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300 Tdi starter current


Troll Hunter
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Good topic here:

Cabling has 25mm2 on it.

Starter current probably in the range of 150-250A, but it is for such a short time very thick leads aren't required.

I've even jump started someone in a pinch with domestic  2.5 T+E  before....

You can't really fuse them, but do put an isolator near the battery.

Lots of kits of varying quality on ebay.

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55 minutes ago, cackshifter said:

I'd be wary of putting it on the front bumper - convenient , yes but maybe also a tad vulnerable? How about the side of the battery box?

Only vulnerable if it is not isolated. I have one fitted just inside the rear door of my 90 for jump starts so it is safe from anyone messing with it and in the dry, it is also handy in that position to connect to the tipping trailer or an electric winch on a trailer. 

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I have one on the battery box of each vehicle. Front foot well of the 110 and rear foot well in the ibex both are fed with 50mm² cable. The 110 has 35mm² jump leads and the ibex 50mm². Neither are fused or isolated. They are useful to charge through as I can just get the crocodile clips in. Just make sure you mount it far enough in that you can shut the door with the jump lead connect (I wish I'd thought about this on the 110).

Mike

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15 minutes ago, L19MUD said:

Only vulnerable if it is not isolated. I have one fitted just inside the rear door of my 90 for jump starts so it is safe from anyone messing with it and in the dry, it is also handy in that position to connect to the tipping trailer or an electric winch on a trailer. 

I was thinking of impacts and road dirt and corrosion rather than electrical. 

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I have 175A Anderson connectors on all my vehicles  .  RRC diesel, Matbro telescopic, JD tractors ( 7.6l diesel) and assorted other plant . I have13m of 50mm2 jump leads .  No problems of excess heat in the plugs when starting at -20°C and  about 20secs of cranking.

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The cranking current on my 300TDi is about 160A, but that number doesn't really have much to do with the rating of jump lead connectors since connectors are rated on the basis of continuous current whereas the starter current is rarely applied for more than a few seconds. 

If all you are doing is providing a boost to a vehicle which has a battery which is flat (e.g because someone left the lights on) but is otherwise known good then your jump leads don't need to be very big because all you need to do is put enough charge in the flat battery for it to be able turn the engine over a few times so it will start. The flat battery will help keep the system voltage within reasonable lmits and there isn't much chance of damaging any electronics on either vehicle. 

However, if you are dealing with vehicles which require a significant amount of cranking to get them started, and/or which have a knackered battery, then you will potentially be drawing the full starter current through the jump leads. In these circumstances you need at least 25mm sq cable, and preferably bigger. You also need really hefty crocodile clips on the ends of the cable, and a good joint between cable and clip.

Sizing of the cable in these circumstances isn't about the current rating of the cable, it's about keeping the circuit resistance as low as possible so that the starter motor on the vehicle being jump started spins as fast as possible. 

IMHO jump leads should be made out of the thickest wire you can reasonably afford. Mine are made out of 35mm sq welding cable. I use these connectors:

https://uk.rs-online.com/web/p/industrial-power-connectors/3826215/

which I think are superior to Anderson connectors since they have a bigger contact area (and hence a lower contact resistance).

I've got one connector mounted on the front of the seat box so it's easily accessible with the passenger door open, and a second one mounted on the box which covers the back of the near side rear lights so it can be used with the rear door open. I've found this combination means that you can pretty much always orient the donor vehicle and the one being jump started so that my 2m long leads will reach far enough (although I do have a 2m extension cable as well if I need it). 

Having the connectors inside the vehicle protects them from weather and road dirt, which otherwise would cause undesirable corrosion on the contacts.

Both connectors are linked back to the battery in 35mm sq cable and can be switched on or off using a battery isolator switch mounted on the seat box.

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I haven't done a precise count, but I get the impression that not fused and possibly not isolated, except by a general battery isolator, are both acceptable options. Many thanks to those who gave details of cable sizes.  I'll certainly use the largest diameter cables I can.  I currently have 35mm2, 3m long jumpers, so it looks as if it'll be those.

Many thanks for all your views.

Mike

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