Induction heater taking too much current

Thread Starter

rahul411

Joined Feb 19, 2018
241
I'm building a induction heater which will possibly melt metals rated for around 2kw. The thing is when i connect the power supply to it the 25V smps voltage drops down to somewhere around 1.7V and one MOSFET get warm, and gets hotter if connected for more than 30sec. The smps is rated for 24v @30amps. I have 3 of such power supplies but for initial test im only using 1 which is set to 25V.
The schematic im following is attached.

A year ago i build a small induction heater which had similar problem in the initial testing but later worked after i connected 2 channels of a bench power supply in parallel and it consumed around 5 amps after being started with nothing in the work coil. But now I'm building big, so what's probably wrong here? Do i need to connect more smps in parallel so as to compensate for the voltage drop? I think this much current is enough for the size.royerIH.gif
IMG_20200209_181338.jpg
This is the size of it.
 

Delta prime

Joined Nov 15, 2019
164
Do i need to connect more smps in parallel so as to compensate for the voltage drop? I think this much current is enough for the size.
I believe you answered your own question hook them all up.
Power supply 24V at 30A is 720W and you want to get 2kW out of it?
A courtesy and a direction was given to you. It's always good to see it from a different perspective clears the mind. Keep us posted of your progress and have a fire extinguisher ready!! This Is going to be good.
 

Thread Starter

rahul411

Joined Feb 19, 2018
241
I believe you answered your own question hook them all up.
Actually not, smps are rated for 30apms and without anything inside the workcoil it should not consume whole 30amps and even more the voltage drops down to 1.7V
Something isn't right here.
 

tsan

Joined Sep 6, 2014
108
Is there a power switch between the power supply 24V and the heater? I don't see it in the picture. Power supply should be turned on and making 24V before connecting power to the heater. Oscillator does not start, if the supply voltage rises slowly or at least that is written on the induction heater description that is on ebay. I have not used royer circuit myself.
 

Thread Starter

rahul411

Joined Feb 19, 2018
241
Is there a power switch between the power supply 24V and the heater? I don't see it in the picture. Power supply should be turned on and making 24V before connecting power to the heater. Oscillator does not start, if the supply voltage rises slowly or at least that is written on the induction heater description that is on ebay. I have not used royer circuit myself.
Yes i know this from previous build that's why I have ordered a 24v 100amps relay but in the meantime I'm switching on the power supply and then after 10 to 20sec i positive lead of induction heater to the positive rail of the power supply. It creates some sparks.
 

Sensacell

Joined Jun 19, 2012
2,567
The Royer oscillator is an all-or-nothing proposition, if the oscillator doesn't start up it's just a heap of burning parts.

Not a good place to be if you want 2kW of power.
 

Thread Starter

rahul411

Joined Feb 19, 2018
241
You're better using a Linear psu with a Transformer instead of a smpsu.
Took out the transformer and filter board from my diy linear power supply and connected it to the input of induction heater and same thing happened. Voltage droped down to 1.5V and i disconnected it as soon as this happened.
To be sure of i did not make any mistakes in board design i soldered everything in air and then tested it.
Here's a photo you might want to look at.IMG_20200210_142541.jpg
 

Dodgydave

Joined Jun 22, 2012
8,866
Your psu isn't giving enough current out, you need 2Kw from a 720W psu, !!

Linear psus are better at giving short pulses of high current , whereas a smps will trip or shut down.
 

Thread Starter

rahul411

Joined Feb 19, 2018
241
Your psu isn't giving enough current out, you need 2Kw from a 720W psu, !!

Linear psus are better at giving short pulses of high current , whereas a smps will trip or shut down.
So how much current this circuit even needs to start oscillating? Given that 30amps is not sufficient enough here.
 

Sensacell

Joined Jun 19, 2012
2,567
Looking at the photo- those toroid chokes don't look like they are rated for anything near 30 A?
The wire they are wound with looks tiny compared to the lead wires?

What are the specs on these?
 

Thread Starter

rahul411

Joined Feb 19, 2018
241
Looking at the photo- those toroid chokes don't look like they are rated for anything near 30 A?
The wire they are wound with looks tiny compared to the lead wires?

What are the specs on these?
Inductors were hand wound on a core i got from a online UPS rated for 3kVA.Originally it was 2mH and had some numbers on the back side but i can't find anything on Google about it. After removing the old wire i wound it with 51 turns of 24awg wire with 6 wire strands in parallel to allow for the current it is going to pass. I think it's enough to handle more than 30A
 

Thread Starter

rahul411

Joined Feb 19, 2018
241
These numbers tell me little about your coils.

You would need to actually know inductance and the core saturation current.
Inductance is 95 to 100uh not sure about the actual value because i don't have a good LCR meter for this. I used transistor tester which gives a reading of 98uh when connected, can't trust these devices really. And the core saturation current is unknown to me. As said, earlier the core belonged to a online UPS rated for 3kva so it must be a beefy one, i suppose.
 

tsan

Joined Sep 6, 2014
108
Are both mosfets IRF250P? The connections are strange on the image in post #11. Working coil should be connected to the drain of each mosfet. This is done with two yellow wires. One yellow wire is connected to the right side pin of the mosfet. On another mosfet, it is connected to middle or left side (can't see clearly). Should be the same position.

Also black "GND/0 Volt" wire from the power supply. It should be connected to source of both mosfets. It should be a same pin on both mosfets, but now it seems to be connected to different pins.
 
Top