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Old 19-06-2010, 18:26   #1
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Looking for EMI Filter

Stereo amp has a loud buzz from EMI when Heart 2000 inverter is in battery charging mode.
Anyone know a good easily obtained filter.
Thanks
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Old 19-06-2010, 19:28   #2
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conducted vs EMI

Your problem is not from EMI it is from what is called "conducted" interferrence. The noise is conducted over the 12V cables affected by the Heart charger 120 Hz triac controlled regulator. There is no effective filter for this problem in the pure sense.

The best improvements made are by using "star" ground and power connections using a heirarchy of attachment whereas the highest current carrying sources/loads are stacked closest to each other and the lowest current attachments are stacked furtherst away in the star. This minimizes the common current loops caused by the charger affecting the low current power and ground connections serving your stereo amp, assuming that the stereo is a 12V item. If it is not then make sure that your bonding/battery negative/grounding system does not have ground loops with the system neutral.
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Old 19-06-2010, 20:08   #3
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Give Rick's advice a shot. I tried to cure the same problem with a big 91,000 mFd capacitor, and it knocked the 120 Hz spikes back about 30%, but that was it. You would probably need something 10 times as big to really get the hum down. I've partially solved the problem by installing a stereo that seems immune to the trash on the DC bus. It still affects audio from the SSB and VHF to some extent, but I'm not often using those devices on shore power.

Chip
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Old 19-06-2010, 20:59   #4
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On our previous boat, the stereo went nuts when I keyed the HAM radio on any band. I tried several fixes, but what finally worked was using coax for speaker leads.

Try hooking up the speakers with really short wiring and see if it makes any difference.
If it does, you could use shielded wire.

I realize that was RF induction, but it might be worth a try.

BTW, it was a home type AC stereo system with CD changer etc.
We bought it because for the features vs the outlay, we could also buy another solar panel!
We came out ahead powerwise by a long way, even with using the inverter.
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Old 20-06-2010, 05:36   #5
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Thanks guys. Time to start sorting out.
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