Melted cables at the control unit

[radvis]

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?

 

[AGS]

I have seen this loads of times. You need to use better quality connectors.

 

[Benjahmin]

Yup, bullet connectors are rubbish. They tend to go loose and hence resistive hence the heating.
You need some xt connectors such as these:

Male MR60 3 Pin Gold Plated Connector with Cap 30A AmassDefault Title

Male MR60 3 pole connector manufactured from high temperature nylon, housed in a compact package designed to prevent a short-circuit. Manufactured by AMASS Current rating: 30A Contact material: gold plated brass Insulator material: nylon

www.switchelectronics.co.uk

Or Anderson connectors:

https://www.amazon.co.uk/Powerpole-Quick-Connect-Battery-Connectors/dp/B07H81ZSNS/ref=asc_df_B07H81ZSNS/?tag=googshopuk-21&linkCode=df0&hvadid=696285193871&hvpos=&hvnetw=g&hvrand=12472249998529570854&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006886&hvtargid=pla-2281435177338&psc=1&mcid=d149338792863716853f350450f8f82f&hvocijid=12472249998529570854-B07H81ZSNS-&hvexpln=74&gad_source=1

Or solder the cables together and cover with heatshrink.

 

[thelarkbox]

If regularly disconnected look at anti-spark XT60 or XT90 connectors too.. will save you many startled experiences..

 

[saneagle]

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?

It's not that common for battery wires to melt. It's normally the motor phase wires that melt. It looks to me like it's gone over the 17A (possible short circuit). Why did you do a routine inspection? Was there a problem? Is it working OK now?

 

[radvis]

Thank you all for the comments and suggested solutions.

 

[saneagle]

Thank you all for the comments and suggested solutions.

Did you find the reason for the short or overload?

 

[radvis]

Did you find the reason for the short or overload?

Since I don't solder every day, I guess I may have soldered the wires incorrectly during the replacement of the control unit. Corrosion may have occurred too as I ride my bike in the rain. I'll start by fixing the connections with better connectors and then see if the heating issue recurs.