After Putting on New Alternator What Should the Amps Read

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Slow Cranking System Examination

Test Your Charging and Electrical Organisation

A lead-acid battery has certain defined characteristics than make information technology easy to evaluate the health of the charging arrangement without fancy test gear. An in-car examination is actually better than taking parts off. I promise this helps people avoid wasting money on parts. Hither'south how we tin cheque a charging arrangement with a few simple pieces of equipment. Basically, you lot just demand a test light and small examination meter.

I accept a full diagram of the 1989 Mustang hither 1989 Ford Mustang Wiring Schematic

Alternator

The alternator converts mechanical free energy into electrical energy. There are unavoidable power losses in an alternator. Some losses are mechanical, primarily heating the alternator bearings and the drive belt. In that location are likewise electric losses. The diodes drop a petty voltage, this makes the diodes get hot. The alternator'south windings and internal wiring has resistance, and that causes ability loss and oestrus. The changing magnetic field also causes some losses. Keep in mind nearly of the alternator's load on the crankshaft comes from the electrical load power drawn from the alternator.

Contrary to myths and what marketing departments and salesmen would have the states believe, using an under drive pulley organization does not gratis upwardly horsepower when racing. Information technology actually tin can do the opposite! It frees up horsepower at idle, just it loads the system heavier when you rev up the engine as the alternator tries to grab up on missing battery charge!

When alternator shaft speed is reduced, the voltage regulator turns up the field current. The regulator, as long as the shaft is spinning fast plenty, increases field current and pulley torque need until the alternator is dorsum drawing exactly the same engine horsepower power it would take consumed turning at normal speeds! Every bit a matter of fact, since efficiency oft drops with reduced rotor speeds, the alternator sometimes draws more engine horsepower and run hotter with an underdrive pulley system than with standard shaft speeds!

The only style to reliably and significantly reduce alternator drag is to plow the alternator off while racing, although turning lights and electrical accessories off during racing certainly helps. Think that when the vehicle is running the alternator tries to supply all the load energy. At reasonable to maximum engine speeds, typically from 1500 RPM to redline with heavy loads, and from idle all the fashion to red line with low-cal electrical accompaniment loads, the battery just goes along for the ride. It really doesn't do anything, except await for the alternator to fall below operating speeds.  A battery volition eat noticeable engine power only when the battery is low on accuse and the missing charge is existence replenished. A battery, when charged, is really just an electrical storage tank.

NEVER pull the battery cable to check the alternator. This very crude test method was marginally OK when nosotros had vacuum tube car radios and point-blazon ignitions, just information technology is a very bad idea now. The bombardment stabilizes the electrical system and loads the alternator, preventing loftier peak voltages or voltage surges as the alternator adjusts magnetic flux to produce the same average voltage at different current demands. If yous rev the engine upward and pull a battery cable, the alternator voltage can spike upwards to 100 volts or higher before the alternator flux dies off enough to bring voltage dorsum down to 14 volts or and so. This tin kill the car's estimator and other expensive electric components. I've seen headlights blow out when a guy opened a battery switch while an engine was revved up. If you hear anyone telling someone this is a way to check an alternator in a modernistic vehicle, stop them!

TESTING the ALTERNATOR, is information technology skilful or bad?

To charge the battery, the alternator voltage output has to exceed a minimum charging voltage. This minimum charging voltage is 13.8 volts dc across the battery terminals, or at the output of the alternator. A unmarried lead-acid cell starts to accuse at annihilation over two.25 volts. Since a 12 volt battery has six cells, whatsoever 12 volt lead-acrid battery needs at to the lowest degree 13.8 volts to kickoff to charge. This voltage volition be enough to fully accuse or maintain the bombardment on a trickle charge, merely charging time will be very long at 13.8 volts.

To fully charge in reasonable times, alternator output  must be 14.2 Five to 14.5 V as measured correct across the bombardment posts . Above 14.5 volts charging voltage, batteries have a greatly increased tendency to release excessive acidic vapors, hydrogen gas, and to corrode things around the battery. The battery terminal charging voltage must exist less than 14.vii volts to foreclose excessive gassing. Charging voltages over 14.7 volts can prematurely dry the battery by boiling out electrolyte, and increase risk of a battery hydrogen gas explosion.

