battery in trunk-cable size? - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• battery in trunk-cable size? by jb86 on 26 Jun, 2011 06:51
• 1991 jetta turbo diesel, 1.6l.
  i have the car stripped down. it was painted a few months ago. i pulled the engine and transmission, stripped the engine bay. its all painted.
  i have a rebuilt engine to go in.
  in the interest of simplifying the engine bay - i've converted to manual steering, left out the a/c.
  and all of the wiring harness and all of the relays that were on the firewall i have pulled together that im leading to a box where the battery used to be.
  the battery i will install in the trunk.
  because it is in the passenger compartment i fugire it is safest to use sometype of sealed battery - no off gassing.
  the optima batteries i have learned dont have thehigh amp draw needed for diesels, ive read this on vw vortex. sears die hard has a platinum battery, gel type, sealed battery with 935CCA, with a full 4yr warranty and pro rated up to 100mos. they say it has welded internals and can take the vibration of a diesel.
  i plan to use that.
  the cables - i have done research on the size and type. welding cable is more flexible and has a high strand count and can carry more current. 1/0 i beleive is enough. listed as able to carry 400amps and 2/0 450amps.
  
  i can run a cable about 18' to the engine bay, i would also use a circuit breaker near the battery. i found a 200amp inline breaker with clamping terminals that 1/0 will clamp into without terminals.
  then a smaller cable to the starter
  the negative, i would run a cable to the body and also another maybe #1 gauge to the engine block.
  does anyone have any input on cable size?
  jon
• #1 by theman53 on 26 Jun, 2011 07:13
• I think there is no such thing as underkill. I have the battery in the stock location and use 1/0. Before I had to buy a 1000ca battery to get my older diesels to start in the winter. I have a smaller battery and it starts better. I would run as big a cable as you can since you are going to have a loss running the 18'. Someone on here bought the summit racing kit that had IIRC 1gauge in the truck relocator kit and it wasn't enough for him and he had to upgrade.
• #2 by bajacalal on 26 Jun, 2011 19:37
• I would use a 2/0 welding wire if not larger. And, I would think, the starter can draw more than 200 amps.
  
  The required cable size depends on both distance and current load. Longer distances require a thicker diameter wire for the same load. From what I recall, 2/0 would be the minimum size for above 400 amps at around 10'.
  This site is ok.
  
  I like to build custom wiring and cables. But I don't like trunk mounted batteries very much. My Fiat had one. The location of the battery was a major source of electrical problems. I couldn't get the voltage above 11.5 at the starter, there was that much voltage drop. At the tail lights it was under 10 due to the return trip back there. There were a lot of other factors though like poor connections. Use peened/soldered copper connectors with screw on terminals on your major wires, that will help and it's better to overdo it when it comes to wire gauge then run into problems later.
• #3 by JGWarner on 26 Jun, 2011 20:58
• What about running several parallel lengths of smaller gauge wire?
• #4 by mystery3 on 26 Jun, 2011 23:07
• Go to the junkyard and pull the cable from an bmw e30. They are huge and with the cost of copper these days you may save a sizable amount of money.
• #5 by silentdub on 30 Jun, 2011 11:05
• Quote from: JGWarner on 26 Jun, 2011 20:58

  What about running several parallel lengths of smaller gauge wire?
  

  
  Excellent idea.
  
  Depending on the theory, this would be the best choice, smaller stranded wires, the more strands the better.
• #6 by R.O.R-2.0 on 30 Jun, 2011 11:11
• Quote from: silentdub on 30 Jun, 2011 11:05

  Quote from: JGWarner on 26 Jun, 2011 20:58

  What about running several parallel lengths of smaller gauge wire?
  

  
  Excellent idea.
  
  Depending on the theory, this would be the best choice, smaller stranded wires, the more strands the better.
  

  
  i imagine 1 length of 4 gauge, for example, would be cheaper than 2 runs of 6 gauge..
  
