| Author | Message | ||
     James Seaman New User Username: jseaman Post Number: 9 Registered: 12-2012 |
I finally diagnosed my problem with not starting, it was fuse B9 non bank 1 which feeds the ECU. It is a 25 amp fuse and the lower leg of the fuse is obviously getting hot (the plastic is turning white through heat). Now, if it was current alone surely the fuse would blow so there is some kind of heating effect, without ripping out fuseboards could anyone suggest any reasons? | ||
| Jeff Young Prolific User Username: jeyjey Post Number: 101 Registered: 10-2010 |
I'm not familiar with Spirits/Spurs, but if the fuseholder is rivetted to the board then a loose rivet will cause resistance and heat. I had this issue with a Lucas relay that would continually melt the plastic off its Lucar connector till I tightened up the internal rivets (and soldered them to the board). | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 899 Registered: 6-2006 |
Hi James, They are prone to this and a slightly higher fuse usually cures it. The continuous load is slightly too high for the fuse so it heats up but not enough to melt. Change it for a 30 amp. Bad connections elsewhere can also cause fuses to run too hot, The connector may already be damaged from overheating so make sure that it is tight in both sides. You may have to swap to a different fuse holder if it is too badly heat damaged. The little things are the most annoying! | ||
| James Seaman Experienced User Username: jseaman Post Number: 12 Registered: 12-2012 |
Many thanks to both, I will switch to a 30A immediately and see what happens | ||
| James Seaman Experienced User Username: jseaman Post Number: 13 Registered: 12-2012 |
Oh and there was a little distortion but the fuse holder is still OK and YES, really annoying problem!! | ||
| James Seaman Experienced User Username: jseaman Post Number: 15 Registered: 12-2012 |
Paul, Thanks again - 30A works a treat, problem solved James | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2727 Registered: 4-2003 |
The melting of this particular fuse is chronic and was the subject of a service bulletin located in the TSD6000-series set of publications (TSD4736). That involved mounting the fuse external to the fuseboard, which helps but does not cure the overheating caused by the extreme harmonics in the load. Even after my Turbo R was so modified under warranty, the fuse overheated and melted (it never blew) several times over the years. A larger fuse will not help this matter. The only permanent cure that I found is to fit a circuit breaker in place of the fuse. The breaker I used is a compact high-speed one, a generic automotive device costing maybe $20, screwed to the front of the fuseboard. The system has never had a problem since. RT. | ||
| James Seaman Experienced User Username: jseaman Post Number: 17 Registered: 12-2012 |
Richard, Thank you for the info - what do you make of this one: http://www.ebay.co.uk/itm/251196193853?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 James | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2728 Registered: 4-2003 |
Hi there, You may try that, but the one I fitted is more like this and is self-resetting (although it has never tripped): http://www.ozautoelectrics.com/20-amp-automatic-reset-metal-circuit-breaker.html which looks like the Supercheap one by the way: http://www.supercheapauto.com.au/online-store/products/SCA-Automotive-Circuit-Breaker-20-Amp-Automatic-Reset.aspx?pid=120461#Description I do prefer the more sturdy mounting and the bolt-on terminals, but it is probably no big deal. I overstated the present price. They are as cheap as chips these days. RT.  | ||
| Graham Burn Experienced User Username: graham Post Number: 34 Registered: 6-2013 |
My '87 Turbo R has suffered from this problem before it came to me and a PO has moved the fuse to one of the spare locations in the fuse block as the original position was totalled. Had a search for the metal circuit breaker suggested but couldn't find anything similar here, the closest I got was one which plugs in to the fuse position to replace the original blade type fuse, auto reset when powered down. I'll put my fuse tester on later and see what current the system draws when in use. Graham | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1147 Registered: 6-2006 |
If the fuse holder is still good then a slightly higher fuse will cure the problem. We've been doing it for years and have never had a problem afterwards. If you have a 20 or 25 amp fuse then replace it BEFORE the fuse board gets damaged. This circuit should not be prone to surges that should be ignored. If there is a real problem than it should be located and repaired, so I would not advocate a self resetting circuit breaker in this instance. Mechanical type circuit breakers take longer to blow than a fuse. Great for higher load items but not so great for electronic components. | ||
| Graham Burn Experienced User Username: graham Post Number: 35 Registered: 6-2013 |
Cheers Paul, I think I might mount the larger fuse in a remote holder for a bit of belt and braces  Graham | ||
| Ernest Carty Experienced User Username: edcarty Post Number: 36 Registered: 12-2012 |
Hi Graham, Paul has said words of wisdom ,you should NEVER fit a Circuit breaker into a system designed for a fuse,I agree your best option is to fit a fuse into a Remote holder but do not use an in line holder as these are also prone to failure and as they are enclosed can get even hotter if any additional resistance ocours. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2973 Registered: 4-2003 |
Ernest, Nice in principle, but the FI fuse is a special case on 20k cars. The design error is only solved by fitting a breaker with the appropriate i2t (i squared t) rating. R.. | ||
| Mark Aldridge Prolific User Username: mark_aldridge Post Number: 123 Registered: 10-2008 |
Richard, is there any merit in fitting a manual reset breaker, 20 amp are easily available in the UK.Also what is the i2t rating ( sorry i'm an accountant not an engineer) Mark | ||
| Ernest Carty Experienced User Username: edcarty Post Number: 37 Registered: 12-2012 |
