DIY Metcal 13.56 MHz RF Supply

[cwalex]

Hi Chris,

Have you had a chance to fix the board yet. I don't use eagle but if you just upload the gerbers I will just send them as is to itead. Hope you don't think I'm trying to rush you, I just thought I'd check in and see how you got on.

cheers,

Alex

[mamalala]

Hi Chris,

Have you had a chance to fix the board yet. I don't use eagle but if you just upload the gerbers I will just send them as is to itead. Hope you don't think I'm trying to rush you, I just thought I'd check in and see how you got on.

cheers,

Alex

Hi Alex,

damn, forgot to create and upload the Gerbers... Here they are, V0.3, each fits in the 10cm x 10cm service.

What changed in V0.3:

Controller:
- Replaced +5V DC/DC converter with 7805 linear regulator in SMD
- Moved filter caps so they don't interfere with the caps on the RF board
- Added 100n to the backlight pins of the LCD connector
- Added 22k pullups for unused data lines of LCD
- Swapped pin1 & 2 of the LCD connector.

Since i drive the LCD backlight with PWM, some displays had trouble with data corruption if there was no 100n cap there. The pullups are normally not required, but i had one display that needed them. The display i initially used had pin1 & 2 swapped, that is, VCC on pin1 and GND on pin2. Most displays have GND on pin1 and VCC on pin2, however.

RF-Board:
- Added extra caps for filter section, so no more stacking of caps required

OK, that's it for now. I'll prepare the controller board doc in the next days, a combined one for the V0.2 and 0.3 boards. Hope to finish the firmware soon as well.

Greetings,

Chris

[mamalala]

Hi Chris,

My boards just arrived safely here in Portugal, they look great, ones again thank you very much.
...

Paulo Almeida

Hi Paulo,

thanks for the feedback!

Regarding the readouts, i have my adc.c source attached. Note that this is for a PIC18 chip, but you should get the idea anyways. Basically it constantly reads the ADC inputs and sums the last 16 samples of each channel, this is done in adc_process(), which is called from the ADC interrupt periodically. adc_get_reading() returns either the 16x reading for forward/reflected, or the voltage of the DC/DC output of the RF gen board, depending on the given argument. In the latter case, the value is in 0.01V steps, i.e. 2200 means 22.00 volts.

calc_rf_data() calculates the SWR from the forward/reflected values. It also calculates a value to display for the RF power, altough that one is not really the exact power but made so that it looks nice when displayed as a bar.

Hope that helps a bit.

As mentioned previously, i hope to have the firmware completed soon, so that i can upload the sources here as well.

Greetings,

Chris

[mamalala]

And here are the Eagle files, plus PDF of the schematics. The tValues/bValues stuff in the Eagle files is not cleaned up yet, since i usually only put the tNames/bNames stuff on the silkscreen anyways.

Greetings,

Chris

[Paulinho19]

My WAG220SA enclosure arrived today!!! 




I also Laser cut some Plexiglas tops to test my layout, fits like a charm.

In the front is the LCD, the F type connector for the hand piece and a pushbutton for Wake up/Boost.


In the back a power switch and a PC power connector with a 0,5A fuse.

Everything fits inside.



Next Step, assemble the RF stage board.

Paulo

[mamalala]

Looks good! But i would not use Plexiglas here. Keep in mind that, after all, this is a RF generator. The 13.56 MHz is also used by RFID systems. The first harmonics is 27.12 MHz, which is in the 11 meter CB band. Having non shielded sides will surely allow quite a lot of RF emission which may interfere with other stuff. If possible you should really use the aluminium plates there.

You may also want to use some type of filtering on the AC line connector, or at least put the AC leads to the transformer through some ferrite beads. There is a lot of wire on the transformer, which will act as an antenna to pick up the RF emissions, and thus couple them into the mains.

Greetings,

Chris

[Paulinho19]

Hi, the Plexiglas is just to test my layout, in the end I will use the aluminum tops that came with the enclosure.

Thanks for the tip about the Filter, hadn't thought of that yet.

I will keep you updates. 

Paulo

[dfnr2]

Chris,

This is, in my opinion, by far the coolest project I've seen on this forum, and the coolest I've seen in a long time, based on its general utility.  And very nicely thought out with the self-contained RF module and the optional controler module. 

Very well done!!!

[Paulinho19]

Hi everyone,

here is my fist take on te controller board now compatible with Arduino based on the ATMEGA 328P-AU.