  4ga is too small for a battery cable that long tho.. i would use atleast 2 ga, if not 0 ga..
• #7 by bajacalal on 06 Jul, 2011 11:20
• I think it would work (using 2 cables) but remember that electricity is going to travel the path of least resistance so if one is significantly longer, looser or more corroded than the other, you will leave yourself with basically 1 cable which may not work at all.
• #8 by burn_your_money on 06 Jul, 2011 11:25
• Quote from: bajacalal on 06 Jul, 2011 11:20

  I think it would work (using 2 cables) but remember that electricity is going to travel the path of least resistance so if one is significantly longer, looser or more corroded than the other, you will leave yourself with basically 1 cable which may not work at all.
  

  
  I don't think you would basically end up with 1 cable. You would just have a higher percentage of the amperage flowing through the better wire.
  
  With whatever size cable you go with, do a voltage drop test over the length of the cable and see how much you are losing. Ideally you should lose 0.0v but under 0.5v is acceptable (but certainly not ideal). Remember to test again in the dead of winter with the glowplugs and starter cranking away for 20 seconds.
• #9 by dl_sledding on 06 Jul, 2011 19:02
• CAUTION: SCIENCE CONTENT
  
  Check this out:
  http://www.stealth316.com/2-wire-resistance.htm
  
  If you want to really understand why a larger cable is needed, this site explains some of the mathematical calculations, and also has a calculator.  Even has some real-world examples, including "Battery move to trunk".
  
  My "real" job is in the Telecom industry.  I work with DC power all the time (at -48v, up to 3000 amp).  The quality of the cable is so very important: typically in large cable, the more flexible it is, the "better" it is.  Better=more load handling.  The reason for this is that the very flexible cable is made from thousands of extremely small strands, rather than a few larger ones... This results in more circular mils, allowing more electrons to flow and creating a higher load handling capability.  Also, aluminum cable is 1.5 times more resistive than copper, so you need to size higher if using aluminum rather than copper.
  
  You may want to rethink your wire sizing... I am thinking 1 AWG minimum if the distance is 18' at 200A.  The very last thing you want is to overheat that cable!  Also, make darn sure that you have really good grounds *everywhere*.  I am guessing you are going to ground to the body; make sure that the body-to-engine ground cable is BIG and well connected.
  
  Personally, I would run ONE larger cable rather than two smaller cables, even though the cost is higher.  It just makes everything easier: no stacking connectors, etc.  I don't believe that the cost is going to be too much different...  Just my opinion.
  
  One other note: use lots of dielectric grease on your connections: it will prevent power-robbing corrosion and the heat that goes along with it over the long term.
• #10 by shwak23 on 06 Jul, 2011 19:25
• Quote from: dl_sledding on 06 Jul, 2011 19:02

  CAUTION: SCIENCE CONTENT
  
  
  

  
  Good info. THX!
• #11 by RabbitJockey on 06 Jul, 2011 19:34
• Quote from: burn_your_money on 06 Jul, 2011 11:25

  Quote from: bajacalal on 06 Jul, 2011 11:20

  I think it would work (using 2 cables) but remember that electricity is going to travel the path of least resistance so if one is significantly longer, looser or more corroded than the other, you will leave yourself with basically 1 cable which may not work at all.
  

  
  I don't think you would basically end up with 1 cable. You would just have a higher percentage of the amperage flowing through the better wire.
  
  With whatever size cable you go with, do a voltage drop test over the length of the cable and see how much you are losing. Ideally you should lose 0.0v but under 0.5v is acceptable (but certainly not ideal). Remember to test again in the dead of winter with the glowplugs and starter cranking away for 20 seconds.
  

  
  thats right
• #12 by mystery3 on 06 Jul, 2011 21:43
• Quote from: mystery3 on 26 Jun, 2011 23:07

  Go to the junkyard and pull the cable from an bmw e30. They are huge and with the cost of copper these days you may save a sizable amount of money.
  

  
  Check out this article: http://jalopnik.com/5107178/junked-bmw-e30s-provide-cheap-easy-way-to-trunk+mount-your-battery
  
  BTW- the cable is 00.
• #13 by DieselBalz on 06 Jul, 2011 22:32
• Oh I am so doing that! I was just considering the kit from Summit for 150. Ef that!