Potting

As I mentioned in a previous post, I've replaced the voltage regulator (and by this, I mean the regulator/rectifier combo) on my Sportster. I would like to have simply tested each device within the regulator and replaced only the individual device (transistor, diode, etc.) rather than have to replace the entire regulator. What prevented me from doing that was the block of black epoxy the circuit was embedded in. This stuff is called potting, and it's commonly used in electronic circuits. On motorcycles, potted circuits can and often do include regulators, ignition systems, and engine control units. Understanding why potting is used and why potting can be a hindrance when doing repairs may help you decide whether to pot your own custom motorcycle circuits.

You might be wondering why circuits are potted to begin with. Perhaps manufacturers simply don't want you servicing your own circuits rather than buying parts from your local dealership. But there are actually good reasons to pot, especially for a circuit that is a part of a motorcycle. Motorcycles often vibrate a lot. And even with relatively smooth-running motorcycles, there's bumps and potholes on the road that can jar a circuit. Circuits have to deal with thermal stresses due to engine heat and weather. These mechanical and thermal stresses can damage solder joints, circuit board traces, component leads, and wiring. Surrounding a circuit in epoxy or other hard substance helps hold everything together.

That's not to say that manufacturers mind that potting gets in the way of customers doing their own circuit repair. And that's not just a matter of greed. Most people are not qualified to do their own circuit repair, and even those who know a bit about electronics can accidentally damage something. Suppose a customer has engine problems and they monkey around with an unpotted ECU damaging it in the process. They bring it in for repair and it's under warranty. How does the dealership know that the defective ECU was damaged by the customer. If the circuit is potted, it's not even a consideration.

So as someone who may want to do component level trouble shooting or repair of an ECU or regulator, this means doing so is going to be a huge pain in the ass. It's not impossible, though. You can do a google search to find several pages describing the removal process. This, of course, can cause further damage to the circuit.

As someone who may want to build your own regulator, ECU, or other circuit for your motorcycle, you need to consider whether the benefits of potting are worth the future hindrance to repair. While potting can get in the way of repair, it might mean that you don't have to repair as often if ever. Then again, being that you don't have the R&D resources of a large motorcycle manufacturer, it's likely you'll need to diagnose design flaws with your circuit. That's kinda hard to do with potting in the way. Perhaps potting might even be causing problems by trapping heat leading to overheating components in your circuit.

Perhaps you can simply pot with something that's not so easy to remove. Guitarists sometimes use beeswax to pot their guitar pickups. Parrafin wax might work quite well. Using silly putty might be worth a try. Granted silly putty isn't as rigid, but it may still provide as much mechanical support as you need.

So while potting might prevent you from repairing circuits from a manufacturer, it has a purpose and can still be useful for your own custom circuits. Choosing an easy to remove potting material can make repair easier. And if you choose not to pot, you might find that you simply didn't need it to begin with. In a worse case scenario, you might simply have to resolder a joint or repair a circuit board trace.