Faster Heated Bed

Check out how others are building and modding their own heated beds
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dpmacri
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Re: Faster Heated Bed

Postby dpmacri » Thu Jan 07, 2016 12:23 pm

I'm using a D1D40.

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Re: Faster Heated Bed

Postby Tincho85 » Thu Jan 07, 2016 12:41 pm

Hi, just to give peace of mind to people willing to buy a Fotek.
I've been using a 100a Fotek SSR for almost a year and it's all good. It doesn't even get hot while printing.

I THINK that the ones that burnt (possible Fotek knockoffs?) might have done the wiring interrupting the + instead of the -
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Re: Faster Heated Bed

Postby nitewatchman » Thu Jan 07, 2016 12:43 pm

I think that the Crydom D1D40 has become the go to standard with good solid service. I snatch up every "reasonable" one I can find and have used them for several projects. Key on a used unit is to test them to assure they are working. With that said, out of a dozen or so used D1D40 SSR's, I have had one that was inop.

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Re: Faster Heated Bed

Postby IMBoring25 » Thu Jan 07, 2016 1:38 pm

So far so good with D1D40 here...

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Re: Faster Heated Bed

Postby e_hutch » Mon Jan 18, 2016 11:26 pm

I just picked up a 600w 25a supply, and a D1D40. I am curious if we can't add additional resistance into the circuit and not need the SSRs? I assume we just end up heating the resistor? I am no electrician!

Also, what are you using for the bed PID settings?

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Re: Faster Heated Bed

Postby nitewatchman » Tue Jan 19, 2016 1:08 am

No not really. The SSR is actually MOSFET that is switched on and off rapidly by the incoming signal (think 20,000 times per second) it therefor mimics the Rambo current pulse to the hot end but with a much higher power capacity. You could think of this as an amplifier and in fact a common use for MOSFET's is to amplify power to devices. Stepper and Servo drives for instance.

Adding additional resistance to the bed circuit in fact lowers the power output of the circuit and while the Rambo could handle the lowered power with no problem, the bed would likely not even get warm.

Btw - you don't mention but I assume that your 600watt power supply is 24VDC. raising the circuit voltage to 24 from 12 will increase the wattage of the bead heater from 120watts to 480watt. If the power supply is still 12VDC the bed output will remain at 120Watts and you will see little if any improvement in the heating of the bed.

As long as the bed resistance is `1ohm and power supply voltage is 12VDC using a 1,000,000watt power supply won't heat the bead any faster.

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Re: Faster Heated Bed

Postby Xenocrates » Tue Jan 19, 2016 1:43 am

In theory, you don't need the SSR at all. It's a precaution as the Rambo boards are only barely rated for 24V, and some people prefer it as with a second (much cheaper) relay, you can set it to fall-back on the 12V supply if you accidentally hit an over-current limit on the 24V supply. (you can use a form 2 C DPDT ice cube relay, with the coil wired to the 24V supply, to switch the signal from the rambo to to the SSR when voltage is present, and to the bed when it isn't, it costs about 10$ if you buy both the relay and the proper wiring base, or 5$ if you omit the base and just connect to the pins). Just stick a larger automotive fuse it. As far as adding resistance to decrease your power draw, well, if you want to double, rather than quadruple the power going into the bed, and thus keep the amperage the same, you need something with a fairly high power dissipation per ohm. You can get those. But a 1 ohm 300W power resistor costs in the neighborhood of 30$. I don't know what sticking a resistor like that in would do (I am not an electrical guy. I do however, get along quite well with the electrical faculty, so I could ask later) But at some point, it's worth it for the added flexibility to just bite the bullet and go for the relay, as mike has had success with a 20$ relay. There have been days where I ate that much worth of cheap pizza (5$'s a pizza, 1 pizza approximately every 4 hours.)

