Power needed for CD and Radio?

[Guest]

I've just fitted my Christmas present - a new JVC 'car'radio and CD player with two 40w (max) power speakers to my Sadler 25. The trouble is, not understanding these things very well and not being able to find the info in the fine print - How many amps does it draw from my 12v battery when running the a) radio and B) CD player on fairly normal volume? Exact answer not needed; just a general idea please.

 

[ccscott49]

5 amps should cover it. In the supply line to the radio will be a fuse, have a look at that, the radio will not draw more than the fuse is rated!

 

[Guest]

With both speakers putting out 40 watts and a 12 v supply you could be drawing 6.6 amps. This does not take into account any voltage drop through resistance of wiring length. If voltage drops say to 10.5 volts then the amperage could be 7.6.
Presumably you won't be using it like a ghetto blaster so you should have no problems.Just ensure it is fed from your leisure battery not your starting battery.

 

[Chris_Stannard]

When you fit it look carefully at the instructions, Some car radios require a hold up voltage to be permanently present and you have to direct wire that line from a source before the battery switch. If you do not do this the radio may not work, or the memory may fail so that you have to retune each time you switch on. It is the same thing as having to reset your car CD after the battery has been diconnected.

I took mine back to Halfords and felt a right berk when this was pointed out.

Chris Stannard

 

[ccscott49]

I think you are getting a bit mixed up, 40 watts of music type power at the speakers, does not mean 6.6 amps requirement, not in my experience anyway, however I could be wrong.

 

[VMALLOWS]

Don't be put off by these stories of 5 AMPS!
As CCSCOTT says the 40w figure is a so called 'music power' rating and in any case would only apply to the very peaks of music at absolute maximum distortion (sorry, volume).

A typical car radio draws 0.5A (500mA) at anything between zero and reasonable volume (I guess it must be a class A applifier in old fashioned technical terms).
This is still surprisingly high compared to usual portable/domestic radios. Even this is not insignificant if you have the radio on all day for several days at anchor.

As also mentioned, most car radios require a 'permanantly on' connection in addition to maintain the station presets (and heaven forbid, any any-theft immobiliser functions which might decide to permanently dissable your radio).
I have measured this at around 20-50mA, and although not huge is not a drain I want for weeks at a time when not onboard. I therefore shut off all power and reprogram next time I use the radio. I don't know why they don't use non-volatile memory. (maybe they do now and I'm outof date?).

The CD is not likely to be a problem...perhaps 0.5A-1.0A but only when operating.

 

[Guest]

You may be right. I know that HiFis etc tend to quote output in amps but they do tend to qualify it with things like RMS etc.Anyway I'm a plumber so you as an Oilwell Bender probably are correct.Anyway what the hell is an Oilwell bender.
See that you are in portugal. A friend of mine recently sailed his Sabre 27 from here in the bristol channel to the costa del sol via North Africa, and rather than go through the canals went across biscay and down the portuguese coast exploring the Rias on the way,and were very impressed with Portugal.

 

[robp]

Probably "Music" or "Programme" power yes. This is a little off the subject but prospective purchasers should note that some lesser brands tend to claim figures like *40 WATTS TOTAL POWER*. One can often start off by (very) roughly halving that for RMS figures and then again for a per channel figure, meaning 10 W per channel. JVC is a reputable name, however and it will probably be made clear. As a mean level, you will use a fraction of this power. Actual power usage is already well explained elsewhere in this thread.

 

[Robin2]

If a permanent supply is needed and you disconnect it you will probably have to re-enter the anti-theft code for the radio. I found this out the hard way with a secondhand car. Luckily the previous owner had written the code on the underside of the radio.

As long as it is not obvious that the code is written on the radio this is not insecure.

The purpose of the code is to stop someone taking the radio - not to force the thief to give it back to you when it won't work.

 

[WayneS]

Robin, I am amazed at the Aerodynamics of you boat. A few weeks ago I commented about this and she still seems to be airborne in what looks like a calm day. Pray tell me, how..........

 

[bedouin]

Disagree - most reputable equipment quotes power in Watts RMS per channel. (The so called 'Music power' is total peak - conversion is a factor of three or so).

