Earth Cable getting hot

[river]

Hi,

Well the best way is to put a jumper lead form the -ve terminal of the battery and clamp it onto the engine block somewhere and see if it makes a difference.

The main earth cable from the battery consists of a bunch of copper strands. If some strands are broken, this will limit how much current it can pull and therefore I would expect to have a localised hot-spot in this area. However, as the entire cable is getting warm then I assume it's pulling too much current, which could be a starter motor issue.

Although these cables are getting old, I can't see it magically increasing resistance and reducing it's load carrying capacity unless it's been bent and twisted to the point where some strands have been broken, or it's oxidised to the shithouse along it's length.

seeyuzz
river

[Mr Ed]

I disagree with you on this. Per sqmm copper is in fact the better conductor, hence the reason that copper is used in most instances for power cabling.

Per cross sectional mass however, aluminium is the better conductor, which is why it is used in long aerial cables where weight on the power pole is an issue.

Apart from that, I agree that the battery to body cable is fubar and should be replaced.

Cheers, Owen

Copper is used because it is cheaper and more ductile

If aluminium is a better conductor, its a better conductor. Cross-section area has nothing to do with it.

[DoctorDubb]

Im with Oman on this one. Looking at electric resistivity at 293*K:
Copper: 1.7 × 10^-8 Ohm M.
Aluminium: 2.82 × 10-8 Ohm M.
Therefore as electrical resistivity = R A / L
R is the electrical resistance, L is the length of the specimen,A is the cross-sectional area. It does rely then on cross-sectional area. And it means that Copper is the better conductor (less resitivity).
As aluminium has a smaller atomic mass, 1 mole of aluminium(atomic number 13) will weigh less then 1 mole of copper(atomic number 29). If you are then worried about weight (as oman said say ontop of a light pole)Then if you look at ResitivityPer unit mass(say a mole) then aluminium is actually the better candidate.
Hope this clears things up.
Steve

Edit: Aluminuim will weigh less, stupid typos thanks mos

[BradW]

Is the cable from the engine to the body thicker than the cable from the body to the battery?
If so, there is your problem .

[Mos]

I disagree with you on this. Per sqmm copper is in fact the better conductor, hence the reason that copper is used in most instances for power cabling.

Sorry, I stand corrected - copper has better conductivity than aluminium.

However, when cross sectional area is taken into account, an aluminium engine component will usually conduct better than a copper cable.

Although these cables are getting old, I can't see it magically increasing resistance and reducing it's load carrying capacity unless it's been bent and twisted to the point where some strands have been broken, or it's oxidised to the shithouse along it's length.

I've seen it before... ("magically" increasing resistance ) 4" length of battery to body cable looked perfect on the outside, but was warm and had an 8V drop across it when cranking. Admittedly I didn't cut it up, so I don't know what happened inside, but developing a high resistance does happen. Don't forget that cable gets bent and twisted ever time you remove or disconnect the battery.

As aluminium has a larger atomic mass, 1 mole of aluminium(atomic mass 13) will weigh more then 1 mole of copper(atomic mass 29).

Don't you mean the opposite?
Copper has a larger atomic mass (atomic number 29, atomic mass 63.6) than Al (atomic number 13, atomic mass 27.0), and 1 mole of Cu will weigh more than 1 mole of Al.

Is the cable from the engine to the body thicker than the cable from the body to the battery?
If so, there is your problem

Having the battery to body cable thinner (if it's not a lot thinner) is not really a problem if it's doing its job (in this case it's not, so it's a problem).
Modern engines seem to have thinner battery to starter and battery to block cables than older engines. The cables on a JZX100 VVTi 1JZ are smaller than what I remember seeing on the old 4K-C...

Mos.

[RT104GT]

Hi Guys,

What are the causes for this? bad earth? could I have missed another earth cable somewhere along the line?

I have an earth cable bolted to the bottom of the intake manifold (alloy) do alloy components give a good earth, or should this be bolted to something cast iron?

thanks for your help!

OHMS LAW.

Bad earth, bad or corroded connector inside where you cant see it.

I had this happen even on an aircraft the other day, the main earthing lead made of aluminium corroded inside where you could not see it.

results slow cranking and earth wire from battery to frame heating up.

Another reason people havent spoken of here is your starter motor armature may have thrown some solder by cranking it too much so you need to check the cold crank amps of the starter motor.

Its all about resistance and voltage drop and keeping leads as short as possible between battery and engine/starter.

Non geared TOYOTA starters are pretty crappy at the best, try to fit a geared one it drops the crank amps and ups the torque.

2C.

[DoctorDubb]

Thanks mos, edited original post to reflect that. Thats what i meant just cant type and think at the same time

[SilverGhost]

Thanks to all who replied to this thread....I have determined that the earth cable is starting to go. But the reason why i had to crank so much is because it wouldnt start....


it wouldnt start because the distributor was out a couple teeth. With a bit of mucking around I got it started and while running the cable didnt get hot...

Im going to replace it anyway as i see the heat as a warning sign. but atleast i know she runs!

now i gotta figure out why she is overheating....gotta look at the thermostat first i think.

thanks again fellas!

[BradW]

Having the battery to body cable thinner (if it's not a lot thinner) is not really a problem if it's doing its job (in this case it's not, so it's a problem).

Mos.

If there is no earth cable from the battery to the engine, then both the earth cables (B- to body and body to engine) need to be capable of carrying starter current. If one is thinner than the other it will not be able to carry as much current and may heat up while cranking (especially with extended periods of cranking).
If there are seperate cables for B- to body and B- to engine then the B- to body cable can be thinner without any issues as it will not be required to carry starter current.
Just wanted to clarify this for others .

I would leave the cable from B- to body and run a new cable from B- to engine.