Making Noise Filters/Coils
Be careful with what you connect to your cars
electrical system. If you get a LCD that runs on 12V and connects it
directly you will get trouble. The voltage in a car is not anywhere
near stable and clean, when you start the car for example. the
voltage can drop much, maybe to around 5V, and when running it can
be somewhere between 14 and 8V. There is also much noise, spikes and
stuff on the power lines.
The LCD will certainly not be very glad about
this and I recommend that you get a power supply that is made to be
used in a car for it.
DIY (cheap filter)
I desperately looking for a solution to cure the
alternator whine of my portable LCD TV (Chinese made). i used ready
made coil from local audio shop and tied it with +12v wire before my
custom made power supply but no luck, LCD TV is producing the
annoying alternator whine (thru the cigar lighter socket). I even
tried connecting the TV direct to battery but the whine is still
So I just used tie wire rolled like a rope as inductor core, and
a 4700 uF 35V capacitor and it worked like a charm.
here are the materials I used:
5 meters of tie wire .30$
4700 uF 25V cap .60$
6m gauge 12 wire 3$
project box .30$
Left about 8 inches of wire (this end will tied
to the +ve terminal of car battery) and
start winding on tie wire core with 12 awg wire as close and tight
as possible in layers.
Now sold +ve side of the cap to this wire by
striping small area and tape it carefully, this end of the wire will
go to the LCD.
Sold other -ve end of the cap to the piece of
small black wire and tape this joint also, this black wire will
connect with the negative terminal or ground of the car.
.. and you filter is ready !
Meanwhile I am looking out to use coils from the
salvage computer power supplies as they contain many of these filter
coils. The value of the coil isn't particularly critical. Dead PC
power supplies are a good source for these.
Wire the filter so that incoming
+12V passes through the coil, then add
filter caps between +12V and ground on
both the input and load sides.
capacitors... Most car audio equipment has
this same type of filter circuit on the power input, so an old
cassette head unit, etc. would be another good source for the coil.
Few other Workarounds:
If you are using dc/dc converter then try to to
get another dc/dc adapter... with the right voltage and amperage
(18.5v 3.5a), instead of one of those universal type ones...
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