mkblade
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| posted on 11/3/08 at 07:18 PM |
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battery cut of switch
i want to fit a device that i can cut all power from the battery.
i was going to cur the neg lead and fit something in there (under nose cone) ive got a cut off switch (red key) but its a bit bulky anyone eles got
something along these lines fitted
thanks
simon
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brynhamlet
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| posted on 11/3/08 at 07:39 PM |
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I've got on off these battery isolator switches and yes they are bulky, but don't forget your switching potentially 30A or so. I'm
going to mount mine on the vertical face of the scuttle, so it protrudes into the cockpit under the dash, slightly to left of centre. Then the leads
can be short and hidden under the bonnet. I'm going to break the live feed though, because if you break the negative you've got to take
into consideration, you will have to break all the starter motor current as well as the running load. If you break the positive, you would still not
be able to start the car as you will still disable the starter, on the low current side.
Also check the recent thread I started and the answers
http://www.locostbuilders.co.uk/viewthread.php?tid=84547
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nitram38
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| posted on 11/3/08 at 07:53 PM |
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Unless you use the fia isolator which discharges the alternator and cuts the ign, then your engine may run on or destroy your alternator diodes 
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LBMEFM
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| posted on 11/3/08 at 07:58 PM |
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As "nitram38" say's if you disconnect the battery while the engine is running you will fry the rectifiyer. See the posting a few
days ago on this subject.
Barry
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britishtrident
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| posted on 11/3/08 at 08:19 PM |
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Correct MSA way to wire a battery master switch is to break the negative line.
You can get more expensive "FIA" master switches that are combined with switch contacts to break the posative feed to the igniton/fuel
pump/main relay and also switch the alternator output to earth via a ressistor.
However you don't need this if the switch is purely an anti-theft device.
[Edited on 11/3/08 by britishtrident]
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britishtrident
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| posted on 11/3/08 at 08:23 PM |
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FIA Masterswitch
http://www.autoimagination.co.uk/?page=manufacturers&id=60&product=1019
 
Rescued attachment master switch.jpg
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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dhutch
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| posted on 11/3/08 at 09:29 PM |
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Also if you only want it to cut power while your working on it, you dont need the extra conections.
- It could also be argued that in an emergancy situation like and electracl fire, the cost of a second hand alternator is a small price to pay.
Sometimes they survive, as well.
Also worth point out you can fairly easly set up a pull-cord-to-isolate setup. Which is often the simplest/neatest way to put the switch somewhere
handy.
You may potentially be switching more than 30amps as well. Or certainly drawing far more than for a short space of time while starting. More like
300amps peak.
Daniel
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britishtrident
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| posted on 12/3/08 at 08:20 AM |
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You can also put a 100 or 150 amp circuit breaker in the main (+ve) feed to fuse box.
http://stores.ebay.co.uk/Exclusive-Parts-HK_Circuit-Breaker_W0QQfsubZ13267681QQfrsrcZ1
 
Rescued attachment 3da4_1.JPG
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nz_climber
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| posted on 13/3/08 at 08:07 AM |
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I have been thinking about this to..
Wouldn't leaving the main starter wire and main alternator wire attacted to the battery work, and have the switch just isolate everything else
(ecu, ignition, fuel pumps, everything else) work, this will still cut an engine when turned off, and also allow the path for the alternator current
to go when engine is winding down? This means you are only drawing 30A or so through the switch, and not 100A + on start up..
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