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How can I replace the ground in my car?
March 6, 2012 11:26 AM   Subscribe

How do I replace the "big 3" (battery to chassis ground, engine block to chassis ground, battery positive to alternator) on a Honda s2000?

My battery keeps dying (not just losing voltage, my replacement batteries die after about a year). It's not the alternator, the alternator charges the battery just fine - it's just that all my batteries start refusing to hold a charge for longer than a day or two. I've tested my resting electrical drain, it's within normal.

My mechanic (and the rest of the internet) is telling me my amp's killing my battery . (My amp is only 800 watts -- I know it sounds big but its a loud car). The most obvious first fix is to replace the "Big 3" with 0 gauge wire, according to the above sources.

The problem is under the hood of the s2000 is a hassle. I can't even find the route the positive wire takes to the alternator. I don't want to take out the engine to do this. I also can't even find the engine block ground. About the only one I can find is the battery-to-chassis ground. *sigh*.

I don't want to pay a mechanic to do this, because it should be easy, and wire, even high-quality 0 gauge wire, is cheap.
posted by skybolt to Travel & Transportation (11 answers total) 2 users marked this as a favorite
 
The stock alternator is rated for ~70 amps and your amp alone draws 67. It's worth pointing out that the alternator output is peak; nominal is usually much lower.

The charge/recharge cycle you are experiencing is very bad for conventional "starting" batteries. I'm impressed that you've had as much success with them as you have. My son's BFF has a Neon with a 500w amp and he's burning through batteries every few months. I guess that's cheaper than building it right.

Replacing the cables might get you some more headroom, but I can't imagine it would be that big a difference.

I would suggest that you get a better battery for your use case - like an Optima yellowtop or some other deepcycle/starting dual use battery. A higher rated alternator wouldn't be a bad idea, either - but if you have a garage, a really good charger would work, too.

A secondary battery would probably also work, but balancing the draw can be tricky if you're looking to top performance.
posted by Pogo_Fuzzybutt at 11:43 AM on March 6, 2012


Are you 100% positive your alternator is fine? Because only two things kill lead-acid batteries: overcharging (loss of electrolyte) and time spent below max charge (letting the plates sulfate). So you're either undercharging it, overcharging it, or you've too large a load and are preventing the battery from remaining fully charged.
posted by introp at 11:49 AM on March 6, 2012


Thanks for the quick answer --- I should elaborate somewhat. I will be getting a different battery, but until I trace the root of the problem I don't want to subjecting my battery to the constant spiking; I'd rather fix the root problem before upgrading equipment.

I should point out 800 is the high end of what the manufacturer claims the _output_equivalency_ is, I doubt it's actually pulling 800 watts. That said, my charging cycle is quite good. After driving less than a half-hour, the resting battery voltage (of 11.9) is increased to about 12.7, with the engine off. It'll hold that for awhile, but by the end of the day, it's back down to 12.1, 11.9 or somewhere else around there.

The issue as I understand it is the pulsating draw against the battery when it should be pulling it from the alternator. Apparently lead-acid batteries do _not_ like to have spiky high-amp voltage draws (anywhere from once per second to 200 times per second). Upgrading the "big 3" should allow the alternator to supply the amp instead of the battery, and since the ground and positive in this car has been described as "weak" and "barely adequate" it should be my starting point.
posted by skybolt at 12:35 PM on March 6, 2012


I know that the fact that it's a toasted battery complicates things, but 11.9 V is really, really low. 11.7 is considered a fully discharged (0%) battery. If your battery is getting that low EVER, something is really draining your battery. If the battery is sitting overnight at anything but about 12.6 V, you're sulfating the thing and killing it.

It sounds like you have a parasitic load on the battery even when the car is off.
posted by introp at 12:58 PM on March 6, 2012



Upgrading the "big 3" should allow the alternator to supply the amp instead of the battery, and since the ground and positive in this car has been described as "weak" and "barely adequate" it should be my starting point.


The problem is that's not how it works. The battery runs your electrical system. The alternator keeps the battery charged.

Look at it this way : the alternator cannot respond well to instantaneous draws - it has a comparatively long ramp up time - and the max current output is capped as a function of engine RPM, anyway. So, the battery adds the capacitance necessary to keep the system voltage (somewhat) constant despite changing loads.

