Straight of the bat, apologies for the long post…
I have some noob questions about the capability of OEM battery and alternator to support my audio set up. I will try and break down what I have and how much I think every part consumes and my calculation for experts here to review.
I have BMW M5 F10 running 676 hi fi system with following changes:
a) stock amp driving rear 2 speakers only so I believe it is only drawing 25x2w (am I right in thinking if I am not using any other channel there is no more power usage?)
b) Audison Bit 10 connecting the above amp with my 2 aftermarket amps. I am not sure about power usage of this processor?
c) JLAudio XD400/4 v2 amp (75w x4 @4 ohms) driving door speakers (Focal K2 10cm) and Focal iFBMW v2 sub
d) Hertz HCP-1D monk amp (700w @2 ohm and 380w @4 ohm driving Hertz HX250 sub (400 watts). I was thinking of running this at 2 ohm, dialed down for lower power sub but I am concerned if 700w is too much for the car’s electrical system to handle. I will use 380w below in my calcs
Stock amp - 25 x 2 = 50w
Multi channnel amp - 75 x 4 = 300w
Mono sub amp - 380w
Total = 730 watts
Account for 30% inefficiency gives me power draw of 1043 watts (730/0.7)
Using 13 voltage to get to amp hour - 1043/13 = 80Ah (this is peak volume draw)
or worst case scenario of 12v = 1043/12 = 87Ah
So, my question is regarding the combined output of car’s alternator and battery. I am not entirely sure but from what I found on the internet alternator is 210Ah and battery is 95Ah.
When the car is up and running I understand that up to 60% of alternator output could be used by the car so I am left with 40%, i.e., 84Ah plus battery’s powe, therefore, I think I should be fine with the set up.
1. Could anyone familiar with car’s power management system have a look and check if my calculations are right and I can proceed with this set up without any risk to any component due to insufficient power?
2. Am I right in running my mono amp at 4ohm instead of 2ohm thereby saving about 320w (or 450w accounting for inefficiency). I don’t think I have enough power to run at 2 ohms and I should not be using battery when the car is running. Alternator should suffice my needs in most cases without drawing power from the battery.
Thanks
