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21
Project Logs / Re: Induction heater project
« Last post by eskoilola on Today at 03:35:08 AM »
Here is my interpretation of an induction heater.




This device needs two separate power supplies. First, the high power supply delivering juice to the heater coil through the driver. The other power supply is for all other functionality like control logic, water pump and fans. The high power supply can be switched on/off by the control logic whereas the auxiliary power supply has a real user operated switch.

The high power supply needs a soft start circuit which consists of two relays and a resistor. This is because the transformer I have is a toroid transformer and that devil will blow the fuse every other time if cold connected to mains. The high power supply will be switched on only when needed.

The rectifier and smoothing is just a couple of full bridge rectifiers connected in parallel using resistors (0.1 ohm). I have a box full of 10 amp rectifiers and if I connect 10 of these in parallel that should be more than enough for this application. The smoothing consistsa of 2 capacitors size of a Chevrolet piston each worth of 100.000uF.

Voltage sensor in just a resistor divider. The current sensor I probably make out of a hall sensor glued on top of a wire. If the sensitivity is not enough just cut a gap in a ferrite toroid and stuck the hall sensor in there. The wire then goes through the toroid hole. These sensors are used to cut off the driver in case the voltage is too low or the current is too high.

The FET array switch is a bunch of FETs connected in parallel. I have another box full of 30A/150V fets. Having 10 of these in paralle should do it. With FETs there must be quite a lot of margin as the FET resistance grows when it heats up which again raises the temperature ....

The fans and the pump will be ran only when needed. The temperature sensor is used to switch the heater off if the temperature raises too high. The flow sensor is used to see that the coolant is really moving. The level sensor is used to check that there is enough coolant in the system. These should cover all probable scenarios of overheat, coolant blockage and other situations when cooling is not functioning properly.

The control logic will most likely be a MCU board having an Atmel AtMega64 on it. The user interface is power switch, current (average) and temperature meters, power adjustment, ontime adjustment, heat on/off buttons and indicator lights. Should do it. Will show the desighn of that one later.
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Project Logs / Re: Induction heater project
« Last post by eskoilola on Today at 01:38:02 AM »
Just reading the "Data Sheet" of the coil driver. Definitely a google translation. Here is an extract from the document. This part is warning about the slow rising voltage. Somehow I fin this hilarious:

You must pay attention to when using switch power supply, because the high-power switching power supply usually have soft start function, namely the output voltage is slowly rising, and if the voltage rise to 10V before connected induction heating circuit will be caused by lacking voltage lead to circuit can't afford to vibrate, so that the two MOS tube conduction and burned components at the same time, so be sure to switch the power supply voltage stability and then access the induction heating circuit.

Here is another:
The minimum input voltage of the module is 12V, it doesn't mean all the 12V power supply can be used, some novice buyers may use a smaller power supply. This module has specific voltage and current requirements, the voltage 12V current must be more than 10A power supply can be used, if the power is too low will lead to the power output is greatly reduced, when the voltage is lower than 12V, it will lead to two MOS at the same time conduction, will burn MOS tube;

After reading this it seems like the circuit does not need a kick to start - it just does not oscillate if the supply voltage is below 12 volts. So switching with a FET array should be safe. This is actually a BIG assumption but I am used on exploding FETs - they are actually quite fun.

I am thinking on how to control the output power of this device. Basically there are two options:
1. Control the on-time. Sort of slow-motion PWM.
2. Control the input voltage. Maybe 18V to 48V. I could make a BUCK regulator for that.

From those the first one is more appetizing as it does not alter the operation parameters of the circuit. It is also easier to do. Could do the switching from the low-side with a FET array thus avoiding usage of high-side FET drivers.

And here is another funny extract from the documentation:
When heating the metal objects do not to heat too large metal, otherwise it may be overloaded with power, please add a 35A fuse or ammeter and air switch will be better. (package does not inclues)

So it seems like a current protection should be applied. Apparently sticking in a copper bar of 50mm in diameter will be a no-no-no.
After laughing my ass off while reading the documentation I have decided to do this in a certain way ... will add a block diagram later today.

