Heated bed setup help.

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Heated bed setup help.

Postby shadedurza » 2016-Nov-Mon-03-Nov

Hello,
I recently bought a printrbot simple metal with the intention of upgrading to a heated and larger bed myself. I went with the Matrix Precision 8x8 option and so far that installed great but I have some questions about how I should go about wiring the heated bed. After browsing around on here and elsewhere a lot I have found some really good information but some things are still a little unclear. I'm still a complete novice at electronics and wiring things in general so please forgive any obvious questions.

First a little information to start from:

    I live in the USA and have 120v from the wall.
    Rev. F6 Printerboard so the 6 pin ATX power connector kind.
    Silicone Heater pad 20x20cm 500W 110V from ebay seller "keenovo"
    Fotek SRR: 24~380VAC 3~32VDC input
    450W SilverStone power supply

Now for questions:

1. I found this wiring diagram which was the simplest for me to understand. I believe I understand the basics of how the SSR works and it would seem if I wired it this way it would simply switch the 120v from the wall directly into my heater pad based on when the printer board wanted the bed on/off.
SSR Wiring.jpg

This is the diagram provided by the ebay seller Keenovo however not really being the type of person to trust the first simple thing I find on the internet here is where my uncertainty comes in. Since it would be switching 120v directly into the heater pad and I can see the spec for it states 110v so would this be bad? Also the stranded a̶l̶u̶m̶i̶n̶u̶m̶(edit: actually tinned copper) wires for powering the pad are 1.5mm or around 16 awg when I measure without the shielding. With (very) limited understanding here I have read the wire size should be at least 12 awg for this purpose. Although when I chopped apart one of those standard computer power cables I found the wire size to be 1.5mm b̶u̶t̶ also in copper. Would anybody be able to clear this up for me?

2. Assuming the above method was too simple to be correct I dug deeper and found that most people need to hook up an atx power supply from a computer when upgrading to a heated bed. A lot of the posts I found were old and referenced printer boards with 4pin power connections while mine has 6. I did find that I do have a power supply that appears well suited for this but the cable that fits is a little weird and looking for a not weird one didn't yield much.
psu2.png

The blue end of the cable fits in the black port on the bottom left and only has 6 of the possible 8 pins inside the connector. Also the end that would plug in to my printer board is of the 6 + 2 type. Intuition tells me these things are probably fine but again I am unsure.

3. If the power supply method is the way to go then I would think the next straight forward step is to plug the power supply into the printer board using the cable above and then the 2 wires from the heater pad into the green screw terminal labeled "HOT BED". This, again, seems too simple and being a pretty big fan of keeping magic smoke inside of stuff I wanted to ask about this first.
RevF6prinrbrd.jpg


Let me know if any more information / pictures would be helpful. I'll try to respond as quickly as possible although I do work during the day.
Thanks in advance for any help! :D

Note: I haven't forgotten about wiring up the thermistor I'm just pretty sure it's the same no matter which way I do this.
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Last edited by shadedurza on 2016-Nov-Tue-19-Nov, edited 1 time in total.
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Heated bed setup help.

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Re: Heated bed setup help.

Postby RetireeJay » 2016-Nov-Mon-07-Nov

Hi Shadedurza. Welcome to the forum, and congratulations on doing some research so you knew how to post pictures; that's a big help.

I'm quite concerned that you got a heated bed that's rated for 110 V. That, and the aluminum wires it came with are the big departures from what most people have done.
- Having live 110V on the bed of a metal-framed printer is a potential safety hazard to you if ever there's a short circuit from the bed to the frame of the printer.
- Aluminum wires are not very good for repeated bending; they will break internally and cause hot spots in the wire and/or loss of heat to the bed
- 500Watts is a huge amount of power, much more than you need.

shadedurza wrote:1. I found this wiring diagram which was the simplest for me to understand. I believe I understand the basics of how the SSR works and it would seem if I wired it this way it would simply switch the 120v from the wall directly into my heater pad based on when the printer board wanted the bed on/off.

Part of your picture is cut off, but it seems like you have the right idea in principle.

shadedurza wrote: Since it would be switching 120v directly into the heater pad and I can see the spec for it states 110v so would this be bad?

