Heatbed Heater Options

I'm in the process of doing some much needed upgrades to my printer's heatbed, and I'm trying to workout my best option.

The existing heated bed was done with 4 x 4.7R power resistors (aluclad type) and the temperature maxed out around 70C. I have just mounted 4 x 2.2R power resistors, but I haven't tested them yet. They're 8W as opposed to the 15W ones that were there, and although they have a max temp rating of 300C, I'm a little apprehensive about them, and the wire that connects them. It's really thick, but by my calculations, there's going to be something like 21A through the wire, and I'm not sure if it (or my RUMBA board) will take that. The power supply DEFINITELY will, as it's rated for 58A at 12V. Pics of the current bed and wires (I put in a normal single core wire beside it for comparison):




Anyway, this all has me considering some other heater solutions, but there's a few issues involved, and I'm trying to do this as cheap as possible really.

So, PCB. I'd be looking at a 300x300mm one, but because of the existing gantry, the corner mounting holes wont work. The one in the middle is fine, but I'd need to drill new holes in a PCB heat bed, and I don't know if i can do that. I have a vague recollection of some site saying it was fine provided it was outside the white outline of the text/border on the top surface of the heatbed. Confirmation of this would be great

The other two options are Polyimide or a silicon heater mat. With the polyimide, same principle of having to drill it applies. The silicone mat, same thing.

I think i'd prefer the PCB option so i can keep the weight down, but I'm a bit stuck on this one. As you can see on the image of the bed, the mounting holes are the problem with the options, but it would be less so if I could drill a PCB heater.

Anyone able to shed some light on the situation?

I don't know any suppliers of 300x300mm heater PCBs. Why not use one or more undersize silicone heaters and an aluminium heat spreader plate? I found some inexpensive 12V 100W 235x100mm silicone heaters on eBay. Two of those should do the trick. You could drive one from your Rumba board, and use an external mosfet to drive the other, to avoid overloading the Rumba.

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I've come across a few. Apart from the ones on aliexpress, I have a few shops bookmarked on my laptop, but it'll be tomorrow before I can get at them.

The silicone ones, although they seem to be good solutions, they seem messy between relays and using mosfets etc. and it still leaves me with the problem of the awkward mounting holes on the aluminium plate. I'd feel more comfortable with the PCB, just going PCB>Glass>print, but i just don't know if I can drill the perimiter bit. By the looks of things, I might be able to, but it will depend on where the traces stop I'm guessing.

Am I wise at this stage to rule out things like nichrome wire etc?

you should go to i higher voltage, as the Rumba mosfet also supports higher voltages on the Board-switch, this will reduce your ampere taken from the board.
with such a large bed you should at least use six powerresistors otherwhise you only get some hot-spots where the bed is reaching it`s temperature, especially the corners will be very cold.
so there should be a resistor near every corner at least, and some in the middle.

I´m using some foil heates for my 300x360 heatbed, although they are reated for 12V i`m powering them with a 230W 19V notebook powersupply, you just have to calulate what power they take at 19V.
The resistance may become very low which may cause a safe shutdown to the powersupply when heating up from cold, so i made a serial/parallel switch to first warm up to 35°C and after that switch to parallel to heat up with all power.

How is the Bed mounted on the printer (what printertype), normally the holes of a Printbed are in the corners and not in the center ?????

Chri

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[chrisu02.wordpress.com] Quadmax Intel Delid Tools

Quote
twicx
The silicone ones, although they seem to be good solutions, they seem messy between relays and using mosfets etc.

You are likely to need an external mosfet with ANY heater solution for a bed that large because of the amount of power involved, unless you increase the voltage, e.g. connect the two silicone heaters I suggested in series and use 24V. The mosfets, connection blocks and copper traces on most controller boards are only designed to carry about 10A. I wouldn't even put 10A through the Rumba mosfets, because of a design flaw. The type of mosfet specified in the schematic (PSMN7R0-60YS, see [reprap.org]) is not designed for 5V logic drive, so its on-resistance is not guaranteed for gate drive voltages less than 10V. No professional electronics engineer would choose that mosfet for that circuit.

Quote
twicx
. and it still leaves me with the problem of the awkward mounting holes on the aluminium plate.

