DIY heated bed questions

[Extrudo]

Hi all, I'm interested in creating a heated bed, as here in the UK I can't find any available that will fit my printrbot simple 1405. Smallest I've seen is 210x210mm, which is too large. I've seen loads of posts talking about DIYing them but several things still puzzle me even after searching for answers. I'm sure they are dumb questions but I don't want to end up frying anything so best to ask first.

-How do people regulate the temperature of their DIY beds? Is this simply done by using Repetier software after plugging a DIY heated bed and a 100k thermistor into the printrbot circuit board?
-I want to use this 500W atx psu I have spare. Is it suitable please? Pic attached below.
-I read somewhere that you need 105C rated thick wires to take the current when attaching to a bed? Would standard UK 3pin power cables work for this? I think they are only rated about 80C. Is the 105C type crucial?
-I've connected the green+black power lead wires of my PSU so it powers up without a switch. I believe the yellow+black 4 pin plug can be plugged directly into the printrbot circuit board. I read somewhere that you need to put something on the wires to make it all safe. I can't find where I read this so does anyone know what might be needed?
-My plan is to use nichrome wire and create a 6x4" bed. Is a certain gauge of wire required or will thin stuff from a old hair dryer work fine?
-I've read you can't use normal solder on nichrome wires. I have some silver solder (I've made silver jewellery in the past) so will this be suitable to attach the nichrome to the power cables?

In retireejay's post here:
viewtopic.php?f=6&t=3922
... the pic shows the heated bed connector has 4 pins. Which pins are which? Is it 1x positive 2x ground 1x negative? Do all 4 have to be connected or can you just use two pins?

Thanks for any assistance.

[RetireeJay]

[Extrudo]

Thank you for the comprehensive reply Jay. I will study up on all the things you mention.

I forgot to mention that I have a Rev D board.

[Extrudo]

I've bought a 3mm thick piece of aluminium sheet and cut it to the custom size I want (6x10 inches). I've already done an X-axis upgrade so I can modify that easily to fit with my plans below.

I'm no stranger to DIY projects, and I can solder, etc, fairly well, but I am always nervous when it comes to electricity. There are lots of unknowns in my build plans at the moment so I'd like to ask a few more questions which may help me narrow these down if you can indulge me please. Please forgive any stupid questions.

----

I want to print in PLA only (no plans to ever use ABS), and have the heated bed no hotter than about 80C. I've bought some kapton tape (rated up to 280C), a 100k thermistor (rated up to 300C) and an IR non contact heat gun to check temperatures safely.
I plan to harvest some nichrome wire from an old hairdryer or old toaster, but as I have not done so yet, I don't currently know the gauge or length I'll have. I also plan to use silver solder to attach the nichrome wire to some thick wire leading to a psu 12V lead (I have now tested this silver solder with a small piece of nichrome I had and it attaches to the wire with a strong bond very well).

I plan to eventually etch some channels underneath the aluminium to sit the nichrome wire. Before putting in the wire I will attach kapton tape to the bottom of the aluminium, to stop any contact between the two, then tape over the top of the wire with more kapton. This should hopefully insulate it all.

A piece of picture-frame glass (2mm thick) will go over the top of all of this, however the aluminium is unfortunately not 100% flat, and is slightly curved directly in the middle of the sheet, sagging by about 2mm. I guess I need to put something in between this and the picture-frame glass to make a better thermal contact seal? And to make sure the glass doesn't break.
I've not been able to think of anything to do this, except maybe some wool, which seems to have a high ignition temperature of 600C, so if all goes to plan (80C max temp) it would not get anywhere near the level to cause any fires or other issues. Maybe someone can think of a better material for this job?

I don't want to be blowing up my printrboard by directly plugging my 500W psu into it, I'm very nervous about this after seeing all those images of people's connectors melting, so thought it best to use the original power supply that came with the printrbot to keep powering it, and use my 500W psu to power the heated bed separately. This means that I won't be plugging anything extra into the printrboard except the thermistor, of course this means that the printrbot will have absolutely no control over the heat produced by the bed.

Will it be safe to do this, if I get the correct length and gauge of nichrome wire to create enough resistance that it should naturally never get any hotter than around 80C.

I would also like to add an led to show power is on/off to the bed, so I think I will need to add a resistor for that? But maybe this would mess up the nichrome wire temperature? I am unsure of this part. Not sure what sort of resistor might be required for this. Maybe a high rated one with a heatsink is neccessary?


