Figuring out what alts and number of batterys

[ChaseinBass]

So I ordered a triple alt bracket for my truck and am figuring out what I am going to need to run an 8k amp (crossfire probably) and my PPI 900.4 amp. And from what I am reading does this sound about right ?And I will be wiring at .5 on the subs.

900w + 8000w=9000 ish 9000/ 70% ? efficiency =12857 w/13v = 989 amps needed ?

so 3x 270 alts =810 - 50 ish for the truck = 760 amps

and 3x 110 ah batters = 330

760 +330 =1090 amps avail or will I really need another battery still ?

does this look right ?

Click to read more...

 

[adulbrich 5,000+ posts]

Alternator is the best for electrical upgrading. I was going to do a big alt setup with less batteries, thinking it would save weight, mpg, ect.

I have a 320 amp hairpin right now, and will be adding a 400 amp hairpin soon. Here is the surprising experience I've had with batteries:

I originally had One XS D3100 under the good. My car charged between 15v and 15.2. Only at 14.8v when it was really really hot. I had one Banda 7k and dropped to 12.8v-12.9v full tilt at idle. I did not have audible belt slipping, surprisingly.

I sold my Banda 7k and bought a DD M4a. I then sold my XS D3100 and bought five Exide group 49's. With the same alternator I now charge at 14.8. The lowest I drop full-tilt at idle without clipping is 14.4v. However, the belt slips audibly when you're standing outside the car and the bass drops.

Both amps were wired to 1 ohm nominal on the same sub. I find the voltage drop weird because I thought the Banda was supposed to be wayy more efficient. Many people say that adding batteries will not solve voltage drop issues. They say batteries only help at "battery voltage", which is somewhere between 12.6v and 13.6v.

However, I think batteries do hold a little bit extra "float" voltage above their resting voltage (for a short time). Yes, they are a load to the alternator, and that explains why my overall voltage while idling is 0.2v lower. However, they did actually help with voltage drop. @av83; and I were talking about it yesterday

My battery bank is 500ah for a 7k. I would suggest adding more batteries to your bank when you add alternators.

 

[massivespl]

I had my crossfire 8k at .5ohm with two 350 alts and 4 3100s and I can stay 13.4v on average full tilt.

I've also ran crossfire 8k .5ohm on just two 350alts and one northstar batt under the hood and I still stay above 12v

 

[adulbrich 5,000+ posts]

I had my crossfire 8k at .5ohm with two 350 alts and 4 3100s and I can stay 13.4v on average full tilt.
I've also ran crossfire 8k .5ohm on just two 350alts and one northstar batt under the hood and I still stay above 12v

So you also got less voltage drop with more batteries?

 

[massivespl]

So you also got less voltage drop with more batteries?

Ya batteries do help out. Lol

 

[adulbrich 5,000+ posts]

Ya batteries do help out. Lol

Well yea, but for a while everyone here was like: "don't add a battery, it won't help"

Especially your favorite member..

 

[massivespl]

Well yea, but for a while everyone here was like: "don't add a battery, it won't help"
Especially your favorite member..

Don't get me wrong if I have the option to ad alternator over batteries I will. But yes betteries will help. Voltage will drop fast without them.

 

[adulbrich 5,000+ posts]

Don't get me wrong if I have the option to ad alternator over batteries I will. But yes betteries will help. Voltage will drop fast without them.

Yes, I would also like to add another alternator. Alternator>batteries up to a certain point. I would also like to try caps, as I have no first-hand experience with them. I have heard mixed things about using both caps and batteries in your bank.

After I drop the M4a down to .25 nominal and see what drop changes to, I'll ad the alternator and more batteries depending on how bad it is. Then I'll buy my new amp after I sell some stuff

 

[ChaseinBass]

I had my crossfire 8k at .5ohm with two 350 alts and 4 3100s and I can stay 13.4v on average full tilt.
I've also ran crossfire 8k .5ohm on just two 350alts and one northstar batt under the hood and I still stay above 12v

So I should be fine with 3 270 alts and four juice box grp 31s ?

 

[massivespl]

So I should be fine with 3 270 alts and four juice box grp 31s ?

Yes that should be plenty