Electrical circuits

Hello again people,

I have modified the size of my build plate from 1300 x 800mm down to 800 x 800mm. This makes things a lot easier as I only need to used 4 heatbeds to heat the plate instead of 8.

The problem I am having is connecting the beds together. I don't know what configuration would be best.

The bed I plan to use requires 12 V and 270 W with a thermistor resistance of 100k. I want to connect 4 of these beds together. If I connect them in series then I would need to draw out 1080 W (P = V*I where total voltage is 12 x 4 = 48 V and total current I is P/V = 270/12 = 22.5 A; therefore, total power is total voltage x total current = 48 x 22.5 = 1080 W). the thermistors don't have to be connected in series too, right?

Whether the beds are connected in series or in parallel, it's the same total power required. What I would like to know is which is better in this case? Series or parallel? One advantage I can see with series is that if one bed fails then it can be noticed straight away (because all the other beds are not on either). I should also mention that these beds will be powered via mains supply and connected to the board via an SSR (solid-state relay). Also, please correct my calculations if you see anything wrong.

Any help would be much appreciated, thank you.

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The (getting better) Noob

Zapadee zoopidee.

If you are going to run the beds from the mains then you need to use an appropriate voltage. For example, if your mains is 230V then for 4 beds in series they need to be 57.5V each.

The series connection is simpler, and as you say, it will be obvious if one goes open circuit. If the beds are well-matched in terms of resistance, it should work well enough. Using 4 beds rated at 230V (or whatever your mains voltage is) instead gives you the option of controlling them independently with an SSR each, if you find you need better temperature control.

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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 that the beds would require 57.5 V each however, it says that the bed is rated for 12 V. Therefore, wouldn't 57.5 V cause the bed to short circuit?

Thank you

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The (getting better) Noob

Zapadee zoopidee.

You can get silicone heaters custom made by some Chinese suppliers quite inexpensively, for example [alirubber.en.alibaba.com]. So sourcing 57.5V heaters may not be difficult. The same supplier advertises that they can make heaters up to 1200mm wide with no limit on length. So a single heater is another possibility.

Edited 2 time(s). Last edit at 03/30/2015 10:31AM 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].

Okay sounds good. So I can request for a specific voltage rating for the silicone bed?

I have a question regarding highly flexible high voltage cables, roughly how much does it cost for, say, a metre of such cables?

Thank you

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The (getting better) Noob

Zapadee zoopidee.

Quote
3DPrintingNoob
Okay sounds good. So I can request for a specific voltage rating for the silicone bed?

Yes, tell them the size, shape, voltage and power rating you want. Also whether you want a thermistor included in it.

Quote
3DPrintingNoob
I have a question regarding highly flexible high voltage cables, roughly how much does it cost for, say, a metre of such cables?

Here is an example: [www.rapidonline.com]. It's less than GBP1.00 per meter for a 10 metre length. Make sure you use a cable restraint at each end of the flexing run, otherwise it is likely to break at the terminations.

Edited 2 time(s). Last edit at 03/30/2015 12:39PM 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].

Okay perfect. Once again thank you!

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The (getting better) Noob

Zapadee zoopidee.

I thought I should add that the bed will be moving vertically, yes, however, it will be extremely slowly. So I don't think the cables need to be highly flexible. What I really need are cables that can withstand high temperatures, i.e. 150+ deg-C. Where would you suggest I can find some? I have found some suppliers but I thought maybe you would know better ones.

Thank you

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The (getting better) Noob

Zapadee zoopidee.

Quote
3DPrintingNoob
I thought I should add that the bed will be moving vertically, yes, however, it will be extremely slowly. So I don't think the cables need to be highly flexible. What I really need are cables that can withstand high temperatures, i.e. 150+ deg-C. Where would you suggest I can find some? I have found some suppliers but I thought maybe you would know better ones.

The rate of speed that the bed moves doesn't dictate how flexible they are. The amount they are moving does. Take a piece of solid wire and slowly bend it back and forth...after enough cycles it will break.

Stranded PTFE or silicone wire typically have the temperature rating you need. Just check with the manufacturer to see what it's listed at.

This cable should do the job, it's rated at 6A and 180C: [www.rapidonline.com].

Edited 1 time(s). Last edit at 04/07/2015 06:00PM 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].

Thank you! But I think I will need a wire with a higher current rating. I found a really good one with [lapplimited.lappgroup.com]. I am awaiting their reply on costs.

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The (getting better) Noob

Zapadee zoopidee.

Quote
3DPrintingNoob
Thank you! But I think I will need a wire with a higher current rating. I found a really good one with [lapplimited.lappgroup.com]. I am awaiting their reply on costs.

What voltage are you running the bed circuit from then? 6A @ 230V = 1380W which is more than you are likely to need.

Edited 1 time(s). Last edit at 04/08/2015 04:44AM 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].

I am thinking of using heat mats at 12 or 24 V as they can then be powered by the controller directly. At least, I assume they could be.

Thank you

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The (getting better) Noob

Zapadee zoopidee.