Battery Cut-Off Wiring?

Any preference on wiring one up (positive vs. negative). NHRA requires the positive be switched but I can't find anything in either rules that speaks to how it's wired.

I see 2 ways. To switch positive: battery > switch > starter/accessories. With the alternator charge cable run to the battery side of the switch to kill all power to ecu/fuel pump.

Or just simply switch the negative to cut power.

Anything I'm missing????

---

-Jason

Jason,

Most sanctioning bodies say to switch the positive.

I prefer to switch the negative.

You may want to consider using a relay to ground the field on the alternator. This would prevent the alternator from continuing to power the ignition in some systems.

I don't know or care if it's legal, but I am running a Painless Wiring remote battery cut off relay on my 91 Golf.

Robert.

---

Robert.

"You are way too normal to be on Rally Anarchy." Eddie Fiorelli.

Rallymech Wrote:
-------------------------------------------------------
> Jason,
>
> Most sanctioning bodies say to switch the
> positive.
>
> I prefer to switch the negative.
>
> You may want to consider using a relay to ground
> the field on the alternator. This would prevent
> the alternator from continuing to power the
> ignition in some systems.
>
> I don't know or care if it's legal, but I am
> running a Painless Wiring remote battery cut off
> relay on my 91 Golf.
>
> Robert.

are you talking about this?
http://www.vichubbard.com/auto-part-detail/painless-remote-master-disconnect-kit-ppp-30204.html?dpi=527119

I follow you on the relay part...but you lost me on 'continuing to power ignition in some systems'? can you elaborate?

I need to relocate my battery, thx.

---

Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

Jon Burke Wrote:

> I follow you on the relay part...but you lost me
> on 'continuing to power ignition in some systems'?
> can you elaborate?
>
> I need to relocate my battery, thx.
>
>
>
>
> Jon Burke - KI6LSW
> Blog:
> 'Holy Shit!' @ 4:10

If you disconnect the battery while the engine is running, the alternator can continue to supply power to the engine/ecu to allow it to continue running.

So you either neet to wire the alternator's output to the battery side of the switch (so alternator power is going only to the battery and is isolated from the ecu by the switch) or using a switch that can also turn off the ecu/fuel pump thereby causing the engine to stop running so the alternator stops providing power.

---

-Jason

ok,I get it...makes perfect sense. Thanks.




Last question (for now), I've seen batt relocation kits that have a 15ft positive wire, but only a 3 foot ground...so is it acceptable to just put a ground post next to the battery and run ground through the chassis from there?

I realize you'd also have to make sure the alternator is grounded properly in the engine bay as well.

i'm trying to minimize voltage drop...I have a LinkG3 ECU and its pretty sensitive electrically. My tuner basically said to NOT relocate the battery, but for space and a few other things, I need to move it.

Thanks in advance.

---

Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

Jon Burke Wrote:
-------------------------------------------------------
> ok,I get it...makes perfect sense. Thanks.
>
>
>
>
> Last question (for now), I've seen batt relocation
> kits that have a 15ft positive wire, but only a 3
> foot ground...so is it acceptable to just put a
> ground post next to the battery and run ground
> through the chassis from there?

Jon, think about this yourself--follow along.
What does the battery ground to in the original location?
Right the body shell.

Next, is the bodyshell in the front of the car connected to the bodyshell in the back?

Right its all the same steel.

In fact all the circuits use the bodyshell as the ground.
Ground the battery to a good clean spot and all is well.


>
> I realize you'd also have to make sure the
> alternator is grounded properly in the engine bay
> as well.

Think now: whats the biggest load?
Right, the starter.

Now if we feed it with a big fuckin fat cable, you do know that you have to have an equally large ground dontcha?
Soooooooooooooooo, just run a ground, like as fat a cable as the fat + cable to the starter, from block to say the old original ground.

>
> i'm trying to minimize voltage drop...I have a
> LinkG3 ECU and its pretty sensitive electrically.
> My tuner basically said to NOT relocate the
> battery, but for space and a few other things, I
> need to move it.

Why?
Isn't VREF like 5V?
>
> Thanks in advance.
>
> Jon Burke - KI6LSW
> Blog:
> 'Holy Shit!' @ 4:10

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Most of the rally cars in Colorado don't run master power switches anymore. Most of us use a breaker on the ground if we need to kill power and it'll pop if something shorts out.

---

Grant Hughes

john vanlandingham Wrote:
-------------------------------------------------------
> Jon Burke Wrote:
> --------------------------------------------------
> -----
> > ok,I get it...makes perfect sense. Thanks.
> >
> >
> >
> >
> > Last question (for now), I've seen batt
> relocation
> > kits that have a 15ft positive wire, but only
> a 3
> > foot ground...so is it acceptable to just put
> a
> > ground post next to the battery and run
> ground
> > through the chassis from there?
>
> Jon, think about this yourself--follow along.
> What does the battery ground to in the original
> location?
> Right the body shell.
>
> Next, is the bodyshell in the front of the car
> connected to the bodyshell in the back?
>
> Right its all the same steel.
>
> In fact all the circuits use the bodyshell as the
> ground.
> Ground the battery to a good clean spot and all is
> well.
>
>
> >
> > I realize you'd also have to make sure the
> > alternator is grounded properly in the engine
> bay
> > as well.
>
> Think now: whats the biggest load?
> Right, the starter.
>
> Now if we feed it with a big fuckin fat cable, you
> do know that you have to have an equally large
> ground dontcha?
> Soooooooooooooooo, just run a ground, like as fat
> a cable as the fat + cable to the starter, from
> block to say the old original ground.
>
> >
> > i'm trying to minimize voltage drop...I have
> a
> > LinkG3 ECU and its pretty sensitive
> electrically.
> > My tuner basically said to NOT relocate the
> > battery, but for space and a few other
> things, I
> > need to move it.
>
> Why?
> Isn't VREF like 5V?
> >
> > Thanks in advance.
> >
> > Jon Burke - KI6LSW
> > Blog:
> > 'Holy Shit!' @ 4:10
>
>
>
>
> John Vanlandingham
> Sleezattle, WA, USA
>
> Vive le Prole-le-ralliat
>
> www.jvab.f4.ca


