Rearranging underhood battery grounds

[shepherd92683]

As some of you may know I have had a hell of a time with the charging system in my '08 TB, mainly because Im a car stereo addict ... I am about to buy some new wire and lugs to do some re wiring to try to optimize my set up. Here is the way I have it at the moment (I'm not getting into rear battery setup at all on this):

Pos. battery term to Alt Pos. with 1/0 wire
Neg. battery term through sensor to strut tower with 1/0 wire
Neg. battery term through sensor to fender with 4 ga.
Strut tower to engine block with 4 ga.

I am thinking it would work best this way:

Pos. battery term to Alt Pos. with 1/0 wire
Neg. battery term through sensor to alt. mounting bolt with 2/0 wire
Alt. mounting bolt to strut tower with 1/0 wire
Strut tower to fender with 1/0 wire

I was suggested to do it like this:

Negative battery terminal through sensor to alternator mounting bolt
The same alternator mounting bolt to frame rail
The same bolt on the frame rail to the strut tower.

My question is why connect a wire from alt bolt to frame and then frame to strut tower if the strut tower and frame are welded together and the current runs through them both together? The 'suggested' way also does not mention making a connection to the fender which IS a factory connection that runs though the sensor.

My theory is that the 2/0 cable that goes to the alt mounting bolt sees all the current in the system. The alt is mounted to the block so that eliminates the use of adding an additional ground to the block. All grounds are daisy chained off the ground to alt bolt which run through the current sensor. I can't think of a better way to do this but if anyone has an idea I'm willing to take any and all feedback on this. This is a measure twice cut once approach so any help is welcome!

 

[jimmyjam]

when it is running off battery, all ground will go through the bat<->alt ground, yes. but when it is charging under alt power, the current will be reversed through that wire. unless system voltage drops below battery voltage that is. so i wouldn't bother buying 2/0 just for that.

and yes, the frame ground would be redundant. I assume you are grounding your amps directly to your frame. unless your strut tower welds look bad, then there is no reason to. if you really want to ground to a point on the frame then do one or the other.

also, daisy chain is the wrong term, that would deonte a series connection, more like star or hub topology


I don't know much about the battery sensor but it seems like ideally if you have a large system then you want to get that tuned out of the PCM if possible. otherwise i think it will lower the alt output voltage when the ecm "senses" the battery is charged, you'd probably rather it not do that, but I don't really know, you should do some googling on the subject.

 

[shepherd92683]

I am only spending about $15 on the 2/0 and ring terms so its not that bad to me to have the biggest wire I can use. May not need it but it will never need upgraded lol. My amps are being grounded right now to the rear seats. Reason for that is I was going to ground them to my rear battery (which is grounded to the frame) but I got a NASTY ground loop from it so I temporarily grounded them where they are now. I may revisit trying to ground my amps to my rear battery which is what I ideally want to do, but need to figure out what on earth caused the ground loop (aside from the amps being grounded at the same point which my be the only thing causing it). I don't know where else to ground the amps unless I drill holes in the floor to go to the frame.

 

[jimmyjam]

well if you are grounding to the chassis then who cares what size your alt to frame ground is? the ground is coming from the fender in that case

also if you have 2 batteries then you deffinately need to figure out how to delete that sensor since you're only "sensing" one battery

edit* wait a minute, your rear battery is grounded to your frame, but your amps are grounded to the chassis? dude you need to pick one, no wonder you're getting nasty ground loops

the more i read this the more confused i get....

 

[shepherd92683]

When my amps are grounded to the battery that is grounded to the frame I get the ground loop and it goes away when grounded to the chassis... No that does not make much sense but thats how it is.

 

[phillyflapjak]

i havent ran any additional ground wires thru the clamp that is on the negative side and i havent had any issues at all and im running way more power and alts than you. Hit me up and we can talk about it

 

[shepherd92683]

I got my alt reinstalled today. I also added my 2/0 shca wire (about the size of 4/0) for my battery through the sensor to the alternator mounting bolt. Initial test was good, I'll find out more going to and from work tomorrow. On full tilt on a 25hz note I dropped to 13.1, not too bad. My stock alt was going to the low to mid 12's.

 

[shepherd92683]

Also, how are most people grounding their rear batteries and amps using multiple amps/batts?

 

[shepherd92683]

After a week after the alt install, it's a whole new system practically. On basically full tilt on punchy bass lines, it only drops about .2-.3. On heavy bass drops clipping slightly (based off my AQ bass knob clip indicator) it only drops .6-.7.

The one thing I still don't understand and can't figure out the consistency is why sometimes it charges at 14.2 and others at 13.6. There is no regularity on when it occurs for me to better manipulate a higher charging voltage. It seems that all of the rearranging and increased size in wire helped out.

Does it make any difference if the batteries are grounded to the frame and the amps are grounded to the chassis when the engine block/chassis/frame are all together? Some people have said it does but I don't see how it could.