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Old 11-08-2019, 07:25   #1
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Power supply filtering for battery charger, this one has none

My old, very old Raritan charger has an issue with my very new VHF radio.
60 cycle hum when broadcasting.
I am thinking of adding filter caps to the output.
Anyone familiar with the concept?

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Old 11-08-2019, 10:05   #2
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Power supply filtering for battery charger, this one has none

First thoughts-
1: a battery is a fantastic filter. Check the ground for the vhf and the charger. Make sure they have independent runs to the battery minus or at least very heavy solid good short connections.
2: you could put a filter on the VHF but the real problem is likely elsewhere.
3: If you put a filter in the wrong place, ie between the chargers circuit breaker and the battery minus it will keep the SCR (8) from turning the charger off.
4: check for an independent connection in the positive leads of the charger and VHF as well as the ground.

Ground issues are easier to overlook though.
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Old 11-08-2019, 12:12   #3
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Re: Power supply filtering for battery charger, this one has none

the battery itself should be the filter. I have seen bad batteries do this. replacing battery fixed the tx hum
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Old 11-08-2019, 12:40   #4
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Re: Power supply filtering for battery charger, this one has none

Noise will be minimized if you have dedicated wiring between your radio and your battery or battery switches.
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Old 11-08-2019, 14:35   #5
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Re: Power supply filtering for battery charger, this one has none

I would recommend just getting a new charger. Looking at the photos I see a circuit board that looks like it belongs in the 60s. On top of that, if you add "new" components in with the old, you might create more problems as the old components start to break down. I wouldn't be surprised if that cap is starting to dry out.

Probably best to retire to old fellow and let a newer, younger fellow do the charging.
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Old 11-08-2019, 17:41   #6
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Re: Power supply filtering for battery charger, this one has none

SCR-controlled chargers are inherently and unavoidably noisy electrically. They produce the least noise at full output. Even with a good battery and good connections, it often difficult to quiet things down. The noise can be anything from 60 Hz buzzing to RF noise into the tens-of-megahertz. It will vary depending on how much load is being fed by the charger.

Some possible solutions:
Make sure the batteries are good. Measure the AC voltage at the batteries, which will be the noise voltage. Ideally, it should be zero.

Use separate wires from the charger directly to the battery(with appropriate circuit protection), both positive and negative. Any noise from the charger that is present on a common wire can be coupled into the loads.

If none of that works, you can try a good power-line filter at the load that gives you the problem. Ideally, the filter will have an inductor and a capacitor, maybe more than one of each. But these kind of filters arenít small and arenít cheap ($20-30).

There are good reasons that simple 60-Hz SCR-controlled battery chargers have gone out of style.
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Old 12-08-2019, 11:37   #7
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Re: Power supply filtering for battery charger, this one has none

Scrap that old charger. Extend the life of your batteries. Get a new smart charger that will take better care of your batteries.
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