Suggested solution to the big fuse problem
Discussion
The car's not even arrived yet and I'm already making a list of jobs that I need to do. Today, I've been thinking about a more permenant solution to the "big fuse" problem.
As I understand it, the problem is that the 100 amp fuse is marginal, and a number of the circuits it feeds are sensitive to minor variations in voltage. When slight corrosion of the terminals occurs, then the small voltage drop causes all sorts of things to start playing up.
So, my suggestion is this:
I've got all sorts of old audio components lying around, so could easily replace the bolts and nuts on the fuse holder for gold ones. OK, the fuse can still corrode, but at least when you chuck a new ones in there you start agin from scratch, rather that with a fresh fuse, but corroded terminals.
My concern is that using two different metals could create an electrolytic effect, accelerating the deterioration of the fuse material itself.
Thoughts?
(is it probably better to just smother the thing in conductive grease?)
As I understand it, the problem is that the 100 amp fuse is marginal, and a number of the circuits it feeds are sensitive to minor variations in voltage. When slight corrosion of the terminals occurs, then the small voltage drop causes all sorts of things to start playing up.
So, my suggestion is this:
I've got all sorts of old audio components lying around, so could easily replace the bolts and nuts on the fuse holder for gold ones. OK, the fuse can still corrode, but at least when you chuck a new ones in there you start agin from scratch, rather that with a fresh fuse, but corroded terminals.
My concern is that using two different metals could create an electrolytic effect, accelerating the deterioration of the fuse material itself.
Thoughts?
(is it probably better to just smother the thing in conductive grease?)
like mine? piccie on this thread http://www.pistonheads.com/gassing/topic.asp?h=0&f=6&t=426311
It is marginal as the current can peak way beyond 100A from the alternator, alhough the main reason is due to the position - fatigue sets in due to heat and vibrations. You can get 150A fuses and some TVR dealers have started to recommend fitting them instead of the 100A ones. It's not a long or difficult job to do - even by the road side. Just get yourself some spares and carry some tools and gloves.
morebeanz said:
But if it's failing due to heat and vibrations, how is a higher rated fuse going to help? 
True. And personally (as a Chartered Electrical Engineer) I wouldn't recommend increasing the size of, or bypassing fuses. It might be ok until you have an electrical problem and then it's flames and bye bye car. Not only that, but if the car did catch fire due to an electrical problem and the correct fuse wasn't fitted, in theory it would invalidate your insurance.morebeanz said:
But if it's failing due to heat and vibrations, how is a higher rated fuse going to help?
High peak currents can cause fuse fatigue over time too. You only need hair line cracks and the fuse is degraded especially with regards to providing maximum current.RayVonn said:
True. And personally (as a Chartered Electrical Engineer) I wouldn't recommend increasing the size of, or bypassing fuses. It might be ok until you have an electrical problem and then it's flames and bye bye car. Not only that, but if the car did catch fire due to an electrical problem and the correct fuse wasn't fitted, in theory it would invalidate your insurance.
A friend of mine - who has a T350 - was talking to a dealer when his went. They said that the peak current can be more than 100A - especially when the car is hot and stuck in traffic with air con on, fans switching in and out, etc. As a result, they've been fitting higher rated fuses.Most cars don't have a fuse between the Alternator and battery as too much current will cause the Alternator rectifier to burn out. Some Cerb owners have bypassed the fuse for these reasons.
Personally, TVR fitted a 100A fuse so I leave mine connected and at 100A. It's just one of those jobs that needs doing on occassions. I'm going to always get mine replaced during a 12k mile service - just to be safe.
thegreengoblet said:
A friend of mine - who has a T350 - was talking to a dealer when his went. They said that the peak current can be more than 100A - especially when the car is hot and stuck in traffic with air con on, fans switching in and out, etc. As a result, they've been fitting higher rated fuses.
This doesn't quite add up. The add-con compressor is mechanically driven via a belt by the engine - therefore it presents no electrical load as such. If you're at idle then the alternator may not be spinning fast enough to produce enough output to charge the battery, running the aircon reduces the idle speed, possibly compounding things, but I can't see where the 100A fuse is involved. It's there to prevent an excessive current from reaching the battery from the alternator. Things like the fans are separately fused via the fuseboard in the boot unless I'm much mistaken. A wiring diagram would clear this up though. Steve.
Steve_T said:
thegreengoblet said:
A friend of mine - who has a T350 - was talking to a dealer when his went. They said that the peak current can be more than 100A - especially when the car is hot and stuck in traffic with air con on, fans switching in and out, etc. As a result, they've been fitting higher rated fuses.
This doesn't quite add up. The add-con compressor is mechanically driven via a belt by the engine - therefore it presents no electrical load as such. If you're at idle then the alternator may not be spinning fast enough to produce enough output to charge the battery, running the aircon reduces the idle speed, possibly compounding things, but I can't see where the 100A fuse is involved. It's there to prevent an excessive current from reaching the battery from the alternator. Things like the fans are separately fused via the fuseboard in the boot unless I'm much mistaken. A wiring diagram would clear this up though. Steve.
