powerbank.  Any my help would be appreciated a lot.  Kind regards.  Scott. 

Topic by ScottL190   |  last reply


Can a 10 watt solar panel giving off 20V DC directly power a flywheel motor assembly with a 12V DC motor?

I am doing a science fair project that involves a solar panel, connected to a charge controller, connected to a 12V battery, connected to a switch system that can either go to a flywheel with a 12V DC motor or straight to a DC to AC inverter which leads to light standard light bulbs. The system worked (light bulbs lit) when I connected the panel to the controller to the battery to the inverter. However, when I had the battery power the flywheel and then have the flywheel output its energy to the inverter, the inverter shut down and would not work (red alarm went off). The flywheel is producing more than 10V (starts at about 11V) for at least 30 seconds, and the inverter's low voltage shut down in 10.5 plus or minus 5 volts. So why doesn't it work? Is the inverter messed up or is the flywheel outputing AC power? Also, when I connected the solar panel to the charge controller to the flywheel, the charge controller completely shut off. Are charge controllers not able to be directly linked to motors? And if I tried to directly connect the solar panel (which has 20V) to the flywheel (with a 12V motor), without a charge controller in between, what would happen?

Question by valmic   |  last reply


9V-12V from portable battery to usb hub?

I have a portable battery: http://www.xpalpower.com/us/products/xp18000/ I would like to run the output labeled DC9-12V (or DC16-20V) to a 5v/2.1a usb hub that I have.  I was thinking I could strip down a 12v usbhub car charger, but I wouldn't know how to manage the connector.  Has anyone done anything like this? Thanks

Question by 9zpvwz   |  last reply


Wanted: OpAmp IC's (those with 8 pins and two OpAmps inside)

Hello, Would it be possible for someone to send me some OpAmp IC's (8-pin DIP) with two OpAmps inside? (for free? :) ) They don't have to be power OpAmps, but just regular OpAmps with a Vccmax of at least 20V. I need them for some PWM projects I have. If you are interested or if you want some more information, please send me a PM :) Thanks in advance, Electorials

Topic by DELETED_Electorials 


looking for 200VA transformer with many taps Answered

For awhile, I have worked on a linear power supply design, and I think I have a circuit which is pretty stable with 47uF output capacitance, capable of 100mV to 15V and at least 5A (or more) on a single rail supply, and I can of course also mirror the circuit to generate a negative voltage rail fairly easily. However, to ensure my supply can regulate power efficiently without dissipating too much power (say 50W max TDP) I need a good few voltage tabs, maybe about 5V increments. -20V, -15V, -10V, -5V, 0V, 5V, 10V, 15V, 20V. (unless I do some sort of voodoo with the rectification and inverting voltages, IDK. Ideas?) I added my design for something that generates voltages between -25V and 25V with only 5 tabs, but due to half-wave rectification, I do not think this design will be suitable. Drawing even 5A from the +25V rail causes current spikes reaching 90A and beyond. Of course series parasitic inductance and resistance would greatly reduce that, but I don't like the looks of it. I checked sources like Mouser, and Ebay but it appears that transformers with such a number of taps are uncommon to say the least. Where could I source such a transformer?

Question by -max-   |  last reply


two different voltages in parallel?

I have two solar cells. one has an output of about 15-20v depending on the light. The other has an output of about 30-40v depending on the light. what will happen if I connect then in parallel? will the lower voltage one subtract voltage of the higher voltage one leaving me with about 15v? Will the amperage still double with both cells in parallel?

Question by carrierpilot1357   |  last reply


How do I increase 3A fixed output current of a buck converter?

Basically I am making a solar inverter without any battery or charge controller that will directly convert the dc output coming from solar panels (6 connected in parallel) into 220V AC.I am using solar panels 50W each, having an open circuit voltage of 20V and the voltage varies between 15-20V during the entire day provided a minimum amount of sunlight is there. Next, I am using a 12V buck converter circuit using an LM2576 (here is the datesheet of lm2576)and few more components to get a stable output voltage of 12V out of the panels. Now this 12V DC is fed to an inverter circuit which converts it into a square/modified sine wave 220V AC at approximately 50Hz. But, I am not getting desirable power output. From 6 panels, all I am able to power is a 45W LED bulb along with a small 3W LED bulb. Probably, one problem is with LM2576 buck converter IC. This IC although providing a constant 12V output but it is rated at a 3A fixed output current. And I think probably this is the reason why we are unable to drive more loads. Is there a way to amplify current in this case? Or something else should be done which I am missing here ?

