24v power supply question

[MorbidSlowBurn]

I just installed the mhackney aluminum plate for the heated bed. In the process I added another set of wires for the onyx bed. After reassembling everything I now get a lot less on heat on my bed thermistor. I confirmed that the glass is also about the same. Nice even heat but max temp is now about 55C where in the past I was able to get close 70C if I waited a half hour and 60C after about 15 minutes.

So I am thinking of getting a 24V power supply but have read a couple of different methods. Want to know what everyone thinks is the best route. I plan on keeping the hot ends and steppers at 12V since I don't want to stress them. So based on the power consumption of the onyx heated bed and the limits of the Rambo board what would the appropriate hardware be; fuses, relays, power supply...? I know there have been posts on what has been done but also want to hear if there is anything they would change to their setups.

[mhackney]

Is this the stock 12V supply? My 3rd party 12V did much better than that by kicking it up to 15V.

My Recommendation based on a recent resistor blowout at 24 Volts:

Power the Arduino, motors, and mosfets with 12V. Only power the heated bed (the top most of the 3 power terminals when looking at it mounted on the door) with 24V.

You don't need anything else, the 24V supply hooked right up to the connector. I posted the link to the PS I used in my build thread. You should then enjoy 4-5 min heatup's to 80°C with both the aluminum plate and glass installed.

[MorbidSlowBurn]

Yes I still have the stock power supply.

And with driving directly through the Rambo (version 1.1) I was concerned of the amperage going though the traces. I am a mechanical engineer so the electronics stuff I get a little concerned of over driving. Plus I thought I read something about increasing the fuse size.

Should the resistor for the LED on the bed need to be changed for the higher voltage?

BTW thanks for the quick reply

[mhackney]

The RAMBo 1.1 is designed for this so no problem. If you have a rev 1 RAMBo then you should probably change the fuse as described on he RepRap RAMBo page. Even your steppers are fine with the increased voltage. It's the resistors I had blow on me. Maybe unrelated but I've never lost a resistor until now.

I didn't change my LED and it is working fine.

[cambo3d]

you will be over drawing the current on the board in my opinion for a 15amp fuse. at 24v the onyx draws around 20amps just for the bed alone.

if you look at my build log you can see what i did there.

[MorbidSlowBurn]

cobo3d- that was a concern of mine. In an effort to get more info I read one of mhackney's lengthy but informative posts. Basically in his post, he goes through the calculations of Power and Voltage. At 24V the onyx would draw about 19Amps, this would require a 450W power supply. Since mhackney, I believe, is using a 350W 24V power supply this results in approximatly 14.5Amps of available current at 1.3Ohms (Onyx resistance). If I was to replicate and use a 350W 24V power supply I will stay within the 15Amp capability of the Rambo board. This would allow for a minimum of components and still give a reasonable heating time for the Onyx with limited concern of damaging the Onyx.

Edit: Found this power supply on Amazon that looks like it fits the bill.

[cambo3d]

that will work but you will be using all available current from that supply, with no margin for anything else and running a power supply at its limits all the time is not good and decreases longevity.

[MorbidSlowBurn]

The heated bed is the only thing I plan on using the 24V power supply for. And with the Rambo board using PWM it would not be running "continuous". It would be pulsed once it reaches temperature, not sure if that is any better.

If anyone can think of any add-on's that I would need 24V for I would get a bigger supply. I would still like to limit the Oynx to 15 amps as it really wasn't designed for 24V @ 19Amps. Don't want to find the weak link.

Current add-on's planned for my Rostock are:
Second extruder (maybe a Tool changer if I see it waranted)
LED ring
Cooling fan

[cambo3d]

it wasnt designed for 24volts period