In this case the bombardment charging voltage is 14.61 volts with the engine at high idle. 14.4 volts is the gassing threshold. The bombardment above will slightly gas, but non enough to be harmful, and the bombardment will get a quick full charge recovery after starting. fourteen.8 would beginning to be a worry (there might be liquid or corrosion on the battery) and fifteen volts would exist a real business organization, merely 14.6 is fine. Less than xiv.iii would exist a "weak" alternator or regulator. Much less than 14.2 at a fast idle is bad wiring, bad alternator or regulator, or a bad connection or fuse link. When running at a normal wearisome cruising engine RPM, the voltage across the battery terminals should stay over 14.3 volts even with full load, like lights, heater blower, and everything else, running. If this system was in a restored 1966 GT coupe, I would probably change the regulator to reduce maximum alternator voltage. This would prevent deterioration of metal around the bombardment from excessive charging vapors. It's OK in my daily driver as long as I lookout man the battery for purged acid deposits.

If you lot measure out battery voltage and it is anywhere over xiv.2 volts and less than 14.eight volts with the car running at slow cruising engine RPM speeds and maximum loads on, you lot already take a bigger alternator than you need. If voltage is over 14.two under maximum loads when at cruising RPM, buying a bigger alternator or a new alternator is a waste of fourth dimension and money.

Plough the motor off with no load (headlights, etc. all OFF) and read the battery voltage.

With the engine but shut off, the battery voltage should be 13.two volts to 13.eight volts. The exact voltage varies with the bombardment, how quickly you read it, and the state of battery charge. This voltage is not besides important because the battery will slowly and steadily settle to a new voltage that indicates the true state of battery charge, but the voltage measured correct at engine shutoff is a very clear indicator if the alternator or charging system is charging. If the voltage is over 13.2, the bombardment was just being charged.

So what happens if your battery goes dead all the time, but the alternator seems proficient?

Measuring electrical system leakage current

To test the electric organization for unwanted loads draining power, shut everything in the car off. Do just like you would exercise things when parking the motorcar overnight. make certain all the lights and accessories are off.

Remove the negative postal service wire and cheque current describe with all electrical loads off using a test low-cal. (I made a test light from an onetime tail lamp seedling.)

The dull glow in the lite filament indicates a current drain problem. At this point I practice not want to connect a current meter to check leakage because the brusk could damage the examination meter! If a small clear examination lamp like this does not light, then it is generally safe to directly measure current drain with a test meter.

Measuring Parasitic Current Drain

With all electrical loads off connect the meter, on a low amperes scale of about 1 ampere or so, in series with the battery negative postal service to ground. The positive meter pb connects to the car chassis, and negative meter lead to the negative post of the battery.

A practiced electrical system battery drain

This is measured on the 20mA scale. The mA scale reads in thousandths of an ampere. My 1989 Mustang Lx, later I changed a bad alternator diode, at present has about 1.73 mA of battery drain. This drain is all from the EEC-IV computer memory. Unlike radios and different computers might have different standby drains, every bit might  accessories similar clocks, but in no example should "overnight off" leakage exceed 25 mA or so. 100 mA is similar leaving a small interior dome calorie-free on!

My Kenwood stereo draws 1.5 mA when connected. If you have a digital clock that stays on, an alarm, or some other load this electric current volition be higher. At 75 mA, leakage could compromise battery life of infrequently driven vehicles. mA is milliamperes, or one 1000th's of an ampere.

The meter above is on the 20 mA calibration, and is reading ane.73 mA. That is nothing. The battery charge would probably last for months of sitting.

Bad battery parasitic Bleed

If the test calorie-free lit, yous will want to locate the wire loading the battery. Start make sure all lights are off. You can do this by having someone open and shut things with lights, like the trunk, and watching for a define large load change. You should encounter a definite load change when shutting doors with lights, like the glove compartment.

