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  #1  
Old 10-31-2007, 07:14 AM
Svxswede Svxswede is offline
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Strange electrical short due to alternator overvoltage, HELP!

Hello everyone. If anyone has a clue what I should do, please help me.

What happened was when I drove home the other day the dashlights were getting quite bright, and the front wipers were going back and forth almost twice normal speed. Needless to say as it was friday, I thought iŽll deal with it in the weekend....

As you know these cars have mindreading capabilities, thus it pondered for a few miles, felt neglected and flashed (exploded) a couple dashlights, welded the fanrelay and the light relay closed, and blew a bunch of fuses, both boxes, including the fusible link.

I draw the conclusion that the regulator finally died or shorted out, grounding the anchor and pushed out a lot of volts.

I unplugged the alternator and replaced the link and the mpfi fuse so I could get home. Barely made it.

Now I have been tearing into the system. I use the wiring diagram from the svx cd, some differences because I have a Euro SVX.

So, my findings are: shortcircuit at

front wipermotor; toggling breakers,
winter/summer switch (wiper)
(fuse 6)

meters; (fuse 15) and powersteer/cruise (fuse 18) I have unplugged time control unit, a/c relays, cruise unit to no avail.

I have a dvm and decent electronic skills, but I feel more and more desperate.
Not to mention how hard it is to find all components.

So,

If anyone had a similar mishap, or has any guidance or tips please feel free to share.

I also need the Euro wiring diagram for the intrumentcluster as it is not the same as US/JDM.

Alexander
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  #2  
Old 11-01-2007, 02:30 AM
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Greetings Alexander,


Sorry for the delay in reply, as I thought someone in the UK, with similar car would immediately come to your assistance.

I have been posting here for over four years and have never seen anything reported in any way along the lines of your problem.

It would appear that both engine and transmission computers survived, which proves that they are well protected by having excellent voltage regulators built in. What I find strange is that the main fuse link opened, as this would require current in access of that which could be produced by the alternator. Therefore there must have been a short circuit path, battery eo ground, as part of a fault sequence. Also strange is that the contacts on two relays carried massive current, I gather that both must have been closed at the time and you do not mention the headlight bulbs as being burnt out.

You have my sympathy, as many components are difficult to access. I will post a reference in the European forums as an extra way of drawing attention for you, from those more likely to have the data you require.

Please keep us posted on progress and the final outcome.
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Old 11-01-2007, 03:14 AM
Svxswede Svxswede is offline
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Progress..

Hello Trevor,

Today, fiddling with the wiper assembly (motor assy) i found it was ok. Next was to check the wiper control unit. In the box there are 3 relays on the pcb. One was welded short, giving power to both switchpoints (its a two way toggle relay). Do we have a winner?

Replaced it with another similar, and, yes the wiper works and no short at fuse no 6.

My next move will be to unplug all units associated with the meter fuse no 15.

I have already unplugged the instrument panel meter cord, timer unit, cruise unit and powersteering unit, still a short. Now I will go out to unplug a/t unit and abs unit to see if the short still persists.

It seems that the overvoltage contition cooked my relays for lunch.

Its truly odd no one has had a similar experience...For info, the car had zero electrical issues before this happened.

So, any input is truly valuable. The only problem with my present diagrams are that the instrument diag. differs (us/euro) and thats a big problem.

Regards,

Alex
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Old 11-01-2007, 03:41 AM
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Good one Alex.

All you can do is to follow your nose. It is apparent that you know what you are about and are on the right track.
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  #5  
Old 11-01-2007, 06:03 AM
Svxswede Svxswede is offline
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Update

So I unplugged the abs unit under the passenger seat, and now fuse 18 doesnt blow. Might be a problem with the abs unit.

Does anyone know how to take the unit out? I unfolded the carpet from the door but its not enough...Slide the seat out forward? How?

Still got a short at fuse 15. Will check power window relay at once...

Standing request for euro wiring diagram

Edit: What is a normal powerdrain at "on" but not running???

I get 15 amps, wich to me seems very high.

alex
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Last edited by Svxswede; 11-01-2007 at 08:57 AM. Reason: new question
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  #6  
Old 11-01-2007, 11:02 AM
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What a strange problem

Since the voltage level is determined totally by the battery and the alternator, and it is not possible for the battery to produce more volts that we need because of the material it is made of, the alternator had to be the culprit.
That is because the voltage level is regulated and produced within the alternator unit itself. Of course, the alternator has to be replaced and the excess voltage will not exist. All that is left to do in "clean up the mess"
So sorry...
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Old 11-01-2007, 03:57 PM
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Quote:
Originally Posted by kwren View Post
Since the voltage level is determined totally by the battery and the alternator, and it is not possible for the battery to produce more volts that we need because of the material it is made of, the alternator had to be the culprit.
That is because the voltage level is regulated and produced within the alternator unit itself. Of course, the alternator has to be replaced and the excess voltage will not exist. All that is left to do in "clean up the mess"
So sorry...
Obvious, but how did the alternator generate sufficient current to open the fuseable link?
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Old 11-01-2007, 04:21 PM
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Quote:
Originally Posted by Svxswede View Post
So I unplugged the abs unit under the passenger seat, and now fuse 18 doesnt blow. Might be a problem with the abs unit.