Question by DELETED_MakiY2   |  last reply


ATX Power Supply Conversion

Hi Again, My question is when building an ATX power supply, Can you join the 12 volt leads with the 5 volts leads to make 17 volts? If not how can I get lets say 20 volts. I am going to use a DC to DC converter to make a variable power supply. I would like at least 20V in then I can adjust from 1.2 to 60 volts out. I use it now running directly off battery but would like to add it to the ATX build case. Thanks for any help again.

Topic by Shorty954   |  last reply


Diy BrainPort device

These brainport things look cool. Basically they use your highly-sensitive tounge nerves to feed data into your brain. Totally safe and non-invasive, they can even allow blind people to see, which is, of course, amazing.https://www.youtube.com/watch?v=xNkw28fz9u0I'd like one for fiddling with (eg, monitorless computer? what kind of other data can you feed into your brain? Other stuff??) But since the gizmos are like ten grand apiece... not likely!Then again, its just an array of contacts that deliver 5-20v at low amps so how hard could it be? Thoughts? Links? Circuit ideas?

Question by PS118   |  last reply


How do I build a 24v 8-10amp power supply?

I am trying to "repair" an old massage chair... for every movement (except vibration) it uses different engines rated 24V and 6 to 8 amps, I tested each one with and old notebook PSU (20V 12A) and they works, but they are a little slower/weaker than before because of this 20V instead of 24V. Now I have to choose between 2 ideas: 1) bridge 2 old PSUs like in this guide https://www.instructables.com/id/Two-ATX-PSU-One-juiced-24-V-DC-PSU/ to get 0 > +12 > +24 (that would be extremely good since the vibration engine takes just 12V) but I am not sure about the "theory" of putting PSUs in series and I am concerned about the risks of grandma (main user of the chair) being fried after failures of this configuration. 2) I have scavenged a big (and heavy) 220Vac to 12Vac and 24Vac transformer... but I am not sure how many amps I can get out of it and, with my "useful" backgroud as chemist, this time I have the theory of rectifiers but I miss practice... I don't know what I should exactly look/shop for... (in this case it would be nice to take the 12Vdc from it too but if it gets hard/expensive I can go with a "secondary"  power adapter refurbished from a dead cellphone charger)

Question by Lagash   |  last reply


How do I transform a power supply to other voltage value?

Hi! I need a 9.0 V AC  1.0 A power supply but despite I have a lot of power supplies around, no one has this values. The most I have are 12 V DC I suppose there must be some method to lower or rise the voltage of a power supply to meet the required voltage. Also, the resulting power supply must be AC (I also have a 20V AC power supply if this is easier than converting from DC to AC) Please, tell me what do I have to do.

Topic by jedikalimero   |  last reply


how can i make about 4 phone chargers directly from the solar panel which rates 24v and 20 WATS. Answered

Suppose I have got 4 cellphone of which each charges at 5.0V. and 500Am how can i design a 4x(+& -) branches where I can connect my charging pins? the solar panel produces 24V and 20 watts. Now I know 5.0vx4 is equals 20V means i have sufficient voltage. also voltage out = {(R2x volt(in)} / {R1+R2}.  are there some other formulas that I can use to solve the problem? please help!

Question by Sheen Amon   |  last reply


Laptop Power

Hi all. I have a really old dell laptop(given to me) that is missing a power supply. It requires 20v and 3.5 amps to run. I want to make a digital picture frame out of it. I wont be using the battery or cd player and maybe not even the hard drive(not yet decided). Any idea's on what to use as a power source? I don't need to charge a battery just need power. Could I use an old pcu? I know that I could combine the two 12v lines to get 24 ish volts but won't that fry the old thing? I don't want to buy a replacement power adapter cause it is so old and may not work anyway(plus I wont lie I'm cheap lol). Any suggestions?

