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szamelsz

over 7 years

Hi thanks for this project. I fixed the circuit for myself and its working perfectly. Just look there: http://www.mosaic-industries.com/embedded-systems/_media/instrumentation/opto-isolated-high-current-driver-digital-output-ssr/opto-isolated-mosfet-simplified-schematic.png You need the +12v or +24v from the psu, take out the R2 resistor and put the 5v regulator fed by +12/24v connected to collector of optoisolator. Thats all. But please check the datasheet of MOSFET what you are using, look at the Transfer characteristics, I used 75344G and for me the 5volts on gate is enought for 60A drain current cca.

JonnyBischof

over 7 years

I'm swamped at the moment. Plus I won't be needing to build any of them myself in the near future (v2 works fine for me) so it could take some time, sorry :( You could look into version 2, which should work fine as long as you read the whole description and make sure your setup matches with the version 2 requirements.

edis

over 7 years

When you think you can post updated design? I really love the idea of isolating printer from heated bed.

JonnyBischof

over 7 years

The problem with the design as it is, is that the "positive" wire coming from the heated bed isn't actually positive anymore as soon as the heated bed is switched on. I didn't see that, but it renders the whole thing completely useless because there is no more gate voltage for the mosfet to work with. I suppose that, what actually happens, is that the mosfet gets only partially switched on, up to a point where it's resistance is around the same as the heated bed (instead of almost zero) which leaves half of the heated bed voltage on the bed, and half on the mosfet. The problem is, it also leaves half of the power on the mosfet which blows it pretty much instantly... I know, it's not "half" but somewhere in that region. In any case, it won't work.

edis

over 7 years

Yay... I've tested this few weeks ago and got some smoke instantly, now there's a short in first diode and after reading this i'm no longer sure that it was my fault. Haven't noticed a flaw in design...

JonnyBischof

over 7 years

Hi Peter, Dang it, you're right. I didn't see that... I need to think this over. Your workaround is fine, but needing another wire isn't what I wanted. Sure that can be done better... I thought I used the same terminal blocks, maybe I accidentally picked the wrong 3D model o.O Thanks for pointing that out, and sorry for the inconvenience!

Peter1956

over 7 years

There is a mistake in the schematics. The Gate voltage is schorten by the MosFet. The MosFet burns out in a few seconds. You need V+ from the Heatbed Power on the Voltage divider (R2/OC/R3). Then it works fine. By the way, the X2-terminal is to small. Yon need a bigger one like from the V2. Peter

JonnyBischof

almost 8 years

Hi koyashi, I don't know about the ANET A8 (or any Prusa i3) in detail, but it should work without any problems as long as you get the right components for the right voltages. You can also use two of these in parallel with the same external power supply because they are isolated and should not interfere with each other. Best regards, Jonny

koyashi

almost 8 years

Hello Jonny. I have a ANET A8 and was wondering if this is suitable for both the heated bed and the extruder? Just wondering because I wanted to order enough parts from mouser to build 2 of them. Thanks.

PROTOTYPE: Heated bed mosfet relay V3

By JonnyBischof

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