h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I need an estimate of the power usage of a car stereo (a basic unit with CD player, radio, LCD screen). Watts or amps is fine. Anyone know? The manual with the player I have* gives the specs for everything else under the sun except for power usage

*Sony CDX GT170S

And if you want a laugh, the unit is called XPlod.

Ah, a former Police radio then

Not much I'd say. An exact figure would be a guess though, sorry.

Good one.

Would it be much different from a domestic one of similar performance?
I rather doubt it.

Google on Sony CDX GT170S says "High Power 208W" so power usage will be a teensy bit more than that...

However, Interestingly, the spec says Max output power 52W so maybe that 208W actually IS the power usage?

Anyway, if in doubt drive 10,000km with it on full blast then return with it switched off. A simple calculation using petrol used in each case should tell you...

208 Watts is 17 amps, which is far too high*, so it can't be that. I assumed the 52W x 4 thing was something to do with speaker output or ?

*I'm expecting 2 -3 amps or less.

How are you working that out?

Or to put it another way, I'm sure the radio does not take its leccy directly from the battery in the same way the starter motor does - otherwise it would be fried.

I'm sure there's a transformer of some kind in between and you may be misinterpreting the voltage going to the stereo.

Of course the main power consumption of a music system is probably the speakers so if they're powered separately then that 200W figure will be much lower.

200W is about a tenth of a kettle which sounds fairly reasonable to me.

It's on 12V, so W/V=A. Is that right? 208/12=17

The stereo isn't in a car, but is being run off a 12V car battery.

My computer uses about 2.6amps. I think the stereo would be in the same ball park.

I would think a kettle would use quite a bit more power.

Well a car battery is more than capable of delivering 17 amps. However I agree the power usage is more I'm the same ballpark as a pc. That power outage quoted at 52W per channel is for full on maximum volume remember. And it must be attached to mean machine speakers to deliver that.

I guess large speakers at top volume will draw a large current.

The actual stereo device itself, excluding speakers will use very little power in comparison.

I'm now thinkning that's why only a max figure is quoted. It depends upon the speakers and how many.

A kettle is about 1.5 to 2 kW I believe

I'm confused now (well, before I never understood about measuring speakerage in watts either). Is the input into the stereo in watts, the same as the output to the speakers in watts (maximum)?

My kettle says it's 2400W, but I don't think that can be right, because that's 10amps and if anything else was plugged in at the time it would blow the fuse

Well the overall input must be more than the output to cope with inefficency (and everything is inefficient to some extent).

But a stereo system consists of several bits - CD player, radio tuner etc. that all supply information to an amplifier - that amplifies that signal to the speakers. By far the greatest draw on current will be the amplifier and speakers. Each component will share overall input but a transformer, capacitor and other electronics for each will adjust the amount of electricity that is used for each bit.

Your kettle is heating a resiting element to red hot temperatures, it most certainly will draw 10 amps. Has it a 13 amp fuse?
Other electrical items are on separate circuits and again have initial transformers and such to limit the input to a suitable level.

Oh yeah, the circuits are all on 20 amp fuses

So the maximum usage will be more than 208W for the stereo. Is the limiting factor always the speakers then? If I use the two speakers I've got (40W x2) then the usage will be somewhat above 80W or a 6.6 amps (when used at full volume). Still doesn't tell me what I need to know though.

You have 20 Amp fuses in NZ then? yikes.

Domestic stuff is limited to 13 A in the UK.

Well generating the sound is what takes most energy (at least for useful stuff) as you are physically moving air around plus the bits of the speaker that do this around. Almost everything else is just cunning uses of electrical components to tell other bits what to do and stuff.

Heat loss from transformers and amplifier chips might be a significant power draw too though.

I should point out that I'm no electronics expert though. Electronics is significantly outside my technical comfort zone.
Noone's complained yet though

And yet sadly, as you point out - I still can't give you an exact figure I'm afraid.

More importantly, does the volume go to 11?

Steve gave an answer in another thread:

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The power consumption of a car radio is not the same as the maximum power output of the amplifier.

Here is a link to the wiki about it, if you understand it you are doing better than me,

http://en.wikipedia.org/wiki/Audio_power

I think an average power consumption of a car radio is about 10 - 20 watts.
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