Sorry, I don't understand why. Using the two silicone heaters I suggested, the edges and the centre of the aluminium plate will be clear, so no problem for mounting holes there.

As for drilling a PCB heater pad, you are safe to drill outside the area of the copper traces.But I would expect the copper traced to go quite close to the edge of the board, except where there are pre-drilled mounting holes.

Edited 1 time(s). Last edit at 11/27/2014 04:18AM by dc42.

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So by the sounds of it, I'm going to need something between the Rumba, the power supply and the heater(s). This makes it tricky.

The first problem is the mounting points. Because of the design of how the bed is mounted to the z axis gantry, the mounting points for anything is going to be a tricky issue. My printer (Felix 1.5 Rev.E) uses 3 mounting points for the Heated bed. One is in the centre of the heated bed, and the other two are in the corners. However, if I move to a larger print bed, for example, 300mm x 300mm, Those two corner mounting points move up along the edge by about 1/3. So the centre mounting point would be the same, but the two other corner ones would still be on the edges, but about 40-60mm from the corner. Looking at the PCB option, I think I made an error in thinking that the holes in the middle of them are another mounting point. I think they're for the thermistor.

The next problem is the power supply. I've already gotten a new ATX power supply that puts out 58A at 12V, so I would like to try to stick with that one, rather than go to 24V.

This brings me back to the whole heater issue. By the sounds of it, I need something to manage the power (it's going to be >10A) in or around the Rumba/Heater/Powersupply. What would be my cheapest/best/easiest solution for that?

As for the heaters, I still like the convenience of the PCB one in that I can keep the weight of the heat bed down. It looks like I can drill outside of the white boundary line where the traces are, but then I still have the problem of that 3rd mounting point in the centre of the board, which I'm not so sure how to tackle. I'm still very reluctant to use the silicone ones, and I'd favor the kapton foil option over those, as they're cheaper, adhesive, and maybe 4 x foil heaters might be an option.

Edit:
[www.alibaba.com]

This is the kind of printbed I have in mind. The ideal (albeit optimistic) setup would be that, use the center hole as the 3rd mount point, drill two new mount points up from the corners (you can also see the white border), and then figure out how to manage the power supply bit. Is this possible?

Edited 1 time(s). Last edit at 11/27/2014 06:57AM by twicx.

Quote
twicx
So by the sounds of it, I'm going to need something between the Rumba, the power supply and the heater(s). This makes it tricky.

The first problem is the mounting points. Because of the design of how the bed is mounted to the z axis gantry, the mounting points for anything is going to be a tricky issue. My printer (Felix 1.5 Rev.E) uses 3 mounting points for the Heated bed. One is in the centre of the heated bed, and the other two are in the corners. However, if I move to a larger print bed, for example, 300mm x 300mm, Those two corner mounting points move up along the edge by about 1/3. So the centre mounting point would be the same, but the two other corner ones would still be on the edges, but about 40-60mm from the corner. Looking at the PCB option, I think I made an error in thinking that the holes in the middle of them are another mounting point. I think they're for the thermistor.

The next problem is the power supply. I've already gotten a new ATX power supply that puts out 58A at 12V, so I would like to try to stick with that one, rather than go to 24V.

This brings me back to the whole heater issue. By the sounds of it, I need something to manage the power (it's going to be >10A) in or around the Rumba/Heater/Powersupply. What would be my cheapest/best/easiest solution for that?

As for the heaters, I still like the convenience of the PCB one in that I can keep the weight of the heat bed down. It looks like I can drill outside of the white boundary line where the traces are, but then I still have the problem of that 3rd mounting point in the centre of the board, which I'm not so sure how to tackle. I'm still very reluctant to use the silicone ones, and I'd favor the kapton foil option over those, as they're cheaper, adhesive, and maybe 4 x foil heaters might be an option.

Edit:
[www.alibaba.com]

This is the kind of printbed I have in mind. The ideal (albeit optimistic) setup would be that, use the center hole as the 3rd mount point, drill two new mount points up from the corners (you can also see the white border), and then figure out how to manage the power supply bit. Is this possible?

Try looking at a Solid State Relay these can be driven by your Rumba board easily and still switch the high current dc that you need They are available in various Current rating's

Doug

Quote
dougal1957

Quote
twicx
So by the sounds of it, I'm going to need something between the Rumba, the power supply and the heater(s). This makes it tricky.

