How to check current leakage in a car with a multimeter: find and independently measure the permissible values with a tester

Many car owners have encountered a situation where they were unable to start their car in the morning. And everything was fine in the evening. And the battery itself is new and in good condition. The reason here may be battery leakage current. This phenomenon exists on any car, but must fit within a certain norm. If the leakage current limit is exceeded, the battery will discharge while parked. As a result, you will have problems starting the engine. It's time to figure out what causes battery leakage current and how to bring it back to normal.

What is the danger of current leakage from the battery?

Checking the battery for signs of energy consumption is a necessary measure for those who want to extend the life of on-board equipment. The first trouble that threatens the unlucky driver is the complete failure of the battery. And even recharging its capacity will only temporarily solve the problem.

As is known, acid batteries are structurally composed of plates placed in an electrolyte based on distilled water and sulfuric acid. When this equipment is discharged, acid salts accumulate on its plates. Because of this, the working surface capable of conducting current is reduced. Salts crystallize and become unable to dissolve even in an electrolyte. The battery capacity immediately decreases, and the product itself fails earlier.

You should know for what reasons such a phenomenon as excessive consumption of electric current can occur. First of all, you need to monitor the actual capacity and charge level of the car battery. A leak often occurs due to the negligence of the driver, who forgets to turn off one of the consumer devices in a closed car. Another common cause is electrical wiring faults.

So, in addition to light sources or a radio that have not been turned off for a long time, other causes of current leakage can be:

short circuit in the wiring that occurred due to unprofessional installation of equipment;
damage to the insulating layer (insulation) of electrical wiring in the on-board circuit;
oxidation of contact groups, terminals, connection sockets due to the accumulation of a thick layer of dirt and dust;
mechanical wiring damage;
melting of wires or contacts due to their close location to the motor;
using a very worn battery.

Timely diagnosis of current leakage will allow you to quickly eliminate the problem and drive without the risk of getting into an unexpected situation. This will also extend the life of a car battery of any brand.

Instead of an afterword

When buying a used car, it is useful to know how to find an electrical leak and understand its cause. Take a multimeter to inspect your car - you will save yourself from unpleasant surprises, such as a suddenly dead battery, power surges or burnt wiring.

For the same purpose, check the car's history. This can be done directly during a conversation with the seller. It is convenient to use the Autocode service - monitor information from 13 sources at once: traffic police, RSA, EAISTO, banks, tax and other services. The verification will take 5 minutes.

Afterwards you will find out the actual mileage, number of owners, history of fines, as well as information about theft, participation in an accident, restrictions on car registration and much more. Be carefull!

Having fully studied the online report, it is still worth taking a closer look at the technical nuances of the car when purchasing. And if you are not confident in your knowledge, or it is not possible to go for an inspection, order an on-site inspection service. The specialist will conduct a diagnosis for you and make a detailed conclusion from a professional point of view.

Checking current leakage in a car with an ammeter

If the machine is operating normally, the on-board network will consume no more than 70 mA. But this indicator is not achieved instantly. At the very beginning (when the circuit consisting of an ammeter and the on-board network is connected), the electric current consumption will be 120–130 mA. However, if the multimeter reading is higher, then there is a malfunction. The first thing you need to do is inspect the fuse box. When checking for current leakage in a car with a multimeter, the fuses should be removed one by one.

Disconnect the wire from the negative terminal of the battery and connect the multimeter. Don't forget to turn off the car. The multimeter at this moment will determine the amount of electric current that the car consumes when it is off.

When checking the current leakage in a car with a multimeter, we remove the fuse and, using a test lamp, determine whether current flows to the fuse when the car is not started.

When the car is not equipped with an alarm system, players and the like, the amount of electricity consumed will be no more than 70–80 mA.

Acceptable battery current consumption standards

Modern machines have a certain number of consumers of electrical energy on an ongoing basis. This could be a clock, ECU memory, immobilizers, alarms and other similar equipment. They are connected to the network and consume electricity. And all the time.

For example, let's take the volatile memory of an ECU. If you erase it, the unit will begin the relearning process and will again remember all current settings. Security systems only start working when the car is parked. From this we can conclude that low electrical energy consumption is a normal situation.