Thanks John, I forget how scary simple electricity is sometimes.

and I'm not sure on the vref for this ecu...all I know is I was having a 'hesitation' issue between certain RPMS for a while....we pulled plugs, coils, etc...everything was fine, but the ecu was pulling timing for some reason. (like 17 degrees of timing)

Battery was +3yrs old, but car started fine, no issues. But sure enough, put a new battery in there an everything was fine. What I don't get is, nothing is supposed to run off the battery when the car is running and the alt is fine, so its annoying for sure.

I emailed the mfg about it, we'll see what they say...but I would think a 1ga wire from the back of the drivers seat should be fine.

---

Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

Jon,

The battery is an important part of the electrical system when the car and alternator are running. The battery acts as an electrical ballast to keep any spikes in voltage out of the system. One should never purposely switch off the battery when the car is running or the resulting spike as the battery 'load' on the system is removed can damage a lot of electrical stuff. It's not guaranteed to happen but it sure can. (For example, older Ford electromechanical regulators were guranteed dead the instant the battery was disconneted; ask me how I learned that one!) With ECU's and such I would never disconnect a battery on a running car. I have to wonder if your 3+ year battery had an intermittent cell short or open that was causing this.

Regards,
Mark B.

So bad idea for a "master" battery off switch?

What about just running all of my accessories through one of these switches then to a normal on/off switch.

That way in an emergency the master off can kill everything (ecu, fans, lights, fuel pump, etc) without actually removing the battery entirely.

Or is this overkill, just put them on normal switches that are easy enough to flick off in one swoop of the hand rather than fiddling with a twisting knob thing

---

-Jason

starion887 Wrote:
-------------------------------------------------------
> Jon,
>
> The battery is an important part of the electrical
> system when the car and alternator are running.
> The battery acts as an electrical ballast to keep
> any spikes in voltage out of the system. One
> should never purposely switch off the battery when
> the car is running or the resulting spike as the
> battery 'load' on the system is removed can damage
> a lot of electrical stuff. It's not guaranteed to
> happen but it sure can. (For example, older Ford
> electromechanical regulators were guranteed dead
> the instant the battery was disconneted; ask me
> how I learned that one!) With ECU's and such I
> would never disconnect a battery on a running car.
> I have to wonder if your 3+ year battery had an
> intermittent cell short or open that was causing
> this.
>
> Regards,
> Mark B.


learn something new every day! That makes sense. Well, makes a LOT of sense since the new battery fixed the issue.



I'm thinking two master switches is a good idea....a master switch on the battery (pos) and then the above master w/relay for the starter/ (with the relay switch somewhere in the interior).

---

Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

Jon, on my car the kill switch is on the positive running from the engine bay to centre console to battery in back seat.

The ignition switch, start button and kill switch are all beside each other where the radio/HVAC used to be.

Theres a ground from the battery to chassis and extra grounds from alt/starter to chassis.

To shut the car down I can kill the ignition and THEN the battery.

---

Gone fishing

No, it's 100% the right idea to have a master cutoff to the battery. Just don't turn the switch off while running normally. The reason you DO want to cut of the battery entirely in an emergency/wreck is the you could have a major short in the car due to the damage, and the amount of energy that a battery can put into a hard short will start fires in very short order. Also, a rapid discharge of a battery through a hard short can cause so much heat in a bettery that it can explode or melt the top off and catch on fire. FOR REAL! You do not want a shorted battery discharging anywhere close to anyone or anything.

The separate fuel cutoff switch is an excellent idea too. Cut that off and the engine will stop running very quickly, 'specially on a high pressure pump of an FI car. Putting it in line with the coil to the fuel pump relay or it's control line form the ECU is a good place. For carburated cars, just use it to control the fuel pump power directly, or through a relay.

Place both switches where either driver or navvie can reach them but not where they can be easily bumped by accident. And kick yourself in the a** the first time you forget to re-enable the fuel pump switch after you cut it off for some work, and then panicked 'cuz you thought something had died!!

Regards,
Mark B.


mack73 Wrote:
-------------------------------------------------------
> So bad idea for a "master" battery off switch?
>
> What about just running all of my accessories
> through one of these switches then to a normal
> on/off switch.
>
> That way in an emergency the master off can kill
> everything (ecu, fans, lights, fuel pump, etc)
> without actually removing the battery entirely.
>
> Or is this overkill, just put them on normal
> switches that are easy enough to flick off in one
> swoop of the hand rather than fiddling with a
> twisting knob thing
>
> 94 Golf
> www.Mack73.com

In 2004 I went off thanks to a patch of glare ice and gravel tires in my rally car while driving through the mountains to a rally cross. A pole came under the bumper and took out a few components and shorted some wires to the ground. I was almost instantly on the master battery kill switch after the wreck, but still ended up having to replace a large amount of the wiring harness that had burnt.

With my current setup, the short would have tripped the breaker on the battery ground and the harness would have probably survived.

---

Grant Hughes

Ok so I guess I'm back to my origional question: Switch the positive or negative?

I would rather switch the negative for easy of wiring. Good, bad, indiferent?

Grant: what size breaker do you have on the ground? 100? 150? 175? amps

---

-Jason



Edited 1 time(s). Last edit at 02/28/2009 12:02AM by mack73.