Alternator amp question

[joetiii]

I am wondering if anyone is running the older 55 amp alternator in an early car with a large stereo amp. I do not run AC or power windows or cruise. I have a JL audio 300 watt amp I want to install along with a 100 watt powered sub.

If anyone has first hand experience if this works please let me know.

thanks

[HawgRyder]

55AMPS @ 12Volts is 660 Watts.
You do the math....is 660 Watts enough to run all of your equipment?
Remeber...you have to allow for ignition and lights (plus brake lights) at all times when driving.
Also...in cold or hot weather...the fan and/or air conditioning.
660W sounds a little thin to me...but then my car had no radio at all.
Bob

[47silver]

you would be running your alternator almost flat out. i think they are sized to run at a lower % of operation.
with lights at 120 watts minimum and 400 watts of music, plus engine and fuel pump need another 150 or so watts you are going to burn out your alternator in no time.

[Canada Kev]

And that alternator measurement is probably at 100% efficiency, and then there's the resistance in wiring... Mind you, you likely won't be running your amps at full capacity, either. If you're concerned about it, just measure your current draw and go from there.

Burning out your alternator is a very real possibility. Personally, I'd be wary of having that much current draw with a 90 amp unit.

[blucille]

but does that 300 watt amp really require 300 watts of power, or is it an advertising gimmick....if the alternator would have handled power windows, A/C etc, I'm sure it can drive a moderate amplifier with no ill effects. Best bet is to check actual power draw of the amplifier.

[Plays with cars]

Won't the battery also bridge the gap if there is a transient spike in total amperage draw if all accessories are drawing max amperage at the same time? How often will stereo, lights, wipers, ... be at max draw at the same time?

Another alternative is to install a power cap (very large capacitor) in parallel to the battery that will supplement when the stereo amp has max draw.

[HawgRyder]

You could have 5 batteries and any number of caps in parallel and the poor little altenator will still give out trying to charge everything.
Depending on the efficiency factor of the amp...it will draw up to 300W (which is 25AMPS)...you better have at least a #10 wire feeding it...also a #10 ground wire too.
And...if the amp is more than 10 feet away from the battery/fuse panel....go to a #8 wire.
This is so the wire does not heat up...(heat=resistance=power dissapation).
Power amps are rated in Watts...but the power scale could be true watts (Volts X Amps)...or several other scales.
A true 300W amp at full volume would destroy your eardrums at 30 feet....so your amp is probably rated using "music power" or some other power boosting scale designed to impress you and get your cash out of your pocket.
I was once asked to build a 1000W amp for a guy...which I did...It weighed almost 400 lbs (old style..tubes and transformers)...he almost dirtied his pants....LOL
The point is...even with solid state devices...and they are not 100% efficient...the current used will be very large...and don't forget the heat involved...think of a 300W heater when you mount it.
Bob

[Chuck.H]

BTW, there are newer amps (Class D I think) that use MOSFET's and are WAY more efficient. Might be good to consider one of these if you have a 55 Amp alternator...

Chuck.H
'89 TurboLookTarga, 336k miles

[wwest]

I would be VERY surprised if you could comfortably remain in the car with an AVERAGE audio power use above 50 watts.

[joetiii]

This is all good information. I currently have the amp installed in my targa which has the 75 amp alternator and have not had a problem. The amp is never driven to Max since my ear drums would probably bleed, but I do turn it up pretty loud running down the highway with the top off but I'm sure there is plenty of clean output in reserve.

I will do some testing and see what the amp does in fact draw. I just may end up staying with the known 75 alternator.

[HawgRyder]

Personally...I still can't figure out why anyone would put a radio in one of our fine automobiles...but...each to his own...LOL
Bob