Basic electric Q...or is it?

Michael · Post by **Michael** » Sat Jan 13, 2007 4:54 pm

General Q here....why can car electrics be so difficult for the manufacturers to get right? Most cars seem to have problems at some point.

It just seems a bit strange cos the circuits must be so simple in relation to those in the rest of the world of technology.

Is is simply wire fatigue because of the car constantly bouncing around and the metal in the wire breaking?

Robin..you'll know!

Rich H · Post by **Rich H** » Sat Jan 13, 2007 5:04 pm

Cheapness probably. Had a 406 coupe for a year, fantastic car but the electrics (That means everything!) were shoddy. To the extent that the owners club recommended removing some of the most crap connectors and soldering all the joints permanently!

Your right though, the electric involved are generally the push button=move mirror type. My watch is more complicated and runs for ages on a tiny battery while withstanding being knocked about daily.

bertieduff · Post by **bertieduff** » Sat Jan 13, 2007 8:24 pm

It's a pretty hostile environment some parts have to endure- constant vibration, condensation, water, salt & other corrosives, large temperature variations, ageing etc. Add lots of separate components, joints moving parts etc...

Nothing that can't be soved, but as a car is designed for obsolescence ayway the manufacturers ain't gonna spend the money making some bits last forever I suppose.

Considering how much more complex car electrics have become in the past couple of decades I think they're surprisingly reliable overall.

(Lotus excepted

)

robin · Post by **robin** » Sat Jan 13, 2007 9:38 pm

Exactly. Modern cars (i.e. stuff built in the last couple of years) are shifting towards primarily CAN bus architectures, where there are just a couple of circuits in the car and all the peripherals (lights, 100's of motors that control everything from your seat position to the head light aim, wipers, etc., etc.) are all controlled by local microcontrollers attached to the bus. Then when you press the head light on switch, a code is sent down the bus and the head light controller recognises the code and switches the light on (or, more likely, finds a very good reason why it shouldn't and says "no" instead!).

Most of the problems are caused by loom connectors that pass reasonable current (all the motors, lights, injectors, etc.). As the connectors vibrate they can lose contact a bit - this causes an increase in resistance in the junction. A similar result can happen if any moisture gets in there (and eventually it always will). At that point the resistance causes a bit of heat to be generated, which makes the resistance worse and eventually you get connection failure.

The copper strands in the wires can fracture also, either from vibration or heat or both.

It's a hard problem to solve, that's for sure - hence the bus architecture - it might be expensive but we only have a couple of circuits to route and protect rather than 100's that you would need for a modern car.

Cheers,
Robin

Michael · Post by **Michael** » Sun Jan 14, 2007 8:30 pm

Is the bus a processor where lots of circuits are held in compact form by any chance?...a microchip basically?

robin · Post by **robin** » Mon Jan 15, 2007 9:14 am

No, the bus is a long single (well actually dual, but that's a minor detail) cable that stretches right around the car. Then there are some rules on who can place data on the bus and when. The controllers sit inside the peripherals are microprocessors that obey the rules of the bus.

Go look up CAN bus on 'tinternet if you want to know more about how it works (wikipedia probably has several good pages on this).

Cheers,
Robin