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Old 11-24-2010, 04:32 PM
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Battery and wiring safety

This could have been posted in the electrical forum but this is pretty basic and as such, some of the lesser experienced people might not see it there... so I posted it here.

The recent fire in Neil Young's warehouse which damaged almost a million dollars worth of memorabilia and classic cars reminded me how important wiring safety is for our home built cars. So.... I decided to post the system I'm using on my deuce so others can see a simple way to keep your battery and electrical system safe and isolated when your hot rod is not in use.

First and foremost it is essential to use a safe effective basic wiring system. I'm not going to get into that much as this post is more about battery and electrical safety while the car is NOT running. And it really doesn't have much to do with what aftermarket wiring kit someone might decide to use. Most wiring kits pretty much start at the fuse box but what happens before the juice gets there is what concerns us now. So... I will post for reference a very good example of a primary wiring schematic that works very well for home built cars. I wish I could take credit for this system but credit belongs to Mark at Mad Electrical. Its a simple system that improves on the GM style wiring that most of us (and the aftermarket) use, and it makes the best use of either a three wire or one wire alternator.



All that aside, what this post is concerned about is the safety of the main electrical system and how to keep mistakes, chaffed wires and/or bad connections from causing a fire when the car is parked in your garage, (or while you're working on it for that matter).

Although Mad's method keeps the line from the battery to the starter cold at all times except during cranking, it isn't enough to ensure complete safety as the distribution block for the wiring harness is hot all of the time just as any other system would be.

What is also needed is a battery disconnect to remove any chance of any wire anywhere in the system being "hot" when the car is not in use. Most of the major sanctioning bodies require a disconnect and most people still think the jury is out on which is the best side to disconnect, positive or negative. The truth is that either will work but the best is to disconnect the negative side. Many people don't realize this but contrary to popular belief the electrical load actually travels from negative to positive, not the other way around. So by disconnecting the negative side of the battery this eliminates any flow of electricity. I know the NHRA says to disconnect the positive side but whoever wrote that in their rule book just didn't understand how electricity travels, but like I said disconnecting the positive side will work but its not the best choice. That is why the manufacturers of most "on battery" style disconnects make their unit to fit the negative side. Yes the two posts on your battery are different sizes for a reason. A lot of people don't know that little fact.

So..... to keep my deuce safe, as it will only be driven on weekends, I'm using Mad's schematic with an added negative disconnect switch. Here's a pic of the battery and Ford starter solenoid installation. Keep in mind that the Ford starter solenoid is really nothing more than a heavy duty relay and can be used just like any other relay is used, essentially switching a heavy load on and off by using a light load to flip the switch. In the Mad style schematic this is what keeps the line from the battery to the starter dead except during cranking. Note: When a Ford solenoid is used this way, you do need to add a jumper wire from the bat post to the "S" post on the starter or it won't crank.

What you see in this pic is the hot lead from the battery goes to the left lug on the solenoid and the lead that goes to the starter attaches to the right lug on the solenoid. There will be a wire from the ignition switch that will attach to the "S" small lug that will actuate the solenoid which has not been added yet. You can also see the inexpensive negative terminal disconnect. For this installation I had to extend the handle in order to clear the top of the box but other than that its right off the shelf.



That's pretty much all you need to do to keep your battery isolated and eliminate the chance of an electrical fire when your car is unattended. Disconnecting the battery is simple and only takes about 30 seconds but it is the best way to keep from frying your ride.

Here's the finished battery box. Just a twist of the knob is all it takes to "turn it off".



Hope this helps some of the newbies.


Centerline
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Last edited by Centerline; 11-24-2010 at 04:51 PM.
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Old 11-24-2010, 04:42 PM
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Iīve had this setup in my car for quite some years now and itīs very good.
The idea of the solenoid at the rear with the battery is very important and not debateable.
Not long ago ChevyHiPerformance did an article on trunk mounting the battery but completely failed to set the solenoid in the rear as well to avoid the live starter cable though the car.
I did e mail them to point it out but got no responce.

I also use several of those distribution blocks as well, brilliant idea.

