![]() I needed to do some work requiring the battery, tray and air box removed. I started to notice a strange yellow/white patch on my driveway but couldn't see any leaks under the car. I fitted a new Exide battery back in February and not done many miles during covid lockdowns. This won't be everybodys battery problem but I'll explain a battery problem that can catch you out. I have now wrapped some red insulating tape around all the wrenches in my toolbox that fit the battery clamp bolts. Of course they do put batteries in plastic insulated boxes, but most 6-9 inch wrenches can find some metal close by. When refitting a battery you reverse the procedure by fitting the positive terminal first, then the negative terminal. Therefore if you start releasing the positive terminal first and your uninsulated wrench touches it, there could be a loud 'bang' and in the worst case the wrench welds to the bodywork and your battery explodes in your face!īy removing the negative terminal first, you reduce the risk of shorting the positive terminal to the chassis and the risk of life long disfigurment which your wife would not like. The car body metal work is grounded to battery negative on most cars. Most will be using their standard open or ring spanner wrenches to remove battery terminals. Returning to the misconceptions, removing the negative lead first and replacing it last is a safety procedure you follow when installing and removing vehicle batteries and has nothing to do with avoiding sparks setting of hydrogen. The second point is that chargers should not allow the battery to overcharge and gas, when far more hydrogen is released. When you need to disconnect a charger from a charging battery you should SWITCH OFF AT THE CHARGER WALL SOCKET first. It makes little difference to explosion risk if you disconnect the positive OR negative first whilst the battery is charging - sparks and arcs can still occur at the negative terminal.Įxplosions arise because the battery could be giving off loads of HYDROGEN and as we all know from the early history of airships, hydrogen only needs a static spark to cause an explosion. I must now correct some misconceptions about disconnecting positive and negative battery cables. The modern geared starter motors are more tolerant of abuse than the old direct drive starter motors but they still can fail from electrical overload just like the older starters. The contact welding is usually avoidable collateral damage from trying to run the starter motor for an extended period of time to start the engine after the battery voltage begins to drop - 15 seconds is the longest I would allow the starter to operate before switching off before trying again if unsuccessful after 4 attempts, it is essential to allow the starter to cool down before further attempts. If the voltage decreases to a point where the motor will not turn, the amperage will try to increase to the motor Locked Rotor Current value until the battery fails or the motor windings burn out. The cause of the welding is the fact that the heat generated by an electrical current is a function of the amperage squared. The power rating of the starter motor is effectively constant so if the voltage is decreased, the amperage has to increase. The answer is based on basic electrical theory - Power = Amps x Volts. Somebody can work out why that might happen. Whenever you try to start a car with a low battery (<9V) there is a high chance the starter relay contacts will weld themselves together and hold the starter on. ![]() You could make sure the battery post terminals are clean and check the engine/chassis grounding post. ![]() But then there are plenty of old school mechanics that will tell you to hit things with a hammer first! By 'clutching at straws' you can do more expensive damage. Once you start seeing those kind of random dash light problems you need a known good battery and diagnostics to help you. In fact, even starting it with a totally dead battery is a big risk because the alternator is capable of producing high level damaging pulse spikes which are not smoothed by a flat or faulty battery. Whenever you jump start a modern car full of electronics you take risks. You clip the probes to the battery terminals and measure the voltage, then follow a number of scenarios of putting loads on and repeating. Why don't you guys and gals with these types of problems go and buy a cheap digital multimeter? After all you have already bought an expensive car.
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