NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Basic Electronics » Deciphering power resistors

February 25, 2010
by treymd
treymd's Avatar

I pulled some power resistors out of an old Boss car amp, and I don't get the markings.

they say 5W0-3(ohm symbol)K

why is the K after the ohm symbol and is the 0-3 part meaningful?

February 25, 2010
by mongo
mongo's Avatar

The K is probably meaningless in this instance. It sounds like it's either a 3 ohm or a 0.3 ohm, 5 watt resistor. The lower range is some times more difficult to measure, unless you have a decent digital meter.

February 25, 2010
by bretm
bretm's Avatar

Usually when the "units" symbol appears in between the two digits, it means put the decimal point there and then move the units to the end. So 5W0 means 5.0W (5 watts) and 3ΩK means 3.0KΩ. Measure the resistance and let us know, I'm curious.

February 25, 2010
by BobaMosfet
BobaMosfet's Avatar

I would agree with bretm. However, if that is true, then E = 122.47. Which seems high for that environment.

February 25, 2010
by mongo
mongo's Avatar

hmmmm...

Ya both have a point. It very well could be a 3K 5W resistor...

If it came from an audio amplifier, it's not unheard of to have higher voltages.

February 26, 2010
by treymd
treymd's Avatar

Meter swings between 0.3 - 0.5 ohm. I cross checked that with a 33 ohm resistor and it read 32.9 so I know I'm reading the meter right.

Not sure how I'm supposed to get 0.3 from 3(ohm)k, but when in doubt get out the multimeter is the lesson learned!

February 26, 2010
by treymd
treymd's Avatar

I was evaluating the possibility of using these suckers to keep my coffee cup warm, I'm wondering if basically the resistance is not high enough? I know my homemade power supply uses a 10W 10ohm resistor and it gets fairly warm.

February 26, 2010
by BobaMosfet
BobaMosfet's Avatar

treymd

What makes you think it is a resistor? It could be an induction coil. The numbering on the side might have nothing to do with what we are suggesting.

BM

February 27, 2010
by treymd
treymd's Avatar

I'm just going on how they tend to label things, power resistors look one way caps look another, but Assuming that I know it all is folly, you are right. The only way I could know exactly what it is would be to tear it apart right?

Coils are for inductance i think? There is no way to measure that is there?

March 01, 2010
by BobaMosfet
BobaMosfet's Avatar

Well, You can play with it, with a meter a little bit, and learn some things. The reason I asked, is because you stated:

"Meter swings between 0.3 - 0.5 ohm."

That behaves like a coil/choke. Coils have reactance. You can think of it kind of like resistance (and it is a form of it), but it is a component of impedance. With a coil/inductor, voltage leads current (the two are out of phase with voltage peaking first). It will appear "iffy" like you are seeing on your Ohmmeter.

Another reason I suspect this, is because You're dealing with an audio system-- which generates an AC waveform-- which is a place you'd find an inductor.

Please let us know. BM

March 01, 2010
by BobaMosfet
BobaMosfet's Avatar

By the way, ground both terminals of the item before you put your meter across it. If it's a capacitor, it could dump a lot of energy into the meter-- which you don't want.

BM

Post a Reply

Please log in to post a reply.

Did you know that you can follow NerdKits on Facebook, YouTube, and Twitter? Learn more...