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How to design a 12V 2A power supply

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  How to design a 12V 2A power supply boomer#6877250@none.com - 2017-02-15 23:36 -0600
    Re: How to design a 12V 2A power supply mike <ham789@netzero.net> - 2017-02-15 21:45 -0800
    Re: How to design a 12V 2A power supply bitrex <bitrex@de.lete.earthlink.net> - 2017-02-16 01:58 -0500
      Re: How to design a 12V 2A power supply Sylvia Else <sylvia@not.at.this.address> - 2017-02-19 18:24 +1100
    Re: How to design a 12V 2A power supply tabbypurr@gmail.com - 2017-02-16 00:01 -0800
    Re: How to design a 12V 2A power supply Pimpom <Pimpom@invalid.com> - 2017-02-16 18:12 +0530
      Re: How to design a 12V 2A power supply mike <ham789@netzero.net> - 2017-02-17 22:09 -0800
    Re: How to design a 12V 2A power supply Don Y <blockedofcourse@foo.invalid> - 2017-02-16 05:54 -0700
      Re: How to design a 12V 2A power supply jurb6006@gmail.com - 2017-02-16 05:34 -0800
        Re: How to design a 12V 2A power supply Don Y <blockedofcourse@foo.invalid> - 2017-02-16 07:09 -0700
          Re: How to design a 12V 2A power supply Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-16 13:33 -0800
            Re: How to design a 12V 2A power supply Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-02-17 00:44 -0500
              Re: How to design a 12V 2A power supply krw@notreal.com - 2017-02-17 22:39 -0500
                Re: How to design a 12V 2A power supply Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-02-18 05:45 -0500
                  Re: How to design a 12V 2A power supply krw@notreal.com - 2017-02-18 10:28 -0500
                  Re: How to design a 12V 2A power supply Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-18 07:52 -0800
                  Re: How to design a 12V 2A power supply Jasen Betts <jasen@xnet.co.nz> - 2017-02-19 06:40 +0000
                    Re: How to design a 12V 2A power supply Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-02-19 02:51 -0500
                    Re: How to design a 12V 2A power supply "Dave M" <dgminala@mediacombb.net> - 2017-02-19 17:33 -0600
              Re: How to design a 12V 2A power supply Don Y <blockedofcourse@foo.invalid> - 2017-02-18 05:37 -0700
      Re: How to design a 12V 2A power supply Clifford Heath <no.spam@please.net> - 2017-02-17 03:48 +1100
      Re: How to design a 12V 2A power supply Jasen Betts <jasen@xnet.co.nz> - 2017-02-18 09:47 +0000
        Re: How to design a 12V 2A power supply krw@notreal.com - 2017-02-18 10:33 -0500
    Re: How to design a 12V 2A power supply Martin Brown <|||newspam|||@nezumi.demon.co.uk> - 2017-02-16 13:17 +0000
    Re: How to design a 12V 2A power supply Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-02-16 08:37 -0500
    Re: How to design a 12V 2A power supply Jasen Betts <jasen@xnet.co.nz> - 2017-02-18 09:39 +0000
    Re: How to design a 12V 2A power supply dakupoto@gmail.com - 2017-02-19 03:38 -0800

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#447913

On 16/02/17 23:54, Don Y wrote:
> On 2/15/2017 10:36 PM, boomer#6877250@none.com wrote:
>> I bought a stereo amplifier on ebay for $7.
>> But I want to use this in the house. It requires 12VDC at 2A.
> Find a "brick" for an LCD monitor (many LCD monitors are DC powered -- no
> "AC power cord" into the monitor itself).  These are typically 12VDC @
> ~3-5A.
> They are regulated power supplies (not just a xformer and rectifier) so
> their output is more stable with load variations.

Power amps almost never have a regulated supply. The amp itself can
be seen as essentially an AC regulated supply, tracking an input.

By definition, an audio power supply drives a load which might
at any time consist predominantly of any audio frequency.

Unspecified regulated switch-mode supplies that feed such a load
will quite likely behave inappropriately when the load frequency
interferes with its control loop.

Much better to use a simple unregulated supply, and let the amp
"regulate" it.

Clifford Heath.

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#448141

On 2017-02-16, Don Y <blockedofcourse@foo.invalid> wrote:
> On 2/15/2017 10:36 PM, boomer#6877250@none.com wrote:
>> I bought a stereo amplifier on ebay for $7. It's a complete amp except
>> for a housing. I'll make my own housing. It's made to be used in a car.
>> It has output of 15W per channel.
>
> Then it will probably operate on ~9-15VDC -- though whether or not it
> will actually deliver 15W into a load over that range is questionable.

15+15W out from 13.5V @ 2A in is most unlikely, but ISTR car audio Watts
aren't the same as engineering watts.