The first problem is the mounting points. Because of the design of how the bed is mounted to the z axis gantry, the mounting points for anything is going to be a tricky issue. My printer (Felix 1.5 Rev.E) uses 3 mounting points for the Heated bed. One is in the centre of the heated bed, and the other two are in the corners. However, if I move to a larger print bed, for example, 300mm x 300mm, Those two corner mounting points move up along the edge by about 1/3. So the centre mounting point would be the same, but the two other corner ones would still be on the edges, but about 40-60mm from the corner. Looking at the PCB option, I think I made an error in thinking that the holes in the middle of them are another mounting point. I think they're for the thermistor.

The next problem is the power supply. I've already gotten a new ATX power supply that puts out 58A at 12V, so I would like to try to stick with that one, rather than go to 24V.

This brings me back to the whole heater issue. By the sounds of it, I need something to manage the power (it's going to be >10A) in or around the Rumba/Heater/Powersupply. What would be my cheapest/best/easiest solution for that?

As for the heaters, I still like the convenience of the PCB one in that I can keep the weight of the heat bed down. It looks like I can drill outside of the white boundary line where the traces are, but then I still have the problem of that 3rd mounting point in the centre of the board, which I'm not so sure how to tackle. I'm still very reluctant to use the silicone ones, and I'd favor the kapton foil option over those, as they're cheaper, adhesive, and maybe 4 x foil heaters might be an option.

Edit:
[www.alibaba.com]

This is the kind of printbed I have in mind. The ideal (albeit optimistic) setup would be that, use the center hole as the 3rd mount point, drill two new mount points up from the corners (you can also see the white border), and then figure out how to manage the power supply bit. Is this possible?

Try looking at a Solid State Relay these can be driven by your Rumba board easily and still switch the high current dc that you need They are available in various Current rating's

Doug

Forgive my ignorance, but how are they connected up? is there somewhere that has a good guide on them?

Although those Fotek DC-DC SSRs are easy to wire up, unfortunately they have quite a high maximum voltage drop (1.6V, see [www.fotek.com.hk]) and hence there will be a lot of heat to get rid off. You would be better off using 2 mosfets (chosen for very low Rds(on) @ 4.5V gate voltage) wired in parallel.

---

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].

Quote
dc42
Although those Fotek DC-DC SSRs are easy to wire up, unfortunately they have quite a high maximum voltage drop (1.6V, see [www.fotek.com.hk]) and hence there will be a lot of heat to get rid off. You would be better off using 2 mosfets (chosen for very low Rds(on) @ 4.5V gate voltage) wired in parallel.

I still don't get how I would connect these up, or what kind of mosfets to go for.

But that aside, does that mean I could go for a big PCB board (assuming I solve the mounting issue) and just use the two mosfets between the board and the heater?

Ok so after looking at the SSR option, I'd rather avoid having to wire up two plugs for the printer. What's the deal with the mosfet option? How is that wired up? Is there a guide somewhere?

What you need is something like the SevenSwitch, but with 2 mosfets in parallel to handle the extra current. See [reprap.org] and follow the link to github for the schematic.

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

Now this seems like a really interesting solution! A little board and some mods to the firmware, I think that's manageable!

As far as the MOSFETs in parallel, I had a read through the SevenSwitch research pages, and had a little look at a few other sites and I'm just wondering if there's any reason why I couldn't just use a different MOSFET to handle the higher current? For example, IRF3708 is good for 62A Digikey

Edited 1 time(s). Last edit at 11/29/2014 07:17AM by twicx.

Ignore the current rating of the mosfet. Instead look at the Rds(on) value measured at Vgs=4.5V and Id at least as high as the current you want to switch. For the irl8743 used in the SevenSwitch it is 3.9 milliohms at 4.5V and 20A. Multiply that by the square of the current to get the power dissipation. To avoid needing a heatsink, you want the power dissipation to be no more than 1W. That's why the SevenSwitch is rated at 15A. To carry 20A you want the Rds(on) to be no more than 2.5 milliohms.

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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].