Topic by jmiller634   |  last reply


Voltage regulator circuit design

Hi, I'm trying to make a DC - DC voltage converter. The real purpose is to power an old USB hub in a car. This is because so many of my electronics these days use USB to power them and rather than have a nasty mess of car power adapters I want to use a single 12V supply for the hub and then plug all of my goodies into it. Now for the meat of the question..... What is the best circuit design for using a voltage regulator. I have looked at some stuff in data-sheets and it just seems way too simple. The part I'm looking at using is a National Semiconductor LM1085-5.0. Input voltage 6.5 - 20V output 5V max of 3A

Topic by Sailing_Nut   |  last reply


Mosfet Question

Hey guys, I am doing the arduino controlled rgb leds (1 watt leds) project and I am going to use mosfets for the leds. I ordered 3 IRF540 mosfets, 1 for each color of leds (Red, Green, Blue). the arduino is going to use pwm to control the leds but the arduino can only supply 5V at 40mA max. The mosfet have gate-source voltage of +/- 20V and a gate-threshold voltage of 2.0V to 4.0V. Do i need a driver circuit between the arduino and the mosfets and if not is 5V sufficient to run the mosfets in pwm? If i do need a drive circuit, does someone have a schematic since i am inexperienced at electronics? Would i need a heatsinks for the mosfets? thankx for any insight...

Topic by Slisgrinder   |  last reply


USB type C

Greetings, USB type c please? So I have spent alot of time researching different ways to light small ornament designs. I have considered EL lighting and LED, yet, in order for these lighting techniques to work sufficiently, you need 12v of power. There are Instructables to power these lightning methods per USB, however this ofcourse only provides the lightning with 5v. What I find quite surprising however is that there are no tutorials whatsoever with the new usb type: USB-C. Since USB-C can apparently provide 20v I wonder why there is little to no information available concerning these subjects. Are there technical limitations I dont know about? If not: would anyone please help me make usb-c powered led strips ^^

Topic by zeepjes   |  last reply


mA on high intensity LED?

I bought a couple of red "Coast LED Lenser" LEDs from Frys (www.frys.com/product/4137893). They are in the standard 5mm package, but they give no forward voltage and the mA looks a bit high, being without a heatsink . If anyone can tell me if it looks correct and not a misprint, i would be very grateful, since coast doesn't have them on their website anymore. Oh yeah, while trying to light one I ran 8.5V@4.5A (PS2 adapter) accidentally (forgot the resistor) and it exploded loud pop instead of melting or burning out the junction like the 3mm LEDs from ebay, if that helps. The specs.   Intensity :                       10,000 mcd   Directivity:                      15* (degrees)   Operating Lifetime:      Up to 100,000 Hours   Wavelength:                  620nm   IF30:                               mA   IFP:                                 100 mA   VR:                                  5V   PD:                                  120 mW   Topr.:                              -30* to +100* (degrees) I'm guessing the forward voltage would be about 2.00V +/- .20V

Question by LuciferTengu   |  last reply


NPN BJT strange behavior? Answered

My linear power supply design has been using a PNP MJE2955 pass transistor wired to a 2N4401 as a complementary darlington configuration, but this was not an inherently stable design, and would oscillate when adding output smoothing capacitors, particularly MLCC types (with very low ESR). So I decided to try the far more common darlington arrangement, although I am not fond of the higher voltage drop. However the output was oscillating at approximately 3KHz with 1uF output capacitance, with NO input to darlington. I removed the 2N4401 so all I had left was just a 2N3055 transistor with the emitter connected to the output and the collector connected to a 20V supply. The output was ringing like crazy. The oscillation frequency could be changed by adding/removing output capacitance. Why is this happening? How should I go about stopping this oscillation? I originally had a 4.7k resistive load on the output but it did not significantly affect the output oscillation.

Question by -max-   |  last reply


Trying to build a square wave generator (high frequency) and H-bridge

Hi, I was wondering if someone could help me out at building a high frequency variable square wave generator. Specs: 100kHz - 1Mhz (better if I can get up to 3Mhz), 5 to 20V, square wave. Right now I have a LM555 timer. I have read online that I can get it to run at maximum 1Mhz. I don't know what I'm doing wrong, but I can't get it to output at higher frequencies. Also, does anyone know of a good H-bridge circuit schematic that could output 24V pk-pk at 3A. I will be using the signal from the square wave generator to feed to the H-bridge, therefore, is there a H-bridge design that can handle high frequencies? Or, is there another driver circuit that I could use instead of a H-bridge that could do the same job or better?

Topic by sonny301   |  last reply


Does a 12V DC motor output DC current? ?