Connect the test light in series with the negative post, and get-go pulling feed wires. The first to bank check is the heavy charging wire from the alternator.  A bad or leaky diode in an alternator is a very common source of overnight battery drain.

Connect wires ane at a fourth dimension to run across what pb is drawing current. In my case it was the alternator lead! Even though the alternator was charging fine, it was also draining the battery. My problem was a bad alternator diode. There could be a multifariousness of other problems, like a bad voltage regulator or a stuck relay contact.

Download a wiring diagram

I downloaded this from T. Moss'southward website , which I find much more useful than other sources. Tom Moss goes out of his way to help people, and is a genuinely overnice boyfriend. AutoZone and others have some free schematics up too.

 T.Moss's diagram (linked in a higher place) showed me the heavy dark dark-green wire from my starter relay causing my "drain trouble" went straight to my car'southward alternator output.  In my case 1 of the diodes (the little black "arrows") in my auto'southward alternator was bad. This electric current loss also made my alternator slightly warm to the bear on, fifty-fifty when sitting off for several hours.

Other Helpful Voltages

Battery voltage tin exist higher than 12.6 volts immediately after charging.

Open Excursion Voltage of 12V battery later car is off for i hr	Relative charge
12.half dozen V	100%
12.4 V	75%
12.2 V	50%
12.1 V	25%
Less than 12 volts	Dead

Any open terminal voltage below 12 volts is considered full discharge or a dead battery.

Testing Starters

Starters sometimes can exam good out of the car, but can exist bad. Ane common problem with cheaply built or lacking starters is starting torque loss when hot. This usually happens considering the iron loses ability to hold magnetic flux (starter current skyrockets when hot), or because the wire is undersized and goes up in resistance (starter current drops when hot), or the starter seizes up (also causing high current).

The all-time way to test a starter is by measuring voltage and current.

To test a starter and wiring with a simple meter:

• Clip the meter positive lead to the starter feed wire going into the starter
• Clip the meter'south black negative lead to the ENGINE Cake
• Make sure the meter is on volts, and set up to the lowest voltage scale possible that reads at least 15 volts.  In other words if your meter has two.5-volt, 25-volt scale, and 250-volt scales, apply the 25-volt scale. The 25-volt scale is the closest calibration to xv volts, but is not nether fifteen volts.
• With the meter clipped across the starter, watch the meter while cranking the engine.

Make sure the battery is good. There is a voltage table above for battery charge. The no load (everything off) battery post voltage should be at least 12.6 volts and as high as 13.viii volts.

If the starter cranking voltage goes beneath 9-10 volts, you accept a problem with starter current, engine grounding, or battery.

Measure beyond the battery by probing directly into the battery posts (NOT the terminals that clench to the posts, but poke direct into the lead posts coming out of the bombardment), and meet how much the bombardment drops when cranking. If it drops and you are sure the alternator is working, take the battery to an automotive parts store that tests batteries. Unlike starters, testing batteries is VERY easy and very reliable.

If the battery stays up on the posts and the starter voltage sagged down, you probably have a bad starter wire, footing wire, or some other wiring problem. If the battery mail service voltage tests good but sags abnormally with your starter, you probably take a starter problem. You need to take starter current checked.

Inexpensive or poorly manufactured starters show up mostly when the starter is very hot. Starters very oft cannot be tested accurately on a demote, because they often can fail only when very hot. I encounter very few tractors, cars, and trucks that crank OK when common cold and practise not crank when hot that have problems other than a starter! My diesel fuel tractor was a bitch to offset when hot, only cranked like a dream when cold, and information technology was the starter. My tractor does not have headers, either. Simply the cake heat was enough to make the starter quit. I've had the same experience with cars. When cold, the starters work and exam skilful! Marginal starters can accept enough oomph to start properly when the organization is cold, but fail when hot.

Bad alternators or batteries evidence upwardly mostly when the car is very common cold, merely both alternators and batteries can be tested reliably to see if they are good.

Installing a larger alternator will not gear up a bad starter, bad battery, or bad wiring.

   Changing to LED Warning

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Source: https://www.w8ji.com/battery_and_charging_system.htm