Battery disconnect.

[DaveEFI]

Have one of those. A battery isolator device which goes between the battery negative and lead, so quick and easy to fit.



It is very simple. The battery side has a flat plate a bolt head screws down into. The output side a 10mm long thread the bolt goes into. The halves of the device separated by an insulator.

Mine failed. Turn on ignition - fine. Go to use the starter and nothing - dash lights etc go out and stay out. Undo the bolt and redo - works fine until the next time.

So gave it a good clean with a wire brush. Bolt is brass and comes up like new. Plate the bolt head clamps onto clean too. Which only leaves the thread the bolt goes into.

Noticed the body isn't made of brass, but some metal which doesn't rust and plated to look like brass.

Could it be that plating is acting as an insulator after a few years use?

[stevieturbo]

good clean with a wire brush ?

With it connected and bad, what sort of volt drop is there across it ? Must be pretty bad if it won't even try and start ?

Looks like it's only the bolts contact with that top surface, and then the threaded part underneath that carry all current ?

Clean and try a larger diameter brass washer under the head of it so it has more contact area ?

[Ian Anderson]

For less than £10 buy a new one!

https://www.carbuilder.com/uk/quick-bat ... t-terminal

If you have one of these in the circuit
https://www.carbuilder.com/uk/battery-i ... rd-version

That would more likely be the cause……. Cut a circle of Manila card diameter of the key and drop it in the hole, This will tension the contacts a bit more and the problem will go away till you wear out the cardboard washer! But that is cheap and easy to replace

Ian

[DaveEFI]

Sorry - to clarify. It worked just fine for a few years. Just curious why a heavy load like the starter made it go totally open circuit - like a fuse blowing. Then fiddling with the wheel bolt gets it going again - for a while. Basically, wondered what sort of chemical process or whatever was going on?

I have replaced it with a new one. Sadly they all seem to be the same design - unless you go for an isolator switch which would be far more difficult to install.

I'd happily pay more for one made totally from brass.

[ChrisJC]

Once I rebuilt a starter motor solenoid using titanium instead of copper for the terminals / contacts.
It worked once, then the spark on the contacts caused the titanium to oxidise and form an insulation barrier.

I built it about 3 times before the penny dropped...

Chris.

[DaveEFI]

Yes - I was just curious. I'm not sure what the base metal it is made of is. It hasn't rusted where the plating has worn off. Something easy to cast - but a bit stronger than pot metal. I'm guessing some form of corrosion between the metal and the plating? Other people have had exactly the same with theirs, so mine ain't a unique fault.

[stevieturbo]

Is the material magnetic ?

Terminations, corrosion can all cause very strange things even whilst a connection might look ok.

A while back I was working on a car...over a period of 2-3 years it had been around a few different garages, they all did some bizarre things, charged the customer money, and never fixed the problem.

The symptoms were relating to signals to a diff controller, which caused strange behaviour off that diff when driving, which could have resulted in transmission damage.
But aside from that largely it appeared to start and drive ok.

The list of things other places charged for is too long to list. But after investigating it and testing a few things for a few days, it was fairly obvious a bad earth was to blame. And it was simply the main earth from battery to engine and chassis.
But it was the original cable, it was not damaged, but in general the contact areas were fairly corroded. But visibly not worse than many other cars of similar age etc.

Even just using a jumper cable from battery earth to the engine fixed the problem. Cleaning up all contact points with the same cable....fixed the problem.

But in such a case, you'd have thought it would present starting/starter issues too, but nope. All good in terms of ability to start and cranking speed etc.
It did play haywire with some of the cars systems though