But there is a norm for current leakage in a car. This norm is a certain constant value - it can be calculated. It is necessary to sum up the consumption of each consumer in the on-board network. For example, alarms require no more than 20 mA. The clock requires 1 mA to operate. The audio system consumes about 3 mA and so on. In total, the total figure will be in the range from 50 to 80 mA. It's quite a bit. Even one lamp in the headlight, which they forgot to turn off, consumes 500 mA. And the current leakage rate in a car of 50 A cannot cause a complete discharge of the battery even in winter.

You can determine how much consumption there is using a multimeter. And if during the measurement process the consumption level is higher than permissible, that means. There is a problem in the on-board network. It needs to be found and eliminated.

How to check current leakage in a car with a multimeter

When the first signs of such a malfunction appear, it is necessary to check the current leakage in the car using a device.

Check sequence:

1. Before performing work, you need to find a diagram of the location of the car's fuses. This can be done by downloading the car's operating manual and asking the appropriate request in a search engine. In some cars, the fuse code is located on the fuse box cover. You need to find all the places where there are fuses in the car.

2. The positive terminal of the battery is removed. The ignition and all electrical equipment of the car must be turned off. Some experts recommend monitoring via the negative terminal. There are no fundamental differences, the circuit is still the same. When monitoring using the positive terminal, it is easier to search for a specific leak location.

3. The multimeter switches to the 10 Ampere DC measurement mode, the probes are installed in the appropriate connectors. It is better to put crocodile tips on the probes.

4. Next, the positive (red) probe is carefully secured to the positive terminal of the battery, the negative one - to the removed terminal going to the vehicle equipment. The location of this connection must be protected from accidental contact with the car body (you can simply temporarily insulate it with a rag) so that there is no short circuit.

5. The digital display of the multimeter will indicate the leakage current. If its value is less than 0.2 Ampere, no further control can be performed. If the current is more than 0.5 Ampere, that is, the critical value, it is necessary to proceed to further operations.

In the case when its value is in the range from 0.2 to 0.5 Ampere, the decision on the advisability of further actions is made independently. If the current exceeds the upper measurement limit (as shown in the following photo), you should stop measuring immediately and call a specialist.

6. If the leakage current in the car is greater than the critical value, begin to search for the specific cause and its source.

An assistant is needed for this. He will sequentially remove and insert fuses into their original places. At this time, the “operator” of the multimeter must monitor changes in the device readings.

If, with the fuse removed, the readings do not change significantly (by more than 5%), it means that practically no leakage current flows through this fuse.

It is more correct to start turning off - turning on with powerful fuses designed for high currents. This can speed up the search process. Usually along a chain of large rated fuses there are several smaller fuses.

If, for example, when dismantling the fuse responsible for the body control unit, the leakage current has decreased significantly, it is necessary to move on to monitoring small fuses responsible for lighting equipment, wipers, washer and other elements of body equipment.

Video - finding a current leak in a car:

It is best to go through all the fuses using this method. Car alarm fuses are usually not installed in standard places; they can “hang” next to the main alarm unit.

Some auto electricians use a sophisticated testing method. It does not require an assistant.

7. Complicated method. In this case, the positive terminal of the battery is connected back. The fuses are pulled out sequentially. The multimeter probes are installed in the connectors of the removed fuse, monitoring the current in a specific circuit. This method is more labor-intensive, but accurate.

8. Having deciphered all the circuits through which current flows from the fuse layout diagram, proceed to establish the specific cause of the leak in these circuits. To do this, you need experience working with car electrical circuits. The most common reasons:

wiring short;
relay sticking;
failure of electronic components.

9. To temporarily eliminate the problem of current leakage, you can not replace the fuse through which the leakage occurs. For example, if the cause of the leak is a malfunction of the car radio, you can turn off the corresponding fuse while parked.

How to look for a breakdown?

Experts recommend checking the leakage current (in the car battery) with a multimeter and then visually carefully inspect all non-standardly installed devices, their parts, and wires.

