This is the first of a series of four articles that MOTORwill publish during 1999. “Mastering the Basics” is de-signed to build up or refresh the level of knowledgeamong technicians who are repairing today’s vehicles.Our “Basics” series also will provide shop owners withgood training material they can give to their employees.

One trait that all outstanding technicians have isthat they understand basic system technology. Call ittheory of operation, fundamentals or basics, the “su-per techs” know system theory, which enables them tomake their way through today’s complex vehicle sys-tems to find and fix problems fast. One “super tech”we consulted for this series had this to say:

“Basic testing will find 99% of what’s wrong, afterwhich you’ve earned the privilege of using the remain-ing 1% of your knowledge. That’s the creative testingthat mechanics dream about. To top it off, fundamen-tal solutions to difficult problems are usually waitingthere to be picked off by a pro, while other would-betechs spend hours chasing their tails.”

That comment reflects how highly intelligent peoplehave the skill to make complex things seem simple.

This past summer, a seminar on “Electrical SystemFundamentals” was held at a national trade show. Theseminar was a review of electrical system basics andthe application of those basics to diagnose automotiveelectrical system problems. Everyone who attendedthe seminar raved about the content. They knew it wasa review of basics, but that didn’t matter; they thoughtit was excellent!

There will always be a need for basic training infor-mation in this profession. Therefore, this series will re-view the principles of various vehicle systems andshow how theory applies to diagnosing problems ineach system. We’ll try to take a complex system andsimplify it so technicians understand what they’re do-ing and relate theory to practical, real-world repairs.The first subjects are the core components of the vehi-cle electrical system—the battery, starter and chargingsystem.

The relationship of the bat-tery to the starting andcharging system is really acontinual cycle of convert-ing one form of energy to

another and then back again. It’s achicken-and-egg sort of relationship inwhich the mechanical energy of theengine drives the alternator, whichforces electrical energy (current) into abattery, where it’s stored as chemicalenergy. The chemical energy of thebattery then gets changed back to elec-trical energy when it supplies currentto the starter motor, which uses me-

chanical energy to crank the engine.Then the engine’s mechanical energyagain drives the alternator to rechargethe battery so it can supply more cur-rent to the starter when needed.

It doesn’t matter where you pick upthe cycle as a starting point, as long asyou recognize how the battery, alterna-tor and starter relate to one another.

Battery BasicsMost complaints that point to the bat-tery or the charging or starting systeminclude a symptom of hard starting orfailure to start. Slow cranking, long

cranking times or failure to crank canhave their root causes in any—or all—of these electrical areas. Often, the jobis to fix a no-start problem, period. Sowhere do you start troubleshootingsuch a problem? With the battery.

Beyond a simple blown fuse or abroken wire, you can’t troubleshootany electrical problem without a fullycharged battery. A good battery hastwo characteristics: First, it must deliv-er the electric current demanded bythe starter and other electrical deviceson the car. Second, it must maintainenough voltage to force that current

BY KEN LAYNE

BATTERY, STARTER &CHARGING SYSTEM

21January 1999

An open-circuit (no-load) voltage test will indicate the approximate state ofcharge of the battery. It’s a necessity on maintenance-free batteries.

through the car’s circuits. Basic batterytests include an open-circuit voltagecheck, a load test and maybe a three-minute charge test. Most batteries soldtoday are maintenance-free units, withnonremovable vent caps. If the batterydoes have removable caps, though, getout your trusty hydrometer and checkthe specific gravity of the electrolyte.

Remember, battery electrolyte issulfuric acid and water. So checkingthe specific gravity of the electrolytesimply means “weighing” it. The spe-cific gravity of water is the baselineand, therefore, has a value of 1.000.Sulfuric acid is heavier than water,while electrolyte is about 35% to 40%acid in a fully charged battery. Thatworks out to a specific gravity of1.260 to 1.280. When the battery isfully charged, all of the sulfate part ofthe acid stays in the electrolyte. Asthe battery discharges, sulfate ionsmove from the electrolyte to the leadplates, and the electrolyte becomesmore water and less acid. And as itgets diluted, the battery’s state ofcharge drops as follows:

Specific Gravity State of Charge(at 80°F) (%)

1.280 - 1.260...................................1001.250 - 1.230.....................................751.220 - 1.200.....................................501.190 - 1.170.....................................251.160 or lower ...................Discharged

If the battery in a problem car is amaintenance-free unit (as most are to-day), you can’t use a hydrometer. As analternative, start by checking the open-circuit (no-load) voltage. To do this, re-move the surface charge from the bat-tery by turning on the headlamps forabout 10 seconds. Then turn the lightsoff and connect your voltmeter acrossthe battery terminals. The voltagereading will indicate the approximatestate of charge, as follows:

Voltage % of Charge12.72 - 12.60...................................10012.45.................................................7512.30.................................................5012.15.................................................25

If either the specific gravity test orthe open-circuit voltage test indicatesthat the battery is 75% charged or bet-ter, you can continue with a load test.If the battery is less than 75%charged, you should roll out the bat-tery charger before doing more test-ing. In either case, this is a good pointfor a basic inspection.