Current unknowns:

-Thickness and length needed for nichrome wire with enough resistance.
-Will picture frame glass warp and affect prints when heated to around 80C?
-Will the 3mm aluminium piece of the size I'm using warp and affect prints at around 80C?
-Can I add an led to show power is running through the bed, without messing up the temperature limit of 80C I plan to acheive?
-To connect up... the PSU, to thick wires, to nichrome wire under the aluminium, can I just cut the ends off two molex connectors from my PSU and attach the yellow 12V lines to spread the load and make sure no wires melt or have issues?

Thanks for any assistance.

[RetireeJay]

[Extrudo]

Thank you again Jay. Lots more for me to study up on and take into account. I think that relay might be a good idea for me. Also sounds like bending the aluminium slightly might be a better option than using an insulation layer so I will see how much clearance I have underneath to play with and try to find a piece of steel( or something else solid) that would serve this purpose. I want to take my time over this, but sooner or later I will start piecing bits together and put up some photos of my progress, so hopefully (maybe) helping others out who may be in the same situation.

[Extrudo]

Would this be a suitable SSR please? Or is 40A too much?
http://www.ebay.co.uk/itm/1-2-4-SSR-40D ... 0742439711
or maybe a lower rated 25A one:
http://www.ebay.co.uk/itm/SSR-25-DA-Sol ... 1508454189
I can't find any for 12V, but it says its variable so would this even work?

I see in your post here:
viewtopic.php?f=80&t=6303&p=42143&hilit=heat+bed+relay#p42191

...that a diode isn't needed if using an SSR. Your diagram shows one so I assume I should just ignore that part.

[RetireeJay]

[Extrudo]

Jay, thanks yet again for your patience and great info. It's going to be a pain to try and find a relay over here in the UK I think then. I've looked at the car part type relays but they dont usually show the pinouts, so it looks like a guessing game to know which pin does what. I will keep looking for a suitable ssr. All I've seen so far for 12V are 10A or lower rated relays.

[thawkins]

[Extrudo]

Thanks thawkins. Some contact connectors would be a good idea with that I think. Also I think I read somewhere that you said these automotive relays 'clicked' so I would need to add a diode to stop the flow of the current in it's tracks as presumably this is a mechanical relay?

[Mooselake]

From another thread PB may have changed the recent firmware to use PID for the heated bed. This means rather than staying on until the bed is at the right temperature, and then turning off, it will rapidly switch the power off and on and try and find the amount if on time that keeps the bed at the set temperature. SSRs handle this just fine, but mechanical relays will have problems. You can recompile and reload the firmware (there's no need for PID with the print bed, and it can stress the Printrboard MOSFET).

Kirk

[RetireeJay]

[Extrudo]

The mechanical ones look like they don't need a heatsink so I assume they don't get that hot. Does the diode need cooling of some sort instead?

This one seems to come with the wiring and a diode, although they don't seem to say what sort of diode it is:

[RetireeJay]

No, the diode won't need a heatsink. It only dissipates power in very brief bursts when the Printrboard turns off the current to the relay coil.

I'm not sure, but it looks like the diode is correctly wired in to the "wiring loom" provided with that relay. From all I can see, it looks suitable (and very cost-effective).

[Jdublu]

All the relays I bought at the local NAPA store (20Amp is not enough) came with an internal diode. Some show it on the block wiring diagram, some don't but when tested with a multimeter for continuity in both directions, they were there.

[Extrudo]

Thank you everyone. I have ordered that relay I linked before. Will have time to read up on the links shown above and hopefully figure out how to wire it all up properly.

[Extrudo]

[Mooselake]

Jay wrote a on flashing firmware.

I'd just wait, unless somebody can confirm that that version does use PID; not sure when they changed the config for the bed. If you hook up the relay (diode...) and it clicks then no worry. If it buzzes then you might need to do something. One choice would be a DC-DC SSR, which would save you the effort of compiling and reflashing. I guess that would depend on whether you see that as a fun project, or something to avoid. I still use the version that came with my Kickstarter Plus 2 year ago since it still does what I need; after many years as a development programmer rebuilding firmware is too much like work and I'd rather print than be a flasher. Now if they'd add jerk controlled acceleration I might have a reason.

The version on github you linked to has bed PID disabled in Configation.h; the // in front of the #define makes it a comment and thence undefined.

