Aluminium Heat Bed I have just changed my old reprap "printed circuit" type heat bed for an aluminium reprap type. It seems well made and a lot more rigid. Nice and flat. However it takes an age to heat up, like 30 mins+ to reach 110 deg C. Is this normal? I am using 12v on pin 1 and pins 2 and 3 are earthed together. I was thinking about recessing the hole for the thermistor so it fits in a bit better. The spring mounts for the bed are also running hot. I was thinking of fitting fibre washers to insulate against heat losses. Any thoughts? https://reprap.org/forum/read.php?4,477710,477710#msg-477710 Thu, 16 Jul 2026 10:33:32 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?4,477710,887920#msg-887920 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,887920#msg-887920 Justinjjhcs1 Reprappers Tue, 18 Jan 2022 21:05:58 -0500 https://reprap.org/forum/read.php?4,477710,522319#msg-522319 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,522319#msg-522319 LINK and went for it, but yeah looked around too. Bang Bang is what I used, but going to switch to PID once I get a Nice Big Capacitor to sit in between the SSR and the power supply the fast switching of that big of a load is not safe for the power supply.]]> AquaticsLive Reprappers Tue, 16 Jun 2015 13:51:38 -0400 https://reprap.org/forum/read.php?4,477710,522302#msg-522302 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,522302#msg-522302
Quote
AquaticsLive
Make sure the Solid state relay is a DC/DC one and a name brand one. The cheap ones on Amazon and ebay tend to be DC/AC with a new label. You can tell they are fake when they get hot, allot of them will be sold with a big heat sink. I have a Crydom D06D60 LINK just gets slightly warm with a my 360 Watt silicone heater. I tried the cheap FOTEK SSR ESSR-DD100A and it got super hot even with a heat sink and failed after a week in the closed position so be careful.

Which is why I was wondering if there were some 'solid' wiring diagrams, BOM's etc, regarding this modification. I'm certain with all the experience out there a quick lessons learned, here's the schematic, parts list and misc. other things would have been generated.]]> Viper97 Reprappers Tue, 16 Jun 2015 12:42:02 -0400 https://reprap.org/forum/read.php?4,477710,522296#msg-522296 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,522296#msg-522296 LINK just gets slightly warm with a my 360 Watt silicone heater. I tried the cheap FOTEK SSR ESSR-DD100A and it got super hot even with a heat sink and failed after a week in the closed position so be careful.]]> AquaticsLive Reprappers Tue, 16 Jun 2015 12:25:31 -0400 https://reprap.org/forum/read.php?4,477710,522242#msg-522242 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,522242#msg-522242
1.5 seconds of google searching later

-a]]> alan richard Reprappers Tue, 16 Jun 2015 10:43:05 -0400 https://reprap.org/forum/read.php?4,477710,522232#msg-522232 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,522232#msg-522232 Viper97 Reprappers Tue, 16 Jun 2015 10:12:15 -0400 https://reprap.org/forum/read.php?4,477710,522104#msg-522104 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,522104#msg-522104
Quote
mmutch
i have the same issue where my Mk3 bed wont go above 70c the thought i have is what about buying a second 24V supply and a relay (12v/24v) then running the 12v bed power cable from the ramps to a relay thats 12v on the coil then run the 24v power supply thro the switching side direct to the bed wired in 24v configuration that way whenever the ramps tells the bed to warm the relay will aloow for 24v direct to the bed with no other load however unless you got a solid state one you would get the click each time it turned on and off

anyone else see an issue with this?

No problem as long as both PSUs share the same wall socket or the 24V-GND is completely separate from the rest of the printer. ( fed directly to the heatbed and +24V is switched by the relais.)
-Olaf]]> o_lampe Reprappers Tue, 16 Jun 2015 04:05:40 -0400 https://reprap.org/forum/read.php?4,477710,521906#msg-521906 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,521906#msg-521906 link for a pic. Rated up to 250 F 120C so safe for the temps I use; cut the time to heat my 350mm x 450mm to 5 minutes. and no bounce in temps. If I want it to heat up super quick I will toss a piece of cardboard on top of bed while it is heating.]]> AquaticsLive Reprappers Mon, 15 Jun 2015 15:54:13 -0400 https://reprap.org/forum/read.php?4,477710,521496#msg-521496 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,521496#msg-521496
anyone else see an issue with this?]]> mmutch Reprappers Sun, 14 Jun 2015 14:11:45 -0400 https://reprap.org/forum/read.php?4,477710,490539#msg-490539 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,490539#msg-490539
Quote
alan richard
For on/off (bang bang) control, which is just like a regular thermostat, a mechanical (high current) relay is better, an SSR is a pointless expense that just drops voltage passing through it, if dc42 is to be believed and I think he probably is.