I am doing a science fair project that involves a solar panel, connected to a charge controller, connected to a 12V battery, connected to a switch system that can either go to a flywheel with a 12V DC motor or straight to a DC to AC inverter which leads to light standard light bulbs. The system worked (light bulbs lit) when I connected the panel to the controller to the battery to the inverter. However, when I had the battery power the flywheel and then have the flywheel output its energy to the inverter, the inverter shut down and would not work (red alarm went off). The flywheel is producing more than 10V (starts at about 11V) for at least 30 seconds, and the inverter's low voltage shut down in 10.5 plus or minus 5 volts. So why doesn't it work? Is the inverter messed up or is the flywheel outputing AC power? Also, when I connected the solar panel to the charge controller to the flywheel, the charge controller completely shut off. Are charge controllers not able to be directly linked to motors? And if I tried to directly connect the solar panel (which has 20V) to the flywheel (with a 12V motor), without a charge controller in between, what would happen?

Question by valmic   |  last reply


Charge unprotected lipoly with desktop power supply? Answered

I have a few, almost dead 700ma li-polies taken from a macbook battery that would not charge. I have no formal Li-Poly charger, and most commercial charger will refuse to charge these batteries anyway- because most of them are lower than 2.7v right now. I wanted to see if I could revive these, which I have read can be done, using constant voltage and current.  My problem is how to charge these using a common desktop power supply. My setup right now is a charger set on 3.7v, multimeter in parallel (to measure the cell voltage), and a current of 20ma. So far, nothing dramatic has happened thus far. Thing is, the "shorted" light on my power supply is on, and the voltage says its around 2.8v right now (rising slowly). Is this just due to the battery charging? I mean, is this behavior normal for an unprotected cell charging on a power supply?  Also, please note that I do know what lipolys can do. I am not just gonna hook this thing up to 20v and leave to go to town. I am monitoring it, and have it in a large, thick plastic box that is 2ft from a door. I will not leave it on unsupervised. 

Question by astroboy907   |  last reply


Why won't a flywheel with a 12V DC motor producing 11V for 30 seconds run through a DC to AC inverter that requires 10V?

I am doing a science fair project that involves a solar panel, connected to a charge controller, connected to a 12V battery, connected to a switch system that can either go to a flywheel with a 12V DC motor or straight to a DC to AC inverter which leads to light standard light bulbs. The system worked (light bulbs lit) when I connected the panel to the controller to the battery to the inverter. However, when I had the battery power the flywheel and then have the flywheel output its energy to the inverter, the inverter shut down and would not work (red alarm went off). The flywheel is producing more than 10V (starts at about 11V) for at least 30 seconds, and the inverter's low voltage shut down in 10.5 plus or minus 5 volts. So why doesn't it work? Is the inverter messed up or is the flywheel outputing AC power? Also, when I connected the solar panel to the charge controller to the flywheel, the charge controller completely shut off. Are charge controllers not able to be directly linked to motors? And if I tried to directly connect the solar panel (which has 20V) to the flywheel (with a 12V motor), without a charge controller in between, what would happen?

Question by valmic   |  last reply


Replace just 1-2 bad li-on cells?

I've got a fairly new DeWalt 20V Lipo Battery pack that got a bit of water inside it's case, causing 1 of the 10 cells inside to go bad. Pertinent info: * Battery pack is configured as 5x2 (5 series stages of two parallel pairs each) * Other cells are in near-new condition. * OEM Factory battery exact matches are rare and quite overpriced.  (1500mah x 15A discharge rate @ $10-20 shipped.) * Due to improvement in battery tech, I can get batteries that outperform OEM in every spec for 30-40% of what the OEM costs (2500mah x 20A discharge rate @ $4-6 shipped.) * The battery pack is always charged on a cell-balancing charger. Assumptions:  (Correct me if I'm wrong here, especially on the 2nd one) * The partner cell to the dead one is now suspect, due to being undercharged (down to <.1V)  by it's dead partner. * I should be able to just replace the bad cell and it's partner with the higher spec'd batteries and it shouldn't be a problem Is this workable, or will having non-identical cells for 2 of the 10 cells cause problems?  (I'm totally fine with the pack only being as strong as the weakest link, and only getting OEM performance out of the replaced cells.) I'd rather not have to replace all 10 cells, but I'd rather do that than replace 2, and -then- have to replace all 10 because the combination didn't work.