//#define PIDTEMPBED

Somebody else said a while back that a 3D printer is like a tool rather than an appliance. You have to learn how to use it, and the learning curve can take a while. Think of all the times you hit your thumb with the hammer while you were learning to pound nails (and other things...) I still hit it occasionally.

Marlin's firmware version didn't start with 1.0, and the Printrbot V1, V2, V3 designations don't really have a lot to do with Marlin's firmware versions, so don't worry about that 1.0. The extruder count is the maximum number of extruders possible, not how many you have. It must have been bumped so PB could sell their multiple extruder versions.

Kirk

[Extrudo]

I don't mind doing these things as I'm in the category where I find it interesting, as I'm sure we all are, but when it comes to something that can effectively kill an expensive hardware component (or myself) I like to take it super slow and check all facts first. I'm not confident in my abilities when it comes to anything to do with electricity, as it's something I see as needing respect and care. Not trying first, then regretting it later. Or being dead.

Also I was hoping this would be a relatively easy project and had it set in my mind that I was nearing the end and could soon chuck it all together, printing nice non-warped objects, but as is usual in life things are rarely as simple as they first seem.

The search function on this site is pretty messy. I'm finding it hard to keep up with threads as the dates all seem to be off but maybe it's just for me, so getting the latest posts and all the info is a challenge.

Just very glad all of you folks are trying to help me out which I appreciate a lot so thanks again everyone.

P.S. I've never hit any fingers with a hammer, and I've built lots of wood projects, including furniture. You've probably jinxed me now though.

[Mooselake]

[Extrudo]

Well I've managed to get hold of some nichrome wire, but it's in ribbon form, so I'm unsure how to measure and calculate the length I will need, as I've only seen online calculators for round wire, none for the ribbon type. It's 1mm wide and I believe it's 0.127mm thick and apparently it's then 0.08835ohms/cm. It's also currently 207cm long (I have two other pieces which are 107cm each in length of the same 'gauge' if needed). Anyone have any ideas please?

87a on the relay is unused? Nothing needs to be connected to it?

I have a feeling my 18awg wires (cut from old psu's) may not be thick enough, so I will need to double them up.

Is one 12v wire enough or should i remove the connector and solder two together from the power lead? Not sure what gauge they are, but I assume as I'm only running 12v one wire should be enough.

Hopefully this is all ok so far in pic below.

[RetireeJay]

The place you do not need to double up on wires is between the Printrbot board and the relay. The current in the "control" side of the relay is very small. Even "hookup" wire (22 gauge) would be fine.

On the other hand, you DO need to make sure all the heavy current-carrying wires have adequate capacity. That would be the wires from the power supply to the heated bed, including the wires to and from the relay that are carrying heater current.

The LED as you have shown it will never light up, since it's "shorted out" by the red wire. You connect one end of the LED + resistor string to one side of the heated bed, and the other end to the other side of the heated bed (the LED + resistor are in parallel with the nichrome wire).

You're right that nothing is connected to 87a.

And you're right in how the diode is connected, assuming that you connect the wires to the Printrboard as you've shown.

It might be worth pointing out that not all 100k thermistors are created equal. There are different models with different temperature / resistance curves. More than one model is available within the Marlin firmware - but you would need to edit, re-compile, and flash your own version of the firmware if you are not using the standard thermistor. The standard one is Epcos B57560G1104+000 or B57560G1104+002 (the difference is in how the leads come out of the glass bead).

I'm afraid that nichrome ribbon is not optimal. If you want a heated bed for 144 watts (i.e. 1.0 ohm at 12V) then you would only be using 11.3 cm of nichrome wire. That won't wrap around the way you want in a bed that's 10 X 15 cm. What you show is basically (6 X 15) + (10 * 2) = 90+20 = 110 cm of wire. So you would need to use a nichrome wire with 1/110 ohm per cm: 0.0091. On the other hand, if you in effect broke it up into three equal zones wired in parallel, then you could use 34 cm of wire for each zone. This is a rough sketch of what that might look like.

ParallelNichromeWires.GIF

[thawkins]

[Extrudo]

[Extrudo]

I have soldered up, insulated and plugged in that thermistor and it appears to be working perfectly. Is detecting ambient room temp correctly, and also my skin temperature spot on.
I might have to re-solder the end parts as I've only used the 18awg 90c wire i had spare for the test, and perhaps I need some higher temperature rated wire for being right next to the hot aluminium heat bed part.

