School me: Battery and Alt. diagnosis with ohm/ volt meter

[Hilux]

Ok class, here's my dilemma.

Moms 96 Corolla drags about every other start.(thinking exciter in alt at this point) A few good revs, shut off, restart, and it'll start fine no drag.

I am NOT good at electrical stuff and have never had to do anything like it.


I've seen a BMW tech touch the leads to a battery and immediately he found something out, what I don't know.

How do I test and alt output while it's running?


school me please. I know AZone will do it for free, but if it's that easy I could use learning this.



Battery Alternator alt diagnose diagnosis diagnostic exciter

 

[raydouble]

What you describe sounds like one of the battery cables, the battery or the starter.
Is the battery light on... on the dash?

What is standing voltage @ battery not running? 12.00 to 12.80 is normal. < 11.80 battery should be charged or replaced.
What is voltage @ the battery while running? 13.50 to 14.50 should about normal.
Voltage at battery while cranking should not dip below 10 volts.

Lots more............but let's see what you come up with.

 

[Hilux]

prolly the terminals. But I could use the procedure for both the Alt and Batt anyways.


Do you check the Alts output via the battery? Or, do you ground out the tester and touch the post under the Alts insulator?


ie, engine off: get the battery's voltage

engine on: the Alts voltage?

???

 

[Hilux]

12.61 VDC off

13.86 VDC running and holding....still running, just cleaned terminals

 

[WristPin]

Your muilti function meter probably has a amp meter. but it probably only is rated at 20A or less. If it had a higher rating, to utilize that feature, you disconnect the positive cable from the battery, and hook up the probes in line with the batt. and cable.

When using the volt function like you have done, you simply hook one probe to each terminal.

By determining the starting draw, and the charging draw, you can figure out if the alt is suppling current.
at low rpm, it will supply say 45Aout of a possible 60A. and at higher rpm it will do 50A. when you turn on any accessory, light head lights, the alt is supposed to sense that demand, and put out the max amps of 60A. if the test reveals that there is no fluctuation in amperage, the regulator is faulty.

the main parts of an alternator consist of:. the diode rectifier plate, which converts Alternating Current (AC) into Direct Current) the rotor (the part the pulley is connected to, which spins inside the windings, called the stator. Somtimes the stator can become loose, or a wire will come unsoldered or break. when this happens, the output can be both good one minute and bad the next. Cause the connection loose, opening and closing the circuit. The voltage regulator controlls or creates a small amperage to regulate the field circuit. And of course the brushes, which are serviceable parts. All they do is carry the generated current and volts (I and E if you know Ohm's law )

The field windings are connected with the ignition switch and charge warning light. when the key is on, engine off (KOEO) the light glows. Once the engine is running and the alternator is generating, a separte diode, (Not the diode rectifier plate. usally part of the instrument cluster) it feeds the field current from the alternator main output. that equalizes the voltage across the warning light which goes out. The wire supplying the field current is what you call the exciter. But if this diode fails, then your exciter circuit is no longer closed, and the alternator wont charge. So first check to see if the charge light comes on with KOEO.

 

[raydouble]

Check for loose connections at starter and at ground (of battery cables)

You also need a load tester to properly test the battery.

What was the battery voltage drawn down to while cranking?

Voltage drop test for battery cable integrity
Place black lead on neg. of battery and test with red lead at battery post, cable terminal, and connection at starter should be within about .3 volts of each other...... ideally they should all be the same.
Do the same test with red on pos. and test at battery post, cable terminal and at the body and engine connections.

 

[haryv]

Hilux check these items in order

Audiable drag in the alternator is usually the cause of worn out berrings. If it is near the belt check for tightness of the vbelt. Grasp belt and rotate it 90 degrees between alternator and harmonic pully. Should be difficult to rotate the belt. If it is easy then the belt is loose and will squeel when there is a load placed on the belt but will be most noticable when wet after a rain storm.

I usally check all the basics besides what is the obvios because it seems I find more then one issue when working on past customers cars.

Check the battery fluid level. It should be just slightly above the plates. Any one cell that is low or below the plates can mean a cell may be toast and would req battery replacment if it cannot be recovered.

Check battery top for cleanliness and security of terminals. There should be no copper oxide buildup on the terminals. Do a simple battery voltage drop to check to see if there is some voltage drop between the battery terminal and the collar. Check for corrosion of the battery cable. Run your fingers up and down the ground and positive cables for swealing. Swealing means that moisture has migrated into the cable and the cable is seriosly corroded and causing a big voltage drop. While is rare it is somthing to inspect. If you can borrow a battery load checker use it to test the draw down test. Battery under a load test for 10 seconds should not dip bellow 10 volts. If it has then its possibly time for a new battery.

Check all grounds for security. A bad ground can cause a BIG voltage drop and would mimic a slow turning starter with bad berrings . It can also affect the charging circuit.

Check the output of the alternator.
Check the output with a voltmeter across the positive and negative terminals of the battery. The voltage should be charging at a full load no less then 13.5-14.5 volts. If it is less then 13 volts suspect a blow diod in the alternator, brushes or bad regulator . Turn on all electrical assesories such as Air Cconditioning and Bright lights defrost window elements ect. This will not put the entire load on the alternator but is a good stating point. Check the voltage at the battery and at the alternator. The charging voltage should not drop when placing a load on the alternator.

If you have any more questions please let us know.