Lotus Elan

Ammeter open circuit

PostPost by: Elseezed » Fri Jul 27, 2018 3:42 pm

PMK 397F ran great to Silverstone and back. Just came to start it, no power. Batt ok, fault was wire to alternator had shorted to chassis and burnt right through. The consequence of this was the ammeter had blown like a fuse, hence no power to anything. Removed ammeter and joined the thick brown cables, all works fine.
Will be looking in autojumbles for ammeter in future.
Lucky it did not set on fire good old Lucas thought of everything.
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PostPost by: MarkDa » Fri Jul 27, 2018 8:43 pm

At least something cut off supply of juice.
I'm beginning to think there's a case for having (and using every time one leaves the car!) a battery isolator.
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PostPost by: Elseezed » Sat Jul 28, 2018 8:40 am

Good point Mark. There is a battery isolator fitted, strapped out for whatever reason by PO. Will look at reinstating it and using it. Also acts as an anti theft device.
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PostPost by: david.g.chapman » Sat Jul 28, 2018 9:30 am

It might be possible to repair the ammeter.

The wire link inside the meter has probably blown like a fuse, leaving two ends looking at one another. If these ends are soldered together the meter will work once more. The soldered joint should not be too thick. or flow over the cut ends too much, otherwise the resistance of the link will be lowered significantly and the meter will under-read a bit.

The same thing happened to me over 10 years ago and my ammeter is still working OK.

Dave Chapman.
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PostPost by: Elseezed » Sat Jul 28, 2018 10:53 am

Thanks Dave, a small link did fall out of the ammeter. Useful info, will have a go. Replacement ammeters seem to be priced at around ?50.
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PostPost by: gus » Sat Jul 28, 2018 11:36 am

You had a dead short somewhere

Look at the alternator wire

Buy a new ammeter and steal the shunt out of it
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PostPost by: Elseezed » Sat Jul 28, 2018 3:08 pm

All back to normal. Ammeter working. Looking forward to the next fault, not.
img_0554.jpg and
Ammeter repair,

It was the wire to the alternator that shorted, repaired yesterday, alternator survived ok.
Now where's that battery isolator.
Les
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PostPost by: Quart Meg Miles » Sun Jul 29, 2018 9:30 am

david.g.chapman wrote:The wire link inside the meter has probably blown like a fuse, leaving two ends looking at one another. If these ends are soldered together the meter will work once more. The soldered joint should not be too thick. or flow over the cut ends too much, otherwise the resistance of the link will be lowered significantly and the meter will under-read a bit.

Dave Chapman.

The link is a fuse! If it were a shunt then the ammeter movement would have been destroyed once the link broke.Too much solder short-circuits the fuse so removes the protection.
Meg

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