[sdiy] Can I use two 1/4w resistors instead of one 1/2w ?

[Needham, Alan]

Ohm's law say's V=I*R and P=V*I
In your original post you say the design states a 1/2W 1k2 resistor
So what current could it carry?
We know R and P (worst case) - find I
P=(I*R)*I = Isquared*R (or I^2*R)
So I^2 = P/R = 4.167^-4
I = 20.4mA (worst case)

Now the 100R resistor is carrying all of that 20.4mA
P=I2*R = 0.0204^2*100 = 0.04167W or 42mW, way below 1/4W so that is not
the problem!

Are you saying that the resistors DO get hot (must be a wiring fault
somewhere)?

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Gil W.
Sent: 23 June 2009 09:14
To: Magnus Danielson; synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Can I use two 1/4w resistors instead of one 1/2w ?


Interesting.

I ended up using a set of two 2.2K in parallel, connected in series with
a single 100ohm resistor, to create 1.2K . They are all 1/4w.

I then let the synth run for 10 minutes. It initially worked fine, but
after a few minutes it froze.

I now see that using different values makes different current flow in
each of the combined resistors, which is not what we wanted in the first
place.

I'll just get a 1.2K 1/2W resistor today and use it I guess....

But as for the freezing, can we assume it's the resistor combination
causing it (the resistors gets hot too much) or should I replace the
regulators, for example ?

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