Most car batteries are designed for fast, high draw loads - starting is a great example - and they do fine with it. What they don't do well with is being partially discharged much of the time. 11.7 volts is almost fully discharged. It should be well above 13 at rest.

Obviously, the amp doesn't draw 800 watts all the time, but I would bet it's duty cycle is both higher and faster moving than the alternator. Even if the amp uses half the rated draw on average (400 watts), and the alternator always runs full on, you're spending 50% of your alternator's rated maximum to feed that one device. That's not nearly enough headroom, and that's a best case.

Changing the cables won't do anything but reduce the voltage drop a couple tenths across that run. You'll gain somewhat better performance in reduced resistance (and temperature gain), but it will be small. And of course, cleaning and reseating the connections never hurts. But, you have bigger problems than that will solve.

For the time and money, you're better off upgrading your alternator and/or getting a dual-use battery. Barring that, get a good trickle charger and plug in at night.
posted by Pogo_Fuzzybutt at 1:28 PM on March 6, 2012


Amps are notoriously energy ineffecient. An 800 watt _output_ does not mean it has an 800 watt draw. My guess would be at least 50% effeciency (does the amp have big cooling fins on it? and does it get hot to the touch?) which means it actually has a 1200 watt draw, it may be much, much worse than that. You need a bigger alternator, a smaller amp, or a better muffler. Increasing the wire size is only going to 'clean' the draw and make it less spiky and gain you a margin in the effeciency. I will agree Honda never designed the electrical system (including the grounds) for such a point load but that means you need to upgrade the whole system, not just one segment. Its like any other substantial modification to the car. If you put forced induction on a normal aspirated engine you need to modify the pistons, fuel delivery, camshaft, maybe rods and mains, exhaust to get the full benefit of that change. And now that you have a genuinely more powerful car you need better brakes to slow you down and a suspension to help with higher corner loads and so on.
posted by bartonlong at 1:54 PM on March 6, 2012


Voltage regulator.

I would check this first, replace even if I found nothing wrong. It has to be the VR.

If replacing the VR doesn't do it, replace the alternator.

You need to be seeing around 14v in a 12v system with a good battery and a working alternator and VR.

Also seconding checking the parasitic leakage: with everything 'off', there should be a tiny current draw eg alarm, but not enough to significantly affect the charge state of a sound battery over a week or more.

You might be fighting two (or more) problems here.

And the absolutely last thing I would be doing is replacing wiring. If you do anything with the wiring, make sure the terminals are clean and securely fastened. Mr Honda spent a lot of money on that car, I can't believe he would skimp on the electrical wiring.

On rereading: 'Loud car'? You are not referring to the exhaust? In that case, I am betting that one of your aftermarket stereo bits is unswitched (ie is on all the time). Try this: disconnect ALL of that stuff for a week, and see if the problem goes away. Be sure that you have disconnected ALL of it, and thet the car is running in factory configuration electrically. If that fixes the problem, reconnect each bit, one per week, to identify the component causing the problem (it may not be as simple as this, but it will identify the circuit causing the problem).
posted by GeeEmm at 1:59 PM on March 6, 2012


On reflection, and after reading bartonlong's comments, forget DIY, take it to an auto electrician/sound shop, and be prepared to take the hit on your wallet.

You need (competant) profession help here, and I would rethink my relationship with my mechenic if I was in your shoes.
posted by GeeEmm at 2:06 PM on March 6, 2012


spelling! sigh
posted by GeeEmm at 2:07 PM on March 6, 2012


Apparently lead-acid batteries do _not_ like to have spiky high-amp voltage draws (anywhere from once per second to 200 times per second).

Isn't this what a capacitor is for? Also, if your battery dies after a couple days unattended then I would think you have some kind of parasitic drain on your battery when the car is off (bad car alarm/audio install could be the cause).
posted by knave at 5:10 PM on March 6, 2012


A final thought.

Did this problem start after a particular modification was made? Often that can point at the source of problems - there might be something wrong with the item/its installation, or it was significant enough to overstretch other systems on the car. Think turbo leading to overheating, or big(ger) amp and electrical problems...

Good luck!
posted by GeeEmm at 7:15 PM on March 6, 2012


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