Inspect theNuts & Bolts & BeltsYou can find and fix lots of basic prob-lems with a simple inspection duringthe early steps of your troubleshooting.Now is a good time to look for loose,glazed or otherwise damaged drive-

belts. Remember, the alternator can’tget up to speed and keep the batterycharged if its drivebelt is slipping.

Neither the alternator nor the batterycan move enough current throughwiring that’s frayed or otherwise dam-aged. Loose or corroded wiring termi-nals and ground connections also addresistance to circuits and reduce currentflow. And then there are the battery ter-minals themselves. Many no-start prob-lems have been fixed just by cleaningand tightening battery connections thathad a great growth of “gray fuzz.”

The Load TestA load (capacity) test indicates howwell the battery can deliver high cur-rent while still maintaining enoughvoltage to operate the ignition. A loadtest is the basic way to test a mainte-nance-free battery and an importanttest for any battery. Check the open-circuit voltage again before loading thebattery to be sure it’s fully charged.

To determine the amperage load forthe test, check the battery top to see ifit’s printed there. If it’s not, divide thecold-cranking amps rating by 2 or mul-tiply the ampere-hour rating by 3. Youalso can use these guidelines:

Engine Test Amperage4-cyl., small 6-cyl. ...........................170 - 190Small 8-cyl. (up to 5 liters).............175 - 250Large 8-cyl. (above 5 liters)...........225 - 300

If the battery was charged just beforethis test, don’t forget to remove the sur-face charge by turning on the head-lamps for 10 to 20 seconds. The tradi-tional load-test method requires a volt-amp tester (VAT) with a carbon pile toapply the test load. Connect the testerto the battery and turn the control knobto draw the desired current for about 15seconds. Note the voltmeter readingand turn the control knob to Off.

During the test, voltage should stayabove 10 volts. The customary accept-able minimum voltage is 9.6 at 70° to80°F. If the voltage stays above 10.0with the full current load for 15 sec-onds, the battery is okay. If the voltagedrops below 9.6 or if the specified cur-rent can’t be applied, the battery can be

22 January 1999

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: Ken

Lay

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tested further, although the usual con-clusion at this point is that it has earnedhonorable retirement. If battery voltageis between 9.6 and 10.0, charge it andretest before deciding its fate.

If you don’t have a VAT, you can stilldo a load test with a digital voltmeter.This works particularly well if your me-ter has a Min/Max recording function.Simply connect the meter across thebattery terminal clamps and select theMin/Max function. Then disable the ig-nition, turn on the headlamps and crankthe engine for about 10 seconds. Checkthe recorded minimum and maximumreadings on your meter. Once again, thebattery voltage should not drop below9.6 during cranking.

Although you don’t measure the cur-rent load during this test, it’s a realisticmeasure of the battery’s cranking abilityunder the load of its own engine andelectrical system. The test is easy, andit’s quick—well under a minute. As evi-dence that old-fashioned, basic testshave a place in the world of high-tech,Fluke programmed this load test intothe menus of its top-of-the-line Model98 Scopemeter. You can even graph thevoltage drop if you’re so inclined.

Starter Current Draw,Voltage Drop & Speed TestsIf the battery qualifies as okay, you canmove on to some basic starting systemtests. To check cranking current drawand rpm, you basically repeat the alter-native load test with an ammeter con-nected to the starter motor circuit anda tachometer connected to the engine.Crank the engine for about 15 secondsand note the voltmeter, ammeter andtach readings. Again, the voltageshouldn’t drop below 9.6. If it does,you’ll have to return to square one withthe battery or look for a whopping cur-rent draw.

Cranking current should be withinmanufacturer’s specs. If it’s above, lookfor a short in the starter or an enginethat’s binding for some reason. If am-perage is below specs, look for high re-sistance in the starting system orrecheck the battery.

Cranking speed for most engines is

about 200 620 rpm. Low crankingspeed plus high current draw pointsyou to the possibility of a binding en-gine. High cranking speed with lowcurrent draw points to a badly wornengine—burned valves or pistons, orsomething else that drastically lowerscompression. Interestingly, nothingmakes an old pushrod V8 crank fasteror smoother than a jumped timingchain...but it’s not going to start.

The cranking current draw, voltagedrop and speed tests will lead you topinpoint voltage drop tests for thestarting system. For these tests, we di-vide the system into the control circuitand the insulated and ground sides ofthe motor circuit. Test points will varyfrom one vehicle to another, so youshould have an accurate wiring dia-gram from a manual, unless you knowthe system by heart.

The starter control circuit is madeup of the ignition switch, the neutralsafety switch (or switches) and the coilside of the starter relay or solenoid.Disable the ignition, then crank theengine over with the ignition switchduring these tests. Don’t use a remotestarter switch because you want to in-clude the voltage drop across the igni-tion switch and its wiring to completelysatisfy the test requirements.

