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Old 16 Jun 2011
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Bike electrics workshop at the Germany HU meet

As promised at the HU meet Germany this year, I’ll try to give a brief summary of the things we talked about in the workshop. Probably it will be extremely basic and not very comprehensive, but maybe it’ll motivate the one or other to take a second look at bike electrics – because after all, the basics aren’t that difficult.

!!! The post is still a draft and not even half-way done, so bear with me until I find the time to finish it :-)


  • Overview of bike electrics
  • Starting problems - where do I look?
  • Battery and charging problems + diagnosis
  • Adding accessories – what to keep in mind
  • Spares, tools and aids for your toolkit

Overview of bike electrics

We briefly talked about the various electrical components that most bikes have to put things into perspective. I find it often helps to simplify things down to its basic components, and I recommend you try and do that if you are stuck someplace with an electrical gremlin on your bike. Because most of the times, finding the fault will be a process of elimination.

In general, electrical components on a bike fall in one of two categories: they are either involved in generating electricity, or they consume electricity. The consumers in turn can again be divided into two categories: must-haves (required for the bike to run, e.g. the ignition) and nice-to-haves (not required for the bike to run, but still nice, e.g. lights). Components that are involved in generating electricity obviously also fall into the must-have category, as does the battery (and a bunch of cables/fuses), which is the place where all the above components come together. On the energy-consuming must-have side, we can make one more division: this is usually the ignition system (CDI, coil, spark plug, etc) and the e-starter system (if present). Because a picture says more than a thousand words, maybe the following diagram makes things a little clearer:

As I said before, finding faults is often a process of elimination, and I find it helps to think of the components in the categories laid out above. E.g. if you are having a problem that is likely on the consumer side, you could disconnect all the nice-to-haves and see if your problem persists. If it disappears (e.g. by pulling all the relevant fuses - easy to do), you may not have fixed the problem, but at least you are not stuck anymore.

Before moving on to finding faults, just a few more basic words of explanation on each of the important component groups:

Ignition system

The ignition is the definite must-have on the consumer side. At minimum it includes the CDI, an ignition coil and a spark plug. In addition there will obviously be a bunch of cables, and maybe some other components. In a nutshell it goes something like this: The CDI determines when the spark should fire, i.e. when exactly the fuel/air mixture in the cylinder should be ignited. Ignition timing depends on several factors, e.g. the revs, so this part tends to be a complex one that when broken will probably have to be replaced (unless you know exactly what you are doing). When the CDI triggers a spark, the signal is first transferred from the CDI to the ignition coil. The purpose of the coil is to transform the 12V from the CDI to several thousands of volts, which are required to create a suitable spark for the engine. The spark plug then is the last missing piece: the high potential from the coil causes a spark to jump across the gap at the end of the spark plug, which in turn ignites the fuel in the engine. Also more or less part of the ignition system are a bunch of switches, such as the kill-switch, side-stand switch, etc that can break the circuit and prevent ignition.

- pic will follow –


In case you don’t have a kick-start, you somehow need to get the engine going. Bump-starting aside, that means that you will want to have a functioning e-starter. As far as electrics go, the starting system is fairly simple: triggered by the starter button, the battery feeds a small electric motor. Via a small transmission/clutch system, this motor turns the engine so the spark plug can do its job J

- pic will follow –

Charging system

If we were to only have a battery, an ignition system and an e-starter, we would sooner or later run out of energy. Somehow we need to replenish the energy that the ignition, the starter and all the other gadgets from lights to accessories consume, and that’s what the charging system is for. Here we have three basic components: an alternator, a rectifier and a regulator. The alternator/stator is basically the same thing as an electric motor, it is just operating the other way round. Turning a coil in a magnet (or magnet in a coil) induces an electrical current. The fly-wheel which is connected to the crank shaft and thus to the engine does exactly that, i.e. as long as the engine is running, the alternator produces an electrical current. This current is an alternating current (AC) and its magnitude depends on the RPM of the engine. As our bike electrical system and its battery require direct current (DC) of a more or less constant power we need two more components. The rectifier functions a little bit like a valve by letting electricity pass only in one direction, which will convert AC into DC. The resulting direct current still is neither smooth nor independent of engine RPM, hence there is a regulator that controls the output of electrical power to prevent damage to the bike if you are racing too fast and the alternator produces too much power for the bike to handle. That’s why the regulator looks a bit like a radiator – excess energy is dissipated as heat. By the way: on many bikes these days, the regulator and rectifier will be one component.

- pic will follow –

Starting problems - where do I look?

Coming soon …

Battery and charging problems + diagnosis

Coming soon …

Adding accessories – what to keep in mind

Coming soon …

Spares, tools and aids for your toolkit

Coming soon …
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Old 18 Jun 2011
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thank you for taking the time to do this, found your talk in Germany very instructive.
Andy L

From the midnight sun to the silk & rhubarb roads, 2014
I am not an adventure rider, just a biker that has adventures.
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Old 19 Jun 2011
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This is an excellent thread - wished I could have been at the HU meeting to see your talk but currently in Vladivostok heading west back to UK.

I am looking forward to the rest of your presentation as shown in the "coming soon" headings.


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