Cheers for that! I might actually be ok with just the normal sevenswitch. The resistance of the heatbeds are between 1.1 and 1.4 ohms, and if the 15A is going to be just for the heatbed, I might be ok. Wouldn't leave me with much in the way of tolerances, but it could be ok. I guess my best bet would be to get the heater, measure its resistance, then decide on what to do then.

FINALLY getting a chance to put some time over this. I've been working crazy hours, and studying for my professional exams, so my printer has been in parts for the last few weeks!

From looking at this again, I think a solid state relay seems to be the easiest solution, but as there's always a risk of damaging something, I'm doing all the research I can. First and foremost, from looking around, it seems like my wiring diagram will be this:



There's a few questions I have on it though.
1. On the RUMBA board, there's 2 terminals for HB-PWR, which normally connects to the PSU. They're right beside the HB-OUT. If I'm using a SSR Relay, what do these connect to?

2. This was one of the diagrams I was looking at for working this out: RELAY CONFIG
The pinouts are a little confusing, as far as +/- on the board, +/- on the heat bed, and +/- on the relay. I would have thought that the +/- have to all line up. I know this sounds like a realy electrical noob question, but it's essentially just a loop from +12V on the ATX to the GND on the ATX (like in my diagram?) Is this correct?

3. I've seen a few diagrams with things like lamps and resistors and diodes across things, and others without them. I know it was mentioned earlier that I will need to test my new PSU to see if it needs a load at the 5V to power on, and if so, there's a few options like a fan or a resistor, but I'm specifically talking about the head bed/relay section. Do I need all these extra diodes and lamps?

4. As far as the relay itself goes, my preference is to order something from this site: http://ie.rs-online.com/web/
I'm going to be ordering some stuff from them in the new year for a completely un-related project (Guitar amps) and it would save me on shipping. The only problem is, they have about 2000 different SSRs, and I have no idea what the exact one I'm looking for. They have things like zero-cross over things and I'm a bit lost. What would be the most exact description of it?

Again, MASSIVE thanks for the help on this.

Quote
twicx
1. On the RUMBA board, there's 2 terminals for HB-PWR, which normally connects to the PSU. They're right beside the HB-OUT. If I'm using a SSR Relay, what do these connect to?

To +12V and 12V ground as usual. You can link them across to the other 12V terminals - no need to run separate 12V power to them in this case.

Quote
twicx
2. This was one of the diagrams I was looking at for working this out: RELAY CONFIG
The pinouts are a little confusing, as far as +/- on the board, +/- on the heat bed, and +/- on the relay. I would have thought that the +/- have to all line up. I know this sounds like a realy electrical noob question, but it's essentially just a loop from +12V on the ATX to the GND on the ATX (like in my diagram?) Is this correct?

The Load- terminal on the SSR connects to the + terminal on the heated bed, but otherwise the + and - should all line up.

Quote
twicx
3. I've seen a few diagrams with things like lamps and resistors and diodes across things, and others without them. I know it was mentioned earlier that I will need to test my new PSU to see if it needs a load at the 5V to power on, and if so, there's a few options like a fan or a resistor, but I'm specifically talking about the head bed/relay section. Do I need all these extra diodes and lamps?

No, not for the heated bed/relay section. But you will probably need a load on the 5V output from the ATX supply to keep it happy. If you will be using an LCD display, the backlight of that display may be enough load for the 5V output, and by connecting the backlight there instead of to the Rumba 5V output, you will keep the 5V regulator on the Rumba cooler.

Quote
twicx
4. As far as the relay itself goes, my preference is to order something from this site: http://ie.rs-online.com/web/
I'm going to be ordering some stuff from them in the new year for a completely un-related project (Guitar amps) and it would save me on shipping. The only problem is, they have about 2000 different SSRs, and I have no idea what the exact one I'm looking for. They have things like zero-cross over things and I'm a bit lost. What would be the most exact description of it?

Zero-crossing and random-fire only refer to SSRs used for switching AC loads. You cannot use an AC SSR to switch DC. This rules out most SSRs. In the parametric selector on the RS Solid State Relay page, under "Output device" deselect "triac" and "paired SCR". Of the ones left, this one [uk.rs-online.com] is the cheapest I found that can handle 20A. Check the datasheet for heat sinking requirements - the 20A rating is with a heatsink. You may be better off using an SSR rated at e.g. 40A, because at 20A it will need little or no heatsinking.