Topic by SvdSinner   |  last reply


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   |  last reply


Led downlight transformer converting to a battery charger/power supply?

I know everyone will just say make the Ible and be done with it, but... I got a bunch of 11.5V LED downlight transformers, 35-105W. Upon inspection I realised their design is dirt simple but quite effective. Switchmode for the beginners so to say LOL The pros: Changing the output voltage is as simple as adding or removing windings from the output transformer. In my first test I was able to go up to 20V with no problems by adding a few turns and down to 5V by replacing the secondary with far less but thicker windings - impressive 12A until my windings started to produce smoke LOL Only imple parts, no microcontroller or other complicated stuff like opto couplers... The big con: These transformers are about 20 years old, so I would say first or second generation of LED transformers. That means I have no clue if something very similar or even identical can still be bought in shops or online. And what is the point of an Ible that noone can do because the main ingredient is nowhere to be found? I can take some pics of the circuit board later on for comparison but it would be great if some people with LED downlight transformers could provide some pics too. If it turns out other transformers are still in the same simple design I would like to use all provided for an Instructable. Credits for the pics will be left if you want or simply add your username to the pic as a watermark or such.

Question by Downunder35m   |  last reply


How do you make an annoying buzzer?

I want to do a practical joke at work.  I want to use IR LED'S to make a sender and receiver so that when I push my remote it will activate the buzzer, but when I let off of the button, the buzzer will stop. I am assuming that the sending part would be easy, pretty much a battery, button, and perhaps a resistor (and the LED), but how would I make the receiver so it will set off the buzzer? Thanks! Edit: I just went to radio shack and got this emitter and detector: http://www.radioshack.com/product/index.jsp?productId=2049723 I also bought this buzzer: http://www.radioshack.com/product/index.jsp?productId=2062394 I did a quick hookup (with electrical tape).  I used a momentary switch from an old computer for the emitter.  I know it was working because I used my video camera to detect it.   When I pointed it at the detector/buzzer nothing happened.  I was using about 2 volts, (buzzer votage is 1.5-3VDC).  I just went to the site to look up the detector and it says the phototrasistor detector is 20V at 25 mA.   On the package the max is 70 V.   My question, If I use the following configuration, should it work?  I dont want to try this and blow out  my buzzer before I get an opinion.   Thanks I cant seem to get the pic to upload here, so I put it on my site: http://www.gamesfree4u.com/detectorsch.html EDIT: 12/30/09 Well, I bought a breadboard and tried to wire it up.  Not a lot of room on those things.   I used 3 9volt batteries for the receiver.  According to the site, they use from 20 to 70 volts, unless im reading something wrong.  I didnt use any resistors, which I should have.   As soon as I hooked up the power the diode burned up. lol.   Oh well, lesson learned = $1.00.  I'll have to give this  more thought.

Topic by pennsteve   |  last reply


I'm trying to build a welder from microwave transformers, but I got this weird looking transformers instead.

I recently got two old microwaves from a junk yard and wanted to build an arc welder with its transformers by connecting both in series and getting an output of around 40V all together. But when I open the microwave instead finding the big chunky laminated iron core transformer as shown by many youtube videos, i found a small weird looking transformers instead. ( as shown in the pictures) I read somewhere stating that the primary coil should at least have 1 turn per volt. However, this transformer only had around 17 turns in the primary. The core was also not laminated and it had a copper wire holding it in place. The primary coil was made of a thick litz wire and the secondary was a very thin wire. Anyhow, I still continued the project and I experimented with one first. I use the same primary and made my own copper wire for the secondary. I made the secondary by using thick copper wire which I found in some antenna wire and I stacked it up and twisted it and put a heat shrink tube on it. Base on a few tutorials i saw i need an output of 20V from each transformer coming from an input of 240V AC. So with 17 turns in the primary i need around 1.5 turns in the secondary. When i finished everything and connected it to the power supply, it vibrated for awhile and then blew the 13A fuse in the plug. So i added a light bulb in series hoping to increase the resistance and reduce the current but this time nothing happen and it didn't even vibrate but the bulb did light up. I think its because the primary coil has a resistance around 5 ohm and the bulb have resistance of 100 ohm so the potential differences is very low on the primary coil. I am not sure why isn't it working. Please help me as i can't find any tutorials on how to make a welder with this form of transformer. There were no other transformer in the microwave so this was definitely the main transformer. Is the problem because it has too little turns in the primary coil or it has too low resistance? I don't know please help me. Thank you!!

