Alternators: A technical question...

[Rochester TVR]

Background: Week old Clio RS200 broke down... reason; main supply fuse from battery blew. (not sure on the Amperage size but its a biggie, bolted in even).

Anyway... Renault dont have a reason for why it blew. They suggested it could be if the car was started in gear. It wasn't.

So Im thinking it could be a problem with the alternator not regulating the voltage being sent back to the battery while driving...

Renault have done their checks and found no problems, but fuses (esp. big ones like these) dont just blow for no reason... so this weekend I am going to get a volt meter and do a few checks of my own.

Questions I need help with:

1. The voltage the alternator produces increases as the engine rpm increases, does its behaviour change if its driven or in neutral?

2. If the alternator is heathly what voltage range should it be operating within? What voltage would alarm bells start ringing for you?

Any other tips would be great, thanks.

[Sk93]

Rochester TVR said:

Background: Week old Clio RS200 broke down... reason; main supply fuse from battery blew. (not sure on the Amperage size but its a biggie, bolted in even).

Anyway... Renault dont have a reason for why it blew. They suggested it could be if the car was started in gear. It wasn't.

So Im thinking it could be a problem with the alternator not regulating the voltage being sent back to the battery while driving...

Renault have done their checks and found no problems, but fuses (esp. big ones like these) dont just blow for no reason... so this weekend I am going to get a volt meter and do a few checks of my own.

Questions I need help with:

1. The voltage the alternator produces increases as the engine rpm increases, does its behaviour change if its driven or in neutral?

2. If the alternator is heathly what voltage range should it be operating within? What voltage would alarm bells start ringing for you?

Any other tips would be great, thanks.

1: Nope. I believe the alternator varies the current based on the voltage supplied from the voltage regulator. It shouldn't alter (much) with revs once you've got above a fast idle.

2: 13.5 to 14.8v is normal



at least.. that's my understanding

Edited by Sk93 on Wednesday 11th August 15:02

[Rochester TVR]

Sk93 said:

1: Nope

2: 13.5 to 14.4v is normal

Cheers.

The Clio has a 12v battery, is it usual for the alternator to produce more than the battery is made for?

What amount of voltage would be seen as a cause for the fuse blowing?
(sorry if thats impossible to answer given I dont know the fuse size.)

[tvrgit]

Sk93 said:

1: Nope

2: 13.5 to 14.4v is normal

I'd agree with both of those answers!

The alternator should show much the same voltage throughout its rev range - it might drop a little at idle, but that's it.

Remember that it doesn't "put out" volts - its output is measured in amps, so unless you have a high range ammeter and some good cable (or one that can read the current through a clamp) it's very difficult to measure.

[ewenm]

Rochester TVR said:

Sk93 said:

1: Nope

2: 13.5 to 14.4v is normal

Cheers.

The Clio has a 12v battery, is it usual for the alternator to produce more than the battery is made for?

Yes.

Rochester TVR said:

What amount of voltage would be seen as a cause for the fuse blowing?
(sorry if thats impossible to answer given I dont know the fuse size.)

As others have said it's the current (amps) that blows fuses, so something is drawing too much current and popping the fuse.

[Sk93]

Rochester TVR said:

Sk93 said:

1: Nope

2: 13.5 to 14.4v is normal

Cheers.

The Clio has a 12v battery, is it usual for the alternator to produce more than the battery is made for?

What amount of voltage would be seen as a cause for the fuse blowing?
(sorry if thats impossible to answer given I dont know the fuse size.)

To be able to charge the battery, the alternator must supply more voltage than the battery, so this is normal.

If you're seeing above 14.8v, then it could be the regulator has gone, which is likely to be blowing some fuses (I believe - I'm not a master at auto-electrics!)

[Rochester TVR]

tvrgit said:

Remember that it doesn't "put out" volts - its output is measured in amps, so unless you have a high range ammeter and some good cable (or one that can read the current through a clamp) it's very difficult to measure.

This is what I'll be using...



oh... and here is the blown fuse in question. Fixed now.

[ExPat2B]

Have you considered that the fuse itself might have been faulty ?

And your multimeter is going to be totally useless. Too high a voltage does not blow a fuse. To many amps blow fuses. Most multimeters will only register a TINY amount of amps safely before getting fried.

[Sk93]

ExPat2B said:

And your multimeter is going to be totally useless.

But not for checking if the alternator / voltage regulator is faulty,
as voltage is precisely what you should be reading.

[Rochester TVR]

ExPat2B said:

Have you considered that the fuse itself might have been faulty ?

And your multimeter is going to be totally useless. Too high a voltage does not blow a fuse. To many amps blow fuses. Most multimeters will only register a TINY amount of amps safely before getting fried.

Apparently the fuse wasn't faulty... so Renault say anyway. Hence why Im wondering what actually caused it to blow.

Ok, so what equipment would I need to measure this amount of Amps ideally?

(A reletive owns an electrical contracting company so should be able to get hold of whatever I need).

Edited by Rochester TVR on Wednesday 11th August 15:18

[ewenm]

Rochester TVR said:

ExPat2B said:

Have you considered that the fuse itself might have been faulty ?

And your multimeter is going to be totally useless. Too high a voltage does not blow a fuse. To many amps blow fuses. Most multimeters will only register a TINY amount of amps safely before getting fried.

Apparently the fuse wasn't faulty... so Renault say anyway. Hence why Im wondering what actually caused it to blow.

Ok, so what equipment would I need to measure this amount of Amps ideally?

