First step is to know the resistance of the heated bed in ohms. Typically they are around 1 ohm. Then the wattage will be V*V/R (v squared over r). So if the voltage is 12V and resistance 1 ohm, 12V will give you 144 watts. To get 360 watts (that's a lot - I have 100 W which is slow but 200W I would think is enough) take the square root: 19V (if 1 ohm heated bed). If it's 2 ohm's heated bed then 12V gives you only 70 watts. 19V gives you 180 watts and 27V is needed to get 360 watts.

So it's good to understand ohms law and the power law. They are extremely simple formulas but really knowing subconsciously them is very helpful when doing anything with electricity.

If the manufacturer tells you the heated bed is "1 to 2 ohms" well that's a HUGE range. You really need to know this before you can pick the ideal power supply.

If you get a 2000Watt supply but it only puts out 12V and the bed is 1 ohm then you will only get 144 watts into that heated bed. The 2000Watt is a maximum, not a given.

This is frustrating when ordering a heated bed because you don't know how many ohms it is until you get it. Also the resistance changes when it gets hot. So you kind of need to know the resistance when it is at the extremes (room temperature and 70C) so you know if you will draw too much current (too much power) for your power supply.

For example if they tell you it's 2 ohms at 70C but don't mention that it is 1 ohm at room temp. And you buy a 400 W supply at 27V. When you hook it up it will try to draw 729 Watts and probably the supply will go into protection mode.

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## owen 19

You should decide which HBP to buy and find out what power it consumes at what voltage.

Then buy a PSU that supplies that voltage and a wattage greater than that required.

The wires from the PSU to the HBP need to be thick and flexible.

Before you turn it on get an electrician or similar to check it over.

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