You still did not answer all the questions, including what is the supply voltage that you consider for this?

A supply Voltage of 12 Volts and power consumption of 15 Watts.

The specs of the electromagnet does not matter now since I gave up on that idea.

 

He said he wanted a source of IR. Maybe a soldering iron would make a better source.

Do you mean an IR soldering iron made from a car cigarette lighter like this one

 

Thanks.
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I have used a 300 W FIR lamp for healing since I got in SFO in the late 80's. It uses a fluorescent mineral coating on Silicon carbide disk back heated by short IR with tungsten wires like a toaster. It converts 1 um to 5~25 um using minerals like Germanium and has a deeper skin depth. Most accupuncture Dr's have this unit. I was one of the first to get one. The Chinese called it a Mineral Therapy Lamp from Dr. Lee It works and from 1ft feels like a warm sun.

I also have a unit like the original from Slovenia called the Tesla Stym which uses > 1kW of RF to heat tissue to slightly warm briefly then vibrate it from 5 to 15 Hz in a 15 second cycle like ocean waves . The planar handheld coil (~5"D) is water cooled with a 1" hose and fan. This excites deep tissues with no skin current like Dr. Ho's electropads and has 5 levels. It also cured my dog's knee dysplasia (walking on 3 legs) in a couple months that would have cost $8k+$4k in surgery and physio. The Stym is $25k. My Chinese clone cost me $2.5k. It works.

LED's and a coil are like comparing a Bic lighter to a blow torch. But maybe you know better.

 

LED's and a coil are like comparing a Bic lighter to a blow torch. But maybe you know better.

I was calculating that 4 amperes of current flowing through the electromagnet could flow through an IR device in series but the LED diodes is a bad idea since they have voltage drops and as pointed out, it would do disaster in series with the inductance of the electromagnet.

FIRs use high power, I am experimenting with devices that can use max 50 to 60 watts of power.

 

 

nice and simple 100mA constant current.
12k and mosfet are normally always on. but 6.8Ohm and NPN on a right are forming a current limiter (~0.6V/6.8A is ~0.1A).and the NPN on the left can be used to dim it.

thanks to limiter, this will produce pretty constant current regardless how many LEDs are in the string (as long as sum of Vf of connected diodes supply voltage... in this case that means less than 12V). one such circuit gives you some 1W (at 12V) but you can connect several such circuits in parallel to get more diodes and power.

you can use same circuit for 50 (or 49) LEDs to get 10W by reducing 6.8Ohm resistor, then connecting more LED strings in parallel. it would be a good idea to replace one of LEDs in each string by a balancing resistor. since LED specs vary (even in a same batch) you could have one string with bunch of LEDs with Vf of 1.2V and another string with bunch of 1.4V. but using resistor helps balance it out so all strings are equally bright.

since one LED is about 1.3V and 100mA, a substitute is balancing resistor on the order of 1.3V/0.1A=13 Ohm.

12 Ohm is a common value and power dissipation is P=I^2 * R = 0.1A *0.1A *12 Ohm =0.12W= 120mW
the current for 7strings instead of 1 is of course 7x larger so 6.8 Ohm/7 = about 1 Ohm.

 

the other option is to use LED drivers... everyone makes them but China is where most of LEDs and LED drivers come from. also that is where they are lower cost so using JLC for example and PCBA means you could get them regardless where you are. if you prefer to make own PCBs and solder your self (a great for developing skills and experience) you can buy parts from LCSC. they ship everywhere and that is what you see in all the 12-24V beacons sold on Amazon.

you did not say what part of the world you are in but if getting el cheapo parts (RT9293, PT4115 etc) does not work for you, use search function of some popular electronics distributors (Mouser, DigiKey, Farnel, ...) to identify candidates. or ask Google for 10W LED driver IC for 12V.

https://www.mouser.ca/c/semiconductors/driver-ics/led-lighting-driver-ics/?q=LED driver