Perhaps something has been subjected to mechanical stress. If we talk about signaling, then these could be limit switches. If there are no signs of damage, burning or corrosion, you need to move on to more complex diagnostic methods. They will allow you to significantly narrow your search.

For example, automotive electricians often pull out fuses one at a time and see if the contacts spark. If there are flashes, and there should be no voltage in this circuit, then there is a current leak in the car. How to check it?

Tester to help. When a suspicious location is found, it is necessary to find a short circuit in the circuit. To do this, each wire is tested with a tester for integrity. This is done using the same multimeter. But it will already work in resistance measurement mode.

Other reasons for battery discharge

What to do if the driver measures the current consumption and it does not exceed the norm? As mentioned above, difficult starting after a long period of parking may not be caused by leakage currents. Some of the most common causes of this problem may include:

High battery self-discharge.
Generator malfunction.

Testing the battery for self-discharge

To determine the condition of the battery, you need to remove it from the car and wipe it clean with a rag soaked first in a solution of baking soda, then in water. If the battery is serviceable, you need to check the density and electrolyte level in each section (there are 6 in total). The battery is then fully charged by the mains charger to normal voltage (12.7 V without load).

All that remains is to leave the unconnected battery for several days and then measure the voltage at the terminals again. If the voltage loss is more than 0.2 V, then the problem is in the battery. You will have to buy a new battery or try to restore the damaged one, at least temporarily, by contacting the appropriate specialists. If the battery “holds”, then either the problem has been eliminated (for example, water was added to semi-dry jars), or the problem is different.

Checking the functionality of the generator

The problem may also be in the generator, which simply does not charge the battery when the engine is running. Of course, almost every car has a warning light that comes on if the battery is not charging. But it can also deceive if, for example, there is a charging current, but it is too small. In this case, the battery is not able to replenish the energy spent on starting the engine, and when a powerful load is turned on (headlights, heaters, etc.) it may even begin to discharge.

The multimeter switch must be set to constant voltage, the measurement limit should not be lower than 20 V.

First of all, it is necessary to measure the voltage at the battery terminals with the ignition off. For example, let it be equal to 12.7 V (battery is fully charged).

Voltage on the battery when the ignition is turned off (use a different type of multimeter).

Now you need to start the engine at idle speed, and turn off all consumers (headlights, radio, heaters, etc.). The voltage at the battery terminals should rise to 13.8 - 14.5 V (depending on the state of charge of the battery).

The voltage on the battery is sufficient to charge it when consumers are disconnected.

Now you need to connect energy-intensive consumers - headlights, heater/air conditioner, heated windows/seats, radio, etc. The voltage at the battery terminals should drop to 13.5-13.7 V.

The generator copes with the load and continues to charge the battery.

If it is lower, then the generator cannot cope with the load, and you will have to repair it. But that's a completely different story.

Never check the serviceability of the generator by disconnecting the battery while the engine is running. This method was suitable 30 years ago, when all the electrical equipment of the car consisted of a kilometer of wire and five relays. Modern car electronics will not forgive such an experiment. In addition, simply “throwing off” the terminal will not indicate a malfunction if the generator is running, but its voltage is not enough to charge the battery.

Any car, both domestic and foreign, is equipped with a certain set of standard and non-standard electrical equipment. At the same time, during operation, quite often you can encounter such a problem as a discharged battery.

As a rule, in this case, owners immediately begin to check the battery and the condition of the battery, diagnose the relay regulator, generator, etc. However, not everyone knows that the source of problems may not be the battery itself and charging systems, but a current leak in the car.

What should you keep in mind?

When carrying out preventive maintenance on the battery, we recommend checking the leakage current of the car battery. On a modern car, the norm is a value of 15─75 mA with the on-board network consumers turned off.

In any case, leakage current exceeding the norm cannot be ignored. After all, this can end not just with a dead battery, but also with a fire in worn-out wiring. Be careful and good luck on the roads! If you have additions or feedback to the article, write them in the comments below. Return to content

Source

How to find an energy consumer?

