Auto Service Professional

JUN 2018

Magazine for the auto service professional

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J u n e 2 018 A S P 11 pared to current battery technology (see "OEM battery trends" article on page 18). When we tested batteries from years back, many of us would use the "toaster" type testers which would essentially draw a fixed current of anywhere of 100 amps to 300 amps. is just wasn't a very ac- curate test but would kind of give us an idea on the condition of the battery… sort of. As you know, when performing a battery test, the battery has to be able to accept a full charge so a proper test can be performed. Today's mod- ern day battery testers will test the battery using the capacitance type test, where the tester injects a very small AC voltage (E) of known amplitude and frequency into the battery. In this article I'm not going to go into the specifics of battery testing techniques, but will concentrate on battery diagnostic problems. Battery testing When we receive a customer concern that the battery is dead and the engine won't start, a cou- ple of things need to be performed. First off, the battery needs to be fully charged and then needs to be tested. is will tell the tech- nician the current condition that the battery is in. If the battery won't hold a charge let alone accept a charge, then a battery replacement is in order. An important step in battery testing is to test the battery without the battery cables connected. Having the cables of the vehicle still hooked up to the battery will give you an inaccurate read- ing as you are testing the extra resistance of the components in the vehicle such as the battery cables, starter, etc. You want to isolate the battery separately from the vehicle and that also includes batteries that are used in series. Another diagnostic tip is to make sure that the battery doesn't have a lot of corrosion on the surface. at "Chia Pet" buildup will play a part in your battery diagnostics in that it will add un- wanted resistance to your test results and possibly give you a false reading which could potentially lead to premature battery replacement. Clean the surface well with a good battery cleaner before you recharge the battery and before you test it. Start-stop systems Let's fast forward to today's modern day battery systems and battery management. One of the newer features in some of the vehicles we see to- day is the "start-stop" system. e start-stop sys- tem has been added to the vehicle to primarily in- crease fuel mileage. e engine will shut off when the vehicle has come to a complete stop as if the engine has stalled. When the driver takes their foot off of the brake pedal, the engine will restart. is is monitored by the vehicle's body com- puter to watch the system voltage. Once the volt- age has dropped below a predetermined specifi- cation due to other system inputs like the HVAC blower fan, headlights and various other electri- cal demands, the engine will restart and resume normal operation. For example, on a 2017 Chevrolet Cruze the battery management system relies on a sensor to constantly monitor the condition of the bat- tery based on the input that's received by the ve- hicle's charging system and the loads placed on the electrical system. e battery current sensor is a sensor that acts just like an amp clamp. e battery cable is routed through the sensor itself. e battery current sensor is a serviceable com- ponent that is connected to the negative battery cable at the battery. e battery current sensor is a three-wire Hall affect current sensor. Figure 2: If the cables remain attached to the battery, variables such as extra resistance of cables, starter, etc., contribute to inaccurate readings. By testing this 950 CCA-rated battery this way it showed that the rated capacity was only 744 CCA and only 78% of the rated capacity of a fully charged battery. The next screen shot showed that the battery was bad and needed a recharge and retest or a battery replacement.

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