Help with electronic/electric setup

Hello everybody.

I'm writing my first post and I'm asking for help. I know it does not seem too "contributive", but I'm pre-new (yes, that's even before being new) into the 3D printer world and cannot help much nowadays. I hope I will be able to contribute in the short-term future.

Now, I'm designing a custom 3D printer (300x300x300) which with the requirement that it should be foldable and fit in a box for easy storage (that's my wife's requirement).

On the mechanical design part I have few doubts, as I've read a lot of forums and documentation and everything seems to be clear in my mind (then, we will see when the thing goes out of my mind into the real physical world...).

On the electronic/electrical area I have more doubts. I'm really bad at calculations of voltage, power, amperage, inductance, etc... So I'm asking for your help here.

My design will be centered around a DuetWifi controller with a 7" inches PanelDue, as I plan to make it full 24V and I like the WiFi and web interface thingy, together with the touch display. The DuetWifi and PanelDue power requirements are rated at 5V and around 500mA each one, so that makes 5W but let's assume 15W just in case something is connected to the USB port or for expansion boards.

Then it will have 5 stepper motors 17HM19-2004S (4 for the axis and one for the extruder) rated at Rated Current/phase: 2.0A, Voltage: 2.8V, Phase Resistance: 1.4ohms, Inductance: 3.0mH ± 20%(1KHz). I will be running them at 24V (I don't know if that's possible/advisable. Please advice) So I guess it will be 5x2A = 10A or 5x5.6W = 28W

For the heatbed I plan to use a RepRap MK3 300x300mm 480 Watt ALU Heatbed, with 24V power in order to reduce the needed amperage (I don't know if this is right/advisable. Please advice.) So I guess I will need 20A here.

I still don't know what will be the hotend I still don't know what will be the heater cartridge, but I will be using a 24V one. I've seen there is one with 40W and another with 80W. I guess that the more W the faster it heats and higher temperatures can be reached, but also I will need more Amps and it will consume more energy. My initial idea is to use the 80W, as in the future I plan to upgrade the printing head to a diamond one with 3 filaments. (I don't know if all that makes any sense. Please advice.) So it will be 3.3A

For the fans, I need at least one 24V (30mm) (0.08A) for the printing head and most probably another 24V (50mm)(don't have any other element to calculate amps) one for the DuetWifi/PanelDue. But I don't think they are much relevant for the power needs/calculations (Please advice.) Let's assume 1A or 2W, to play safe here

The thermistors I plan to use are the "Screw-on M3 Stud Thermistor" which has a built-in thermistor 104GT-2 for the print head, and then the Thermistor - NTC for the heatbed. Again I don't think that those are relevant in terms of power consumption/calculation. (Please advice.) (You have the specs for the 104GT-2 here [eu.mouser.com] and for the NTC here [www.reprap.me] ) (in the range of 0.1mA, so not really relevant, I guess)

So, all together will draw around 24V/36.3A from the power supply unit and 605W, so I guess that I will need something like a 750W power supply (adding a 25% margin) which at 24V results in 31.5A. And here is where calculations don't match, which I guess it's due to the Voltage of the PanelDue and DuetWifi being 5V... or a mistake in my calculations.

But in any case, I feel that the 750W power supply will be enough. I guess that something like this [www.sunpower-uk.com]

Now... am I missing anything? Am I completely wrong? Any further advice?

Thanks in advance for sharing your knowledge and experience with me!!

Hi again,

I've been reading some specs on the heatbed (MK3 300*300 Aluminium). It seems that it has a resistance of 5-5.5Ohms. That, at 24V, results in between 105W and 115W. Against the 480 that I took into account for my former calculations.

I am confused now (yes, more). Should I take into account the 115W or the 480W.

If the answer is 115W that would result in a total wattage requirement of 240W (= 300W with the 25% security margin).

Of course, finding a 24V/300W power supply is easier and cheaper than a 24V/750W.

Can someone help me here?

Thanks!!

Welcome to the forum! Don't worry about not contributing yet, we all start out as novices.

You will find a guide to working out the power requirements at [duet3d.com].

Here are a few comments on your particular figures:

- Yes you can use 24V power with those stepper motors. The power draw will be a little over 5 x 5.6W allowing for losses in the drivers if you run them at full rated current, so I suggest you allow 30% more than this.

- Bed heater: I suggest 0.4W per sq cm. So that's 360W for a 300x300mm bed. PCB bed heaters are usually under-powered. An alternative solution is to use a piece of cast aluminium tooling plate (e.g. Ecocast in the UK) with a silicone bed heater a little smaller than the plate stuck to the underside. This is a good solution for a bed that moves in the Z direction. It's less suitable for a bed that moves in the Y direction because of the extra mass of the tooling plate.

- Yes 24V power makes it easier to heat a large bed without the current getting too high. 360W @ 24V would be 15A, which is within the 18A rating of the Duet WiFi. The alternative is an AC mains voltage bed heater controlled by a zero-crossing SSR, but that brings additional safety concerns (grounding, insulation, strain relief).

Edited 1 time(s). Last edit at 08/31/2017 11:58AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks a lot!

So, can I regulate the amount of amps that I send to the heatbed from the duet? It's that done through the firmware? I understand that from your sentence "I suggest 0.4W per sq cm", where it looks like I can choose that amount somehow.

On the other hand I would prefer not to use SSR, to keep the electronic as simple as possible.

Finally, my printing bed will move on the Y axis, so I guess I will go for the
Print carriage (in 3mm alu, which I will try to reduce in weight as much as possible by machining it) + PCB heatbed + borosilicate glass. All that will move over 8mm rods will scs8luu and pulled/pushed by one stepper motor and a 2gt 20teeth pulley and belt.

The 0.4W/sq cm figure is what you should aim for when choosing the bed heater for your printer. So for your 300x300mm bed, look for a bed heater with a power draw of about 360W.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I understand now.

It's not easy to find a 300x300 heatbed rated 360W (most of them don't include any details on resistance, amperage or wattage, only voltage). So, I will proceed as follows:

1. I will buy that one.
2. With a multimeter I will measure the real resistance, and will calculate the wattage and the amperage at 24V.
3. If amperage is below 18A, I will run it through the DuetWifi directly.
4. If amperage is above 18A I will run it directly from the power supply. In that case I plan to use 2 power supplies, one (24V/240W/10A) for the DuetWifi, DuetPanel, extruder/s, steppers, fans, etc... and another one (24V/600W/25A)for the heatbed, controlled with an SSR by the DuetWifi heatbed output.


I hope the plan makes sense.

Quote
Otura
It's not easy to find a 300x300 heatbed rated 360W (most of them don't include any details on resistance, amperage or wattage, only voltage). So, I will proceed as follows:

just search for keenovo heaters in ebay or at net. they can do custom heaters and their quality seems pretty ok.

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Delta Printer
Duet 0.8.5 firmware 1.19

Gaou thanks for the tip!

I will have a look, but "custom design" together with "single unit production" usually equals to "high prices".

In any case, maybe there is something already done by them in bigger quantities and available on ebay as you mention. It's worth looking.

Thanks again!

Here's a slicone bed heater to that specification: [www.aliexpress.com]. You would need a flat aluminium plate to mount it on. I recommend using a bed plate about 15mm larger all round, to leave room for fixings and bed clips.

Edited 1 time(s). Last edit at 09/01/2017 10:12AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].