Bob C
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| posted on 25/2/06 at 06:15 PM |
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Chassis earth connections
I've just welded 3 M6 bolts to my chassis for earth connections (front rear and middle).
I couldn't think of a better reliable connection. I'd sort of thought I'd use rivnuts or something but when it came to the crunch
decided I couldn't trust them to give a good reliable high current connection.
Unfortunately this is AFTER chassis/body had been painted. . . . .
So if you're building a chassis - think about wiring too. And if anyone's got a better system I'll just go and bash my head against
a brick wall.....
cheers
Bob
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COREdevelopments
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| posted on 25/2/06 at 06:59 PM |
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hey bob. im at that stage to and was wandering the same thing i need earth points but was wandering about good earthing, i would like to use rivnuts
as they are much simplar but they are aluminium. i think you can also get brass ones which would be even better as they are more conductable, me
thinks???
hmmmmm what to do
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MkIndy7
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| posted on 25/2/06 at 07:08 PM |
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That brick might hurt!
You could always tap the Chassis, then this can be done after powfer coating and wherever you find nessacery,
kinda a step up from how the big car companies do it with self tappers!
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flak monkey
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| posted on 25/2/06 at 07:10 PM |
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Aluminium is more conductive than brass. Infact its what overhead powerlines are made of (the sheath is reinforced with steel so the cables done break
under their own weight).
Incidently silver is the most conductive metal, contrary to popular belief!
David
Sera
http://www.motosera.com
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Bob C
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| posted on 25/2/06 at 07:18 PM |
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Any contact of dissimilar metals is asking for corrosion near the join. Add to the misery by whacking starter motor currents through it - I guess you
see why I ended welding bolts on. Toyed with the idea of welding nuts on - this would be less obtrusive but easier to get wrong (nut getting b*ggered
by the welding - bolt bottoming out when making connection - more likely to strip thread etc)
I just wanted to make the point to think about this when doing the chassis - not a year later!!!
Bob
PS in industrial electrical design we're taught not to rely on electrical contact between a bolt and it's nut (if you know what I mean ..
from thread to thread)
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MkIndy7
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| posted on 25/2/06 at 07:27 PM |
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quote:
Originally posted by Bob C
PS in industrial electrical design we're taught not to rely on electrical contact between a bolt and it's nut (if you know what I mean ..
from thread to thread)
Whats the difference between a nut and bolt and a nut on a stud then? which is how industrial and 3phase motors etc are wired up
I can see no difference other than electrical threads tend to be a finer thread (BA)
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paulf
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| posted on 25/2/06 at 07:28 PM |
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I just put a heavy duty flexible earth strap between the engine mountings , one end under a mounting bolt on engine and the other to a 10mm bolt on
the other end of the mounting. I used lugs onto any convenient chassis bolting point for the rest.
Paul.
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Bob C
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| posted on 25/2/06 at 07:29 PM |
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In yer 3 phase motor the studs are on an insulating block - the electrical connection you rely on is between the flat bits on the rings on the wires,
the inderside of the head of the bolts etc. You obviously do get good continuity between nut & bolt via the thread, you're just not allowed
to rely on it. It's a major factor in the design of earthed housings - a screwed on metal lid with a rubber gasket under is not classed as
earthed unless there's metal to metal contact somewhere OTHER than through the screws!
cheers
Bob
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JoelP
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| posted on 25/2/06 at 07:34 PM |
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i welded bolts on too, its by far the most perminant and conductive way of doing it. You can do it before powedercoating and then protect the threads
with a few nuts, can be easily tidied up afterwards.
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MkIndy7
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| posted on 25/2/06 at 07:39 PM |
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Tru, suppose you could screw a stud into the chassis, followed by a lock nut and then put the electrical connections ontop of that. (think thats what
we did).
Although the only high amperage connection in a car of our type is the starter and thats wired str8 to the battery!. There's only maybe an
electric fuel pump that takes any siginificant current and I suppose the headlights, the rest is well under 10A (no Elec windows and heated rear
screen to worry about  )
[Edited on 25/2/06 by MkIndy7]
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Bob C
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| posted on 25/2/06 at 08:04 PM |
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Yeah - I'm doing a BEC so my electrics are a bit more eclectic... no alternator, I have a separately mounted rectifier/regulator, plus
I've got an electric reverse to consider.
At the back of the car the lights are on the plastic bit so I need somewhere to ground them, and the tank (protect from static & ground for the
fuel gauge sender)
cheers
Bob
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RazMan
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| posted on 25/2/06 at 08:15 PM |
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I try and make sure that all of the earths from lights, horns, relays etc come back to just a couple of earth points (welded bolts for me). I have one
central earth stud under the dash and one in the engine bay (also connected to the neg battery terminal) This makes the loom a little fatter but
minimises any resistance problems and makes fault finding a lot easier.
