Bad alternator by the numbers?

[Surfslinger]

Hi,

Vehicle is a Japanese made 1994 Camry, 5SFE, original alternator, 169k miles. Belt is very snug, w/o any slip on alternator pulley and wire connections are tight. Battery is a less than year old Johnson Controls battery above OEM CCA that has proper water level, terminals are clean and tight. Voltage not running is 12.54v.

Engine warm running @ normal idle, brake pedal not applied, no load shows 14.44v.

- Turn headlights on (low beam only) and drops to 13.75v and will stabilize to 14.29v

- leave low beams on, apply and hold brake peddle and it drops to 13.46v, stabilizes to and holds 13.65v

- Switch on high beams while holding brake pedal down, voltage drops to 12.5v, and will drop a bit more as brake pedal is held down.

Headlights on, and or blower motor running will flare/go up a good deal going from idle to acceleration or stepping on brakes. High beam dash light is dim, then flares upon acceleration too. No alternator MIL, and if you start engine with the oval three pin connector not attached the alt MIL does not light.

Guessing the alternator is the problem especially with the very low numbers with brake applied at idle and H beams on? Maybe a bad ground/bad wire somewhere? There is no idle-up when lights are switched on, or in the held brake peddle situation.

Your diagnostic help is appreciated! Thank you.

[93celicaconv]

Sounds to me that everything is working normally.

An alternator, running at low engine idle speed, is not made to deliver that kind of current output involving high beams on (and all the other lights associated with headlights being on) plus brake lights plus HVAC blower motor on high. Put your rear window defroster on too, and watch the lights dim even more. The faster an alternator is turning, the more curernt it can put out (if more current is needed).

You should take your car to an auto parts location (AutoZone, Advance Auto Parts, to name a couple) and have them do a free electrical system diagnostics on your car, while you are there, to see if there is any problem with the alternator, battery, starter, etc. Then you would know for sure if you have a problem that needs repair.

[Surfslinger]

Thanks 93. I agree, the numbers seem reasonable considering the load/situation; just seems there is a disproportionate amount of dash bulb, headlight flare/fan motor speed raising/lowering going on despite the numbers, not to mention the prolonged 12.5v under load without idle-up compensation. I guess this ECU does not trigger such idle-up with such low sustained voltage, as would happen with the A/C flicked on, or PS activated?

Makes me think there may be some pesky corrosion/bad ground or connection somewhere?

Thanks again.

[93celicaconv]

No, not on a 94 Camry 5S-FE. Idle-up for A/C & PS aren't handled through the ECU - each has a VSV that triggers when these systems are turned on, allowing air under vacuum to be pulled through the VSV into the intake manifold to increase engine speed. No such system involving high current devices being used when the engine is at low idle. So your lights will dim slightly when engine speed drops, and will brighten up when engine speed in increased.

Seeems normal in doing this writing, but I'm not seeing what you are either. So I would still consider getting an auto parts store put their electrical system tested on your vehicle and do a quick diagnostic of your electrical system, just to be safe.

[zzyzzx]

Seems OK to be, I'd be more concerned with the alternator brushes wearing out at an inconvenient time, since you are overdue for them if they are still the originals.

You could rerun your voltage tests at 2000PRM and you will see more stable voltages under those loads.

[heartdisease]

Seems fairly reasonable to me. Maybe take the connections off at the terminals and clean re torque them, never a bad thing to do.

[carsrus]

Clean your grounds, put those readings are within spec. Its normal to see a slight dim when opening/closing windows etc. Output of alternator goes up with RPM.

[godot]

Put a DVM between the alternator case and the minus battery terminal under load. There should be little or no voltage measured. You are measuring the drop between alternator and battery ground. Eberybody checks the PLUS connections, ya gotta thinka bout the other side of the circuit as well . A new regulator/brush assembly is not expensive, bearings and windings seldom fail. There are some companies making very good high output rebuilds now, with core credit you can get away for less than $150 the last time I checked. Try Magnamaniacs (Google it) IF you need one. They send you an rebuilt and a box to ship the old one back in. They gave me full core credit for a Denso with over 200 K on it. The load test, BTW, is a good idea, if honestly done.

[RonR]

Normal battery voltage at idle should be 14vDC, maybe 13.8vDC, below that could mean one of the 3 fields in the alternator is not working, this is not uncommon.
And is fine for most situations to keep the battery charged and system working.
But would be noticed as a significant dimming of the lights as voltage dropped to 13.2-13.6vDC at idle, they were at 14vDC at higher RPM.
Lights will always dim and come back when you turn on a high current accessory that is just the voltage regulator lag time, but if they dim and don't come back up then you could have a field out in the alternator.

[CrystalMethod]

Originally Posted by carsrus

Clean your grounds, put those readings are within spec. Its normal to see a slight dim when opening/closing windows etc. Output of alternator goes up with RPM.

It's actually not supposed to output more when the car is revved (temporary, to make up the sudden draw on the system {dip, rev, then return to normal}, but not constant). The I.C. circuit (inductive current circuit) is supposed to handle that. It is supposed to balance power draw from the alternator when the car is running and adjust the power to the alternator's field accordingly.

When there is an increase in load on the system, the IC circuit "should" increase the charge on the field to make up for difference.

[93celicaconv]

Originally Posted by CrystalMethod

It's actually not supposed to output more when the car is revved (temporary, to make up the sudden draw on the system {dip, rev, then return to normal}, but not constant). The I.C. circuit (inductive current circuit) is supposed to handle that. It is supposed to balance power draw from the alternator when the car is running and adjust the power to the alternator's field accordingly.

When there is an increase in load on the system, the IC circuit "should" increase the charge on the field to make up for difference.

You are technically correct. But, when current demand reduces the system voltage level and the alternator responds by increasing current output, it can only output as much current as it is capable at the speed it is being driven. If at idle, it is very likely system demand exceeds the alternator output capability, so system voltage drops a bit (which is seen as lighting dimming slightly). Increase engine speed, and the current output capacity of the alternator increases significantly, to the point where system voltage is at the level set by the voltage regulator, so the lighting brightens slightly.

Take a look at an alternator's operating chart (should be furnished with every new/rebuilt alternator, test output data), and it shows a curve of output amps vs. alternator speed. You will see current output capacity increases proportionately to alternator rotor speed, until the upper speed range of the alternator at least.