PC power supply efficiency & running a car stereo.

[David Paste]

I have a car radio I'd like to set up in the garage, powering 4 speakers from it. To power it I thought about a PC PSU as they have 12 volt output and can supply 10 amps.

1. I understand that they need some altering to 'wake up' the main power supply, so does this mean that the PSU would be unable to supply a low-current 12 volt supply to the accessory supply to maintain radio tuner memory, etc?

1. How much power do these PSUs draw when they are supplying nothing to whatever they are connected? Being a switched mode unit, I understand that they have a constant draw of power.

My understandings, of course, may be wrong.

Last idea is to run the car stereo from a small lead acid battery (which I already have, so no cost involved) and to connect a small trickle charger to the battery to keep it topped up. Any comments on this idea?

Thanks very much for any helpful info you can give me.

David Paste.

[The Natural Philosopher]

IIRC you need a load on the 5V

A lot of peole did this to create a 12v source for field battery chargers for models, but in the end I actually bought an ex CB radio mains power supply off Ebay.

It was cheaper and neater than spending hours on a lashup

[Syd Rumpo]

I have a car stereo in the kitchen, it fits nicely under the cupboards with a slot cut out of the trim. I use a 12V 2A plug-in supply, which is perfect, but if you want loud you'll need more. Ebay has plenty of

12V 5A units for less than a tenner, and I'd go for this rather than a PC supply.

Being a car stereo, it's supply needs are fairly robust, so a switcher is fine. Mine loses presets if there's a power cut - I suspect that's usual as it saves a penny or two on non-volatile memory.

Cheers

[Adrian]

Do you need anything _close_ to 10A?

[jack]

Yes.

No. You can supply what the radio thinks is the battery and that will keep the radio tuner memory etc fine.

You have that backwards, it's the alternative linear supplies that do that.

It is.

The simplest trickle chargers aren't very good for the battery and so they don't last all that long.

[The Natural Philosopher]

Even they dont do that although quiescent draw may be higher

however the battery is really just a sort of big regulator and capacitor. This actually works. Even with a 90% destroyed battery.

[Roger Mills]

That's the one I'd go for - but I'd have the charger on a timer rather than on trickle all the time, or I'd just switch it on when the battery started to get flat.

[Brian Gaff]

For a start, most of them never produce nothing, as the system powers usb sockets assoon as the unit is plugged in. It may well be that the on off switch wakes up the 12 volt supplies though but you can see this in manyweb sites which use such supplies for other uses.

Brian

[Dave Plowman (News)]

Depending on the charger design, you may well get mains hum from it on the radio.

[David Paste]

Thanks all. I think I'll go with the car battery option. Lidl are selling little smart chargers for car batteries, which will be useful to have.

Thanks again.