Further search for current leakage in the car is carried out using the fuse box (usually installed under the hood near the windshield). The procedure is as follows:

Leave the ammeter connected to the battery terminals and remove the fuse box cover.
Alternately pulling out the fuses from their sockets, monitor the readings on the multimeter display. If the manipulation does not produce results and the current value remains the same, insert the element back into the socket and move on to the next one.
When you notice a drop in current to normal, find out which electrical appliances are “hanging” on the circuit of the pulled fuse. Look for the “culprit” using the method of elimination, checking each consumer separately.

Example: a high-consumption circuit powers 3 pieces of equipment - a cigarette lighter, a rear window defroster and a courtesy lamp. It is not difficult to deal with the cigarette lighter and the light bulb - you need to turn off these devices and measure the current at the relay contacts that close the heater circuit. If the readings are higher than normal, disconnect the heating element connector and try replacing the relay.

Several consumers are powered directly from the battery, bypassing the fuse box. This includes the electronic engine control unit, starter and generator. If manipulations with fuse links do not bring results and the display readings have not changed, proceed to checking the electric generator:

Disconnect the positive battery terminal.
Unscrew the power wire from the generator and wrap the exposed end with any dielectric (you can use a rag) to avoid a short circuit.
Connect a multimeter to the battery open circuit and check the current value. If the diode bridge in the generator fails, consumption will drop to normal.

Typically, a broken alternator diode causes a large current draw, measured in amperes. The loaded winding acts as an electromagnet, which can be easily checked using a metal key attached to the unit pulley. If the key is pulled, the electric generator is probably faulty and is wasting battery power.

In a similar way, you can measure current leakage in other directly connected circuits. Look at the electrical diagram of the car and disconnect the wires one by one, bypassing the fuse box. If for various reasons the multimeter is missing, try to solve the problem in the following ways:

carefully inspect the inside of the car for a burning light in the glove compartment or trunk;
try with your hand the glass with built-in electric heaters;
check if the seats are heating up;
Turn off the burglar alarm and stereo amplifier completely.

When faced with current leakage and battery discharge, remember what non-standard equipment you happened to install on your car in recent days. The reason probably lies in the incorrect connection of the device.

What will you need?

Multimeter (read which one is better to choose);
Key 10 or 13 (to remove the terminal);
Screwdriver;
Tweezers.

It is much more convenient to do the work together.
In this case, you will record the ammeter readings, and your partner will turn off the devices one by one. Preparation

. Please note that there are devices in the car that clearly consume energy. For a more accurate result, it is better to disable them. These include light bulbs that illuminate the engine compartment and interior. Turn off the video recorder and radio. After which you can proceed to the search procedure. Also leave a window open. Sometimes during work the central locking is activated.

Malfunctions of switching equipment

Loads connected to live wiring through switches or relays may cause increased leakage current.

In any case, the source of problems is the contacts, no matter the switch or relay - burnt and deformed from overload, they may not open completely, maintaining, albeit large, resistance through which current will flow

However, such cases are rare. But in modern cars with complex control systems for on-board consumers, the circuits are switched by semiconductors, and not by classic relays. And any semiconductor also has a reverse current - in switching transistors it is negligible, but in the event of a malfunction it increases to noticeable values, not to mention cases of breakdown of the transistor when the load is no longer disconnected from the power supply.

Diode bridge reverse current

At one time, this was the main reason for excessive battery discharge - the generator remained the only device directly connected to the battery after the ignition was turned off. A car generator is a three-phase (rarely four-phase) alternating current machine, which must be straightened for use in the on-board network. The diode bridge is responsible for this - a characteristic “horseshoe” of powerful semiconductor diodes, which is connected in the car circuit between the stator windings and the battery.

An ideal semiconductor diode conducts current in one direction, which is the basis for their use in AC rectifiers. But in practice, the diode also has a reverse current - when connected to the battery, the diode bridge slowly drains the battery onto the stator windings. Normally, the reverse current of the diode is several milliamps; taking into account the fact that there are several of them in the bridge, the normal reverse current of the assembly is considered to be 20-40 mA.

However, semiconductors degrade over time, which leads to a change in the parameters of the diode, including an increase in the reverse current. So leaks can increase significantly - and the constant load can be a hundred or two milliamps.

