46 replies to this topic

[FastEHHolden]

Umm you guys didn't get too many wedgies at school did you?

You are showing your nerdy sides.

[Dr Terry]

Hi devils.

I agree with you to a point, I use the word 'wire' for the small stuff & 'cable' for higher current (thicker) stuff, but where is the cut-off or is that just too pedantic.

Dr Terry.

[davelh]

wire is a single core (as in building wire) and cable is two or more cores in a sheath (twin and earth, etc)
no body told me i was a nerd, oh well, ill go sit on the pile of money i make being a nerd
cheers
dave

[Toranamat69]

I use nickel antisieze and S/S bolts for my earth connections - I have never had an issue with poor earth connections.

The actual device for measuring resistance of a join is a "ductor" - Basically just a device which does the current/resistance measurement as described above, just all in one test meter - has 2 pointy probes so you can make sure you get a good connection through the surface corrosion either side of the joint you are measuirng. (Todays useless bit of trivia).


M@

[davelh]

can i have one as well
hotrodder, if you dont understand stuff - just ask
sometimes explaining something in a non technical manner can cofuse people even more
cheers
dave

[Dr Terry]

Hi Guys.

I'm with devilsadvocate on this one.

What's wrong with serious in-depth technical discussion about a small item that someone thinks is trivial. I enjoy a bit of mental exercise, aside from just answering questions.

OK, maybe a simpler version to answer a question from a newby, but I think we need more guys like devils' on this forum.

Dr Terry

[tinkers]

Dr Terry has made it to Devil's chrissy card list?

[davelh]

All i want is a bloody christmas card
its the only reason im here!!!
cheers
dave

[dattoman]

OK
Since you asked nice we'll put you on the gmh-torana official Xmas card list (cards not printed yet)

Just forward your postal address to torana (@) hi-powered.net and you might just get one

[tinkers]

wait til christmas and see if santa brings one hehe

[davelh]

[Dangerous]

Boy, the things that happen when I go on holiday for a few weeks - I miss out on all the fun stuff

Going right back to the start, ALX76 has exactly the right attitude when if comes to earthing, ie that just about perfect is only just good enough. Even a cheapy $20 digital multimeter can be a big help when tracking down bad earths, or even ones that are OK but could be improved upon. I have a $600 digital meter that I hardly ever use unless I need really accurate readings, and a $20 Jaycar autoranging unit that tends to go everywhere and get used for most things, as it doesn't really matter if it gets crunched.

A couple of things to highlight when working with car electrical systems -

12 volts is not really much to play with, so every 0.1 volt you can 'save' by improving an earth is time and effort well spent, especially on the big current draw items such as starter motors, headlights and big stereos. To a lesser extent, but still important, even ignitions and engine sensors/gauges can benefit from saving that 0.1 volts too.

Cars of the Torana vintage are not really designed to be really good earths, as far as their chassis/bodies go, so don't assume for example that a good earth in the boot area is going to translate into a good earth up in the engine bay somewhere - always check voltage drop under load, and go looking for what's causing the drop. If you've got a boot mounted battery for example, measure the battery voltage with the headlights on, then go and measure the voltage at the headlights themselves - you might get a nasty surprise on how much less it is. Original Torana earthing points and cable sizes (or is that wire sizes? ) are pretty average as well, and can always be improved upon. Torana dashboard and radiator support (for teh headlights) earthing for example is woeful, and very easily improved.

As has been said, when checking earths by measuring voltage drop, it's important to have a reasonable current flowing through the earth. You can measure the 'static' resistance of the joint with no current flowing, but quite often it's the high current flowing through the joint which will cause an increase in resistance - in other words, your meter set to resistance range might only measure 0.1 ohms resistance or less on a 'cold' joint, but fire up a few loads to get current flowing through the joint, and the same meter set to volts range might measure a voltage drop that equates to a significantly higher resistance.

Every part of the circuit is going to contribute something to the resistance, including the wire itself, fuses, switches, connections and relays. If we pick on the poor old headlights again, one way to thoroughly check the whole circuit is to firstly measure the voltage drop from battery earth to headlight earth, and then try to minimise it. From there, measure voltage between the battery earth and all parts of the +12V circuit, ie from the battery +ve, fusebox, headlight switch, firewall connector (if the loom has a plug & socket arrangement), relays if fitted and then at the headlight itself. Pay attention to the larger voltage drops first, and you'll probably end up with significantly brighter headlights without having to spend money on better globes.


As far as getting technical on the forum, well, I do that too from time to time. HR, I know DA tends to get stuck into the detail from time to time, but from what I can see, he always tends to start out explaining in simple terms, but does get into technical detail if the discussion is still confusing or misleading. I don't think that's a bad thing, as long as everyone can dig the right answers to the question out from somehwere in the thread. I'd rather see that than a thread slow down and stop while it still had incorrect or misleading information in it.

[TerrA LX]

^cheers