Switching 480W DC with MCU

[rthorntn]

Hi,

I want to switch on/off a 48V DC @ 10A joule heater with a MCU, I guess I could use two 5A cartridge heaters.

Will these finds on Element14 work (Filter: Contact Current = 10A    Contact Voltage VDC = 125V):

Honeywell SZR-LY2-N1-DC24V
Omron LY2I4N 24DC / MY2IN124DC(S) / MY2IN-D2 24DC(S)

The device has very noisy fans and so the relay click isn't an issue.

The mechanical lifetime of the relay contacts only needs to be around 60000.

Thanks.

Richard

[JS]

What other rails do you have available?

You could use Mosfets, might be easier to deal with, there are logic level mosfets if you don't have other intermediate rails. Or you could use optocouplers for reliability and switch on the 48V rail but you probably want fast switching to avoid heating the mosfet, so driving the gate hard to the appropiate voltage and back to ground is optimal. Mosfets are usually prefered over relays as they waste less energy and dont have arcs at the contacts.

In any case, clamping the load with a diode as if it is inductive is a good idea to avoid any kick back. You don't really need 10A diodes but don't go with too small ones either.

JS

[rthorntn]

Thanks JS!

I would probably have either a 12v or 24v rail as well.

Could you please do me a huge favour and point me to a Mosfet example that could handle that?

Cheers
Richard

[JS]

12V rail is great to work with mosfets.

From my bin I could choose an IRF1010 which should do the job with 5V at the gate and even better with 10V or 12V. That doesn't have too much voltage rating to spare but switching fast and not often will work without too much heat at all.

There are many to use, run your parametric search on the usual places and you will find a lot of options, some much smaller than a to220...

JS
 Ps a circuit like this could do. Minor tweaks to ensure voltage to the mos doesn't get over the ratings but a resistor and a zenner could do.

[rthorntn]

Thanks JS, I was going to ask for an example circuit based on a IRF1010 to switch a 48V heater on/off with a 12V "trigger" voltage, I'm not sure if your "Ps" meant you were going to attach something?

Ps a circuit like this could do. Minor tweaks to ensure voltage to the mos doesn't get over the ratings but a resistor and a zenner could do.

[JS]

It did but it seems not be working, I'm trying to attatch it here but it's hard, it doesn't seems to upload the pict.

https://goo.gl/images/L6o4hL
In any case spmething like that, but you need differrnt supplies for the load and opto coupler to the gate as your load voltage is too much for the gate, hence 12V seems ideal.

JS

[radiokot]

Do not forget about the cooling of the mosfet. As the temperature rises, its resistance increases in the open state(Dependency graph attached).

IRF1010 Rds(on) = 0.012Ω

10A:
P = I*I*Rds(on) = 10A*10A*0.012Ω = 1.2W stand out at the mosfet in the form of heat.

And through the mosfet and the comparator, you can monitor the breakage (malfunction) of the heater.

[radiokot]

Heater break detection circuit