Attached is also the Firmware for the ATMEGA.

Paulo Almeida

[mamalala]

Chris,

This is, in my opinion, by far the coolest project I've seen on this forum, and the coolest I've seen in a long time, based on its general utility.  And very nicely thought out with the self-contained RF module and the optional controler module. 

Very well done!!!

Thank you, much appreciated!

Greetings,

Chris

[mamalala]

Hi everyone,

here is my fist take on te controller board now compatible with Arduino based on the ATMEGA 328P-AU.

Attached is also the Firmware for the ATMEGA.

Paulo Almeida

Hi Paulo,

nice! However, you may want to keep that "notch" in the controller board's upper-left that was originally there, and move the reset connector a bit instead. In case someone want to use a smaller enclosure, like a 100 x 100 mm type, or wants to mount the RF/controller board stack on a 100 x 100 mm heatsink and enclose that with aluminium sheets, that notch makes space for the RF coax cable of the RF board underneath it so it can exit to the top.

Greetings,

Chris

[Paulinho19]

Hi Chris,

Ones again you are right.

Done, The "BOOST" pinheader can be a vertical one.

Paulo

[Paulinho19]

Hi Chris,

I just finished the assembly of the first part of the RF Stage board and I’m getting 12.35 volts at the output of L2, do you think its ok?

Paulo

[notsob]

Just to add some historical info - as I have a Metcal PS2E in pieces atm. The mains transformer is 115V/28VCT 100VA 3.6A RMS rated secondary.
It is a custom version of a Signal Transformers 241-8-28 and as far as I can see, the only difference is that the metal mounting frame has been removed and it is bolted down via the existing holes in the EI core. It weighs 2.75 lb

If you are non US a similar transformer would be a DP-241-8-28 (it has 2 x 115V primaries, so you can use it as 115V or 230V). Both transformers are approx $US30 new.

Cheers

Peter

[notsob]

I forgot to add the Signal Transformers pdf

[HeliEye]

 
hi all

My first post here...  I'm watching this one with interest, as I have 2 Metcal soldering stations.. an MX500 and MX5000, plus Talon and desoldering gun with compressor etc.

The old MX500, is only used as a backup now, still handy as the both take the same tips..
I've not been tempted to open up my MX5000 yet, as it's still under warranty ;-)

After using Metcals now for many years, I could never go back to the Toy Irons with conventional heater tech, yuk..
I even binned 2x Weller stations, as they couldn't keep up on one manual soldering production run.
I'm still amazed at the speed my 5mm heavy tip melts solder in under 4 seconds from stone cold ;-)

This project would be cool if it can be made to run on 12VDC for field work ;-)

Steve
 

[Paulinho19]

For a 12VDC version you could use a Step up converter like this one:

http://www.ebay.de/itm/Convertidor-fuente-step-up-d-10v-a-12v-hasta-35v-regulable-dc-power-supply-BOOST-/221178279108?pt=LH_DefaultDomain_186&hash=item337f40b4c4#ht_3763wt_1344

Paulo Almeida

[mamalala]

Hi Chris,

I just finished the assembly of the first part of the RF Stage board and I’m getting 12.35 volts at the output of L2, do you think its ok?

Paulo

Hello Paulo,

i assume that you mean just the DC/DC converter section, with no other sections assembled yet.

Did you put a load between the output of L2 and GND? When i did the measurement i connected the GND of the load to the GND pad for the output FET. When measuring unloaded i can imagine the output voltage to be a bit higher. Under load there will be a slight voltage drop across L2 (and due to the copper traces, etc.) Add to that the tolerances of the resistors and the regulator IC itself. 11.7 Volts is what i had here, using a cheap and old handheld DMM, so i wouldn't worry about it too much. 12.35 Volts is in the same ballpark.

Greetings,

Chris

Edit: And sorry for the late reply. I'm quite busy currently, so i mostly read the forum between compiler/jtag-upload runs at the moment...

[mamalala]

This project would be cool if it can be made to run on 12VDC for field work ;-)

From what i understand, Mike (mikeselectricstuff) wants to check the circuit to redesign it for 12 Volts. Basically it's just replacing the DC/DC converter with a boost converter type, instead of the buck converter it currently uses.

