Earth Cable getting hot

[SilverGhost]

Hi Guys,

I finished reassembling my shitbox run around, but when i try to start it it will crank slowly but wont turn over. When I inspect the battery the earth cable bolted to the body is quite warm.

There is a second earth cable running from the same ground point on the body to the motor, this cable is cold however.

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!

[twentyEight]

I would say that something that you don't want to earth is earthing... Faulty wiring somewhere...

[oldcorollas]

bad cable? getting yucky inside?

the earth cable from body only goes to the manifold???

you should have a cable running directly from the body to the engine block.

when you try to start, you have maybe 100 amps running from battery, to starter motor, through the block, and then back to the battery somehow.
unless you painted the startermotor it should have good connection to the block.

if your only earth is from the manifold, try getting a set of jumperleads, and running one from the battery negative, straight to the engine block, and see if it makes a difference..

oh.. is battery charged?

[river]

Hi,

Sounds like there's some resistance in there somewhere, or your starter is pulling too much current 'cos it's under too much load or binding.

Does the cable get warm when you put on the headlights for about 30secs? If so, then start looking at your earthing points. Unbolt them, clean them up and also clean-up the anchor point where they connect to the chassis/engine/manifold.

If the cable only gets warm when trying to start then disconnect the battery, disconnect the main cables (+ve and -ve) to the starter, clean them up, clean up the anchor points. Then remove the batter clamps and clean both posts and the inside of the clamps. Re-connect the battery and try again.

If it's still doing it then check your starter as it may have a shorted coil, hence the extra load in pulling amps from the battery, plus why it's starting slowly.

seeyuzz
river

[Mr Ed]

How thick is the cable? If its really narrow try adding a few more earth lines or upgrade to a big cable.

[SilverGhost]

the battery is charged fairly well. its definitely servicable but is getting a little old.

That seems to make sense, There is a brace that goes from the block to the underside of the manifold and the earth cable usually bolts up to that, but for some reason im having difficulty lining up the bolt holes with the bracket, so the only way to try and start the car was to attach the earth where the brace would normally bolt on the manifold.

I assumed there is a good enough connection between the head and the block through head bolts etc, but ive alwyas thought earths should connect to the block.

Assuming the starter is fine, and the cable itself is in good nick, bolting the cable to the block should solve the 'hot wire' problem?

[MWP]

Sounds like the cable running to the block is bad or has bad connnections.
This would cause the starter to draw current through the chassis cable instead, heating it up like you describe.

[river]

Hi,

Assuming the starter is fine, and the cable itself is in good nick, bolting the cable to the block should solve the 'hot wire' problem?

Definitely worth a shot. Due to the large current the starter draws you want the biggest and best cable and connections going to it. And, as the starter is bolted to the block it is wise to have a large earth cable also connecting to the block.

seeyuzz
river

[ViPeR_NiPPleX]

There is typically three earth cables. Thick one from battery to block, and two skinnier ones, one from block to chassis, and the other is battery to chassis. Ensure that all cables are in good condition, the crimps are good, and the mating surfaces are clean. Beyond that, you have bigger problems.

[Mos]

Grab a mutli meter and measure, while cranking, the voltage drop across the cable that gets hots. It sounds like this cable has a high resistance (regardless of how good the crimps or insulation might look) but the voltage drop will confirm this, as will the jumper leads.

(Edit) Even though Copper has better conductivity than aluminium there is no benefit to fitting a longer cable (of maybe 10mm^2) to save using a much larger aluminium bit.

Mos.

[SilverGhost]

well the bracket and cable are back in place....but the cable still feels warm...the -ve terminal of the battery is also warm....

could it be the battery itself?? heat transfer down the cable?

[oldcorollas]

get two jumper leads, jumper from block directly to the neg terminal (which you freshly clean and make sure has good contact)
and then see what happens

[Mos]

Your cable is probably fu*ed. You probably need to replace it. No amount of searching for another solution will solve a cable that has developed a high resistance - you need to replace it, period.

Dodgy contact points will cause heat at the contact point only - obviously heat will transfer but not in any practical sense in this context. If the whole cable is hot, the whole cable is fu*ed. If the cable has a point somewhere where it is more fu*ed then everywhere else, it will be hotter at that point.

Heat at the battery terminal only usually means bad connection between the terminal and the clamp - this won't heat up the whole cable.

Having the cable bolted up to the wrong place on the engine won't cause it to heat up.

The way it reads, you have one cable going from the battery negative to the body of the car (giving you problems - warm), and another cable going from the body of the car to the engine. It makes absolutely no difference what you do with the body to engine cable, if the battery to body cable is fubarred.
Those short battery to body cables get manipulated a lot and in something that is very old can have many broken strands - hence the cable is thinner than it should be, and heats up.

I'm sorry I'm worked up, but in another thread it took 3 pages to convince someone they had a problem with their brakes - meanwhile they kept driving their car. Between 10:31am and 8:55pm you could've easily taken a set of jumper leads and "jumpered" the suspect cable to convince yourself the cable is stuffed, or to convince us the problem is somewhere else.

Mos.

PS. And you're also stuffing up my rep to post ratio

[Mr Ed]

EDIT: 10char

[o_man_ra23]

Aluminium has better conductivity than copper so there is no benefit to fitting a longer cable (of maybe 10mm^2) to save using a much larger aluminium bit.

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.

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