Unfortunately, DC SSRs are expensive. If the Rumba board made the HB drive signal available externally, then I would suggest using two SevenSwitch boards in parallel instead - but from what I can see, the Rumba doesn't provide that signal externally.

Edited 1 time(s). Last edit at 12/23/2014 12:38PM 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].

Quote
dc42
No, not for the heated bed/relay section. But you will probably need a load on the 5V output from the ATX supply to keep it happy. If you will be using an LCD display, the backlight of that display may be enough load for the 5V output, and by connecting the backlight there instead of to the Rumba 5V output, you will keep the 5V regulator on the Rumba cooler.

Ok grand. My instinct is to run one of the always-on fans off this, as I'm not using an LCD display, or maybe something like an LED. Something simple.

Quote
dc42
Zero-crossing and random-fire only refer to SSRs used for switching AC loads. You cannot use an AC SSR to switch DC. This rules out most SSRs. In the parametric selector on the RS Solid State Relay page, under "Output device" deselect "triac" and "paired SCR". Of the ones left, this one [uk.rs-online.com] is the cheapest I found that can handle 20A. Check the datasheet for heat sinking requirements - the 20A rating is with a heatsink. You may be better off using an SSR rated at e.g. 40A, because at 20A it will need little or no heatsinking.

Ah ok, well at least now I'm clear on what I'm looking for. I would be inclined to pay that bit more for the 40A one to avoid the heatsink. I think the heatbed is going to end up with a current draw of something between 10 and 15A, but i'll have to wait till it arrives to measure it exactly. At least now it's a bit clearer.

Thanks again for the help. Its top of my to-do list after my exams on the 6th.

Quote
twicx

Quote
dc42
No, not for the heated bed/relay section. But you will probably need a load on the 5V output from the ATX supply to keep it happy. If you will be using an LCD display, the backlight of that display may be enough load for the 5V output, and by connecting the backlight there instead of to the Rumba 5V output, you will keep the 5V regulator on the Rumba cooler.

Ok grand. My instinct is to run one of the always-on fans off this, as I'm not using an LCD display, or maybe something like an LED. Something simple.

Quote
dc42
Zero-crossing and random-fire only refer to SSRs used for switching AC loads. You cannot use an AC SSR to switch DC. This rules out most SSRs. In the parametric selector on the RS Solid State Relay page, under "Output device" deselect "triac" and "paired SCR". Of the ones left, this one [uk.rs-online.com] is the cheapest I found that can handle 20A. Check the datasheet for heat sinking requirements - the 20A rating is with a heatsink. You may be better off using an SSR rated at e.g. 40A, because at 20A it will need little or no heatsinking.

Ah ok, well at least now I'm clear on what I'm looking for. I would be inclined to pay that bit more for the 40A one to avoid the heatsink. I think the heatbed is going to end up with a current draw of something between 10 and 15A, but i'll have to wait till it arrives to measure it exactly. At least now it's a bit clearer.

Thanks again for the help. Its top of my to-do list after my exams on the 6th.

try something like this 40A DC-DC SSR

That's a damn sight cheaper. I might go for that, or, at the very least, use it as a reference for finding what i need.

Thanks again!

Quote
twicx
That's a damn sight cheaper. I might go for that, or, at the very least, use it as a reference for finding what i need.

Thanks again!

I quoted this earlier in the thread and DC42 did say that they have a high Voltsdrop across them so you may have to increase your supply Volts to it or use a slightly lower resistance on your bed to compensate for it (I am no expert on SSR's and I plan on using a AC Fed silicon heater on my large build).

Doug

Quote
dougal1957

Quote
twicx
That's a damn sight cheaper. I might go for that, or, at the very least, use it as a reference for finding what i need.

Thanks again!

I quoted this earlier in the thread and DC42 did say that they have a high Voltsdrop across them so you may have to increase your supply Volts to it or use a slightly lower resistance on your bed to compensate for it (I am no expert on SSR's and I plan on using a AC Fed silicon heater on my large build).

Doug

Yes it does quote a relatively high voltage drop on the datasheet (1V maximum), but so does the 40A one from RS. Either of them is likely to need a heatsink to carry 15A.

