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Example battery: https://www.amazon.com/Lectron-Pro-7-4V-7600mAh-Battery/dp/B01AAVM1MS

I see many different RC batteries that are have very High "C" ratings but all of them use connectors rated for very low current. According to the formula the continuous current out of that battery would be 75C * 7600mAh = 570A. 570 A is way more than any deans connector is rated for.

Also the wire off of that battery looks like 12 gauge wire. From charts I find the gauge would have to be below 1 gauge to work effectively.

Is the "C" rating for RC batteries just much greater than it needs to be and they are in a sense selling a spec that really doesn't make any difference?

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  • \$\begingroup\$ But what load does it need to supply? The wire may be rated for that only... \$\endgroup\$ – Solar Mike Jun 21 '18 at 22:10
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    \$\begingroup\$ The manufacturer of the pack is just dishonest, it can't deliver 570 A continously (maybe half of that if you really push it). Unfortunately this is the rule, not the exception, with RC battery discharge rate "ratings". \$\endgroup\$ – jms Jun 21 '18 at 22:13
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    \$\begingroup\$ Linking to an Amazon/eBay/AliX/etc item and asking "Why does this not make sense" more often than not has a very simple answer: You linked to an Amazon/eBay/Alix/etc item. \$\endgroup\$ – Asmyldof Jun 21 '18 at 22:13
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    \$\begingroup\$ Describing it as a "continuous" rate is probably a bit wishful thinking. If nothing else, a battery discharged at 75C would last about 48 seconds before it was flat (assuming it wasn't already on fire). \$\endgroup\$ – Simon B Jun 21 '18 at 22:52
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This battery is for RC toys. The RC toys usually run in open air and at high speed, which provides good thermal exchange with ambient. Also, nowhere it says 75C continuous. The RC toys, however, can have near-stall conditions which might require high peaks of current to start-stop-reverse. So it is not given that the battery should be used at 75C dead short situation, the rating has likely a specific meaning as an indication of peak capability, aka "burst rating".

On the other hand, the gauge ampacity ratings are for industrial applications of copper wires inside enclosures and conduits, and must meet stringent safety concerns. The ratings usually are for 10 deg.C temperature rise, both for wires and connectors.

If you allow 50 deg.C overheat for a 2-minute ride, these short wires won't melt even at 200 A. And yes, RC batteries and wires are getting hot when toys are running. BTW, the battery itself has 4-mm connection, normally rated at 75A, and you don't have to use their supplied adapter, which uses XC-60 (60 A) on the other end, and something even smaller.

So, there is not much contradiction between industrial ampacity and toy's specific applications and area-specific marketing monikers.

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