Leakage current in the car is normal and increased. In the second option, there are unpleasant problems with the battery and starting the engine after idle time. Another exorbitant leak sometimes causes a car fire. And this is dangerous and expensive. Current losses, if they are too large, must be able to determine by indirect signs, correctly measure them with a multimeter. It is also useful to know how to find the cause of increased consumption and, if possible, eliminate it without a workshop. This will be discussed in the article.

What is current leakage in a car

To make the essence of current leakage in a car understandable to everyone without exception, let's start with basic concepts. To do this, take the simplest electrical circuit, consisting of a battery, a switch and some kind of consumer. We connect the consumer to the battery so that it can be turned on and off at will.

Now, if we close our electrical circuit with a switch, current will flow through it. The consumer will work, and the battery will be discharged. When we break the circuit (with a switch), no current will flow through it. At least it shouldn't. The consumer will not work, and the battery will lose stored energy.

In cars, the following can act as a switch:

  • egnition lock;
  • mass disconnect button;
  • electronics.

That is, by moving the ignition switch to the extreme position before parking the car, we break the electrical circuit. If the machine has electronics that go into standby or sleep mode, then it also works. However, despite these measures, the current in the circuit still flows. Why?

First, appliances that go into standby or hibernation continue to consume power. Secondly, the ignition switch is not a “major” switch, that is, it does not turn off everything. And only when the mass button is turned off or the terminal is removed from the battery, the car is completely de-energized.

Now it's time to divide the leakage current into normal and increased. Let's not talk about numbers for now. We'll get to them. So. If the energy of the battery while the car is parked is spent on the operation of the necessary devices, then this is a normal current leakage. Such consumers include a burglar alarm, a “sleeping” radio tape recorder, a recording video recorder, and so on.

Increased current leakage usually indicates that battery power is being wasted. This includes, for example, accidentally left side lights on. Another increased leakage current occurs due to incorrectly connected external devices that do not go into sleep mode when necessary. All in all, it's all a waste of energy.

Let's sum up the intermediate results.

A vehicle drain is any consumption of energy from a battery while the vehicle is stationary. Since it is essentially an electric current, then its losses are measured in amperes. The size of the leak depends on the number of devices operating during parking, and on the power of each of them.

There are two types of leakage current - useful and harmful. The first type refers to the energy consumption to perform the desired work. For example, to protect a car or record what is happening around. Harmful leakage is a waste of energy.

By and large, if the energy of the battery is spent on doing useful work, then it is not entirely correct to call it a leak. But in the case of a car, anyway, it is customary to consider any current consumption during a long stop as a leak. To understand all this, it is necessary to disassemble the concept of the current leakage rate.

Normal leakage current in a car

Normal leakage current in a car
Normal leakage current in a car

Now let's figure out a little what the current leakage rate is, and what is its value in specific numbers. The complexity of this item is that different cars have different indicators, and depend on many factors. However, there is still something to focus on. But first, let's briefly list the factors on which the current leakage rate in the machine depends.

These include:

  1. The abundance of regular electronics.
  2. Availability of external equipment.
  3. correct connection.
  4. Burglar alarm model.
  5. Algorithm of work of standard electronics.

Let's go through the points. The more standard electronics in the car, the higher the current leakage rate. Accordingly, if the car is relatively old and simple, there can be no losses on this item at all. If there is electronics, then a lot depends on how it goes into standby mode and works in it. Some cars, after being parked for a long time, “fall asleep” far from immediately, continuing to consume a lot of energy from the battery for some time.

External appliances are the most common cause of abnormal current leakage. The more of them, the higher the rate can be. Also, a lot depends on how competently they are connected to the on-board network. The simplest example is a radio tape recorder. Often, due to laziness or insufficient qualifications, this consumer is connected to the battery directly (and it is necessary through the ignition switch), as a result of which the current consumption increases.

Signaling. On average, all modern models consume about the same in standby mode. However, there are often options due to which the leakage current is noticeably beyond the scope of any norms. This is without taking into account breakdowns, marriage and crooked connection by unfortunate masters.

Concerning the rate of current leakage, opinions often differ. Someone says that it should be no more than 70 mA. Others say that for a modern car, 120 mA is still within the normal range. Although this is almost twice as much as in the first version. If we approach this issue as flexibly as possible (taking into account many factors), then the range from 0 to 120 mA can be considered normal.

Even for a “tired” battery, it doesn’t make much difference what kind of leakage current the user will consider the norm - 70 mA or 120 mA. Both options should be taken as a good indicator. We will return to this issue at the very end of the article. Now this is not the point.

