Rear batt voltage drop when amps are on

[Xprime4 10+ year member]

My rear batt is isolated from my under the hood one. When the car is off the batt rest around 12.7v. When i start the hu, the amps power on. The voltage drop to like 11.5v for no obvious reason, even with volume at 0. If i put some juice into the amps, the voltage drop to 10v, car off. I guess this ain't good for the amp but they don't even shut off.

What could it be? Is it possible that my battery ground ain't great? I mean, when i put a little charge on the batt (amp at iddle) , i get a .8v drop. otherwise what could it be? is it bad for the amp to play in the 11ish without dropping too much ( not like 14v to 10v....)

Click to read more...

 

[thevic24 5,000+ posts]

could be bad, iam shure the power supplies dont like it. mabie the battery is bad. bad batteries can show good voltage at rest but when a load is applied, thats when the truth shows.

can you take it to an auto parts store to have load-tested?

 

[Xprime4 10+ year member]

well it's not even a month old and my ground is suspicious ... i'm using the metal that was holding the spare tire, but it look attach solidly to the frame

 

[Xprime4 10+ year member]

also even if i push the amp some time, the battery doesn't seems to discharged fast at all. I played it 10min at medium level and the battery was only .1v discharged

 

[Xprime4 10+ year member]

also about the amp not loving the 12v less. Every car off is under that with a moderate load, so it can't be that bad???

 

[thevic24 5,000+ posts]

i ment 11v or less for the amps. mabie the battery has a weak cell. even witha weak cell, the battery may take a load for a while.

 

[Xprime4 10+ year member]

i'm pretty sure the batt is fine. Like i said ground is suspicious. I'll need to remove the box to get acces to the batt and find a new ground point....

Any one else on amp at 11v with less than a 1v drop

 

[rocky 59 5,000+ posts]

when i had my amp trouble i grounded the shit outta my batt's directly to sanded frame and grounded the engine block and i was all set

 

[Xprime4 10+ year member]

yeah grounding the amp that the rear seems like a good idea. There is like 4 feet betweens the batt and the amp.

 

[rocky 59 5,000+ posts]

i grounded the neg. batt post then attached the amp ground to the batt neg. terminal all good //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[Xprime4 10+ year member]

so it's the ground for sure? a bad ground can make huge drop (.8v) just from putting the amp at iddle?

 

[Xprime4 10+ year member]

lil bump on 1) battery droping .8v just with amp at iddle

2) amp running in the low 11ish without droping really (car off)

 

[loopkiller 10+ year member]

My rear batt is isolated from my under the hood one. When the car is off the batt rest around 12.7v. When i start the hu, the amps power on. The voltage drop to like 11.5v for no obvious reason, even with volume at 0. If i put some juice into the amps, the voltage drop to 10v, car off. I guess this ain't good for the amp but they don't even shut off.
What could it be? Is it possible that my battery ground ain't great? I mean, when i put a little charge on the batt (amp at iddle) , i get a .8v drop. otherwise what could it be? is it bad for the amp to play in the 11ish without dropping too much ( not like 14v to 10v....)

The reason why you see a draw at startup is the amps internal caps need to charge. As soon as the amp sees the turn on signal via the REM wire, it turns on and the caps fill. That is to be expected.

Now when the voltage drops to 10.0V, that is very bad. Do NOT run your amps that low. You will damage them for sure. You might be best running the engine to support the battery. I guess that battery is not enough by itself to support your system after all. That does not mean it is defective, just not up to the task.

If you have the amp grounds running directly to the battery, then the chassis ground never even comes into play. The chassis ground would only be needed when using the alt to power the amps.

 

[Xprime4 10+ year member]

The reason why you see a draw at startup is the amps internal caps need to charge. As soon as the amp sees the turn on signal via the REM wire, it turns on and the caps fill. That is to be expected.
Now when the voltage drops to 10.0V, that is very bad. Do NOT run your amps that low. You will damage them for sure. You might be best running the engine to support the battery. I guess that battery is not enough by itself to support your system after all. That does not mean it is defective, just not up to the task.

If you have the amp grounds running directly to the battery, then the chassis ground never even comes into play. The chassis ground would only be needed when using the alt to power the amps.

so, i wouldn't need to ground the rear batt on chasis if i had all my amp ground on the neg of that batt

i'll put my dash voltmeter on my back batt, so i'll monitor the drop better with car off. Considering that once the amps power on, i'm down to 11.7ish, what should be my maximum drop to keep it safe? not under 11v i guess, but i would like your opinion Loopkiller

btw, you should be the moderator of this wiring and electrical forum. //content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif

also, bassracers must burn few amps per year with low voltage?

 

[Xprime4 10+ year member]

The reason why you see a draw at startup is the amps internal caps need to charge. As soon as the amp sees the turn on signal via the REM wire, it turns on and the caps fill. That is to be expected..

also , once the amp caps are charged, should my "iddle"battery voltage goes up? I just check today and i was around 11.70 with music playing at confortable level.