Battery relocation question... amperage drop?

The cross-section of a steel frame will carry much more current than the potential of a car battery. One MIGHT be able to measure the voltage drop, but it would be LESS than that of a one foot long battery cable. There is no downside of connecting the battery to the frame at the rear of the car and grounding the starter/motor block at the other end so long as the contact area is properly prepared. I'm a "ground fanatic". Tail lights, etc. will never fail due to a bad ground on my jalopies! On supplimental/redundant grounds to the frame I clean the hole with a spotface and tin the area surrounding the hole with torch and solder. Attach the cable to the frame with bolt made of brass, copper, or cad-plated steel..

 

I like the way you think. Access, redundancy, reliability.

 

Given that most cars (and frames) are made up of a bunch of stamped steel parts spot welded, partially welded together (and sometimes glued together) I personally will try not to use it when I can to complete an electrical circuit from one end of the car to the other end. Not to say that I have never done so I've seen my share of problems that I've had to correct. I look at how a lot of cars are put together.
A person might attach a ground wire from the main starter battery in the rear to the taillight panel and this cross sectional area is pretty large but then it goes through spot welds that attach this part to the next part in line like the trunk floor pan and probably the quarter panels. The trunk floor and quarter panels I have to agree too also have a large cross sectional area but now these panels get spot welded to other metal panels like the rocker sills and roof and then continuing on are yet spot welded to even more sections of metal with spot welds again before it finally ends by the motor and then this person runs a wire from the firewall down to the engine block. Yes, there is a lot of cross sectional area there but there are also a bunch of parts spot welded (and chances are very good not fully welded together on the overlapping seams). The spot welds are the electrical connection between all of the different stamped steel parts that make up most auto bodies.
I have used one frame rail under vehicles on one side of the car to complete or tie things together electrically but I also look to see if it's one piece between the two points I have chosen. If in the middle one section is welded to the other I also look to see how well it is welded. You might have a bigh cross section of two pieces of metal attached to each other but it may only be with a small cross sectional weld.

The best bet on any thing is not hoozhwahing it together and I can agree that redundency can have it's benefits.

I too have seen many cars like Ferrari, Mercedes and Jaguar (and also just seen it last week with a 2008 BMW) with the batteries at the far end of the car from the engine and yes it can be done and it can also have problems.

If it's done properly then it should hold up but if it's rushed and not thought out then things can go wrong.

Jim

 

Man, I hope this answers a question that's nagged me a long time. PLEASE NOTE, I plan to keep my '55 Fireflite fairly stock and (believe it or not) including the six-volt system, at least for now. BUT, I've done some very mild customization (all parts saved, so it could be easily restored inside a few weeks).

One of the alterations I wanted to make was/is to move the battery to the trunk with fabbed hold-down, to keep it secured and away from carpet, etc. This is ONLY for aesthetic reasons, as I always thought the battery -- RIGHT THERE -- obscured the view of the cool Hemi. I GUESS THE ONE REMAINING QUESTION I have is, everything on this thread applies to 12-volt systems, am I right? If so, does all advice hold true for six-volt as well?

 

It does - BUT - with a six volt system you need twice the current (amps) to provide the same amount of power. This is because the voltage is half (12 vs 6 volts). Therefore, with a six volt system you need even larger cables than with a twelve volt system. Don't forget that you can double up cables in case the one really large size you need is not as affordable.

 

http://www.hitmanhotrods.com/en/adm...tsGraphs/wire_sizing_chart2_titled_filled.jpg

Check this chart out...

 

Interesting discussion that kind of got off the point but if I may, the nice thing about running both leads from battery to engine is one knows where it flows...

 

Yes, of course, including using the frame for the ground route. Wild ass liberal guess would be; Take the cross section of your heavy duty Battery cable, and run three cables in tandem back for the Power cable. If the starter is sluggish, add another. Of course you're going to find all of that copper worth it's weight in gold!

 

wow a huge amount of good info here
not much i can add
but im posting so i can find this later

 

Sorry mate, but do not use multiple leads. One conductor sized correctly.