On different cars, as already mentioned, the current leakage rate may be different. Exceeding the norm should be considered indicators significantly exceeding 120 mA. For example, 300 mA is already a serious problem. Not to mention cases when, due to critical malfunctions in the on-board network, the leakage current reaches 1 A or more. Such indicators are no longer just a violation of the norm. They talk about danger. Including, the ignition of the car mentioned at the very beginning is not excluded.

Total: the current leakage rate in a car is in the range from 0 to 120 mA.

What threatens a large leakage current on the machine

What threatens a large leakage current on the machine
What threatens a large leakage current on the machine

The most common (although not the worst) problem due to exorbitant current leakage in a car is a rapidly and frequently draining battery. This is usually noticed when the battery has served for several years, and is no longer able to accumulate a lot of energy. Excessive leakage current may have appeared on the machine much earlier. However, while the battery is “young and vigorous”, its reserves are enough for multi-day consumption of several milliamps. The old battery has fewer ampere-hours than the new one, so it sits down quickly.

For a new battery, large leakage currents are also far from useful. A constant load will, a lot or not - it doesn't matter if the battery is drained. And starter batteries retain their resource the longer, the more time they are in a fully (or almost) charged state. If, on the other hand, every single day the battery will land a little at first, and then up to half, and so on, it will be possible to start the engine in the morning, but the battery life will quickly decrease. The sulfation of the plates will begin, the capacity will gradually decrease, and goodbye to the new battery a couple of years after the purchase.

More serious problems can arise when the current leakage in the car is caused by short circuits, damaged insulation and water ingress. In such cases, heating of conductors or parts of electrical equipment is possible. And it already threatens spontaneous combustion. And, worst of all, because of this, the car often lights up at night when there is no one around. Accordingly, no one takes timely measures, as a result of which the car burns out to a bare body.

This, of course, does not happen all the time. But less terrible problems, such as when a new battery runs out, are unpleasant and indicate a malfunction. And this means that you need to know about the possible causes of current leakage.

Possible causes of increased current leakage in a car

Short circuit
Short circuit

There are a lot of them. But those that are more common than others are on this list:

  1. Incorrectly connected consumers. Most often it is a tape recorder. In order for it to be switched to the minimum power consumption mode, its power must be connected through the ignition switch. For this, a third wire is provided (except for ground and main plus). But, as a rule, this wire is simply attached to the positive one, and the whole thing is connected directly to the battery (at best, through a fuse).
  2. Breakdowns in systems operating in standby mode. Electronics is not eternal. Sooner or later, it breaks down, and stops turning off completely when the user turns it off. This happens not only with freelance devices, but also with standard ones installed at the factory.
  3. Short circuits. Far from always cause abundant sparking and instant burnout of everything in a row. It all depends on how good contact is formed between plus and minus. It happens that somewhere it just shortens a little. As a rule, due to oxidation of conductors or water ingress.
  4. Insulation damage. It also sometimes leads to short circuits, in which nothing burns out instantly, but the energy from the battery is consumed slowly.
  5. Wet electrical wiring. Water, if it contains salts, is capable of conducting electricity. At the same time, it is not at all necessary that it was originally salty. Even distilled water, if it gets on oxidized contact pads, turns from a dielectric into a current conductor. Wiring usually gets wet after rain, driving through puddles or careless car washing.
  6. Generator malfunctions. One of the most difficult causes of current leakage in a car to diagnose. Difficult because it is not detected by the standard method of pulling fuses one by one.
  7. Abandoned consumers. Most often, they forget to turn off the music, parking lights, freelance navigator or DVR.

Quite rarely, but it happens that backlight bulbs are slowly taking energy from the battery. For example, in the trunk or in the doors. The button to automatically turn off such a light bulb gets stuck, or water gets in after rain or washing, and the light bulb glows around the clock. She consumes, in general, a little. But this is only when the battery is peppy. If he is tired, then even a small light bulb is enough to drop the battery to zero in just one night.

Measuring current leakage in a car with a multimeter

Multimeter - instrument for measuring current leakage
Multimeter - instrument for measuring current leakage

Now consider the most important thing - how to measure the current leakage in a car. All you need is absolutely any multimeter. When measuring, it is extremely important to adhere to safety rules. Otherwise, you can burn the multimeter, and injure yourself, and damage the car's electronics.

