The question is I get asked is why do I need to spend £30/40/50+ on Jump Leads when I can get some down the market for £3.99?
And the answer is VOLTAGE DROP!
If you take a pair of cheap Jump Leads they have 4/5/6 mm cables and the cable is made of a mixure of Alloys (Copper Is Expensive) and the first thing that strikes you is the cable is not what i would describe as Multi Strand (enen though it has 6 alloy strands) and when you first open the cables they feel like coat hangers in construstion, by that I mean that you can straighten them out and hold them up verticle, these were never designed to be long lasting or good performers.
Does It Matter Which Cable I Connect First
Yes actually it does
If the two jumper cables are attached together, as is often the case, then the positive connection must be completed first, and then the grounding connection. The reason for this reversal is that because the cables are joined, when one clip is fastened, the opposite one is left dangling near it, unless an assistant holds it up. The dangling clip is likely to touch something that is grounded, like the chassis or engine block. Therefore, the clip that is left dangling should be the negative one which is intended to be grounded anyway. If, incorrectly, the negative clip is connected, while the positive one, left dangling, touches something that is grounded, an instant short circuit will result when the corresponding positive connection is later made at the opposite end. For the same reason, it is also important not to connect both clips on one end first to one car, because then the clips on the opposite end of the cable may touch, causing a short circuit.
Cheap Jumper Cables
If you use a set of the cheap Jump Leads then you will find that when conected from the master sorce (the spare battery or another vehicle) upon cranking the leads perform badly, if the sorce voltage is 12v+ on cranking the voltage on the slave vehicle could be as low a 6-8v. These cables in my opinion are only suitable to supply current from the boosting vehicle to put a charge the dead battery.
After several minutes enough energy is transferred to allow cranking of the engine. If the connections are good and the cables are large, the boosting vehicle battery may also supply part of the cranking current. In an extreme case, it is possible to crank and start a vehicle with no battery in it if the cables are heavy-duty.
Cranking current drawn through light-gauge cables will damage them by overheating and they will melt and the insulation catch fire.
Due to the placement of the battery in the boot of the Mini and the possibility of hydrogen gas trapped inside the following sequence is followed when jump starting a disabled Mini.
- Connect the two battery's (+) terminals with the red cable
- then connect the earth cable to the disfunctional car's (-) battery terminal.
- finally connect the remaining earth cable to the earth connection of the jump starting vehicle, on a point such as the engine block
- This is done to avoid a spark which could ignite any hydrogen gas within the Minis Boot Enclosure
And remember if your Mini Battery is Completly Flat 0v and no sign of life on the dash warning lights, your battery needs replacing as a lead acid battery will never recover to provide good service.
Edited by KernowCooper, 29 March 2013 - 02:05 PM.