Starter motors, excitation.

[tom2207]

Ok, found the problem.

The 4mm section cable from the ignition switch to the starter motor was the issue.

Replaced with a bigger section cable, all sorted.

Thanks for everyone's thoughts.

well done.

 

[Neilj]

Excellent

 

[500e]

Was it corroded, connections, or long length? would have thought 4mm (32A) plenty to carry solenoid pull in current,
Always interested to know for future problems have hundreds of little snippets in the brain that may come in useful one day, it's just remembering them now

 

[Barking Mat]

Was it corroded, connections, or long length? would have thought 4mm (32A) plenty to carry solenoid pull in current,
Always interested to know for future problems have hundreds of little snippets in the brain that may come in useful one day, it's just remembering them now

No, seemed fine, possibly the fact that the Lucas style yellow connectors were not fit for purpose, cable seemed fine, not cooked.

I'm not 100% sure this story is over, but for the moment it works.

This is the same loom, that the engine temperature gauge went pear shaped last year.

So we're going to replace the loom this winter.

 

[PhillipM]

Wire corroded under the insulation maybe?

 

[Turbo]

No it's exactly the same*

Conductor cross section governs the resistance of the wire which in turn dictates the current carrying capacity limited by heating effects.

* there is a subtle difference due to skin effects when you are using AC but by and large if its rated at 13A at 240VAC(RMS) then it'll handle 13A at 12VDC perfectly fine.

Power (Watts)= volts x amps or amps=watts/volts

For a 60w bulb @240v 60/240=0.25 amps , @12v 60/12=5amps

As you decrease voltage the current must increase to supply the same load, basic electrical principle whether ac or dc! Therefore you need thicker wire for lower voltages for the same given load.

 

[sako243]

Power (Watts)= volts x amps or amps=watts/volts

For a 60w bulb @240v 60/240=0.25 amps , @12v 60/12=5amps

As you decrease voltage the current must increase to supply the same load, basic electrical principle whether ac or dc! Therefore you need thicker wire for lower voltages for the same given load.

I never said that it couldn't handle less power (at a lower voltage), I stated that it can handle the same current.

If you re-read your original post then what you have written (at least to me) reads that 1.5 flex will handle less current (than 13A) when running at 12V compared to at 240V. No where do you mention power.

If that's what you meant then fair enough but it's not the way I, and the way I'm sure others, read and understood your post.

I would suggest that the 1.5mm2 cable you used to test it is a bit too weedy, some starter solenoids can take a fair few amps to pull them in. At 240v 1.5 flex will handle up to 13a but at 12v it's a whole lot less!
Vehicle flex is usually measured in swg & you'll find a conversion chart online between swg & mm2 plus a chart giving current capacities of swg cable at 12v.
Also note that due to the low voltage (12v) you get more voltage drop so on long runs you need thicker cable.

 

[Justme]

I never said that it couldn't handle less power (at a lower voltage), I stated that it can handle the same current.

If you re-read your original post then what you have written (at least to me) reads that 1.5 flex will handle less current (than 13A) when running at 12V compared to at 240V. No where do you mention power.

If that's what you meant then fair enough but it's not the way I, and the way I'm sure others, read and understood your post.

I agree.

Amps capacity is the same but power capacity is less.

 

[Dave-sparks]

As you decrease voltage the current must increase to supply the same load, basic electrical principle whether ac or dc! Therefore you need thicker wire for lower voltages for the same given load.

No it doesn't, as you decrease voltage to the same load the current will reduce proportionally as the impedance remains the same. The basic electrical principal here is V=IR

Current will only increase as voltage is reduced if you have a constant power load, such as certain SMPSUs.

I think what you are trying to say here is that a load which dissipates 1kW at 240V will have far less current flowing through it than a load which dissipates 1kW at 12V.