13-04-2014, 09:52 AM
(13-04-2014, 09:34 AM)richard296 Wrote: I think i understand now. It's the readings taken on the components or the load it's taking or the circuit that feeds it. Not what someone has added later. Am i getting there. Reason for confusion the smallest resistor i could get in alloy case is 25 watts. I thought this would throw all calcs out. What i did was place a sheet of alloy on top of the ceramic resistor. 50 x 50 x 8mm no paste. I may be imagining things but the plate wasn't even warm. I could even keep my hand on the resistor. It had been on for 2 hours or so. If this is ok. I will solder resistor other side of board it will then protude through the top of alloy case after cutting a hole. I will then fasten plate to resistor using contact paste. What do you's reckon.
Yes, it's the voltage/current measurements that count, 15 watts written or stamped on a resistor doesn't mean it's going to dissipate 15 watts, it's the actual current flowing through it that determines the actual power it will dissipate, that's why earlier on we asked for the voltage measurement on the input and the output side of the resistor, from that you can work out what power the resistor is dissipating.
Once you know the power it's dissipating you can choose a wattage rating to suit, the higher the wattage rating is above the dissipated power the cooler the resistor will run.
Lawrence.
