Alrighty then... I'm hoping my 350W PSU is large enough to drive both printer and HB...
My heated bed is a MK3 alu heated, and specs say about 5.4 ohms of resistance when powered by a 24V supply... that makes around 107W... Adding the 160W of the Ultimaker should still leave me with enough... hopefully
I just managed to switch off the not selected stepper in Marlin. The power consumption indeed droped from 160W to 140W...
Wow... So you are telling me 120W were going to the steppers and a few fans?
No, the 120W is the total supply of the UM-Origonal (19V at 6.32A). So take 40W off that for the first heater. Then, take another 40W for dual-extrusion. Which gives 40W for everything else. Which is more then enough, unless you add a heated bed.
The steppers are current driven, they are driven with 1.1A, but not 19V. The drivers regulate the voltage to get the proper current. That's where you go wrong. Look at the specs of the motors:
https://github.com/Ultimaker/UltimakerOriginal/tree/master/1082_X%2CY-Motor
They have 1.68Ohm resistance, 1.1A, with V=A*R that gives 1.848V, not 19V. So that's about 2W per motor.
We are not talking about the same side of the PSU. I'm talking about the primary side (230VAC). The consumption of the stepper motor itself certainly is as Daid pointed out. But on the way to the motor current quite some power is lost in the electronics (dissipated heat) by voltage regulation and current control respectively. If it wouldn't be that way, the stepper drivers would not have to be actively cooled.
Daid, It don't think it's that simple.
I had a lot of electronics in school and forgotten most of it. However, I believe your estimate of 2W is for DC.
Because the motor coil forms an inductor, the current and voltage will be different than the DC values as the coils are switch on and off to move the rotor.
An inductor resists the change of current through it. So if you start with an unenergized motor (in other words, zero current flowing) and apply a voltage to it, it will take time for current to build. The coil will look like an open circuit and then start to appear as a decreasing resistance with increasing current. The rate the current builds is dependent on the amount of voltage applied to it.
For steppers, to increase the step rate, you have to build the current faster so drivers apply much higher voltage that the V=I*R of the DC characteristics would indicate. Once the desired current is reached, the driver starts to chop the voltage to control the current.
During this process, much more than 1.8v will be applied to the coil. This implies that you will also see much high power used by the motor.
The actual power delivered to the motor will be dependent on the frequency of the chopping and the rate of stepping.
Hi!
I also got a 24V PSU with 400W for my HB which consists of a silicone heater for 18V currently driven by a relais
Now I also like to move the whole UM system to this single PSU and use PWM instead of BangBang for HB supply.
Any hint on the conversion appreciated!
imho the best solution is to use a car DC/DC converter like it was shown before, and use it to power the entire UM electronics from the 24V PSU.
This way, you don't change anything on the UM1 and don't have to worry about any effects this might have (like quicker nozzle heating, maybe even throwing it's regulation out of balance).
Also, these car DC/DC converters are really cheap and easy to use: something that can also be recommended to less experienced users.
As for my part, I'll just keep the two PSUs separate. There is no big benefit to replacing the standard brick as long as it's working fine, except that you'll save some space and one mains socket.
What can be much more of a performance impact is using a good MosFET instead of a relay. Relays usually have contact resistances somewhere around 0.1 Ohms, while a good MosFET can have as low as 0.005 Ohms.
That can be quite the difference if your heater only has around 1 Ohm resistance. You lose several % of the energy in the relay, while you lose pretty much nothing in a MosFET.
As soon as I get to it (I hate that sentence...) I'll put up a simple little MosFET "relay" board that anyone can make for themselves and that works without losing any noticeable energy.
Also, the clicking of the relay would drive me mad within a few minutes 
I also hate this sentence but as anybody else, we have only limited time in our days... :-)
Thank´s for your info - looking forward to hear from your solution, especially as my silicon pad has app. 1,5 Ohm. Nevertheless, to use PID/PWM would be interesting too...
Technically, PWM is still kind of bang bang (or maybe tappity tappity). The real improvement comes from switching to PID, (which of course requires something like PWM or other form of precise current/voltage regulation).
Like Jonny said, a Mosfet/SSR is a big improvement over a relay and they are pretty cheap.
For voltage regulation, there is a large number of high efficiency single chip solution available. One could probably find one that is pin compatible with the one of the UM board and can step down 24V to whatever the UM uses without any problem. I don't personally, like the idea of layering voltage regulators without cause. Seems like it could potentially introduce some sort of problem.
Besides all this, it seems like it can only be good to have the power supply for the UM board and heater be separate. It would help insulate the UM board from fluctuations in voltage as the heater is turned on and off/ or any sort of electrical problem with the heater.
Guys, I think you're overcomplicating this. All of the 350/400/500W Chinese power supplies I have used from ebay can be adjusted with a preset on the board down to 19v, which can power your whole setup with no issues at all. I have run like this for 18 months now.
After a while I changed the 7812 to a switching one, and put the volts up, but outside of a marginal change in warm up time, it makes no difference, 19v is plenty into a reprap PCB/Al heater, and I subsequently turned it back down to 19v to keep the power down.
If you solder direct to the tracks, the on board mosfet is quite capable of driving the bed directly, with bang bang or PWM.
This i what I wa planning to do:
Remove the Bead MOSFET from the UM board
Take a wire off the gate pin on the UM board.
Solder the FET you have taken off of the UM board onto a small bit of strip board.
Take the wire that you have put onto the gate pin on the UM board onto the gate pin of the MOSFET on the external board.
Tie your 24V PSU and the 19V side GROUNDS (Drain on the MOSFET) together.
Put HB in between the Source of the MOSFET and your 24V PSU.
Cost: Nothing if you have a bit of strip board lying about.
There is no need for another MOSFET or SSR. Uses parts that you have already too.
Will upload a diagram soon.
Hmmm... This was also my first attempt but now it seems that I already ordered (accidentially) a nice 0-24V PSU with 400W...
So bring it to 19V should be no problem. Nevertheless, now it's to late to change my order...
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Dim3nsioneer 557
Forget the fans. It's mostly the steppers. There is a reason why they get hot (up to 60°C). Daid recently posted that the standard adjustment of the steppers is about 1.1A. As it is driven with 19V (in steps down to 12V and something like 2-3V, but I think the voltage is not transformed but divided, isn't it?) this makes something around 20W per stepper. And as there are 5 steppers enabled and the electronics itself needs 14-17W the number makes sense...
But don't forget that I measured on the primary side of the PSU. The power factor of 0.86 might also be overestimated. I think the accuracy of the measurement device relates mostly to the power measurement and maybe less to the measurement of the power factor.
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