New Induction Heater circuit with no center tap.

spec said:

I do not see any problems with the bootstrap circuits. Garry has got a handle on that and posted a perfectly reasonable approach and TCM and I have discussed this area with him. This is a normal design process.

spec

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Doesn't seem that way to me. Seems to be fighting to not adapt what you and tcm have been saying. Look how much it took to change from mosfets to IGBT's. Don't think it's sunk in yet that those are high side switches.

tcmtech said:

Increase the system operating voltage to compensate. If he's at 22 now take it to 36 and have reserve.



As far as I know he shouldn't be sticking his fingers or anything else on any of the circuits while they are active any way.
As for the induction coil standard air core inductance calculations for the given dimensions and operating frequency will tell exactly what the new turns ratio and sizing will need to be.

Say he is running a 5" dia 5" high coil with 5 turns at 40 KHz That gives him and inductive impedance of ~ .5 ohms and an effective energy input ~ 1000 watts with his 22 volt input.

Same coil dimensions but at 60 KHz with 15 turns and a 150 volt input gives him~7.5 ohms and an effective coil energy input of ~ 3000 watts.

Take the same coil up to 300 volts and drop it back to 40 KHz and it's good for ~18 KW and about the realistic limit he could runoff a 240 VAC 100 amp power circuit factoring in system loses and a bit of circuit overhead.

The way I see it given the size and capacity of his switching devices he has loads of room to cheat the system with just by changing input voltages which given since he insists on running off crappy rewound MOT's it's way faster and cheaper to do rewinds than go after theoretically optimal capacitor bank design.

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Useful information about the coil parameters. As said before I agree that increasing the voltage would increase the power, but I think it is wise to start with an isolated +-24V system first and get that working before moving on to anything grander. That would then provide a test bed for further development... gently gently.

spec

shortbus= said:

Doesn't seem that way to me. Seems to be fighting to not adapt what you and tcm have been saying. Look how much it took to change from mosfets to IGBT's. Don't think it's sunk in yet that those are high side switches.

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Don't worry, we will get an induction heater working which hopefully will be the basis for future development.

I didn't see anything wrong, in general that is, with Gary's PSU approach- quite neat I thought.

spec

spec said:

Useful information about the coil parameters. As said before I agree that increasing the voltage would increase the power, but I think it is wise to start with an isolated +-24V system first and get that working before moving on to anything grander. That would then provide a test bed for further development... gently gently.

spec

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That's largely where I am at as well. A practical base circuit running off +- 24 volt rails just comes off as being the simplest to work with given common parts. Also with the adjustable frequency and duty cycle driver circuit tuning it to work best with any coil even remotely close to being right shouldn't be much of a problem.

Tuning and adjusting the user to function 'sort of well enough to work with' is the biggest challenge and already has me largely played out on the issue.

Just a thinking out loud comment here. I've seen it suggested in this thread to use a switching power supply to power this, isn't that a bad idea? Many things like stepper motors, that switch at frequent and high speeds recommend against the use of switching power supplies and say a linear supply is better, wouldn't that also apply here?

shortbus= said:

Just a thinking out loud comment here. I've seen it suggested in this thread to use a switching power supply to power this, isn't that a bad idea? Many things like stepper motors, that switch at frequent and high speeds recommend against the use of switching power supplies and say a linear supply is better, wouldn't that also apply here?

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I can't think of a problem with SMPs in this application, but it is worth checking this.

spec

Rube Goldberg said he's fine with the concept.

I have these diodes. I can not find data on these anywhere. I am guessing they are at least 50 volts or higher and probably 100 or 200 amps. I also have a box of industrial SCRs that I think are 600 amps. I also have about 50 capacitors 47,000. uf 200 vdc i have been saving for a rail gun project.

**broken link removed**

**broken link removed**

Those were common in old Linde welders and related power supplies and typically had at minimum 400 volt 300 amp capacity.

They were made and labeled as a 'proprietary design' which basically meant they could charge 4 - 5 times what their generic standard labeled version sold for.

I have a bunch of them too. Never have managed to kill one either.

Yours were made during the 25th week of 1974.

They sound like real man's devices.

spec

Meh. I have a collection of 'Hockey Puck' rectifier diodes and SCR's that make these look like wall wart power supply level components.

I think the biggest salvage units I have are well over 2400 amp @ ~2100 volts or something like that. At least 2000+ on both amp and volt ratings anyway.

tcmtech said:

Meh. I have a collection of 'Hockey Puck' rectifier diodes and SCR's that make these look like wall wart power supply level components.

