Battery Cable Size

[Jerry O]

I'm finishing all the wiring on my streamliner and only have the battery cables left to make. I know on the high compresion V-8 engine most guys go for large cables, but since my engine is a four cylinder motorcycle engine, do I need to use the same size cables.  What are you motorcycle powered lakesters and streamliner guys using. My cables will need to be 6 foot long. Don't want to go too small but also don't want to carry more weight than I need. Any advice would be a great help. Electrical not one of my strong points.  Thanks.........JerryO

[donpearsall]

I think 6 gauge would be fine. I have about 5 feet of 6 gauge cables on my bike. Good for about 150 amps I think.
Don

[Stainless1]

are you running the cable from the battery, to the shutoff at the back and then back to the motor?  What will be battery powered? fans, pumps, computer... The 10 oz that you save will probably bite you later. 
We run heavy gauge for battery electricity.... O or OO, if you use a wire too small for the  draw the little electrons will be waiting at the gate to get through to go to work...

[Milwaukee Midget]

Bigger is better, especially on longer runs, and especially with direct current.  Less resistance to current flow. 

Cylinder count has less to do with it than the accessories - an ignition system, despite being able to produce 40,000 - 80,000 volt sparks, actually draws very little amperage.  The high compression V-8's need the bigger cable to power the starter without smoking the cables.

An electric fan or pump requires a lot of juice.  Making you connections of smaller gauge wires to the terminal black as short as possible is also helpful, as is the use of relays.

Stainless1 has the right idea.

No news there.

[manta22]

"...especially with direct current."

It doesn't matter whether it is AC or DC.

Regards, Neil

[Milwaukee Midget]

"...especially with direct current."

It doesn't matter whether it is AC or DC.

Regards, Neil

Neil,

Sorry to commandeer this post, and I know there are electricians and electrical engineers out there, but am I missing something here?  Neil, I'm questioning it because you are, and having read your posts in the past, I'll reconsider my "facts" if they aren't what I thought they were.

On top of that, how many posts have we read that say, "I'm not good with electricals?"  Might be a good way for all of us to teach each other.

Here's how I was lead to understand it.  Resistance (R) increases by the square of increased current (amperage) regardless of AC or DC.  AC transmission lets you up the voltage and decrease the amperage, giving you a smaller current proportionally to the voltage, which gives you less resistance, but retains essentially the same wattage. 

Applying that, by quadrupling the capacity of the conductor (wire size), you can only double the current capacity at the same voltage.  There's a proportional relationship between current and voltage, and therefore resistance in AC.  The relationship between resistance and current in DC linear.

So that's my understanding, as best as I can spell it out. 

Help

Chris "when in doubt, put a relay in the circuit" Conrad

[manta22]

Chris;
The voltage drop in Volts across a resistor is equal to the current in Amps times its resistance in Ohms.
E=IR (Ohm's Law) where E= voltage, I= current, & R= resistance.
It is the same for AC or DC but as you go up in frequency and if there is a reactive component (inductance or capacitance) then you have to use "impedance" for the AC calculation instead of "resistance". Don't worry about this-- for the stuff we do it doesn't matter if its AC or DC.
Where you are getting confused is you are thinking about power transmission. There the use of AC allows the voltage to be stepped up by a transformer; the power into and out of the transformer is (ideally) the same but the current required for a given amount of power goes down.
P=EI where P= power (in Watts), E= voltage (in Volts), & I= current (in Amps)
So if you step the voltage up by 10 times with a transformer, the current required to generate the power goes down by 10 times.
Example:  we have a voltage of 220V AC and need to transmit it over a 10 mile power line. If we simply put 220V into the line at one end and have a load at the other end that draws 100 Amps, there will be a drop in voltage that is proportional to the resistance of the power line. Let's say the line resistance is 1 ohm-- the voltage drop will be 100A times 1 Ohm, or 100V. The voltage at the load will be 220V-100V or 120V. You could make the wire larger to cut down on this loss but that requires lots of copper. If we step the 220V up to 22,000V the current will go down by a corresponding ratio-- only 1A.  The drop is then only 1V less than the 22,000V-- We then put that high voltage into a step- down transformer and deliver the 219.99 V into the load, trading voltage for current at this end.
With DC you can't use a transformer so it is only suitable for short distance power transmission. That is where Edison screwed up and Westinghouse got it right.
Regards, Neil  Tucson, AZ

[Cajun Kid]

Jerry, I would not use anything smaller than 1 ga. prefer 0/00

Roulette  0 and 00  are green... Green = GO  !!!!!

So go for 0 or 00 cable size.. Some use welding cable,,, I prefer  American Auto Wire cable and end kits.

