Lead acid battery capacity meter. Instruments for testing lead-acid batteries. What determines the current battery capacity?
A modular version of a visual and accurate battery ampere-hour meter, assembled at minimal cost from computer waste.
This is my response to the article.
A little foreplay...
Under my patronage there is a fleet of 70 computers, of different years of manufacture and condition. Naturally, the vast majority have uninterruptible power supplies (in the text - UPS). The organization is budgetary, of course they don’t give you money, like, do what you want, but everything must work. After short tests with a load in the form of a 150-watt light bulb, I discovered that 70% of the UPSs do not hold the load for more than 1 minute, the APC UPSs are faulty with the switching relay contacts (it switches to the battery, buzzes and beeps, and the output is completely zero). Of course, no one let me check all the UPSs at once. The solution turned out to be simple: once every six months or a year I took the computers for cleaning, lubrication, and at the same time the UPS for testing and inspection of the internals.
Of course, there are UPSs of different brands and capacities (there is an old 600-watt model from 1992, the original battery died this fall, before that I had to undergo intensive care 4 years ago). If anyone is not aware, household and office UPSs use batteries of different types, housings, voltages and capacities. A typical representative is GP1272F2 (12 Volt, 7 A/h). But they also come across 6V - 4.5 A/h.
Battery prices often exceed half the price of a new UPS. Moreover, in the office (where I work part-time), dead batteries also accumulate. The question arose: what is the actual capacity before and after being lifted from the trash can, and how many minutes of operation can be expected from the UPS. And then an article caught my eye I. Nechaeva In the magazine "Radio" 2/2009 about such a meter.
Of course, I didn’t like some aspects, I’m such a bastard.
And so let's start with...
This is the original diagram from the article
TTX: discharge current 50, 250, 500 mA, cut-off voltage 2.5-27.5 Volts.
I'll list what I didn't like: the maximum discharge current is only 0.5A (and it’s not interesting to wait until 7 Ah is discharged), the cut-off range is too wide and it’s easy to knock it down, all the current goes to the start through the button, the current stabilizer on the field strip for the LED is overkill, the diode in the control output increases the required drop on the current resistors is up to 1.8V and in the event of a breakdown, 317 walkers will be stuck.
About the discharge current: In batteries, it happens that the active mass is sealed in a coating (not to be confused with sulfation), while the mobility of the electrolyte decreases and if it is discharged with a low current, it can completely discharge the capacity, but when installed in a UPS, the test will not pass. Well then you need to discharge it with a small current and charge it, i.e. treat.
The good thing about the modularity of what I got is that you can make 2 or more discharge modules (you can also switch 1 current resistors) of different power or even type and 2 cut-offs for 6 and 12-volt batteries or 1 with a switch.
Photos of my meter:
We see: cut-off block, current load, Chinese walkers.
I repeat, I work as a sysadmin, sometimes I repair motherboards, so there is a certain pile of dead iron.
I’ll start in reverse order: the walkers are slightly modified so that they can run on a power supply from 1.5 to 25 Volts.
Scheme of walker modification:
1117 pulled from a dead motherboard.
A 2 kOhm resistor is the minimum load of the stabilizer.
accordingly the scheme:
This is 2 amps. Since R1 turned out to be greater than 0.75 ohms, I had to add 2 resistances (this is R3, two in one in the photo) so that the current would be 2 amperes. In case someone hasn't noticed, there are no gaskets between the micro and the transistor on the radiator. You can, of course, use another circuit, such as in radio 3/2007 p. 34, just add a reference voltage.
317 (real) has current and thermal protection.
Well, the worst part is the cutoff.
Super 3D installation, but only 3 cm cubic, it will be much larger on the signet. Polevik, if it’s on a 6V battery, then it’s very desirable with a logic control.
This part is almost no different from the original one, the start button has been moved from the drain-source to the collector-emitter, the variable has been replaced with a fixed divider, a Chinese super-bright LED through a resistor.
Possible variations: replace the upper arm (according to the original circuit this is R4) with a resistance + variable, thus limiting the setting range (required when the discharge current is commensurate with the battery capacity); other ideas are possible.
For formulas Uref=2.5v for regular 431, and for 431L it is equal to 1.25v.
Fixed voltage cut-off:
Formula for calculation: Uots= Uref(1+R4/R5)
or R5=(Uots- Uref)/(Uref*R4)
Adjustable Voltage Cutoff:
Formula for calculation: Uots = Uref(1+(R4+R6)/R5)
or R5 = (Uots- Uref) / (Uref*(R4+R6))
But here you need to count from the alternator, on it, with a discharge of 0.1s, it should drop (Udelta) 1.15v for a 6v battery and 2.30v for a 12v battery.
