Is UM2 PSU underdimensioned?

[gregwar 1]

Hello,

Let's do some simple sum:

1) The Hot bed is 3.3 Ohm at 24V, it's like 7.2A heating

2) The nozzle is like 24Ohm, let's say 1A heating

3) Steppers are configured to ~1.3A, there is 4 of them (XYZE)

4) (not even considering fans, leds and electronics)

This reach a total of 7.2+1+1.3*4 = 13.4A, for a 9.2A PSU

This is like, underdimensioned right?

[Dim3nsioneer 356]

The steppers are not running at 24V but at something around 1.5V or even lower (I believe they are rated 2.8V).

You have to add up power, not current.

[gregwar 1]

You mean that each motor is 2W or so? That sounds really low

[zoev89 72]

The power consumption of the steppers is dynamic. When it is holding still yes it is consuming little power. But when turning fast it will consume much more, that is why they get hot when in use.

[gregwar 1]

Ok, but don't you think that 9.2a is short anyway?

[zoev89 72]

I don't own a UM2 so I can't say much about the actual power consumption. Measure would give the correct answer. I would assume that Ultimaker did its work and that the power-supply is up to the task. Note that originally the power-supply has a spec to also support a second hotend.

The actual power consumption is not always the sum of the individuals. For example the heated bed I don't know the resistance but if 3.3Ohm is measured cold it will be higher when warm. PCB heaters tend to increase resistance at rising temperature variations of 20% are expected. When heating the motor's are not active. So when heating up in the very beginning it should deliver 7.2A for heating but that will go down with rising temperature. Once on temperature it starts printing.

None of the motors are running at the same time and also it is very unlikely that all of them would draw maximum power at the same moment.

So to be exact you really have to measure.

My UMO has a 400W power-supply but note I put 260W into my heated bed when it is on.

[nallath 527]

When it is holding still yes it is consuming little power.

 

This is not true. Holding still consumes a lot of power.

[zoev89 72]

As I said you have to measure since it is very difficult to predict the actual power usage.