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Testing some circuits...

Today I began testing some circuits for my induction heater.

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In particular, I thought I'd brag about the bottom-right corner of this one:

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I started with 30T of 26AWG on a small EI ferrite transformer (used to be a monitor horizontal output transistor driver transformer, if that gives any vague bit of information), followed by 40T of 26AWG and 5T over the top with some hookup wire. C112 is 0.047uF and R112 is 2.2k (like the R makes a difference). I started with a 2N4401 and it worked pretty good, but got kinda sloppy with 500 ohms loading each output (actually a 1k across both outputs). It wasn't getting very toasty so I dropped in one of those puny-assed ZTX651's and that sharpened up the waveforms nicely. :-)

From +17.5V input I get +24V and -20V likewise, at 130mA (330 ohms across both outputs). 5.7W output for maybe a quarter watt in the transistor ain't bad for a self-excited class C oscillator. :)

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams
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Oops! :-[ Started off with 7908's, then decided against it...

Ya. The last delay being "okay" time to make sure the relay is settled (well settled, I guess) before the circuit is turned on.

Yeah, that wouldn't be that bad an idea. HV voltage divider to a comparator, plus a convienient delay (to slow possible switching errors) could be used for RL3.

Thanks. Hey, I'll try to remember that one, then post a video for you. ;-)

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

Nice. BTW - you have a typo in that corner. You show -8 V coming out of a 7906, so when you update the other values update that, too.

I don't get the sequencer (?) in the middle. Why not power good logic instead of the second delay (for RL3)? Is the idea to give the HV caps 2 seconds to charge through the resistors, and another

2 seconds charging with the resistors bypassed before the bottom supply is turned on? I'm thinking something like: (320V good) + (VdR110 = 0) + (VdR111 = 0) = RL3 on I don't know if that's too much belt + suspenders.

I love the pictures you've posted in the past! The last one made me think of the ballpark beer peddlers' pitch, modified:

"Hey! Getcha hot caps here!" I wonder what would happen to one - just one - of those caps if you ran the heater with the cap in the inductor. :-)

Ed

Reply to
ehsjr

Thanks.. I just tight-wound it around a form, after annealing it, then stretched the turns apart for the proper spacing. Then because it was still pretty soft, I stretched and compressed it a bit to put some hardness into the copper (copper work-hardens very nicely). Maybe your tubing was full-hard?

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

I like the clean way you derive the delays!

Well, it adds parts count, so I'm not sure if it's a good idea or not. But if you want to go the whole nine yards, you need to do more than HV->divider->comparator to make it iron clad. HV could come up through the resistors only - the relay could be bad or have bad contacts. If you sense the voltage drop across each R (110 & 111) and find 0 v, input to the bridge is good.

:-) Love those pictures! Also - grumble - on my best day I couldn't bend that tubing as beautifully as you did. Makes me drool!

Ed

Reply to
ehsjr

I suspect the problem is cockpit error. :-) The tubing was soft - maybe too soft? I dunno. I may try again, now that I've seen how beautifully it can be done!

Ed

Reply to
ehsjr

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