Therefore, the formulas are transformed and the calculation is somewhat different.
Umin see the table below.
R5 = Uref * R6 / Udelta
R4 = ((Umin -Uref) * R5) / Umin
Greetings, citizens of Datagoria! Let me introduce you to my next creation - a battery capacity tester. The device, of course, is not for every day, but sometimes you can’t do without it!
I needed to measure the remaining capacity of the acid battery, in winter, after all, every Ampere counts, maybe it’s time to replace the battery? Simple tests with a load fork and density measurements did not suit me; they did not give me information about whether I would have enough energy to warm up the car for 40 minutes on the RV (about 8 A/h) and then start the car with the starter.
Battery capacity tester circuit
Like any child, it was born in pain. Mainly due to the mistakes of the “obstetrician”.Fragment excluded. Our magazine exists on donations from readers. The full version of this article is available only
Controlled discharge controller
Fuse placement when programming the ATmega8A MK
5. All part ratings are indicated on the software.
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Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine
Printed circuit board in LayOut: ▼ 🕗 10/24/14 ⚖️ 144.03 Kb ⇣ 124 Hello, reader! My name is Igor, I'm 45, I'm a Siberian and an avid amateur electronics engineer. I came up with, created and have been maintaining this wonderful site since 2006.
For more than 10 years, our magazine has existed only at my expense.
Good! The freebie is over. If you want files and useful articles, help me!
The most important parameter of each battery is its battery capacity. It determines the amount of energy given to them for each period of time. This applies to all batteries from car to telephone. Knowing about them and understanding the device is important because using the wrong battery capacity can cause serious problems in starting these devices.
The units of measurement for this quantity are Amperes or Milliamps/hour. Based on this parameter, the battery for the equipment is selected, guided by the recommended values. If the recommendations are violated, for example, the car may not start in winter.
What is the capacity of a battery or accumulator
All batteries are usually decorated with inscriptions like 55, 70 Ah or 1800mAh. This designation indicates that the capacity of this battery is, respectively, 55 Amperes or fractions of Amperes per hour, only translated into English - A/hour. It must be distinguished from another parameter - voltage, which is written in Volts.
Standard battery
The Ah indicator shows how long the battery will work for an hour at a load of 60 Amps and a voltage of 12.7V. In other words, capacity is the amount of energy that a battery can hold.
And if there is less than 60A load, the battery will last longer than 60 minutes.
How to quickly check the capacity of any battery
Most often, battery capacity is measured using a tester. This is a device for quick measurements. It works automatically and does not require any additional knowledge to use it. The time required is no more than 15 seconds. All that is required is to connect the tester to a power source and press a single button, after which it begins to determine the capacity of the connected batteries.
It is used when choosing a battery, comparing the residual and nominal capacity, which is officially indicated on the device. If the difference is more than 50%, then the battery cannot be used.
Which device to use to accurately measure the capacity of any battery
The capacity indicator determines the density of electrolytes; it is determined using a special device - a hydrometer. New batteries always indicate the basic parameters. However, this value is determined independently.
Small battery
The simplest way is with ordinary testers like “Pendant”. This device is used to measure the capacity and voltage of the battery in a car. This requires minimal effort and time while achieving reliable results.
To use the “Pendant”, you need to connect it to the battery terminals, after which it will begin to determine the voltage and capacity.
There are many other ways to calculate these parameters. The classic method is to measure a car battery using a multimeter. In order to do this, it must be fully charged and connected to the consumer (an ordinary 60W light bulb is sufficient). However, even this does not guarantee absolute accuracy of the readings.
Multimeter device
The first step after assembling the circuit from the battery itself, a multimeter, or a light bulb is to apply voltage. If the light does not go out within 2 minutes (if this does not happen, the battery cannot be restored), take the “Coulomb” readings. As soon as the readings drop below battery voltage standards, the battery begins to discharge. Having measured the time required for the final consumption of energy and the load current of the consumer, you need to multiply these readings by each other. The resulting number is the battery capacity.
If the result differs from the official value, the battery must be replaced. A multimeter allows you to calculate the capacity of any battery. The disadvantage of this method is that it takes a lot of time.
In the second measurement method, the battery is discharged using a resistor according to a special circuit. Using a stopwatch, the discharge time is determined. However, it is important not to completely discharge the battery, protecting against this using a relay.