Greetings,

Chris

[mikeselectricstuff]

This project would be cool if it can be made to run on 12VDC for field work ;-)

From what i understand, Mike (mikeselectricstuff) wants to check the circuit to redesign it for 12 Volts. Basically it's just replacing the DC/DC converter with a boost converter type, instead of the buck converter it currently uses.

Greetings,

Chris

If I ever get time, what I'd like to do is use a buck/boost front end so it will run from either a 12V-ish battery or a 20v laptop charger. I also want to do the regulation & PWM  on a MCU to slash the parts count & cost. May be a while though....

[Paulinho19]

Hi, Greetings from Portugal,

I just finished the assembly of the RF Stage board. But I don't seem to be able to adjust the output voltage at L2 with R19, it won't go over 5.6V. I double checked everything and I think the problem is my RF dummy load. I used a 50ohm 15W that I had here. My question is, can I use a dummy load with more than 50W (like 100W) or are the 50W important for this adjustment?

Thanks,

Paulo

[mamalala]

Hi Paulo,

could you post an image from the assembled board viewed from top? Sharp (non-shaky) and having the board fill out all of the image area? Maybe i can see something then...

In any case, some pointers:

- You have used a trimpot for R25 instead of two equal SMD resistors. Make sure that you have half the 5V supply voltage at the center pin of that trimpot. It adjusts the offset of the OpAmp used for the control loop. If that is off too much you will not get the proper values.

- The dummy load just needs to be big enough to handle the output power, which can be way over 30 watts. A smaller dummy is OK if you only use it for short periods of time. If you want to test for long(er) periods, you need 50 watts or bigger. In any case, it must be a purely resisitve load. That means you can _not_ use things like wirewound resistors, since they are way too inductive.

- Verify that the supply voltages are all OK and stable. Check the main supply and see if it keeps up under load.

- Are you sure that you have 5.6 volts at L2? In the scope screenshot there is 60 volts peak-peak, unlikely to reach that with only 5.6 volts supply into the RF output transformer. At least not when there is a proper 50 ohms dummy load connected to the RF output.

- Check the RF signal at the junctions between L3/L4 and L4/L5. The concept of the regulation is to keep the RF voltage at the junction of L4/L5 more or less constant. A mismatch at the output will cause more RF energy to be reflected back, increasing the level there. Which in turn will cause the buck regulator to decrease it's output voltage. A matched load will cause a drop at L4/L5, causing the buck to increase it's output voltage. If you see a much higher voltage between L4/L5 than what you have at the output, then something is wrong with the load.

- Have you done the inital adjustment of R32 properly? It sets the maximum possible DC output from the buck regulator.

- Also make sure that no external signal is connected to the VLIM input (pin 3 on SV1). Applying a voltage there will cause the buck regulator to decrease the output voltage. Pin 5 is next to it and has the +5V rail, so make sure that there is no short or something.

In any case, as said, please upload a clear hi-res image of the board, so i can check things out and compare to what i have here. After all, there is always the chance that i made a mistake in the docu or such.

Greetings,

Chris

[Paulinho19]

Hi Chris,

Here are some pics I took today, the first is the voltage on L2 (with the 50ohm 15W dummy load and 60V p-p RF output).

I will take some better photos tomorrow.

- I checked R25 and I have 2.5V there.

- Power Supply is Stable

- I Adjusted R32

I will try the rest tomorrow.

Thanks,

Paulo

[Paulinho19]

Couldn't it be the dummy load reflecting back some power being only rated for 15W?

Paulo

[mamalala]

Hi Paulo,

i just rechecked my circuit against the doc i wrote. In the doc i had 2k2 for R23, and 22k for R24 (the two resistors next to the OpAmp, going to the R25 trimpot). However, on my actual circuit i have 22k for both, so please change R23 to 22k. However, this actually reduces the gain (from ~2 to ~1.1) of that stage, so you should have been able to get the proper DC output anyways.

Instead of the trimpot R25 i have populated the fixed resistors R33 and R34, each with 2k2.

What FET did you use in the RF stage? Doesn't look like an IRF510. The IRF510 has a rather low gate charge, suitably fast turn on/off time and a rather "high" RDSon at 540 miliohms. Be aware that you can not just drop in any other FET.

Greetings,

Chris

Edit: the 15 watts dummy load would not reflect more or less than a 50 or 100 watts dummy. However, it would have problems whith continued operation when putting more than the 15 watts into it: it will overheat, and eventually burn out. So, check that the dummy is still 50 ohms!

BTW, what kind of dummy load do you actually use?