canbus system

Could someone please explain to me how the canbus system works , specifically how it manages to carry high current through such small wires without melting them ? re the high power to the halogen headlamp .

CAN stands for Controller Area Network, which doesn’t really help.

In simple terms, the CAN network is a robust, data-only network, which passes information between nodes. The nodes might be a TFT dash panel, switches, lights, heater, radio, GPS, satnav, echo sounder, radar, wheel speed sensors, etc, dependent on the vehicle in question.

They are widely used in boats and planes, and all road vehicles, afaik.

The data wires are two, very low power wires, typically at 3.5 Volts or thereabouts, and carrying no more than a few tens on milliAmps.

The power for the lights, heater, whatever, is carried by separate cables, not the bus, though thongs like switches might be able to run from a separate +12V that is typically run through the CAN harness, along with a ground wire.

You might ask “if you have to have separate power and data, why bother?”

Main reasons are that you can have much shorter power cables, which saves power and copper, and you can share data around the vehicle, and of course, with diagnostics.


A good summary Simon. I work for a Tractor manufacturer and our products have lots of interconnected ECU’s, using CAN to talk to each other.
The biggest benefits are data-sharing and automated/distributed control. For example the engine ECU puts out its speed, fuel usage, boost pressure etc onto the network, and any bit of software in a different ECU that needs the information can access it. Similarly the engine ECU can receive commands from multiple sources such as throttles, cruise control, headland sequence control, traction control etc. and decide what to do based on priority set in software.
I suppose the negative aspects relate to the average fitter/mechanic being able to diagnose problems, although understanding the principles is now included in training.

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Thanks simonD and ranton-rambler for your replies , I’m still confused about the heat in my v7 850 e5 special’s headlamp , the wires to the headlamp are VERY thin ??

is the regulator positioned in there ? they get warm
or if its an LED light. the drivers can get bit toasty
something to do with keeping the smoke in !!

One other thing to consider is that it may be thinwall cable. That is the copper core has a very thin insulator. So it appears thinner but can carry same current. Eg 0.5 mm2 core with a thinwall insulator has an od of anout 1.5mm and can carry 11amps => 132watts in a 12volt system

thanks , no it’s a standard h4 halogen bulb , it get REALLY HOT ! I don’t understand how the really thin wires cope ?

H4 halogen is 55/60W (not supposed to use both together!) so around 5A.

This suggests that 0.85mm diameter would be sufficient to limit the temperature rise to 75C which is very hot to touch, but acceptable in that it’s well below the limit for the insulation.

Please note that anything that is CAN controlled will have some sort of electronics between the wiring and the load. At minimum a chip and some passive components.

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Rec Reg is screwed to front downtubes behind forks, so gets full wind blast. :grin:

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Yes I would expect this is the modern ‘thin-walled’ wire. The insulation is thinner to better allow heat dissipation. That’s the explanation I’ve got anyway.

Just read this again, where or how are you feeling this heat? I assume you’re feeling it.

Hi Mike , thanks for your reply , it’s the headlamp glass and shell [ plastic ! ] that get REALLY hot even after a run , you’d think the air flow would cool it down but it doesn’t ??
Apparently the H4 halogen 55/60w is the standard bulb unlike the v7 850 stone !
You have an 850 special , how warm/hot does your headlamp get ?
regards Derek

To be honest I’ve never felt it, (oo missus) never had a need to check for heat. I’ve now had the bike 2.5 years, nothing’s melted yet. Or as far as I know. Also it’s got a Philips X-treme H4 in there. If that makes any difference.

Dip beam would be 55 Watts, and that will be hot.


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Thanks for your reply Mike , my next question to you would have been to ask what bulb you had in your bike ! Perhaps the next time you run the bike you might check the temperature of glass and shell ? , it doesn’t take long to heat up !

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Bear in mind that approx 70C is too hot to touch, which is not very hot at all in “engineering terms.”


Gents, Just a point of note. The installation instructions usually state that the glass of halogen bulbs should not be touched by fingers, as the grease from one’s skin can cause hot spots which will weaken the structure. The exceptions are double glassed bulbs. Headlight bulbs are not usually double glass. Just offering a reminder.


I will try that, if I remember.

The first time I start it I usually check all the lights (you get into a habit of doing this if you’ve ever had a Ural :smile: ) put hand in front of headlamp to make sure it’s on, usually feel some heat then. Unless I’ve got a glove on.

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