How to make a device with your own hands
If you don’t have the necessary equipment at hand, you can implement the device yourself. Load forks will do. There are always a lot of them on sale, but they are also collected independently. This option is discussed below.
Plug diagram
This fork has an expanded scale, which allows you to achieve the highest accuracy of readings. Load resistance is built in. The scale ranges are divided in half, thereby reducing the reading error. The device is equipped with a 3-volt scale. This makes it possible to test individual battery banks. Scales of 15V are achieved by lowering the voltage on diodes and zener diodes.
The current reading of the device will increase as soon as the voltage values become greater than the opening level of the zener diode. When a voltage of the wrong polarity is applied, diodes provide protection. In the picture: SB1 is a toggle switch, R1 is a transmitter of the required current, R2 and R3 are resistors intended for M3240, R4 are determinants of the width of narrow scale ranges, R5 is a load resistance.
How to find out the capacity of a telephone battery at home
When using a cell phone, its battery is subject to constant degradation. This process cannot be avoided; it is natural. This happens regardless of the model, price, or features of the phone. To accurately understand how long the battery in your device will last, you need to measure its current capacity. This will allow you to replace the battery in time before it starts to turn off at the most inopportune times.
Swollen battery
First of all, you need to inspect the battery. Dangerous problems in a lithium battery are immediately visible: the case may swell, be full of traces of corrosion, and greenish and white spots.
If signs of swelling are detected, it is dangerous to continue using such a battery. This can cause short circuits in the phone's electrical circuits. The swelling may begin from a small bulge to serious deformation. Another worrying factor is the rapid loss of charge in the phone.
Today, there are many applications to measure the current capacity of a phone.
To accurately determine the battery capacity, the advanced charger method is used. The battery is completely discharged, then connected to this device. It, in turn, calculates the battery capacity taking into account time and current value.
Load differences
The parameters of each car are different. Their engine sizes and battery capacities differ. In a passenger car, a battery usually has a capacity of 40-45A, and in a large car it is about 60-75A.
The reasons for this lie in the starting current - the smaller the battery, the less electrolytes, lead, etc. it contains. The larger it is, the greater the amount of energy that can be given off at one moment. Based on this, large batteries can work successfully in a small car, but small ones cannot be inserted into a large car.
Case dependency
Batteries of different sizes
Capacity is directly related to the number of electrolytes and lead in the battery. Because of this, small capacity batteries will be much smaller in volume and weight than larger batteries. For these reasons, large batteries are never installed on a small car, since this does not make sense - these cars have little space under the hood. And the small battery does an excellent job of starting the engine.
Capacity reduction
Any battery is subject to depreciation and its capacity decreases over time. Conventional batteries last about 3-5 years. The highest quality specimens remain in good condition for up to 7 years.
As capacity drops, the battery loses its ability to provide sufficient starting current. Then it's time to replace it. The main reasons for the drop in capacity include:
- Accumulation of sulfuric acid on the positive plate. It can completely cover all surfaces, contact with electrolytes deteriorates, and capacity decreases.
- The plate crumbles due to overcharging, then there is a lack of electrolytes. This leads to an immediate decrease in battery capacity.
- When the bank is short-circuited and the negative and positive plates are connected to each other, the battery capacity decreases. However, it is being restored.
What determines the current battery capacity?
Throughout the life of a battery, its capacity changes. At the beginning of their work, they have the highest capacity, since the plates are actively being developed. Then there is a period of stable operation, and capacity remains at the same level. Then the capacity begins to decline due to wear of the plates.
Battery test process
The capacity of the battery varies depending on the presence of active materials and the design of the electrodes, electrolytes, their temperatures and concentrations, discharge current values, battery depreciation, the concentration of additional deposits in the electrolytes and many other factors.
As the discharge current increases, the battery capacity decreases. With a rapid, specially provoked discharge, batteries lose less capacity than in smoother modes with low current values. Based on this, indicators for 4, 15, 100 hours of discharge are recorded on the case. The capacities of the same batteries vary extremely greatly. The capacity is least at 4 hours of discharge, and most of all other things are at large periods of time.
Also, the capacity indicators change with increasing temperature of the electrolytes, however, with an increase in the maximum permissible standards, the service life decreases. The reasons for this lie in the fact that at elevated temperatures, electrolytes penetrate into the active mass, because their viscosity decreases, and on the contrary, their resistance increases. Because of this, there is more active mass in discharge reactions than during charging at a lower temperature.
At particularly low temperatures, the capacity of the battery is reduced as well as its useful effect.
