Mains powered heatbed safety
I'm building a 40x40x40cm corexy and I am quite impatient so I want the heated to reach the target temperature as fast as possible, so I ordered a Keenovo silicone heater
It is a 220VAC 1200Watt bed, so I really want to make sure that it is safe to use.
I also bought a Crydom D2450 SSR.
Could someone tell me if the wiring in the diagram I made below is safe?
Do I need to put a fuse or some other kind of safety?
@franc-navarro-cifani your conection is correct and your new heater will work like a clothing iron, will heat extra fast. normally the heat bed heats with in 5 minutes with one grid (12v) and with in 2 minutes. using both grids (24v).
@CarlWitthoft you are right, however, it is a long time if you consider that I like to seat by the printer and watch the first layer to make sure everything is fine before I leave, so it reduces considerably the amount of time that I spend at the beginning of each print
heads up: one thing to watch out for: crydom and fotek SSRs are extensively copied and sold by unscrupulous Chinese manufacturers and sold on ebay and amazon for much less than the ~$15 retail each should cost. If you have a clone, it's NOT going to follow the official specs in terms of heat, capacity, and insulation.
Tom van der Zanden Correct answer4 years ago
The most important thing is the following: make sure that any exposed metal surfaces of your printer are properly grounded. This includes the frame if it is made of metal, or the aluminium plate you might use as your heated bed. In the event of a fault, having the metal surfaces grounded protects you from getting shocked when you touch the printer. If any surfaces are aluminium, be aware that the oxide layer that forms on aluminium does not conduct very well, so make sure that you get a good connection.
You should consider adding a thermal fuse or bimetallic switch to the heated bed so power gets cut in case the bed overheats (to protect against the relay failing closed or firmware errors).
In principle, if the wires used are thick enough (capable of carrying at least 16A), then there is no need for a fuse. Assuming you are in a normal European household, then the mains line will already have a 16A fuse. If your printer connects to the mains using a IEC C13 connector (kettle lead, very common) then you should have a fuse rated (at most) 10A somewhere because this is the maximum rating of the connector. For a very small amount of added safety, you could use a lower-rated fuse instead (for instance 7A) but this is not required. Your heated bed can draw up to around 5A so you can't use a fuse lower than (or equal to) that. If you are indeed using an IEC socket to connect your printer to the mains, then it might have a fuse holder (or try to find a socket that does).
Your image suggests two possible fuse positions. It would be advisable to place the fuse near the live/hot connection, but as European power sockets are non-polarized, this is essentially a moot point.
I didn't know about the oxide layer, thanks a lot!
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Carl Witthoft 4 years ago
The time to heat the bed is inconsequential compared with the time to execute the print. Rethink your priorities. For example, small changes in the infill percentage can have huge changes in print time.