Charles

[jl222]

Chris;
The voltage drop in Volts across a resistor is equal to the current in Amps times its resistance in Ohms.
E=IR (Ohm's Law) where E= voltage, I= current, & R= resistance.
It is the same for AC or DC but as you go up in frequency and if there is a reactive component (inductance or capacitance) then you have to use "impedance" for the AC calculation instead of "resistance". Don't worry about this-- for the stuff we do it doesn't matter if its AC or DC.
Where you are getting confused is you are thinking about power transmission. There the use of AC allows the voltage to be stepped up by a transformer; the power into and out of the transformer is (ideally) the same but the current required for a given amount of power goes down.
P=EI where P= power (in Watts), E= voltage (in Volts), & I= current (in Amps)
So if you step the voltage up by 10 times with a transformer, the current required to generate the power goes down by 10 times.
Example:  we have a voltage of 220V AC and need to transmit it over a 10 mile power line. If we simply put 220V into the line at one end and have a load at the other end that draws 100 Amps, there will be a drop in voltage that is proportional to the resistance of the power line. Let's say the line resistance is 1 ohm-- the voltage drop will be 100A times 1 Ohm, or 100V. The voltage at the load will be 220V-100V or 120V. You could make the wire larger to cut down on this loss but that requires lots of copper. If we step the 220V up to 22,000V the current will go down by a corresponding ratio-- only 1A.  The drop is then only 1V less than the 22,000V-- We then put that high voltage into a step- down transformer and deliver the 219.99 V into the load, trading voltage for current at this end.
With DC you can't use a transformer so it is only suitable for short distance power transmission. That is where Edison screwed up and Westinghouse got it right.
Regards, Neil  Tucson, AZ

   I thought the cross country high voltage transmission lines were DC?

                JL222

[interested bystander]

Read up on Steinmetz ans Tesla!

And don't forget the right hand rule.

[krusty]

Jerry, you know that the cars you built @ Yates never had a primary cable larger than 2 ga between the battery and the master switch, and that length usually was about 100". Most of the Cup cars I wired never used anything larger than 4 ga. until we arrived at the multiple front brake/bead blower era combined with the high end driver coolbox; then the advent of the 150 amp alternator, etc. Just figure out your total amp load with all loads (blowers, fans, ignition) that are needed during a run. I'm guessing that you'll be safely oversized at 8 ga., but I'd use 6 ga. to be super-safe. If you want the best cable it's at Brown & Miller in Concord but it costs about $4/foot. (Make sure you tell them Vic sent you). If I wasn't still finishing the new Bonneville car I'd come over and "consult". Sorry I missed seeing you and your car @ Maxton;I had ours there, too, for a "pre-tech".    Remember, good grounds are the real key to success in 12 volt  electrics.     vic

[Seldom Seen Slim]

There are mostly AC high-voltage cross country electrical transmission lines, but more than just a few DC high voltage lines.

DC is more efficient to transmit long distances because of the high average current (continuous amps, vs. the sine wave variations in the AC current), and also because of the reactance and impedance.  That's that.

High voltage lines have been all AC for most of the history of long-distance transmission because a transformer is a reliable and relatively easy-to-build method of stepping up the voltage to needed levels.  Transformers have losses that can be minimized -- but they're still there.  Notice large transformers, such as at big substations, and you'll notice they've got cooling fins with large fans to move air across them.  Transformers are often filled with a liquid to aid in transferring heat from the coils of the inside to the cooling system, but the liquid (until recently) was a PCB-based chemical that's nasty towards living things.  That's why so many hazardous workers have to show up for the cleanup when a transformer blows up or burns.  New methods of cooling are being introduced and have been coming along for at least a decade.

DC is relatively MORE efficient to transmit over long distances, partly because of the various factors I've already mentioned, and also because only two wires are required per circuit -- vs. three for regular three-phase power.  Even with the addition of a static (ground) line -- two wires weigh less than three, so all of those big towers can be somewhat smaller and also need to be less sturdy because there's somewhat less wind load on the (reduced) number of conductors.

But as noted elsewhere, DC doesn't work in a transformer -- there's no easy way to change the voltage without throwing away energy in a resistance pack.  With the ever-growing sophistication of solid state devices, however, the DC can be (and is) used to power a large inverter that turns it into AC, which can then be "transformed" to the desired voltage, then rectified back into DC or used as AC.  There are losses in the transfer of DC to AC -- and they're on a similar order of the losses in transformers.  The big drawback to DC high voltage transmission was that inverters couldn't work at the required voltages and currents -- today's stuff is able to do so, and getting more capable/efficient all the time.

There's an HV DC circuit going from the Minneapolis-Minnesota iron range, for instance.  It's been running for a decade or more.  There are other HV DC lines that we see as we drive from home to the Salt. 

It's therefore a coming thing, especially with the NIMBY folks resisting having HV line towers installed in their neighborhoods.

Q.E.D.

[manta22]

So people in Minnesota are AD-DC?   

Regards, Neil  Tucson, AZ

[Jerry O]

Thanks all for your help!!              JerryO

[Jonny Hotnuts]

A cable like Monster 300 series 4 gauge can transfer 200+ amps x 12 volts @ 8'.
High hp car audio cable is the finest cable money can buy and can transfer unreal amounts of current for their size. If you are that concerned about weight go to any high end audio store and look at their power cables.

I use welding cable.....its not Monster but the price is right and is surprising good!