As the concentration of electrolytes increases, the battery capacity also increases. However, the battery deteriorates faster, as the active mass of the battery is loosened.
Thus, checking the battery capacity is necessary at all stages of its life.
Car battery capacity meter
The article provides a diagram of a car battery capacity meter. The basis of the circuit is a microcontroller PIC16F873A. All information is displayed on an LED indicator with a common cathode.
In general, I composed this diagram and program at the urgent request of one of the site visitors a long time ago, but this insistent visitor suddenly disappeared somewhere. That’s why I post everything for everyone.
In principle, the circuit consists of already tested working fragments from different devices, so I did not implement this device into hardware. The operation of the meter was simulated in PROTEUS 7.7 SP2.
Circuit operation
On transistor VT1 and op-amp DA1.1 - LM358N, an electronic load equivalent is assembled with stabilization of the incoming discharge current of the battery under test.
The discharge current level is set using trimming resistor R5. Low-resistance resistor R7 is a current sensor for the DA1.1 amplifier, and the signal for the microcontroller ADC - a digital ammeter - is also taken from it. A comparator for limiting the battery discharge voltage is assembled at op-amp DA1.2. The controlled voltage from the discharged battery through the voltage divider R8 and R9 is supplied to the inverting input of the op-amp DA1.2. The division coefficient of this divider is 1:10, the same voltage through switch SA1, pins 1-3 is supplied for digitization to the RA1 input of the DD1 microcontroller. This is a digital voltmeter. The non-inverting input of op-amp DA1.2 is supplied with a reference voltage from the divider R2 and R3. Resistor R9 adjusts the digital voltmeter readings. Resistor R3 sets the battery discharge limitation voltage. The magnitude of this voltage can be viewed by moving switch SA1 to the lower position according to the diagram. Transistor VT2 is a pulse amplifier for the sound signal of the end of battery discharge. By changing the value of resistor R13, you can change the sound volume of loudspeaker BA1. The DA2 chip is a microcontroller supply voltage stabilizer, and since the controller supply voltage is selected as the reference voltage when digitizing signals in the program, the value of this voltage must be adjusted by resistor R11 at 5.12V. LED HL1 is an indicator of the end of the measurement process.
Device setup
Without inserting the programmed microcontroller, we supply power to the correctly assembled device. Using resistor R11 we set the voltage at the stabilizer output to 5.12 volts. Remove the supply voltage from the board and insert the microcontroller. We move switch SA1 to the upper position, turns off the collector of transistor VT1, and applies a control voltage of 12 volts to the battery connection connector. We achieve the same reading on the voltmeter indicator using resistor R9. We move switch SA1 to the lower position and set the discharge limitation voltage, for example, 10.5 volts. In this case, the voltage at the output of op-amp DA1.2 should be equal to zero. We begin to smoothly reduce the control voltage and around 10.5 volts the comparator should operate, and the voltage at its output should increase to approximately five volts (logical unit). The controller will record this unit and give an intermittent sound signal, indicating the end of the battery capacity measurement. At the same time, the HL1 LED will light up.
We include a control ammeter in the battery discharge circuit, set the required current (the discharge current of car batteries is chosen in accordance with the formula C/10, where C is the battery capacity) of the discharge with resistor R5 and compare our readings with the control ones. The accuracy of our ammeter mainly depends on the accuracy of the value of the current sensor resistor R7. If the readings are too high, then the value of resistor R7 will need to be reduced.
Working with the device.
Take a fully charged battery and connect it to the device. The countdown of the discharge time begins immediately. On the left indicator according to the diagram we will see the value of the discharge current, on the middle one - the voltage on the discharged battery, provided that SA1 is in the upper position. The right indicator will display the current capacity values over time. Capacity is determined accurate to tenths. It follows from this that the capacity readings will change every 6 minutes. After the voltage on the battery decreases to the limit you have chosen, the LED will light up and a signal will sound. The controller will record the measured capacity, but the discharge process will not stop, keep this in mind.
That's all, good luck, K.V.Yu.
You can download the full project here ↓.
It is no secret that over time, the capacity of rechargeable batteries becomes smaller, and they can no longer supply the device with the amount of current that they could supply before. In this regard, many users often have a question about how to measure the battery capacity, or more precisely, how to find out the indicator of its residual potential, with which you can understand whether the battery will need to be replaced in the near future.
If you start from the concept that the capacity indicator is the amount of energy or current given by the battery over a certain period of time, it simply will not work. If we are talking about how to find out the real capacity of a battery in the form of AA batteries, you will have to first measure the current, and then use some simple calculations so that the indicator is as accurate as possible. As for any Android-based mobile phone, using a small USB tester.
