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Topics - kamelryttarn

Pages: [1] 2
1
Electronic Circuits / DIY SMAW welder (stick welding)
« on: January 23, 2020, 08:32:56 AM »
I sometimes have a need to weld stuff and I always have to turn to people for help since I don't have the knowledge/skill or equipment for it. The latter can be remedied by getting a welder and what better way than to build one, right  ;D

What I have that may or may not be useful

* A large DC power supply capable of 150A continous @ ~45VDC
* Some film capacitors taken from different welders
* A couple of BIG stud diodes (I think they are rated at 300A)
* Two HUGE chokes, one at 25mH @ 50A and one at 35mH at 50A. They are built on what I believe to be silicon steel sheets so maybe not suitable for high frequency.
* A lot of IXYS IXFN520N075T2 mosfet trench gate modules rated at 480A each

From what I understand a stick welder works best with a constant current power supply so I was thinking that I could build some kind of low frequency PWM controlled constant current curcuit and attach it to my big power supply. Can this be done in a crude manner with the parts I have together with some kind of simple microcontroller to monitor the current and adjust the PWM duty cycle?

2
Transformer (Iron Core) / Possible use for large inductor (laminated core)
« on: December 09, 2019, 09:43:11 AM »
I scored two huuge (and heavy - probably around 100kg each) inductors probably made from a regular laminated core. One has a hand written label that says 35mH and the other has a label from manufacturer that says 25mH 50A.

These were bought on an auction so I did not have any chance to inspect before I bought them and since they were in a lot with a couple of 10kVA three phase transformers I had hoped/assumed at least one of them was a three phase choke of some kind but that was not the case.

Can these be used for something fun? Are they only usable in DC applications or can they be used for 50Hz AC as well?

3
Electronic Circuits / Driving Nixie-tubes with arduino
« on: December 03, 2019, 09:04:42 AM »
There are many circuits out there using arduino and some extra components to drive nixie tubes but I am trying to figure out a cheap way that don't take up too much space so I would like to use ULN2003 if possible.

When looking at the IN12 Nixie tube drive voltage seem to be around 145V DC and recommended current is 2,5-3,5mA. Do these thing behave like a resistor? Can I assume each digit is like a ~48k resistor? If so I should be able to use a bussed resistor array with 7 pcs of 22k resistor to make sure the ULN2003 is never exposed to more than ~45V (50v is ABSOLUTE MAX according to the data sheet).

Assuming that the internal DC resistance of each digit is never LOWER than ~48k I should be safe right?

The other potential problem is the current when the digit is NOT lit. There will still be close to 2mA running through each digit. Will they be dark or will the probably be dimly lit?

4
First off I would like to ask you to refrain from suggesting non Hantek oscilloscopes.

I am looking for a 4ch USB connected oscilloscope. I bought the Hantek 1008 a couple of years ago and I like but it has very limited bandwidth at only 100kHz. When fiddling around with the royer induction heater I realized I couldn't view the mosfet gate signals with much detail so I need higher bandwidth.

The problem is that I don't really know what bandwidth I need and what the difference between bandwidth and bandwidth limit is. Hantek has a couple of promising candidates but the Hantek6204EU for example has 200MHz bandwidth but 20MHz bandwidth limit. What does this mean?

I would like to be able to see the ringing on the mosfets gate to help me pick the best gate resistor so I guess that if my switching frequency is let's say 40kHz the ringing has an even higher frequency.

Is perhaps 100MHz enough for most of what I need it for or should I go even higher than 200MHz?

5
Sell / Buy / Trade / eBay tip for induction capacitor
« on: August 26, 2019, 10:58:31 AM »
Just found these. I am extremely interested in buying one myself but I just have too many other projects at the moment

https://www.ebay.com/itm/Induction-Heating-Capacitor/153605789972

6
Electronic Circuits / Ultrasonic transducers for cleaning
« on: July 03, 2019, 04:04:53 PM »
I thought it would be interesting to build my own ultrasonic cleaner using transducers available from ebay but does anyone know the best way to mount them to the stainless tank? I know most people glue them but is it possible to attach them with a screw instead? And what is that little screw thingy you can see in some pictures?

https://www.ebay.com/itm/1pc-New-120W-28KHz-Ultrasonic-Piezoelectric-Cleaning-Transducer-Cleaner/232776275029

[edit] found more than I bargained for here: http://www.ultrasonic-resonators.org/design/transducers/transducer_design.html

7
Electronic Circuits / Choke-input DC-filter
« on: June 20, 2019, 11:43:58 AM »
The other day I received an arduino shield for my motorcycle tachometer project. It will be used to convert the ~12V system to 5V and also provide a little backup power.

