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Messages - kamelryttarn

Pages: [1] 2 3 ... 6
1
Electronic Circuits / Re: DIY SMAW welder (stick welding)
« on: January 24, 2020, 10:11:51 AM »
I have thought a lot about what you have written and I think I begin to understand.. A very low frequency circuit probably wont work well and my chokes are, as we both say, suitable for ~50Hz up to perhaps a few hundred Hertz. However they are rated for continuous use at around 50A so as far as welding current is concerned I think they will work well.

Would it be feasible to use linear regulation instead with a ton of NPN-transistors? I realize I need to cool of a ridiculous amount of heat loss in the transistors but I don't regard that as a problem... yet... ;)

2
Electronic Circuits / Re: DIY SMAW welder (stick welding)
« on: January 23, 2020, 01:29:01 PM »
Larger inductance also means lower ripple current at the expense of more loss, more money and slower response due to the LC output filter formed by both.

I believe I have enough "juice" to put in to compensate for the losses. And you are correct about the cost but since I have two VERY big chokes just laying around in the workshop I thought I might as well put to good use.

3
Electronic Circuits / Re: DIY SMAW welder (stick welding)
« on: January 23, 2020, 11:38:18 AM »
I have thought about replacing the choke in my power supply which is the original ESAB choke that I have measured to about 1,8mH with the 25mH and perhaps use the smaller one to the actual welder. I think that will give less transients back to the mosfet modules.

I thought a lot about the current sensing yesterday and although I have a few shunts from the welders I have scrapped I feel that ~50mV is too low voltage. I would like closer to 2,5-3V @100A but the heat losses would be a pain. Then I thought about using copper brake lines (the same I use for the induction heater) and circulate water through it :) I haven't figured out a suitable dimension and length yet though.

Since the chokes I have available are not suitable for HF my plan was to use 50-400Hz PWM frequency.

When it comes to caps I could perhaps use one or more of the film caps I bought for my power supply but I really like them where they are. Wouldn't the required capacitance be dependent a lot on switching frequency? Higher frequency cold perhaps get away with fairly low capacitance?

4
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?

5
I took the lid of the smaller one of the chokes and took a couple of pictures yesterday. Is it two "halves" connected in parallell to increase the current rating?

I also started to look into the three phase transformers. I think they can be used as is connected in "Wye" configuration with 230V AC between Live and Neutral. It would be a shame to scrap these for the copper so I would like to find a way to use them instead.

6
Thank you all for great input. I will try and take some pictures of the internals and post in a couple of days.

7
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?

8
Electronic Circuits / Re: Driving Nixie-tubes with arduino
« on: December 03, 2019, 02:14:00 PM »
Perhaps SN75468 with its 100V rating would work instead? A transistor array instead of using discrete transistors would save space and make it much easier to connect.

9
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?

10
It's probably better to hit it slowly (gate rising over 100s us?) in case there's a lot of inrush current.

Better still to put in a current measurement circuit and control the gate accordingly, but that's maybe not so big a priority with well behaved power supplies.

Tim

You are probably right but I don't have the "know how" to adjust switching time and to measure current at the speed probably necessary.

To better explain the intended use for the IXYS module I will use it between my power supply and the induction circuit. Mosfets inside the IH are NOT IXYS modules!

My power supply (as showed in another forum thread) is a 6kVA three phase transformer connected to 3+3 45L10/45LR10 rectifier diodes rated at 150A. After that I have a large choke from the ESAB welder the transformer came from and after that 5 pcs C4DEFPQ6380A8TK capacitors. The plan is to connect the IXYS module as close as possible to the ground rail of the capacitor bank of the power supply.

The water blocks are for the mosfets in the induction heater since these get quite hot and I will most likely water cool the gate resistors and the tank capacitors.

The main reason I need a robust switch to turn it on and a power supply that can supply a stupid amount of current instantly is that I must start it with the object intended to be heated already inside the work coil.

11
Nah, fast turnon. Let the power supply bleed :)

I think you want to raise voltage so fast before oscillator starts operating and it might show any kinds of unstable behaviour.

My power supply almost scares me a little. The three phase 6kVA transformer is massive and the five parallel Kemet C4DEFPQ6380A8TK film-capacitors can supply an insane amount of peak current and I suspect that an unintentional short circuit would result in all sorts of smoke, flash and fire. My power supply is definitely NOT the weakst point of my setup.

I haven't done any work on my induction heater for about a year :( I bought some water cooling blocks for the mosfets but I haven't got around to putting it all together yet.

12
@kamelryttaren- for a induction heater I would definiately look into the large gate capacitance on that. Those are probably best for a 12/24V switching converter.
But for a power supply on/off modulation to the converter it should work even if 75Vds is quite close to 50ish volts.

