load on battery concerns.

[Deimus]

Ok I think I figured out about mounting the stereo but now I am concerned about how fast or well my old motor will charege the battery.

I have a 68 merc 1000. does it take alot to turn it over? how fast will it recharge? Dual baterries?

Thanks for all the help! These forums have been a god send. I feal alot more confertable working on my boat now.

Thanks all!d

 

[Dunaruna]

Re: load on battery concerns.

[colour=blue]Unless you have an amplifier that will power a small city, don't worry too much, a stereo doesn't draw much juice.

Is that the only electrical device you have? Why do you have two batteries?

 

[Texasmark]

Re: load on battery concerns.

Your engine will pull around 150 amperes to start but only for a few seconds. Hence not that big of a deal to the battery.

A stereo of 50 watts rms output power will pull a little over 50 watts from the battery AT FULL POWER. At less it will draw proportionally less.

So 50 watts from a 12v battery is about 4 amperes. Theoretically, a 400 amp (hour) battery will run your stereo for 100 hours before pooping out.

Mark

 

[bruceb58]

Re: load on battery concerns.

First of all, a stereo amplifier rated at 50W means 50W per channel and an amp would have at least 2 channels. By your logic it would be drawing over 100W total since no ampifier is 100% efficient. Fortunately, the actual power being driven is a fraction of that and subsequently the power input requirement is much less.

Second, a typical boat battery is going to be around 60 A/hr. Where did the 400 number come from? Are you confusing cold cranking amps with capacity?

 

[Texasmark]

Re: load on battery concerns.

:% Just threw some numbers out. Didn't say that 50W was per channel; how about 25 per channel for a stereo.

Back when i was in the business, the output power was measured at the output stage(s) of the amplifer and it was the measurement of plate (collector) voltage x Plate (collector) current (hence watts consumed!).

Since they were Class A or AB amplifiers, current flowed all the time, biased in the center of the operating range, and the plate (collector) swing went from near 0v to near applied Plate Voltage (Vcc) on maximum signal swings at full volume........but regardless of the volume, the quiescent power was still being dissipated. Signal was then AC coupled to the loudspeaker, amplitude dependent upon the setting of the volume control.

I didn't add any efficiency numbers and obviously nothing is 100% efficient.

Don't know where you got 60 AH. You can go to Continental or Exide and get your answers. CCA is a measure of the internal resistance of the battery. AH is a measurement of the area of the plates.

Mark

 

[bruceb58]

Re: load on battery concerns.

Here is the spec sheet for a marine Optima battery. Its capacity is 55Ah

Optima Spec

Not sure what your business was you are referring to but it certainly wasn't design of amplifiers.

A typical 2 Channel amp rated at 50W into 4 ohms is going to have an idle current of around 2 or 3 amps. Depending on the load of the speakers if they are 2 or 4 ohms, you could pull upwards of 30A at full power. This won't happen in normal operation,

 

[Texasmark]

Re: load on battery concerns.

This is doing nothing to help further the cause of the forums.
--------------------------
The Exide Stowaway is a 105 AH battery in size 27 (according to their wwww data sheet) and about as "typical" as you can get for a boat; least wise boats around here. Now if you want to talk about yachts or ships, who knows.

I made a statement about drain on a 400 AH battery. Didn't specify what battery, and I did check in my EE handbook today to refresh my memory on what I said. Seems there are several things that affect capacity besides area of the plates as I stated.

I described a Class A single ended amplifier conducting for 360 degrees of the input signal. If you had push pull Class B (2 required; each conducting for 180 degrees of the input cycle) then they are biased off so they don't pull any power till driven and the power drain (idle) would be for the drivers and preamplifiers. Looks like you are referring to the latter and I agree on the peak instantaneous power output capability being high and who knows what the "typical" amp of today idles at. Guess you are up on that; I'm not.

I haven't had my nose in an audio amplifier design book in many years (like 40) and didn't design them for a living at the time. I fixed them and had to understand the workings to do that. No doubt designs have changed over the years and accordingly so would power requirements.

Anything else?

Mark

 

[bruceb58]

Re: load on battery concerns.

Mark,

I am a EE so I have done some amplifier design in my 24 years as an engineer.

You are correct about the 105 Ah of the exide.

 

[Texasmark]

Re: load on battery concerns.

Peace bro. d I just retired after 36 years but I wasn't designing audio amps.

Mark