Project Mu

While they may seem like little more than a pair of cables with alligator clips at each end, there is a bit to know when purchasing a set of your own to throw in the back of your vehicle. First of all, the quality of the conductors and insulators used in the cables have a huge impact on the performance, longevity and cost of the jumpers, with the cheapest options mostly constructed with aluminium conductors insulated with PVC sheaths. While aluminium can be fine if sized correctly, aluminium is more brittle, and also has a reduced current carrying capacity, when compared to conventional copper conductors. PVC is also less than ideal and, while quite hard wearing it offers little resistance to high temperatures. This can make working with PVC cables a bit of a challenge. At the other end of the quality spectrum you’ll find high quality oxygen free copper conductors wrapped in dual layer insulators consisting of hardwearing PVC wrapped in flexible, abrasion resistant, chemically and UV stable nitrile. Jumper cables made using pure copper insulators and high quality double insulated nitrile sheaths are not cheap, but can provide a lifetime of service provided they are looked after.

Other materials to look out for are aluminium coated copper conductors, which offer excellent conductivity and resistance to corrosion. Copper clad aluminium on the other hand is markedly inferior in almost every measure with the exception of cost, and is best avoided if you’d like to be able to rely on your jumper cables when the time comes to use them. Silicon rubber is also a common insulator type, which is wonderfully flexible however offers little mechanical protection for the conductors, which means they are easily pierced or torn if treated poorly or exposed to rugged conditions.

If you are familiar with the look and feel of PVC verses silicon and nitrile then a physical inspection should be able to tell you what insulator is used. As for the conductors, copper is substantially heavier than aluminium, so the weight of the cable is the best indicator of what is inside.

Most jumper cables consist of a pair of conductors just long enough to bridge the gap between two vehicles when parked nose to nose, terminated on each end by pairs of large alligator clips. Short jumper cables start at a length of approximately 2.5-metres, which is basically the minimum length required to bridge the distance between the batteries in two vehicle. Longer lengths are available, allowing greater flexibility in bridging gaps between the stranded and jumper vehicle. Grabbing longer jumper cables is highly advisable for this reason, especially if yours is an offroad vehicle or a mid-engine vehicle like a work van, however they must necessarily be markedly larger in capacity due to the compounding effect of inline resistance as the cable gets longer. Longer jumper cables capable of transferring the same amount of power as a shorter set will inevitably have a larger cross sectional area, and cost significantly more, due to the increased size of the conductors.

In terms of sizing, how much current you need to start your vehicle largely depends on the the size of the vehicle and the type of engine, but there is a few rough rules of thumb that can be applied. If you have a small to medium sized compact petrol-driven passenger vehicle then you are probably going to be fine using a set of jumper cables rated for 200-Amps of current flow. Medium to large sized petrol-driven passenger vehicles will likely need no more than 400-Amps worth of current capacity. Larger vehicles like pushrod V8s and diesel driven vehicles like dual cabs, 4WDs and light commercial trucks can need 600A plus. Check the current rating of thejumper cables you select prior to purchase to ensure you select a solution that meets the minimum requirements you need for your particular vehicle.

With the advent of lithium battery technology and the proliferation of modern, lithium battery based portable jump starters, you could be forgiven for thinking you may no longer need to carry a  good set of jumper leads. Jump starters can however deteriorate over time, or fail outright, so even if you have a modern jump starter pack it is highly advisable to keep a set of jumper leads in your vehicle for situations where your jump starter pack doesn’t cut the mustard.

While not a replacement for a trusty set of jumper leads, you should always have a decent battery charger on hand. This is beneficial for several reasons. First of all, a battery charger will help you ensure your battery is returned to a full state of charge after needing a jump, especially if you aren’t gonna be running the vehicle for a long enough period following the jump to fully recharge it. More importantly, a battery charger can be placed on your circuit racer, 4WD, boat, motorhome or other recreational vehicle when left to sit for an extended period, in order to prevent it from needing a jump in the first place.

When jump starting one vehicle with another, there are a few things you can do to minimise the risk of something going wrong. The first thing to do is get the batteries in each vehicle as close together as you can. This usually involves parking nose to nose, as each battery will usually be located in the engine bay. If the battery is on the left side of one vehicle and the right side of the other, it may also be suitable to park the vehicles with the front quarter panels overlapping. Ensure you do not allow the two vehicles to touch, as they must be electrically isolated from each other in order to avoid damage to the sensitive electronics in each vehicles. Once you have the two vehicles positioned, join the positive posts of each vehicle together using the red jumper cable, starting with the vehicle to be jumped, followed by the vehicle which will be doing the jumping. Double, and triple, check your connections prior to attachment in order to avoid any risk of damage. Next attach the black jumper cable to the negative battery post of the jumping vehicle, then attach the other end of the black jumper cable to a solid grounding point on the vehicle to be jump stated. Some modern vehicles will have a designated point to which you should attach the negative jumper lead, otherwise any quality grounding location should do the job. Do not connect the negative jumper lead directly to the negative post of the battery to be jumped, as this will likely result in a hefty spark that can give you a fright, can damage the battery terminal and can even lead to an explosion in the right conditions. If you vehicle doesn’t have a designated grounding point for attachment of jumper cables then look for a clean and unpainted bolt or similar metal point you can attach the alligator clip to. A shock absorber mounting point is often a good option, if a better one cannot be found. Check to make sure the cables are routed in such a way they do not obstruct any moving parts like the engine belts or thermofan. Next start the jumping vehicle, and leave it running for several minutes.