Batt Relocation Lessons?

[RemCharger]

Either run the alt power wire to the battery or relay to cut the regulator

 

[dvw]

Here’s my thinking on negative disconnect …

All vehicles run off the alternator - battery is only used for starting. Alternator is grounded through the body.

Our stock wiring runs direct from the battery to starter and from the alternator to the starter relay where it branches to the fuse box and to the battery.

Assuming you relocate the battery to the trunk but maintain the same wiring configuration, a disconnect on the positive battery cable will NOT shut a car off, it will only prevent it from starting. However, in that same configuration it will prevent the battery from receiving any charge current from the alternator.

By the same token, because the alternator is grounded to the engine and subsequently the body, a disconnect on the ground battery cable also will not shut the car off - since the positive current from the alternator is still running through the starter relay.

So in all cases, the "shut off" in either positive of negative battery cable alone will not shut a car off.

So as far as NHRA rules go, there has to be some other component not mentioned that will shut down a running engine and the rest of the electrical system. What is it ???

Read post 17
Doug

 

[65CopCar]

Many new cars have the battery located outside of the engine compartment. NONE have solenoids or fuses in line with the main positive cable.

I helped my cousin remotely today on a 2005 Mazda. It has a 200 amp main fuse. I was surprised.

 

[padam]

Here’s my thinking on negative disconnect …

All vehicles run off the alternator - battery is only used for starting. Alternator is grounded through the body.

Our stock wiring runs direct from the battery to starter and from the alternator to the starter relay where it branches to the fuse box and to the battery.

Assuming you relocate the battery to the trunk but maintain the same wiring configuration, a disconnect on the positive battery cable will NOT shut a car off, it will only prevent it from starting. However, in that same configuration it will prevent the battery from receiving any charge current from the alternator.

By the same token, because the alternator is grounded to the engine and subsequently the body, a disconnect on the ground battery cable also will not shut the car off - since the positive current from the alternator is still running through the starter relay.

So in all cases, the "shut off" in either positive of negative battery cable alone will not shut a car off.

So as far as NHRA rules go, there has to be some other component not mentioned that will shut down a running engine and the rest of the electrical system. What is it ???

I put a relay on my ignition box (msd) feed. Per dvw’s advice. It works to kill the engine via the cutoff switch.

You have to be careful if using a Denso alternator because if you just cutoff the battery it will kill the alternator.

 

[gkent]

There are only two ways to blow that fuse. 1) a short to ground or 2) trying to crank over a siezed engine. Frankly, I think its a good idea but I can tell you from experience that there are likely weaker links in the circuit that would blow first. Once I dropped a spark plug and it shorted across the starter terminals and I heard what many people around thought was a gunshot. The battery was in the trunk and grounded to the wheelhouse. It blew the end of the ground cable off. The weakest link !!

 

[dvw]

I put a relay on my ignition box (msd) feed. Per dvw’s advice. It works to kill the engine via the cutoff switch.

You have to be careful if using a Denso alternator because if you just cutoff the battery it will kill the alternator.

Padam is on point here. You don't want to have the alternator output go to an open circuit. If you open the alternator output to the battery. Make sure it still feeds the water pump, fuel , pump, fan etc. Otherwise the output will try to go to the moon. It doesn't take long to melt it.
Doug

 

[65CopCar]

You don't want to have the alternator output go to an open circuit. If you open the alternator output to the battery. Make sure it still feeds the water pump, fuel , pump, fan etc. Otherwise the output will try to go to the moon. It doesn't take long to melt it.

I would need help understanding that issue. An alternator is a 3 phase synchronous generator. You vary the field current (magnetic strength) with the voltage regulator to vary the output voltage which then varies output current based on output load (resistance/impedance). Synchronous generator output voltage is affected by field strength and rpm. The higher the rpm the more voltage it will put out for a set field current. The effect of rpm and field strength is non-linear.

With that said, the output voltage of the alternator is controlled by the voltage regulator. The voltage regulator varies the field current so that the alternator voltage does not exceed what you want. If you lose feedback to the voltage regulator then the alternator output voltage would go through the roof (I have personally measured over 120 volts at the alternator when the fusible link opened up in my 85 Charger) and then you can hurt the alternator. But just not having a load will not hurt an alternator. Losing voltage feedback to the regulator would.

But perhaps I am missing something.........

