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Old 06-05-2009, 05:54 PM
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JimN JimN is online now
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Originally Posted by proporjet View Post
Im not an alternator but an engineer with an opinion. You know what they say about opinions...
A 30A alternator sounds weak in this application. Keep in mind the maximum power specs that your speakers can handle, amps can supply....are just that Max RMS specs. Running at a lower volume is lower than that maximum power your system will use plus the wasted power that is giv4en off in the form of heat...
Running around for the day at some low or moderate volume is going to appear and possibly be OK. The only way to really see what is going on with the charging system is to take some measurements. This is not really easy but you can measure the charging current (and check the voltage)to the battery(ies) and measure the current and voltage out of the battery. Normal rectifier (thing that turns AC to DC) voltage is ~13.3-13.6V but with a large current drain the voltage will be on the low end if not closer to 13V. Make the measurements with the stereo system off, on at low volumes and on at high volumes. See what you get. I dont think you need a 140A alt but think you should have more margin than what I'm guessing a 30A alternator provides during Sandman cranking at full volume...
I don't think a 30A alternator has been made since the '60s. With no extra load, the voltage at idle will usually be close to 12VDC and at about 2000RPM, it's usually around 14.2-14.6VDC. Once the load kicks in, idle usually shows about 10.5VDC- 12VDC unless there's some way to fill in the gaps.
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