I don't fully understand what you mean. I haven't paid too much attention to the gate capacitance yet but my power supply is close to 50V so I believe I am safe in regards to the Drain to Source maximum voltage. The gate signal will most likely be handled by a proper mosfet gate driver like MCP1407. The IXFN520N075T2 would be used to turn the induction heater on and off. I have other mosfets in the induction heater circuit. From my previous measurements I feel like time it takes for the trench fet IXYS mosfet module to fully conduct is probably shorter than the time it takes for the induction heater to start oscillating so I think that losses in the mosfet module will be reasonable.

When it comes to the power supply I am confident mine can supply 150A without sagging.

[sidenote] What is the "Kelvin Source ( Gate Return ) Terminal" mentioned in the picture?

13
Beginners / Re: Chokes and inductors?
« on: October 04, 2019, 11:10:42 AM »
A capacitor is a current source and a inductor is a voltage source.
Sorry that's backwards.
And inductor behaves like a current source, a capacitor behaves like a voltage source.

Thank you, that actually makes sense. I think the subject isn't trivial and it takes a bit of experience and patience to get a fairly good understanding of it.

14
When it comes to switching on and off I plan to try IXYS IXFN520N075T2 since I have a few of them I got a year or so ago. Any thoughts on using this kind of power mosfet module?

15
Wow thank you both for excellent information!

Yes the 20MHz limit seem to be a switchable feature and I did find some information about it in on of Hanteks user manuals. One of the reason I think I prefer a USB oscilloscope as opposed to a bench model is the compactness. I can bring it with me practically anywhere and connect it to almost any computer I can install the software on.

Absolute accuracy is not extremely important. I need to get a good visual representation of the wave form so I can decide if a change in component value make things better or worse. The specs of the Hantek models is different depending on where on their site you look which makes it hard to compare the different models.

It is a bit outside my price range but their DSO3204 looks promising. However the series comparison specifies the rise time of the 200MHz model at 1,7ns but on the product page it says 3,8ns.

http://www.hantek.com/en/ProductDetail_2_134.html
http://www.hantek.com/en/productdetail_144.html

I like the possibility to have an external trigger and still have 4 usable channels. The network feature could also possibly useful to me.

Is the input capacitance of 25pF considered high and might that be a limiting factor? I tend to use regular RG58 cables and solder them in at my measuring points and I think that could add a lot of capacitance as well. I know it's not optimal but a good scope AND proper probes cost a ton of money so I am aiming for "good enough" but still want a fairly good scope. My dirt cheap 8 channel Hantek has helped me out a lot and I like it but as I said, 100kHz bandwidth is VERY limiting when dealing with frequencies above mains or audio. The fact that it's DC bias only also presents a challenge a lot of times.

EMC immunity is one thing to consider but the another is ground loops. I use a small "galvanic separator" with a built in DC-DC-converter but it has a connector for 5V-power so I could use battery or an external DC-supply of my choice. The built in works well with my Hantek1008B but perhaps I will not be able to power a higher end USB oscilloscope.

16
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?

17
Capacitor Banks / Re: Can crusher attachment
« on: August 29, 2019, 08:03:50 AM »
WoW! Beautiful workmanship! What kind of capacitor bank do you use?

18
The signal is quite good with this setup. Here is a pic of the signal at the optocoupler. As you can see there is no need for more filtration so I am happy with the setup. I was just surprised with the big difference between the two different types and sizes of inductors. I still don't fully understand what they do and how they work so it is very educational for me to try different components and analyze the different results and try to learn from it. Hopefully the results can also help others.

19
Long overdue update to this project. I have been experimenting with a series choke on the ignition pulse and things are looking really good. I also realized that the reason the signal looked so clear at first was that I hit the "roof" of my oscilloscope input voltage. When I hooked everything up with a 20:1 passive attenuator I realized the voltage was actually ~400V which explains my shot optocoupler and constant current driver I was using.

Having realized this I started looking for ways to dampen the ringing and get voltage levels way down. The only thing I had to try at first was a Hammond choke bought for another project. It is specd at 330mH and when I hooked it up with a 680 Ohm resistor to ground I got REALLY nice pulses but the fall time looked a bit too filtered and it is a very bulky choke so I bought a couple of axial ones, one 100mH and one 330uH and tried them out yesterday. They do the trick but I was surprised at how big difference it was between the Hammond one that looks like small transformer and the axial 100mH. The inductance value is about one third but the signal show much more ringing than the big iron core choke. Could this be due to the difference of core material?

The axial one is a Vishay IHD3EB104L

The pic 100mh inductor.gif  shows about 400V but this is due to a software bug and the actual voltage is about 40V

20
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

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