Battery monitoring and analysis for automotive system

The term ‘‘Battery Monitoring’’ is used in a wide range of meanings, from occasional manual readings of voltages, of electrolyte gravity SG and level, and visual cell inspection, through periodical tests of capacity or manual measurement of battery resistance, to fully automated on-line supervision in critical applications with means for real-time estimation of residue bridging time, or of battery wear and tear.

Here the term Battery Monitoring is used for supervision without manual engagement, which is state-of- the-art with many cycling batteries in automobiles like automatically guided vehicles (AGVs), forklift trucks, submarines, electrically driven cars and trucks, as well as with standby batteries in telecom and UPS applications. With consumer applications, any mobile phone, laptop or pocket computer, or even a wristwatch is equipped with a device providing some information with respect to energy being left.

The specific situation of the automotive battery becomes obvious, technically impeding Battery Monitoring in the automotive fields:

• They are scarcely ever been completely charged, i.e. ‘opportunity charge’ is standard.
• Recharge is performed with a wide range of different current rates.
• Discharge virtually never starts from a full SOC.
• Discharge is performed with a wide range of different current rates. Sometimes full discharge or (unfortunately) even over-discharge occurs.
• Operational temperature may even exceed the window from 30 to 70 degrees

While the term ‘‘Battery Monitoring’’ comprises

• Taking and/or receiving data from and/or about the battery
• Processing of this information, including predictions of performance, and
• Being or a unit, i.e. only passive surveillance and evaluation

The term ‘‘Battery Management’’ means active feedback to the battery. This may comprise control of current or voltage levels, control of recharge conditions, limiting of the operational windows with respect to SOC and/or temperature, battery temperature management, etc.

An appropriate Battery Management may enhance and improve, but is not a precondition for, a successful Energy Management. It is Energy Management, preferably including Battery Management, which, based on the information from Battery Monitoring, allows for a self-standing operation of a system without manual input—the comfort and the technical necessity requested for a vehicle at the beginning of the 21^st century.

Battery Monitoring allows for best use of the capability of a battery of given size, to guarantee power supply for high reliability devices, and for replacement strategies. Further-more, monitoring of the actual state-of-charge allows for an electrical power management which may include both reducing consumption of electrical power by limiting of operable luxury applications as well as increase of power generation by appropriate control of alternator or even idle speed and automatic gearbox control.

Battery Monitoring may be needed if

1. Energy has to be provided for a component which is essential for operation, e.g. an Electromechanical Power Steering (EPS) or an Electro-hydraulic Power Braking (EHB) system, an electrically powered suspension stabilization system, or an automatic gear shift;

2. An Electrical Energy Management (EEM) has to guarantee, e.g. for future cranking capability;

3. The cranking capability has to be supervised to operate a stop/start-system;

4. An indication of battery fatigue is needed for garage service to replace the battery.

Battery Monitoring consists of data acquisition, data processing, and some prediction of the future. For different technical goals, different information with respect to the future is needed. Any approach for Battery Monitoring may be classified according to the following criteria, which may be combined, too, e.g. data acquisition from both long-term and the nearest past, and prediction of both battery status and behavior.

A. Data Acquisition

1. Type of data: Battery status/battery behavior/operational conditions

2. Time scale of data acquisition: From long-term history/near past

3. Source of data: External battery parameters /internal battery parameters (e.g. electrolyte properties)/vehicle data (e.g. engine rpm, speed, and environmental temperature).

4. Data achieved from: Undisturbed battery behavior/ after electrical stimulation.

B. Data analysis

1. Analysis of operational history (i.e. conditions the battery had to suffer so far).

2. Analysis of previous performance (i.e. behavior the battery has shown so far).

3. Analysis of actual performance (i.e. recent and actual battery behavior and status).

C. Prediction of battery performance under a hypothetical future electrical load

1. Point in time for prediction: Near future (just now, with the present battery status)/medium future (in several hours or days, when the battery charge and temperature may have been changed).

2. Type of predicted battery data: Status (temperature, state-of-charge)/load behavior.

D. Determination of available electrical energy

This is a special case of C, with the standard capacity test scheme as the hypothetical (future) electrical load.

E. Determination of battery degradation (state-of-health (SOH) figure of merit).

While Battery Monitoring may provide information about the status of the battery, this knowledge is not a goal by itself. The final technical benefit has to be made clear, and a strategy and means to achieve this goal have to be worked out, to find out the relevant properties of the battery which have to be considered and evaluated.

Choose right inverter for home during power cuts

Power cuts are a very common feature is many parts of India. Glaring gap between supply and demand is increasing power cuts by every passing day. More and more people are looking for solutions to manage their homes during power cuts and power inverters are becoming popular. Although they are of great help during power cuts but if not chosen or installed or maintained properly, they can cause a significant hole in your electricity bills. The inefficiency can cause you to pay much more for the same amount of electricity during the power cuts. With this article we will try to help you understand the impact of an inverter on electricity bills and how to choose a right inverter.

What are inverters and how do they work

Inverters (as we know them) are a form of power backup which has 3 units: 1) A charger 2) A battery and 3) An inverter (as it is truly called). The charger is connected to the power supply and it charges the battery when the electricity is coming from the utility. Inverter, a device that converts Direct Current (DC) to Alternating Current (AC) gets activated when electricity from the utility goes off, and as the inverter is connected to the power point, it starts providing electricity to the house.

Efficiencies in Inverters

There are 2 cycles in inverters where efficiencies have to be considered:

1. Charging: During charging the efficiencies depend on the battery efficiency. A lead acid battery that is typically used in inverters is not 100% efficient. When the battery is half charged or less the efficiency may be over 90% that can drop to 60% when the battery is above 80% charged. It is very important to maintain the batteries regularly so that the efficiency levels remain good.