P.S. Nite, if you added a 1 Ohm resistor, you can get 288Ws, about double what you have with 12V. Also, the Rambo is capable of dealing with the amperage, if only barely. and since he mentioned the amperage, it's easy to see it's 24Vs. and if you're switching 20K times a second, even with the 10M switch life that SSRs are rated for, without a load, you hit the lifespan limit pretty quick. If you take Crydom's loaded lifespan estimate, you have about 5 seconds of switching before you have exceeded the rated loaded lifespan of most relays. 8.5 minutes for the unloaded life-span limit. (these are worst case, thermally, mind you.) not to mention that it would require you to flip the power more than once per rambo clock cycle. Maybe drop a zero off there? Maybe two?
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Re: Faster Heated Bed

Postby e_hutch » Tue Jan 19, 2016 8:38 am

thanks for the info, my brain is starting to get wrapped around these concepts. my next question is: wouldn't it be cheaper to add a second 30a 12v power supply in series with the one we have? can you verify what the output amps would be, I assume you would have 24v/30a? I have an identical supply lying around I could test with. You could still use the ssr to regulate the second power supply, but also connect the two outputs on the other end of the ssr. I also assume the reverse biased diode mentioned below would have to be downstream of the ssr on one and downstream of the Rambo on the other? I think this would also help with the problem of a failing ssr, if it fails "on" you would only get 12v trying to heat the onyx, which will have a hard time over heating it and causing a fire..

The Google meister tells me "the output connections for each power supply should have a reverse biased diode wired across them (see drawing). This will assure that, if one supply comes up to voltage before the other(s), it won’t apply a reverse polarity voltage to the other(s) through the load and possibly damage it (them) or cause it (them) to lock up. Each diode’s PIV and current rating should exceed that of the entire series string. Note that when remote sensing is being used, the voltage drop in the output wire connecting the supplies is compensated by extending one supply’s sense lead to the output terminal of the other supply."

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Re: Faster Heated Bed

Postby Xenocrates » Tue Jan 19, 2016 10:02 am

I believe it's workable, as RC enthuasists have modified server supplies to do this. I believe there is a DC ground you'll have to remove in the second one, but it should be workable, in theory at the very least, and likely in practice.
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Re: Faster Heated Bed

Postby nitewatchman » Tue Jan 19, 2016 6:22 pm

Good luck with "creative solutions" there are many like you describe and most work.

Caution you however to keep you eye on the primary problem in increasing the wattage draw of the heated bed, the Rambo just doesn't do well in very high current situations. While it can switch 15A and perhaps a little more, (Onyx bed at 24VDC is 24A's), the termination points on the top edge of the card as many have learned the hard way on this forum are just not up to the wire size or current requirements. There have been many occurences of the terminals be melted and the terminals really struggle with wires bigger than a #14. Using an SSR reduces the loads on the Rambo to nearly nothing eliminating these issues.

In late night stupor mental math failed me, the D1D40 switching rate is 100 microseconds and it's max PWM rate is 900Hz.

Also while it is true that adding a resistor will make the total current more manageable, the added wattage will be dispersed in the added resistor. The Onyz bed with a resistance of 1ohm will still only produce 120watts for the rest the resistor will just get hot.

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Re: Faster Heated Bed

Postby e_hutch » Tue Jan 19, 2016 9:46 pm

what about using one of these for a reverse current diode?... https://www.jameco.com/Jameco/Products/ProdDS/1558444.pdf

Xenocrates wrote:I believe there is a DC ground you'll have to remove in the second one, but it should be workable

not following on the DC ground, can you explain?

nitewatchman wrote:Caution you however to keep you eye on the primary problem in increasing the wattage draw of the heated bed, the Rambo just doesn't do well in very high current situations. While it can switch 15A and perhaps a little more, (Onyx bed at 24VDC is 24A's), the termination points on the top edge of the card as many have learned the hard way on this forum are just not up to the wire size or current requirements. There have been many occurences of the terminals be melted and the terminals really struggle with wires bigger than a #14. Using an SSR reduces the loads on the Rambo to nearly nothing eliminating these issues.

