Designing a Waterproof or Submersible Electric Vehicle Propulsion System

The term “waterproof” is very open to interpretation much like the word “natural” is in the food industry. Luckily the IPXX rating system was created to set a standard for Ingress Protection. The first number 1-6 is the degree of protection against dust/ solids and the second number 1-8 is the degree of protection against water (the higher the number per column, the higher the protection.) These ratings usually do not include salinity levels or some depth and duration test ratings, unless specified by the manufacturer.

By far the most difficult item to waterproof or make submersible is the battery pack. At China Cycle Show 2018 there was a new IP65+ battery for share bike usage.

To make a battery on a mass scale truly IP68 is nearly impossible from a handmade manufacturing standpoint. Other IP redundancies would be needed to protect the battery from water ingress like; protecting the charger port (possibly adding a short circuit lead in the charger port to make the port live only after connecting to the connector) or dipping the pack in a potting gel and adding a double inner/ outer IP68 waterproof case.

We discovered a new IP67 charger that has an IP67 connector which can withstand some basic submersion and moisture. While an external charger is not an integral part of the vehicle, why not protect against moisture and splashes if the option is available?

Controllers have to be potting in either a hard epoxy potting material or a shock absorbent gel silicone. If submersion in salt water is necessary, a sealed watertight IP68 tube or case would be required to ensure longevity.

Most threaded signal connectors are IP67 by default but by adding an exterior layer of “marine-grade adhesive heat-shrink tubing” over the entirety of the linked connector, our tests are showing we can increase the IP level from IP67 to IP68.

There are some higher amp rated IP68 press-fit connectors but they are quite large and costly. The secret is to use softer TPU material and longer pins (with each pin being a mini rubber/ metal connector upon itself.)

As for waterproof motors, generally most 3 phase motors will work underwater if you protect the connection leads with marine epoxy.  However, oxidation starts to occur when the motor leaves the water and is in contact with the air. Winding with oxygen free copper and encasing the wound steel stator in a block of vacuum sealed or molded/ machined epoxy is your best to protect the stator from oxidizing. Other considerations are spraying the galvanized/ zinc plated magnets with epoxy coating and choosing special ceramic or underwater stainless bearings.

Submersible displays/ controls are more difficult, there are some completely double encased LCD displays but they are quite costly and susceptible to screen crazing from UV and salt water. We have sourced some IP68/ IP69K LED buttons and switches with programmable multi-functions that are more robust for salt water conditions.

Any other ideas just let us know!

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