 

Cool info, guys. A HELL of a lot of opinions. So, Sloo, what gaugue would you use? I assume I'll have to buy the cable & put the end on myself, of course.

It's ONE thing to put on something that looks "trick," but if it doesn't do the job, it's a bust. PLEASE, stay with me, as I don't wanna dump the 6-V -- at least until I can afford to upgrad the WHOLE system, YA KNOW, MATE?

And, BTW, I don't say MATE in a funny sense or disrespectully. Australian inventiveness in roding is pretty much legendary, and -- today -- saw somebody from South Africa weight in an important question on another thread! Shoot fire and save matches! (West Virgina saying) The HAMD ROCKS!!!

 

I like the Aussie way of speaking, so mate is good...beats the hell out of dude EH!
First time someone called me mate was a Welsh chap that I worked with, talk about cool lingo....
And now back to are regular channel...
Check out the chart that I posted and 6 volt is double the current, therefore size to that current requirement...make sence..
I would put my own ends on as SOA-NOVA indicated, I like his thinking as thats the way
to wire boats, which is more critical than a car (imho).

 

Let's back up a second. I thought you WANTED to keep the 6V. If it's merely a economic decision, since 6V battery will need replacing someday, the time to do the conversion is when that happens, the practical route is inevetable anyhow. Total conversion cost might be less than all that heavy duty cable to carry the 6V to the other end of the car, since the major expense of the conversion is a 12V alternator and a new battery. The rest of the conversion is a mere pittance. I would recommend you delay the battery move until your 6V batt, or generator fails, whichever comes first, then do the complete conversion.

 

You should learn to use the "subscribe" function...it's definitely an awesome tool. Once you are in a thread go to "Thread Tools" in the red bar at the top of the thread and when it pops down click on "Subscribe to this Thread".

A lot of opinions here, but the theme is the same...do it right and don't shortcut, make sure the gauge is heavy enough based on the distance, and make sure that ground connections (wether frame or straps) are solid and metal is clean and has integrity.

 

Go get yourself some 1/0 welding cable, it's about a buck a foot, and it'll be more than enough for anything you'll throw at it. Always bought some extra and used it for frame grounds... My guy will crimp the big lugs on for me, but usually I just sweat them on like you would any old plain copper water pipe.

 

Awesome input, guys! THANKS, 29Nash. I stand CONVINCED: Do it ALL AT ONCE.

 

I agree...this turned out to be a great tech thread.

 

From an electrical perspective, the key words above are 'conductor sized correctly'. Using a fatter cable is just like using however many skinny cables in parallel - with them in the same wrapper. Think about it.

While it is more convenient and neater to run only one big cable, running two skinnier ones that combine to the same resistance as the fat one is irrelevant to the electrons rushing about.

Say you had a fat stranded welding cable. Let's say that there are 100 individual strands. The resistance end-to-end of the fat cable (for any given length) IS THE SAME as if you ran 100 parallel runs of wire the size of an individual strand. Now of course, no one would do this, but if you did the battery and starter would not know the difference.

This is true for DC, in AC things get funky as the frequency increases. At higher frequencies (way higher than our 60 Hz mains) a phenomonem called the skin effect comes into play, where the current only flows on the outside of the conductor. The inside could be lead or cardboard or air, because nothing is flowing there. AC definitely adds wuite a bit of complexity, with the effects multiplying as the frequency increase, or as the load moves from resistive (zero power factor) to inductive (lagging power factor) or capacitive (leading).

Thank goodness we only have to deal with DC on our rides as even with this simpler construct there is a lot of confusion and myth. The electrons, though, they obey strict rules.

BTW a nice thing about wiring for 6 volt currents but then converting/running at 12 is that you then have an overkill situation. All of the conductors are sized exactly twice as "strong" as they need to be. This reduces voltage drop, hence heat, increases reliability (a few frayed strands have little if any effect), and so on. The down side is increased cost as you will be paying for a lot more copper.

 

Maybe some day I will post a Tech article on the fundamentals of electricity - car style: 'everything you need to know to wire your ride'.

 

The big problem with multible conductors is if one or more fail in any manner, then what exists is over current in the working leads and potential fire hassard. If one lead, all you have is a starter that will not crank and will know then of the problem...