Question by KhayhenS   |  last reply


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-   |  last reply


Making a better spot welder....

I am in the process of building a proper spot welder from scratch. Proper more in terms of the electrical and electronics part but not so much in looks ;) My problem now is to find useful info on what power levels are required for certain tasks. I realise that welding thin sheet metal won't need as much time and amps as welding a 3mm stainless steel rod - but what is a "good" power level? I watched a bunch of Youtube videos showing various approaches but for many it seems the producer had no clue about the difference between creating a short with burn marks and a weld... Especially when it comes to creating battery packs with a capacitor bank as the main power provider you can clearly see the device burns holes but does not really create a welded spot. On the other hand there are a few videos showing spot welder made from a MOT that seem to produce a proper melted and welded connection. When I used a proper spot welder at work it had timing settings, power levels and even a feature to adjust how the current rises.... Not to mention a gauge that checks the pressure and only activates the welder once the set point is reached... There is a ton of info out there that after a thausand words still tells you nothing you need to know :( So is there anyone here who can shed some light on the actual process of spot welding in easy words for everyone to follow? I am aiming for a max output of around 400A @ 1.5 -2.5V with an adjustable shunt in the transformer core to avoid oversaturating the core. In a later stage I will add power control over the primary side but until then it is only time control, from a few ms to a max of 5sec if the damn controller arrives one day. Big questions: 1. Is a power control really required or is it possible to cater from thin to thick just by using different timing settings? 2. Since a MOT is used for the power supply: Is it better to leave the shunts out to fully avoid saturation by adding an inductor in line with the primary or is it still better to adjust the shunts under load to get the maximum power possible? 3. Aluminium and other materials benefit from using AC but would be good to have a DC output too, if so then what materials really need DC? 4. All I could find is that copper is used for the electrodes, due to resistance and heat transfer - are there other options apart from using copper? 5. Tricky one: I would prefer to use the secondary winding as the new primary to avoid core saturation and to lower the load on the power outlet. Where can I find very thin copper bar material that I can coil up and insulate as I would quite a few more turns to get at least 1.5V out of it? Just don't like the idea of spending days rolling a copper bar thin enough.... For the advanced model at a much later stage: Of course I would like to be able to use a proper power control instead of a motor dimmer or similar. For obvious reasons an inverter microwave jumps to mind. But after checking one I noticed one big problem: there are not really that many windings on the primary of the transformer at all! Same way our modern switchmode power supplies only use a few turns these things do exactly the same. After some quick and dirty initial tests I realised that even a single turn of thick wire already results in over 20V on the secondary. Wasted a lot of wire and time making one coil with 5 turns less and one with 10 turns less but the system would not even start with it. Seems these things need a fixed inductivity on the primary that matches the frequency used, in my case 36kHz. Would love to overcome this problem so I can at least go down to a single turn to get under 5V on the output side as space is non existing on these inverters. Can I cheat? Do I need to change the circuit to match the new primary coil? Am I thinking in the wrong direction altogether here? And added bonus would be to be able to adjust the power from around 15% to 100%, so far the electronics don't allow anything below 45%. Is it possible to drive these inverters in resonance? (Ok, off topic as I would like to use this for a beefy HV supply) Last thoughts: I know people already used Arduinos and Raspberries with displays and all but so far I have not found anything that shows how to do it properly. Seems all that counts is to create connection one way or the other and to call it a spot weld even if it is just a burn hole from discharging a capacitor bank through a needle like electrode.... For obvious reasons I don't want to create just another spot welder that makes a professional pee himself laughing about it. IMHO nothing beats personal experience with something but I don't really like wasting my time by trying what other people alread did a long time ago. So if YOU already built a MOT based spot welder and used for more than a few spots I would love to hear from you! Let me know what type you used, what problems or shortcomings you noticed or where you feel it just does not work out the way you expected it. From simple things like always getting bad sparks or arcing, over how easy or hard it is to get consistand results to whatever really annoys you while using your homemade spot welder. I hope that your feedback here will help me to write an Instructable on building a spot welder that does what you expect it to do, not once or twice, but everytime you use it. Mechanics might vary the same way the electrode style does but the weld should always be a proper weld that won't tear apart ;)

Topic by Downunder35m