 

[padam]

I would need help understanding that issue. An alternator is a 3 phase synchronous generator. You vary the field current (magnetic strength) with the voltage regulator to vary the output voltage which then varies output current based on output load (resistance/impedance). Synchronous generator output voltage is affected by field strength and rpm. The higher the rpm the more voltage it will put out for a set field current. The effect of rpm and field strength is non-linear.

With that said, the output voltage of the alternator is controlled by the voltage regulator. The voltage regulator varies the field current so that the alternator voltage does not exceed what you want. If you lose feedback to the voltage regulator then the alternator output voltage would go through the roof (I have personally measured over 120 volts at the alternator when the fusible link opened up in my 85 Charger) and then you can hurt the alternator. But just not having a load will not hurt an alternator. Losing voltage feedback to the regulator would.

But perhaps I am missing something.........

I don’t know about the magic involved.

I just know that I tested the switch, motor kept running, but after that the alternator would not charge. It was a brand new denso alternator that is internally regulated.

I also found in some Toyota literature (alt is from a 80s 4 runner IIRC) that you should not run the car without a battery.

 

[pedal2themetal]

HI,
What about capacitors instead of a Battery??
I saw a few video's on it .. I forget what size they were , but they looked like about 6" tall and 2 1/2"4 about around and they used like 6 of them..
All a battery does is store energy to start the motor the rig's runs off the alternator.. right? .. they got to be lighter than a battery...

good luck take care be safe
tim

 

[451Mopar]

HI,
What about capacitors instead of a Battery??
I saw a few video's on it .. I forget what size they were , but they looked like about 6" tall and 2 1/2"4 about around and they used like 6 of them..
All a battery does is store energy to start the motor the rig's runs off the alternator.. right? .. they got to be lighter than a battery...

good luck take care be safe
tim

I have seen super capacitors used for a battery, but capacitors have a fairly large leakage current, so they self discharge. On the few setups I seen, the vehicle would need to be started every few days to re charge the capacitors. I recall Tesla bought into Maxwell (Super capacitor manufacturer), and I was thinking they might develop a hybred battery/capacitor setup to reduce charging times?

Anyway, on the Battery relocation. If it does not need to be NHRA with cutoff switch all you really need to do is run a 1/0 welding cable from the battery positive back to the engine compartment. If car is an automatic, the clutch linkage hole is the correct width for a battery bulkhead connector like this:
Summit Racing SUM-G1431-RED Summit Racing™ Bulkhead Cable Connectors | Summit Racing

The 200 Amp MaxiFuse at the battery can be used.

On the ground side, I connect body ground to the wheel well as shown on the white car, but also run a 4 AWG wire from there up to the passenger side kick pannel to have a good ground bus connection for the dash and electronics. Under the car I have ground cables that run from the unibody to the back of the cylinder heads.

I haven't done this next part yet, but it might be a good idea if using a kill switch, or also just to get better voltage regulator function, and that is to mount the voltage regulator in the trunk also. It would need a mounting plate that is grounded and can also be used as a heat sink for the regulator. This would give the best temperature compensation inside the regulator to match the battery temperature in the trunk. It would have to be activated through a relay triggered by ignition power.

 

[65CopCar]

Anyway, on the Battery relocation. If it does not need to be NHRA with cutoff switch all you really need to do is run a 1/0 welding cable from the battery positive back to the engine compartment. If car is an automatic, the clutch linkage hole is the correct width for a battery bulkhead connector like this:
Summit Racing SUM-G1431-RED Summit Racing™ Bulkhead Cable Connectors | Summit Racing

The 1/0 in my professional opinion is WAY overkill. I am doing some cleanup on my race car now and it has #2 from the battery. It is welding cable so very fine stranded. Been there probably close to 40 years. It has no problems cranking my 15:1 engine. If you want to be conservative go with #1 AWG. I did in my GTX street/strip build I am doing.

I was looking at some of the voltage drop calculators online and most are wrong for DC applications. They are using inductive reactance in the formula but that is zero at DC. I don't believe there is enough ripple in the current to worry about for the voltage drop calculation in our cars.

 

[6PKRTSE]

I have the battery mounted in the trunk in one of my cars with an external Flamming River on/off switch with a custom mount i made and a customextensionrod I made to bring it out between my bumper and rear valance. Routed and wired up like several have mentioned already.

 

[malex]

How about this.
1 G red leads to trunk batteries
1 G black leads to starter
10 G red leads to starter sol.post
12 G blue leads to Bosch relay

Most solenoids are rated at 80 amps. This reduces the cranking amps through the solenoid.