Slater
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| posted on 5/2/09 at 08:14 PM |
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connect battery - small spark?
Hello
Every time I re-connect my main lead to my battery +ve, I get a very tiny spark. It does not happen if I remove the fuse for the indicators/hazard. So
must be something in this circuit causing it.
Is this normal? Maybe a capacitor charging up in the flasher relay????, or does it mean something is not wired up properly.
The indicators and hazards work just fine, by the way.
Keith.
(I am about to send of the SVA application)
Why do they call Port Harcourt "The Garden City"?...... Becauase they can't spell Stramash.
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GeorgeM
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| posted on 5/2/09 at 08:18 PM |
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always connect the +ve first, then -ve
helps to make sure nothing shorts out
(assuming -ve earth!)
GeorgeM
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prawnabie
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| posted on 5/2/09 at 08:20 PM |
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Hazards are always live, so I would say it is sparking because the hazard relay is pulling a small draw though the battery live?
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mistergrumpy
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| posted on 5/2/09 at 08:28 PM |
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What George said. Connect +ve first. I remember this after a lad in the RAF I was working with did it the other way round causing a spark which
ignited the batteries venting gas and it blew up in his face. He looked like a black and white minstrel, not very nice though.
Hopefully that would stop the lead sparking or limit it to avoid this happening.
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Slater
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| posted on 5/2/09 at 08:37 PM |
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Good advice about connecting the +ve first. Thanks. I have been doing it the other way round for the last 3 months of the build. Doh.
Why do they call Port Harcourt "The Garden City"?...... Becauase they can't spell Stramash.
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speedyxjs
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| posted on 5/2/09 at 09:09 PM |
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i always thought it was the other way round as if you connect the positive first, you basically become the earth. So if you are leaning on the car and
accidently touch the positive, you get a bit of a shock.
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David Jenkins
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| posted on 5/2/09 at 09:20 PM |
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I was given the same advice, but for a very practical reason...
If you have to use a metal tool such as a spanner to undo the battery bolts, then if you touch the chassis while undoing the -ve terminal then nothing
will happen. Once the -ve is disconnected, if you touch the chassis while undoing the +ve terminal then again nothing will happen, as there's
no circuit.
Now, if you start by undoing the +ve, and touch the chassis - masses of sparks, and a red-hot tool (ooer, missus!)
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LBMEFM
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| posted on 5/2/09 at 10:27 PM |
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I agree with speedyxjs and David, thats what I was taught as a apprentice mechanic, undo the earth terminal first.
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BenB
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| posted on 5/2/09 at 11:23 PM |
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Same as jump starting cars 
The spark means you're drawing some current somewhere. The hazards are (as already said) constant live and can run down the battery.
One reason I fitted a battery isolator between the battery and the hazard wiring....
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neilj37
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| posted on 6/2/09 at 08:02 AM |
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Keith,
OFF TOPIC - How did the wheel arch protectors go. Was the sizes approx correct?
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bassett
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| posted on 6/2/09 at 09:29 AM |
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At college(vehicle engineering) always told on battery removal neg then pos
battery reconnection pos then neg
for the same reason as above negative removes the chance of earthing a tool to the chassis and touching the pos creating the circuit. if the neg is
disconnected this cant happen
My MNR Blog Updated Jan 2010 - Track Day Prep Begins!
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coozer
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| posted on 6/2/09 at 09:57 AM |
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As mentioned removing the neg first saves that curious little spark turning into a fireball or big bang!
1972 V8 Jago
1980 Z750
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02GF74
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| posted on 6/2/09 at 09:59 AM |
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quote:
Originally posted by bassett
At college(vehicle engineering) always told on battery removal neg then pos
battery
reconnection pos then neg
for the same reason as above negative
removes the chance of earthing a tool to the chassis and touching the pos
I've been thinking about that the other day - this is the correct sequence.
re: the small spark; it is because you are drawing current, and as you say, by removing the fuse to the hazards you have indentified the culprit.
I have to admit I am a bit surprised that the realy is drawing current - surely it becomes only active then the hazards button is pressed?
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iank
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| posted on 6/2/09 at 11:06 AM |
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Put a multimeter switched to current measurement in place of the hazard fuse.
You can get a small spark from low current inductive loads (like relay coils or motors) at switch on but best to be safe.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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Ninehigh
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| posted on 7/2/09 at 02:34 PM |
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Since taking a nasty shock at a young age I'm paranoid of electricity and messing with live cables is something I only do with thick gloves, an
electrically shielded spanner, rubber soles and full arm's length. I'd shut my eyes and turn my face away only I'd lose balance and
electrocute my nuts or something (yeah I'm proper fearful of electricity, 240v at the age of 7 does that to ya)
A spark is normal, there's a good few things on a vehicle that draws power. My missus's car radio drained it once, and it wasn't
even switched on 
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Macbeast
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| posted on 8/2/09 at 09:14 AM |
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Whereas, a professional would never use rubber gloves, insulated tools etc as this makes them careless with a false sense of security - but
you're right to treat it with respect. I'm ok with working with hot 240V wiring but boy, am I careful :-)
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Ninehigh
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| posted on 8/2/09 at 09:40 AM |
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Ooh no I couldn't do that, I even have to knock once before touching a metal door because of the number of static shocks I've had
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