Mosfet Induction Heater for silver-brazing...

Thread Starter

PackratKing

Joined Jul 13, 2008
843
heater 1.jpg PCB 1.jpg Amateur jumping off the deep end here...

I am attempting to build a small induction heater, to braze carbide inserts onto standard lathe tools... [ I totally suck at torch-brazing...] It took a lot of looking, but I finally found a circuit I can work with...

Since it will be one of a kind for now, I etched the PCB... the hard way...
My resist-pen had dried up, and received an infusion of denatured alcohol to hopefully wake it up... so in the meantime...

I laid out the circuit traces in red magic marker, and then clear package tape over it, and rolled it down good and tight... then carved some relief around the pattern... so there are large areas of copper left, ... it actually worked !!! as it stands in this edition, I haven't removed the tape yet

The circuit uses a IRS2155[1]D to drive the IRF540 mosfets... so I'm hoping the whole thing will fly... I shall update as time goes on...
 
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MaxHeadRoom

Joined Jul 18, 2013
19,033
What is the anticipated power level of that circuit, It seems a little on the low side for what I would expect needed for silver soldering solid steel.
You will also need to match the frequency to the tank circuit.
Max.
 

Thread Starter

PackratKing

Joined Jul 13, 2008
843
At a wee bit of a disadvantage here... No LCR meter to measure inductors... I will ahve to set up the 33K / .001 as I understand that sets up the frequency the mosfet gate driver runs on... and the resonance of the circuits makes a great difference in the performance of the working coil... still learning...

I have an 40 MHz Dual Trace O'scope to measure the driver freq., so will have to wing it a little to match the tank circuit.
IF this thing will get a 3/8 " or 1/2 " square HSS tool hot enough to braze a carbide on... I will be happier than a kid in a candy store with a found quarter.
 

MaxHeadRoom

Joined Jul 18, 2013
19,033
Usually the power required for that application also needs water cooling.
The resonant frequency can be calculated if the tank components are accurate. I work that to 220Khz.
The tank capacitor has to also be the right composition, WIMA MKP4 for e.g.
Max.
 

Thread Starter

PackratKing

Joined Jul 13, 2008
843
My tank cap, is slated to be a rolled polyester film, very close to the nano, but 600 volt... I'm really winging it for the inductor... it is a random ferrite 1" toroid cross section approx 3/8 " wound with 24 turns #18 teflon insulated stranded wire
The working coil is 1/4 " copper tubing, 1" ID, 6 turns, fitted for siphoned water cooling until I can contrive a pump setup
 

shortbus

Joined Sep 30, 2009
6,979
[ I totally suck at torch-brazing...]
.
If you get the correct silver solder there is nothing to it. Lathe tool bits are not done with a wire type of silver solder. They are done with sheet silver solder. Cut the sheet to the shape of the insert, put flux on both the insert and the shank pocket and the sheet solder between the shank pocket and the insert. Then heat with the torch until cherry red, then let cool in still air.

But with the low price of soldered insert bits, unless you are getting all your supplies for free, you can't make them for the price they charge for factory made.
 

Thread Starter

PackratKing

Joined Jul 13, 2008
843
I am going for some custom configs, that one cannot get from the likes of harbor fright... and to get them from a machine supply company, ain't much better... Anyway it's all more fun !!

Dang thing is going on the back burner for a bit... seems none of my collection of mosfets were any good...........
 
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