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Old 20th July 2007, 05:48 PM   #1
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Default Filtering alternator noise

Dear All,
I just install a TV in my car. Without turn-on the engine, the picture looks very good, clear, sharp.
As soon I start the engine, the picture become blur, and there is also stright line moving up and down and up and down.

I think this is mainly caused by the noise of the alternator.

Anybody know, how to filter the power line in automotive system?

Thanks.
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Old 20th July 2007, 06:02 PM   #2
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Almost the only way is a supressor capacitor across the alternator terminals.

Don't try and do it away from the alternator as the noise is then already all over the wiring.

Since it is a TV, you may be getting pickup from the spark plug HT to the antenna inputs. This used to be very prevalent with old VHF TVs

To prove this, turn the engine over but with the LT disconnected from the coil - no sparks. The engine will not fire but if the noise doesn't change it is not HT.
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Old 20th July 2007, 06:09 PM   #3
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Quote:
Originally posted by cliff
Almost the only way is a supressor capacitor across the alternator terminals.
What do you mean by suspressor capacitor? Is it large value capacitor, such as 1 Farad capacitor, that usually found in car.

I was thinking simpler solution such LC filter from ACC/Key to B+ of the TV, do you think this will effectively filter the noise?

Thanks
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Old 22nd July 2007, 09:11 PM   #4
Eva is offline Eva  Spain
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Your problem looks more like a ground loop in the video cable. Try to ground the TV and the video source to the same point and with short wires. Use a video cable as short as possible too.
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Old 22nd July 2007, 11:12 PM   #5
jnb is offline jnb  Australia
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Excuse me darw82 if I ask Eva a question, If a headunit and amp (which is under the seat) have a ground loop should the h/u be grounded at the body behind the dash and the amp at the same place via a few feet of wire?
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Old 22nd July 2007, 11:37 PM   #6
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Eva,
Thank you for your help.
I have try it, the picture much better, although the annoying stright line still exist.
I'll try to add an LC filter in the power line, hope this will clear the picture.
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