Over the next few weeks I will be adding to it a different subject, in testing the Ignitors in electronic ignition, Ignition lead testing and basic test on the coil.
Maybe these could be pinned if the staff approves? as we don't seem to have any here on TMF
Battery Testing
Most wet cell car batteries these days are sealed and therefore you cannot use the old method of a hydrometer, so the testing has to be done with a Digital Volt Meter with an accuracy of 0.5% or better. It is important before any testing is done, a visual Inspection of the battery is carried out.
Before carrying any visual checks on a wet cell battery ensure there are no naked flames or anyone is smoking in the area.
1.Check for a leaking or damaged battery case which is showing signs of wetness around the damaged area. If there are signs of wetness the battery must be replaced and you must not carry out any more testing
2. A batteries voltage while standing can give an indication of its state of charge from the voltage below. Batteries tested should be left to stand after being charged by the car for approx. 4hrs to avoid an error on the float charge reading which will be above the 12.65v 100% charged state.
12.65v = 100% Charged
12.45v = 75% Charged
12.24v = 50% Charged
12.06v = 25% Charged
11.09v = Fully Discharged
Wet Cell Batteries should never be allowed to be completely drained flat 0v, as once a wet cell battery reads 0v the battery is permanently damaged and will never give good service.
Some batteries have a built-in "Magic Eye" hydrometer, which only measures the State-of-Charge in one of its six cells. If the built-in indicator is clear, light yellow, or red, then the battery has a low electrolyte level and if non-sealed, should be refilled and recharged before proceeding.
If you have a battery where you are able to top up the electrolyte level, then never stand with your face over the battery when topping up with water (Distilled Water Only Tap Water has minerals in which will short the plates inside the cells)
If the battery has not been checked and no signs of water are visible over the plates then filling with distilled water may not enable the cell to work as the acid content to make the chemical action would be weakened in strength, you should take the battery to a specialist for testing.
3. If the battery passes all the above tests the battery is found to have a voltage of 12.65v it is fully charged.
Never stand over a battery with your face while the battery is put under load either by a specialist battery drop tester or while cranking, as a battery with a faulty cell will bubble and eject battery acid from the battery vent holes!
4.You can fit a higher amp/hr battery to your car as it will have a bigger reserve capacity and the cars alternator will not have any problems charging it under normal driving.
A vehicle laid for should have its battery trickle charged to prevent battery failure
Checking the Condition Of The Battery + & - Cables.
1.Checking the condition of the battery cables and the battery terminals for any signs of fraying or corrosion is important to ensure a good electrical circuit. The cables and battery connections should be free from any corrosion and should be a tight and secure fit.
The old type of Top Hat Battery connections should be checked with caution, as they with age wear and no longer fit the taper on the battery post correctly, so when the centre retaining screw is done up the only electrical connection is at the top of the post and contact is made only by the holding down screws tension. You should not be able to rotate the connection on the post, if so a conversion to a clamp type post is in order.
2.Lubrication of the battery terminals will prevent acid corrosion on the lead terminals and you can buy special grease or use Petroleum Jelly. Do not use oil as it will seep inside the contact faces and cause a high resistance.
3.Checking the cars earth straps can be done visually for signs of tightness or corrosion as well as electrically.
To test for a good electrical connection you will need a multi meter, set the meter to Impedance on the rotary scale and touch the 2 probes together and the meter should read 0 or short circuit, this indicates a perfect connection.
Place the red probe on the battery – connection and the black probe on the connection to the body on the end of the earth strap, note the reading on the meter is in ohms and a high reading indicates a poor connection on the cable/strap your testing, so strip/clean as necessary.
The rest of the cars cables can then be tested in the same way.
Always start at the battery and work your way forward.
Never place a multi meter set on impedance between a live feed and earth!
Testing the Alternators Output
Before any testing of the Alternators output and charging rate the above checks on the Battery and Connections should be made.
Before any output checks on the Alternator you should visually make a check of the following
1.The Alternator mounting bolts are tight and the electrical connections into the alternator are secure and the cables are visually in good condition, and the Alternator pulley is inline with the water pump and crank pulley.
2.The Alternator belt is in good condition with no cracks or splits ( you may have to remove the belt to verify) when the belt is off check for play in the water pump and alternator bearings, and replace if worn and movement can be felt in either the Alternator or Water Pump make sure the belt is correctly tensioned.
3.Basic Alternator Output check can be carried out with a volt meter set on the 20v digital scale, place the red probe on the + battery connection and the black probe on the – battery connection, start the engine and increase the revs to 2000rpm the alternator should increase the batteries voltage to between 13.7-14.2v with all the cars accessories turned off. If the battery voltage increases to between 13.7v – 14.2v this indicates the alternator is charging and is reaching the inbuilt voltage regulators pre-set limit. If the voltage does not increase above the batteries 12.65v the alternator is faulty, or if the reading goes above 15v the Alternators regulator is faulty and should be taken to a specialist
Now with the engine idling turn on the cars headlights, heater blower and other electrical items used like a rear fog light and the wipers, take the rpm up to 2500rpm and observe the reading on the digital volt meter, it should now be reading between 12.8v-13.4v indicating that the basic output test that the alternator is not only charging but is providing enough amps to charge the battery when a heavy load is placed on the electrical system.
If the battery voltage on the Digital Volt Meter drops below 12.65v then the battery is providing current to the circuit and the alternator is not capable of running the system and keeping the battery charged, if this is the case either the alternator should be taken for repair or an exchange unit fitted.
4.Advanced Alternator Output checks will require a clamp type meter such as a Fluke which has a DC Amps Range, this is placed on the battery cable and the reading taken exactly of the cars charging rate.
If you Mini or other vehicles meets and passes all the tests above your battery and charging system is in working order, but remember even with a working system it’s still possible on short trips to take more out of the battery than you put back, in which case the vehicle should have a upgrade on battery size which will give it more capacity and help lengthen the problem between recharging or a suitable means of trickle charging over night to solve the problem.
Edited by KernowCooper, 18 March 2013 - 03:01 PM.
