Testing car battery voltage drop test,cheap batteries for cars in uk london,best battery life smartphone australia - Step 3

06.06.2015
To check your battery's state of charge, connect the RED or POSITIVE voltmeter test lead to your battery POSITIVE terminal. The photo at the top of this page shows a battery voltage reading of 12.29 volts, which means the battery being tested is low with only about half a charge. If your battery voltage is less than 12.45 volts (75 percent charged), it is low and should be recharged. Automotive lead-acid batteries should be maintained at a 75 percent charge level or higher for best performance and life. A good battery is essential for reliable starting, especially during cold weather because cold weather increases the cranking load on the battery.
Warning: Do NOT attempt to recharge your battery if it has run down and the liquid inside is frozen.
A GOOD battery is one that will accept and hold a charge, and is capable of producing close to its rated amperage output.
Most car batteries only last about 4 to 5 years, so if your battery is 4 or more years older and is not holding a charge (keeps running down), or it does not seem to crank your engine a normal speed, you probably need a new battery. A low or dead battery does not mean your battery has failed, or that it needs to be replaced. CAUTION: Conventional wet cell car batteries are filled with a mixture of water and sulfuric acid. The other (and must faster) method for testing your battery is to use an electronic "conductance" tester like the one shown here. Some electronic battery testers can also analyze the battery's CCA capacity, which can be used to estimate the battery's remaining service life. Diagnostic Tip: You also can use a digital voltmeter to check for voltage drop across all circuit connections, too.
Whether your battery tests GOOD or BAD, make sure the battery is fully recharged before returning it to service.
Diagnostic Tip: If the alternator on your car has failed, it might mean your battery is not building up normal resistance as it accepts a charge. A replacement battery must have the same post configuration as the original (top post or side post), and fit the battery tray.
Next, you have to figure out how many CCAs the vehicle needs for reliable cold weather starting. Another number that is important is the months of prorated warranty coverage provided by the battery manufacturer.
The first sign of alternator or charging system trouble may be dim headlights or an engine that is slow to crank (or will not crank). Charging problems can be caused by electrical faults in the charging system itself, by poor wiring connections at the battery or elsewhere, or by a slipping or broken drive belt.
Once battery voltage drops below a certain threshold, the onboard electronics, ignition and fuel systems may stop working normally and cause the engine to stall.


Recharging the battery or jump starting the battery with booster cables from another battery or vehicle may get the engine running again, but it will not be for long if the charging system is not producing normal voltage. Warning: Never disconnect a battery cable while the engine is running to "test" the alternator. The alternator's charging output increases in proportion to the electrical load on the charging system and engine speed. Charging output of the alternator is controlled by a voltage regulator which may be mounted inside or on the back of the alternator (internally regulated), or somewhere else under the hood (externally regulated).
When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage. The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature.
In addition to checking the alternator's voltage output, you also need to check its current or amperage output. Charging output can be measured with an inductive amp probe clamped around the BAT (B+) wire that connects to the alternator.
ALTERNATOR OVERHEATING High underhood temperatures are hard on alternators, and high electrical loads create even more heat. If the alternator is working hard under a heavy load at low RPM (especially during hot weather), there may not be enough cooling to prevent the unit from overheating. The alternator may be forced to work harder than normal if the battery cables, ground straps or other electrical connections in the charging circuit are dirty or loose.
The electrical system is, after all, just a big series of loops that carry current from the charging system to the battery, and from the battery to all of the vehicle's electrical accessories and electronics. One of the most common causes of charging problems is the failure of one or more diodes in the alternator. When the engine is running, charging current from the alternator flows through the diode trio via the BAT (B+) connection on the back of the alternator. If one of the diodes fails, it may cause the charging system indicator light to glow dimly. A bad connection or open circuit between the alternator output terminal and the positive battery terminal will force the charging current to follow a parallel route through the diode trio and out of the alternator. With the engine idling, touch one test lead of your voltmeter to the battery positive (+) post, and the other test lead to the BAT (B+) terminal on the alternator.
If you see a voltage reading greater than 0.2 volts, it means there is excessive resistance somewhere in the circuit causing a voltage drop in the wiring circuit. A negative side ground circuit test is made by touching one voltmeter test lead to the alternator housing, and the other test lead to the negative battery post (not the terminal clamp) with the engine running and charging system loaded. If the alternator output circuit and ground circuits test good (voltage drop less than 0.2 volts) and the vehicle has a history of repeated alternator failures due to burned out diodes, check for a shorted indicator light terminal. Checking for voltage drops in a circuit is a good way to find hidden problems that may be causing a charging problem.


Loose alternator mounting bolts and brackets can cause vibrations which may damage the alternator. One way to reduce this problem is to take your old alternator to an auto parts store with an alternator bench tester and have it tested BEFORE you buy a replacement. Voltage drops on the negative side can cause overcharging (fools the voltage regulator into thinking the battery is low). Get the correct alternator pulley.Make sure the pulley on the replacement alternator is the same as the one on the old unit.
Peak loads and prolonged idle conditions can result in battery discharge, since the alternator cannot keep up with the power usage.
Some testers can also measure the amps drawn by the starter while cranking the engine, and analyze charging system output under load once the engine is running. This, in turn, makes the alternator keep charging the battery at a higher than normal rate. As a rule, the higher the warranty months on the battery, the higher the battery CCA rating and the better the battery. Though all automotive batteries today are still based on lead-acid chemistry, redesigned grids, thinner plates and new connectors allow more amps to be packaged into smaller cases.
It measures low current draw for 20 hours while maintaining a minimum post voltage of 10.5 Volts at 70 degrees F.
Also, check the negative battery cable ground connection and the integrity of any engine ground straps.
Doing so can cause high voltage spikes that can damage the alternator as well as other electronics. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage.
If the serpentine belt has more than 50,000 miles on it, throw it away and replace it with a new one. If the automatic belt tensioner is rusted, weak or stuck, it won't maintain the proper tension on the serpentine belt, allowing it to slip. So consider upgrading from a basic 36-month replacement battery to a premium 72-month battery. AGM technology also makes batteries more resistant to vibration damage and helps extend battery service life.



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