Timeline for How to choose proper size of high power DC cable connections
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| Mar 3, 2016 at 19:41 | comment | added | Voltage Spike♦ | The ampacity tables are calculated with unit lengths, the length and resistance form a ratio. The heat through the insulation is also a function of length and ends up being a ratio which is dimensionless. What does depend on the length is the total resistance. | |
| Mar 3, 2016 at 19:33 | comment | added | user57037 | The length of the cable does not matter when using ampacity tables. As I have said over and over, the purpose of the ampacity table is to make sure the wire does not get too hot and possibly cause a fire. The cable temperature is a function of the current and diameter, but not length. So start with this. The AWG from the ampacity table is the smallest you can use without a fire risk. THEN figure out if the voltage drop is acceptable. With a 1m (2m round trip) current path, the voltage drop will probably be small, but calculate it anyway. | |
| Mar 3, 2016 at 17:03 | comment | added | Voltage Spike♦ | Do you know what material the insulation is made out of? If you know its made out of PVC, then search for this google.com/… or google.com/… | |
| Mar 3, 2016 at 11:18 | comment | added | jumpjack | @laptop2d To do my own calculation I'd need to know thermal resistance of copper-insulator and insulator-air and proper formulas, but after months of useless searches I gave up and switched to ready-made tables... with no luck. How to determine which temperature my cables will reach appears an impossible task up to now. :-( | |
| Mar 3, 2016 at 11:14 | comment | added | jumpjack | I highlight the topics in my question: I found several tables for AC, but I don't know if/how they can be applied to DC - I read about "ampacity", but it too is applicable to AC and I can't understand if it is also useful for DC. - I also can't understand on which length are awg/ampacity tables calculated: shouldn't AWG also depend on line length?!? | |
| Mar 1, 2016 at 23:25 | comment | added | user57037 | Basically, there are two issues. Fire, and voltage drop. The ampacity table gives you the minimum size to make sure you don't have to worry about fire (or overheating the insulation). For lower voltage applications such as yours (70V), you may need to worry more about voltage drop in the cable. So start with the AWG from the ampacity table. Then calculate the voltage drop for your AWG and wire length at 100 Amps and see if it is acceptable. Remember that the positive and negative cables both have the same current and the same voltage drop. I can't make it any simpler than this. | |
| Mar 1, 2016 at 18:50 | comment | added | Voltage Spike♦ | What I'm telling you is to ignore the charts and run your own calculations, with the power equations. Then ask yourself if it matters. | |
| Mar 1, 2016 at 18:46 | comment | added | jumpjack | I already knew all this thing. I need clarifications about differences between DC and AC when sizing cables. | |
| Feb 29, 2016 at 21:00 | history | answered | Voltage Spike♦ | CC BY-SA 3.0 |