nichrome heated bed
September 24, 2012 10:04AM
I am a little unsure of a few things regarding the nichrome heated bed.
Its the electrical side which I am not familiar with, I have used a calculator program to work out what wire I need.
I was planning on doing 8 rows of nichrome making my length required 215cm (my build platform is 290mm).

According to the calc below I need 18 guage (AWG) 1.016mm at 12 V to get 149C.
Current required is 4.07
Watts required is 48.84W
Resistance per foot 0.4219
Total resistance 2.9884583

[www.jacobs-online.biz]

Can anyone confirm that I have not made an error with that?
I presume I need to aim for a maximum bed temp a bit higher than abs bed temp - 149C do you think this is about right?
Do I need a PID controller or is a thermistor fine? Is this thermister suitable? G550 NTC thermistor,10kohm at 25deg C
I am looking at the schematic on the mendel heated bed page: [reprap.org]
I am following it but instead of using ladder of nicrome and crimping together. I think it will be easier to use 1 solid piece.
It says: 'There are three copper wires, with two ladders of nichrome between them.' For what reason have they done this?
Sorry about all the questions. If they made a heated bed the size of my platform I would just buy one.

thanks in advance

Edited 1 time(s). Last edit at 09/24/2012 10:23AM by dave584.
Re: nichrome heated bed
September 24, 2012 11:22AM
are you sure about using Ni-chrome wire heated bed? I've had issues with hot spots in Ni-chrome, where 1 spot gets hot enough to melt! I now have been using exclusively use pcb copper trace beds. resister beds seem to work, but don't get near as hot. not to mention the fire hazard associated with Ni-chrome. if heated pcb bed goes thermal on you the trace will likely melt and that will be the end of it.

can you provide some more insights to your design such as layout, protective layers, how you are mounting it , and thermal controls? you definitely need PID. otherwise Ni-chrome will heat up way faster than the heat can be transferred.

I'd hate to give you some advice, not knowing how safe your setup was.
Re: nichrome heated bed
September 24, 2012 12:05PM
thanks for the reply.
My plans for heated bed top to bottom:
borrosilicate glass top,
thermal grease,
2mm alu sheet,
nichrome attached to bottom of 2mm alu sheet with kapton tape, I
2 layers of alu foil for added heat insulation,
1mm viton rubber sheet insulation,
1mm alu sheet screwed through to the top aluminium sheet to hold it together.

In terms of how safe the setup is, with regards to insulating live nichrome I would use at least a couple of layers of kapton tape to provent it shorting on aluminium.
I was going to use a PID to control the temperature. Do you set temp through the reprap software or is it done on PID?
Mounting the normal way with smaller lower 4mm alu sheet and the heated platform attach to that. See pic bellow, the platform sheet is not shown. (its upside down)

I can't think of any more safety aspects but I am sure you can tell me something I have missed?
I would be open to using another method as you say copper trace beds would be good but I did a search and could not find a copper pcb trace that was big enough for my bed (275x290mm). Any suggestions?
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Edited 3 time(s). Last edit at 09/24/2012 12:23PM by dave584.
Re: nichrome heated bed
September 24, 2012 03:49PM
Personally I'd go for a resistor based bed - they're so easy to make, just epoxy all the resistors on the bottom of an alu sheet, and wire them up. Mine tops out at 144W, which keeps it easily at 70C with a light breeze, but could probably do an awful lot more if I bothered to insulate the bottom of the bed.
Re: nichrome heated bed
September 24, 2012 05:12PM
resister bed may be a good option for the larger sized bed, also if you do decide on ni-chrome, get the glass insulated. if pid glitches then kapton tape wont be melted thru as fast. also put aluminum foil over kapton tape, and use fire retardant insulation. think sandwich and bolt everything together, at the very least along the corners. also place a thermal fuse inside, possibly rated 20deg C higher than your highest temp. your printer will be on for possibly over 4-7hrs for larger prints.
Re: nichrome heated bed
October 03, 2012 06:03AM
I've been using nichrome wire for nearly a year now without any problems and just posted a Nichrome Wire Heated Build Platform Tutorial on my blog.

[airtripper.com]

I used exhaust heat wrap as a good thick insulator to protect the 3d printer below the heated platform.

I went for the nichrome wire option because it was the cheapest and best solution for my printer at the time.



Mark

Edited 1 time(s). Last edit at 10/03/2012 06:05AM by Airtripper.