(A reletive owns an electrical contracting company so should be able to get hold of whatever I need).

Edited by Rochester TVR on Wednesday 11th August 15:18

An inline ammeter I'd have said. However, you already have a minimum level that you know is being drawn (assuming the fuse is good) as you know the rating of the fuse. Removing the fuse and replacing it with an ammeter to measure the current will give you a better number but may harm whatever the fuse was protecting. Leaving the fuse in will just blow that at the rated level again (assuming it's a recurring problem).

Not an easy one to investigate.

[ExPat2B]

Rochester TVR said:

ExPat2B said:

Have you considered that the fuse itself might have been faulty ?

And your multimeter is going to be totally useless. Too high a voltage does not blow a fuse. To many amps blow fuses. Most multimeters will only register a TINY amount of amps safely before getting fried.

Apparently the fuse wasn't faulty... so Renault say anyway. Hence why Im wondering what actually caused it to blow.

Ok, so what equipment would I need to measure this amount of Amps ideally?

(A reletive owns an electrical contracting company so should be able to get hold of whatever I need).

Edited by Rochester TVR on Wednesday 11th August 15:18

Centech user manual states :

Do not test current on circuits higher than 10 amps.

Charge current of cars is between 5 and 40 amps.

You need an ammeter with a minum of 50amps capability, 100 or more would be better

Now, personally, the route I would take is to find your local auto electrician. There will be a guy in your area that all the local garages use for auto electrical work. The ones I know have ahuge amount of experience and can usually spot a problem in under 15 mins. They will have all the kit to hand and the knowledge to correctly interpret the readings.

I would not be poking about under the bonnet of my brand new car with a multimeter.

[freecar]

fking auto electrics, I hate them and many lies/falsehoods are told about them.

That big fuse will only blow again if there is a current draw present. All you know by the fuse blowing once is that there was ONCE this current draw .

Problem is, if the problem is still there the fuse will blow the instant power runs to it. If not you wont have any current draw to measure.

Definitive answer.

Replace fuse, start car, drive car.

If fuse blows agan, then worry about it. If not, ignore.

For full piece of mind (what an album!) as you said the car is a week old (I assume from new, not from previous owner) phone renault and ask them if it is likely for the car to catch fire if you replace the fuse. If they have any concerns then they'll take the car in to look. If they say you'll be fine, when you catch fire they'll pay!

[ewenm]

As it is a brand new car, and the fuse has done its job (blowing before any damage) then I'd be tempted just to leave well alone until it happens again (if it does) and then make it clear with the dealership that you want it fixed (problem not symptom) or a replacement car.

One fuse blowing maybe a faulty fuse, two blowing would indicate a real problem.

[bikemonster]

The first thing to do should be to look at what is "downstream" of the fuse.

Something drew more current (amps) than the fuse was rated for and the fuse did its job by blowing before something worse happened.

I do not believe that the alternator is the culprit here.

[Rochester TVR]

ExPat2B said:

Centech user manual states :

Do not test current on circuits higher than 10 amps.

Charge current of cars is between 5 and 40 amps.

You need an ammeter with a minum of 50amps capability, 100 or more would be better

Now, personally, the route I would take is to find your local auto electrician. There will be a guy in your area that all the local garages use for auto electrical work. The ones I know have ahuge amount of experience and can usually spot a problem in under 15 mins. They will have all the kit to hand and the knowledge to correctly interpret the readings.

I would not be poking about under the bonnet of my brand new car with a multimeter.

If theres a possibility I could damage anything then Ill take your advised route of seeing an auto electrician...

I have a relatively good knowledge of engines, but not the electrical side... hence some of my questions may sounds stupid to those with the experience.

Doesn't sound like its an easy thing to test.

Edited: I got the car back yesterday and have driven it about 30miles since with no problems... so maybe the leave alone until / if it comes back might be the best approach.

Car is brand new. 320 miles on the clock.

Edited by Rochester TVR on Wednesday 11th August 15:38

[8400rpm]

For a start, what circuit is that fuse on?

I accidentally blew an ignition circuit fuse on my old CRX, 50A, screw in job.

Being stupid when I replaced the battery, I put the negative terminal on first, then the positive. Got a spark and it popped the fuse. Had to wait 2 days for Honda to get me a new one, it is so bloody rare they pop, they never have them.

The circuit that the fuse is on will give you a clue about what to look at.

[Rochester TVR]

8400rpm said:

For a start, what circuit is that fuse on?

I accidentally blew an ignition circuit fuse on my old CRX, 50A, screw in job.

Being stupid when I replaced the battery, I put the negative terminal on first, then the positive. Got a spark and it popped the fuse. Had to wait 2 days for Honda to get me a new one, it is so bloody rare they pop, they never have them.

The circuit that the fuse is on will give you a clue about what to look at.

Pass. Not sure...

Ive got a few more photos Ill put up that might help...

[Rochester TVR]

Not sure if these will give a clearer picture of the fuses job...

Edited by Rochester TVR on Wednesday 11th August 15:48

[ewenm]

I think you really have two options here:
1. Leave it and wait for it to happen again if it ever does.
2. Take it to an auto-electrician to investigate.

As the car is brand new I'd choose option 1 and raise hell with Renault if it happens again. Like most of us, it seems you don't have the electrical knowledge to investigate it yourself (I certainly would be able to either) so it's not worth messing around with it. Plus the auto-electrician will charge for the investigation and I'd rather Renault paid for that.