I'm looking at buying a 300W tubular adjustable resistor. Like this: https://www.digikey.com/product-detail/en/vishay-dale/RBEA03001R000KFB00/541-10193-ND/9765057
Digikey has four part numbers in that RBEA series, 1Ω 25Ω, 50Ω, 100Ω. All of them are 300W, For any of these, how do I know the adjustable range for a given part number?
UPDATE: For background, I want to build a dump load and I would like it to be a little bit flexible, if I can. I'll end up wanting somewhere around 0.5Ω to about 2.0Ω per resistor (I'll probably have four of these in a 2S2P array). It doesn't need to be quick to adjust, and the resistance doesn't have to be dead on. I'll be dumping a max of about 600W and have a plan for a fan and nothing flammable around.
Answer
Figure 1. The resistors in question.
simulate this circuit – Schematic created using CircuitLab
Figure 2. The symbol and normal method of connection.
The adjustable range is from 0 to the specified resistance. Figure 1b shows the normal way of wiring these so that if the wiper fails to connect for any reason then the circuit will see the maximum resistance rather than an open circuit. This is preferable in most situations.
Note that the 300 W rating relates to the full length of the resistor being used. If only using half of the resistor (wiper in the centre) then the rating will be reduced to 150 W. This is because the resistance wire will be rated by power per unit length. Other settings will have the same proportional relationship.
Also, be aware that 300 W will be the power you need to dissipate in your enclosure or space where the resistor is used. The derating curve in the datasheet shows it can work (at low power) up to 400°C so make sure you test this, allow adequate cooling and clearance between flammable components.
No comments:
Post a Comment