Recommended power alternator per RMS


Unregistered guest
according this site ( i should have a 120 alternator at least in order to handle a 800 RMS audio system.
I'm thinking about buying a 800 RMS kenwood amp to power my 2 12" subs. My alternator only works at 70 amps.
Should be enought to handle it ? What about buyin' a 1 farad capacitor, should it help without upgrading the alternator/battery. I just want to know if my alternator will work for 800-900 RMS.


Silver Member
Username: Illuminator

Post Number: 343
Registered: Apr-05
It probably can't handle more than 550watts rms at the moment and you still have to consider the car's other electrical components that require power.

Bottom line:The cap won't compensate for that much lack of power and the alt will have to be upgraded.

Bronze Member
Username: Zootreeves

York, Yorkshire UK

Post Number: 22
Registered: May-05
Power (Watts) = Current (Amps) x Voltage

So 70A x 12V = 840W so should be ok especially as the voltage is probably higher (at 14V you get 980W).

But if you go over the RMS you may not get enough power and so could damage your amp/speakers so I would recommended getting a new alternator


Silver Member
Username: Illuminator

Post Number: 345
Registered: Apr-05
Actually, the 840w needs to be divided by two. The 840w is max, not RMS. Also, most car systems use about 13.8v configurations rather than 12v.

Gold Member
Username: Carguy

Post Number: 3059
Registered: Nov-04
Your car may have 70A alternator, but more than half of that is used up by your car. So most likely you only have around 30A or less to play with.
A capacitor will only help as long as your power requirement is less than what it holds.

Unregistered guest
ok, i got the point, so if i don't want to waste money in upgrading the alternator, i should buy the 450 RMS one.
And as i read in other threads, a capacitor will only add extra load to the alternator in my case, so it wouldn't help anything ?


Silver Member
Username: Msully701

Stratford, Connecticut US

Post Number: 132
Registered: Apr-05
you need 15 amps every 100 watts of power
« Previous Thread Next Thread »

Main Forums

Today's Posts

Forum Help

Follow Us