-- 
This email has not been checked by half-arsed antivirus software 

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#448166

On 18 Feb 2017 09:47:07 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

>On 2017-02-16, Don Y <blockedofcourse@foo.invalid> wrote:
>> On 2/15/2017 10:36 PM, boomer#6877250@none.com wrote:
>>> I bought a stereo amplifier on ebay for $7. It's a complete amp except
>>> for a housing. I'll make my own housing. It's made to be used in a car.
>>> It has output of 15W per channel.
>>
>> Then it will probably operate on ~9-15VDC -- though whether or not it
>> will actually deliver 15W into a load over that range is questionable.
>
>15+15W out from 13.5V @ 2A in is most unlikely, but ISTR car audio Watts
>aren't the same as engineering watts.

They are "engineering watts" but because you don't understand the
issues invloved, they may not measured as _you_think_ they should be
measured.  The purpose of the amplifier isn't to heat the interior of
the car.

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#447851

On 16/02/2017 05:36, boomer#6877250@none.com wrote:

> I bought a stereo amplifier on ebay for $7. It's a complete amp except
> for a housing. I'll make my own housing. It's made to be used in a car.
> It has output of 15W per channel.

A car battery on charge with the alternator running is typically ~14v so 
almost any laptop power supply of the 15v nominal output ought to do. 
Most are good for 3-5A. Newer ones are 19v which is pushing it and the 
amplifier might not like that much extra voltage.

You won't get 15W out if it is on a true 12v supply more like 11W and 
distortion will rise rapidly at about half of that rated power.
(assuming it does genuinely output 15W when on a car battery)

Worth looking up the chip used in the amplifier and capacitor ratings 
since with a bit of care the amplifier might operate with much lower 
distortion if powered with a higher voltage than in automotive use. You 
might need extra heatsinking or just be gentle with the volume control.

> Lastly, do they sell 12VDC wall transformers that are rated at 2A? That
> too would work and be easy to connect. I have seen them rated at 12VDC
> 1A, but never seen 2amp ones.

Yes. But buying or scrounging a redundant ex laptop PSU with about the 
right output voltage would be my choice. Just get the polarity right!

-- 
Regards,
Martin Brown

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#447854

On Wed, 15 Feb 2017 23:36:03 -0600, the renowned
boomer#6877250@none.com wrote:

>
>Lastly, do they sell 12VDC wall transformers that are rated at 2A? That
>too would work and be easy to connect. I have seen them rated at 12VDC
>1A, but never seen 2amp ones.

Yes, you can buy a safe one from Digikey for about $15 qty 1. Eg.
Phihong PSAC24A-120L6. Higher currents too- up to 3A from several
vendors, for maybe $5-8 more. 

Or roll the dice and get one offshore sans (non-counterfeit) approvals
for about $3.50 including shipping. Risky, y'know $20 is $20 and
everything we do has a certain amount of risk. 

--sp 

-- 
Best regards, 
Spehro Pefhany

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#448140

On 2017-02-16, boomer#6877250@none.com <boomer#6877250@none.com> wrote:
> I bought a stereo amplifier on ebay for $7. It's a complete amp except
> for a housing. I'll make my own housing. It's made to be used in a car.
> It has output of 15W per channel. 
>

> Lastly, do they sell 12VDC wall transformers that are rated at 2A? That
> too would work and be easy to connect. I have seen them rated at 12VDC
> 1A, but never seen 2amp ones.

Yeah, prices start at $3 online, but the cheap ones may be junk.

eg:  https://www.aliexpress.com/item/1PCS-12V2A-AC-100V-240V-Converter-Adapter-DC-12V-2A-2000mA-Power-Supply-EU-Plug-5/32281921836.html?spm=2114.40010608.4.11.uM1xTs


-- 
This email has not been checked by half-arsed antivirus software 

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#448338

On Thursday, February 16, 2017 at 11:06:24 AM UTC+5:30, boomer#...@none.com wrote:
> I bought a stereo amplifier on ebay for $7. It's a complete amp except
> for a housing. I'll make my own housing. It's made to be used in a car.
> It has output of 15W per channel. 
> 
> Instead of buying those cheap computer speakers which seem to never last
> more than a year, and dont have very good sound anyhow, I want to
> connect this amp to some quality bookshelf speakers that I already have.
> 
> But I want to use this in the house. It requires 12VDC at 2A. I'll have
> to find a 12V (Or?) power transformer, and a bridge rectifier, plus a
> capacitor and of course a switch and power cord. 
> Pretty basic....
> 
> But do I need a transformer with higher voltage? I know there is some
> voltage drop from the rectifier. And what size cap should I use? Do I
> need anything else? 
> 
> HOWEVER, I'm wondering if I already have what I need, if I take the
> power supply out of an old (early pentium) computer and just use the 12
> volts from that? I have several old computers that are too slow for
> modern use anyhow, so if I can recycle the power supply, I will, and it
> wont cost anything. But do they output 2amps or more?
> 
> Lastly, do they sell 12VDC wall transformers that are rated at 2A? That
> too would work and be easy to connect. I have seen them rated at 12VDC
> 1A, but never seen 2amp ones.

No problem at all. Just connect the DC outputs of two 12 Volt, 1 Amp to a common bus, and drsw poert from that common bus. Add a reasonable capacitor bank for output voltage stabilization. 
We have designed, built and sold 12 Volt, 5 Amp power supplies, based on this concept. Hope that helps.

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