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# what can be used as the dummy load on a converted power supply

I dont have a 10 watt 10 ohm resistor for the dummy load but I do have several others like 7 watt 6 kohm ,or 5 watt 300 ohm and some 10 watt 7 kohm can I use any of these if so how to wire them

## Comments

8 years ago

A light bulb of suitable voltage and wattage or close often makes a good dummy load + you can see the PSU is on.

Answer 8 years ago

Yea I tried that I didnt like the way it looked If I decide to do something In It has to be correct . It is a 300 +watt power supply from an old dell computer. I custom built a metal box it has 6 120 v ac plugs 4 usb charging ports molex plugs sata power and others

8 years ago

Dummy load just needs to draw a few watts from the 5v rail. It doesn't have to be specifically 5 watts (10 ohm at 5v). So long as the ohm rating doesn't draw enough current to over-watt the resistor you're fine. Try to draw 2-10 watts and you'll be fine.

Answer 8 years ago

So one 5 watt 300 ohm or one 7 watt 6.2 k ohm should work fine i knew the wattage needed to be between 5 and 10 watts but wasnt sure about the ohms

Answer 8 years ago

NO!

It's not the watt rating, it's the 'make sure you draw 2-10 watts' part that is important. The watt rating is just how much heat it can dissipate without exploding!

Using ohms law you can calculate how much power it will dissipate:

V= IR

Volts = Amperes (Current) * Ohms (Resistance)

at 5 volts:

300 ohms

5 = I*300

I = 5/300 = 0.0166 Amperes

V*I = Watts

5 * 0.0166 = .083 watts. <<< NOT ENOUGH!

Say you want to draw 3 watts, work it backwards.

at 5 volts, 3 watts is 3W/5V = 0.6 Amps

V = IR

5 = 0.6 R

R = 5/0.6

R = 8.3 Ohms.

You need an approximately 8 ohm resistor RATED FOR better than 3 watts, 5-10 watts is a safe rating to make sure it doesn't blow up.