Since there is a fair amount of noise on the electrical system I figured it would be a good idea to add some kind of filter on top of the filtration the shield will provide for me so I bought a DC choke of 320mH rated for 600mA with a specified DC resistance of 7.8 Ohm. My goal is to remove some of the worst spikes and dips but do I NEED a capacitor as well and should I place it before or after the choke? I know a capacitor will make the filter circuit perform BETTER but what I would like to know is if I MUST place a capacitor just before or after or if it's just good practice. Can a choke WITHOUT a capacitor even make things worse and possibly break certain components?

My initial plan is to use my oscilloscope and measure before and after the choke to see what kind of difference it makes but if just a single choke can actually make things worse and damage my shield I do not want to do that before I have checked with people who has a better understanding about this than I do. All information I can find about chokes refers to using the after a rectifier bridge @ 50/60Hz

8
A while ago I bought a motorcycle and even though there is not need for it, I thought I would make a small arduino-based "computer" for it to monitor different parameters and one thing that would be neat to have is tachometer to see the current rpm. My plan was to use the ignition pulse before the ignition coil. I took my Hantek 1008 oscilloscope and hooked it up and was very pleased with how the signal looked.  It was way cleaner than I had first thought it would be.

Some time later when I had a plan of how to construct it and also an embryo of arduino code for it I connected everything and things did not work as expected so I hooked up my oscilloscope again and this time things looked a lot different. Even though screenshots suggest the time base is the same it was not. The first time I had the software set too 500ms but then I zoomed in and since the actual bandwidth of the 1008 isn't very good I fooled myself a little bit when I looked at the pictures.

I now realize I need the clean up the signal before I send it to my optocoupler and my question is: What is the best way to filter out the noise/ringing without sacrificing too much of the part of the signal I need?

My idea was to basically construct a "speaker crossover" consisting of two capacitors and an inductor in between creating a third order CLC-filter. The two main components to filter out is the ~2kHz ringing when the coil discharges and a much larger in amplitude ringing or possibly "bounce" happening when the coil is charged and that one looks to be close to 17kHz according to my readings.

9
Beginners / Resistor tolerance?
« on: February 10, 2019, 05:46:39 PM »
I would like to user fixed resistors as calibration for a couple of Pt100 and Pt1000-to-4-20mA current loop converters and I was wondering if a fixed resistor (metal film or wire wound) with extremely low temperature coefficient changes value or if it can be considered stable?

For example, if I order a 0.1% resistor specified as 100 Ohm, the actual resistance may vary between 99,9 and 100,1 which isn't much but when translated to degrees Celsius it's roughly -0,2 to +0,2.

My question is: Apart from temperature drift, will a fixed resistor shift in resistance value or can I use a low ppm fixed resistor of any value and type and attach a small note to each stating the corresponding temperature once I have been able to accurately determine that?

10
Vacuum Tube Tesla Coils (VTTC) / Usable vacuum tube?
« on: November 06, 2018, 12:56:44 PM »
I think I have a 5867 tube with the necessary transformers (heater and HV) and was wondering if it's possible to use it for a VTTC. I found a schematic that use a pair of 811 tubes but I am unsure if it's possible to use a single triode. Any thoughts?

11
I found a small, embedded machine that I wanted to turn in to a small firewall. It's an x86-based industrial computer with 3xNIC and a 9 pin D-sub connector for console access. The OS  and applications are stored on a CF card and with the software I intend to use I needed to get the serial access going so I could make the initial configuration but no matter what baud rate I tried I could not get it to work. 1200 baud was the "best" but still only gibberish so I had to figure out a way to examine the signaling on the serial port and determine the actual baud rate from that. I found some web sites that explained how an oscilloscope could be used so I tried it. It worked OK but I wanted to get more data and also the signal so I connected the transmit pin to an optocoupler (through a constant current limiting device) and fed the signal to my logic analyzer. At first I tried the "auto baud rate function" and a lot of different settings but then I looked at the signals and looked for the "shortest time" or "highest frequency" which was 680Hz. Half of that time equals 1360 which is the baud rate that was used. After I figured that out I could decipher the information sent on the serial port and start configuring my device.

