 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Electronics : Long 12V cable - limitations?
| Author | Message | ||||
| neil0mac Senior Member  Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Exploring some possibilities .... !! I would like to run a 60 metre cable from a 100Ah battery to a 12V to 240V pure sine wave inverter to run a few bits of electronics (couple of lappies and a modem and wireless router). Possible? Cable size? Thanks. |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Anything's possible 
What wattage inverter, and if you know it, whats its cutout voltage. We can then work out the minimum cable thickness to run at full power without the inverter shutting down. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
muddy0409 Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 125 |
Personally, I would put the inverter as close as possible to the 12v supply and run the long cables at 240v. The current at 240v will be about 1/20th of the 12v current, therefore 1/20th of the voltage loss over the long cable run. This is the basic reason why power distribution is at 33,000 volts or higher, less loss in the cables the higher the voltage. Don't poo poo conspiracy theories. Remember that everything ever discovered started somewhere as a theory. |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Glen, The noname inverter doesn't give any clues at all - except that the current +ve and -ve DC wires are 3.5mm. Bit of a gamble, eh? muddy, On second thoughts, I can put the inverter about 35 metres from the battery using two 6mm single cables to cut down some of the DC loss - and then run 240V 3.5 twin and earth cable to the equipment ? This cabling I have on hand from a temporary house power supply cable used after a fire some years ago. |
||||
| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Are you talking about 6mm diameter, or 6mm squared (area) cable ? Big difference. 70 metres of 6mm squared works out to 0.200 ohms. One volt drop for each 5 Amps 70 metres of 6mm diameter copper works out to 0.0426 ohms. One volt drop for each 23.5 Amps. Cheers, Tony. |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
|
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That is BIG cable !! Should work and be quite practical, depending on how much power your inverter draws. If you already have the copper, no sweat. But I sure would not like to have to buy all that copper brand new. 70 metres of 10mm diameter copper works out to 0.0153 ohms. That is 65.4 Amps per one volt drop. That is one 35 metre run there, and one 35 metre run back = 70 metres loop resistance. Cheers, Tony. |
||||
Wombat Regular Member  Joined: 27/05/2011 Location: AustraliaPosts: 72 |
Hi neil0mac, Personally I would not use any 'heat treated' cable. Chances are it will become brittle. I think 6mm dia would be to small for your run. Without doing the math, (had a few beers), 10mm dia is about 50mmm2, 12mm dia is about 70mm2 which would be a good start. I sure others out there can be more precise. I always work on mm2 cable. The bigger the better. If you can run 2X 10mm dia @ 35 metres each, I think that would do a good job. Where are you located? I may be able to help you out with some lengths. It's all fun, regards Russ  |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
It's pretty easy to work out, you only have to remember one number. A "rod" of pure copper 1mm x 1mm and 1 metre long has a resistance of .0172 ohms at normal temperature (20C) Burn that .0172 number into your brain, and you can very quickly calculate the resistance of any length of any diameter copper wire. 10mm diameter cable has an area of pi R squared, or 3.14 x 5 x 5 = 78.5 square mm. A one metre length of this cable will have a resistance of .0172 divided by 78.5 = .0002191 ohms. And 70 metres will have a resistance of .0002191 x 70 = .015337 ohms Cheers, Tony. |
||||
| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Nice simple formula. Where to find information on acceptable resistance? Suppose Ohms formula will give answer on Voltage drop over certain distance George |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Resistance by itself does not matter. What does matter is the voltage drop you end up getting from that resistance. How much voltage drop is too much is entirely up to you. With that .0153 Ohms, you would lose 0.153 volts at ten amps, and 1.53 volts at 100 amps. Cheers, Tony. |
||||
 Print this page |