I think I follow you here, do other boards (I.E. Duet/Smoothieboard) have the same problem? What is the max 12v current that can safely be drawn through the Rambo? I may just experiment with serializing the power supplies prior to the ssr and tapping off one to power the board with essentially the same solution as proposed by the OP. I am afraid that this may just overload the power supply that is feeding the Rambo. The idea behind all this is just to reduce the overall footprint of the additional power supply and possibly keeping the cost down while still being easy for others to replicate. I already bought a 24v power supply, so this is mostly academic, but I would prefer to use the smaller/lighter one for portability purposes if it is feasible.

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Re: Faster Heated Bed

Postby Xenocrates » Wed Jan 20, 2016 12:47 am

there should be a connection to the case of the unit, or the ground plug on the IEC socket, from the DC side of the unit. This needs to be removed for it to work. I'm not entirely familiar with the process, but I have found a thread on an RC forum which seems to discuss it (not for your unit though I think) http://www.helifreak.com/showthread.php?t=335915
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Re: Faster Heated Bed

Postby nitewatchman » Wed Jan 20, 2016 1:09 am

nitewatchman wrote:Caution you however to keep you eye on the primary problem in increasing the wattage draw of the heated bed, the Rambo just doesn't do well in very high current situations. While it can switch 15A and perhaps a little more, (Onyx bed at 24VDC is 24A's), the termination points on the top edge of the card as many have learned the hard way on this forum are just not up to the wire size or current requirements. There have been many occurences of the terminals be melted and the terminals really struggle with wires bigger than a #14. Using an SSR reduces the loads on the Rambo to nearly nothing eliminating these issues.


I think I follow you here, do other boards (I.E. Duet/Smoothieboard) have the same problem? What is the max 12v current that can safely be drawn through the Rambo? I may just experiment with serializing the power supplies prior to the ssr and tapping off one to power the board with essentially the same solution as proposed by the OP. I am afraid that this may just overload the power supply that is feeding the Rambo. The idea behind all this is just to reduce the overall footprint of the additional power supply and possibly keeping the cost down while still being easy for others to replicate. I already bought a 24v power supply, so this is mostly academic, but I would prefer to use the smaller/lighter one for portability purposes if it is feasible.


Have no knowledge of the other boards, can't help. Problem with the RAMBO is that it is just real hard to make a good termination with a large gauge wire with the terminal tucked up in the corner. Simplified "rule of thumb" which has a huge number of qualifications and exceptions suggests using #14 wire for 15A and #12 wire for 20A. These numbers may be tweaked when the wire in in air verses in a tube has high temperature insulation, etc. but #12 for 20A is generally 100% safe and conservative.

What I chose to do was to basically run every thing from the 24VDC p/s and btw your p/s sounds perfect. The 24VDC p/s has a loop through the SSR to the bed and back to the p/s. Everything else is still run at 12VDC allowing you to use the same fans, hotend heaters, leds, firmware setting as a stock RMv2. This is done by attaching a 24VDC to 12VDC p/s (http://www.amazon.com/HOSSEN%C2%AE-Conv ... +converter) to the output side of the 24VDC p/s and then wiring this to the rest of the printer exactly as the instructions show. Mine has now run a little over a year like this with no issues at all. No heat generated in the SSR's, no board issues and the RT to 100C heating time for ABS is 4-1/2 to 5-1/2 minutes, I also use a 1/16" copper heat spreader which while making the surface temperature MUCH more uniform does slow the heating by a noticeable amount.

This way everything remains stock from a hardware setup, no changing fans to 24V, LED ballast resistors, hotend cartridges or firmware settings. The bed operates on 24VDC, RAMBO doesn't know this nor care that this is occurring and there are no high current loads or large wires on the RAMBO top terminal strip. BTW - If the RAMBO terminal strip is burned or melted, it can be repaired or some have just soldered the larger wires directly to the board traces. I would prefer to not have to deal with either.

I have a bit of a background in large industrial electrics and electronics. You learn here that it pays to be a little conservative. If you want to see an example of a high current SSR Switching operation, google Flash Butt Rail Welding.