You’re going to use your voltmeterto check voltage drops around the cir-cuit to pinpoint high resistance. Re-

member, according to Ohm’s law,every point of resistance in a circuitwill drop part of the source voltage.Excessive resistance at any point dropsmore than its share of voltage anddoesn’t leave enough to push currentthrough the circuit. High resistance inthe control circuit won’t usually cause aslow-cranking problem. More likely, itwill keep the engine from cranking atall because there won’t be enough cur-rent to close the relay or solenoid andturn on the starter motor. Sometimesthe relay or solenoid will chatter asborderline current tries to energize itbut just can’t quite get the job done.

While cranking the engine, con-nect your voltmeter across all theswitches and coils in the control cir-cuit to measure voltage drop. Just asimportant, check voltage drops acrossall the connectors and all the lengthsof wiring in the circuit. These are themaximum allowable voltage dropsthat you should see:

Any length of wire or cable ......................200mV (0.2 volt)

Any switch ....................300mV (0.3 volt)Any ground

connection..................100mV (0.1 volt)Any other circuit

connection ........................0mV (0 volt)

If you haven’t solved the no-startproblem after checking the starter con-

23January 1999

A traditional volt-amp tester is the tried-and-true way to load-test a bat-tery, as well as test starter current draw and alternator output.

trol circuit, or if you’re troubleshootinga slow-cranking problem, move yourvoltmeter to the motor’s power circuit.The insulated side of the motor circuitis the part that supplies battery voltage(B+) to the motor. It contains the posi-tive terminal of the battery, the heavycables, the power contacts of the relayor solenoid and the motor itself. Theground side of the starter motor circuitstarts with the motor’s ground to theengine and includes the low-voltageground path through the frame orbody, plus the ground cable to the bat-tery negative terminal.

For the motor circuit tests, disablethe ignition and use a remote starterswitch to crank the engine. For the in-sulated side of the circuit, put yourvoltmeter positive lead on the positivebattery terminal (not the cable clamp).Then probe backward through the cir-cuit with the negative meter lead fromthe high-current cable connection atthe motor to every high-current con-nection on the solenoid and back tothe battery positive cable clamp. Look

for the same voltage drops—or less—listed for the control circuit.

For the ground side of the circuit,put your voltmeter negative lead onthe negative battery terminal (not thecable clamp). Then probe backwardthrough the circuit with the positivemeter lead from the ground connec-tion of the motor to the engine, thenback to the battery negative cableclamp. Again, look for excessive volt-age drops.

If it looks like we’re dealing with alot of small voltage and resistancereadings, we are. But what’s a fewtenths of a volt or ohm among friends?The answer is, plenty! Using good oldDr. Ohm’s law (E=IxR), you can calcu-late that as little as 0.01 ohm of resis-tance in a starter motor circuit causes a2-volt loss of electromotive force. Andthere’s your slow cranking problem.

Charging SystemOutput TestThe final steps of this electrical exer-cise will ensure that the charging sys-tem can put back into the battery whatthe starting system took out. Aftercranking the engine, the battery isslightly discharged, and this is a goodtime to check the alternator because itwill deliver high current and voltage assoon as the engine starts.

With your voltmeter and ammeterconnected to the engine, turn the ig-nition on but don’t crank the engine.Read the discharge current on theammeter. This is the ignition primarycurrent and, on some vehicles, the al-ternator field and blower motor cur-rent. Now start the engine and run itat 2000 rpm, then read the chargingvoltage and current. Next, hold en-gine speed at 2000 rpm until the cur-rent drops below 10 amps. Thencheck the voltage again and return theengine to idle.

Add the current reading taken withthe engine off to the highest outputcurrent reading with the engine run-ning. This is the total output currentand should be within 10% to 20% ofthe alternator’s rating. The regulatedvoltage should be from 12.6 to 15.5volts. When the current drops below

10 amps, the voltage should be at theregulated maximum. Check a manualfor exact specifications. If current andvoltage are outside the general limits ofthis test, you’ll want to go for pinpointcurrent and resistance tests.

Because of the variety of alternatorsand regulators on late-model vehicles,it’s a good idea to check the specs andwiring diagrams in a manual for thesetests. When you test charging systemcircuits, however, you’ll still be takingresistance and current measurementsthat are applications of basic electricaldiagnosis. Remember what one techni-cian said about troubleshooting: “Basictesting will find 99% of what’s wrong,after which you’ve earned the privilegeof using the remaining 1% of yourknowledge.”

A lab scope to test a battery? Whynot? Basic electricity meets hightechnology. The traditional load testis a programmed menu selection onthe Fluke 98 Series II Scopemeter,and you can even graph the crank-ing voltage if you want.

After cranking and starting the en-gine, charging voltage at the batterybounces back to 12.68 volts.

For a free copy of this article, write to: Fulfillment Dept.,

MOTOR Magazine, 5600 CrooksRd., Troy, MI 48098. Additional

copies are $2 each. Send check or money order.

24 January 1999