It is also important to choose the right kind of batteries so that the efficiencies are good. It is better to buy a branded battery as local made batteries do not have good efficiencies. Local made batteries may be cheap but the inefficiencies can cause a lot of expenses in electricity. There are 3 types of batteries available in the market:

1) Flat Plate Batteries

2) Tubular Batteries

3) Maintenance Free Batteries.

Of these 3 Flat Plate Batteries are cheapest, but the battery life is less and maintenance required is high. Maintenance Free batteries have medium life span but the maintenance is low and cost high. Tubular batteries have long life, medium maintenance and high cost.

Do not use car batteries for inverters, as they are not suited for the kind of requirements at home

Conversion from DC to AC by inverter: Efficiency of inverters vary from 90% when it is being used at peak load to just over 50% when very less power is used . Inverter draws power from batteries even when no power is being used. Thus the efficiencies are very low when low power is drawn from it. Thus it is very important to size the inverter properly. You should look at the load in your house before buying an inverter. Typical load of inverters is mentioned in VA (Volt-Ampere) which is roughly equal to Watts (W) (assuming power factor of appliances is 1). So to calculate load required, just sum up the wattage of appliances you want to run on inverter.

There are 2 types of inverters available in market: 1) Modified Sine Wave and 2) Pure Sine Wave inverters. Modified Sine Wave inverters are cheaper but less efficient. They can work with majority of low-end appliances but they produce a buzz sound. Electricity is wasted in form of heat through this kind of inverters. These are also not good for health of some sensitive electronic appliances. Pure Sine Wave inverters are expensive but the most efficient types of inverters. These types of inverters are necessary to run high-end appliances like audio systems and video game consoles. They produce the same kind of power as supplied by the utilities and thus are the best in terms of efficiency and usage.

An inverter can be very useful during power outages and can provide a lot of relief. But it can be a huge drain of electricity if right one is not chosen or is not maintained properly. Make sure that you keep operational costs (cost of using inverter) in mind before you buy a new one.

Safety Precautions and Installation Tips for Inverters

A power inverter changes direct current (DC) power from a battery, usually 12V or 24V, into conventional mains alternating current (AC) power at 230V. This means that you can use one to operate all kinds of devices ... electric lights, kitchen appliances, power tools, TVs, radios, computers, to name but a few.

Small Inverters (up to 500W)

Most leisure and marine batteries will provide an ample power supply for 30 to 60 minutes even when the engine is off. Actual time may vary depending on the age and condition of the battery, and the power demand being placed on it by the equipment being operated by the inverter. If you use the inverter while the engine is off, you should start the engine every hour and let it run for 10 minutes to recharge the inverter battery.

Larger Inverters (500W and above)

We recommend you use deep cycle batteries which will give you several hundred complete charge/discharge cycles. If you use the normal vehicle starting batteries they will wear out after about a dozen charge/discharge cycles. If you do not have a deep cycle battery, we recommend that you keep the engine of your vehicle running whilst using the power inverter. When using the inverter with a deep cycle battery, start the engine every 30 to 60 minutes and let it run for 10 minutes to recharge the inverter battery.

Appliance Cautions:

• DO NOT use an inverter to directly recharge nickel-cadmium batteries through appliances. Always use the charger provided with that appliance.
• DO NOT plug in battery chargers for cordless power tools if the charger carries a warning that dangerous voltages are present at the battery terminals.
• Some fluorescent lamps may not be fully compatible with an inverter. If the lamp appears to be too bright, flickering or fails to light up at all, do not use the lamp with an inverter.
• Some fans with synchronous motors may slightly increase in speed (RPM) and increase in noise when powered by an inverter.
• Certain chargers for small nickel-cadmium batteries can be damaged if plugged into a modified sine wave inverter. In particular, two types of appliances are susceptible to modified sine wave:
• Small, battery-operated appliances such as flashlights, cordless razors and toothbrushes that can be plugged directly into an AC receptacle to recharge.
• Certain battery chargers for battery packs that are used in some cordless hand-tools. Chargers for these tools have a warning label stating that dangerous voltages are present at the battery terminals.
• DO NOT use modified sine wave inverters with the above two types of equipment.

Safety Warning:

240V of electricity can be lethal. Improper use of a power inverter will result in property damage, personal injury, or loss of life. Please read and follow carefully the instructions in the instruction manual provided with every inverter for important safety considerations and precautions.

General Safety Precautions and Installation Tips:

• Place the inverter on a reasonably flat surface, either horizontally or vertically.
• The inverter should not be installed in the engine compartment, due to possible water/oil/acid contamination, and excessive heat under the bonnet, as well as potential danger from petrol fumes and the spark that an inverter can occasionally produce. It's best to run battery cables to a dry, cool mounting location.
• Keep the inverter dry. Do not expose it to rain or moisture. DO NOT operate the inverter if you, the inverter, the device being operated or any other surfaces that may come in contact with any power source are wet. Water and many other liquids can conduct electricity which may lead to serious injury or death.
• Avoid placing the inverter on or near heating vents, radiators or other sources of heat. Do not place the inverter in direct sunlight. Ideal operating temperature is between 10° and 30°C.
• In order to properly disperse heat generated while the inverter is in operation, keep it well ventilated. While in use, maintain several inches of clearance around the top and sides of the inverter.
• DO NOT use the inverter near flammable materials.
•  DO NOT install inverters in unvented battery compartments.