Just to clarify:

DC/AC SSRs are great for controlling mains-voltage heated beds. They drop about 2V, but that is of little consequence when switching mains voltage at relatively low current. SSRs need heatsinking unless they are run well below their rated current, but even so, an SSR-10DA (rated at 10A) should be fine for driving a 230V 500W (2.1A) heat bed without a heatsink, and an SSR-25DA can be used for more powerful heat beds.

The problem with DC/DC SSRs is that they also tend to have around 2V voltage drop at full current, despite the fact that the mosfets they use for the output stage can drop much less voltage. I believe this is because they derive the gate voltage needed to turn on the mosfet from the secondary side. The voltage drop has two consequences. First, it reduces the voltage at the heated bed, resulting in a reduction of heating power. For example, a 12V heated bed run from 10V will only produce 70% of its rated power Second, it generates heat, e.g. 2V drop @ 20A = 40W of heat to get rid of.

It would be possible to make a DC/DC SSR that derives the gate voltage from the primary side, but I don't know of any SSRs that do this. I'm tempted to manufacture some.

An automotive relay is an alternative to a DC/DC SSR, but there will be quite a lot of arcing on the contacts, so it may not last very long. But it is cheap and drops negligible voltage. Remember to connect a flyback diode in parallel with the coil.

Unless you need isolation between the heated bed and the printer electronics, then the best solution is usually a mosfet, or two or three mosfets connected in parallel.]]> dc42 Reprappers Mon, 30 Mar 2015 10:54:56 -0400 https://reprap.org/forum/read.php?4,477710,490485#msg-490485 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,490485#msg-490485
The hotend uses pid control, anyway, hence why the flashing indicator light (On my RAMPS board) flashes at different rates as it gets close to temperature. It's not putting out a variable voltage its just switching on and off quickly.
The current consumption of the hotend is low enough that a small onboard MOSFET transistor can handle switching the power through it, unlike the power of a heated bed.

As for 'burned out SSR's' - The simple answer is to check the cycle rate of your SSR against the cycle rate of your firmware.

In my case a Fotek SSR 25 DD has a min switching time of 10ms which gives 100Hz.
Marlin firmware switches at just under 8Hz

A 'safe margin' I would say.

For on/off (bang bang) control, which is just like a regular thermostat, a mechanical (high current) relay is better, an SSR is a pointless expense that just drops voltage passing through it, if dc42 is to be believed and I think he probably is.

Much as I like the idea of pid control, I've just gone for on/off myself. It is 'near enough' and the thermal inertia of my print bed is such that it's not going to change temperature very quickly.

a]]> alan richard Reprappers Mon, 30 Mar 2015 09:07:24 -0400 https://reprap.org/forum/read.php?4,477710,490194#msg-490194 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,490194#msg-490194 Ecky: I measured the temperature using the printer bed thermistor.
I have previously used an IR gun to check the temp but it gave a low reading. It is due to the emmissivity of the aluminium surface. A highly polished surface will give a low reading. A matt black surface, a higher reading.

krwynn: on/off control works fine. It overshot to 114 deg C initially then quickly settles down and cycles within a 2 deg C band or +/- 1 deg C. This is adequate for bed control I think. I cannot see how an SSR can work with PID control. The SSR is itself an just an on/off switch. How can it work proportionally and give a variable output? Unless it switches very very rapidly.

I am very happy with the setup. The bed now reaches temp just before the nozzle! It means I can be printing within 5 mins of turning the printer on. I only do ABS and it is much better than I had before. I have also done away with the glass sheet and clips which reduces weight. I have kapton tape directly on the aluminium. So far so good.]]> dave3d Reprappers Sun, 29 Mar 2015 13:58:32 -0400 https://reprap.org/forum/read.php?4,477710,489944#msg-489944 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,489944#msg-489944
Quote
dave3d
A final follow up. I have now fitted the second 24v power supply unit to power just the bed. It is rated at 17 amps.
I still use on/off control via a SSR. I adjusted the output voltage of the 24v PSU so it gives around 15 amps, just to allow a margin.
It now heats up to 110 deg C in about 3 mins!
]]> krwynn Reprappers Sat, 28 Mar 2015 21:20:25 -0400 https://reprap.org/forum/read.php?4,477710,489941#msg-489941 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,489941#msg-489941 Ecky Reprappers Sat, 28 Mar 2015 21:01:24 -0400 https://reprap.org/forum/read.php?4,477710,489824#msg-489824 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,489824#msg-489824 I still use on/off control via a SSR. I adjusted the output voltage of the 24v PSU so it gives around 15 amps, just to allow a margin.
It now heats up to 110 deg C in about 3 mins!]]> dave3d Reprappers Sat, 28 Mar 2015 14:16:43 -0400 https://reprap.org/forum/read.php?4,477710,484694#msg-484694 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,484694#msg-484694
However, I have 2 layers of cork sheet (each about 2.5mm thick) held underneath the bed by a thin aluminium sheet. During warm-up I also put a piece of corrugated cardboard on top to help things along, until the print head is about to move.]]> David J Reprappers Tue, 17 Mar 2015 09:08:59 -0400 https://reprap.org/forum/read.php?4,477710,484185#msg-484185 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,484185#msg-484185
I found my existing 12v PSU is voltage adjustable after all; my mistake, I am new to this. It can be screwed up to 14.5v but as I mentioned I do not wish to supply my Arduino/Ramps/LCD panel at a higher voltage.

