Cable size for power delivery. - Page 1
Forum section: electronics / beginners

author: Jackster
author_rank: Frequent Contributor
timestamp: February 12, 2022, 04:58:04 pm
content: Hi all.My project uses batteries that voltage ranges from 11v to 16v.At 15.5v my project uses around 65mA on average so ~1.125w.At the lowest voltage on the battery, we would be using ~102mAWhat is the minimum cable size I can get away with at 1 meter?Currently using 0.1mm2 2 core and it looks to be fine. Very little voltage drop.

author: TimFox
author_rank: Super Contributor
timestamp: February 12, 2022, 05:19:56 pm
content: Seehttps://www.engineeringtoolbox.com/copper-wire-d_1429.htmland do the arithmetic.You don't have a country flag set, but if you are metric there are other tables and the conversion is simple.For example,https://www.kbe-elektrotechnik.com/en/service/awg-table/

author: themadhippy
author_rank: Super Contributor
timestamp: February 12, 2022, 05:37:55 pm
content: Take your maximum permissible volt drop,divide it by the current the circuit needs,thats the R in ρ = RA/l, you know l,the length. ρ depends on the material of the conductor,for copper its 1.68×10−8,and A is the bit your after, the area of the conductor.Don't forget theirs 2 wires so your length will actually be 2m

author: TimFox
author_rank: Super Contributor
timestamp: February 12, 2022, 05:42:59 pm
content: Note that in the formula above, the resistivity “rho” is in ohm-meters.(Spell check wanted me to write “Rhonda”, as in “Help me Rhonda, yeah…)

author: Terry Bites
author_rank: Super Contributor
timestamp: February 12, 2022, 05:57:11 pm
content: Dont aim for a minimum cable size but for onen that can comforatbly handle current draw at the maximum temperature- only crooks try to "get away with it". As Mr Fox says- there are plenty of tools to help you find the correct CSA/ guage. Keep an eye on price, larger guage wire isn't always the most expensive. For most home and consumer applications, regular PVC wire will do. Exotic insulation materials can cost a lot but no one really cares if your making a satelite or a medical device.

author: TimFox
author_rank: Super Contributor
timestamp: February 12, 2022, 06:43:21 pm
content: For relatively low currents such as this, the series resistance and its voltage drop are probably the most important variables.It doesn't hurt to check the nominal current capacity of the wire, which is based on temperature rise.

author: floobydust
author_rank: Super Contributor
timestamp: February 12, 2022, 07:26:50 pm
content: Also don't forget the FUSE so the wire does not overheat and catch fire, in the event of an overload.

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 12, 2022, 10:08:55 pm
content: For such an application I would simply pick a cable that is strong enough so an accidental jerk on it won't break it off. With such a cable it would not worry about overheating or voltage drop.

author: IanB
author_rank: Super Contributor
timestamp: February 12, 2022, 10:13:24 pm
content: Quote from: Jackster on February 12, 2022, 04:58:04 pmConsider also mechanical strength, vibration resistance (solid core or stranded?), and maybe even heat resistance. Voltage drop is not the only consideration.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: February 13, 2022, 11:26:10 am
content: If this is for vehicle Tempature is also a consideration 18 Ga. is minimum for lower power that I would use.Jeff

author: Jackster
author_rank: Frequent Contributor
timestamp: February 18, 2022, 10:23:39 pm
content: Nothing like a load test to see if the cable can take it or not...1 amp through the cable, I could hardly feel it warming up if any.The crocodile cables were actually warm...This one is 27 AWG as far as I know.

author: wizard69
author_rank: Super Contributor
timestamp: February 19, 2022, 09:20:00 pm
content: Quote from: floobydust on February 12, 2022, 07:26:50 pmThank you for saying this, I was about to respond in the same way until I read your post. The reality is that the current draw is so low here that other factors come into play, safety being one of them and mechanical strength another. It is pretty easy to imagine that the battery is big enough to fry the wiring relatively quickly.

author: mariush
author_rank: Super Contributor
timestamp: February 19, 2022, 09:39:52 pm
content: You may also want to consider using 4 thinner wires instead of 2 thicker ones.For example, maybe you'd want to use a ribbon cable with 4 AWG28 or AWG30 wires instead of just two thicker wires.2 wires gives you some redundancy in case one wire isn't making good connection. wider header may solder better, may be more reliable etc... with 2 wire connector you may need some locking mechanism to prevent connector becoming loose, with 4-5 pin header friction lock or something else may be easier and cheaper.You could maybe have a 5 pin connector and use one pin as key, to prevent reverse insertion and reverse voltage problems.Or maybe use the 5th wire for a battery temperature sensor or something or to get a more accurate battery voltage reading (because you'd get battery voltage - voltage drop due to current if you measure at the other wires)