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Old 13-01-2018, 10:05   #1
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Electrically quiet 12 VDC power supply

This does not necessarily relate to boats, but for some boats it could relate. I am looking for a super quiet 12 volt DC power supply that when plugged into a 120 volt wall outlet does not produce any 60 Hz electrical hum.

The application is a subwoofer amplifier powered by a 12-volt lead-acid battery. The amp is a car amplifier (Rockford-Fosgate) connected to an unpowered subwoofer (JL Audio).

I have tried three automotive type car chargers and they all produce a 60 Hz hum that I can hear through the subwoofer.

All I need is a 10 amp or so charger which would be enough to keep the battery topped up which is long enough for two movies when connected to a Group 24 battery.

I have found 13.8v fixed voltage chargers that HAM operators use but those are not regulated chargers...which I believe could overcharge the battery? Or not?

I know, why not just disconnect the charger before watching a movie and turn it back on when done? The answer is that I am trying to make things more convenient.
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Old 13-01-2018, 10:11   #2
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Re: Electrically quiet 12 VDC power supply

You don't state what power you require. Note that most good inverters / transformers will seek to manage internal temperatures. Using fans or some form of forced air cooling is common.

You'll also need a charger to help keep battery voltage constant. Cheap chargers can be electrically noisy.

If you are experiencing rf type noise then again good inverters / transformers are better at shielding both incoming and outgoing rf noise. Commonly referred to as emi / emc.

You're amp may also be noisy. You can use a combination of chokes and bandpass filters to deal with specific noise.

You need to think of the system and not just the individual components.
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Old 13-01-2018, 10:19   #3
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Re: Electrically quiet 12 VDC power supply

I only need about 10 amps output to keep the battery topped up.

The subwoofer has no 60 Hz hum or any noise when there is no powered on charger connected to the battery.
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Old 13-01-2018, 11:13   #4
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Re: Electrically quiet 12 VDC power supply

Would the Hydromax 150 do the job? It has enough output but I don't know about speaker hum.
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Old 13-01-2018, 15:29   #5
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Re: Electrically quiet 12 VDC power supply

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Would the Hydromax 150 do the job? It has enough output but I don't know about speaker hum.
I Googled it. I don't think I need one specifically for charging fuel cells. I do appreciate the help.
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Old 14-01-2018, 08:27   #6
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Re: Electrically quiet 12 VDC power supply

You could have a ground loop problem rather than hum on the power line. To start with, make sure the power supply is on the same phase (ideally, power bar) as the rest of the audio system. Many new supplies are switching types, which operate at 10-200 KHz, so any 60Hz hum would be power-line induced (i.e. ground differences) rather than from the supply itself. Another approach might be a simple transformer-based supply with NO connection between AC ground and chassis/negative ground.

One test is to connect the supply to the battery and ONLY the AC ground - not powering the supply itself. If hum appears, it's obviously ground induced, not coming through the supply but rather "around" it.
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Old 14-01-2018, 08:35   #7
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Re: Electrically quiet 12 VDC power supply

I would have a look at Newmar (https://dcpoweronboard.com). I don't have experience with them, but in past research their power supplies/converters/etc appeared to be aimed at noise free application (based on their marketing literature).


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Old 14-01-2018, 08:50   #8
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Re: Electrically quiet 12 VDC power supply

With a car battery, a 13.8 charger will be fine.
Automobiles operate at 14 + or - .2V Maybe if left on continuously, in a couple of years You may have to buy another car battery, but taxis and other cars run nearly continuously at 14V and seem to do fine.
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Old 14-01-2018, 08:53   #9
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Re: Electrically quiet 12 VDC power supply

Make sure that your inverter produces a sine wave. The modified sine wave ones will produce a lot of noise.
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Old 14-01-2018, 09:19   #10
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Re: Electrically quiet 12 VDC power supply

A converter/charger will do the job. I installed one in my camper van and it works quite well as a multi stage charger and will supply 12v for your stereo, etc. Check out Progressive Dynamics PD2120 (20 Amp) Converter/Charger.

https://www.progressivedyn.com/marine/pd2120-20-amp-convertercharger/
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Old 14-01-2018, 11:48   #11
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Re: Electrically quiet 12 VDC power supply

Try an IOTA charger. They are designed work as a DC power supply but also a 4 stage (three stages plus equalization, make sure the model includes the IQ4 stage). Mine seems to be very quiet.

Also if I recall btrayfors uses one to power HF radios which can be very sensitive to 60 Hz hum.
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Old 14-01-2018, 12:42   #12
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Re: Electrically quiet 12 VDC power supply

Hi ,,, I use a ICOM PS-50 power suply is as quiet as you will get its an old amateure radio 20 amp regulated power suply for HF radio transmition , and its selectable from 110 vac to 250 vac ,
are you getting a 60hz hum thru the amp ?
have you tried fitering the ac voltage getting into your system
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Old 14-01-2018, 13:55   #13
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Re: Electrically quiet 12 VDC power supply

I second Robert Tilbury. I’ve had great service with mine and designed with quiet foremost. I would shop the second hand Ham gear sites.
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Old 14-01-2018, 18:05   #14
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Re: Electrically quiet 12 VDC power supply

You've identified the most obvious, simplest solution - run your sound from the battery, and recharge with any crappy cheap charger after you finish watching your movies
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Old 14-01-2018, 19:37   #15
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Re: Electrically quiet 12 VDC power supply

Quote:
Originally Posted by David M View Post
This does not necessarily relate to boats, but for some boats it could relate. I am looking for a super quiet 12 volt DC power supply that when plugged into a 120 volt wall outlet does not produce any 60 Hz electrical hum.
All power supplies produce 60 cycle hum. The trick is to filter it out. Most have some amount of capacitive filtering. You can add more. Just get a big capacitor with a comfortably larger voltage rating than 13 volts. A 35 volt capacitor would be a good choice. 10,000 uF ought to do it.

https://www.amazon.com/Elna-10000uF-...SIN=B00DGK0DAS

They're cheap, you'll spend more money on an enclosure and connectors.

It is wise to put a drain resistor across the cap terminals, so that it doesn't hold a charge for very long when the power supply is turned off. A half watt 470 ohm should work.

If that doesn't work as well as you like, you can use more (in parallel) or larger (in uF) capacitors, or add a choke in series with the capacitor.
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