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Old 26th September 2014, 09:35 AM   #1
KHesse is offline KHesse  Denmark
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Default Using 12v battery charger as power supply for a TA2020

I recently got a 5.1 soundcard for my pc, and decided to repurpose some old bookshelf speakers as my rear speakers. I decided to use a TA2020 based amp as my amplifier because 230V amps usually don't come in that price range.

For power, I could've gone the way of getting a dedicated 230v-12v supply, but I already had an adjustable battery charger laying around (it has a slider to select 2v, 6v or 12v output), with an output of 600mAh which should be enough for a TA2020. I decided not to cut off the alligator clips on the ends because I might still need it in the future.

Well, right now when I hook up my speakers, screw the power wires into the sockets and then clip the other ends of the wires with the alligator clips, nothing happens. Bummer!

My question is, can a battery charger even work as constant power supply? Would it work if I snipped off the alligator clips and screwed the unisolated cables right into the amp? What if I bought 12v Switching Power Supply? Could I strip the isolation off a standard 3-pin power cable, plug the wires into that and then things would work?

Or what about this 12v power supply for a printer. If I stripped that, it should potentially work, correct?

Thanks for your help guys
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Old 26th September 2014, 09:39 AM   #2
Mooly is offline Mooly  United Kingdom
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Depends on the battery charger...

It might detect that the amp has no voltage of its own (like a battery) and see the amp as a faulty (0 volts) battery and refuse to power up.

Battery chargers also have the ability to go way over 12 volts to charge batteries. Voltages up to 16 to 18 volts could be seen under some conditions. The output may also be non smoothed (just half wave rectified pulses).

Simple answer... don't use a battery charger

Edit... a laptop PSU would work. I'm not sure about the one in your link. Can it deliver the current needed ?
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Old 26th September 2014, 09:48 AM   #3
KHesse is offline KHesse  Denmark
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Yeah it doesn't list output in mAh so I'm not sure of it. What about the switching power supply?
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Old 26th September 2014, 09:53 AM   #4
Mooly is offline Mooly  United Kingdom
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Many use laptop PSU's (switching supplies) to power these kind of amps and that really is like the one in your link. It should be fine. Just remember to fuse the output.
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Old 26th September 2014, 09:54 AM   #5
KHesse is offline KHesse  Denmark
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Fuse the output? Could you please explain what that means, I'm not quite a pro at all this yet
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Old 26th September 2014, 10:21 AM   #6
Mooly is offline Mooly  United Kingdom
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Add a suitable fuse in the 12 volt feed to the amp. I would guess at something like a T4A (that's a time delay fuse) should cover it. Its as much to protect the PSU as the amp.
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Old 26th September 2014, 11:44 AM   #7
KHesse is offline KHesse  Denmark
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Oh, of course! What rating would you recommend? .5A, 1A?
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Old 26th September 2014, 12:17 PM   #8
JMFahey is offline JMFahey  Argentina
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Quote:
I already had an adjustable battery charger laying around (it has a slider to select 2v, 6v or 12v output), with an output of 600mAh which should be enough for a TA2020.
600mA not enough , you need around 2A per channel or 4A total.
That besides all other possible problems Mooly points out.
So : no

Quote:
What if I bought 12v Switching Power Supply?
Looks good.
Should work.
Only thing that's slightly nagging me is that it might be noisy, because they suggest only non audio applications where it would not matter (fans, Led strips, lamps, cameras, etc.) but really it should work, it costs the same to do it right than to do it wrong, let's trust the designers.
And the price is right, try it.

Quote:
Or what about this 12v power supply for a printer.
Looks too small.
Wouldn't trust it for more than 1A, tops.

So far the best option is the real 12V SMPS
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Old 26th September 2014, 12:30 PM   #9
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12V 1A or even 2A wall bricks are ever so cheap on E-Bay.
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Old 26th September 2014, 01:10 PM   #10
KHesse is offline KHesse  Denmark
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Alright, so I think I'm getting this.

I just now remembered that I have an old laptop charger right here. It's rated for 19.5V output, with 4.6A current. Now, with my basic knowledge of Ohms law I've calculated that to downgrade this to a 12v supply I'd need to solder in a 1.5Ohm resistor, rated at about 32W. But wherever I go to look, there's tons of different resistor types, and ratings are usually super low, like 1/2W. What kinda resistor would I need to get if I wanted to repurpose my old charger?
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