How quickly can current leakage drain a battery?

Many car enthusiasts, even after a superficial study of this topic, cannot understand how such small currents can drain the battery to zero. Let's try to clearly explain how this happens in different situations. Moreover, such an outcome is quite possible when a completely new battery “does not survive” until the morning even with leakage currents not exceeding the norm.

Situation one. A brand new 60 Ah battery is available. Pre-charged fully from a stationary charger. The leakage current does not exceed the norm - say, 60 mA. How long will it take for the battery to run out completely in this situation? We count. With such a leakage current, the battery “loses” 60 mA in one hour. For one day, that is, for 24 hours, respectively - 1440 mAh or 1.4 ampere-hours. It follows that the previously stored 60 Ah will be enough for about 40 days. A lot of? Maybe yes, if you drive a car often. But if you left it in the parking lot and went on vacation, then it’s enough. Do not forget that these were ideal conditions described - a new battery and normal leakage current.

Situation two. The same new battery is available and the leakage current is normal. But before parking the car for a long time, we did not specifically charge anything. As a rule, even if the car's battery charging system is fully operational, the battery is very rarely fully charged at the end of the trip. That is, it no longer contains the 60 Ah of energy discussed above. Knowing the principle of calculation, it is easy to estimate how quickly a 60-70% charged battery will “die” in this situation.

Situation three. We have a used battery and normal leakage current. A battery of any technology inevitably loses its capacity over time. That is, even with proper operation (which is rare), after a couple of years, out of 60 Ah, only 25-35 Ah remains. Calculate for yourself how long it will take for such a battery to run out if it is not fully charged first.

Situation four. We have a not very new battery and a leakage current of about 300 mA (much higher than normal). As mentioned above, a non-new battery cannot have a capacity of 60-70 Ah due to natural wear and tear. Let's say there are 25 Ah left there. After another short trip, we did not specifically charge the battery, that is, it could be recharged from the generator, say, by 80%. In total, we park it with an energy reserve of 20 Ah. With a leakage current of 300 mA, our battery will completely “die” after 60 hours, that is, in just two to three days.

Situation five. To the not new battery and the leakage current beyond any norm, let’s add a haphazardly working charging system. That is, a worn-out generator, an incorrectly functioning relay-regulator and other problems that occur in cars all the time. Let's also add short trips with the headlights, heater and music on.

In the described situation, not only is the battery, in principle, unable to accumulate a lot of energy, but it has nowhere to get this energy from. You spent a lot on starting the engine, then drove for a short time, and then parked the car. Meanwhile, the battery has no more than 10 Ah of energy left in reserve. How long will it take for it to dry up if the leakage current is at least 300 mA? That's right - after 30 hours a deep discharge will occur. But it won’t be enough to start the engine even after 4-6 hours.

Let's add aggravating factors to all this. For example, negative air temperatures, at which the battery charges poorly and discharges faster, or even completely, can completely freeze. You should also remember that to successfully start the engine, the battery must be charged at least 20-30 percent. If it is more discharged, then even if there is some reserve of energy for the starter to operate, there will not be enough starting current. The latter will “squeak” sluggishly a couple of times, after which there will be silence.

Self-diagnosis with a multimeter

It's time to analyze in detail the step-by-step steps that will explain how to find a current leak in a car with a multimeter. In addition to the multimeter itself, you need to prepare gloves, a pen with a notepad, as well as an open-end wrench and clamps. The step-by-step steps from machine preparation to inspection are as follows:

Disabling electronics and implicit current consumers.
Eliminating the ignition and removing the key from the lock.
Fixing the hood in the open position.
Loosening the negative terminal on the battery using a wrench.
Closing car doors. Open windows are a must.
Activate the ammeter mode on the multimeter (switching the device to 10 A).
Creating an open circuit by connecting one ammeter wire to the weakened terminal using a clamp. Next, the terminal is removed from the battery.
Another wire is connected to the negative terminal of the battery.
At the final stage, all that remains is to turn on the device and record the received readings on paper.

The permissible current leakage in a car with modern electrical appliances is 15 - 70 mA.

