A “dead” battery in a car is not such a rare phenomenon. And if you need to go urgently, the fastest and most reliable way to start the car is to find a “donor” and use the starting wires. That’s just not every set of wires will allow you to “light” quickly and safely.
The starter of the car at the moment of starting the engine consumes a current of 400-600A. Accordingly, it is highly desirable that the cable current specified in the characteristics is not lower.
However, you should not blindly rely on this characteristic. Let’s take two cables – one with a resistance of 0.005 ohms, and the other – 0.01 ohms. Both of them will withstand a current of 400 A , but the voltage drop on the first wire will be 2 V, and on the second – 4. This means that only 12 – 4 = 8 volts will come to the starter through the second wire, which may simply not be enough for the starter.
In addition, many unscrupulous manufacturers of budget starter wires overestimate the maximum current, “drawing” on the packaging values of 600-800 A with a wire cross-section of 5 mm 2 and flimsy “crocodiles”. Therefore, if you see too attractive a price with impressive characteristics, like more expensive wires, then most likely they are trying to deceive you.
Cable material and cross-section
Cables starting wire may be made of copper or aluminum (sometimes – copper coated) have a cross section and from 4 to 16 mm 2 . Both the material and the cross-section affect the cable resistance, and this is the most important parameter of the starting wires.
The resistivity of aluminum is twice that of copper. That is, with the same resistance, an aluminum cable should be twice as thick as a copper one. In addition, aluminum bends worse and breaks faster. For these reasons, copper cable is preferred over aluminum.
However, copper wire is more expensive. Therefore, manufacturers, in order to reduce the price of the product, reduce the cross-section – 4 mm 2 and even less. But his resistance is lower, so it’s okay?
The specific resistance of copper is 0.0175 (Ohm · mm 2 ) / m, so the resistance of a meter copper cable with a cross section of 4 mm 2 is 0.0175 / 4 = 0.004 Ohm. A pair of four-meter cables of this cross-section will give 0.008 Ohm and 3.2 V voltage drop at 400 A – a bit too much. The minimum cross-section of a three-meter copper cable should be 5mm 2 (or better – 9 or even more), and aluminum – 10mm 2 . But an aluminum wire of this cross section bends very badly, so it is better not to take aluminum starting wires at all.
Both materials are used in both budget and expensive wires, so you need to look at the cross section, and not at the cost.
Length of cable
How long should the cable be? On the one hand, less is more. On the other hand, “lighting” is usually done when both batteries are in their regular places in cars and it is simply impossible to place them close to each other – no matter how you press, a meter and a half between the terminals remains.
In addition, it is not always possible to press the donor car close to the desired side. Especially in winter, if trouble lies in wait at a parking lot half-covered with snow, when it’s not possible to get close on foot from all directions. Here you need three meters , or even more .
But the longer the wire is, the greater its resistance. To compensate for the increased resistance, the cross section of the long wire must be larger. For a four-meter copper wire, a minimum cross-section of 9 mm 2 is desirable . As a result, the cost of a long wire is always higher than a short one.
Inexpensive starting wires are insulated from polyvinyl chloride or polyethylene, and at positive temperatures such a starting wire behaves quite “decently”. But already at -15 ° C PVC “dubs” – the cable becomes difficult to bend / unbend, it strives to jump out of the hands and curl back into the bay. In more severe frosts, such insulation can crack, causing damage to the wire and a short circuit.
Starter wires STELS 55919 1 550 *
A high-quality starter wire has a special cold-resistant insulation that retains its strength and elasticity in the most severe frosts. This, of course, increases the cost of the product. But it is better to overpay than to suffer in winter with oak wires, because it is in cold weather that the battery fails most often.
An important element of the starting wire is the clamps that fasten the wires to the battery. In inexpensive starting wires, these are clamps stamped from thin sheet metal, often loosely assembled, with backlashes and with a weak clamping fastening of the wire. The contact resistance of such clamps can be several times higher than that of the conductor itself.
To ensure tight, reliable contact, the following conditions must be met:
Reliable fastening of the wire to the clamp, and it is better if the wire is attached not to one jaw of the clamp, but to both. It is undesirable for the wire to be crimped, it is better if the wire sits on a screw terminal or when welding.
The clamp spring must have a large force on the compression of the jaws, preventing it from spontaneously coming off the battery terminals.
The jaws of the clamp must provide a large contact area; clamps stamped from thin metal are undesirable.