power consumption of car radio

Well quite, the 5kW per speaker on the side of the box seems to be delivered from a mere 5 amps at 12 v.

I've actually heard someone claim that was the way an amplifier works, i.e. the

60 watts of electrical energy was, er, amplified... ;)

Scrap it "OM" and get a "new" one. Last I saw it was rusty as hell.

eh?

prolly an amp or two, maybe three at most. That could be as much as having one car headlight on. Older cars were often having their batteies flattened by using the radio while square wheeled.

Just use a DMM and check it, it's not difficult!

I have a table-top radio that consumes 800mA (12v) and audio pwr max is about 1 watt rms. You claim 0.33A for a 2 watt system? Have you measured this?

In a stationary car, with no tyre roar/engine noise etc. to compete with, then 1 watt each channel will be plenty for a reasonably loud sound. Total output is

2x1=2 watts, typical efficiency of a Class B audio output stage is around 60%, so input power is 2 x100/60=3.33 watts. At 12 volts input that is 3.33/12 amps = 0.28 amps approx. There will be some extra power taken by the radio for the display and radio stages, not normally more than 50mA unless there's a very bright display, so the total is 0.33 amps average but it will jump up and down with the music/speech.

Doh! I think you're referring to a perpetual motion machine. Made by the same company who make skyhooks and spirit level bubbles.

It is however a reasonably comparable measure, unlike PMPO which appears to be totally imaginary.

huh....

efficiency is watts in for watts out. class B as you say is about 60% efficient, so for 1 watt DC in you will get about 600mW Audio power out.

i think that is what you meant to say! no worries, we all do it!

mike

In message , mike writes

I am sure he meant what he said; you are both right but one of you is basing his calculations on power input, the other on power output Trev

in news:954D79D214263471AE@127.0.0.1, Simon G slurred :

Depending on the background sound levels and suchlike, it will probably be drawing something in the region of 0.3-0.5A when the radio is operating, so a typical car battery should stay above 80% charge for a good 10+ hours. If it's a diesel (bigger battery) then somewhat longer.

in news: snipped-for-privacy@news.xtra.co.nz, snipped-for-privacy@xtra.co.nz slurred :

WTF are you on about? The RMS factor for DC is 1. It is perfectly feasible to compare sound output power in watts to electrical input power in watts. The relationship between the two is the efficiency of the amplifier. It doesn't matter whether the input is taken from a DC or an AC source.

'RMS and all that' does come in when making a useful measure of both input and output powers, but there is no fruit mismatch involved.

I have measured hundreds of radios and my calculations are good for most but not all. There's lots of ways of skinning a cat, so you're right and I'm right.