I have decided the easiest way is to mount two power supply units, one 12v and one 24v, side by side under the printer (an OrdBot). Physically they are the same size. The one I have ordered is rated at 15 amps.]]> dave3d Reprappers Mon, 16 Mar 2015 08:12:35 -0400 https://reprap.org/forum/read.php?4,477710,480664#msg-480664 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,480664#msg-480664 Resistors weren't my ideal choice. I just happened to have some that add up to that number. I couldn't find an ideal 12v heater pad of my size and power requirement.The alu would be a heat spreader for a glass sheet on top.
I hadn't considered the volts drop. Fotek SSR 25DD data sheet only mentions leakage current 1mA nothing about V drop.
Being on Reddit doesn't make it more true Kr. SSRs are designed for fast PID controlled switching - no one mentioned melting
The notes in Marlins config specifically reference PID control of SSRs. People do use it.
Trusted opinion seems to vary though.

A]]> alan richard Reprappers Sat, 07 Mar 2015 16:38:03 -0500 https://reprap.org/forum/read.php?4,477710,480510#msg-480510 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,480510#msg-480510
"running an SSR like this in PID can also contribute to thermal runaway so be sure to switch your heated bed to bang bang control and check the frequency of the temp checks."

"As someone mentioned here, you'd want to set your bed PID to bang bang mode otherwise you'll melt the SSR. Also disable PWM.
For safety, I'm putting a 10A fuse into the mains circuit, so I can hopefully salvage my SSR if the bed decides to short out."]]> krwynn Reprappers Sat, 07 Mar 2015 11:13:34 -0500 https://reprap.org/forum/read.php?4,477710,480426#msg-480426 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,480426#msg-480426
Have you considered using a Kapton or silicone heater instead of resistors?

Your DC SSR will almost certainly have a higher voltage drop than a mosfet, possibly as high as 2V. Check its datasheet to see what voltage drop it has, and allow for it in your calculations.]]> dc42 Reprappers Sat, 07 Mar 2015 07:10:55 -0500 https://reprap.org/forum/read.php?4,477710,480407#msg-480407 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,480407#msg-480407
I hope I am not 'hijacking' but rather creating a bigger pool of information for this page.

I am currently assembling a 3thk Alu plate (305x250) with 6 off 50W 5ohm power resistors in parallel to give 0.8333 ohm.

About 14.4A or 172W at 12v, by my sums. fed via a 25A DC SSR

Can I ask-

Do I need a flyback diode across the SSR output?

As dc42 stated; The wiring diagrams for heating/ resistive loads generally do not show a resistor, however, as these are surely wire-wound resistors, won't that be a partly inductive load?
Will it matter?
What sort of spec. diode should I be looking for?

Also
The notes in Marlin would imply to me that PID control is recommended for this set up

Can/ should the PID switching speed be altered?

Should MAX BED POWER be reduced?

Sorry to drift away from dave3d's original question but with all the above comments, this thread is becoming a bigger resource. It would be useful for a wiki page.

