GW8IZR Posted March 2, 2015 Share Posted March 2, 2015 Cheap jump leads from eBay are often advertised as 600A 1200A etc, when you pick them up they are ever so light. Often not much copper in those 14mm diameter cables. Quote Link to comment Share on other sites More sharing options...
UdderlyOffroad Posted March 2, 2015 Share Posted March 2, 2015 175 A continuous rating. 300-odd A through for a few seconds whilst cranking is fine Quote Link to comment Share on other sites More sharing options...
rrr47 Posted March 2, 2015 Author Share Posted March 2, 2015 I'm no electrical engineer, but I think the thicker the wire, the more amps you need or lose pushing power through it. That's why good Hi-Fi speaker wire, welder's cable and good jump leads have lots of fine copper wires, each can only carry a small amount of amps, but a bunch of them combined can carry a lot with very little loss. While cheap jump leads made of thick copper wire can cope with higher amps, but they will use up power transmitting the power, and, they will also turn that wasted power into heat. Quote Link to comment Share on other sites More sharing options...
GW8IZR Posted March 2, 2015 Share Posted March 2, 2015 I'm no electrical engineer, but I think the thicker the wire, the more amps you need or lose pushing power through it. That's why good Hi-Fi speaker wire, welder's cable and good jump leads have lots of fine copper wires, each can only carry a small amount of amps, but a bunch of them combined can carry a lot with very little loss. While cheap jump leads made of thick copper wire can cope with higher amps, but they will use up power transmitting the power, and, they will also turn that wasted power into heat.You are on the right lines but the important thing is the amount of copper. The more the better.Cheap thick jump leads often contain the same amount of wire as cheap thin leads .. Remember rubber and pvc insulation is far cheaper than copper. Quote Link to comment Share on other sites More sharing options...
heath robinson Posted March 3, 2015 Share Posted March 3, 2015 I've got stacks of 50mm-sq multistranded welding cable, so I'll make some up out of that, and just buy the kit of anderson bits from ebay. Cheers. Quote Link to comment Share on other sites More sharing options...
GW8IZR Posted March 3, 2015 Share Posted March 3, 2015 I've got stacks of 50mm-sq multistranded welding cable, so I'll make some up out of that, and just buy the kit of anderson bits from ebay. Cheers. Yep thats a very good way to go, I used some similar cable that I had in stock which is very low volts drop but way too stiff for the job. they are good and long but the minimum bend radius means they fill the 90 when I carry them ;-) Quote Link to comment Share on other sites More sharing options...
heath robinson Posted March 4, 2015 Share Posted March 4, 2015 The other advantage to this is that I've got a bunch of 3000F supercapacitors, meaning that I can bung an anderson on a bank of them and have a lightweight jump pack. Quote Link to comment Share on other sites More sharing options...
rrr47 Posted March 4, 2015 Author Share Posted March 4, 2015 What's an 3000F supercapacitor? Quote Link to comment Share on other sites More sharing options...
muddy Posted March 4, 2015 Share Posted March 4, 2015 Dunno but it sounds F cool. Quote Link to comment Share on other sites More sharing options...
heath robinson Posted March 4, 2015 Share Posted March 4, 2015 Have a look at this - That's basically what I've got, but those are 350 farad caps, mine are 3000... The first time we filled up a 24v one (goes on our solar rig to smooth out the spikes of current the bass amp pulls for our stage) so much current flowed that the 50mm-sq cables went solid in my hands! A bit of back-of-fag-packet calculating and I came to the conclusion that it'd pulled in somewhere in the region of 30,000 joules of 'leccy IN THE FIRST THIRD OF A SECOND! These things are awesome, and scary, in equal measures. Hell of a jump pack though! It's so good that I've built one into my van in parallel, and i'm putting one my capri too, but with golf cart battries. The van (lt35 2.4) starts brilliantly, even after being ignored for months. Quote Link to comment Share on other sites More sharing options...
GW8IZR Posted March 4, 2015 Share Posted March 4, 2015 Do you have to limit the inrush current? Quote Link to comment Share on other sites More sharing options...
heath robinson Posted March 4, 2015 Share Posted March 4, 2015 Do you mean in respect to ecu etc? It's never been a problem, but then I'm running it in parallel with a battery, mostly on fairly old vehicles. The capri has an ecu (eeciv running a granada cosworth v6 ), and that doesn't seem to mind it. And thinking about it, that's the reason we use it on the big solar rig - it's parallel to the big batteries, to cater for the draw from the two 3kw (6kw peak) inverters, one of which feeds the honking gurt big bass amp for our honking gurt PA system. The other one runs the digital mixing desk and lots of other bits of sensitive gear. Never a flicker, and arguably the best sound at any given festival to boot! Sorry if I sound a little smug, it's taken us 10 years and a hell of a lot of work to build this up to this level, it's kind of my baby. Or are you meaning it could pull too much recharging after starting? They can't pull what isn't there, if you see what I mean, so to just top up the deficit from starting is fine, it'll either take it from the battery (which is only a fraction of the battery's stored energy - it might deliver a lot very fast, but it's still a fraction of the Ah rating of the average car battery) or charge from the alternator. In fact the best way we've found of charging them is either an alternator or a solar panel (handy, seeing as I'm surrounded by the bloody things!), they'll only pull what they're given. Quote Link to comment Share on other sites More sharing options...