I think the biggest salvage units I have are well over 2400 amp @ ~2100 volts or something like that. At least 2000+ on both amp and volt ratings anyway.

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Wow

The big thing with high power diodes, IGBJs, SCRs, etc is, not only do they increase reliability, but they also give high efficiency because of their low voltage drop, which in itself increases reliability.

spec

I've always been a fan of using them in experimental projects just because they are so dang hard to destroy when you do screw something up!

A 600 volt 50 amp SCR in a TO-247 package will take a line short hit for aobut 1/10th of second before it explodes even if it on a heatsink . Whereas even a basic stud type or mini puck 1600 volt multi hundred amp device without any heatsinks will take out a 240 VAC 100 amp circuit several times back to back without issue.

tcmtech said:

I've always been a fan of using them in experimental projects just because they are so dang hard to destroy when you do screw something up!

A 600 volt 50 amp SCR in a TO-247 package will take a line short hit for aobut 1/10th of second before it explodes even if it on a heatsink . Whereas even a basic stud type or mini puck 1600 volt multi hundred amp device without any heatsinks will take out a 240 VAC 100 amp circuit several times back to back without issue.

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Now that is what I call real electronic engineering.

As a matter of interest, with 170V DC reverse voltage, what sort of leakage current would you get with those monsters, if the rectifier junction were up at 100 Deg C? If you bought a new one what would the cost be?

Some 50A automobile alternator diodes I checked years ago leaked around 20mA, or thereabouts, with 20V reverse. I thought the diodes were dud at first.

spec

I did have 16 hockey puck diodes I salvaged the aluminum heat sinks weigh 15 lbs each. I sold all but 2 they are lost some where in my work shop. I don't know the value someone once told me 800v 800a.

I found a transformer I can use instead of a MOT EI laminates are too small for more than 100 turns on the primary plus the secondary. The properly designed transformer needs 200 turns on the primary and I have plenty of room for 3 secondary windings. The original transformer is rated 1500w continuous and is large enough for 3500w peak.

spec said:

Now that is what I call real electronic engineering.

As a matter of interest, with 170V DC reverse voltage, what sort of leakage current would you get with those monsters, if the rectifier junction were up at 100 Deg C? If you bought a new one what would the cost be?

Some 50A automobile alternator diodes I checked years ago leaked around 20mA, or thereabouts, with 20V reverse. I thought the diodes were dud at first.

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I've always been fascinated by the high power electrical and electronics. Anything under a few hundred amps at a few hundred volts just doesn't thrill me any more.

Nearest size SCR's I can find are these at Digikey. https://www.digikey.com/product-det...ion/VS-ST1230C16K0/VS-ST1230C16K0GI-ND/359264
1600 volt 1745 amp ~$300 a piece so I have to guess the bigger ones I have would be in the $400 range.

The ones I got came from a huge DC motor drive that ran a ~1000 - 1200 HP 600 VDC motor for who knows what and I have pulled dozens of other sizes of SCRs, diodes, transistor and IGBT power bricks from other huge devices like VFD's, power conditioners and massive UPS units. A buddy of mine runs a salvage yard so I get to pick through the odd electrical and electronics salvage items they get in when I go and visit so that's where most of it comes from.

Depending on the alternator diode design some are pretty crappy and others or outstanding. I have bunch of salvaged 24 volt 100+amp Leece Neville commercial alternators and I have done megger tests on them to see what their PIV breakdown voltage was before reconfiguring the windings on one for higher voltage output and they tested at greater than 2 gigaohms on a live 1000 volt megger test.
I like using the big Leece Neville alternators for that sort of experimenting being they are typically wound as 2 - 4 parallel windings per phase and configured in a Delta output so reconfiguring one to run at any output voltage up to around 200 VDC unit is pretty easy.

gary350 said:

I did have 16 hockey puck diodes I salvaged the aluminum heat sinks weigh 15 lbs each. I sold all but 2 they are lost some where in my work shop. I don't know the value someone once told me 800v 800a.

I found a transformer I can use instead of a MOT EI laminates are too small for more than 100 turns on the primary plus the secondary. The properly designed transformer needs 200 turns on the primary and I have plenty of room for 3 secondary windings. The original transformer is rated 1500w continuous and is large enough for 3500w peak.

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Sounds good. The first move will be to get the PSU sorted.

spec