Low Power, Low heat induction heater

puckilie

Joined Dec 9, 2017
7
hi all,
first of all sorry if there is something "misswritten" i have some problems with english .
i searched the internet for some time now because i need to build an induction heater for one of my projects.
all the induction heaters i could find on the internet use really much energy and bring the metal up to a red glowing point.

i dont need red glowing metal...

what i need is an induction heater that heats the metal object to around 210 °C and then holds the temperatur at 210°C

how would i be able to accomblish that ?
could you run such an induction heater on very low voltage (around 5 volts)?
how much Amps would it draw if it doesnt go over 210 °C
and how much time would it take to heat up at 5 Volt xx Amps?

PS: the metal doesnt need to heat up in 30 seconds or so like the ones i saw on the internet do

thanks a lot for any help

AlbertHall

Joined Jun 4, 2014
8,518
1. The answers to any of those questions depend on the size and shape of the metal object.
2. To control the temperature you will need some kind of temperature sensor attached to the metal.

How important is it that the temperature is even throughout the metal?

puckilie

Joined Dec 9, 2017
7
oh sorry i forgot the size
its a cylindrical piece of brass. it has a height of 12.5 mm and a diameter of 5mm

and i read something about that the temperature depended on the frequency aswell so i thought about if it was possible to calculate which temperatur will be achieved if there is a certain frequncy through the coil (regarding temperatur control)

puckilie

Joined Dec 9, 2017
7
and the temperatur doesnt need to be even if part of the metal is at 210 °C its fine

Joined Jan 15, 2015
4,585
oh sorry i forgot the size
its a cylindrical piece of brass. it has a height of 12.5 mm and a diameter of 5mm

and i read something about that the temperature depended on the frequency aswell so i thought about if it was possible to calculate which temperatur will be achieved if there is a certain frequncy through the coil (regarding temperatur control)
I think what you will find with induction heating is the actual power will be the biggest factor controlling temperature of the heat. You will likely want a "dwell time" for the applied power. So to control temperature you need a temperature sensor providing temperature data to a temperature controller which will control either dwell time or the level of power applied to the induction heater. Starting with the sensor you need the most practical and efficient way to attach the sensor to the load (your piece of brass) or use for example IR sensing and know the emmisitivity (non contact) of your work piece. Once ypou determine sensing then you move on to control which can be any number of control methods.

As to the actual induction heater? I have used them experimenting with annealing brass cartridge cases and rather than build it was easier and less costly to simply buy any of the units from China. This being a single example and I have seen them for much lower cost.

Ron

puckilie

Joined Dec 9, 2017
7
i cant really buy one because my project is pretty small space and the pcb is to big to fit

but i have decided to use a 5V 2.1 Amp power bank which should be around 10 Watt or so can it do the job or is 10 Watt to little energy for induction heating?

Joined Jan 15, 2015
4,585
Using induction heating 10 watts is not going to get you very far or much heat. Not using induction heating anyway. Your brass rod is the "load" and you need to figure out how much energy is needed to raise the temperature of the load. Without even doing the math I can pretty much tell you that 5 volts at a few amps will not work for induction heating the load you have.

Ron

puckilie

Joined Dec 9, 2017
7
hi i went online and searched for the heat capacity of brass found it in this list
then i went to calculate 1 g of brass needs 0.380 J to heat up 1 °C then with the formular "Watt = Joule / seconds" i calculatet. first i multiplied 0.380 with 2 to get the joule requiered for 2 grams because my piece of brass weights ca. 2 grams (its hollow) there after i multiplied the result (0.76) with 210 to get the joules i need to heat up the 2 grams of brass. i got 159.6 J thereafter i used the formular from above to calculate the watt i would need if i heated over a periode of 30 seconds

the result: i need 5.32 Watt so 10 Watt should be more than enough or am i doing something wrong here?

AlbertHall

Joined Jun 4, 2014
8,518
Your brass will be losing heat to the air so you will need more than that.
The induction heater will be less than 100% efficient so you will need more again.

Joined Jan 15, 2015
4,585
the result: i need 5.32 Watt so 10 Watt should be more than enough or am i doing something wrong here?
OK, a very light piece of brass. Good going, so I would look at any of the dozens of circuit designs online and try what you have come up with. I would consider what I see Albert just posted. The problem being we do not work in a perfect worls so loss needs to be figured into things.

Ron

tcmtech

Joined Nov 4, 2013
2,868
the result: i need 5.32 Watt so 10 Watt should be more than enough or am i doing something wrong here?
Theoretically yes but realistically a small DIY induction heater might be lucky if it can hit 20% energy transfer rates. My advice would be to go with a 12 volt system that uses a few 10's of watts of power which can be made with a very simple push/pull circuit and the proper capacitor set to make it work as a simple LC tank circuit. 6 - 10 pieces depending on the design and it's way easier to turn down an excess of power in larger than needed circuit then try to squeeze out more efficiency out of underpowered one.