We have several of these machines, the largest being 430Kv and weld rail to rail and rail to large castings. While the machine has an 800A 480VAC primary this is quickly rectified to DC in a water cooled rectifier/transformer tank, tank is connected to a 30Ton Chiller for a heat sink. Output of the rectifier goes directly to a bank of 48 VERY large MOSFET's modules which control the current and voltage at the weld by rapidly switching on and off.

Typical welding voltage and current for a 141RE to 141RE rail during the fusing operation is 3VDC and 90,000Amps to 115,000Amps. Makes lots of sparks. If for example a steel straight edge 3" wide by 1//4" thick is left across the electrodes, it is vaporized with a huge bang.

This is basically the same logic albeit larger that I use to control my hot bed.

If I needed or wanted to go even higher in the heating rate range the only change would be a higher voltage p/s or higher wattage bed provided I stayed inside the rating of the SSR and the ampacity of the wire. The Rostock/Rambo side would never know anything had changed. I have also considered going to one of the AC Silicon beds that some here have found. To make this change the SSR is simply swapped to a DC-AC SSR (Thyristor type) rather than a DC-DC (MOSFET) type and the Silicon Pad Heater hooked up across the mains. http://www.amazon.com/KEENOVO-Circular- ... heated+bed

Hope this helps.

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Re: Faster Heated Bed

Postby e_hutch » Thu Jan 21, 2016 9:05 pm

nitewatchman wrote:What I chose to do was to basically run every thing from the 24VDC p/s


I think I will do this, thanks!

nitewatchman wrote:I also use a 1/16" copper heat spreader which while making the surface temperature MUCH more uniform does slow the heating by a noticeable amount.


I am using an aluminum heat spreader, It just takes way too long to heat up right now! My end goal is to enclose it too, and I will be switching to a duet board with fsr's for auto-cal.

nitewatchman wrote:Hope this helps.


Definitely, everyone on this forum is very helpful. BTW I grew up in BHam too, hope to get back to the southeast some day! Roll Tide!

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Re: Faster Heated Bed

Postby AlanZ » Tue Feb 02, 2016 10:53 am

I am going to connect my Onyx bed to an SSR today, and run 24 volts to the bed.
What wire gauge should I be attaching to the bed and run to the SSR? 14? 12? Make much of a difference?

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Re: Faster Heated Bed

Postby Xenocrates » Tue Feb 02, 2016 11:00 am

For handling the 21A current, no less than 12 would be my suggestion, and preferably 10 or so. It is my opinion that a design factor of about 1.5 is desirable, and for loads at 90C, 12 is rated for 20A exactly, while 10 is rated for thirty, which gives you a slightly less than 1.5 safety factor in the design, where 12 is not quite rated for the ~21A load of the bed on 24V. (the onyx is specced for around 1.1-1.2 ohms, and at 1.1, draws 21.81A @ 24VDC, while at 1.2 it draws 20 precisely)
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Re: Faster Heated Bed

Postby Jrjones » Tue Feb 02, 2016 1:55 pm

Xenocrates wrote:For handling the 21A current, no less than 12 would be my suggestion, and preferably 10 or so. It is my opinion that a design factor of about 1.5 is desirable, and for loads at 90C, 12 is rated for 20A exactly, while 10 is rated for thirty, which gives you a slightly less than 1.5 safety factor in the design, where 12 is not quite rated for the ~21A load of the bed on 24V. (the onyx is specced for around 1.1-1.2 ohms, and at 1.1, draws 21.81A @ 24VDC, while at 1.2 it draws 20 precisely)


While that is true for constant loads, the heated bed will only be on continuously for a short period (~5 minutes or less from what I've read from people who run 24V.) Since your duty cycle is not 100% you can get away with smaller cable than what is required for a constant load.
Also I'm not sure where you get your reference from Xenocrates? Most of the popular references for DC Ampacity have 16 AWG (copper) having a max rating of 22A. ie. http://www.powerstream.com/Wire_Size.htm

