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Hey! So I've gotten my Rostock MAX together and gone thru the initial calibrations. I've done a test print and it's behaving alright, but I'm not too pleased with how long it takes the bed to heat up. I've heard that the Onyx bed hits its sweet spot at around 19V so I'd love to swap out the power supply for something that can provide more juice. I read elsewhere on the forum that the rambo board can accept up to 24V. Is this true? If necessary I could just replace the bed power feeds with a higher voltage supply and leave the rest on a 12V supply.

Also, does anyone have any suggestions for power supplies around 19V? I'm figuring around a 20A supply would make sense, right? Thanks!

JeremyAgost wrote:Hey! So I've gotten my Rostock MAX together and gone thru the initial calibrations. I've done a test print and it's behaving alright, but I'm not too pleased with how long it takes the bed to heat up. I've heard that the Onyx bed hits its sweet spot at around 19V so I'd love to swap out the power supply for something that can provide more juice. I read elsewhere on the forum that the rambo board can accept up to 24V. Is this true? If necessary I could just replace the bed power feeds with a higher voltage supply and leave the rest on a 12V supply.

Also, does anyone have any suggestions for power supplies around 19V? I'm figuring around a 20A supply would make sense, right? Thanks!

Welcome to the forum!
There are numerous examples of using 24v power supplies on the forum. The power supply we like is listed here: http://www.ebay.com/itm/Meanwell-Power- ... 41780219cc
It has more than enough output and is quite sturdy. The output can be varied from 19V to 24V. We usually power the supply using a DC-DC SSR with the input to the SSR coming from the heatbed output of the Rambo. That way all the current passes through the SSR rather than the Rambo. You can read about it here: http://forum.seemecnc.com/viewtopic.php ... 8&start=60
Happy Printing!

Thanks, you mean a solid state relay (SSR)?

JeremyAgost wrote:Thanks, you mean a solid state relay (SSR)?

Yes, a solid state relay. Sorry about the typo, it has been fixed. The SSR is DC-DC not the ordinary DC-AC. Here is a listing: http://www.amazon.com/Sunkee-Solid-SSR- ... =DC-DC+ssR

Haha, yes I already found one of those! http://r.ebay.com/vu4mrt

The RAMBo is fully capable of running on 24 volts. No need for an SSR.

Nylocke wrote:The RAMBo is fully capable of running on 24 volts. No need for an SSR.

What would the power draw of the bed be at 24V? I've heard elsewhere here that the rambo is rated for 15A thru the bed terminals.

JeremyAgost wrote:

Nylocke wrote:The RAMBo is fully capable of running on 24 volts. No need for an SSR.

What would the power draw of the bed be at 24V? I've heard elsewhere here that the rambo is rated for 15A thru the bed terminals.

16.6 or so amps. The resistance of the bed is approximately 1.5 ohm. The reason the people on the forum who have converted to 24V power supplies
have used SSRs to drive the heatbed is because they didn't want to take any chance of ruining the Rambo. Although it is rated at 24V I think the
fuse for the bed is 15 amps. When you can buy an SSR for less than $15 it only makes sense to use one rather than send that much current through
the Rambo. I believe Edward, Cambo3d, Myself and MHackney and I'm sure others have done this conversion and everyone has used an SSR.
You may be right when you say it is not needed but you are in a minority feeling that way again I ask why take the chance?
If the power supply I mention above is purchased it can be adjusted from 19V to 24V with a 31A capacity. Very well made. Fan is a little loud.
At first everyone was concerned if the Onyx could withstand 24V and it was found out that it could. No burnouts as far as I am aware.
Edwards conversion is here: http://forum.seemecnc.com/viewtopic.php?t=2578&p=19352 Cambo3D has it in his build thread.
Happy Printing, Nylocke

Three independent power rails for flexible input power configurations
Heated Bed, 15A 12-24V (version earlier than 1.1 limted to 14A 16V due to fuse rating, see rambo_development for hacks)
Extruders and fans, 5A 12-24V (fuse can be exchanged for up to 10A capacity) 10V-26V input voltage
Motors and logic, 5A 12-24V (fuse can be exchanged for up to 10A capacity) 10V-26V input voltage


So the heated bed should be run at a max of 16 volts, unless you do some "hacks", aka

The heated bed circuit's voltage is limited by the RGEF1400 PTC fuse which is rated to 16V. If a higher voltage is required this fuse can be replaced with a jumper wire and off board fuse holder. Make sure that your wire and solder are sufficient to carry the high current of this rail.

So from the looks of things, just use a larger fuse and it sounds like it would be aok, if you're really worried, you could run everything on 24 volts (I've heard of some benefits from running the steppers on 24V) except the bed input on the RAMBo, which you could get a small 12v 1 amp wall wart style PSU (I'm assuming the SSR can be operated by 1 amp) and do the SSR approach. Just more options.

If you run the whole board at 24V what happens to your 12V fan outputs? Do they have their own regulators?

626Pilot wrote:If you run the whole board at 24V what happens to your 12V fan outputs? Do they have their own regulators?

The ones connected to the outputs on the Rambo can be controlled via firmware PWM.
If you have directly connected fans that are 12V you would need a 24v - 12V converter.