Blog - [airtripper.com]
Extrude Filament Force Sensor - [airtripper.com]
Re: nichrome heated bed
October 03, 2012 08:19AM
is that ni-chrome with wood directly below it. is that a fire hazard in case PID fails? do you have any thermal cut off fuse?
at bare minimum i would sandwich the bottom with a piece of glass in between the wood, and for further safety not run that machine again without a thermal cut off fuse.
Re: nichrome heated bed
October 03, 2012 09:37AM
There is a thermal barrier between the wood and the nichrome wire, however, the printer is always monitored during use. Since the entire printer is made of wood, there is no part of it safe from failures, from either the heated platform, hot end or electronics.
I'm the only user of the printer so the risks during usage are always controlled.


Blog - [airtripper.com]
Extrude Filament Force Sensor - [airtripper.com]
Re: nichrome heated bed
October 03, 2012 09:42AM
i understand, a thermal fuse is less than 2$
Re: nichrome heated bed
October 08, 2012 09:29AM
dave584 Wrote:
-------------------------------------------------------
> I am a little unsure of a few things regarding the
> nichrome heated bed.
> Its the electrical side which I am not familiar
> with, I have used a calculator program to work out
> what wire I need.
> I was planning on doing 8 rows of nichrome making
> my length required 215cm (my build platform is
> 290mm).
>
> According to the calc below I need 18 guage (AWG)
> 1.016mm at 12 V to get 149C.
> Current required is 4.07
> Watts required is 48.84W
> Resistance per foot 0.4219
> Total resistance 2.9884583
>
> [www.jacobs-online.biz]
> .html
>
> Can anyone confirm that I have not made an error
> with that?

That calculation does not take into account the total heat loss from a heated build platform, it only applies to a bare wire in non-moving air. With a build platform, you're not going to achieve anywhere near 149C with 48 watts. I'm running two 20x20 cm heated beds, both bottom-insulated. One is 80W and it can just barely reach 110C. Other is 180W and it heats crazy fast compared to the other one (haven't tried the maximum temp since I'm concerned about melting the ABS bits in the Y carriage). Your considerably larger bed would need larger wattage, probably at least 150W to comfortably reach ABS printing temperatures.
Re: nichrome heated bed
October 08, 2012 10:52AM
I=V/R
12v
--------------------------------- =4.amps (4.015448366805051A)
Total resistance 2.9884583ohms

power is V*I
12v*4A=48watts

BUT...

use glass threaded ni chrome not the wire only. ni chrome can have hot spots, so some areas will use more current.

Also you should never have it on long enough to get red if it is against a surface. it gets red and emits light about 500c, it should be pwm and may require more power because you do not want it on 100% of the time. wood burns about 320C
Re: nichrome heated bed
October 10, 2012 12:48AM
I can not get Prusa MG2 to exceed 105 C often (115C with much difficulty) and not using a fan (light fan < 65C). I think it draws around 40-50 watts like your numbers say. So 150C seems difficult to me unless you insulate the bottom. Did it work yet? I love the Nichrome idea, it so cheap and simple.
Re: nichrome heated bed
October 10, 2012 12:31PM
i love your idea

simply cos i had a thought of it too, my base build size is going to be about 2feet x 2feet. in theory, my nichrome bed, the wires is about 1 cm spaced (yours look like 1 inch spaced?) and is similar to your version of glass plate with bottom thermal insulation. grinning smiley

and my machine frame is also WOOD ! grinning smiley

Edited 1 time(s). Last edit at 10/10/2012 12:31PM by redreprap.
Re: nichrome heated bed
October 10, 2012 05:15PM
My nichrome wire heated bed is about 140 watts and the wires are an inch apart, ideally for window glass, the wires should be a bit closer for a more even heat spread. The wire spread might not be a big deal for a small bed like mine but for a larger bed, I'm not sure what the effects will be.

You can't go more than 100 degrees C with this glass I think, but since I only use PLA, it does not matter to me. Ceramic glass or oven glass is good up to 800 degrees C and easy to get cut to order on-line in the UK.

Tomorrow I'll be testing a testable, resettable thermal cut out safety switch which goes further than just adding a thermal fuse to the heated bed. This should satisfy an earlier poster to this thread smileys with beer. It should be my next blog post in a week or two.
Re: nichrome heated bed
October 11, 2012 06:45AM
awesome, can't wait for the update!
Re: nichrome heated bed
December 11, 2012 08:21PM
Ok! I'm doing one of these!!!
Re: nichrome heated bed
August 14, 2013 05:42PM
I am hoping that this is the place to figure this out... I have read every DIY article on making these NiChrome heatbeds and keep coming back here to read the tips and alternative ways to achive an accurate heat bed.

I will try to keep it as simple as possible, I think I am a little bit over my head on some aspects accomplishing this on my own.

