Alternator Capacity with Stereo Install

Still getting all my stereo equipment together for this install and noticed that the alternator rating on the RTP310 engine is 70 amps. Does anyone know if a 70 amp alternator can handle running a second battery and a medium size stereo system amp?

watts/volts=amps

^^That formula is pure theroy, and not real world. Real world is very dynamic. It will depend on your batteries, wiring, amp type ( class) the type of music you listen to, and the volume, to name a few. Do you know how many watts?

A 70 amp alt is pretty small. It would be very cheap insurance to upgrade to a 90-105 amp. Most in that range are built very well and use good parts and decent prices. Any higher and price really starts to jump ( for the quality stuff).

Stay with a good charging routine and a 90-105 amp alt should get a medium sized system fed with enough power.

MC uses 70 or 90 amp alternators and the 90 alternator is 330$. Not sure if I'd call that cheap but I understand your point.

Gary it absolutely can. I have three amps and my system is around 2500rms I use the stock alt. with two batteries. I have two optimas, or previouslly I had an optima to start and two 6volt golf cart batteries to run the stereo. search the threads I found all my info here. you will also need an combiner, (I use a Yandino )and a perko switch.

Gary, I have the OEM 70 and 90 amp alternators in stock. Get me some numbers off the one you have and I will get you a wholesale price. If it is a prestolite it will be 180-190 or if it is a delco 7 si it actually puts out closer 90 amps. But the newer indmar's use an 11si which is rated at 95 amps and am guessing it puts out 100 amps or so. This would be under $200 or so.

Get as many of the numbers you can off the unit so I can try and find something for you.

Also along the combiner I would recommend a Sure Power 1314 isolator/combiner. It replaces the switch and you never have to touch it. It is also only around $50.

Ok sorry but what is a combiner?

i have the 07 x star with the 70 amp 5 amps and 4 battiers it will work fine

Get the blue sea add-a-battery system.... has the combiner/isolator and switch all in a pretty inexpensive package. Mine works awesome.

Maybe this guy sells junk (but i've got 2 years on an alternator from him without a problem. And I've tested the output.) I picked up a ~200amp alternator from him for around $200. Note: you'll also need to upgrade your circuit breaker if you go with something this high. I've got 3 big deep cycle batteries + a small starting battery and I can keep my 2500wrms system bumping for hours with very quick recovery.

http://stores.ebay.com/DB-Electrical-Starters-Alternators

Get the blue sea add-a-battery system.... has the combiner/isolator and switch all in a pretty inexpensive package. Mine works awesome.

Maybe this guy sells junk (but i've got 2 years on an alternator from him without a problem. And I've tested the output.) I picked up a ~200amp alternator from him for around $200. Note: you'll also need to upgrade your circuit breaker if you go with something this high. I've got 3 big deep cycle batteries + a small starting battery and I can keep my 2500wrms system bumping for hours with very quick recovery.

http://stores.ebay.com/DB-Electrical-Starters-Alternators

Whats considered small,medium and large systems when it comes to wattage?

I have a 65 amp alt. pushing three amps two subs eight speakers . three blue top batteries two caps . rope winder knight rider light bar with seven lights. never had a problem Joe

My system it very basic, 4 cabin speakers and the amp is only 65 wrms x 4. Sure would seem like it should handle that.

Gary, IMO you only need a non stock amp when pushing multiple high power subs.

Thanks everyone, my setup is so tame compared to some of you music hounds I should be ok. I'm going to save this page for future reference in case I have any problems or I decide to upgrade my stereo system.

Upload Alternator_calcs-347874.xls (17.4 k)

Gary, I meant it would be very cheap ( $40-80) to have your current alt rewound, the casing should be the same as a 90 amp alt. ( I think). Go to a reputable shop and they'll give you a lifetime warranty on it.

Nice spread sheet Nacho, have you tested out your formulas in real world to see how close everything is?

Bob,

I threw that spreadsheet together. I does not do a bad job, accurately predicts my systems performance. There are a few inputs that have a large influence on the outputs, you need to know what type of gear you are installing and do a good prediction of how you will be operating the system.

Any system is highly dependent on your operating patterns. A 70A alternator can power a 5000 watt system if your duty cycle is low. A 200A alternator will struggle on a 2000 watt system if your run time is low and your listening time is high.

Gary,

I use the Blue Sea add-a-battery and it has worked perfect for me with stock alt.