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

[Gil W.]

They get hot, but do not fry...

The system freeze happens about 10 minuted after I power it up. The system works perfectly before it freezes.

What to check for ? bad regulators maybe ?





--- On Tue, 6/23/09, Needham, Alan <Alan.Needham at centrica.com> wrote:

> From: Needham, Alan <Alan.Needham at centrica.com>
> Subject: RE: [sdiy] Can I use two 1/4w resistors instead of one 1/2w ?
> To: "Gil W." <gil_we at yahoo.com>, "Magnus Danielson" <magnus at rubidium.dyndns.org>, synth-diy at dropmix.xs4all.nl
> Date: Tuesday, June 23, 2009, 11:59 AM
> 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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