In case You want to read the complete documentation it is readable in THIS eBay location.
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Project Logs / Re: my way to billd a stuart 10 horizontal engine
« Last post by chipenter on Today at 01:30:30 AM »
I have not long finished a 10v and used 2.5 mm cap heads , as I didn't have a drawing .
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Project Logs / Re: my way to billd a stuart 10 horizontal engine
« Last post by SwarfnStuff on Today at 01:00:09 AM »
KRV,
      Look forward to your build. I made a decision ages ago to only use Metric fasteners. Not that I have built any bought casting models but certainly modified a few imperial drawings to metric.
   I notice that you have BA bolts provided with the castings so perhaps use them as it would seem no tapping on your part is needed.
      At least in my tiny shop using metric I do not have to keep multiple supplies of fasteners, drills, taps and dies. Will not suit the purists but I build stuff for my enjoyment and sometimes frustration. Either way I learn stuff, even if it is not to do something that way again.
   God luck with your build.
John B
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Project Logs / my way to billd a stuart 10 horizontal engine
« Last post by krv3000 on May 19, 2018, 06:49:30 PM »
hi all I no I have projects on the go. but I cud not resist I got my self a Stuart 10 horizontal at Doncaster show  :)  I have  bin after one for sum time as I have the vatical 10 witch I was given I keep saying I will by a proper cylinder casting for it as the one that's on it I made out of steel  but never have any way as my way of getting a way from the (wedding of the year) I started on the engine will post pics tomorrow  not any mashing just cleaning up  the castings only two things not right that will be sent back 1 is the gun metal casting for the bearings for the crank and the other the cylinder all the ports are slanted you see wat I mean when I post the pics and by the time I mashen them they will be to big in one way and not big inuf in a norther way a part from that all seems well but at a Delmer don't no why but Stuart don't do drawings for this engine in MM  :bugeye: I think there not doing them selves any favours by doing this as this type of engine is deemed suterbel for  beginner's and as any one under the age of 50 say in the uk will be learnt metric system that bin sed it ant hard to convert the drawings to MM any way as im making the engine in MM shod I use MM nuts and bolts  or the BA bolts provided  :scratch:  any way as off to bed
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Project Logs / Re: Induction heater project
« Last post by PK on May 19, 2018, 05:52:32 PM »
Quote
So I decided to start a project that I am capable of completing.
That's classic me...
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Gallery / Re: Annoying sprung handles on machines
« Last post by Joules on May 19, 2018, 05:13:59 PM »
No problem Eric, thats a different take on what I did.  My preference is to operate the hand wheel with arm extended so I can keep a close eye on the work and cutter, thatís why I am unable to put enough pressure on.  Fumbling to engage the dog drive even with a lighter spring would also be frustrating, so the wedge was the best choice I could come up with.  Always interested to see or hear how others would tackle a similar issue.
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Gallery / Re: Annoying sprung handles on machines
« Last post by velocette on May 19, 2018, 04:56:43 PM »
Hi
It works that is fine  :clap:
Here I go again Taking the "Devil's Advocate" view of things. Fit a lighter spring or take one step to your right when using manually and push in harder to mesh.   :scratch:  :hammer:
  "Be careful your looped attachment doesn't lock up the hand wheel in one direction when turning, couple of wraps of the string are enough for me".  A "Clove Hitch"will secure it safely and securely.
Many ways to skin a cat as long as you end up with a skinned cat. :-)

Eric
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Project Logs / Re: Induction heater project
« Last post by awemawson on May 19, 2018, 01:26:13 PM »
When I rebuilt mine I had to have crucibles made to order from one of the (then) newly escaped Russian satellite countries - wasn't too pricey - I had a dozen made and ten are still on the shelf. They are totally embedded and not removable without chipping them out. Oddly I had some spam from the firm today which I deleted so I can't look back and see who they are !
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Project Logs / Re: Induction heater project
« Last post by eskoilola on May 19, 2018, 12:43:50 PM »
Yes. I also somewhat believe that the turnout of this one might be interesting for those that want to do some hot stuff but do not have the correct (fireproof) setup for that. With induction heater the energy goes (is supposed to go) exactly where needed without setting the cardboard boxes around on fire.

One thing I need to rhink over is the electrical isolation of the coil. I have seen some pictures of coils having a fiberglass sleeve but I do not feel comfortable with that solution. I would rather mold the coil in some fireproof cement, alumina maybe,  in a way that the the coil is free to move outside that ceramic. I have some coil formers that might be suitable. Those are made of some really tough ceramics ... but I have the faintest idea whether those will survive the temperatures. One option is to get a readily formed alumina tube - another option is to make it myself - I have to renovate our garden grill anyway so why not make it of some impressive material. The quantities one must buy the castable alumina are not small.....
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