Your bed is rated to run on 110V and you are connecting it to 110V, so don't worry about the diagram calling out 240V; that's obviously for people who live where the mains are 240V and the bed is also rated for 240V. As long as the mains and the bed are both the same voltage and the SSR can handle the voltage you are using, you are fine.

shadedurza wrote:Also the stranded aluminum wires for powering the pad are 1.5mm or around 16 awg when I measure without the shielding. With (very) limited understanding here I have read the wire size should be at least 12 awg for this purpose. Although when I chopped apart one of those standard computer power cables I found the wire size to be 1.5mm but in copper. Would anybody be able to clear this up for me?

- Due to the fact that the heated bed is operating at ~ 10X the "normal" bed voltage, it doesn't require as much current to achieve the same power (watts = volts X current). This means that it can operate successfully with thinner conductors in the wiring.

shadedurza wrote:Although when I chopped apart one of those standard computer power cables I found the wire size to be 1.5mm but in copper. Would anybody be able to clear this up for me?

- When you have several wires in parallel (connected to the same source on one end and the same load on the other end) they share the current, so it's as if you had a single conductor with a thicker copper cross-section. The areas of the wires add up.

shadedurza wrote:2. Assuming the above method was too simple to be correct I dug deeper and found that most people need to hook up an atx power supply from a computer when upgrading to a heated bed. A lot of the posts I found were old and referenced printer boards with 4pin power connections while mine has 6. I did find that I do have a power supply that appears well suited for this but the cable that fits is a little weird and looking for a not weird one didn't yield much.

- "Most people" are powering their heated bed directly from the ATX supply, with the power passing through and controlled by the board. That's why they need a beefy power supply. In your case, if you insist on using the 110V heater then you don't need a beefy power supply for the Printrboard. The SSR draws extremely little power from the board; your heavy power circuit is external to the board. So you could supply the board with your original laptop "brick" if that's what it came with.
- I would strongly recommend against using anything but a 6-pin connector from an ATX supply to go into the Printrboard. I know for sure that 4-pin connectors can be plugged into the 6-pin socket but they will absolutely not work. I highly doubt that an 8-pin connector is going to work either. In your picture, it looks like you have a 6-pin connector with another 2-pin connector on a "pigtail" adjacent to it; use the 6-pin one and leave the pigtail floating (not connected).

shadedurza wrote:3. If the power supply method is the way to go then I would think the next straight forward step is to plug the power supply into the printer board using the cable above and then the 2 wires from the heater pad into the green screw terminal labeled "HOT BED". This, again, seems too simple and being a pretty big fan of keeping magic smoke inside of stuff I wanted to ask about this first.

- No harm will come of that, but it won't work. The heater is designed to run on 110V and generate 500W. When you run on 12V, which is about 1/10 the rated voltage, the power will drop by the ratio of the voltage change squared. In other words, the heater will only give you 5 Watts if you run it directly on 12V. The one power level is really about 3 times too high; the other power level is way too low.
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Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
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Re: Heated bed setup help.

Postby shadedurza » 2016-Nov-Mon-12-Nov

Hi Jay thanks for the fast reply.
I seem to have accidentally made a purchase on the extreme side of things.
I'm guessing most people do a 100W heater pad? If that's the case and I were to go that route would I simply follow the connect directly to the green screw terminal process I outlined in question 3?

Also in my research I hadn't heard the aluminum wire was bad as much as I heard people talking about making sure to get fine stranded wire. More strands = better for repeated bending. Do most people do copper?

RetireeJay wrote:
shadedurza wrote:1. I found this wiring diagram which was the simplest for me to understand. I believe I understand the basics of how the SSR works and it would seem if I wired it this way it would simply switch the 120v from the wall directly into my heater pad based on when the printer board wanted the bed on/off.

Part of your picture is cut off, but it seems like you have the right idea in principle.

Sorry about that. Looks like it only gives the horizontal scroll bar if the picture isn't expanded? o.0 I would have posted an imgur album but I can't post links yet...
RetireeJay wrote:
shadedurza wrote: Since it would be switching 120v directly into the heater pad and I can see the spec for it states 110v so would this be bad?

Your bed is rated to run on 110V and you are connecting it to 110V, so don't worry about the diagram calling out 240V; that's obviously for people who live where the mains are 240V and the bed is also rated for 240V. As long as the mains and the bed are both the same voltage and the SSR can handle the voltage you are using, you are fine.

