Anet board - MOSFET replacement?
To learn about printing, and to print the parts for a printer of my own design later on, I've ordered an Anet A8.
I just saw this video, Anet A8 3D printer Review. all you need to know. This guy recommends using an external MOSFET. I was wondering if using a relay instead would also make it safe?
Maybe one which I can use to power the bed directly through the mains. I've seen some forum posts here and there mentioning that it is possible to use mains power (230VAC over here) for your heated bed, but I have no idea if that is applicable to the bed supplied with the Anet printers. Maybe something like a http://www.digikey.com/product-detail/en/omron-automation-and-safety/G3NA-210B-DC5-24/Z918-ND/206389 ?
Do not use a bed which is not made for mains power with mains power.
Sean Houlihane Correct answer6 years ago
There are two areas of this design which seem to pose a risk of connectors overheating, the hot end and the heated bed. The heated bed runs at about 6 amps, 12 Volts. The hot end runs at a lower current, but can itself overheat if the thermistor stops providing feedback.
The problem in this design with the heated bed is mainly the connectors - they work OK when they are good, but can easily come a bit loose. This has two side effects. The bed heats less well, and the connector itself heats instead. Replacing the 2mm plug connector, and 2mm molex with direct soldered connections will help (the on-board mosfet seems OK with the current, unless you increase the power rail voltage).
A mosfet is a good solution for high current switching, the modules available have good screw terminals which should be OK for maybe 25A (well in excess of what you need). Mosfets are efficient when switched fully on, so there won't be much heating.
You would also use a relay (rated for at least 10A), but this will be noisy since the heater is switched repeatedly to maintain the target temperature. A relay also takes more power itself and will ear out if repeatedly switched under load.
Bottom line, if you have a good relay already, it is OK as a temporary (safe) solution. Longer-term a mosfet is better. Pay attention to the connectors at power supply, board (in and out) and heated bed. Using an additional mosfet for the hotend is maybe overkill.
Thanks for your reply. If I'm correct, the drive current on that SSR will not be that high, right? Also your last sentence is a bit hard for me to understand. You seem to indicate that a relay is good as a temporary measure, but then you go on to say that it is a good solution longer term as well. Did you mean MOSFET in one of the two cases? You also mention the connectors. Do you know of any way to improve the connectors? Sorry if I'm asking very obvious questions. The last time I dealt with electronics was in my physics classes almost 20 years ago. It's all a bit rusty.
Oops, correct. I'll edit... Solid-state relay and mosfet are interchangeable in this context. I was talking about an electromechanical relay... Connector wise, you want something with eyelet type connections on a M4 bolt, not a 1mm^2 pin with a spring contact.
The SSR you link is maybe not good for a 12 V load. You'll find mosfet boards on ebay rated for about 30A without cooling, for maybe $10.
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Tom van der Zanden 6 years ago
What kind of relay are you looking to replace what kind of mosfet, and what current and voltage does it need to deal with? There aren't really enough details in your question currently.