I thought this information could be useful to others.

12
Electronic Circuits / Wheatstone bridge and ADC reference voltage
« on: July 06, 2018, 09:56:20 AM »
I want to build a kind of digital scale to measure small weight differences and I was wondering why you seldom see circuits where the excitation supply (usually around 10V) isn't fed to the ADC's reference input via a suitable voltage divider? Since the wheatstone bridge is ratiometric, wouldn't this cancel almost all noise on the supply voltage leaving the digital value much more "clean" and accurate?

13
Beginners / Chokes and inductors?
« on: May 28, 2018, 01:57:07 PM »
I have a fairly good grasp of many components but inductors baffle me.

I try to read up on common mode and differential chokes, DC filter inductors and all kinds of different configurations but I don't understand the fundemental basics of them.

I re-used the HUGE inductor/choke (which is it?) from the welder I modified to a power supply. I connected it between the rectifier and my capacitor bank assuming that it would help smoothing out the ripple in a LC filter configuration. Another thing I believe it helps with is some kind of "soft start" since the DC resistance of the winding should charge the capacitors a little more gentle or am I completely wrong?

I may have a need for a three phase filter of some kind for "analog" SSR that controls a resistive heater load. I have looked at three phase filter chokes which are basically a toroid core with 3 separate windings, one after another, and also three phase inductors that seem to be much large and probably insanely expensive.

What kind of interference can I expect from the proportional triggered SSR and what type of filter components should I try to find or make to reduce the noise on the grid? Am I right in assuming that the frequency of the noise is never higher than the driving frequency? A lot of components seem to be manufactured to filter out noise from SMPS but I need to filter mains frequency (50Hz).


14
Electronic Circuits / Low/Medum frequency royer induction heater
« on: April 30, 2018, 12:49:26 PM »
I modified an ebay induction heater this weekend in order to try and heat up a small brass pipe. I tried to search the web for information about what frequency to use but I couldn't find much info so I tried a few different capacitor banks to see if I could measure the difference and take it from there.

Firstly I made a new work coil by winding a enameled wire about 1mm in diameter around a glass tube. With the default cap bank of 2uF I got about 70kHz without anything in the work coil and about 80kHz when I had the brass pipe inside it.

I used a lead acid car battery that was charged to around 13V for all tests. "Idle current" was 3,3A and "working current" was 11A so I assume the power transferred to the work piece is roughly 100W. This is probably not very accurate but all I wanted to do was figure out I should aim for a high or low frequency.

Next I soldered an additional 6pcs of capacitors to that backside of the PCB doubling the capacitance. When I fired it up I got 48kHz instead at idle and 60kHz with the brass pipe inside the work coil. Currents were 5A at idle and 19A when "working" so I think that brass responds better at lower frequencies.

The final test was made with a 30uF capacitor salvaged from the welder I bought to get my large three phase transformer. Unfortunately I did not get any current measurements but unloaded work coil gave me 19kHz . When I inserted the brass pipe and fired it up it quickly broke down and one of the mosfets started smoking.

The 30uF is probably not going to survive very long under these conditions but it was fun to give it a try. I will try and replace the mosfets and other components and do some more testing.

15
Electronic Circuits / Closed loop control of DC motor
« on: February 28, 2018, 09:41:26 AM »
A while ago I started a build of a simple (or so I thought) magnetic stir plate. I ordered a cheap motor on ebay and a friend helped me to 3d-print a holder for the neodymium magnets. I use and arduino with a mosfet to get speed control by PWM.

The problem was that the magnets locked on to the screws I used to mount the motor in the plastic case so it took quite a bit of force to get it to start so I thought I could use a closed loop to control the speed of the motor. I bought a new motor with a built in magnetic encoder that sends pulses when the motor spins. I wrote a small program for my arduino and connected the pulse output from the motor to one of the hardware interrupt pins. When I tried it I got very erratic behavior that I believe may be caused by the inertia of the rotating axel . Would you agree and do you have any good ideas what I can do to remedy the problem?

To understand the pictures better I will try to explain the code I used. Every time I got a change (either rising or falling edge) from the encoder, the mosfet channel is turned off and the arduino resumes the regular loop that has a pause time (to regulate speed) and the turns the mosfet on again. In the pictures channel 0 is the encoder on the motor and channel 1 is the mosfet driver. The last screenshot is from a test I did where i let the motor spin for a few seconds and the turned the mosfet off to see how long after the power was cut to the motor it still turned.

