mesa177
So I have this board which is not only fumed out but the inductor on it is burnt out as well. If there was a value reading of its inductance, it's no where to be seen. To make things even better, I don't have the schematics of the board and can't seem to find it anywhere.
Usually, when I have an inductor whose value I don't know, I place a sampling resistor whose resistance is way less than the impedance of the inductor (judged by number of turns on the coil) in series, and apply an AC voltage whose frequency is 50 Hz to the series connection. I measure the voltage across the resistor, hence obtaining I(rms), and given V(rms) of the inductor (via measurement or calculation), I can obtain
Z = V(rms)/I(rms). But Z = sqrt(R^2 + X^2) where R is sum resistance of sampling resistor and inductor's resistance (obtained via ohmmeter measurement) and X is inductance of coil ie X = wL = 2(pi)fL where f = 50 Hz => L = X / (2(pi)f) = sqrt(Z^2 - R^2) / (2(pi)f).
But in this case the inductor is fried beyond repair. I was thinking maybe I can carefully unwind it, count the wraps, measure the diameter of the copper coil used to form the inductor, buy myself a copper coil of same diameter and wind it myself. I can then calculate the inductance using the equation:
L(uH)= a²n²/(9a + 10b) where
a = external coil radius (inches)
b = coil length (inches)
n = number of turns.
Unless someone has a better suggestion?
PS: Going to Katranji and asking for a new inductor poses the problem of not finding the appropriate coil, especially when half of the high current toroidal coils found on the website are labeled "Coil", "Coil AC Big", and "Coil AC Blue".
Xsever
Mesa,
Your plan is very sound and your method is very simple and straight to the point.
Keep me updated on how it goes.
mesa177
Hmm, should have posted this before: I followed the second method of calculating the inductance after unwinding the first layer of the coil and counted number of windings while doing so. Then, I measured the length of the unwinded coil (in inches, ps: method only works if b > 0.8a). Then I counted the remaining windings, cross-multiplied, and got total length of the coil. I caclulated L and it turned out to be 30 nH. I bought a copper wire and fashioned my own coil (didn't find one at Katranji), and I used test one to verify the value of the newly made coil. I placed it on the new board: it worked like a charm :)
J4D
Excellent work mesa. That's dedication. another person would have changed the whole board just because of this little bump :)
mesa177
Thanks alot J4D, it means alot to me coming from you :)