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Re: Faster Heated Bed

Postby Xenocrates » Tue Feb 02, 2016 5:20 pm

I'm using http://www.cerrowire.com/ampacity-charts, at the 90 C rating column. Considering that I would rather the wiring not melt or burn should the thermistor creep out, the rambo lock up, or several other improbable but possible scenarios, I tend to go a little overboard (having been taught when doing Hydraulics to size and spec a design factor of at least 2 may contribute to that), I would prefer that any individual component be sufficiently under it's rating that even if it is only barely designed to handle the spec (most parts will have their own design factor, although one shouldn't count on it, especially for cheap or Chinese parts). And since the SSR and 24V PSU will both accommodate that wire size, I would prefer to use it. I wouldn't do something like that through the rambo. I would merely use the largest wire it's rated to take.
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Re: Faster Heated Bed

Postby Jrjones » Tue Feb 02, 2016 9:52 pm

Ah I see, that website seems a little conservative compared to the others. They list that their ampacitys are rated according to NEC Table 310.15 (B) (16), and if you look up that table then 12 AWG is rated for 30A @90°C and 10AWG for 40A @ 90°C.
Nothing wrong with having a safety factor in your printer, I was just curious what ampacity chart you were referencing.

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Re: Faster Heated Bed

Postby AlanZ » Wed Feb 03, 2016 12:29 am

I did the 24 volt upgrade this evening.
Details are in my build thread viewtopic.php?f=42&t=9622&p=83723#p84747

Thanks to all those who helped make this painless by suggesting parts and wiring so I didn't have to guess at how to proceed.

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Re: Faster Heated Bed

Postby nitewatchman » Wed Feb 03, 2016 10:05 am

Outstanding

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Re: Faster Heated Bed

Postby ignacmc » Fri Feb 12, 2016 1:21 pm

Hello to all

I have wired my SSR (Crydom D1D40) as per gchristopher schematics:

[img]/Users/ignacmc/OneDrive/3D PRINTING/24V PSU - SSR/24v_upgrade.jpg/[img]

But when I switch on the printer F3 fuse blows...Any advice?

Thanks in advance

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Re: Faster Heated Bed

Postby Eric » Fri Feb 12, 2016 4:33 pm

ignacmc wrote:Hello to all

I have wired my SSR (Crydom D1D40) as per gchristopher schematics:

[img]/Users/ignacmc/OneDrive/3D PRINTING/24V PSU - SSR/24v_upgrade.jpg/[img]

But when I switch on the printer F3 fuse blows...Any advice?

Thanks in advance


We can't see the image link, since you used a path that's local to your machine. I know OneDrive is technically in the cloud already, but think their permission system currently only allows sharing with other OneDrive users. I'd use some other image hosting service if you want us to see it.

Anyway, the heat bed output is on the F4 blade fuse, not the F3 nano fuse, so unless you're connected to a different output, you may have a problem with something else entirely.

F3 covers all the heater/fan outputs EXCEPT the heat bed. I'd get out your meter and start checking for shorts.

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Re: Faster Heated Bed

Postby ignacmc » Fri Feb 12, 2016 5:24 pm

Thanks Eric for your answer

Yes, it is the first time that I try to attach an image and I will do it better in the future ;-)

My problem is SSR related since if i try to power on the RAMBo with it disconnected, everything seems to be OK

But as soon as I connect the SSR, the F3 blows after power on. I have checked the wiring and I think that it is ok, with the positive wire entering the SSR on "+2" terminal and exiting on "1" terminal and then connected to "+" on the Onyx.

I have even tried a second Crydom D1D40 and the same keeps happening. I am really clueless

Thank for your advice

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Re: Faster Heated Bed

Postby Eric » Fri Feb 12, 2016 7:29 pm

I've no clue what's going on then with the information I have. Why the F3 fuse would blow really puzzles me.

I've never done the SSR thing myself, so probably best to let someone who has jump in. If there's a gotcha, they're more likely to know it.


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