Heated bed query?!

[enesoz]

I was in the middle of preheating my heated bed to 90 degrees ready for a Nylon print, when it reached about 70 degrees it just died and the temperature started plummeting. After opening up and investigating I found the red wire that connects to the RAMBO controller had fried, about 10mm of insulation had melted on the wire, and the screw that holds the wire in place on the RAMBO board was damaged too.

The great support at SeeMeCNC arranged to replace the RAMBO controller but I want to prevent this happening again. When printing with PLA I only ever pushed the heated bed temperature to 60 degrees, but with nylon I needed the bed at a higher temperature. I don't know if its the red wire that can't handle the extra voltage but it's something I definitely want to prevent again. I made sure my wire was screwed in properly so that definitely wasn't something.

Do I get a wire that can handle a higher voltage and simply western union splice the two together? or is there something else I can do, I'll be needing it to heat up to about 80-90 degrees very often so something that speeds up the heating process is also preferable. Whats the best solution / mods?

Thanks

[Xenocrates]

I believe that it was a poor connection at the screw terminal. The wires provided can handle the load (I routinely heat mine to 100C with stock wires). I would re-terminate the wires, and use a crimp on bootlace for the connection http://smile.amazon.com/Generic-Connect ... colour/dp/ which will need a crimper (There's a deal linked on the page for me), if you don't have one.

You can also use an SSR to handle the current, which will also serve you well for moving to 24V power if you find you still need more bed heat. http://www.auberins.com/index.php?main_ ... cts_id=288 works well. Run the bed power through it, and just wire enough power to control it through the Rambo for the bed. That way you can use heavier wiring if you want to, and move the failure point from the Rambo onto a cheaper, separate component.

[enesoz]

I'm still a bit of a newbie so it's going to seem like I'm asking some really basic stuff! I like the SSR option, so where do I start from a fried wire with this option. First step strip the insulation and cut off the damaged wire then connect that into the SSR then have another wire coming off that and connecting to the screw terminal?. You mentioned something about being able to run 24v of power, how do I do that?

[Xenocrates]

So, for the SSR option. It has 4 terminals on it. Two are the load side. Connect the power supply directly to this, and then to the bed. Leave the ground (Black wire) hooked straight to the power supply, without going through the SSR, as there aren't enough terminals. Run small power wires to the Rambo power in for the bed (or full size, it doesn't matter much at all). Connect the heated bed out terminals on the Rambo to the other side of the SSR. There will often be polarity for relays, make sure that it's matched (+ to plus, red to red, ETC). This should now function to switch the bed without putting much current over the Rambo.

If you wanted to go to 24V (which quadruples the bed power by the way, not just doubling it), you need a 500W 24V supply, and fairly heavy gauge wiring (21 ampacity wire is ~12 gauge IIRC). You then swap the connection from the original power supply on the SSR to the 24V one. Nothing else has to change (If you change anything else, you will need to adjust the hotend heaters and fans, as they will also pull 4X power, and will need an even bigger power supply). Of course, you can't fit 2 power supplies inside at the same time (At least not well, a DIN rail AC-DC converter might barely squeak in, but they are kinda expensive and you need at least 90W to run the other stuff well). So you get to make a few choices there, as far as how you handle things.

On the other hand, there is the far more complex, but also more functional auto-fail-over relay controlled setup, which requires a DPDT ice cube relay wired in to swap the 12V connection between the SSR and the bed itself, on the detection of 24V power (Which can fail in interesting ways if done wrong). You start with wiring your relay (It must have a 24Vdc coil, not a 12Vdc, or a 120Vac), in parallel with your connection to the SSR. (Not in series, as you want a completed connection when the SSR is off, so as to trip the relay over into powering the SSR). Then to the first common contact, wire the positive connection from the rambo. To it's NC counterpart (Consult your datasheet, or a diagram of the specific relay, they are mostly standard but sometimes they aren't), connect the heated bed (Note that this is why you need at least a 10A rated relay, preferably one with a 15-20A rating). To the NO contact, connect the SSR. Then do the same for the ground on the second contact set (This will prevent any stray high current from getting to the Rambo, as 20A is a BAD plan for PCBs.) Thus, when 24V power is present, the Rambo will run the SSR, allowing 24V power to the bed. Should the 24V PSU fail or be unplugged (Since it will be an external, separate unit), it will fail over back to the 12V power supply, and the Rambo will switch the full current (Less than Ideal, but also less complex than swapping the voltage to the SSR and reduces the need for high-amp rating relays). If the 24V PSU comes online while it's running, then it will swap over. Of course, this means you still need the full 12V supply, as well as needing the wiring to be able to handle the original load. It's also the most expensive option.

