Hi guys. I am trying to build an accurate dummy load for testing purposes. I know this can be done with resistors and appropriate voltage/amperage input. What I dont know is: 1) what kind of resistors do I need? Do they need to have a specific wattage? 2) Also, since resistors are more like a cylindrical type how can I attach them on an evaporator in order to test it? 3) Is there any way to make an adjustable heat load because as I know a bad thing with resistors is that we can only have a fixed heat load. Let me know. Thanks
so you just want to turn the PSU on outside of the case? im not really sure what a "dummy load" is but if oyu just want to turn it on without a MOBO connect the green wire on the ATX connector to any black wire and your set
1. All depends on the application. The composition you pick will determine the wattage. If you pick carbon film, then you'll be relegated to <1W resistors. If you pick something like sand, then you can go to the +10W area. 2. Not all are cylindrical. There are quite a few that are rectangular, and those are your higher wattage ones. 3. Not true. The watts dissipated is the product of the current running through it and the voltage applied (P=I*V). If you want an adjustable heat output, simply alter the voltage or current. Voltage is probably the easier route, as all resistors have a maximum current rating, no matter what the voltage is, which is equal to (P/R)^.5 (square root of the quantity power divided by resistance).
If you are planning to build a load to test DC power supplies you can use wire wound resistors without much problem. If you wanting to use this to test audio or RF signals then you should use a non inductive or purely resistive resistor since the inductive reactance can influence the device under test. You can get non-inductive wirewound resistors. The turns are wound so they cancel the reactance. To vary the load you can add or subtract resistors to the circuit. Just keep the load resistance at a value that doesn't overload the device under test.
I want to use them to test a waterblock and an evaporator. Whypick1, in (1) I meant if i needed specific watts. For example, I know that if I apply 12 volts and 15 amps to a 0.8 ohm resistor the heat output will be 180 watts. But does the resistor needs to be specific watts?
It needs to be at least a 180W resistor, the rating is the maximum heat it can dissipate if you keep it at 20°C. At higher temperatures the rating falls off, so you need to keep it cool with your heat-sinking. http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=272681&N=401
