0
\$\begingroup\$

I want to connect the cables of a LiPo 7.4 V 2200 mAh battery, to a breadboard. However, the only way to make this happens is to solder the ends of the battery cables with a single-core cable with solid conductor.

Is this a safe option or there is the risk of damaging the single-core cable? As far as I know, the current draw will be about 700 mA.

\$\endgroup\$
  • 3
    \$\begingroup\$ Please add information about wire gauge or core diameter. \$\endgroup\$ – Kamil Jun 14 '14 at 12:39
1
\$\begingroup\$

Theoretically - for 700mA you should use AWG 23 wire. You can use this table for choosing wires.

AWG 23 is 0.57404mm core diameter (or 0.0226 inch core diameter).

Practically - if wire is short (few cm/inches) - you can use AWG24 or AWG25 wire and there will be no damage at all. Even thinner wire probably could survive 700mA without damage.

Note, that wire current ratings are usually determined by voltage drop/resistance. This is not maximum current without damage.

You should worry more about wire<->breadboard connection resistance.

Many breadboards on the market are poor quality and 700mA current may cause some voltage drop on connection between wire and breadboard conductive part. For relatively high currents (>500mA) I'm using double wires sometimes - to make sure that connection is good enough.

\$\endgroup\$
1
\$\begingroup\$

The optimum size for solid-core wire to fit snugly into a solderless breadboard is AWG 22 (0.64mm diameter), and that will be fine. 12" of AWG 22 wire (two 6" leads) will drop only about 11mV at 700mA, which is pretty much negligible.

700mA is towards the upper end for a breadboard, and you may see some significant voltage drop and heating if the contact turns out to be flaky.

Do not use the plug wire style unless you verify the wire size is substantial- I've measured them at about AWG 28 (0.3mm), which is a little light. The actual current rating of wire will depend on the insulation used and the environment (other wires and temperature) but ignoring voltage drop, a couple hundred mA would be a reasonable limit for cheap PVC wire in a lab environment.

enter image description here

\$\endgroup\$
  • \$\begingroup\$ I always thought the cross-sectional area of copper determined current handling. The insulation used defines the voltage handling of the wire. \$\endgroup\$ – Majenko Jun 14 '14 at 14:56
  • \$\begingroup\$ The cross sectional area of copper (assuming it's round) determines the heat load and thus the temperature rise. The wire current capability (for insulated wire) depends on how hot you're willing to allow the insulation to get. If the insulation is rated for 90°C and the temperature in the box could get to 89.9°C, then you can't put barely any current through the wire. If the insulation is rated for 200°C (aerospace PTFE insulation), it's in open air,and you're willing to allow it to get that hot (and drop that much voltage, which is a separate question), an AWG20 wire can handle close to 20A! \$\endgroup\$ – Spehro Pefhany Jun 14 '14 at 15:04
  • \$\begingroup\$ Yes, but how little voltage would you get out of the end of it after all that heat loss? Current handling is about more than just heat - it's about voltage drop. \$\endgroup\$ – Majenko Jun 14 '14 at 15:06
  • \$\begingroup\$ @Majenko There are dual constraints and both must be met. I therefore addressed both in my answer above. \$\endgroup\$ – Spehro Pefhany Jun 14 '14 at 15:11
  • \$\begingroup\$ I could encase a wire in ceramic insulation. But what what use would that be if the copper inside turned to liquid from its own self generated heat? Insulation temperature rating is for environmental temperature, not wire temperature. Only an insane person would take the temperature of a conductor over the voltage drop from the conductor itself as the lower limit. If a wire gets hot enough to even soften the weakest of insulation then you are doing something drastically wrong. \$\endgroup\$ – Majenko Jun 14 '14 at 15:11
0
\$\begingroup\$

Solid core cables lack the flexibility and mechanical robustness that stranded cable gives you. A solid core is more likely to fatigue over time at stress points like where it enters a solder joint. That is why in general flying leads (like power cables, network cables, etc) are stranded cable. Conversely, solid core cable performs better when being used with things like screw connectors, or with individual-wire IDC connectors (such as RJ-45 "punch down" wall sockets), where the cable is fixed in place and doesn't move.

The current carrying capacity of stranded vs solid core is (virtually) the same for the same cross-sectional area of copper.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.