Thanks

Alan]]> alan richard Reprappers Sat, 07 Mar 2015 06:31:11 -0500 https://reprap.org/forum/read.php?4,477710,479552#msg-479552 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479552#msg-479552 nophead Reprappers Thu, 05 Mar 2015 13:01:39 -0500 https://reprap.org/forum/read.php?4,477710,479547#msg-479547 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479547#msg-479547
What sort of noise problem are you referring to - do you mean that the bed is vibrating at the PWM frequency, or tjhe AC mains frequency, or something else?]]> dc42 Reprappers Thu, 05 Mar 2015 12:49:56 -0500 https://reprap.org/forum/read.php?4,477710,479538#msg-479538 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479538#msg-479538
I have been struggling with a noise problem that seems to be due to the bed plate resonating, so I may ditch the heated bed completely and switch to printing on PIR foam instead. That will eliminate all the wiring to the bed, the transformer and SSR, and the need to level the bed (not that leveling is an issue for me), and greatly reduce moving mass in the Y axis.]]> the_digital_dentist Reprappers Thu, 05 Mar 2015 12:37:03 -0500 https://reprap.org/forum/read.php?4,477710,479296#msg-479296 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479296#msg-479296
Quote
the_digital_dentist
Your scope photo is impressive, but the avalanche is over in under 250ns and the ringing voltage has dropped below 20Vpk in under 1 us. The FETs in the RAMPS board are rated for 50A continuous and the SOA curve shows that they can handle >100A for 100 us (that's 400x the duration of the avalanche in your scope image).

Are you sure that SOA curve is 100A avalanche current for 100us? Please link to the datasheet you found it on.

Quote
the_digital_dentist
Marlin PID operates at a maximum of about 7Hz, plenty of time for the die to cool between those brief, in-spec avalanche events. SmoothieWare PID operates at a much higher frequency by default, so it is slightly more possible for it to cause a problem for the FET, but you can easily turn down the frequency with a config.txt variable if you're worried about it or if your FET heats up and you don't want to put a heat sink on it.

I agree that low frequency PID is a better option than fast PID for the heated bed. It's also compatible with mains-powered heated beds switched by zero-crossing SSRs.

Quote
the_digital_dentist
I have never heard of anyone complaining about EMI from a 3D printer. I'm not saying it doesn't exist, I just haven't heard of anyone complaining about it. If I were trying to make a product to sell to consumers and had to pass UL, CSA, FCC, and/or TUV certification I might be concerned. If the EMI interfered with my wife's ability to watch Gilligan's Island reruns because it interferes with the TV or wifi signal I would be concerned about it. If EMI affected print quality I would definitely be concerned about it. But I'm not making a commercial product and it doesn't do either of those other things, so I am not concerned about it. I doubt anyone else is either.

RepRapPro had to go to a lot of trouble to get their Ormerod 2 kits meeting CE industrial standards for EMI when correctly assembled. My understanding is that it doesn't yet meet consumer CE standards, but with the next iteration of the electronics it may.

Quote
the_digital_dentist
My print bed temperature varies by about +/- 1C with PID control and swings about +/-10C with bang-bang as reported by both Marlin and SmoothieWare which are certainly not laboratory grade instrument readings, but they're close enough to tell me what I need to know.

Now I understand why you are so strongly in favour of PID control for the heated bed! If you get 10C swings with bang-bang control, I think there is something seriously wrong with your heated bed construction. Both my printers use bang-bang. One has temperature swings of +0.7 -0.3C, the other has +0.3 -0.1C. I suspect that your thermistor is not in good thermal contact with the bed, and that you have no heat spreader.]]> dc42 Reprappers Thu, 05 Mar 2015 03:30:26 -0500 https://reprap.org/forum/read.php?4,477710,479238#msg-479238 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479238#msg-479238
I have never heard of anyone complaining about EMI from a 3D printer. I'm not saying it doesn't exist, I just haven't heard of anyone complaining about it. If I were trying to make a product to sell to consumers and had to pass UL, CSA, FCC, and/or TUV certification I might be concerned. If the EMI interfered with my wife's ability to watch Gilligan's Island reruns because it interferes with the TV or wifi signal I would be concerned about it. If EMI affected print quality I would definitely be concerned about it. But I'm not making a commercial product and it doesn't do either of those other things, so I am not concerned about it. I doubt anyone else is either.

If you want optimum print quality you have to eliminate (ideal) or reduce (real life) any uncontrolled motion in the extruder carriage relative to the print bed. Likewise, wide temperature swings in the bed and hot-end will affect print quality, so it is best to eliminate wide temperature swings. PID control is the way you prevent temperature swings that occur with bang-bang control which degrade print quality. Regulated bed temperature prevents z artifacts that occur when bang-bang is used. My print bed temperature varies by about +/- 1C with PID control and swings about +/-10C with bang-bang as reported by both Marlin and SmoothieWare which are certainly not laboratory grade instrument readings, but they're close enough to tell me what I need to know.