Remember, car electrics are crude. It ain't no IPOD! It's like a house light bulb. They normally blow not because the filament has broken, but because the filament has degraded somewhat over time and as you switch on the light switch, you're unlucky because you catch the AC cycle at it's peak (it's a 50Hz sine wave) (or surges on the Mains) causing the filament to blow .
So it's surges that cause problems rather than max ratings which are reached relatively slowly. So the theory with the fuse is to protect against the surge not the continuous current. I don't know enough about the rectifier used in the Aternator of the Cerb, so I will stick with 100A.
The alternator can't 'push' current, it can only provide current. The fuse is there to protect components (wires included) from drawing too much current. Drawing huge current generates massive heat, which is why wires melt when there is a short; V=I/R; a short, resistance is near zero and V=12 which makes I close to infinity.
The reason for the 100 amp fuse failing is heat... the more heat put into a conductor, the more resistance it builds, the more resistance that gets built and if it draws the same current, the more the crystalline structure will break down and generate more heat and further break down the conductor. The more flaws in the conductor the more resistance.
The same goes for the battery cables. Granted copper is a much better conductor than whatever that fuse is, but try this... buy a new copper battery cable or jumper cables and for the same length test the resistance of your battery cable (disconnected on both ends) and the new cables. the new ones will have a much lower resistance.
The best solution is to either get a 100 amp fuse made out of really good material or move it to some place out of that heat soak area behind the engine
The reason for the 100 amp fuse failing is heat... the more heat put into a conductor, the more resistance it builds, the more resistance that gets built and if it draws the same current, the more the crystalline structure will break down and generate more heat and further break down the conductor. The more flaws in the conductor the more resistance.
The same goes for the battery cables. Granted copper is a much better conductor than whatever that fuse is, but try this... buy a new copper battery cable or jumper cables and for the same length test the resistance of your battery cable (disconnected on both ends) and the new cables. the new ones will have a much lower resistance.
The best solution is to either get a 100 amp fuse made out of really good material or move it to some place out of that heat soak area behind the engine
Thinking through it a little further would you agree with the following. The battery has a internal resistance (as does the wiring, the fuse and so on) and a voltage. The alternator generates a certain output voltage, the current is simply the difference of the voltages divided by the resistance of the circuit. Since the resistance is low, the current can be quite substantial. If the fans cut in, there's a drain on the battery, altering its voltage (down) therefore the charging current would increase, provided that the power generated by the alternator is at or below its maximum (which is rpm dependent).
methodwares said:
The alternator can't 'push' current, it can only provide current. The fuse is there to protect components (wires included) from drawing too much current. Drawing huge current generates massive heat, which is why wires melt when there is a short; V=I/R; a short, resistance is near zero and V=12 which makes I close to infinity.
However this is ideal. The Alternators rectifier will only operate to a maximum power output (P=IV). For a given Max Power, sinking more than maximum current at 12V can result in voltage dropping (and current increasing) and/or the device blowing. Therefore it is possible to supply more current albeit not at 12V continuously (well nearer 13.5V really). Hence surges, spikes, call them what you will.Steve_T said:
Thinking through it a little further would you agree with the following. The battery has a internal resistance (as does the wiring, the fuse and so on) and a voltage. The alternator generates a certain output voltage, the current is simply the difference of the voltages divided by the resistance of the circuit. Since the resistance is low, the current can be quite substantial. If the fans cut in, there's a drain on the battery, altering its voltage (down) therefore the charging current would increase, provided that the power generated by the alternator is at or below its maximum (which is rpm dependent).
Again this is ideal theory. It depends on how good the rectifier is at regulating the voltage i.e. keeping it constant at all costs. Most cheap regulators will only track around the output voltage across a fairly narrow current range. Again the resistance of the circuit, battery included, will be constantly changing. Heat generated in the engine bay, as well as by the circuits also change the resistance. So it's not quite as simple as black and white and surges can play a part in finally nailing the fuse.methodwares said:
The best solution is to either get a 100 amp fuse made out of really good material or move it to some place out of that heat soak area behind the engine
The latter is what I did- albeit on a Chimaera- a couple of years ago once the third fuse link had cracked over a three year period. The 3rd failure was actually due to the wiring breaking down on the battery side of the link and not the actual fuse (obviously caused by heat though). As I was renewing this wiring, I thought about bringing the fuse position forward away from this heat and it is now cable-tied to one of the diagonal wishbone struts.
Good result in that it's now away from the exhaust and, should it need replacing, I just have to remove the offside front wheel instead of crawling under the car.
Keithyboy said:
350Matt said:
I changed my big fuse for a maxi fuse type of the same rating, its a much better design against fatigue and only a couple of quid, you can buy them from the vehicle wiring products website.
Matt
Link please Matt Matt
Here you go
its the midi one which is a direct replacement
http://www.vehicle-wiring-products.eu/VWP-onlinest...
Matt
its the midi one which is a direct replacement
http://www.vehicle-wiring-products.eu/VWP-onlinest...
Matt
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