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Power Wiring

Posted by FA-MAS 
Power Wiring
December 27, 2017 02:22PM
Designing a new printer and wanted to include a couple of things that weren't on my current.

I'd like to use a Mean Well power supply, an inlet, fuse, and switch.
I would like someone to take a look at the drawing below and tell me if I'd wire it correctly.

I also need help choosing a bed heater and method to power it.
I'll be heating a relatively small build plate. It's a 130mm x 130mm plate of 6mm thick Mic6. I intend to use a 100mm x 100mm silicone heater.
I guess I need help determining what power is going to heat that plate quickly enough, and power it properly.
I need help determining if I can run that heater directly from a Duet Wifi or if I'll need to connect it to mains.

The power supply I intend to use is a 350 watt supply, that can supply up to 14.64 amps @ 24v
I'll be running your average Duet WiFi, hotend, motors, and fans
I'm estimating that running the system, bed heater excluded, would take about 8 amps

Any suggestions?



Edited 2 time(s). Last edit at 12/28/2017 02:38PM by FA-MAS.
Re: Power Wiring
December 29, 2017 12:49AM
I hope the bed is connected after the sw/fuse !
You MUST put a thermal fuse in contact with the heating element unless there is already one embedded in it (as it should be !).


"You failed to maintain your weapon, son" (Harry Brown )
Re: Power Wiring
December 29, 2017 06:16AM
I'd connect the power line ground to the printer's metal frame (if it is metal!). The bed moves, so there's always a possibility of wires getting pulled or broken and shorted, so I added an electrical fuse to that circuit.

Here's how I wired UMMD, my coreXY machine:




Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Power Wiring
December 29, 2017 07:47AM
Most definitely, I had planned to connect the frame to ground. The design is entirely metal, with the exception of the holders for the endstops (opitcal), the endstop flags, and the hotend carriage. The bed will only move in Z direction. I had still planned to ground it also, even though everything is metal.

That diagram clears up a couple of questions I had.

1. I had planned to connect the heated bed after the fuse and switch, either to the output terminals of the switch, or to the terminals on the power supply. It shouldn't matter right?

2. Going off of dc42's blog (where I extrapolated that drawing), it said to use a 6.3A fuse. The power supply I'm planning to use is a Mean Well LRS-350-24. The datasheet says it can draw up to 6.8 amps. If I were to use that fuse, and put it under a load higher than 6.3 amps but still under it's rated 6.8, wouldn't that fuse blow? I mean, I don't really plan on putting the power supply under that heavy of a load, but I would have thought to go with a 7A, like what Dentist's drawing shows.

3. You also answered my other question about fusing the bed heater. Here's my question, Say I originally chose a 7A fuse for everything but the bed heater like in my drawing. I then connect the bed downstream from the fuse. Lets say the bed heater is 300 Watt 120V, that would draw 2.5A. Could I then just increase the value of the fuse to a 10A fuse? Typing this out now, I'm thinking it would probably be better to fuse it separately, so if one part causes the fuse to blow, the other would be isolated.

3. Any suggestions on how I can figure out how many Watts I should choose for the heater? I'll be heating a piece of Mic6 6.35mm thick, measuring 130mm x 130mm

4. Suggestions for other parts, SSR, Thermal Cutoff Switch, etc?

Also Digital Dentist, what's that 3rd fuse there for, the one between the 7A and 10A?
Re: Power Wiring
December 29, 2017 08:12AM
1) it would be better to run it to the switch terminals. Daisy chaining high current loads is generally a bad idea.

2) You want to size the fuse to allow some margin over the power supply full-load draw. I'd probably go for 8A or 10A. Meanwell supplies have their own internal fuses, usually.

3) I prefer to separate the circuits because you can fuse each appropriately. If the bed needs 3A, give it a 4A or 5A fuse.

3) 0.4-0.5W / cm^2 will heat it up quickly and allow the PID control to regulate it easily. That bed size is small and doesn't need a very high powered heater. You have 169 cm^2 so I'd look for a heater that's around 75W. With such a low powered heater you could just run it from the DC supply and save the messing around with line power. The controller board MOSFETs should easily handle switching power to that load.

4) The type of TCO I used is a single-use device like a fuse. It's operating temperature (184C) that is about 24C above the highest temperature I ever intend to operate the heater (160C). Different type TCOs vary in how you select operating temperature, so check the data sheet.

The third fuse is there for a 500W enclosure heater that I am (still...) in the process of adding. Progress has slowed to a crawl lately, partially because my work room is in the basement and it's cold down here!


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Power Wiring
December 29, 2017 08:20AM
Quote
the_digital_dentist
3) 0.4-0.5W / cm^2 will heat it up quickly and allow the PID control to regulate it easily. That bed size is small and doesn't need a very high powered heater. You have 169 cm^2 so I'd look for a heater that's around 75W. With such a low powered heater you could just run it from the DC supply and save the messing around with line power. The controller board MOSFETs should easily handle switching power to that load.

This was actually what I was looking for. My math showed that I needed about a 70 Watt heater (though I did the math at 100mm x 100 mm), I'm sure it would be close to 75W if I did it at 130x130 (the actual plate size). If I went with that, it would draw roughly 3.2A on 24V. I figure that the rest of system would take roughly 6A-8A to run. That would fall far below what the power supply could handle, the Duet WiFi wouldn't have a problem with that either.
Re: Power Wiring
December 29, 2017 02:26PM
So, checking with Mean Well if that power supply has a fuse, if it does, I needn't add one correct? If it doesn't I'll add one.

Looking to get a custom bed heater made, looking to go with 24V and 100W may be the lowest I can order. It would obviously draw more power, but also provide more heat, and would heat up the bed quicker? Shouldn't be a problem right, so long as the power supply and Duet can handle it correct?
Re: Power Wiring
December 29, 2017 04:24PM
Higher power in the heater just means the bed will heat up faster and PID will be able to regulate temperature easily. Should be fine.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Power Wiring
December 30, 2017 10:05AM
Quote
FA-MAS
So, checking with Mean Well if that power supply has a fuse, if it does, I needn't add one correct? If it doesn't I'll add one.
The internal fuse will be rated for the maximum power the PSU can supply, you should add an own fuse for the heat bed that is rated for it, the internal fuse of the PSU might set in to late.


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