6. If the leakage current in the car is greater than the critical value, begin to search for the specific cause and its source.

If, with the fuse removed, the readings do not change significantly (by more than 5%), it means that practically no leakage current flows through this fuse.

Some auto electricians use a sophisticated testing method. It does not require an assistant.

wiring short;
relay sticking;
failure of electronic components.

How to check high-voltage wires on a car with a multimeter

If you feel a loss of car power, see increased fuel consumption, the car shakes, and the idle speed fluctuates, it’s time to check the high-voltage wires. More precisely, measure the resistance in them. Remember the procedure:

disconnect the wires from the machine or disconnect one wire on both sides;
turn the device into ohmmeter mode and place the probes on both sides of the wire.

The normal resistance value is 6-10 kOhm. If the device shows less, down to zero, do not be alarmed. The multimeter numbers are influenced by many factors, for example:

quality of wire insulation;
length;
presence of microdamages;
wire type.

If your car's performance is outside the normal range, it is better to contact a car service center, where the resistance will be measured with professional and more accurate instruments.

Why does the battery discharge for no apparent reason?

Let's start with the fact that there are many reasons why current leakage occurs. In fact, this problem manifests itself in the form of a banal battery discharge. In fact, after the car has been idle for a short time, the driver discovers that the battery is discharged.

In some cases, the starter will turn the engine, but weakly. In others, you may encounter that the starter clicks, but the engine does not turn over. It also happens that the battery is completely discharged, that is, the alarm goes off, and the car cannot even be opened using the central lock.

As many people mistakenly believe, it’s all about the battery and its charge. However, it often happens that the battery is fully charged and 100% operational, the generator charges the battery normally, but a rapid and deep discharge still occurs.

Naturally, the problem needs to be solved, since frequent battery discharges can cause a noticeable decrease in battery life or complete failure of the battery. One way or another, the vehicle’s on-board system will need to be checked.

Causes and consequences

First you need to understand what a car battery is. Like any other battery, it is a chemical current source that has an electrical capacity, the value of which is usually printed on the battery label. It is measured in ampere hours (Ah).

Battery capacity is measured in ampere-hours and shows how much current the car battery will be discharged with.

In fact, capacity determines the amount of electrical energy that a fully charged battery can deliver. Leakage current represents the current drawn from the battery. Let's say we have a serious short circuit in the car wiring, and the leakage current is 1 A. Then the 77 Ah battery given as an example will be discharged in 77 hours.

The main problem is that the battery is deeply discharged. When receiving energy from the battery, the sulfuric acid included in the electrolyte is gradually converted into lead salts. Up to a certain point, this process is reversible, since a similar thing happens when the battery is charged. But if the voltage in the cells drops below a certain level, the electrolyte forms insoluble compounds that settle on the plates in the form of crystals.

These crystals will never recover, but will reduce the working surface of the plates, leading to an increase in the internal resistance of the battery, and, therefore, a decrease in its capacity. In the end, you will have to buy a new battery. A dangerous discharge is considered to be a voltage below 10.5 V at the battery terminals. If you bring your car battery home to charge and notice lower voltage, it's time to sound the alarm and deal with the leak immediately!

In addition, leaks caused by short circuits or melted wiring insulation at sufficiently high currents can lead not only to battery damage, but also to fire. Indeed, a new car battery is capable of delivering hundreds of amperes over a short period of time, which, according to the laws of physics, can lead to melting and ignition in a few minutes.

The electrical system of a car is a complex of complex electronic systems interconnected

After considering all the unpleasant consequences of leakage current, it is worth understanding its causes. Previously, in the days of carburetor cars with a minimum of electronics, the normal leakage current was considered to be its complete absence. In those cars there was simply nothing to draw current from the battery when the ignition was turned off.

Today everything has changed: any car is simply crammed with various electronics. These can be either standard devices or installed later by the driver. And although all modern electronics, accompanied by a friendly march of environmentalists with slogans about energy saving, support special “sleep” or standby modes with very low energy consumption, a certain amount of current is consumed by duty circuits. Therefore, small leakage current values (up to 70 mA) are the norm.

