Battery Voltage

Naresh · Jan 7, 2003

Hi just noticed that the 300w or so rms my amps are pulling are putting a drain on my battery and that the lights dim to the bass but then come back on to full brightness!! /ubbthreads/images/graemlins/blush.gif

Can anyone tell me what the voltage across a healthy battery should be? I measured it recently with th engine off and found it to be around 12.2V.

I initially did this to see if the voltage across my amps was the same as the battery - if its much less then than battery voltage then it means I have a loss somewhere in the system hence explaining my engine noise! Does anyone know that is true or not?? /ubbthreads/images/graemlins/confused.gif

finster · Jan 7, 2003

Alright mate,

I think you need to measure the voltage coming from the alternator when the engine is ON, as the battery is only really used for starting the engine, it is the alternator which supplies power for the car......

May be wrong though.... /ubbthreads/images/graemlins/blush.gif

JohnH · Jan 7, 2003

Naresh, generally when it all dims it could also be the size of your earth. You need to have a really good earth and a fat earth cable too.

Naresh · Jan 8, 2003

Hi John, I was thinking of getting a much thicker gauge earth cable but when you mean "good earth" what would you do if the amp is mounted in a false boot floor? Have you an aftermarket ICE setup too, if so what did you do?

Mine is screwed to a hole drilled in the boot floor where the spare is (all paint was removed around the screw hole).
What I was thinking was making the hole a little larger and fitting a decent sized bolt. Maybe dirt and spray from underneath causes the earth to suffer as its seems like my noise is intermittent! /ubbthreads/images/graemlins/confused.gif How good is the rear seat belt bolt as an earthing point?

Cheers

IML337 · Jan 8, 2003

OK, with the engine running, you want about 14v. With the engine running and the system cranking you may lose half to one volt (I'm talking across the battery here /ubbthreads/images/graemlins/smile.gif )

In my A3 I had two amps - totalling about 250W RMS (but when do you run your amps flat out at full gain?! Never I'd think!) I had 4AwG/gauge/whatever you say cable from the batt to the boot (fused right near the batt) then in the boot there was a splitter box and I had 8AwG cable from the splitter to both amps. This lasted for 3 years without any problems at all. 4AG was slight overkill for my setup, but it's much more elegant and cable cost differences are negligable.

Your talk about your earthing setup confuses me though. Why is the amp being on a false floor relevant? You can mount the amp wherever you like! Or are you saying good earth points are hard to reach from there?!

I used the rear seatbelt anchor points as earth points for my amps (one on each side) and it was fine. The earth cable should be the same gauge as the power cable for your amps /ubbthreads/images/graemlins/smile.gif

Also, as you said, check for voltage drop between the batt and the amp. What cables/fuses are you using currrently?

Tim

Naresh · Jan 8, 2003

Hi Tim. About my false floor, I wanted my amps hidden out of the way and not bolted to the rear seats so I constructed a void in the boot and covered it with a carpeted false floor (no piccies yet!), and earthed it to the boot floor. I just wanted to get a feel for what the best earthing point was in the hope my noise problems could be solved!

I used a power kit for a 300w amp which uses 8 gauge cable with same size earth cable but I will uprate this to 4 gauge and also use the rear seat bolt - how did you get a large enough ring connector to go around the bolt? I can't remember what fuses are being used but I believe they are at least 25-30A.

IML337 · Jan 8, 2003

I seem to remember mangling the connector a bit to fit around the bolt. Wasn't a whole ring, but more like a half ring iirc...

Simon · Jan 9, 2003

The volt meter in my A4 sits at around 15.5v with the engine running - and I see no noticeable dimming, the amps I am running are pushing out about 650wrms in the current set-up.

Power and earth are 4awg Amps are mounted in the spare wheel well and grounded to the bolt hole where the spare wheel retainer used to screw into.

I get no engine whine.

Simon

PunjabiA4 · Jan 9, 2003

/ubbthreads/images/graemlins/frown.gif i wonder what the prob is with mine then? i have one mono block amp which is about 800 watts plus a 2 x 60 watts to run my rear. I have 1 JL 12inch and the lights dimm at decent volume levels!!! i also have an optima battery at the front. /ubbthreads/images/graemlins/frown.gif

however i have one 4awg as a ground attached to the bolt to attach the seat belt..this goes to the distb block which splits the ground to each amp...all wires are 4awg.

is this causeing the problem??? i know the mono PPI amp is quiet hungry.

