I'm currently running a fi audio sp4 15 at. 5 ohms with a hifonics brz. 1700 amp. I have a 350 amp alt and a xs power d3400 under the hood and i'm still having problems with my voltage, when the sub hits hard i drop from 14.5 to 11.7volts at some points, what else do i need? More batteries or is it the alternator? The alt was bought of ebay from BnR parts. Just wondering if i should send the alt back and look for a new alt. And if i did send it back what amp alternator should i be looking for? I plan to get a crescendo 3500 within the next few months.

Does it drop while u hold on the gas or just at idle?

Also have you done the big 3, im assuming yes with a new alt and batt.

Is the XS the only batt you have? If so i recommend a smaller battery up front and put larger in the back next to the amp.

The larger batt will take longer to charge back up, per se.

Check all of your connections to make sure they are solid, especially your grounds. If you suspect your alternator is at fault, test it to determine if it is the source of your issue.

Yes i have the big 3 done with all 1/0 gauge. And yes i can do doing 70 down the highway and have my rpm at 2k and still dropping to 11.8. So small battery up front and bigger in the back?

You have more than enough reserve for your current draw. It does sound like a charging issue. If it were me, i'd test the alternator to see how many amps it is producing with your gear on at normal listening volume.

nah that wont help then.

Sounds like an alt problem to me.

Being at .5ohms probably is sucking alot of juice, but if its claimed to be 350amp alt and ur gassing it and still dropping thats your problem. I mean if its charging to 14.x then it works but isn't 350a.

put it in park and rev it to 3k and see if it still happens, usually HO alts take high revs to produce, so if it works better at 3-4k get a smaller alt pulley and you should be good.

nah that wont help then.

Sounds like an alt problem to me.

Being at .5ohms probably is sucking alot of juice, but if its claimed to be 350amp alt and ur gassing it and still dropping thats your problem. I mean if its charging to 14.x then it works but isn't 350a.

put it in park and rev it to 3k and see if it still happens, usually HO alts take high revs to produce, so if it works better at 3-4k get a smaller alt pulley and you should be good.

ah half ohm that amp will be very hungry, take it to vato zone, and have the alt checked.. they wont be able to tell you if its putting out 300 amps.. but they can till ou if its putting out 130 amps... that will give you an idea.

check your grounds... #1 and all your connections aswell... a body ground simply will not do.

If you suspect your alternator is at fault, test it to determine if it is the source of your issue.

I would check the alt for sure

Also have you done the big 3, im assuming yes with a new alt and batt

If your dropping that low on just that 1700watt amp then I think it would be an issue with the electrical. that or excessive clipping would drop the voltage also. Is it quality 1/0 wire? Do you have a clamp meter to see if your alt is putting out anything close to 340amps?

shouldn't have bought the ebay alt.

alternator should be working fine based on info given.

High voltage and he hasn't gotten stranded anywhere from not charging..

2 things you should really own in car audio- dmm and ammeter.

You can clamp the alt to see what the max current it's putting out but it will be a waste of money.

I can tell you 100% it's not the alternator.

The problem is this-

Vehicles who do not have a dedicated ground run from front to rear will experience up to a FULL 1 volt drop in voltage during max load or after a load has been presented on the cable itself.

Once this happens, a user can measure voltage differences and see the problem.

You have never told us where you are measuring your voltage drop at so i can only assume at the amp itself, correct?

Try measuring voltage drop DIRECTLY on the alternator.

If it's a lot better like in the high 12s at least, then that's your problem.

You would need to do what was suggested earlier-

Small batt up front, D3400 in the rear.

And take it from someone who tests these things- if you got more than 1 battery in the car, the front battery will not help hardly at all unless you run enough cables to compensate for the potential voltage drop from front to rear VS amp to rear batt.. Imagine how many cables that will take

By the time you figure out the cost, you could have bought another battery,

wait did u just say i was right