A simple test of battery capacity with a USB tester and subsequent clarification
The USB tester for measuring battery capacity has very rich functionality - it can be used to measure the battery capacity of a tablet, smartphone, etc. Based on what this device shows, you can get an idea about the wear of the batteries: is it worth changing the battery, or do you need to purchase a new device.
With just one control button, you can measure various indicators, including the battery capacity of a particular device. The button switches tester memory cells and operating modes. If there is a sufficient voltage level in the connected device, the tester turns on.
The meter usually displays the battery capacity indicator in the lower left corner. The measurement accuracy of the tester is not 100% , and therefore it is recommended to use a simple mathematical formula based on the following example.
Let's say you have a certain device (phone, power bank or tablet), which, being completely discharged, charged in a period of time equal to 3 hours. If, out of curiosity, you measured the current using a tester, and its value was, for example, 1.15 A, the actual battery capacity of your device is calculated by multiplying these two numbers together. 1.15 amperes is 1150 milliamps, multiply this number by 3 and get 3450 mAh. This is how real capacitance is measured. If the current “capacity” on your device indicated by the manufacturer is several times greater than the actual one, this is just a standard advertising ploy that should not be trusted.
How to determine battery capacity using a multimeter
It is impossible to determine the battery capacity itself with a multimeter. To be more precise, this device will help in determining the actual capacity indicators.
In order to find out the capacity of an 18650 battery, as well as other batteries, so-called “smart chargers” are used. But their cost is quite high. It’s not worth buying such chargers simply to determine the capacity of a couple of batteries. This indicator will easily determine the usual calculation method with the preliminary use of a multimeter. However, when making calculations, certain subtleties must be observed.
Checking the battery capacity indicator with a multimeter is not just measuring its real indicator, the calculations of which are made using basic mathematical calculations. It is necessary to measure the current level supplied by the battery (any battery) and calculate the exact amount of time during which the battery could continuously and efficiently produce electrochemical energy. It is important to remember that all measurements will not be 100% accurate. But they are the ones that best reflect the true essence of the matter.
They have their own scale of ranks. It shows how much U depends on the charge rate. This is necessary to know: the current flow through the resistance depends on the voltage level. To ensure that this dependence does not affect the measurements, an additional device should be assembled - linear current stabilizer (2.7-3 volts).
Using a linear stabilizer
Using this stabilizer, set the current indicator, calculating it from a 2.7 volt U battery. Then, using the U stabilizer, connect any resistor device (it can be made independently or purchased from an online store). Measure the current that passes through the circuit and set a stopwatch. Next, we periodically check and monitor the voltage at the battery terminals. When it reaches the number 2.7 volts, the stopwatch will need to be quickly turned off and the time obtained recorded.
So, how to measure the capacity of a 18650 battery and other chemical current sources? Real indicator mwe deduce by doing multiplying the current flowing through the circuit through resistance by the same time (in hours) that was originally spent . This is the most accurate measurement of capacitance. In the absence of technical capabilities, it will be more difficult to design a voltage stabilizer, carry out calculations and measurements. Try to find a way out of the situation using a variable resistor.
Using a Variable Resistor
In order to conduct a high-quality capacity test, you can use a smaller battery. For example, 14500, the actual capacity of which is 300 mAh. Let's take a variable resistor of 100 Ohms. Important point: if a direct current resistor is used, the process will be complicated by the fact that it will be necessary to frequently record the results of its readings and carry out calculations of the spent capacitance for certain sections of the scale .
It is possible to average the indicators as much as possible, focusing the calculation on the “arithmetic average” number of the current. In order to understand how to measure the battery capacity, it is recommended to use a variable resistor with a dosed decrease in the resistance value throughout the entire time the battery is being discharged. It is important that the current level is approximately the same throughout the entire process.
Now switch the multimeter to the voltmeter position (measure U) and measure U at the terminals of your battery. Let's say it has an incomplete charge level, say 4 volts. Next, discharge it by applying a current of 450-500 milliamps, lowering the resistance level from time to time and controlling the voltage. When it drops to 2.7 volts, turn off the stopwatch. To completely discharge the battery using 500 mA current , it takes about half an hour, more precisely, 25 minutes. Now let's multiply this current by the amount of time measured in hours. So, the real capacity indicator is 200 mAh.
Thus, it becomes clear how to find out the battery capacity using the most accurate method - not just by measurements, but by mathematical calculations that can most accurately reflect the actual state of the battery and help the user navigate what its potential is in reality.