Alternator Question

[JimN]

Originally Posted by CODY_YARBER07

I guess what my main question is, can I get by with the old alternator?

You'd need to list all of the accessories you want to run in order to tell. The power formula is P=IE, (P is Power, I is Current and E is Volts). Nothing is 100% efficient, so unless the amps state their draw vs output, assume they're about 60%. 300W/ch is 600W total and if it's 60% efficient, that's about a 70A draw if the voltage is 14.4, more if the voltage drops (which it does at low RPM and when the alternator and battery are under heavy load.

[JimN]

Originally Posted by proporjet

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.

[JLeuck64]

Originally Posted by Patrick Hardy

JimN, I was told by two local Marine rebuild shops that my alternator could not be rebuilt to a higher amperage. I thought that was weird, but i just got off of the phone with SKIDIM, they said the same thing.
Actually they said that for my 1996 190 w/ LT1 there are no after market alternator amperage upgrades or kits available to them. He said that they get a lot of calls about this problem w/ the early years LT1. I am waiting for a call back from Indmar about this. This has been a real interesting DIY job.

I would think your current alternator is probably more in the range of 55A...

[JimN]

Just after I posted last time, I called the shop to find out what the next size up can put out and he said about 165A. This case isn't exactly the same size but the brackets still fit. The span at the pivot is the same and it's a little deeper, larger diameter. This shop only rebuilds starters and alternators.