Just to be clear I have 120v from the wall. I checked. Apologies for not clarifying that vs what the diagram says. Despite that discrepancy I believe the rest of the wiring would be the same. In this case the mains and the bed are not the same voltage. I guess I'm still not sure if I'm fine.
RetireeJay wrote:
shadedurza wrote:3. If the power supply method is the way to go then I would think the next straight forward step is to plug the power supply into the printer board using the cable above and then the 2 wires from the heater pad into the green screw terminal labeled "HOT BED". This, again, seems too simple and being a pretty big fan of keeping magic smoke inside of stuff I wanted to ask about this first.

- No harm will come of that, but it won't work. The heater is designed to run on 110V and generate 500W. When you run on 12V, which is about 1/10 the rated voltage, the power will drop by the ratio of the voltage change squared. In other words, the heater will only give you 5 Watts if you run it directly on 12V. The one power level is really about 3 times too high; the other power level is way too low.

Basic question: Am I understanding correctly that the printer board can only supply 12v? This would seem to line up with using a 100W heater pad if that is actually what most people do.
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Re: Heated bed setup help.

Postby Mooselake » 2016-Nov-Mon-14-Nov

I haven't use a 120V bed heater, but it's been done before and I've seen a few posts in other places about them. Besides what RJ said I'd add an insulator (Kapton sheet should work) between the heater and the aluminum bed just for some extra protection, and maybe put a piece of glass over it as a print surface. The SSR input essentially drives an LED, which then triggers an optical switch, so as long as you're supplying the correct type of input the bed should work. I'd test it first before connecting up the Printrboard, use a 12V DC source to trigger the SSR and see if the heater works. Be quick, since you're not controlling the input; the Printrboard will turn it off and on as needed, you're manually pretending to be that controller. Before that I'd take an ohmmeter (like the one in your handy digital meter) and make sure there's no connection between the heater and any other conductive surface, like the aluminum bed. You don't want to have a short to the bed and light up your eyeballs, not to mention all that heart stoppage fibrillation stuff, from the shock if you touch it.

Also, with that aluminum wire get some anti-oxidation grease (like Noalox, Ox-Gard, or similar. Tell your local hardware store you're doing some aluminum electrical wire and they should be able to direct you to the right product). Otherwise the connections will develop an oxide layer and start heating up. Burned down a lot of houses when they first started using aluminum house wiring. I have a 100A circuit out to my barn that uses aluminum wire and the proper oxidation guard that's been working well for nearly 40 years.

With that kind of power you should have a very fast heating bed. Just keep an eye on it - it the driver MOSFET fails on or the thermistor fails the wrong way it'll get mighty hot. This has happened with hot ends on many brands of 3D printers, and in a few cases started fires. As always you shouldn't leave your printer (of any brand) unattended while printing. The types of protection (like thermal fuses) in virtually every household appliance haven't made their way into the 3D printer world so you need to give them more attention than your coffee maker. A smoke detector and nearby fire extinguisher are a good idea.

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Re: Heated bed setup help.

Postby RetireeJay » 2016-Nov-Mon-15-Nov

shadedurza wrote:I'm guessing most people do a 100W heater pad? If that's the case and I were to go that route would I simply follow the connect directly to the green screw terminal process I outlined in question 3?

Actually, probably closer to 150W. And yes, if the heater is rated to provide that power at 12V supply, then you hook it directly to the green screw terminals.

shadedurza wrote:Also in my research I hadn't heard the aluminum wire was bad as much as I heard people talking about making sure to get fine stranded wire. More strands = better for repeated bending. Do most people do copper?

Aluminum is often used for its light weight, e.g. in high-voltage power distribution wires, the kind they string on those tall towers. Lighter weight = fewer towers. Those wires are approaching an inch in diameter or more. But as Mooselake said, you have to be careful how you make attachments. I agree that many small strands is the way to go for avoiding fatigue failure. I just have never heard of fine-stranded aluminum wire designed for flexing. Telephone cords, microphone cords, and cables that are subject to repeated bending in factory automation are all made with fine-stranded copper.

shadedurza wrote:I would have posted an imgur album but I can't post links yet..