As a note, if you do go for 24V power, I suggest, very heavily, that you buy a good quality power supply (A Meanwell or similar), and equip it with a properly rated IEC connector (Which for 500W is only ~5A), as well as a switch, and circuit breaker on the system.

[DeltaCon]

Hmm, a separate switch is actually a very good idea, have to keep that in mind, thanks.
What exactly do you mean by "circuit breaker", do you mean a fuse? English is not my mother language, so I'am guessing...

if you do go for 24V power, I suggest, very heavily, that you buy a good quality power supply (A Meanwell or similar)

I am very interested in the similar part, as the meanwells are sooo expensive...

[Xenocrates]

Close, but no cigar. A circuit breaker is a reset-able over-load protection device. It is usually slightly slower than a QA fuse, and much slower than a SQA fuse, and most are designed to run at 80% load most of the time. It's like a fuse, but can just be turned off and back on when it trips. http://www.automationdirect.com/adc/Sho ... C5-1-NA-SP is an example. https://en.wikipedia.org/wiki/Circuit_breaker for more reading.

A similar unit might be https://www.arrow.com/en/products/pmc-2 ... aQodtYoBVA. But there is no 20$ fix. It really isn't that much cheaper. These are high-amperage industrial supplies. They will be somewhat expensive.

[enesoz]

Thanks Xenocrates very helpful info, so I have attached a quick diagram of how I think it's supposed to be wired, let me know if I have understood you correctly?

[Xenocrates]

[img]http://figures.oreilly.com/tagoreillyco ... 43-web.png[/img]

more like that. You need all 4 wires connected. Admittedly, the input is not 5Vs, but I stole that ready made. Red wire from rambo to the one labeled input 5V (3), and black wire to ground.

[Eaglezsoar]

See this link for a descriptive talk about adding an SSR. http://forum.seemecnc.com/viewtopic.php?f=43&t=7766

[DeltaCon]

A similar unit might be https://www.arrow.com/en/products/pmc-2 ... aQodtYoBVA. But there is no 20$ fix. It really isn't that much cheaper. These are high-amperage industrial supplies. They will be somewhat expensive.

Well, since the meanwell sp-750-24 locally changes ownership for about anything between 200 and 300 Euro (new and without shipment), this one is a hell of a lot cheaper. I found that digikey sells with free shipment for everything above €65,-- So that is a hell of a lot cheaper for us, Europeans. So basically I can choose this one new for the same price as a used meanwell from Thailand or Honkong or so... What would you do? The specs say that it is 600W but that it can give 1200W for a period of 5 minutes. So I guess it has more than enough power in spare. I just ordered one. Thanks for the info Xeno!

http://www.digikey.nl/product-search/en ... 24V600W1BA
(changed link, this one works...)

[Xenocrates]

Heh. I guess that market segmentation is a real bear. If only shipping was reasonable (For example UK to US ~20$, while from in US to US is ~10, and yet UPS says US to netherlands is ~140$ (Estimate was for City of industy CA, to Amsterdam) when the difference in distance is fairly small (I've driven further in a day)), then you could get a Meanwell for about what it costs me (115 with dips to 95 for the 500W unit) plus the shipping. As it stands, you might be able to get it for price+shipping, but shipping is insane (At least with all the quotes I can get).

I'm glad it was a better deal for you.

[DeltaCon]

Yeah, US shipping is often a dealbreaker. I'm guessing DigiKey has a warehouse in Europe from which they can send free shipping.

edit:
http://www.digikey.nl/nl/en/international/europe.html actually tells that everything is located in one facility in Minnesota. Confused as to how they do free shipping worldwide...

So... off to some good deals for a SSR and a step-down! And I really have to continue on my heatchamber also. And someday I will have to get me a duet...
I have more wishes than I can afford...