 

If you have a 100 strand cable and ten strands are broken, you really have a 90 strand cable and you will never know the difference. Same thing if you have 100 single strands and ten of them break.

I am not suggesting that anyone run 100 separate wires.

I am trying to make the point that intuition and bias and personal opinion do not govern how electricity does its job. There are hard and fast rules that have been validated for 100 years now.

Wiring is one of those things that for whatever reason attracts a lot of black-magic statements. That might be because some of the fundamental principles are incompletely understood. For example, the title of this thread talks about a current drop. Current doesn't drop. Voltage drops. Seemingly a harmless switch of words, but very meaningful if you are attempting to understand how this stuff really works.

 

Good info, thanks

 

When I relocate the battery I always run a bigger cable size and always run a kill switch to.

 

Electrical code(not automotive) does not allow multible conductors for the reason I stated, thats not black magic, intuition, or personal bias...whatever...

 

There you go. The kill switch is a great idea. Adds safety, theft prevention and reduces the chance of a drain on your battery when the car is sitting.

 

Anything requiring more than 1/0 needs serious inspection as nothing should require more current than a 1/0 cable can provide. As previously stated, the strand count means absolutely nothing other than convience in bending, the skin effect is only an issue at extremely high AC frequency(and when I say extremely high frequency, I mean HIGH frequency as in thousands of megahertz/gigahertz, nothing anyone on a regular basis would need to concern themselves with.)

If you need more than 1/0, something is wrong. Get yourself 30' of 1/0, that'll give you enough to feed the battery and supply the starter with way more than the current it requires, as well as enough frame groundings. Frame grounding will provide way more than enough cross section to provide a soild ground, assuming the grounds are properly prepared at the battery and alternator. Grounding to the frame allows for much more current flow than any cable, there is no need to run a ground cable from the battery to anywhere, except the chassisi. Lots of overcomplicated information floating around here. Run 1/0, if it don't cut the mustard you have problems beyond the gauge of the cable. There is no need to run a dedicated ground line, ground to the chassis will provide much more current carrying capibility than you'd ever need, spotwelds or whatever regardless. The "skin effect" only occurs at high frequency AC waves, not at all with DC (if you go take a gander at a celluar or PCS bamd wireless provider tower, you'll find they use 1-5/8" cable, with a hollow center conductor surrounded by a foam insulation and another thin outer conductor. These are the frequencies that the skin effect becomes an issue).

If you're paying more than a buck, buck and a half, for 1/0 welding cable find another supplier. I have a good relationship with my electrical provider through my job, but regardless if you need more than 1/0 there is something poorly designed. 1/0, regardless of the strand count, is more than enough to provide the necessary current regardless of where your battery is located. Period.

Run 1/0 from the positive battery lead back to the alternator and to the starter. Use a little extra of the 1/0 for a battery to chassis ground, and an alternator to chassis ground. If that isn't sufficent something is wrong. IMO welding cable cannot be outdone, any of that car stereo shit sacrifices quality for looks. 1/0 welding cable can supply any vehicle with enough current to be just fine. There simply is no reason to run a ground to the battery from anywhere than from the chassis/frame, the current handling capabilites of a well prepared chassis ground will exponentially out-perform a negative cable run.

 

This is not a 'why' don't you like one way or the other subject, it's a 'what' will work subject. Of course, larger cable wil work but I'm a cheapass and cable with large enouogh cross section is expensive. Smaller size, such as junk welding drag-lines are cheap, available at salvage yard, siameesed with good heavy duty end connector will work just fine.

 

ahahahah....you are cheap man, thats about the goofiest shit I ve heard....

 

......you'll hear a lot more stuff that might be goofy to you, from mechanics. I understand that everybody isn't one and those that aren't will probably never understand mechanical devices. Don't keep you from enjoying and drivin', does it?

 

Remember that your grounds are just as important as your power leads. You can build the biggest badass positive cable in the world and still have a screwed up electrical system if your engine, frame, and body aren't properly grounded. This is really REALLY important and is commonly overlooked.