# Resistor Questions

Discussion in 'Electronic Basics' started by Byron A Jeff, May 10, 2005.

1. ### Byron A JeffGuest

Yes. You can always use a higher wattage resistor at the same value.

BAJ

2. ### ChrisGuest

1) No problem with buying a higher wattage than you need, as long as
it fits in the circuit. Resistors are rated for maximum wattage -- how
much wattage they can take before they get too hot and fuse, burn, or
permanently change their resistance value. Any less than full power,
and they'll just be cooler. Higher wattage resistors are usually
physically bigger, though, so you should keep that in mind if space is
limited.

2) If your meter is OK, your 1.2 ohms might just be contact, wire and
probe resistance. But you should check to see that it's not measuring
on a higher range, because your two resistors almost certainly have
different values. The one that says R39 is 0.39 ohms, and the one that
says 39R is 39 ohms. Big difference, but if your ohmmeter is measuring
megohms, they both look like a short circuit. Check things out
carefully before you plug in the 39R one.

Here's how the euro method of labelling resistors works:

R39 0.39 ohms
3R9 3.9 ohms
39R 39 ohms
390R 390 ohms
3K9 3.9 Kohms
39K 39 Kohms
390K 390 Kohms
3M9 3.9 Megohms

and so on. If you see three digits, that usually means a 1 or 2
percent resistor. For instance, 3K92 would mean a 3.92K 1% or 2%
resistor. This isn't too difficult once you get the hang of it, and
it's a lot harder to miss a "K" on a print than a decimal point,
especially if it's a fourth generation Xerox.

Hope this has been of help.

Good luck
Chris

3. ### MacdonaldGuest

Im a hobyest and I have a couple of questions.

I was looking for a .39 ohm 1 Watt Resistor. I went to 3 places which all
didnt have it. I guess I could mail order it but it seems kinda dumb for one
resistor.

So I bought a resistor that was 5 Watts .39 . at one place and then found a
2 Watt .39 Resistor at the other. My first question is since the circuit
calls for a 1 Watt resistor I suppose either one would work?
Its a very simple circut.

The second question relates to labeling of the resistors. The Bill for the
one resistor says 39R and the actual lettering on the OTHER resistor (5Watt)
resistor says R39.
I tested them with a meter and they both say 1.2 ohms on the 200 scale. Im
asuming that the meter just cant read the .39 so they really are .39.

Why does it seem that 39 (with no decimal point ) can stand for .39 . This

Can anyone clarify this.

4. ### MacdonaldGuest

1) No problem with buying a higher wattage than you need, as long as
Thanks all again.

I have never come across the R39 scheme before. In the past I have only delt
with 1/4 watt Resistors and had never know about the "Euopean" method of
listing resistors. I also have never had to have .00 Resistors either so
that was a bit new.
Normally I just looked at the color bands, which all up to this point had
been 1 or above.

Thanks. I learned something.