[worldo]

have searched but couldnt find what i needed so thought id ask.

have set some spotties up on a roll bar and have wired them like this



but they arnt working. can you ground them on there mounting bracket things?

and can you double the wires up like i have done?

cheers ricky

[mnemonix]

Are they a solid earth? ie: bare metal contact?
Run a wire to bare chassis or battery V- to check.

[SuziBlu]

IMO its best to run earth to the battery, quite a drain on the earth leads supplied on the vehicle, and can lead to dramas with all the earth leads, and wiring down the track.

[worldo]

ok sweet. the old man told me to earth it this way but ill swap it round tomorrow cheers guys

[royce]

Running earth to battery is bad, its just more voltage drop, instead put a bigger earth on the battery to body connection

do you have a test light? start looking to see where you have power and where you dont, if they all dont work its likely the fault is in a common place

[worldo]

i have dual batteries, should can i earth it to the second battery would this help the voltage drop royce?

[SuziBlu]

royce wrote:

Running earth to battery is bad, its just more voltage drop, instead put a bigger earth on the battery to body connection

Royce, I know you are a wiring guru, but to me this makes no sense. Please explain how there is voltage drop from wiring to the battery, but to the body there is none.

Seems an oxymoron to me.

Im not questioning, but asking.

In my understanding, its one and the same, but by wiring to the battery, as auto lekkys do, is eliminates the need for greater earth leads.
Mind, I am a great believer in dirty great big earth leads.

I really am interested.

[JrZook]

SuziBlu wrote:

royce wrote:

Running earth to battery is bad, its just more voltage drop, instead put a bigger earth on the battery to body connection

Royce, I know you are a wiring guru, but to me this makes no sense. Please explain how there is voltage drop from wiring to the battery, but to the body there is none.

Seems an oxymoron to me.

Im not questioning, but asking.

In my understanding, its one and the same, but by wiring to the battery, as auto lekkys do, is eliminates the need for greater earth leads.
Mind, I am a great believer in dirty great big earth leads.

I really am interested.

Voltage drop is proportional to the resistance of the wire. Resistance of the wire is proportional to the length and cross sectional surface area of the wire. Car body has a huge cross sectional area to length ratio therefore minimal voltage drop and the wire from the battery to body is super short and thick so minimal drop there.

[SuziBlu]

Ahh, yes, that I can understand.

I use big wire for everything, so voltage drop is a non entity on my side of the fence.

My starter motor leads are 8mm very fine wire welder lead. Bout 11mm outer Dia.

So too is my earth leads.

Every wire is far far heavier than required.

[royce]

yeah like jnr said, the body is like a big fat bit of wire and a nice massive short earth lead will pass a lot of power to the battery with little voltage drop

A lot of my car is wired with Earths running back to the battery, it wasnt until I started designing the headlight looms and were doing calculations of voltage drop on given wire over given distance that I realised that while fat cable does limit it a bit its better to earth as close as you can and put the extra cable into fatter supplies

Of course the downside to this is you are introducing more mechanical joints into the circuit, this is where things can really wrong with connections that are dirty and or loose causing more drop than even skinny wire will

[SuziBlu]

So, from this, I gather, dirty great big very fine wire are the go, regarding voltage drop.

The leads that I have run are from a 300 amp, 3 phase welder, and trully, the difference in starting capacity is chalk and cheese, the original wires were like, rrrrurrr, rrrurrrr, now, they are, broom.

One to positive side of starter, one to negative, one to earthing the body.

It was you who started me on this Royce, and, its so far superior.

I fully understand what you guys are talking about now.

To circumvent this drop, use big, very fine wire leads.

As I understand it, electricity does not travel thru wire, rather, it travels along the outside, and so, a 5mm, 20 wire lead will not pass as much power as a 5mm 200 strand wire.

??

[royce]

I dunno about the whole strands thing, there is lots of talk of it but its never really mentioned in official calculations, more core finer strand resists vibration and bending a lot better though

does your cable still have its mm2 size printed on the side?