One part down...lots to go.

Edit:
I think I've misunderstood you Jay. Are you saying that I can actually use one of the 107cm length 1mm wide 0.127mm thick nichrome wires I have, if I split it into 3 parts (about 32cm each) and run it with thick 8awg wire in parallel like in your diagram for around 144 watts? Or is that if I purchased some different nichrome wire with 1/110 ohm per cm: 0.0091.

[thawkins]

[Mooselake]

30V 15A supply? Did you mean 30A 15V, or are you really using a higher voltage/lower current supply?

Kirk

[RetireeJay]

[Extrudo]

[thawkins]

[Mooselake]

I've got a single 12V 30A supply with the output adjusted so it gets 12V with both the extruder and bed heaters on. It'll reach 60 degrees faster than the extruder will come up to PLA temps; it's been a while since I've used ABS but remember it's being pretty quick there. Doubt it would beat yours, though.

I've been looking at the MK 3 aluminum core beds, but too many other projects underway lately. Outdoor wood boiler ordered (bet you don't have those in the Philippines) and the G0513 (not for firewood) arrives Thursday

Kirk

[Extrudo]

Hmm sorry I do have another question. Does it matter what gauge wire I use for the led and resistor connection, or is it best not to use any wire and just solder (silver solder) them together to the end of the nichrome with the power wires? I was trying to get them further away from the heated bed off to the side if possible, so that the bed isn't so 'bumpy' underneath, and that the LED is visible when standing over the machine.

Revised pic below.

[thawkins]

[RetireeJay]

[Extrudo]

Well originally I was thinking of using a UK standard power cable to strip for wires, but when looking at them they read 0.75mm on the outside insulation which seems to be the equivalent of 20-21awg according to here:
http://en.wikipedia.org/wiki/American_wire_gauge

Inside our cables there are three wires, a live, a neutral and a ground/earth wire. So at least the live and neutral should be 0.75mm each. I think the ground wire is a bit thinner in older power cables. Our grid system is 240v whereas I think the US is 120v if that makes any difference.

As you'll have gathered by now my knowledge of anything electrical is pitiful. I wanted to be sure nothing was going to melt or cause problems but as you say the 8awg does sound a bit over the top for this project, I hadn't thought about the flexibility issue. I think 12 gauge may be a happy medium then. Do I need to add a fuse in between the PSU and relay connector 87? And if so, is a car fuse rated for 20amps ok (pic below)? Our household plug fuses only go up to about 13amps. The car ones react fast enough to prevent damage to electronics I assume.

I do have a multimeter which I'll use to check out the 87 and 87a connectors so thanks for pointing that part out.

[RetireeJay]

The higher voltage in use in many parts of the world means that the power wiring can deliver the same amount of watts of power with smaller-gauge wires (albeit maybe with slightly thicker insulation). So your typical "lamp cord" in the UK and Europe is probably lighter-gauge than the same "lamp cord" in the US.

So your challenge is to find 14 gauge or 12 gauge STRANDED wire. Solid wire would be totally unsuitable because it is not really flexible. In fact, if you can possibly find it, wire with many fine strands will be better than wire with fewer thick strands. You might try looking for "speaker wire" because Hi-Fi speakers are low impedance, meaning that if you have a 100watt stereo system, the current going to your speakers is pretty high - needing heavy-gauge wire. You can google "flexible stranded wire" and find many options. At the high-cost end, there are wires with very high strand count and silicone insulation, making them both extremely flexible and heat-resistant.

In your situation, a fuse is really optional. The power supply already has some form of over-current protection built in so that if there is a short circuit it won't start a fire.

You can use "hookup wire" of 22 gauge or thicker for the LED and resistor; since there will not be any repetitive bending of these components, you can use solid wire or stranded; it doesn't matter.

[Extrudo]

Ok my relay showed up today, and as usual ... I'm confused. I will try to explain why by using a pic.



I have tried to colour code everything to make it a bit easier to view. Top left pics are the relay + the connector with the wires. Bottom right pic is of the other side of the rlay so you can see the diode. Please note I've used grey text to signify the black wire (just to make it easier to see in the photo).

