inductors/ chokes what value?

[sm1thson]

im building my ICE. to stop electical noise (to the head unit) i am going to have an inductor (or choke as its called in cars often) in series (on the power line) with a 100uF capacitor in parrallel with the power inputs. i only need the inductor to take 4 amps as it isnt going to supply the amps.

i know i could just buy an 'electrical choke' from a car audio shop but given that this is just an inductor that i could just buy from maplin, farnell (or RS) at much cheaper i would much rather do that (as i need a few for varyus parts of my system, and have no money)!

my question is what value inductor do i want?

[cooper_nova]

i personally don't know, but wud suggest tht u chat wiv a local ice shop or tell mapins ect wot u want it for and they might b able to give u the info u crave

[Nick]

hmmmmmmmmm

i have an a-level in electronics so if your still stuck i gues i could work it out for you ?

Imnot to sure wot you mean tho, i think it would depend on your Amps/subs/ speakers impedance and how much current they draw, you can't work out a value unless you have other figures.

[Nick]

so, you want to add something in to stop electrical noise from going back to your headunit !?

to be honest i don't think it will make a great deal of difference if that's what you mean.

One way would be to use a Great huge wacking diode as they only conduct in one direction, problem is you suffer a voltage drop across them, of 0.7 v.

i mite be on about something completly different to you here !

[Nick]

Erm, i thought about wot you meant and an Inductor and a Capacitor in paralell just makes a bandpass filter.

All it will do is only accept frequencies through a limited range, set by your Inductor and Capacitor values.

The unductors value varies to the frequency that you put through it.

Xl = 2(pie)fL

Xl is the reactance of the inductor
2 (pie) is 2x Pie (don't have the symbol)
F is the frequency of the signal in Hz
L in the unductance of the inductor

2(pie) x 100000x 0.000470 = 300 ohms reactance.

This would rise to 3k ohms at 1 mhz. So the inductor looks like a peice of wire at low frequencies and a brick wall at high frequencies. Therefor at high frequencies a nice output would be acheived, but at low frequencies it would drain through the inductor and no output would be achived

my advice is, go buy an electrical choke, it's much less hassle !

[TheWeenie]

My advice would be to forget shokes / inductors, and instead make sure you've got a good, clean ground.

Make sure you're either using a dedicated ground or a known good ground. Make sure you use a dremel to strip the paint from around the ground, then securely bolt your ground cable to the ground point via an O ring, tighten, and ensure its insulated.

Measure the resistance between the end of the ground lead and the negative terminal on the battery. It should be very small indeed.

Then re-attach your kit and see if the noise is still there. If it is, you could consider taking the ground wire all the way back to your battery.

TW

[Onnie]

exactly what weenie said ^