[dano_mung]

Finer strands have 2 advantages.
1. more flexible
2. greater cross sectional area to physical size ratio

Though its harder to solder and usually more expensive (more copper = more $$$)

[SuziBlu]

Nothing printed, but, 8mm dia has a cross section of just over 50mm2

D x Dx 0.7854

Electricity does travel along the outside not inside, so, same dia, one with very fine wire, compared to one with heavy duty, so to speak, the fine wire will carry far greater amperage.

This is why welding leads are such fine wire, regardless of the fact that they are better for resisting breakage thru flex.

Low voltage, high amperage.

I do not have the capacity to explain this, but, I can get my mate, an electrician to explain if needed.

[ajsr]

dano_mung wrote:

Finer strands have 2 advantages.
1. more flexible
2. greater cross sectional area to physical size ratio

Though its harder to solder and usually more expensive (more copper = more $$$)

I was told by a bloke I used to know that designed electric motors and other techy shit( mates father), that it has something to to do with the surface area of the individual strands , fine stranded wire more surface area in total and therefore higher carrying capacity.and the power is carried on the surface of the strand.
this conversation WAS about 20 years ago and a lot of brain cells have died since then so dont hold me to this

[SuziBlu]

dano_mung wrote:

2. greater cross sectional area to physical size ratio

This is very true, a fine wire, 10mm flex will have a greater mass than the same dia, course wire, far less air between each strand.

For instance, I was doing some calcs on stability on a boat, it was needing G moved down, I told the boss, he got some lead pellets, 1.5mm dia shot.

When I weighed this, it had a SG the same as solid steel, not of lead. The SG was from memory, remember, lead, of around 7.8, not 11, too much air space between the pellets.

[dano_mung]

Yeah I'm not disagreeing with you assertions, i'm just saying those are the advantages.

Economy comes into it at some point, for a vehicle we're only talking 3-4m maximum span, so finer stranded wire is fine, but for longer spans it becomes expensive fast.

[TheOtherLeft]

This is all good if you have access to welding wire or the $$$ to buy lots of it.

If not then using the body is the more economical way to go.

[royce]

The common formula I have found for voltage drop

2*length(m)*current*0.017(this is a factor for copper material)/cable size(mm2)

Doesnt mention strands, ive only read about the travelling along the surface in audio stuff, if anyone can find some good links about it i'd like to read em

[royce]

http://en.wikipedia.org/wiki/Wire

Quote:

Solid wire, also called solid-core or single-strand wire, consists of one piece of metal wire. Stranded wire is composed of a bundle wires to make a larger conductor.

Stranded wire is more flexible than solid wire of the same total cross-sectional area. Solid wire is cheaper to manufacture than stranded wire and is used where there is little need for flexibility in the wire. Solid wire also provides mechanical ruggedness; and, because it has relatively less surface area which is exposed to attack by corrosives, protection against the environment. Stranded wire is used when higher resistance to metal fatigue is required. Such situations include connections between circuit boards in multi-printed-circuit-board devices, where the rigidity of solid wire would produce too much stress as a result of movement during assembly or servicing; A.C. line cords for appliances; musical instrument cables; computer mouse cables; welding electrode cables; control cables connecting moving machine parts; mining machine cables; trailing machine cables; and numerous others.

At high frequencies, current travels near the surface of the wire because of the skin effect, resulting in increased power loss in the wire. Stranded wire might seem to reduce this effect, since the total surface area of the strands is greater than the surface area of the equivalent solid wire, but in fact a simple stranded wire will not improve skin effect since all the strands are short-circuited together and still behave as a single conductor. A stranded wire will have higher resistance than a solid wire of the same diameter because the cross-section of the stranded wire is not all copper, there are unavoidable gaps between the strands (this is the circle packing problem for circles within a circle). A stranded wire with the same cross-section of conductor as a solid wire is said to have the same equivalent gauge and is always a larger diameter.

However, for many high-frequency applications, proximity effect is more severe than skin effect, and in some limited cases, simple stranded wire can reduce proximity effect. For better performance at high frequencies, litz wire, which has the individual strands insulated and twisted in special patterns, may be used.

[JrZook]

So the traveling along the surface is only really got to do with high frequencies (audio not DC) and even so it will still act as a single strand as they all touch each other anyway.

The only real advantage with the finer strand wire is its flexibility.