The verification algorithm is as follows:

  1. Open the hood and lock the button that signals the security system to open it.
  2. Put the car in park mode - turn off everything except what would normally remain in standby mode. For example, alarm, recording DVR and so on.
  3. Remove the negative terminal from the battery. Contrary to popular belief, you can shoot plus. However, turning off the "mass" is more correct and 100% safe.
  4. Switch the multimeter to the current measurement mode in the range up to 10 A. Reposition the positive probe on the device accordingly. Never attempt to measure leakage current on a vehicle using the short range on a multimeter (up to 200 mA). At the moment the terminal is connected, there will be a current surge that the fuse in the measuring device may not withstand.
  5. Attach one multimeter probe to the removed negative clamp, and the second to the battery terminal from which this clamp was removed. Such a connection is called - in a circuit break. When you removed the terminal, you broke the circuit, and now you have connected a multimeter to the gap.
  6. If the burglar alarm is reset as a result of disconnecting the battery from the on-board network, turn it on again.
  7. Wait a while. In some cases, you do not need to wait - the leakage current can be detected immediately. In machines stuffed with electronics, it is necessary to allow time for all systems to go into standby mode. In rare cases, you have to wait up to 5 minutes. If you do not pay attention to this, then you can panic for no reason.
  8. When the multimeter readings level off, record them. This is the leakage current in your car.
  9. Do not turn on anything during measurements! Even a light load turns on with a current surge, which can lead to a blown fuse in the multimeter.
  10. Moreover, do not try to start the engine when a multimeter is in the open circuit !!! It is designed for only 10 amperes, and during the operation of the starter, a current of 100 - 200 A will flow through the circuit.

Then it remains only to compare the obtained indicators with the norms described above. In general, if the multimeter measured less than 0.12 A (120 mA), then there is no reason to worry. If the current leakage is greater than this figure, then you should start looking for the cause.

Method for finding the cause of increased current leakage

Circuit breakers
Circuit breakers

In most cases, finding a current leak in a car is done by removing the fuses. To do this, you need to know where they are, and what each of them is responsible for. As a rule, the relevant information is applied directly on the cover of the fuse box. You can also try to navigate the electrical wiring diagram. This is a more complicated method, but it has an advantage. The fact is that not always all the fuses in the car are in one place, and the “guilty” can not be found under the hood.

The method is very simple. After measuring the leakage current, the multimeter is left in the open circuit. Next, you need to alternately pull out one fuse from the block, and look at the device. If the readings have not changed, then the removed fuse returns to its place, after which the next one is pulled out. If the leakage current has decreased, then you need to find out what the removed fuse is responsible for.

What to do if the leakage current is above normal, and the method of pulling out the fuses did not help to find the cause? In such cases, it is worth starting with checking freelance devices. For example, you can try to remove the front panel from the radio, or turn it off completely. Then it is worth checking how the leakage current changes when the car is armed. Perhaps the alarm is consuming too much.

If this does not help to identify the cause of the increased current leakage, then there is still a generator, a starter and possible fuses not found in the passenger compartment.

How long does it take for the leakage current to discharge the battery?


In conclusion, we will briefly consider the question of how serious an increased current leakage is for a particular battery. Fortunately, this can be calculated. The only problem here is that it is not always possible to find out the current real capacity of your battery. After all, it has been constantly decreasing since the moment of purchase. And with improper use, after a year or two, it can be no more than 15 - 25 ampere-hours.

Therefore, for starters, let's imagine the situation when the battery is new. That is, its capacity is, say, 60 ampere-hours. Another condition is that the battery is fully charged. Now let's take a large leakage current. For example, 5 times the maximum allowable rate - 600 mA (or 0.6 A). In order to discharge a fully charged 60th battery to zero with such a current, theoretically it will take 100 hours. Or about four days.

Now imagine what will happen with the same battery, but not fully charged. This often happens on cars with a problematic generator, relay-regulator, or when they drive a little, and the starter is pulled often. For example, if the battery was left in the parking lot only half charged, then a leakage current of 0.6 A “eats” it in just two days.

Well, about batteries in which only crumbs remain from the original capacity, even a slight excess of the current leakage rate will be a problem. For example, after 3 - 4 years of careless operation, 15 ampere-hours remain in the battery. And even less. So he sits down in one night, when there is an excess of the current leakage rate. Although much more often this happens because the battery is not fully charged from the generator.

Brief summary

Increased current leakage in a car is a serious malfunction. For the norm, you can safely take everything that is less than 120 mA. Although for some machines this is too much. To measure the current leakage, you need a multimeter and a simple algorithm of actions. Finding the cause of excessive power consumption is also easy. Well, its elimination is a matter of technology.

VIDEO: current leakage