Thread: Whats the difference between

assuming you dont mean the elcheapo Kmart or supercrap ones I cant see why not. The 200 ampers from Kmart Ive cooked trying to jump a dead flat petrol series and the super cheap ones dont look much better.

Just out of curiosity why do you need a positive and negative? whats wrong with a braided earth strap going to an earth near the battery?

I often wonder about the current ratings of the cheap jumper leads. There are so many variables that the real current carrying capacity can be difficult to determine.

See also http://www.alphawire.com/PAGES/383.CFM

To tell the truth, I'd take jumper lead current capacity with a grain of salt and would probably derate it by up to 50%, i.e., consider a cable marked at 400 amp as really 200 amp. In a jump start situation what you are worried about is voltage drop - the load isn't on long enough for the heat from the voltage drop to be of serious concern.

I suspect cables marked as battery cables will be better able to carry the rated current without as great a voltage drop and without heating up as much. Too much heat and your insulation will melt..

Also, I've noticed a few jumper leads that have thicker than normal insulation to give them the appearance of being heavier cables.

I believe that jumper lead ratings are like cheap stereo power ratings - worthless.

Another option may be welding cable.

Ron

Originally Posted by p38arover

I often wonder about the current ratings of the cheap jumper leads. There are so many variables that the real current carrying capacity can be difficult to determine.

See also http://www.alphawire.com/PAGES/383.CFM

To tell the truth, I'd take jumper lead current capacity with a grain of salt and would probably derate it by up to 50%, i.e., consider a cable marked at 400 amp as really 200 amp. In a jump start situation what you are worried about is voltage drop - the load isn't on long enough for the heat from the voltage drop to be of serious concern.

I suspect cables marked as battery cables will be better able to carry the rated current without as great a voltage drop and without heating up as much. Too much heat and your insulation will melt..

Also, I've noticed a few jumper leads that have thicker than normal insulation to give them the appearance of being heavier cables.

I believe that jumper lead ratings are like cheap stereo power ratings - worthless.

Another option may be welding cable.

Ron

I'll second that Opinion!.....all of the above .....especially.....

Welding cable IS a very good choice especially industrial grade [usually rated for longer continuous or more frequent interval use]......but the really good stuff is uber pricy......different construction using more and finer strands of wire......remember that current carrying capacity is a function of cross section area of wire and that electron "flow" is basically along the surface of any wire......thus lots of fine strands plaited together give a markedly greater current capacity than a single heavy wire of same thickness as the bundle of fine wires.

Hi Nigel
Have you looked at Drivesafes website??? He sells all sorts of cable.
Andrew

Originally Posted by byron

electron "flow" is basically along the surface of any wire......thus lots of fine strands plaited together give a markedly greater current capacity than a single heavy wire of same thickness as the bundle of fine wires.

Dunno about that for DC and low frequency AC.

We were taught about Skin Effect when I did my electronics (radio technician) training but only in respect of RF current flow at HF and above. In fact, this was one of the reasons given for silver-plating of tank coils, etc., and the use of Litz wire in IF transformers. (see http://www.surplussales.com/wire-cable/LitzWire.html ), and also the use of copper tubing in HF tank coils in high power (10 kW - 30 kW) transmitters that we had at work

See http://en.wikipedia.org/wiki/Skin_effect


Ron

Another reason for more strands is of couse flexibility. As welding leads are continually moved they need to be more flexible as well as bieng able to carry the current, whereas a battery cable is normaly fixed in a particular spot and never moved.
Brad

Just to be silly where are ya? I have a set of 15m or so long jumper cables made out of cable about as thick as my thumb, they are a little stiff now, still work ok and are my light duty set. I can probabley be convinced to part with half of them if a, when I dig em out and check the cable Its ok for use and
b, you ask real nice and agree to pay postage.

For current flow and the skin rule I was always taught that the electron flow starts at the surface and works its way in. As amps increase so does the depth then if you exceed the rated ability of the wire it gets hotter and hotter till it blows...

On that note ya still havent answered the "whats wrong with a braided strap to a handy earth?" question.

Dont some jumper lead manufacturers put on the non-continuous (cant think uh the word!) current duty on their cables to make it sound good?! Still, I have the majority of a 30m roll of 230A copper cable lyin' 'round at home. Sadly, I dunno if that's close enough. Where're you hiding?! It's...10.25mm in diameter! I think the whole roll cost me around $150. I needed it to wire up my secondary battery...and the batteries on my house!