Does anyone know how to take the unit out? I unfolded the carpet from the door but its not enough...Slide the seat out forward? How?

Still got a short at fuse 15. Will check power window relay at once...

Standing request for euro wiring diagram

Edit: What is a normal powerdrain at "on" but not running???

I get 15 amps, wich to me seems very high.

alex
Alex,

I just checked my car with only the ignition turned on and to my surprise, measured 14 amps. Therefore allowing for tolerance your car is very probably OK.

Interesting that it would appear that the ABS unit does not have voltage regulation, or most certainly insufficient to provide protection.
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Old 11-01-2007, 11:43 PM
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I would say...

Quote:
Originally Posted by Trevor View Post
Obvious, but how did the alternator generate sufficient current to open the fuseable link?
The regulator components went whacko
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  #10  
Old 11-02-2007, 01:28 AM
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Quote:
Originally Posted by kwren View Post
The regulator components went whacko

It is more than likely that the high voltage caused a subsequent short to ground within another separate component, such that battery current became involved in order to blow the link.
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Old 11-02-2007, 03:37 PM
Svxswede Svxswede is offline
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Volt-Ohm-Amperes

My theory is that the regulator crapped out, boosting uncontrolled voltage to the system. I have read somewhere that an unregulated alternator can deliver up to 70 volts. If you double the voltage in a circuit (resistive) the power consumption will double. A relay handling 20 amps on a daily basis will suddenly be loaded with 40 amps at 24 volts.

This would lead to that high current contacts i.e relays can melt.

I have a thread at the european forum also, as my car is euro spec. If you are interested to help me, please have a look at: http://www.subaru-svx.net/forum/showthread.php?t=41640

Alex
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Old 11-02-2007, 06:27 PM
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Alex,

I have US and right hand drive manuals and these show differences regarding the air conditioning and fuse No. 15, so that I can not provide any details which could be of help. You report a time delay before the fuse blows and this would indicate that a relay may be closing against a short circuit.

Six relays mounted in two assemblies are involved in the air conditioning system. It looks like you will have to get your hands on them and I hope someone who has been there, will provide further you with assistance regarding access.

If I were to start commenting as I would wish, regarding the stupidity in respect of automotive electrical systems, the moderators will intervene.

You have my sympathy, Trevor.
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Old 11-02-2007, 11:12 PM
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Sorry Trevor...

Quote:
Originally Posted by Trevor View Post
It is more than likely that the high voltage caused a subsequent short to ground within another separate component, such that battery current became involved in order to blow the link.
The super high voltage from the defective regulator in the alternator provided the voltage through the fuse and blew the fuse. The battery, of course, cannot produce high voltage because of the composition of the two different materials in the cells. The number of cells determine the voltage that a charged battery can provide. In this case, the battery was just along for the ride, as it always is whenever the motor is running and a working alternator is turning.
Hope this helps
Take care,
Keith
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  #14  
Old 11-03-2007, 02:02 AM
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Quote:
Originally Posted by kwren View Post
The super high voltage from the defective regulator in the alternator provided the voltage through the fuse and blew the fuse. The battery, of course, cannot produce high voltage because of the composition of the two different materials in the cells. The number of cells determine the voltage that a charged battery can provide. In this case, the battery was just along for the ride, as it always is whenever the motor is running and a working alternator is turning.
Hope this helps
Take care,
Keith
Keith,

Excessive current is required to blow a fuse, not an excessive voltage. The fuse link or any fuse can pass megavolts without opening. The only limitation in respect of performance being the surrounding insulation.

The fuse link has battery voltage positive potential at each end of the element, with the battery between the alternator and ground. Please explain how the alternator can induce current across the fuse element such that it will blow.

Hope this helps.

Trevor.
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  #15  
Old 11-03-2007, 03:38 AM
Svxswede Svxswede is offline
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Let me try...

Say that you have a single lightbulb connected to the battery. Over the battery poles is the alternator. A 100 W bulb will draw 100/12 =8 amps, and the resistance of the bulb is 12/8 =1,5 ohms.

By applying Ohms law, increasing the voltage also increases the amperage.

There is of course a limit to the powersource ability to put out amperage, a car alternator can put out 100 amps up to quite high voltage levels.

Lets say the alt produced 20 volts instead, the battery will act as a buffer for a while but at a level overvoltage reaches the system and if the resistance of a circuit is 10 ohms and normally consuming 1,2 amps it will now draw almost the double.

Any relay will have to handle twice amps and also the fusible link which handels many powerconsumers will be overloaded.

Still havent found the fault at fuse 15.....

Seems a lot of circuits are involved there.

Alex
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