So that the car does not burn: how to disconnect the mass

A sudden car fire is, fortunately, not too frequent, but it is quite common enough to cause serious phobias in many drivers. Especially those who at least once in their life saw a blazing car or its black “skeleton” on the side of the road … Many believe that only a mass switch will help to escape from this. They are right, but the inconvenience from the switch often exceeds its usefulness. However, at least one correct option to install the switch is.The cause of ignition of the car in motion is fuel leakage, ignition of objects caught on the heated exhaust system, or short circuit of the electrical wiring. In a fire that engulfs a car that stands without outside intervention, in 99% of cases electricity is to blame. There is simply no other reason: the release is cold, and the fuel, oozing or even dripping, almost never ignites by itself. Worry about such a fire is removed using a mass switch, de-energizing the network completely. It will save a simple mechanical manual “switch” for two or three hundred rubles, an expensive “mersedesovskoe relay” Gruner-750, popular in the jeepers’ party, or any other option.

Here are just the minuses of the mass switch is not less than the pluses (sorry for the pun).

On a relatively modern machine, full-time electronics do not like power outages, losing settings, adaptations, and memory. In addition, many units sometimes need tens of minutes to correctly “fall asleep”, and dancing around the open hood, waiting for all electronic processes to complete correctly, then to cut down the mass is insane. Moreover, visually this completion is not defined.

Full and other inconveniences. With the battery disconnected, you will not put the car on the alarm, then you will not open the door with the key fob, comfort systems such as opening the trunk with your foot, closers of glass and much more become useless without power. However, there is a way that will help and protect against fire, and do not de-energize the electronics.

It sounds like a strange and mutually exclusive … But one of our readers, Alexander Tsaplin, shared with the community of “Wheels” his own original and very simple development. This method is suitable for owners of new machines who understand elementary electrics and know from which end to take the soldering iron.

So, the first thing we do is install the mass switch. In the most usual way, as they always do – disconnecting the wire from the body that comes from the negative terminal of the battery, and connecting it back through a powerful “switch”. We use any type of mass switch, which one we like – a manual breaker with a handle or a key, an electrically controlled contactor from a truck, a specialized relay or something else.

Now we need to purchase several meters of wire with a cross section of about 2.5 mm2, the corresponding amount of thin protective corrugations for the wires, two conventional five-contact automotive relays and automotive terminals. From all this, we collect, according to the diagram below, the simplest additional wiring from the battery to the standard high-beam headlamps.

We find the positive wires through which +12 comes to the headlights when the high beam is turned on – to the right and to the left. These two wires are cut near the headlights and in the gap of each one by soldering, crimping or, in extreme cases, with a high-quality twist we connect the contacts and windings of the relays K1 and K2. Also, this additional circuit is connected to the negative terminal of the  corresponding amount of thin protective  to the diagram.

Protection against short circuit in the wiring of the car is ready. Consider the work of this scheme in different modes.

When the mass switch is closed, the battery is connected to the body and the engine normally. There are no nuances here – everything works as usual.

When the mass switch is closed (the engine is started or not – it doesn’t matter), we press the stalk switch that turns on the high beam, our additional relays are activated, and the high beam lights up – here, again, there are no changes and nuances for the driver compared to the standard version .

Now we leave the car, leaving it in the parking lot or in the garage, and we want to protect it from possible fires. Open the hood, turn off the weight by turning the knob, but the minus on the body … does not disappear!

Look at the scheme again. Now the battery minus is turned on to the body by our separate wiring through the normally closed contacts of the two relays and through the parallel threads of the high beam lamps. The resistance of one cold filament of an average head lamp is about 2.5 ohms. Two in parallel, as in this scheme – about 1.2 Ohms. This is an insignificant resistance in the negative circuit, and almost all the standard and non-standard electronics and electrics, which are constantly switched on (bypassing the ignition key) simply do not notice it. For it, disconnecting from the power supply via the negative wire after opening the mass switch simply does not occur.