GW8IZR Posted March 4, 2015 Share Posted March 4, 2015 Yes I was kind of thinking about the excessive current from the battery when charging after starting. I have seen wet LA cells bend plates when traction current breakers trip at the end of a very long line, that acts like a big capacitor which needs charging and it would literally boil the Mercury off the rectifiers and bend the floated batteries. I suppose the charge current is limited by the I2R losses in the alternator and its wiring to the cell and capacitor and they are probably connected together with a very low R cable so the potential difference between them is small. It's an interesting setup and I think it might have an application for an RF amplifier I'm developing which has to be fed at a fairly low voltage but needs a low source impedance supply. Food for thought. Quote Link to comment Share on other sites More sharing options...
rrr47 Posted March 5, 2015 Author Share Posted March 5, 2015 Interesting video, why do we have batteries then? Quote Link to comment Share on other sites More sharing options...
GW8IZR Posted March 5, 2015 Share Posted March 5, 2015 You might want to leave your lights on when the engine isn't running, the capacitor can only provide its energy for a short time but can deliver it very quickly. Ideal for starting but not good for long term discharge. Big push to reduce electric load on cars so you can use smaller batteries = quicker to accelerate/ decelerate and use less fuel etc. Quote Link to comment Share on other sites More sharing options...
need4speed Posted March 5, 2015 Share Posted March 5, 2015 Boy this threads taken a turn..... Quote Link to comment Share on other sites More sharing options...
GW8IZR Posted March 5, 2015 Share Posted March 5, 2015 yes - sorry for diversion. Quote Link to comment Share on other sites More sharing options...
heath robinson Posted March 5, 2015 Share Posted March 5, 2015 We use 2v traction batteries on our big rigs, and the plates on them seem fine after 2 seasons of hard use, so I don't think it's that much of a problem for a car battery - the plates in the big batts are about 3ft long, and if they don't warp I'd imagine that the dinky plates in a car battery will survive. Yup, sorry! I get distracted by the unusual fairly easily. I'll make a little thread on the jump-pack when all the bits arrive, and all this kind of waffle can go in there. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted March 5, 2015 Share Posted March 5, 2015 I'm no electrical engineer, but I think the thicker the wire, the more amps you need or lose pushing power through it. That's why good Hi-Fi speaker wire, welder's cable and good jump leads have lots of fine copper wires, each can only carry a small amount of amps, but a bunch of them combined can carry a lot with very little loss. While cheap jump leads made of thick copper wire can cope with higher amps, but they will use up power transmitting the power, and, they will also turn that wasted power into heat. In a DC application the only reason for lots of fine wires as opposed to several thick ones is to make the cable more flexible physically. It's the overall cross sectional area of the combined wires (whether lots of fine wires or several thick ones) that governs the power loss. The larger the cross sectional area the less resistance and the less power you will lose as heat. Quote Link to comment Share on other sites More sharing options...
rrr47 Posted March 5, 2015 Author Share Posted March 5, 2015 Cheers CwazyWabbit, what about hi-fi speaker cable? Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted March 5, 2015 Share Posted March 5, 2015 With AC the skin effect comes into play, as frequencies rise the current is carried in a layer nearer the surface of the cable, the higher the frequency the thinner this layer. http://en.wikipedia.org/wiki/Skin_effect This basically means there is a higher resistance for the higher frequencies with large strands, so lots of thin strands results in better high frequency performance. Or, multistrand will sound 'brighter' than solid core. Quote Link to comment Share on other sites More sharing options...
rrr47 Posted March 5, 2015 Author Share Posted March 5, 2015 I remember when I purchased a tidy stereo many moons ago, my speaker cable cost more than the speakers. Quote Link to comment Share on other sites More sharing options...
V8 Freak Posted March 5, 2015 Share Posted March 5, 2015 So.. In a Land Rover... Damp string will suffice as speaker wire as you're not going to notice any fidelity differences or potentially hear it at all !! Coat, Hat.. Bye Bye..... Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted March 5, 2015 Share Posted March 5, 2015 So.. In a Land Rover... Damp string will suffice as speaker wire as you're not going to notice any fidelity differences or potentially hear it at all !! Coat, Hat.. Bye Bye..... Surely any string in a Land Rover will be damp anyway ... Quote Link to comment Share on other sites More sharing options...
heath robinson Posted March 6, 2015 Share Posted March 6, 2015 Also there's the purely physical side - vibration will cause fatigue in wires with thicker cores faster, if that makes sense. This is especially pertinent in landys, for obvious reasons... Quote Link to comment Share on other sites More sharing options...
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