[johnnyoxford]

Hi, I am going to fit a battery isolator, just want to know what cable I should use, where I can get it and whether its best to isolate the + or the -?

Any reason I cant use some jump lead cable?

 

[90truckcab]

why not if its thick enough jump cable, id use the same as yer existing , isolate the + as an earth can be taken from anywhere outside / under the motor

 

[Soloby Rob]

why not if its thick enough jump cable, id use the same as yer existing , isolate the + as an earth can be taken from anywhere outside / under the motor

Sound advice. :5biagree::5bsifone:

 

[BuzzLand]

Would a 16 Amp switch suffice for isolating?
Tieing in the wire to it would be tight if the wires is the thickness of the battery cable!

 

[Sean]

Would a 16 Amp switch suffice for isolating?
Tieing in the wire to it would be tight if the wires is the thickness of the battery cable!

did you miss off a couple of zeros ?

 

[ssmn1234]

Go to a welding supply shop and buy the heaviest DC welding cable you can afford, at least 35mm square.
Suggest at a minimum 150amp isolator switch with at least 10mm terminal studs, but go higher amp switch if you can afford it.

 

[Sean]

Go to a welding supply shop and buy the heaviest DC welding cable you can afford, at least 35mm square.
Suggest at a minimum 150amp isolator switch with at least 10mm terminal studs, but go higher amp switch if you can afford it.

where'd you get 150A from ?

 

[discomania]

I would be using something a bit heavier than that - the whole "installation" must be capable of withstanding a cold crank startup, which may also be prolonged in the event of other engine difficulties - you don't want anything to cook - the standard landrover cable gets warm after a lot of cranking, so anything less than this really is a big nono.

The switch is rated at 150amps, which means that it has been designed to allow 150amps through it without any problems, if you were to isolate the supply it would be just fine, but when you connect it up and start trying to draw lots of current through it you will run into issues.

 

[ssmn1234]

where'd you get 150A from ?

plenty places sell them, that's 150amp continueous rating, the intermittent rating is alway higher. lots sell things that are supposidly 1000 amp, but they're not talking continuous just for intermittent use.

 

[The Mad Hat Man]

where'd you get 150A from ?

here - but this mite be betterer.

 

[Sean]

here - but this mite be betterer.

a knows where to get them from

just wondered where peeps are getting this 150A figure from - i realize it's what most of those cheap isolators are rated at continuously but more importantly they tend only to be rated 500A for 10 seconds (intermittent load) - which is bugger all use when you've been cranking that big diesel lump for a minute or 2 on a cold winter morning

 

[bluehaze]

Auto electrics sell a fully prepared cable - £6 or £7 if my memory is working. Definately needs to be sufficient gauge not to melt.

 

[ssmn1234]

For owners of V8's a 150amp isolator will happily power your starter motor till the battery goes flat, as in the very worst case it will only ever draw 142Amps. For owners of 300tdi, in the very worst case, your standard starter motor will only ever draw a max of 184 Amps, so an isolator of 185amp will happily power your starter motor till the battery goes flat. Generally, if all components of your engine are in a serviced condition the amps required to turn the motor are considerably less.

 

[Sean]

where are you getting these figures of 142 and 184 from ?

 

[ssmn1234]

where are you getting these figures of 142 and 184 from ?

based on the 300tdi starter being just shy of 3HP, and a 12V system, should draw at a max 183 amps.

 

[Sean]

based on the 300tdi starter being just shy of 3HP, and a 12V system, should draw at a max 183 amps.

i'll get a headache if i start doing math so early but i suspect there's something not right with your figures - what efficiency factor have you assumed for the starter within the calculation ?

remembering that most diesels have starter batteries rated circa 800CCA