JohnH · Jan 9, 2003

Naresh, Got an Alpine head unit and pheonix gold amp in the boot of my Golf TDi the amp was running two JL 12" 12W3's but my mrs uses the car and wants some bootspace so we are only running a single JL 12W3 in there now. But, you can turn the head unit up to full whack at night without the interior lights dimming or pulsing.

I will have to go out and take a pic of the power and earth cable the installer used. To say its big is an understatement!!!!

Where abouts are you? you going to the windsor meet? If you are I could bring it and you could take a look /ubbthreads/images/graemlins/smile.gif

Simon · Jan 10, 2003

Naresh,

where is the whine comming from, is this still the problem with your rear speakers?

What have you done so far to trace the problem?

Thinking about it logically noise has to be entering the system somewhere and ending up at the speakers, theoretically all you have to do is find where the noise is getting in.

Can you give us a system diagram to think about.

Simon

Naresh · Jan 10, 2003

Hi Simon, I've yet to find the time to remove my false floor to begin the noise search so haven't done much yet plus the noise seems to be intermittent!! Not helpful at all!! I am to check the voltage at the battery and amp while the engine is on and compare values! Oh yeah, the noise comes from the rear 7x10's!

What do you need diagram-wise? I could sketch out my system on paper then scan and mail it to you? Whats your email address mate?

Naresh

Moresauce · Jan 10, 2003

Couple of things:

As mentioned check the earth and beef it up. Clean all connections and replace any that aren't already with Gold plated connections.

Also have you considered uprating your battery to a ICE friendly heavy duty one. I think they are gel filled (???) and are much better for high drain applications

PunjabiA4 · Jan 11, 2003

Optima do the gel filled ones...didn't help in my case though /ubbthreads/images/graemlins/frown.gif

Simon · Jan 13, 2003

Noise is rarely caused by the battery - or indeed solved by replacing one.

Almost exclusivly caused by a problem with the wiring, less often caused by physical failure of equipment.

wiring diagram, start at the HU and map your system back from there - try to include the route the cables take through the car.

email me at Faze_ii@hotmail.com or scan it and put it up here.

Simon

Moresauce · Jan 14, 2003

Have you also tried those in line noise supressors? Don't know if they will cure your problem but they are cheap and wouldn't have thought it would help

Inigo · Jan 14, 2003

What about fitting a capacitor? /ubbthreads/images/graemlins/smile.gif

Naresh · Jan 14, 2003

Simon - I'll draw up my system diagram tonight and send it to you. Inigo - I know what you're saying but I'd rather find the cure rather than firefight the cause with noise suppressors and capacitors etc! With a little investigation I hope to get to the bottom of this noise!! /ubbthreads/images/graemlins/wink.gif

Simon · Jan 21, 2003

***** got to ****** retype this as the damm firewall logged me out and lost the ****** post!!***

Okay only just checked my hotmail as I have been **** off busy!

First off at the 4ch amp switch the RCA's from front to back.

if the noise moves the problem is at the input side of the amp - swap the RCA's back again.

at the HU swap the RCA's front to back.

if the noise moves the RCA is the problem - replace it, if the noise stays at the rear the problem is with the output stage of the HU - get it checked.

If the noise stays at the rears when you swap the RCA's at the AMP then the problem is with the output side of the AMP

Swap the RCA's back again.

now swap the speaker connections on the output side of the amp.

if the noise moves to the front speakers the problem is with the output stage of the amp, get another 4ch amp to test with.

if the noise stays with the rears then check/replace all the cabling between the amp and the speakers - if this all appears to be okay borrow another pair of speakers to test with, your speaker/s could have failed.

what you may well find that disconnecting/reconnecting cures the problem - I had someting very similar with the skyline that I couldn't trace, but by the time I put it all back to how I started the problem was gone.

the only other thing to consider is earthing both amps to the same place. I am not sure how much of this I belive but there are some that theorise that multiple earthing locations can cause alt noise.

hope that helps - it took a lot less typing the second time!!

Simon

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