This is required for cases where your electronics is not prepared to use unmodified ATX PSUs. Modifying a PC Power Supply for general (RepRap) Usage The 5V rail is always oversized (which doesn't matter), attention should be on the 12V rail's capabilities. In the RepRap forum you can find a number of power supply experience reports. 5V 0 to 2A for Balancing_ATX_Supplies or providing a #Base_Load.5V 12V 10A for a 120W heated bed or PCB_Heatbed.12V 2A for a 22W hotend heater (e.g.: J_Head_Nozzle#Heater_Resistor) (or more for a Ceramic_Heater_Cartridge).With temperature control, the bed is turned on and off at a very quick rate, also known as pulse width modulation (PWM). Some voltage regulators inside the PSU apparently have no trouble delivering 120 watts to a temperature controlled heated bed, others need to be oversized. This one is a bit tricky, as some PSUs with identical specifications work better than others. In one case, the load had to be applied to the 5v standby wire (purple) to ground rather than directly to the 5v rail to ground before the power supply would function properly. Connecting a 4.7 ohms 10 W resistor, an old CD drive or a 12 V light bulb (into the 5 V rail, see picture) are well proven methods to generate this "dummy" load. A symptom of this problem is that the PSU will simply refuse to turn on, it immediately shuts down after being turned on or emits a clearly audible high pitch whine, all unless there is a minimum load on the +5 V rail. Whether your ATX PSU requires a base load or not has to be tried. Some ATX PSUs (not all) require a minimum load on the 5 V rail to work properly. ![]() Fully close the housing before connecting mains again.Įlectronics prepared for PC Power Supplies.There are high voltage capacitors inside which discharge slowly. If you still think you need to do so, disconnect the mains cable and wait at least 10 minutes. If you think you have to open the housing, think twice.Don't open the housing unless absolutely neccessary.Don't risk metal parts, like screw drivers, falling into it through the venting holes, either.A PSU is not the right place to place your coffee cup onto. Still, following a few simple rules is a good idea: No high voltage parts touchable unless you open the housing. They have good overload and overheat protection built in. ![]() Generally, power supplies built into PCs are reasonably safe, even when used outside a PC.
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