snowy2
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| posted on 5/7/12 at 11:12 AM |
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not getting at you.........banter is what clarifies a point to a novice wiring diagrams seem to show wires where there are none. i have been asked
where the earth wire on a starter connects to. the understanding that it earths through the engone is not there. i am mot to know your competence by
your posts any more than you would for me.
[Edited on 5/7/12 by snowy2]
sometimes you are the pigeon, most of the time the statue.
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coyoteboy
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| posted on 5/7/12 at 12:27 PM |
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quote:
Even on fairly modern cars a typical circuit will have an unfused switch and a fuse to the consume
Almost all modern car electronic switch systems are digital - i.e. they're usually 3.3/5v and directly connected to a micro, from the micro, and
the micro is a larger unit that is fused. Your headlight switches rarely have any non-digital connection to the headlights any more, they're
based on a super-low-current switch to a processor that determines what gets communicated to the headlight control unit via CAN, which is seperately
fused and does what it desires. Hence most modern switches are rated to milliamps and sub 12v and if you shorted them they'd do nothing as their
switching lines are protected and current limited inside the control unit.
As for looms not failing, you tell that to anyone with a peugeot/citroen from about 1995 until about 2008. You tell that to several of my family
members who've had massive electrical problems with BMWs due to loom failure. Or my friend with a mondeo who lost all power cruising down the
motorway because of fatigue in one of the smaller sections of loom. I can't believe anyone with experience of relatively modern cars would take
that stance to be honest, im a bit shocked!
Loggyboys maks the most sense.
Fuses need to be at source or as close as physically possible or they do no good. There's not strictly a need to run one fuse per switch, you
could have a single fused switch feed for all switches on your dash quite easily but clearly it's sometimes logistically more sense to fuse
individually than go round the car back to the main board.
DIY Wiring looms fail more frequently than OEMs because generally people are not that good at making them and cut corners (and rely on random internet
advice rather than proper training  ).
Has no-one else ever had a fuse fail to HR on the main contacts, heat up, melt and then short the switch feed? Good a reason as any for me to use a
fuse on the switch.
[Edited on 5/7/12 by coyoteboy]
[Edited on 5/7/12 by coyoteboy]
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rachaeljf
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| posted on 5/7/12 at 01:37 PM |
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Splendid! I'm off to buy shares in Rio Tinto and a few Chinese automotive fuse makers. Then I'll stand by my 15 yo Audi with a fire
extingusher as it's going to go wrong eventually! 
Nice red herring with the CAN reference too!
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coyoteboy
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| posted on 5/7/12 at 03:47 PM |
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quote:
Originally posted by rachaeljf
Splendid! I'm off to buy shares in Rio Tinto and a few Chinese automotive fuse makers. Then I'll stand by my 15 yo Audi with a fire
extingusher as it's going to go wrong eventually!
Not really necessary, the advice was just to fit the correct number of fuses in the right places. Pretty simple and cheap as chips. Oh, and the reason
you don't have to stand by the Audi with a fire extinguisher? Because it's properly designed with the correct protection systems in place
quote:
Nice red herring with the CAN reference too!
? What are you on about red-herring? There's no red herring involved here. You have two (or more) low voltage, prtected, low current switched
systems seperated by CAN. Each appropriately fused. The switches don't see remotely high currents.
[Edited on 5/7/12 by coyoteboy]
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Irony
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| posted on 5/7/12 at 04:12 PM |
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quote:
Originally posted by snowy2
not getting at you.........banter is what clarifies a point to a novice wiring diagrams seem to show wires where there are none. i have been asked
where the earth wire on a starter connects to. the understanding that it earths through the engone is not there. i am mot to know your competence by
your posts any more than you would for me.
[Edited on 5/7/12 by snowy2]
Didn't wish to start a argument to be honest.
I agree with the above post. This forum is the best place for information I have found and I simply couldn't have built my car without it.
However sometimes people on here don't realise how little some people know when it comes to electrics. Two years ago when I started my build I
had a 'lightbulb' moment of clarity when I realised that the negative side of the battery is connected to the chassis! What a great
idea!! Then I became confused because people use the term 'earth' for the same thing. I'd been used to house electrics where earth
is a green/brown wire in a plug.
To you guys this may all sound very simple and I may sound thick for saying the above but it's true.
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Irony
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| posted on 5/7/12 at 04:13 PM |
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Thanks for all the replies guys! I think I have it now!
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coyoteboy
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| posted on 5/7/12 at 04:21 PM |
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quote:
To you guys this may all sound very simple and I may sound thick for saying the above but it's true.
Not at all, everyone starts somewhere - you just have to ensure you get good advice which can be tough when people on forums also think they know the
answer and in trying to be helpful give you bad advice. I like forums like this because you can often get access to people who design these things day
to day without paying consulting fees, as well as the banter
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rachaeljf
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| posted on 5/7/12 at 04:55 PM |
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quote:
Originally posted by coyoteboy
? What are you on about red-herring? There's no red herring involved here. You have two (or more) low voltage, prtected, low current switched
systems seperated by CAN. Each appropriately fused. The switches don't see remotely high currents.
[Edited on 5/7/12 by coyoteboy]
Trying to figure out how CAN systems got into a discussion about a basic switch-relay-load circuit!
Anyway, good banter, a good day was had by all and Irony has nipped out to buy a load of fuses and wire!
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coyoteboy
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| posted on 5/7/12 at 05:32 PM |
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Because someone, somewhere said relatively modern cars still run un-fused high load switches for such things and they don't, pretty much
everything is on the CAN! CAN is the bane of my life currently as I'm working on the design of just such modules (And starting to wish I
hadn't offered to do it for free!)
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snowy2
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| posted on 5/7/12 at 09:40 PM |
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yeah the new can bus system designed to save money......at the factory. But a nightmare and expensive out in the real world when it goes wrong.
luckily not something your average kit builder is likely to be looking at......
[Edited on 5/7/12 by snowy2]
sometimes you are the pigeon, most of the time the statue.
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