The reason I'm confused is in my posts further up I've been showing that the diode is placed with the white line on the diode towards pin 86 of the relay... and the relay has shown up through the post today with the diode attached the other way around. Hopefully you can see this in my picture. The white line of the diode is currently attached to pin 85. Perhaps this is because it's originally meant for cars, or maybe it was put in the wrong way around by the person who sent me it (although I'd imagine it would have been done by the manufacturer and should be correct)?

So now I'm assuming that I need to swap it around so it faces the other way, white stripe to 86 pin like we originally discussed?

On the plus side the blue, red and yellow wires are a nice and thick gauge.

[RetireeJay]

The easiest solution, I think, will be to reverse how the relay coil is connected to the Printrboard.

If you refer to the diagram in my posting of 25 Sept, I show a circuit from the Printrboard's power supply +12V going through internal wiring on the Printrboard directly to the heated bed connector, and a circuit from the Printrboard's power supply ground going through a "switch" (actually a MOSFET transistor) to other pins on the heated bed connector. So you simply connect the white lead from your relay, which is the "bar" end of the diode, to the +12V pin(s) on your heated bed connector, and the black lead from your relay to the switched-to-ground pin(s) on the heated bed connector.

Which is which? The two pins nearest the edge of the board are the switched-to-ground pins, and the other two pins (nearest the Extruder Heater connector) are the +12V pins.

The relay coil itself does not have a polarity. You could run current through it in either direction and it would perform exactly the same. But the diode does have a polarity, and if you hook it up backwards you will probably blow out the diode.

[Extrudo]

Thanks Jay. Such an obvious and simple solution yet it didn't even enter my mind until an hour after I posted.

[Extrudo]

Well I've got around to putting everything together but when I got to my plan of using silver solder on the nichrome, well it seems the nichrome just won't have it. Fluxed it up too but it's just not holding on to the nichrome. Really surprised about this as I'd read loads of places online that this would do the trick. Back to the drawing board.

[MrFluffy]

Can you not use a mechanical method of joining instead, ie use a very small nut and bolt, or screw and nut with two washers, and wrap the end of the nichrome and wire around the screw and twist it back on its own shank & flanked either side by the washers, then tighten the nut up clamping everything together to stop it coming adrift. Then insulate the outside with some heat resistant insulation somehow or prevent it from contacting anything which may short it out?

[Extrudo]

Thanks for the idea MrFluffy but I've already found a workaround. I went with normal solder with no flux and to thread the nichrome through the strands of the 12awg wire then solder all around it to hold in place.

Have now taken it all for it's maiden voyage and I'm happy to say it's all working nicely first time.

It takes about 4mins to get up to temperature (80C) which I don't think is too bad for only running at 12v. Then takes a longggg time to cool down. It switches the relay on every 10 seconds or so to keep the bed at roughly the set temperature. Might drive me nuts eventually but it's ok for now.

I'm very happy with it so thanks to everyone who has helped me out.

Just need to remember how to re-adjust the Z axis level and I can start a test print.

Here's a picture of it all, messy wires everywhere, but I'll tidy them up later (n.b. the tape in the middle is just so I could get a more accurate temperature reading with my IR non-contact temperature gun).

[RetireeJay]

Maybe a crimp connector like would work.

Since normal solder doesn't really "wet" the nichrome, you just have a mechanical connection right now. A crimped connection keeps the junction under pressure and thus makes it more reliable.

But anyway, congratulations!

[RetireeJay]

I made this topic "sticky" because it has so much tutorial-type information.

[print mom]

My son wants a 1403 Printrbot with the heated bed for Christmas , he is an engineer student in college. Do I have to buy the Basic metal kit and the heated bed together? The Prinrbot website charges $689 plus tax and shipping. I saw Radio Shack has the basic kit for $599 but I would have to get the heater separate. Is this a good idea or what advice do you have for a "Mom"

[Corey Warren]

[Mooselake]

Mom, I'd agree with Corey. I doubt you'd save any money by buying from the Shack, and then buying a separate heated bed. Buy both directly from Printrbot, or perhaps from Amazon. Amazon might have that configuration in stock, where Printrbot may still be behind in their deliveries after the big Black Friday sale.

My mom didn't buy me a 3D printer when I was in engineering school (well, OK, back then it would have been a rock and a chisel). Lucky student! Get them to show you how to use it and get one for yourself so you'll have something to do together.

Kirk

[subether]

+1 on "buy direct from printrbot" it's the same price as amazon, (well, you'll pay shipping unless you have prime) and it's shipped right from the factory.