eBike battery connection problem-Electrical connector grease case study

eBikes are growing in popularity and so is the battery technology associated with these exciting bicycles. Some problems that can occur with eBikes are familiar to electrical engineers/technicians in a number of sectors; electrical connector oxidation, water ingress, contact wear and even the infamous fretting corrosion phenomena. A private customer of our online shop recently emailed us with some great feedback; the dielectric connector grease called Tribosyn 330 fixed a problem associated with the battery contacts mounted on a Shimano Steps E6000 series motor.

The customer reported that the e-bike electrical drive would cut out during a ride. The customer noted that the problem would appear to be random but sometimes corrected after the battery was removed/unmated and mated again. The battery/system is 250W, 36V with gold plated spade connectors/contacts.  Gold is often used as a stable contact surface for electrical connections, it is a way to reduce fretting corrosion risk and gold will not react with environmental contaminants to form electrical insulating films. Pure gold can have relatively poor sliding wear performance and since gold is soft, it can be scratched or scared easily. One option to make gold harder it so add a hardener such as nickel but the process can negatively effect the otherwise inertness of gold. The solution is to make sure the gold coating applied is of a sufficient thickness. What thickness? There are theories and white papers on the web giving advice on gold plating/coating thicknesses but when gold is applied on a contact surface, much depends on the variables involved such as contact design, contact forces, temperature, expected functional life (number of cycles) etc. Because of the stability of gold, it is the material of choice for contact plating/coating in high performance electrical contact applications.

Gold is often the material of choice for electrical contact coatings but it is softer than other coatings, which means the surface can be scratched away after or during multiple mating and un-mating cycles.

The primary goal is to prevent the eBike from cutting out, so effective lubrication of the battery contacts to prevent further contact surface wear during battery changes is the first challenge. An additional challenge for any connector grease is the working environment for any e-bike; moisture ingress can of course be expected so this is a complicating factor. Plastic compatibility of the contact grease is also an important consideration so that the battery plastics do not swell or crack.

Solution.

• A specialist connector grease based on a polyalphaolefin oil is ideal for this application as there are no extreme temperatures involved, just normal Summer and Winter temperatures.
• A dielectric connector grease is necessary so there is no short circuiting of pins when a grease is applied.
• The connector grease must seal the contact area and resist environmental contamination with water ingress being the most likely problem, so a formulation containing a hydrophobic silica thickener to will make the grease water repellant. Note Silica is completely different to Silicone, we DO NOT recommend using silicone on electrical connections.
• The chosen grease should NOT be conductive in an attempt to fix the problem, we DO NOT recommend using a conductive grease on electrical connectors.
• There must be no increase in contact resistance across terminations as a result of using a connector grease.

Product Selection

Tribosyn 330

Tribosyn 330 is our ‘go to’ dielectric connector grease and can be purchased at our online shop. It has a superb pedigree in a number of industry sectors, most notably the automotive sector. Tribosyn 330 does not cause any increased resistance across the contact surfaces but is NOT conductive and does not contain silicone.

Applying The Grease

In terms of contact surface lubrication, only a thin coating of the electrical connector grease Tribosyn 330 is required for the product to be effective. Quite often, the female side of a connector is the easiest option when wishing to grease connector contact surface but the male spade terminals on this Shimano device are easily accessible, quite large and also it is likely that any squirting of the grease into the female side would not reach the contact surface. So in this instance, the customer applied the 330 very diligently by using a brush to apply a thin coating on to the spade terminals, making sure there was an even coating on each side of the spade contact surfaces.

Tribosyn 330 looks like a clear gel, as a consequence it can be hard to inspect the presence of the gel/grease when applied in thin layers, so a UV dye was included in the formula to aid inspection.

Results

The problem stopped occurring after the Tribosyn 330 was applied. The customer was extremely pleased, now the customer could take care free rides without worrying about the electric drive cutting out/ceasing to work. Considering e-Bikes are a big ticket item/device to purchase, it’s amazing how just a few pennies of grease can make all the difference to the ownership experience of a eBike user.

THE tribosyn 330 prevented the electric motor/battery cutting out and made all the difference to the e-bike owner.

It should be noted that periodic cleaning and re-greasing of the terminals would be considered best practice. The 330 will not dry up or evaporate and the grease does not migrate; however it should be considered that all grease can be mechanically pushed, so multiple battery changes will most likely mean that small amounts of grease will be lost or transferred to the the battery charger as time goes by. Also, although grease does not attract dirt, it could be that debris does slowly accumulate on the battery contact surfaces. A simple wiping away of the grease with a clean rag and the re-application of 330 is a sensible precaution/maintenance task. How often should the 330 be wiped away and re-applied? Hard to say as it depends on levels of bike use and number of battery changes per month/year, but changing the grease once or twice per year would seem sensible.

So what was the problem? What did the use of Tribosyn 330 fix? Impossible for the author to be sure as we did not get to see the contact surfaces in person, but most likely a contact wear related issue and probably oxidation issues. In theory, Au/Gold is a noble metal and so should not react with oxygen under normal conditions. However, usually gold is used as a plating layer over a base metal, if the Au layer is too thin, it will contain holes and will allow oxygen to corrode the base metal, which often sends oxidation products to the surface to interfere with electrical continuity. The 330 will prevent oxidation from occurring on the contact surfaces so an open circuit cannot be created. Fretting corrosion cannot be ruled out either, if the owner/rider experienced the ‘cut out’ mid-ride, it could be that there was microscopic debris building up between the contact surfaces as the ride progressed, building up to a point where one or more contact surfaces were affected enough to cause a failure. Why not find out more about fretting corrosion to understand what could be happening.

A Preventative Maintenance Solution, Not A Magical Repair Product

Very important that the reader notes the Tribosyn 330 is not a magical repair gel/grease. The battery contacts were already damaged prior to Tribosyn 330 being applied but were obviously not too badly damaged to prevent further use. The best use of a connector grease is to apply to your eBike immediately after purchase and prevent the problem starting. The connector grease will prevent further contact wear and any oxidation problems, but a connector grease is dielectric, not conductive….we never recommend using a conductive grease as it most likely lead to further problems.

Why not take a look at our other articles about dielectric connector grease and we also have other case studies that may be of interest.

You can purchase Tribosyn 330 at our online shop.