Melted cables at the control unit

I have a fat bike with a motor in the rear wheel (Bafang 250W). During a routine check of the control unit (voltage 36V, max. current 17A, rated current 8A), I discovered that all the cables connecting the battery (Li-ion Silverfish 36V/21Ah) to the control unit have partially melted insulation (shrink tubing) exactly at the connection point (where the battery cables connect to the unit cables) – see the attached photo.

The control unit is relatively new, installed approximately 15 months ago. The battery is older, installed around 5 years ago. The previous control unit (identical to the current one with the same parameters) was installed with the current battery for about 3.5 years, and the cables never showed any issues; there was no melting of the cables at all.

Does anyone know what caused the current cable melting and how to prevent it?

Probably a less than perfect connection where the wires connect resulting in an extreme hotspot and the heat getting conducted away into the wire melting the sleeve., Look at XT60 connectors popular with users of high power RC lipo batteries.

Are those spade connectors? Whatever they are, they can't tolerate as much current as you're asking of them. You need, at a minimum, something like Anderson Powerpole 45 (crimped), XT60 (soldered) or Deans (soldered) plugs between battery and controller. Replace all the heat damaged sections of wire while you're at it.

Are you using a knockoff version of these solder seal connectors? It's probably just bad solder joints inside, The cheap ones that aren't clear won't show a cold joint,

Agree with the others, and will add:

• Connectors possibly not fully seated
• Connectors corroded or dirty
• Connectors of poor quality

Thank you all for the comments and suggested solutions.