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Battery isolator failure

bassplayer

By bassplayer
in Boat Building & Maintenance

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bassplayer Influencer

bassplayer

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Having got into the habit of switching the battery isolator to OFF when I leave the boat, I have just discovered that I'm still getting 12v at the alternator and starting motor even when the isolator is switched to OFF!

 

A quick check using a multimeter at the back if the switch shows 12v on both terminals in the OFF position. I'm assuming the switch has failed but I'm surprised the failure mode allows current to flow through the switch in the OFF position. Is it normal for it to fail like this? I've ordered a new one anyway....it's one of these....

 

http://pages.ebay.com/link/?nav=item.view&alt=web&id=290778296110

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frangar Veteran II

frangar

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I'm really not keen on those type of switches....they seem to fail for a pastime....bit late if you have ordered it now but have a look at the blue sea or bep range of switches. They are more money but they do work at the given current rating.

 

Cheers

 

Gareth

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bizzard Veteran II

bizzard

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Having got into the habit of switching the battery isolator to OFF when I leave the boat, I have just discovered that I'm still getting 12v at the alternator and starting motor even when the isolator is switched to OFF!

 

A quick check using a multimeter at the back if the switch shows 12v on both terminals in the OFF position. I'm assuming the switch has failed but I'm surprised the failure mode allows current to flow through the switch in the OFF position. Is it normal for it to fail like this? I've ordered a new one anyway....it's one of these....

 

http://pages.ebay.com/link/?nav=item.view&alt=web&id=290778296110

It does happen from time to time. In fact, my own services isolator switch did this a couple of years ago. I discovered it when I was about to do a lighting alteration

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bassplayer Influencer

bassplayer

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It does happen from time to time. In fact, my own services isolator switch did this a couple of years ago. I discovered it when I was about to do a lighting alteration

You'd think the safe failure mode would be open circuit though (although inconvenient)! It would be interesting to take it apart to see how it failed.

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bizzard Veteran II

bizzard

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You'd think the safe failure mode would be open circuit though (although inconvenient)! It would be interesting to take it apart to see how it failed.

You would but the switching contacts are confined in a small space so I suppose the contact wipe can heat up and warp over time and so still make contact when turned off.

My switch that failed was an ancient small Lucas type with the small black knob, can't grumble it was about 40 years old. I've never had any trouble with the type you've ordered as long as you don't load it to exceed it's rating.

 

I bought the same type as the one you've ordered from the big stores called ''Range'' for about £6, works lovely.

Edited by bizzard
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Detling Rising Star

Detling

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Posted

The OP mentioned starter motor so I assume we are looking at an engine battery isolator no the domestic bank. The paddle type isolators regularly fail both open and short circuit and even melt mode ie a blob of plastic with some bolts in it. The engine isolator has to be able to withstand the starter motor cranking a cold diesel engine, and whilst doing that will probably be carrying over 500 amps, but only for the few (if lucky) seconds it takes your engine to fire.

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bassplayer Influencer

bassplayer

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The OP mentioned starter motor so I assume we are looking at an engine battery isolator no the domestic bank. The paddle type isolators regularly fail both open and short circuit and even melt mode ie a blob of plastic with some bolts in it. The engine isolator has to be able to withstand the starter motor cranking a cold diesel engine, and whilst doing that will probably be carrying over 500 amps, but only for the few (if lucky) seconds it takes your engine to fire.

Yes, it's an engine battery isolator. I'd be very surprised if it was drawing 500 amps though. That's 6 kW! I think I read on another thread that starting motors typically draw about 50 to 100 amps but seems open to debate.

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ditchcrawler Veteran II

ditchcrawlerDonate to Canal World

Posted
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Yes, it's an engine battery isolator. I'd be very surprised if it was drawing 500 amps though. That's 6 kW! I think I read on another thread that starting motors typically draw about 50 to 100 amps but seems open to debate.

This one http://www.canalworld.net/forums/index.php?showtopic=10894

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Iain_S Influencer

Iain_S

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I agree with previous posters re these switches, and think their advertised capacity is well over rated, even at 100A. OK if either current is low, or short duration (as when turning starter motor), but not for a long term heavy load.

 

This was the failure mode (open circuit, though)of one on Copperkins ...

 

 

Iain

 

edited to try to sort link!

Edited by Iain_S
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MtB Veteran II

MtBDonate to Canal World

Posted
Posted

Well I've just had to order a new switch like that myself, for a completely different reason.

 

The on/off red handle is not fixed into the switch, and after mine falling out any number of times and me luckily finding it, this time it seems to have disappeared into the bowels of the engine bilge, and I can't find it ANYWHERE grrrrrrrrrrr...................

 

Well actually I've ordered one of these, this time, so the problem should be fixed.

 

$_12.JPG

 

Hopefully this one doesn't have a stoopid fally-outy handle.

 

MtB

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David Mack Veteran II

David MackDonate to Canal World

Posted
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I agree with previous posters re these switches, and think their advertised capacity is well over rated, even at 100A. OK if either current is low, or short duration (as when turning starter motor), but not for a long term heavy load.

 

This was the failure mode (open circuit, though)of one on Copperkins ...

 

 

Iain

 

edited to try to sort link!

Link doesn't work for us non FB types.

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bizzard Veteran II

bizzard

Posted
Posted

Well I've just had to order a new switch like that myself, for a completely different reason.

 

The on/off red handle is not fixed into the switch, and after mine falling out any number of times and me luckily finding it, this time it seems to have disappeared into the bowels of the engine bilge, and I can't find it ANYWHERE grrrrrrrrrrr...................

 

Well actually I've ordered one of these, this time, so the problem should be fixed.

 

$_12.JPG

 

Hopefully this one doesn't have a stoopid fally-outy handle.

 

MtB

That's the same as mine that failed after forty years. An old design that most boats used years ago. I still have one to switch in another cabin battery if needed.

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David Schweizer Veteran II

David Schweizer

Posted
Posted (edited)

Well I've just had to order a new switch like that myself, for a completely different reason.

 

The on/off red handle is not fixed into the switch, and after mine falling out any number of times and me luckily finding it, this time it seems to have disappeared into the bowels of the engine bilge, and I can't find it ANYWHERE grrrrrrrrrrr...................

 

Well actually I've ordered one of these, this time, so the problem should be fixed.

 

$_12.JPG

 

Hopefully this one doesn't have a stoopid fally-outy handle.

 

MtB

 

That is the old Lucas type switch, and it is very robust. There is one on our boat still giving reliable service after 32 years. Don't worry about the handle Mike, it is held on firmly with a machine screw.

Edited by David Schweizer
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Iain_S Influencer

Iain_S

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Linky still not working

 

Hope this one works...

 

Pics 1-4 show the dead switch. 3 shows the rating as 100A continous, 500A intemittant

 

5 is the switch opened up by drilling out the rivets.

 

6 is the moving contact in "off" position

 

7 is "on" position

 

8 is the contacts, with faulty one on left

 

9 is close up

 

10 is a different angle, showing melted plastic

 

11 compares the stud lengths, after one has moved through the molten plastic.

 

 

Iain

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