240v/12v ac/doc transformer

[marki]

Evening all.

Whilst playing in the garage I've set up a car CD/ Radio player and want to be able to plug it into the mains rather than farting around with car batteries.

Could the electrical wizards out there point me in the right direction to get one. I do have one that powered some LED lights but I presume it's not powerful enough as it won't play the CD.

Cheers for now Mark

PS does sound a treat though....

[BlueTR3A-5EKT]

Car battery charger?

[marki]

Hi.

Yes I did think of that but was wondering if there was a simple plug in job, the one I have is only a 1 Amp but I've no idea what is required.

Mark

[RobH]

You want one of the PSUs that radio amateurs use. Something like this:

 

http://www.ebay.co.uk/itm/Alti-3-amp-13-8-v-power-supply-pack-cb-radio-/321934274052?hash=item4af4c72e04:g:az0AAOSwHQ9WWvgk

 

or this

 

http://www.ebay.co.uk/itm/Nevada-PSW04-new-style-3-5A-PSU-supplied-by-Nevada-co-uk-/381377794283?hash=item58cbe350eb:g:EgUAAOxye2lSYvh

Edited December 5, 2015 by RobH

[AlanT]

Get a 10A one and it's useful for testing wiper-motors and similar parts:

 

https://flic.kr/p/jzaz7A

[marki]

Hi Rob.

You're showing a 3amp one, as I know bugger all about electronics would this be enough to power the CD ?

Thanks Mark

[RobH]

It depends on the sound power output of your Radio Mark. Lets say its 10 watts rms per channel - that is 20 watts total = 1.7 Amps at 12v on the loud music peaks. Allow another amp or so for the CD mechanism etc and allow for the fact that is isn't going to be at full sound output much of the time, then 3 A should be enough.

 

If the rated out put is higher then you might need something meatier - but I doubt it. Easiest thing is to try it first on a battery charger and measure the current drawn.

[marki]

Hi Rob.

I do have a charger, but wouldn't know how to test the draw. So if I went for the 5amp I've covered it.

Thanks Mark

[peejay4A]

A word of caution. The output of a battery charger might not be particularly smooth so you could get some buzzing through your setup dependent upon how tolerant the audio kit is. You'd probably be better off with a proper power supply.

[Lebro]

A battery charger will NOT do the job, you need a smooth supply, i.e. one which gives a constant voltage. Most battery chargers give an "undulating" voltage which may damage your CD player, & would give a very load HUM at best.

You could connect a 12V battery to a charger, & then to your CD player, that would smooth out the "ripple" as it's called. or as mentioned above go for a CB type power supply. 5A output should be enough.

 

Bob.

[marki]

I'll go for a 5 amp unit.

Thanks all Mark.

[marki]

Hi Again.

Found this on Fleabay 10 Amp, as I said I know nuffin about electrics so would this be suitable ?

Thanks again Mark

[peejay4A]

No link Mark.

 

This would do it and it has a screw terminal adaptor too.

 

http://www.ebay.co.uk/itm/12V-10A-10-amp-120W-DC-POWER-Supply-ADAPTER-Transformer-LED-Strip-CCTV-/251387187541?hash=item3a87d81155:g:IKMAAOxywXFSbNe3

Edited December 6, 2015 by peejay4A

[RobH]

No link visible on your post Mark, but if its around 13.8 volts regulated DC output it will do nicely.

[marki]

Hi Peejay.

That is the one I was looking at, for some reason I didn't add the link, probably too much Xmas shopping ( or lots of standing around waiting for the boss to shop)

Thanks for the replies sorry to be such an electronics muppet. Mark

[RobH]

Pete/Mark - that 10A one might not be good in this application. Its fine for a constant load like lights for which it is designed but a radio current drain is far from constant - it fluctuates wildly with the music so you need a PSU with good 'load regulation' e.g the output stays constant even with big changes in current drawn. Unless you are sure on the specification I would advise sticking to the type specifically designed for radio use.

[peejay4A]

If it's rated 10A continuous it will be fine.

[RobH]

I don't think you have understood Pete. Its not the load current capability, its the voltage regulation. If the load current fluctuates quickly as it will with music on a radio for instance, the power unit has to be able to 'follow' the changes and keep the output voltage constant. If the transient regulation is poor then when the current drawn dips as the music goes quiet, the voltage can rise momentarily until the PSU catches up as it were - that is what is meant by 'load regulation'. That transient voltage rise can be enought to damage delicate circuitry. A PSU designed for a constant load like lighting may not have good transient response as it is not necessary in that application.

 

However - as I said it depends on the specification for the power unit and I think a car radio will probably be sufficiently robust to survive the odd excursion anyway as spikes are common in vehicle supplies. Personally though, I would opt for the unit designed for this use even though it might cost a few pounds more.

[peejay4A]

Actually I do understand Rob, I began my career a long time ago with GEC-AEI. Practically speaking you're unlikely to find regulation characteristics specified for a budget item such as this. The chances are that it will work fine and I'm trying to simplify the situation for Marki.

[Lebro]

+1

The ebay item will be fine, it is a switched mode power supply & probably has extremly good regulation, and anyway a car radio / cd player is designed to work over a range of voltage approx. 10 to 16 V

 

Bob.

[RobH]

OK Pete. Apologies for misinterpreting your one-liner answer.

[peejay4A]

Touche! But I think I explained why I kept it simple.

Edited December 7, 2015 by peejay4A

[RobH]

Yes I did understand that Pete. Difficult to stop myself launching into technicalities sometimes after a lifetime of having to do so professionally....

[Bill Bourne]

Try Maplin - a bit pricey, but great for bench testing etc.

 

http://www.maplin.co.uk/search?text=variable+power+supply&x=17&y=14