If you buy any of MADīs stuff follow the instructions to the letter especially the terminal soldering.
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Old 11-24-2010, 08:48 PM
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I will not build a car if I can't put a ''battery disconnect'' in it... They are always in ''EVERY'' car I do..
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Old 11-24-2010, 09:30 PM
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I use a Moroso disconnect ...



Started using them years ago on my race cars ( NHRA requirement ) and had great service from them so I now use them on all my Hot Rods also.

.
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Old 11-25-2010, 07:36 AM
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All good in theory . However if any modern electronics with memory is in use the memory will flush; anything like radio stations and the likes will need to be reprogrammed ....... every time you turn the power back on.

Wire the car using the right gage of wire for the loads and the car will be fine.. Chaffing can be eliminated by using these things called clamps and good old fashion good common sense when routing.

That fire in the rockers house was the electric car, could have been a major battery failure cause it was an all electric car, multi batteries way more then your basic 100 amp. Yes 100 amp will cause a fire let me make sure all understand that right off.. But there are other reason that car caught fire, not the same situation mentioned.

Power wires coming out from under a battery box and crossing under the mounting bracket looks a tad problematic, out the side and through a grommet would have been better . That battery box loosens up and starts bouncing on the insulation might cause some smoke there .

Last edited by pepi; 11-25-2010 at 07:42 AM.
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Old 11-25-2010, 07:50 AM
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The electronics memory dilemma with a battery disconnect switch can be solved by just providing a #16 wire fused with a 2 amp fuse off the battery positive. It will be enough to keep electronics from loosing memory but will blow if anyone tries to start your car.

Vince
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Old 11-25-2010, 09:33 PM
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Quote:
Originally Posted by pepi
.....Wire the car using the right gage of wire for the loads and the car will be fine.. Chaffing can be eliminated by using these things called clamps and good old fashion good common sense when routing....
..... and how many novices do you know that do a perfect job of routing wires, and use clamps and grommets everywhere they should? Not many. That's why this thread is in the hotrodding basics forum instead of the electrical forum.

Also, it doesn't matter that Neil Young's fire was caused by his electric Lincoln. Bad wiring in any form can cause a fire under the right conditions. We just lost a major custom shop down in Phoenix due to a fire that is believed to have been started by an electrical problem in one of the cars over night. The whole place was a total loss, not to mention about a half dozen cars.

Sorry you don't care for my battery box. I know the photos don't show it well but it was designed to run the positive line out the side of the box and through a purpose built space under the box to the solenoid. It is mounted in for locations with reinforcing straps and nylocks. The only way it will come loose is if someone cuts the floor out. However, if you have a better idea for mounting a battery in the trunk of a glass car with a convex curved floor....now would be a good time to let us all in on it.
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Old 11-25-2010, 10:54 PM
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A lot of good stuff here, but I feel the need to set the record straight about why you disconnect the negative terminal first.

There is only one valid reason: the chassis is (or should be) connected to the negative terminal. If your wrench, ratchet, whatever, should touch your vehicle chassis while in contact with your positive terminal, you will have just shorted your battery through a very good conductor...your wrench. You may experience several hundred amps, and a possible exploding battery, not to mention a lovely spray of sparks.

It is for this same reason that when reconnecting, you always connect your positive terminal first.

True, electrons do flow from the negative terminal to the positive, depsite current being defined as the flow of positive charge (hey...scientists defined current before they knew what an electron was.....they had a 50/50 chance....and got it wrong ). Disconnect either, and current can not flow in or out of the battery...it is simply the chassis ground that does you in, mentioned as before.
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Old 11-26-2010, 06:51 AM
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While I don't disagree with using the master cut off switch on the negative side (it's also kinda emotional for some), I wired mine to the positive side based on NHRA rules (Para8.4)

"8.4 MASTER CUTOFF
Mandatory when battery is relocated, or as outlined in Class Requirements. An electrical power cutoff switch (one only) must be installed on the rearmost part of each vehicle and be easily accessible from outside the car body. This cutoff switch must be connected to the positive side of the electrical system and must stop all electrical functions including magneto ignition. The external control switch for this cutoff switch will be clearly indicated by a red flash inside a white-edged blue triangle with a base of at least 12 cm (see drawing 25). The positions must be clearly indicated with the word "OFF". If switch is "push/pull" type, push must be the action for shutting off the electrical system, pull to turn it on. Any rods or cables used to activate the switch must be minimum 1/8-inch (3.2 mm) diameter. Plastic or keyed switches prohibited. Switches and/or controls must be located behind rear wheels on rear engine dragsters." (bolding is mine)

With this said and if you want to do some weekend racing, this is the way you have to wire the car.