Still better to post the picture directly to the forum. :)

shadedurza wrote:Just to be clear I have 120v from the wall. I checked. Apologies for not clarifying that vs what the diagram says. Despite that discrepancy I believe the rest of the wiring would be the same. In this case the mains and the bed are not the same voltage. I guess I'm still not sure if I'm fine.

You said in the original post that the bed heater was rated to run at 110V. Since that matches your mains, and your SSR is rated to switch voltages anywhere in the range of 24 to 380 Volts AC, you are fine. If you run a heater designed for 240V on 110V, you will get much less power than the rated power, but no harm will happen. The reverse would not be true: running a heater designed for 110V on a 240V supply will cause extreme heating and likely burn out the heater. (BTW, your SSR uses a DC signal for control on its input, but it is designed to switch an AC current on its output. You won't need it anyway if you use a 12V bed rated for 150Watts.)

shadedurza wrote:Basic question: Am I understanding correctly that the printer board can only supply 12v? This would seem to line up with using a 100W heater pad if that is actually what most people do.

Yes, if you supply the heater's power directly from the board (as a majority of people do) then your source voltage fed to the heater is (basically) equal to the supply voltage going in to the board, which should be 12V.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
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Re: Heated bed setup help.

Postby Mooselake » 2016-Nov-Mon-18-Nov

No Simples here, so I don't know what the underside of the bed looks like or how a heated bed's wiring is routed...
Your diagram shows a barrier strip connecting the heated bed to the SSR wiring. Assuming you can mount a barrier strip (like this randomly picked one)on or near the heated bed, and safely insulate it (inside a small plastic enclosure, for example) you could shorten the aluminum wires and then connect them to something much more flexible (another random eBay pick, this is rated for 600V). With some proper wire routing, and the aforementioned anti-oxidant, the flexibility issue is gone.

I have a meter of 12ga silicon coated wire in the Printrbot upgrade box waiting for the next teardown/mod cycle.

I like the idea of a higher wattage heated bed, assuming proper safety measures are added and/or used, but you're definitely into experimenter territory where there be dragons. Iirc the larger print bed machines often use mains voltages, presumably since their bed heaters would require car jumper cables to carry enough current at 12 or even 24 volts. That's the good cables, not the lightweight single use vaporize after one jump cheap ones from Sam Walton's Emporium.

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Re: Heated bed setup help.

Postby shadedurza » 2016-Nov-Tue-16-Nov

Nice. I've read to be wary of wiring with dissimilar metals. Since the wire from the pad is aluminum and the new wire I would use would be copper (or tinned copper like in your link) does the barrier strip / anti-oxidant negate that issue? Assuming you suggested this because just soldering the two together would be even worse.
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Re: Heated bed setup help.

Postby RetireeJay » 2016-Nov-Tue-16-Nov

You can't even solder to aluminum (at least not without some very special equipment and materials). Mechanical connections to aluminum are the way to go. But that leads to the question of how the aluminum wires are attached to your heated bed. If it's a mechanical connection that can be un-done and re-done, then throw those aluminum wires away and use copper from end to end.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
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Re: Heated bed setup help.

Postby shadedurza » 2016-Nov-Tue-16-Nov

I've sent the ebay seller a message. I'll post the reply here. For now here's the link to the one I have:
h t t p://w w w.ebay.c o m/itm/281275441183?euid=acc14f3d2dc04c8491aabf7928ce4605
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Re: Heated bed setup help.

Postby RetireeJay » 2016-Nov-Tue-17-Nov

Umm... are you sure the wires are aluminum? The eBay web site doesn't say. It's common for some copper wires to be "tinned" so that their color is silvery instead of copper-colored. Tinned copper wires will be shiny; aluminum ones will be dull, duller even than the matte side of aluminum foil. If you scrape a tinned wire with a knife, you'll see the copper under the thin plating.
Frankly, it would be very unusual for them to ship the heater with aluminum wires. I don't think the cost difference between the two metals is very great, and copper is so standard for this kind of use that they would almost have to tell you that they used aluminum.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
User avatar
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Re: Heated bed setup help.

Postby shadedurza » 2016-Nov-Tue-18-Nov

Sooo I learned something today. :D I'll take a closer look at the wires when I get home. The ebay seller will probably be able to confirm or not too.
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Re: Heated bed setup help.

Postby shadedurza » 2016-Nov-Tue-19-Nov

Yup they're totally tinned copper. Apologies for wasting everyone's time!
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