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From the factory equipment in a car, the following devices normally constantly consume a certain amount of energy:

Diodes in the generator rectifier (20-45 mA);
Radio tape recorder (up to 5 mA);
Alarm (10-50 mA);
Various switching devices based on relays or semiconductors, on-board engine computer (up to 10 mA).

The maximum permissible current values for serviceable equipment are indicated in parentheses. Faulty components can dramatically increase their consumption. We will talk about identifying and eliminating such components in the last part, but for now here is a list of additional devices installed by drivers, which can often add another hundred milliamps to the leak:

Non-standard radio;
Additional amplifiers and active subwoofers;
Anti-theft or second alarm;
DVR or radar detector;
GPS navigator;
Any USB powered equipment connected to the cigarette lighter.

Checking current leakage in a car with a multimeter

Now that we have understood the nature of the leakage current, its varieties and the reasons for the increase above the norm, we move on to the main thing - checking the current leakage in the car with a multimeter. This is a simple matter and does not require much experience. It is much more difficult to then find the problem due to which the leakage current is higher than normal.

Checking current leakage in a car with a multimeter is performed according to the following algorithm:

Turn off the engine.
Move the ignition key to a position where it can be removed from the lock.
Turn off all consumers that you can - music, lights, chargers inserted into the cigarette lighter, etc.
After opening the hood, lock the switch, which “notifies” the security system that the hood is open. If the engine compartment is illuminated by a built-in light, unscrew it while taking measurements.
Turn the multimeter into current measurement mode.
Disconnect one of the terminals from the battery (any).
Connect the multimeter to the resulting open circuit (between the battery and the terminal).
Set the car alarm.
Wait a few minutes.
After the multimeter readings have stabilized, evaluate the leakage current and compare it with the norm for your car.

The simplest method for finding the reason why the leakage current exceeds the norm is discussed below. But first, it wouldn’t hurt to talk about common mistakes that car enthusiasts make when taking measurements.

Firstly, while measuring the leakage current with a multimeter, do not start the engine under any circumstances! If you do this, a current of at least a hundred amperes will flow through the multimeter. No ordinary multimeter can withstand such a load. To measure the current consumed by the starter, you need another device - a current clamp.

Secondly, checking for current leakage in a car should not be performed with a multimeter that is not set to the mode for measuring high currents (usually 10 A). A small range of 200 mA may not be enough, and the device will simply fail. Moreover, even if the leakage current in your car is normal (far from 200 mA), when the device is connected to the circuit, the current will always be about an ampere or more. The same jump will occur when setting the car alarm.

Thirdly, there is no point in measuring leakage current without the security system being turned on. Without it, the indicators may be within the normal range, and you will never know objectively how much the car “eats” while standing in a parking lot with the alarm on. Similarly, you should not disconnect the power of those devices that you leave during normal operation of the car - radio, DVR, and so on. The evidence, again, will not be objective.

Fourthly, you should not take as a basis the ammeter readings that it displays in the first minutes after being connected to the circuit. Especially if the car is stuffed with electronics, which need some time to turn on and go into standby mode.

Fifthly, it is highly advisable to check the leakage current when the battery is known to be charged. If it is “dead”, then the device will show underestimated readings, and again you will not see the real picture of what is happening.

What is leakage current and how does it happen?

Let's start with a specific example. Let's say we have a battery, a light bulb and a switch. Let's assemble a simple electrical circuit from all this, so that the light bulb can be controlled using a switch. Now consider two situations - in one the light bulb will be on, and in the other it will be off.

When the light bulb is turned on, an electric current naturally flows through the circuit. Question: can this current be called leakage current? Don't rush to answer. In fact, not everything is as simple as it seems. On the one hand, there is no leakage in this situation, since the current flowing through the circuit seems to be used to perform useful work. What kind of leakage is there if the current flows profitably?

Nevertheless, there is always a current leak in this case. That is, not all the energy that is taken from the battery is spent on useful work. And this is exactly what is not spent on useful work - this is, in essence, a leak. Leakage current. Where is she? Where does the current flow without use? And current leakage in this case occurs in the wires that connect the circuit elements. Since they have some resistance, part of the current flowing through them is wasted on heating them. This is, in principle, also work. But for us it is not useful (and even harmful).

