i want to charge a battery at 14v 1A. Can I use a single LM317 to regulate voltage from 19v without worrying about current limiting? I don't want the battery to draw more than 1.5A.

basically use the schematic in the first page of the data sheet ti.com/lit/ds/symlink/lm317.pdf?ts=1592236938131

@Marla Is there a good reference for induction heating circuits? What I'm finding is the 2 transistor oscillators, which comes across as pretty sketchy to me.

@Hmmm Well which do you want to do? 14V, or 1A?

both

my logic is that LM317 can't provide more than 1.5A anyway does it have a current limit protection?

it's okay to charge it 1.5A even 2A but not more

I guess the question should be what happens if I try to take more than 1.5A from LM317?

@Hmmm That's not how it works. Either you adjust the voltage to maintain a specific current (e.g. 1A) (Constant current), or you fix the voltage and the current is whatever the battery draws (e.g. 14V) (Constant voltage).

If I fix the voltage with LM317 to 14v what is the maximum current the battery can draw?

The circuit using two LM317 uses the first one to limit the current and the second to fix the voltage right?

"The circuit using two LM317..." Which circuit?

If you set the output to 14V, there isn't a way to figure that out definitively what the maximum current is - the limit is to protect the regulator not anything down stream. It isn't a precise limit - typical value is 2.2A, with no maximum.

You won't be able to set a constant-voltage limit for a LM317 in constant-current mode that way, because the constant current regulator needs 3-4V headroom. I don't know how soft that cut-off is, but I wouldn't rely on it.

You might be able to do it with a LDO instead of the LM317 - have the LM317 in constant current mode, followed by a 14V LDO. This circuit will burn lots of power, and everything will need heat sinks.

how's something like this typically designed in modern electronics? current limiting + a switching regulator?

The way that almost everything is done these days - you get a chip that does what you want. :p

ti.com/power-management/battery-management/charger-ics/…

Broadly speaking, you would have a buck converter with current monitoring

you would charge at constant current until you reach your cut-off voltage, and then finish as constant voltage.

yeah I have been looking for a chip. I'll do some more research. USB type c PD is pretty cool and I can request 15v from charger. i will see If can find and easy to use chip for that. I'm designing my first PCB and it's already getting too crowded lol

I'm actually a software engineer but EE is pretty cool so i'm learning a lot

@W5VO . . Commercial induction heating power supplies generally use an H-bridge. Sometimes for low power a boost converter is used. Suppliers keep the control circuits VERY secret and don't even supply board schematics. Just a schematic of the system and how the boards connect. . . . . continued . . .

@W5VO . . . Users of induction heaters are allowed to connect any combination of capacitor and coil and thus the power supply has to protect itself against any load from short circuit to open circuit and for any reactive load in between. . . . continued . .

@W5VO . . Protecting against load capacitor over voltage, output over current, frequency being in band, etc.

The books published in the industry typically focus on coil design and impedance matching.

@Marla Thanks for the response. Users are allowed to connect any combination... wow that's terrifying from a protection perspective

Yes it is

But they can and are made.

It is not too much different from making a transmitter for radio that can survive any antenna connected

Including no antenna. ;)

I also know many of those transmitters only offer "best effort protection against stupidity"

but that's a great point. So how important is the shape of the current waveform in the coil?

At Motorola, we made police radios that had to withstand infinite VSWR, and continue to transmit at whatever power out could be achieved. Emergency vehicles can still communicate even if antenna is broken to the nub.

@W5VO You get induction heating at any frequency that is in the shape of the current, as expected.

ahh, that makes sense.

@W5VO . . one additional note : for induction heating you try to design the coils so that the loaded Q is as low as possible (efficiency) while still having an under damped tank circuit.

Thanks for answering my questions - I'm poking around with the idea of doing some "blacksmithing", and seeing if cobbling together an induction heater would be a good way to play around without fire.

You might look at some of the low power Chinese heaters on the market. VERY cost effective for black smithing.

yeah, I think it's just these circuits look so damn sketchy from my experience with power electronics.

but after working with SiC MOSFETs, I think I'm in the camp of "every MOSFET should be driven by a >2A driver"

SiC was just coming along when I retired, and I really really wanted high power diodes with no reverse recovery loss. All my career. Sigh

We used 9 amp drivers for IGBT

IXYS makes a part like that, I'm not sure if I used that one or a 4A driver.

If you purchased a induction heater, you will get more blacksmithing done, rather than fiddling with the controls all of the time. :)

Eliminating the recovery of the SiC diodes brings out an effect that gets masked in Si diodes - the reverse current from discharging the diode junction capacitance.

You are so right. I just got myself a thermal camera, and I was so frustrated with the features not matching what I wanted that I was about to go to Digikey and buy the raw sensor and make something reasonable.... but then I would have a sensor and not a thermal camera ;)

Heck, maybe get one of the cooking induction heaters and replace the flat coil with solenoid of same inductance.. $100 . worth a try.

@W5VO Then that means you even have gaps in your knowledge. And that you could be wrong. I do know what metacognition is. We did this and practice it for 4 years in school. And I'm not saying otherwise.

@W5VO I think that we both know what I'm meaning by when I say he doesn't have gaps in his knowledge. Meaning he knows what he is doing since he's done it for 35 years. I see exactly what you are trying to do, and it won't work. These aren't only my conclusions. But a handful of professional opinions. I don't just have my opinion but I have facts from professionals. That's something totally different.

I've had several electricians, engineers, physicist, scientists and professors from universities come in. Because I don't know. I'm doing everything I can to get an answer. I am even having physicists from San Diego State University, University of Utah, Oregon State University as well as researchers from Logan Utah come in and examine my machine to find a solution to my questions.

If I can't find a solution then I'll keep looking

@ScientistSmithYT Good luck with your endeavors, I'm afraid I can't help you any more.

@W5VO Ok, thanks :)