For an ICE system 40W/channel sounds about right - 40W PMPO would be too quiet.

Go with a 10A supply!

 

[billskip]

RMS =.707 of peak..or 1.141of peak to peak..

Bill
www.aegeansailing.co.uk

 

[Robin2]

That's the basic difference between cats and keelboats - cats are much lighter because they don't need all the lead to keep them upright!

 

[Guest]

Rarely have I heard such unmittigated - excuse the spelling - french keyboard - in want of a better word RUBBISH than hasd been expended on your query.
The answer is that I do not know - not a clue - NADA - nothing. I could not care less what your speakers are. The only parameter that is of ibterest is the RMS
.. root mean square.. value of the Amplifier.. your speakers can be deep sixed for all I care.... I have your attention.. good .. If you have an amplifier of 40 watts RMS .. is it mono.. steereo.. Quad.. psuedo Quad??? What is the output of the amplifier ....I do not know .. you have not told me. So I cannot give You an Answer .. this is the correct answer to your Question<.

Brian (ecosse) Yacht Electrical Services Cote d*azure France

Brian

 

[ccscott49]

OK smartarse, thanks for your input.

 

[richardknight]

Frankly I can't believe you can be so rude as to post a reply like this. Stay in France - we don't want you over here.

 

[ccscott49]

Well said, Richard, this chap really loves himself, doesn't he!

 

[brian_neale]

Two interpretations of the original question.

One - what size fuse do I need? Fuses are usually used to protect the wiring in case of a fault. Smaller the better, as long as it will handle normal current without blowing but will still blow in the case of a fault before the wiring bursts into flames. Except on musical peaks (very short duration) you are unlikely to use more than, say, 30W output total. Allow for 50% efficiency in the audio amplifier, gives 60W. That means 5A at 12V. A 5A fuse will almost certainly be adequate, 10A (if the wiring will take it) to be really safe.

Two - how long will my battery run my radio? Forget peak output, typical average output likely to be about 5W total. Same efficiency, so supply will provide 10W. Say 1A typical draw. Maybe a little more to allow for panel lights, CD mechanism. Unlikely to be more than 2A average, at a guess. Read another current (sorry about the pun) thread on battery life to figure out how long your battery will last!

More interesting is the comment on the "keep alive" current used to maintain internal memory. Don't worry about it if you want to shut everything down when you leave the boat and do not mind retuning each time (assuming typical digital display). However, more and more radios now have anti-theft protection which is tripped when the power is disconnected and needs a password entered when you switch on again. Woe betide you if you get it wrong three times in a row - can be a "back to the dealer" job! But your radio may not have this feature, so might not be an issue. If it does - 50mA drain is equivalent to 24x0.05=1.2AH per day, 8AH per week. Sounds a little high to me, as I would expect a car battery to be able to handle this kind of load for a few weeks without a major battery drain, so perhaps 50mA is a little high?

Don't know if this helps, but as a practising engineer of sorts I find a few reasonable assumptions and a back-of-the-envelope calculation often gives a "near enough" estimate. For example, you can only choose between a few different fuse sizes, and even one place of decimals is more accuracy than you need!

 

[Avocet]

Do you have a multimeter?

If so, most of the chaep ones will measure small currents. Mine will measure 200mA protected by a fuse or up to 10A un-fused (if you try to measure more than 10A it will burn out). It was about £15 from Maplins. If you have, just connect the radio up temporarily with the meter in series with the positive feed (or the earth if you prefer) and see what current it draws. I'd be very surprised to see more than 2A! Either way, if you measure it, there's no arguments. ALso, Maplins sell a small panel ammeter that reads up to 5A for less than a fiver. One of these would work just as well!

Good luck!

 

[jollyjacktar]

Runs on a flat battery

I have run my radio on a battery so flat that will not even turn the starter. CD uses a bit more, don't worry too much about current drain unless you have some sort of Ghetto Blaster and you are attempting to deafen every one within a ten mile radius. Anyway why worry. If all else fails, a tin whistle and the sailors hornpipe should be sufficient to entertain you hardy lot.