Can Sanguinololu 1.3A control 12V 200W heated bed ?

I use 300 * 400 aluminum bed.100W is too small

Hi !

It would not work. The 1.3a has a RFP30N06LE MOSFET with 47mOhms on resistance. Thermal Resistance Junction to Ambient is 80K/W.

200W Heatbed means 17A bed current at 12V. This gives you 12W thermal power loss at the MOSFET which means without additional heatspreader it results in theoretical >900°C at the package which definitely kills your MOSFET.

I'd recommend to replace the MOSFET with a type that has sufficient lower on resistance.
An option could be the pin compatible BUK954R4-80E from NXP, Farnell No. 2254217 it has a thermal power loss of approx. 1W which results in a device temperature of ~80°C which is 90°C lower than the allowed max. temperature.

Another one can be the sup90n03 from Vishay or SUP90N04-3m3P, SUP85N03-3m6P both also from Vishay and pin compatible. All of them need no additional heatspreader.

Hope that helps!

If you are interested in more, read this.

Edited 4 time(s). Last edit at 05/03/2013 01:07PM by STB.

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Grüße / Regards

STB

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Basics about MOSFETs

Why not run your heatbed through a relay/relais and use the Sanguino to turn the bed on/off and for the rest just pull the power from your PSU or a 2nd PSU if your current PSU doesn't support such a power draw?

I do it like that and all from one PSU, my heatbed heats up so quick, and my hotend also gets onto core temp within 5 minutes. I think heating hotend to 227º and heatbed to 110º takes at max maybe 3 minutes, where before it used to take about 10/15/20 minutes.

@ Ohmarinus:

Hi, I am interested how you connected the heat bed directly to your power supply. I am about to connect my heat bed and am a little woried about the mosfet.

Could you please explain in greater detail how to do this. In particular you mention running the heat bed through a relay.

[ EDIT ] Having just read over the latest Sanguinolu Version 1.3b - Updated April 4, 2012
They changed the MOSFET to SMT versions capable of 76A drain current.

Edited 1 time(s). Last edit at 06/08/2013 05:15PM by Mickman.

Hi Mick, sorry for my late reply, this is how I did it:

> They changed the MOSFET to SMT versions capable of 76A drain current.

This means nothing. The issue is not how much current can the mosfet handle, but rather how much heat it dissipates doing that. You need a mosfet with a very low Rdson.

But more than heat dissipation on the mosfet, I'd be concerned with the traces on the sanguino. You can easily find a mosfet with <=2mOhm Rdson that can drive your load with no or very little heatsinking. But I doubt the traces on the motherboard were designed to handle this current.

My suggestion would be to make an external board to drive the heatbed, something as simple as the attached schematic. You can make this on a perf board, costs about $3, and can drive the load from an extra pin without destroying your sanguino.