The size of the bed is 24" x 36" (rather large)

The layers of the build from top to bottom

- 3mm Tempered Glass (for higher temp if need be)
- 3mm Aluminum 5052
- NiChrome wire on base of previous aluminum (initial was going to use 80 20 - still debating on gauge)
- 3mm Aluminum 5052 (for leveling and heat sheild for very few plastic parts, 99% of the framing is aluminum. I mostly worried about stepper belt)
- the surface is moved by V-Rail (rubber wheels) aluminum extrusion (Inventables.com)

the Controller card that I have is Azteeg X3 Full Featured 3D Printer Controller v1.1 with the Expansion Shield. Which allows for 2 heat beds, so I sepperated the build platform in to two heat beds (attached image). From what I was told this card handles 12v 20amp total and I have two extruders along with the general x,y, and z settpers. I am using a 500watt power supply from makersgeek.com to have as much power as possible.

The main questions that I am getting at...

I wanted to stick to NiChrome wire, I was initially intreaged about Clad resistors.

- The length of each bed if the wire was one piece (for each bed) is 13,753.63 mm or 40.14 ft.
(I have seen in examples DIY where the wire is cut to certain resistence and laid out in rails {which would me back to layout image})

- I used the calculators and equation regarding finding out power consumption. Though if it were to be one wire, who knows what power supply I would need for 40 ft for each bed... I pretty sure that exceeds the controller card. So I do think cutting the NiChrome wire in to segments is the best route.

- I am worried about to much power consumption
- heatting the NiChrome wire to fast
- Generally any advice would be helpfull

Thank you for any of your time reviewing this, I have hit a road block and wanted to ask people to see where I am wrong and where I am not...


p.s.

There is information within the image on length and segments, but it is for one continues piece of wire.

Edited 1 time(s). Last edit at 08/14/2013 05:46PM by bishupz1.
Attachments:
open | download - NiChrome Layout - 20 mm spacing - Final Version.jpg (562.4 KB)
Re: nichrome heated bed
August 14, 2013 06:50PM
When you say heating the nichrome too fast, what exactly do you mean?

BTW, 1000 series aluminium is more heat conductive, is there a reason you chose 5052?


Yvan

Singularity Machine
Re: nichrome heated bed
August 14, 2013 07:32PM
Initially I was going to use the 5052 Aluminum sheet for the build surface, but after learning that most pieces of aluminum are not milled and have variation upon the surface I went back to glass. At first Borosilicate glass, but for cost reasons tempered glass is fine for now. I did not know that 1000 series aluminum is a better conductor, most of the articles I have read lead to the generic statement including 5052. I did talk with a manufacturing company eventually after I learned enough to be able to convey information properly. The lowest series number that the company I am most likely purchasing from is in the 3's. I am not exactly sure of this series full number at the moment, but is series 7 with the letter "O" for softer aluminum is offered from this company online; one of the better ones I have found.

One of the main articles that I am referencing the segments of NiChrome wire from is here

[airtripper.com]

There are others, but none of the others really deal with keeping the wire its' self within a certain range of electricity which I need to do. So my end solution was to make both heat beds ribbed like the example within this tutorial, 20mm spaced apart for consistency within the temperature. So each bed would be 2' x 1.5' in theory, with two rails of segmented NiChrome wire. Each segment would be 8", which I don't have any NiChrome 80/20 wire to test what the resistance would be, but I can generalize from the web page information (https://ultimachine.com/content/31-awg-nichrome-wire-0). Which it is 8 ohm per foot, so 6 ohm for each segment. There are other gauges I have looked at, and bulk NiChrome wire from ebay that is much more affordable at a higher gauge (smaller wire - just in case someone else is reading). The layout I attached previously will change of course, but I wanted to chat with people to make sure I am taking the proper course of action. Basically I am trying to make sure I making a good decision from people that have more experience with accomplishing this feat. I am not the best at electrical aspects, I am more of an artist/programmer so everything else about these wonderful toys makes much more sense to me. It was a long time ago I worked electronics and at a very basic level.

The comment on heating the wire to fast is in regards to things that I have read where people have burnt out the Capton tape or even the wire from either to small of a gauge or too much electricity. More of a precautionary statement, sorry for the distraction on the topic I posted. I just don't want to calculate things wrong or end up damaging the controller board.
Re: nichrome heated bed
August 15, 2013 01:16AM
Wow, that is a big heated bed. I would expect distortion of the glass and aluminium due to heat might be an issue?

Some alloys will conduct quite a bit better than others. Basically, the less is added to any metal the better it conducts heat or electricity as a rule. 1000 series is almost pure, hard to beat for heat dissipation.


Yvan

Singularity Machine
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