Urgent Advice Needed Electrical Problem Help Please

[MikeWhitworth]

Hi Guys

I urgently need advice before doing battle with my alternator supplier .

A couple of weeks ago I fitted a refurbished alternator all seemed well at first but yesterday I kept getting warning lights comming on on the dash ie hand brake , ABs and sometimes the air bag light .

These lights only stayed on for a very brief time . Today I connected a digital Volt meter across the Battery and went for a short drive the Voltage in the main hovered around 13.7- 14ish volts But occasionaly flicked upto 18 volts !!! and then at one point the voltage started dropping down to below 10 volts . the warning lights flicked on and off but I could not see any connection between the volts and the intermittent warning lights .

I THINK !! the voltage regulator which I believe is part of the alternator is faulty . But as it is such a pain to get the alternator out I am reluctant to do that if I am missing something

HELP.

regards

Mike

[shcm]

18V is very often indicative of an alternator regulator failure. In fact it's very often around the highest continuous voltage that an ECU for a 12V vehicle is specificed to withstand or operate at without degradation - for that very reason of alternator reg failure.

However, before you go pointing the finger at the alternator, just make sure all the high current cables (+ and -) to and from the alternator/battery and chassis are good and tight, with no intermittent breaks. It's likely they are OK, as presumably you have no trouble starting the vehicle? However a loose cable, can produce farily nasty voltage transients - due to the alternator loosing it's load (the battery) now and again (because of the loose cable), and the alternator reg not being able to regulate instantly (It takes some fractions of a second to catch up).

This will produce very high voltage transients (spikes). Can be 120V or more, decaying over a couple tenths of a second. Your voltmeter wouldn't show this, but will average out the spike to show something less (like 18V for instance!). To see it, you'd need an oscilloscope.

However, many modern alternators clamp this voltage spike (called a load dump) to around 40V.

[Big Kev]

18V is very often indicative of an alternator regulator failure. In fact it's very often around the highest continuous voltage that an ECU for a 12V vehicle is specificed to withstand or operate at without degradation - for that very reason of alternator reg failure.

However, before you go pointing the finger at the alternator, just make sure all the high current cables (+ and -) to and from the alternator/battery and chassis are good and tight, with no intermittent breaks. It's likely they are OK, as presumably you have no trouble starting the vehicle? However a loose cable, can produce farily nasty voltage transients - due to the alternator loosing it's load (the battery) and the alternator reg not being able to regulate instantly (It takes some fractions of a second to catch up).

This will produce very high voltage transients (spikes). Can be 120V or more, for a couple tenths of a second. Your voltmeter wouldn't show this, but will average out the spike to show something less (like 18V for instance!). To see it, you'd need an oscilloscope.

However, many modern alternators clamp this voltage spike (called a load dump) to around 40V.

Good explie there, Brain.....and welcome to club, Mike.

Big Kev

[crofter]

Hi,Mike,I would suggest that a little more info on your model would help anyone who can help to do so as I believe there have been some advancements between models on that score

Del

[crofter]

Too little,too late.

Apologies all round to shcm.

As usual an informative reply

Del

[shcm]

True Del, the post 2006 models (4.3) have a fairly intelligent alternator field control, where you might for periods see a lower than expected output voltage with the engine running (e.g. around 12V rather than say 14.2V), but it should never be regulating to 18V!

EDIT: Sorry Del, replied to your reply before I saw your other reply - If you see what I mean

[MikeWhitworth]

Hi Guys

Sorry for the lack of details

It is a 2002 Rav4 d4d 2000cc I have checked all the connections to the alternator and to the Battery all seem Ok

The incidense of 18 volts while driving is only now and then . All seems Ok on start up and untill I have been driving for a few miles

Then the warning lights start to come on occasionaly . The Digital voltmeter readings seem mainly to hover around 13.7 v to 14.2v and do not seem stable I appreciate we are only talking about half a Volt but I would have expected at a steady speed the voltage to be reasonably stable ???. This problem has only arison since the new alternator the old one having giving up the ghost completly

I have spoken to the supplier of the alternator on the phone who said Oh just pop the alternator off and bring it in and I will test it !!!!!!!!!!!!!!! anybody who has taken an alternator off a Rav 4 will understand why I am reluctant to do this .

Mike

[Tech01]

Hi Mike,

If I remember correctly, there are 3 small cables to the alternator (all in one connector). One cable is +12v permanent live (always connected to battery), the second is +12v provided by IGN switch, and the third is a Battery voltage sensing connection.

One of these cables is FUSED (usually 5A, fuse labelled ALT-S, in the engine compartment fusebox).

There are then two heavy duty connections for the alternator's output: one goes back to the Battery +, and the other is ground (probably via the alternator and engine frame).

You should check that ALL of these connections are good ones, using a voltmeter to detect any voltage drops or instability. If the supply voltages to the alternator are unstable (perm +12v, IGN +12v, or Battery sensing connection) then the output of the alternator will wander or flutter about, producing highs and lows as it does.

Any good auto-electrician/supplier will be able to bench-test the alternator itself off the car, although you will have the hassle of taking it off.

Hope helpful,

Chris

[SueYorkshire]

Does anyone out there know of a good auto electrician? I have a Rav4 2012, SR, Diesel Auto, that has a bit of damage to the wiring loom under the dash, its just one bundle of about 23 wires that need repair, its the bundle that is near to the fuse box. I am in South Yorkshire and would appreciate any help in locating someone who could repair this for me. Please get in touch. Thanks