AFAIK, PID control is built into every 3D printer controller board and firmware, and it seems silly not to use it when it's there waiting to be used. Of course you need to pay attention to the current drain and supply voltage, more for the sake of the circuit board than the MOSFET. You can always use an SSR or external MOSFET if you're trying to switch higher currents than your circuit board can handle. I'd suggest people check the recommendations of the manufacturer of their circuit board if they're unable to understand the relevant specs.]]> the_digital_dentist Reprappers Wed, 04 Mar 2015 20:51:38 -0500 https://reprap.org/forum/read.php?4,477710,479160#msg-479160 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479160#msg-479160
Quote

The heat generated is directly proportional to the current. Twice the voltage equals twice the current equals twice the heat generated.

No the heat generated is directly proportional to power, which is equal to current * voltage and current ^ 2 * resistance or voltage ^ 2 / resistance.]]> nophead Reprappers Wed, 04 Mar 2015 17:44:17 -0500 https://reprap.org/forum/read.php?4,477710,479143#msg-479143 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479143#msg-479143
Quote
Nophead wrote:
If you put 24V on the 24V connections it wont get any hotter than 12V on the 12V connections (other than reducing the connection and MOSFET losses). It might heat more evenly though. You would need 30V to get the same heat as 15V on 12V connections.

My aluminium bed has connections for a 12v supply and connections for a 24v supply. One would assume it is constructed with two parallel heating circuits etched into the board. When on 12v only one circuit is used with the other redundant. On 24v both are used in parallel so twice the current and twice the heat generation rate.

Quote
the digital dentist wrote:
Running a 12V heater from a 24V supply will dissipate 4X the power at 100% duty cycle

The heat generated is directly proportional to the current. Twice the voltage equals twice the current equals twice the heat generated. Twice the current through a circuit designed for 12v maybe overloading it.

Quote
dc42 wrote:
PID control of the bed is only of benefit if the bed heater is powerful enough that significant temperature overshoot occurs. With the typical Mk2 or Mk3 heated bed used in diy 3D printers, this is not the case unless they are operated with a higher than normal voltage. But some other heated beds do have significant overshoot, and benefit from PID.

Simple on/off control worked well on my old heat bed. There was a bit of initial overshoot but it settled down to very close control around the set point. There wasn't much cycling. This was no doubt due to the thermal inertia of the system - heating the bed and 6mm glass. I did not see any need for PID control and I subsequently modified it by adding a SSR. It worked very well.

However if the heat output of the new aluminium bed is significantly increased and I did away with the glass plate, then I admit temperature cycling could be a problem.]]> dave3d Reprappers Wed, 04 Mar 2015 17:05:45 -0500 https://reprap.org/forum/read.php?4,477710,479061#msg-479061 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479061#msg-479061 nophead Reprappers Wed, 04 Mar 2015 14:27:06 -0500 https://reprap.org/forum/read.php?4,477710,479050#msg-479050 Re: Aluminium Heat Bed https://reprap.org/forum/read.php?4,477710,479050#msg-479050
Quote
the_digital_dentist
PID control is a very good and useful thing to have and use.

I don't entirely agree with you in respect of the heated bed. There are a few issues with using PID control of the heated bed:

1. The power dissipation in the controlling mosfet will be greater, because of finite on/off switching times and/or avalanching. How much greater will depend on the PWM frequency and the mosfet driver circuit. For some controller boards, this may cause excessinve heating of the mosfet.

2. Using PID will result in increased EMI generation from the heated bed and associated wiring.

3. No heated bed driver circuit that I have seen a schematic for includes a flyback diode. But heated beds and the associated wiring may be significanty inductive. As a result, the driver mosfet is likely to avalanche on every PWM cycle, as is evident here (measured on an Ormerod with a 200x210mm 12V 1.2 ohm heated bed):



Note the jagged top of the 50V approx. peak voltage, indicating that avalnaching is taking place, and the ringing that occurs after avalanching due to the inductance and capacitance of the circuit.

Power mosfets generally have a repetitive avalanche rating (as well as a higher non-repetitive avalanche rating), but is the avalanche energy within that rating? Speaking as professonal electronics engineer, I can't recommend using PWM to control the bed unless the amount of avalanching is measured and found to be well within the limits of the mosfet, or precautions are taken to avoid it, and preferably to limit the amount of EMI generated as well.

PID control of the bed is only of benefit if the bed heater is powerful enough that significant temperature overshoot occurs. With the typical Mk2 or Mk3 heated bed used in diy 3D printers, this is not the case unless they are operated with a higher than normal voltage. But some other heated beds do have significant overshoot, and benefit from PID.
]]> dc42 Reprappers Wed, 04 Mar 2015 14:04:34 -0500