16
Electronic Circuits / Current transformers and burden resistors
« on: January 17, 2018, 01:37:10 PM »
I have a need for limiting a large three phase AC load (electric boiler with 7 heating elements of 6kW each) and I was thinking about using three current transformers and an Arduino. Since the transformers give AC on the secondary I need to make some kind of signal conditioning before I connect to the Arduino's A/D inputs.

I have made some tests with a small CT, a schottky bridge rectifier and a burden resistor on the DC side of the rectifier (a tip I found here: https://electronics.stackexchange.com/questions/281048/current-transformer-and-bridge-rectifier-why-the-diode-drop ) and it seem to work very well for what I am trying to achieve. In my application I need to send a signal (logic level) if the measured current goes above a certain level and precision and linearity are not crucial.

But what about the burden resistor? I have found some information that seem to indicate that you can't just calculate a value that gives you a reasonable voltage drop at a certain current, but why is that? In my case  I would like to measure up to about 80A. That is roughly 113A peak. If I have a transformer with a ratio of 800:1 that would translate to 141mA and if disregard the drop over the schottky rectifier and I require about 1.1V at the A/D input pin that would mean I had to get a 8 Ohm resistor. What will happen if I use a burden resistor that is way different from the recommended value specified in the data sheet of the CT?

17
Electronic Circuits / Capacitor for tiny solar charger
« on: October 20, 2017, 01:18:26 PM »
I am setting up a very small off-the-grid installation with a 5W solar panel and a PWM charger

http://www.epsolarpv.com/en/index.php/Product/pro_content/id/773/am_id/136

Since my panel is VERY small I thought I would install a small film capacitor between the panel and the charger, but how should I think when choosing the correct capacitor? I know I want a MKP film cap, but do I need to measure the frequency of the charger before I can properly decide on capacitance value? I guess I want something like 2-5uF.

18
Transformer (Iron Core) / Contant Voltage Transformer
« on: July 13, 2017, 03:55:26 PM »
I have had a 500VA (I could be wrong and it may be a 300VA) constant voltage transformer for a couple of years but never really had any use for it. When I connected it the other day and hooked up a computer (SMPS) and a 40 inch LCD TV (also SMPS) to it the picture flickered as soon as the computer started working. I don't think a healthy CVT should act this way so I suspect the capacitor may be ready for retirement. The heat generated by these things could probably limit the life expectancy of the capacitor, but what kind of capacitor would most likely be optimal? I think motor run caps would probably be a good bet but do you guys have any other recommendations?

http://www.aelgroup.co.uk/faq/faq001.php

My unit is an old 70's or 80's unit labelled Ulweco but was actually produced in France.

19
Printed Circuit Board / Arduino IO-shield
« on: April 25, 2017, 07:41:52 PM »
This will probably we a very long thread. I had originally planned to make an Instructables presentation for this board but realized I will never do that so instead I thought I'd just share it with you.

I have been tinkering with the arduino for a few years but every time I get an idea I would like to try I felt that I always had to start all over again from square one so I decided I would make some kind of labb shield that contained most of the stuff I needed to get started right away. I will try to divide the board into different sections and explain what each section does and why I chose to make it the way I did.

The board itself is made from the cheapest expresspcb-board available, the so called https://www.expresspcb.com/miniboard-standard/ and I tried to squeeze in as much as I could, taking advantage of the double sided manufacturing capabilities. The bottom side of the board is basically just a huge ground plane.

Apart from the pin headers for the arduino there is also room for screw terminals in case you would like to make better connection to something else externally.

The silk screen is not intended to be used and I used the top copper layer instead to print text to the board, but one should desire a more professional look, using the silk screen layer it is easy to move the text to that layer instead.

20
Electronic Circuits / Chinese Ebay Royer induction heater tests
« on: April 16, 2017, 04:37:37 PM »
I received two similar ebay induction heaters a few weeks back that I will use for further tests and measurements before I put my own together. You can see from the pictures that they look alike but there are some small differences. The one on the left uses a much larger area of the pcb to conduct the power, whereas the one on the right relies on extra solder instead. I think the left will perform the best.

I also attached a small picture of the zener diodes I will be using on my own IH. It's a Russian 8W 15V zener diode. I will do some experiments as soon as I have my power supply up and runnig.

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