Hi, hoping someone can help me!
I have an Isuzu NQR 7.5 ton horsebox lorry.
Drove it last weekend, all fine as usual, went to it today and it wouldn't start, symptoms same as flat batteries (dash lights come on when turn key one click but when turn key to starter position lights go out and it's dead).
I put a meter across the batteries individually and both read just over 12 volts, all anciliary electrics work (lights, etc).
With an observer's help, I discovered that when the key is turned to the starter position, a large shower of sparks come from the negative battery terminal.
Any ideas? There are signs of heat on the neg terminal that wasn't there last week. Terminal connections are tight and good as is the connection from earth strap to the body.
I'm guessing there could be some kind of short with the starter motor? Starter relay? Really grateful for any ideas as it's too big to tow and I'm a bit stuck if I can't get it running...
Thanks!
Edited by Dynamic Dave on 21/03/2008 at 19:43
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Remove that terminal and see what's left. It may be tight; but a film of sulphate on the lead post is an effective insulator. That's 1000 amps trying to flow there.
If there's enough left to work, clean both sides of the connexion to shiny with abrasive paper [not a wire brush!] and retry. [Yes; I know horsebox builders never remember to allow for battery access....]
For a settled battery [two hours sitting] 12.6 volts is charged; 12.4 OK; 12.2 flat.
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>>clean both sides of the connexion to shiny with abrasive paper [not a wire brush!]
Why not a wire brush?
I remember seeing high current aluminium bus bars being prepared for joining by being wire brushed with copius amounts of petroleum jelly, presumably to exclude air.
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Wire brushes produce tiny sparks - batteries vent a very explosive mix of pure oxygen and hydrogen gas......
You see where I'm going on this.....?
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Boom and no eyebrows and potentially very few other bits.
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Thanks, I will try this tomorrow. Funny that it has been working up until last week with no problems though?
One other thing, to stop the battery going flat from the tacho when it is left standing, it has a "discarnect" isolator fitted to the terminal which is now sparking. Not sure what this is rated at but the lorry's handbook says the starter is 4.5 kW - by my maths on a 24V system that is drawing 187.5 amps when cranking the engine - maybe this is more than the isolator can cope with? Again, funny that this is the first time we've had problems, but maybe if it has been melting the isolator gradually it has now got to the point where the resistance is too high to let the necessary current through?
Glad to hear you don't think it is a short in the starter motor though, that sounded expensive and as Screwloose points out, horsebox builders don't seem to realise that people may want to get to some of the lorry for future maintenance...
Cheers
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>>You see where I'm going on this.....?
Through the hole in the garage roof ;>)
Thanks for the explanation.
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