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Battery Draw Questions


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Ok i know this can get pretty technical but try to keep it basic. 

 

If i needed 500 amps to feed my system but only can get 300 from my alternator. How many batteries would you need to make the difference up ?

 

How much can a battery actually discharge at once ? I'm guessing it can obviously put out its cranking amp ratings but how long will that last ?

 

and how quickly do you think an alternator could recharge 3 d31 batteries ? (assuming the alt can put out 300 amps ok )

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This guy has a Northstar NSB90 (old version). Watch how much he is pulling from it and how much the voltage drops.

A good guesstimate is you can draw about 100-150 amps from a group 31 AGM with voltage drop to about 11-12 V. If you get 300 amps from the alternator and need 200 more, 2 G31 AGMs should do it but you will have bad voltage drop. It would work probably but it's not ideal. And keep in mind that a 300 A alternator won't give you the full 300 amps, not at idle anyway.

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Excellent post alex912005 !!

so here is a total noob question to follow up on that. And I'm making numbers up so bare with me if they don't calculate out to be exact real world numbers. I think you'll catch on to what I'm asking.. 

 

so let's take my 5000.1d  amp and say it can do 5000 rms @ 2 ohms off of 12volts. 

 

obviously ill need X amount of amperage to achieve this. And for the sake of this question we'll make up an amperage it needs of say 500 amps.

 

now let's say i dropped my ohm load to 1 ohm and now my rms power is capable of pushing 10000 rms. 

 

does the amp need more amps to achieve this rms of 10000 or does the amp become more efficient and still use same 500 amps to get the 10000 rms ?

 

I have couple follow up questions after this too depending on answer. 

 

 

 

 

 

 

 

 

 

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If it makes 5000w at 2 ohms and you wire at 1 ohm, it doesn't really do double the power in real life (you aren't even getting the 5000w rms in the first scenario because of impedance rise). But if it did, it would draw more amps to produce that power. It takes power to make power. And efficiency actually decreases as you wire down. Amps are most efficient at something like 4 ohms (some claim 80% efficiency), but it goes down when you lower the ohm load, so it takes even more power to make more watts.

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ok great. 

so basically it wouldn't be worth trying to lower the impedance because I'm not even maxing  out the amps capabilities at 2 ohms... plus its more efficient there as well. (less heat, less amperage, less stress on components) 

 

my setup is Orion 5000.1d, 2 15" all's, 3 d31 yellow tops, and a toss up between 270 & 370 alt. 

strictly for cruising playing music for a couple hours at a time.. I'm nervous about the small pulley on the 370 ( i have tendency to floor it every now and again reaching 6500 engine rpm which equals well over the rated 16 or 20 thousand alt rpms)

 

 

 

 

 

 

 

 

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20 hours ago, DzNuttzOnYaChin said:

If i needed 500 amps to feed my system but only can get 300 from my alternator. How many batteries would you need to make the difference up ?

Two G31s if youd like to hold very very high 11s. For AGM batteries, 1c discharge equates to initial voltage drop to ~11.6-11.9v. 

How much can a battery actually discharge at once ? I'm guessing it can obviously put out its cranking amp ratings but how long will that last ?

Peak discharge has its place, but what to keep in mind is the discharge curve. The relationship between discharge amperage and voltage is STEEP with AGM.

and how quickly do you think an alternator could recharge 3 d31 batteries ? (assuming the alt can put out 300 amps ok )

When I had my 3 G31s in the back and G27 in the front with a 270A alt, after beating on it for a while, I would immediatey bounce back to mid 13s. It could be 10 mins until I saw above 14 again.

 

On 5/8/2011 at 7:38 PM, Kranny said:
On 5/8/2011 at 7:35 PM, 'Maxim' said:

It hurts me inside when I read stuff like this and remember you're 15

LMFAO so true

:blush:

Mitsubishi 3000GT (Old Build)

Headunit: Pioneer 80PRS

Frontstage: (2) McLaren Audio MLT-2 Tweeters & (4) PRV Audio MR Series Neo 6.5" Mids

Substage: 4 15" Hybrid Subs - Tantric Motors & Sundown Softies

Amps: Banda 2.4D Amp (Tweets), American Bass VFL 350.4 (Mids), and (2) Ampere 3800s

Electrical :Singer 260A Alt & JY Power Lithium

 

2005 Chevy Colorado Ext Cab

Headunit: Pioneer 80PRS

Frontstage: 4 PRV 700Ti Tweets & 6 10" Delta Mids on 3000wrms

Substage: 6 Fi BTL 18s in a 4th Order Walkthrough on 3 Wolfram 4500s

Electrical: Singer "390" and JY Power

My Official Feedback Thread

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41 minutes ago, DzNuttzOnYaChin said:

Thanks for the response.. perfect !!! 

 

If you had to take a guess.. What is the maximum a dead battery (assume a d31) could pull from an alt to recharge ? At any stage of its recharge cycle ?

This video that Mike Singer recorded immediately comes to mind :)

 

On 5/8/2011 at 7:38 PM, Kranny said:
On 5/8/2011 at 7:35 PM, 'Maxim' said:

It hurts me inside when I read stuff like this and remember you're 15

LMFAO so true

:blush:

Mitsubishi 3000GT (Old Build)

Headunit: Pioneer 80PRS

Frontstage: (2) McLaren Audio MLT-2 Tweeters & (4) PRV Audio MR Series Neo 6.5" Mids

Substage: 4 15" Hybrid Subs - Tantric Motors & Sundown Softies

Amps: Banda 2.4D Amp (Tweets), American Bass VFL 350.4 (Mids), and (2) Ampere 3800s

Electrical :Singer 260A Alt & JY Power Lithium

 

2005 Chevy Colorado Ext Cab

Headunit: Pioneer 80PRS

Frontstage: 4 PRV 700Ti Tweets & 6 10" Delta Mids on 3000wrms

Substage: 6 Fi BTL 18s in a 4th Order Walkthrough on 3 Wolfram 4500s

Electrical: Singer "390" and JY Power

My Official Feedback Thread

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