If you drill & tap a chassis member it is worth remembering that you might only have 2mm of contact area to rely on for a good connection. Add a
little time induced surface corrosion and it soon makes a high resistance connection - and a nightmare to fault find.
A welded M8 bolt and loads of ft/lbs is the best method IMO 
[Edited on 25-2-06 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Nick Skidmore
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| posted on 25/2/06 at 08:21 PM |
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'Aluminium is more conductive than brass'
Sorry it's not, it's used for a lot of overhead stuff becase it's cheap and lightweight.
Your electricity company won't let you use ally in your house yet they will sometimes use it to bring your supply in, usual double standards.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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COREdevelopments
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| posted on 25/2/06 at 09:35 PM |
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thats what i thought. a m8 nut tacked to the chassis should do the job, even a brass riv nut along with a good coating of greese to protect it.
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flak monkey
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| posted on 25/2/06 at 09:49 PM |
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The reason you arent allowed to use ally wiring in your house is because Al2O3 (aluminium oxide) doesnt conduct electricity, which means that
junctions in ali wiring systems can get very hot if they are not made under special conditions. AL2O3 is formed instantly on the surface of aluminium
when it is cut. The only way to exclude AL2O3 from an electrical joint is to solder it, still not perfect, but better than an open joint.
Most conductive metals in order are silver, copper, gold and aluminium. Assuming similar cross sections. Aluminium is the best conductor per unit
weight of all metals.
Cheers,
David
Sera
http://www.motosera.com
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caber
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| posted on 25/2/06 at 09:50 PM |
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Reason Ally is not used in house and commercial wiring over here is that when it goes it tends to burn rather than melt. They did use ally in the USA
for a while until it had set hundreds of buildings on fire including a couple of Hotels in the 70s when rather a lot of people got fried so they
banned it as well. It can still sometimes be used for high current busbar risers.
I was thinking about welding nuts on with the chassis tube drilled underneath to allow reaonable length bolts. Unless well protected studs can easily
get bashed making it difficult to thread nuts on.
Caber
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wilkingj
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| posted on 25/2/06 at 10:01 PM |
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quote:
Originally posted by Nick Skidmore
'Aluminium is more conductive than brass'
Sorry it's not, it's used for a lot of overhead stuff becase it's cheap and lightweight.
Ally is NOT as good a conductor as brass, Sorry..
We used lots of ally cables on BT in the 70's & 80's. Within 10 years it was all ripped out and replaced with good old copper. It was
a maintenance liability, even after we had developed special jointing techniques with jelly filled crimps.
I just welded a "L" shaped bit of Angle iron to the chassis with a hole in for my earth point.
DONT use Ally rivnuts, you get dissimilar metals corrosion. I should know... I own a Land Rover (Ally and steel together!).
A bolt welded to the chassis is fine, or even a nut welded to the chassis, or a Lug with a hole like mine. ALL are OK, Make sure you have bare metal
for where the Ring tags go so you get a good electrical connection. Then cover up with a good dob of vasseline, grease, or Waxoyl to stop it rusting.
Thats what I do.
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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David Jenkins
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| posted on 25/2/06 at 10:13 PM |
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I welded a lump of steel into my chassis, near to the battery location. This had a M8 threaded hole in it. When the chassis was plastic-coated I
asked the man to tape over this bit, so that it was still bare metal when the job was finished. This now has a M8 bolt in it, which holds the main
battery and engine earths,
David
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suparuss
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| posted on 25/2/06 at 11:33 PM |
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RS do special copper rivets with a spade connection for earthing.
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Nick Skidmore
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| posted on 26/2/06 at 11:25 AM |
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Ally is not as good a conductor as brass (copper / zinc alloy but mostly copper) as it does not have as many 'spare' electrons in
it's outer shell.
Ally is in fact not a metal it's a semi-metal a bit like silicon, according to the periodic table.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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MikeRJ
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| posted on 26/2/06 at 03:23 PM |
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The most conductive brass alloy I could find on aalco.co.uk is CZ121 with a resistivity of 62 nano-ohms/meter (worst 90nano-ohms).
The least conductive aluminium alloy I can find on there is 5083 with a resisitivity of 58nano-ohms/meter. Most alloys are between 20-30
nano-ohms/meter.
So looks like generaly aluminium is more conductive than brass
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wilkingj
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| posted on 26/2/06 at 09:16 PM |
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My earth Lug. Appologies about my Welding... My other name is Mr Blobby
The hole is for the steady bar to the engine. rubber bushed dumbell sort of thing.
 
Earth Lug (My Welding!!!)
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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