The second situation is when the light bulb is turned off using the switch. Is it possible to detect leakage current in this situation? Of course not, if the system is working properly. What if the switch is faulty? For example, salt water got into it, and even in the off position it does not completely break the circuit. The light bulb may glow with a weak glow or not glow at all, but the battery will waste energy. In such a situation, we are dealing with a real leakage current. Under the conditions described, it flows in our circuit.

Now let's complicate things a little. Instead of a light bulb, let's connect some electronics to our circuit that operate in two modes - main and standby. In a car, such a device is, for example, a radio. When we turn off a consumer of this kind, it goes into the so-called sleep or standby mode. In this mode, the device consumes energy from the battery, that is, current flows in our circuit.

Now the question is: is this leakage current? On the one hand, it seems, yes. Indeed, in the case of a radio tape recorder, we are not listening to music at this moment, which means that work useful to us is not being performed. On the other hand, the current, which many call leakage, is spent by the radio on not so useless work - storing settings, clock movements, and so on.

So what then is leakage current in a car? And this is the current that flows in the circuit, but is not spent on doing useful work.

In the case of household electrical networks, the boundary in this matter is clearer. In properly organized systems, there is even a special automatic circuit breaker that, in the event of a current leak, completely cuts off the power supply.

However, when considering the issue of current leakage in machines, the line is not so clear. In the case of cars, leakage current is generally considered to be any current that is drained from the battery while parked. And this despite the fact that not all energy is wasted in this mode.

Relay test

Another item that needs checking if you have electrical problems is the relay of this component. Relays are used in high power appliances and are electrically activated switches. When you turn on your car, several components turn on, such as the fuel pump, computer, and electric fans.

The switch in your ignition can activate multiple relays, turning all the peripheral equipment without running full power through the ignition switch. Relays can also deteriorate over time and cause electrical problems.

The best way to test the relay is to have a working replacement or listen carefully to how the relay operates while turning on the device. You should feel light pressure and hear a soft click when the relay turns on.

Summarizing

How to check leakage current on a car battery using a multimeter?
There are no exact instructions for action. Regardless of why the charge leak occurs. You should not ignore this problem, even if everything is fine with you. For peace of mind and confident operation of the car, purchase a multimeter, starting leads and a set of car keys. These inexpensive devices will help you save a lot of time, nerves and money, since any problem is most easily solved if you know about it in advance. Check the battery and generator periodically, and you will not find yourself in a situation where you urgently need to start the car, but this is impossible for certain technical reasons. Good luck on the roads and do not forget about the Rules of the Road.

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Repairing the leak

When a leak is identified, it is necessary to begin eliminating the cause. Before performing any operations, the battery terminals must be removed. Solutions:

Accumulation of dirt at the connection areas - dust and dirt should be removed using an alcohol solution.
The insulation is damaged - close the internal conductors and provide protection from further exposure to negative factors (put on a hose to prevent overheating and chafing);
Water or fogging in devices - dry. If water gets inside the alarm unit, you need to carefully open the module. After moistening with alcohol, wait for the water and dirt to drain. After removing fogging, come up with a protective cover that prevents moisture from penetrating inside.
Malfunctioning electronic device - repair or replacement.

Having eliminated the cause of the leak, you should again check the current consumption rate with a multimeter.

In the video you can learn more about constant current consumers and checking current leaks. Two machines are compared that have different current consumption depending on the installed equipment.

How to check a generator on a car with a multimeter

Checking the generator is similar to measuring other elements of the car that cause current leakage.

Traditionally, turn off the ignition, take out the key, turn off the radio, and so on.
Connect the multimeter to the battery.
Measure the voltage. A fully charged battery will produce between 12.5 and 12.9 volts.
After this, start the engine, turn on the heated windows, seats, heater, and low beam.

And measure the voltage again. The norm is 13-14 volts. Maximum - 14.8 volts. In these cases, the generator works like a clock. If the multimeter shows lower numbers, the generator is not charging the battery. So, get ready to pay a decent amount for replacing or repairing the unit.