I'm looking to wire up a relatively simple induction heater (cheapo Chinese board you can get on Amazon/eBay). What I want to be able to do is turn the heater coil on for some pre-specified amount of time before turning it off again, and repeat.

My initial plan was to wire up the 48V power supply through a relay of some sort into the heater, and drive the relay coil using a 555 timer circuit. Problem is, I can't seem to find something rated for a high enough contact current at 48VDC (that doesn't cost in the range of $100). Can anyone point me in the right direction? I'm hoping for something in the range of 20A or higher. Thanks.

 

You could use a MOSFET and that could be easily directly driven by the '555.

 

Wow. I got so fixated on "relay" that I forgot that a power MOSFET is a thing. Thanks; this should be an easy find at the local electronics shop.

 

If your heater needs 20A, make sure the FET is rated for a continuous current several times that and has an adequate heatsink.

 

Thanks, Alec_t. Best I can find is 30A continuous at 100V. I can probably parallel a couple of them, right (I'm thinking probably 3 or 4 to be safe)?

I've got some reasonable heatsinks lying around, and a couple of 120mm fans I'll figure out how to bolt on. It won't be the prettiest-looking project

 

Here is PWM using LM324 that looks capable of 0 to 100% control.

http://www.pcsilencioso.com/cpemma/pwm_erg.html

 

Why not simply turn the AC supply on/off with a switch or a relay if you need automatic/timed control?
The current demand will be less.
Max.

 

Max is correct. I misunderstood your request. I thought you wanted to switch your board off and on PWM style.
What you want being closer to appliance timer, just shorter duration? Several seconds to minutes on before off?
(Darn. Caught up making an assumption on an I'll defined end goal)

 

Best I can find is 30A continuous at 100V.

www.irf.com/product-info/fact_sheet/farnell/10527.pdf

 

Max is correct. I misunderstood your request. I thought you wanted to switch your board off and on PWM style.
What you want being closer to appliance timer, just shorter duration? Several seconds to minutes on before off?
(Darn. Caught up making an assumption on an I'll defined end goal)

Yes, basically an appliance timer. I will try it on the AC side, since that's easier, but I don't know how the power supply is going to like being switched on and off like this. I'm looking to cycle it on for a few seconds after maybe 5-10 seconds of being off, and repeat. I'm not even sure the induction heater will function if I wire it this way; apparently, it fails in a rather spectacular way if the voltage starts out low and ramps up rather than immediately switching to 48V.

www.irf.com/product-info/fact_sheet/farnell/10527.pdf

Thanks for the link. I know there are higher-rated MOSFETs out there, but my local store only has 30A MOSFETs. I was hoping to just have the parts now, rather than waiting for shipment from Mouser or similar.

 

Agree with Max. I made a microwave oven transformer (MOT) based spot welder several years ago. I switched the AC using a zero-crossing solid state relay (SSR) and timed that with a typical LM555 timer to get the number of cycles I wanted (about 170 ms @ 60 Hz = 10 cycles). The relay I used was scavanged from a commercial refrigeration unit. Its Crouzet equivalent is 84134000. The data sheet is a bit hard to find, so here

John