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Quote
dc42

Quote
dougal1957

Quote
twicx
That's a damn sight cheaper. I might go for that, or, at the very least, use it as a reference for finding what i need.

Thanks again!

I quoted this earlier in the thread and DC42 did say that they have a high Voltsdrop across them so you may have to increase your supply Volts to it or use a slightly lower resistance on your bed to compensate for it (I am no expert on SSR's and I plan on using a AC Fed silicon heater on my large build).

Doug

Yes it does quote a relatively high voltage drop on the datasheet (1V maximum), but so does the 40A one from RS. Either of them is likely to need a heatsink to carry 15A.

yeah think so could always mount it on the Alloy bed to help with heating it though not sure if that kind of heat would affect it operation at all?

The 100 degC or so that you need on the hot bed for printing ABS is too hot for cooling the SSR.

I am tempted to design a heat bed switch that has a much lower voltage drop than an SSR but still provides isolation. But I suspect that the demand would be too low to make it worth my while having some built.

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Quote
dc42
The 100 degC or so that you need on the hot bed for printing ABS is too hot for cooling the SSR.

I am tempted to design a heat bed switch that has a much lower voltage drop than an SSR but still provides isolation. But I suspect that the demand would be too low to make it worth my while having some built.

Thought that may be the case If I was to use one it would go under my Bottom plate underneath the printer along with the rest of the Electronics PSU's and motors but as my heatpad is a 400mm x 400mm 230V AC Silicon heater it shouldn't be anywhere near the same issues (I will be using a SSR to switch it). It has an inbuilt thermocouple that I would like to use just not sure how to yet more research is needed I think!

Quote
dougal1957

Quote
dc42
The 100 degC or so that you need on the hot bed for printing ABS is too hot for cooling the SSR.

Thought that may be the case If I was to use one it would go under my Bottom plate underneath the printer along with the rest of the Electronics PSU's and motors but as my heatpad is a 400mm x 400mm 230V AC Silicon heater it shouldn't be anywhere near the same issues (I will be using a SSR to switch it). It has an inbuilt thermocouple that I would like to use just not sure how to yet more research is needed I think!

The current drawn by your mains-voltage heatbed should be very low (I am guessing 1 to 2A), so the heat generated by your SSR will be much lower than the heat generated by twicx's DC SSR carrying 15A. You can use an inexpensive zero-crossing AC SSR.

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

Quote
dc42

Quote
dougal1957

Quote
dc42
The 100 degC or so that you need on the hot bed for printing ABS is too hot for cooling the SSR.

Thought that may be the case If I was to use one it would go under my Bottom plate underneath the printer along with the rest of the Electronics PSU's and motors but as my heatpad is a 400mm x 400mm 230V AC Silicon heater it shouldn't be anywhere near the same issues (I will be using a SSR to switch it). It has an inbuilt thermocouple that I would like to use just not sure how to yet more research is needed I think!

The current drawn by your mains-voltage heatbed should be very low (I am guessing 1 to 2A), so the heat generated by your SSR will be much lower than the heat generated by twicx's DC SSR carrying 15A. You can use an inexpensive zero-crossing AC SSR.

Yep that's what I reckoned as well the heater will be under a piece of Ally that by the time it is all put together will be 9mm thick (Weigh's a ton but as it will only be moving in the vertical plane it should be fine) top plate is 6mm ECOCAST machined flat and that is mounted to a larger piece of 3mm sheet for mounting/levelling purposes (Top is 400x400 lower piece 450x450 mm) this will all be on a CoreXY Machine using NEMA23's for all motion motors and 17's on the extruder's E3D Kraken hotend.

Will start a new thread re the Thermocouple and see what other's say about it.

So this looks like a good option, right?
ebay ssr

Quote
twicx
So this looks like a good option, right?
ebay ssr

Yes, and the supplied heatsink will likely be adequate at 15A. Mount the heatsink with the fins vertically so that convection draws air over them, or else use a fan to blow air between the fins. The datasheet will tell you the maximum surface temperature of the SSR permitted as a function of current.

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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].

the good news is that I have those ordered now, with the heatbed too. The bad news, exams on the 6th and the parts aren't due to arrive till the end of january.