To maintain any memory functions, you do need a separate wire function that is fused and live at all times.

This is mine - the small fuse block in front of the module. The switch box with the rocker is for the trunk lift. The battery is just behind the reinforcing tubing as well as the Ford style solenoid, which works as a distribution switch as my Ford new style starter has a separate solenoid.

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Old 11-26-2010, 08:12 AM
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You're quite correct. The NHRA wants it done their way and if you're going to race you need to have a positive side disconnect. Many won't agree that is the best way, but the NHRA sets their rules and its their ball game.

Very nice wiring job. A great example of how it should be done.
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Old 11-26-2010, 08:30 AM
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Quote:
Originally Posted by Centerline
You're quite correct. The NHRA wants it done their way and if you're going to race you need to have a positive side disconnect. Many won't agree that is the best way, but the NHRA sets their rules and its their ball game.

Very nice wiring job. A great example of how it should be done.
Regardless of the Laws of Physics, it is always the AHJ (Authority Having Jurisdiction) that has the final say. I'm sure the NHRA has the reasons.

I wonder if they would let you use a DPST switch? That would disconnect both sides of the battery and keep pedantic guys like me happy too.
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Old 11-26-2010, 08:45 AM
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Quote:
Originally Posted by nofearengineer

I wonder if they would let you use a DPST switch? That would disconnect both sides of the battery and keep pedantic guys like me happy too.
Probably not. What they want to see is a standard switch like Deuce pictured above.

If you do find one that will handle 180 amps continuous or 1000 instantaneous, post it here. I use a Longacre race switch which like the one above is made by Pollak (http://www.pollakaftermarket.com/)
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Old 11-26-2010, 09:17 AM
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The reason behind this NHRA rules (Para8.4)

Was the switch had to kill the whole system, ''EVEN'' THE MOTOR... They had some guys that would wire the car with a alternator.. And just added the switch into the system.. Tech man would turn it off.. And the motor would still run.. It had to be wire to ''KILL'' the motor..

I saw a picture of a fiberglass street rod sitting on side the road burnt to the ground.. Ever since then.. I put a kill switch to kill the system.. That way if something would short out in start a fire.. You can kill the system,, Then try to stop the fire... It is hard to stop the fire if you still have a HOT system..
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Old 11-26-2010, 10:12 AM
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Quote:
Originally Posted by NEW INTERIORS
The reason behind this NHRA rules (Para8.4)

Was the switch had to kill the whole system, ''EVEN'' THE MOTOR... They had some guys that would wire the car with a alternator.. And just added the switch into the system.. Tech man would turn it off.. And the motor would still run.. It had to be wire to ''KILL'' the motor..

I saw a picture of a fiberglass street rod sitting on side the road burnt to the ground.. Ever since then.. I put a kill switch to kill the system.. That way if something would short out in start a fire.. You can kill the system,, Then try to stop the fire... It is hard to stop the fire if you still have a HOT system..
That would be back feed from the alternator through the ignition switch which will in turn try to "motor" the engine. You can "fix" that with a diode in the sensing line or a 4 post master shut off switch. I have the diode. The two circuits I have that are never dead are the radio memory - and that is protected by 3 fuses and the trunk lift, and that's by two.

There is a Maxi fuse in the #10 wire to my sub panel which is the #1 fuse for both components, a fuse to the actual circuit in the sub panel then one at the stereo itself - and are in declining rated amp value. The trunk lift has a separate fuse along with the Maxi. This is better protection then any new car
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Old 11-26-2010, 10:20 AM
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Quote:
Originally Posted by Irelands child
That would be back feed from the alternator through the ignition switch which will in turn try to "motor" the engine. You can "fix" that with a diode in the sensing line or a 4 post master shut off switch.

I know how to fix it.. I was ''just'' Explaining why it's good to have the kill switch... I know all about how diode's work.. Thanks.. but I was just adding this so the next man would know..
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