DIY: Battery Relo

miguez

Just disconnect something that won't allow the engine to start so it will crank for longer . Or run out of fuel

FricFrac

I've measured the stall current on a 540 can 27 turn motor at 90A... thats just a tiny little motor you'd find in a power drill or R/C car. I suspect under stall conditions a starter could draw more than double that but that's just a guess. Depending on the resistance in the fuse you will probably be droping some voltage on the fuse -not a lot but some. My other concern would be ground loops. I'd definately run a heavy ground up to the front of the car with the positive cable. I would also make sure all the car's computers are grounded to the battery directly to eliminate any issues....

wstar

We'll find out tomorrow if the 200A breaker works.

As for the grounding issues, I don't see any point in running a separate ground wire along the length of the car. The car's body itself should provide more ground path than any reasonable wire could hope to.

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miguez

Agreed. FricFrac, can you add any info tho why you'd recommend that?

wstar

Installed the breaker this evening. The car started fine without tripping it. Then again, it's a hot summer-ish evening and the car had only been off for 5 hours. Might be different on an ice cold morning in the dead of winter with a car that hasn't been run in 2 days. We'll see when I get there in the winter

I also went ahead and prewired a little harness for my trickle charger in case I need/decide to use it. The breaker is mounted to the top of the battery box with superglue (I know, how ghetto of me).

But anyways, yes, the Lightning Audio LCB-200 seems to do the trick, providing short-circuit protection as well as a convenient way to kill the battery power when working on the car.

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FricFrac

The conduction of steel is poor compared to copper. Typically copper is used as the baseline as its is the most common and almost best conductor (wow that english sucked but carry on...). Copper is only surpassed by silver for conductivity at about 106% as conductive as copper. Steel for the record sucks hard at electrical conduction ranging from 2 to 18% for pure steel in comparision to copper. I'd expect our sheet metal to be somewhere around 12% ish.

One of the main issues you are going to have with a vehicle electrically is a good path to your power. Grounding to the chasis is good enough for most applications but when you start involving multi sensors and multi computer controlled systems to your vehicle small glitches in signals and poor grounds can cause problems. IIRC Stillen makes a grounding kit for the car computers because of this very issue. In the olden days if you got 14.4V to the coil or 14.3V who cares - its not gonna make a difference but if a signal gets lost and isn't part of a calculation you carputer need to make a decision you aren't going to perform optimally. That's just voltage I'm not even getting into eddy currents, etc. The car is a horribly noisy environment electronically which is why the basics are so important.

The other issue is your connection to the chassis. Once that iron starts to oxidize you are adding resistance which means power loss. Don't forget that bitty screw in the sheet metal is the best contact point to the steel but you've probably got three or four dissimillar metals there. Dissimmilar metals cause corrosion as well. Although you've got huge surface area in the sheet metal your contact point basically negates its huge current carrying capability. In real life these are minor points but in racing most of us want to know the little details and determine whether they are worth addressing or not.

So in short (oh didn't plan that pun...) your set up will work but we are pit racing here so if you wanna squeeze every last drop or optimize your system that's why I'd recomend running a ground line. At the very least I'd run ground wires from the carputers directly to the battery because they are the most likely to suffer ill effects but that's just me....

wstar

I'm well aware that I have several junctions of dissimilar metals, but I don't plan to let anything corrode significantly. That's why all those joints got coated in anti-oxidant, and why I'll be checking and cleaning them on a regular basis.

And while mild steel may have roughly one tenth the conductivity of copper, there's still a lot of it between the battery and the various sensors and computers you're talking about. It really just comes down to the junction points, and they're sufficient in size for the amperages involved (think about it this way, 1/10th the surface area of that lug screwed into the trunk is still more than enough width of copper for the current involved).

As for the Stillen grounding kit, its primary function is to help ground the engine block to the body. I have it installed in my car. One end does go to the negative battery terminal as well (or did, before I pulled the battery), but clearly its primary purpose is to ensure a good engine-to-body ground, so that a potential difference doesn't develop between the two.

I'm not saying you don't have a point about the cleanliness and stability of the ground reference in the car, but I think you're being overly paranoid about it. If you'd like, I could go measure the resistance of the car body from the current battery ground point to the old one up front for you, and we can compare that to the known resistance of my 15 ft run of 1/0 copper for the positive side, if that provides any insight. I don't think there will be a difference worth caring about.

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FricFrac

..... and I don't disagree with you and I'm also not trying to nit pick on your excellent work. I'm just pointing out some things that may be of intrest to others and things to take into consideration. It may even help people with trouble shooting down the road to have the info - nothing to do with being paranoid. These are the fine details and its up to the racer to decide to what level any of this matters. Like I said its just pit racing...

Solus

*STUPID QUESTION ALERT* I am sure most of you assume if I post its a stupid question and I am full of them, but why relocate the battery? Like what point does it serve?

wstar

There are no stupid questions, only stupider askers

The car is front-heavy from the factory, and so you want to remove weight from the front if anywhere to help get closer to neutral weight balance. Removing weight from the top of the car will lower the center of gravity, giving handling advantages again. Reducing overall weight of course also increases the horsepower:weight ratio, which gives better acceleration, as well as again improving handling (less weight to throw around, so to speak).

So, depending on your priorities, you want to drop overall weight, and you especially want to drop it from anywhere towards the front and/or top of the car. This is where the battery comes in.

The battery is really heavy as far as car parts go. Ours weighs 35 lbs. One option is to simply move the stock battery to the trunk, shifting 35 lbs from front to rear to help balance. Another is to leave the battery where it is, but use a lighter one, shedding weight from the front but not adding any to the rear. The DIY in this thread does a little of both, it removes the 35 lb battery from the front, and replaces it with a 14 lb battery in the rear, giving an overall reduction of 21 lbs, and a 14 lb shift in weight to the rear.

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travisjb

Hi Solus... this car has too much weight on the front... it tends to 'dive' under braking with stock suspension and the rear gets a bit light under hard braking... if you push the car to its limits, you may want to tinker around with the weight distribution to get closer towards even front/rear... some quick google searching on 'race car weight distribution and handling' should give you lots more info if interested

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2009 370Z #104
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bigaudiofanat

I am sorry but why in the world would you want to put your battery in the rear. Nissan setup the car for the battery to be in the front.

miguez

See the two posts above yours.

bigaudiofanat

Got ya LOL

travisjb

good grief ! LOL

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2009 370Z #104
*For Sale*