RICHARD,the original issue raised by James Seaman relates to Fuse B9 0n Bank 1 this is the fuse which protects the ECU if a circuit breaker was fitted in place of a fuse if a fault becomes present in the ECU or associated wiring then the fitment of a circuit breaker as so rightly pointed out by PAUL could lead to disaster and costly at that. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2974 Registered: 4-2003 |
Not quite, Ernest. The fuel injection relay underbonnet does the protection. It protects against overvoltage and has a (replaceable) fuse mounted on its can. There is heaps of protection for the ECU including that fuse. RT. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2976 Registered: 4-2003 |
Item 7 is the fuel injection relay with its integral fuse. You will see that it protects Item 10, the ECU.  Mark, I'll research the UK sites for a suitable breaker or send you one. i2t is a measure used in fuse ratings. The current squared multiplied by duration gives a measure of the intensity of a current surge. The aim is to have a fuse or breaker open not only at a continuous current excess but also if a current surge is detected before that continuous level is reached. RT. | ||
| Mark Aldridge Prolific User Username: mark_aldridge Post Number: 124 Registered: 10-2008 |
Thanks Richard, I thought a breaker was a straight swap for a fuse, fortunately I have not made any sustitutions yet. RS components supply miniature resettable breakers that plug into the fuseboard on SY cars http://uk.rs-online.com/web/p/thermal-automotive-circuit-breakers/7292739/?origin=PSF_419273 Are these as advertised, a fuse replacement or is this not quite as it appears ? Mark | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2977 Registered: 4-2003 |
Indeed there are fuses and fuses. And breakers and breakers. AC. DC. High voltage, low voltage (1,000V) qne 12V petty. A nominal 10A rating is very simplified. That refers to the approximate point at which a fuse will blow under DC or RMS AC conditions. AC fuses have an easy time as the current naturally crosses zero every 10 milliseconds at 50Hz so any arcing is self-extinguishing. DC fuses have a tougher time especially with inductive loads (any coil or electric motor) as the fuse itself extinguishes an arc. There is the time to rupture as a parameter and what causes rupture including the rate of current rise (reflected in the i2t i squared x time rating) as another. There is a nominal voltage withstand to consider in a rating too. Circuit breakers have the same parameters, but are often slower to break the circuit. Not always. Car fuses are very low grade devices. The lowest grade. Slow. Inaccurate. They do the job cheaply and after a fashion. Rubbish by Industry standards. The glass types on earlier cars are better, but those used on most SZs, BMWs, Holdens, Ferraris and all the rest since the 1970s, Littel fuses, are very poor performers. The circuit breaker I showed above moons ago is faster and more precise. That is not any real challenge given the performance of a Littel fuse. Because a car fuse starts from such a low base, a quality breaker has a handy start. Mind you, I am certainly not convinced about those plug-in fuse replacements. RT. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 874 Registered: 9-2004 |
"The aim is to have a fuse or breaker open not only at a continuous current excess but also if a current surge is detected before that continuous level is reached." However with a circuit breaker when it cools and kicks in more than once with say a injection pressure pump before the pump cools, if it is one that is on the ciruit that is under load by a partly blocked filter etc, it may cause damage and may burn the motor out at great expence. A fuse will blow and no damage is done with the car out of action till the cause is found. Unless you are some sort of wiss kid with the types of electrics then just leave out the thought of the breaker, fit a seperate link "slightly higher" fuse in. End of story period. | ||
| Mark Aldridge Prolific User Username: mark_aldridge Post Number: 125 Registered: 10-2008 |
Thanks Gentlemen,I never stop learning and will not modify things I do not fully understand. I will check our Bentley8 fuseboard for signs of overheating. Mark | ||
| Jan Forrest Grand Master Username: got_one Post Number: 532 Registered: 1-2008 |
This is similar to what happened with my smaller battery charger. Although rated at 11 amps output it tended to slowly melt/distort a 15 amp fuse before it eventually blew. Fortunately there was no damage to the fuse holder so I replaced the fuse with a 20 amp one and there has been no repeat of the problem. | ||
| Ernest Carty Experienced User Username: edcarty Post Number: 38 Registered: 12-2012 |
Patrick you have Echoed my words entireley my previous post was about the same thing however those who ignore warnings do so at their own peril and like yourself it should be end of Story | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2980 Registered: 4-2003 |
When a fuse blows, do you blindly put a larger one in its place ? I think not. I hammer away on this from an engineering perspective and not through guesswork. This is a known fundamental flaw on these early 20k cars which I have addressed. As a professional design engineer in the field I am confident in my assessment. RT. | ||
| Jan Forrest Grand Master Username: got_one Post Number: 534 Registered: 1-2008 |
I agree that simply slapping in a bigger fuse is not to be done as a knee-jerk reaction to repeated blown fuses, but it's well known that most car fuses have a lower rating for a constant current than their 'instant' blow capacity. This why you often see fuses that haven't blown in the usual sense, but have obviously been subjected to excessive overheating for a significant period of time and consequently melted the plastic capsule. In those cases I see little if any harm coming from going one step higher in current capacity eg. replacing a 15 amp fuse with a 20 amp. However it's still prudent to check if the protected circuit is taking more current than it's supposed to. In any car that is even more vital due to the amount of highly flammable materials that are present. I've seen what can happen when a car catches fire and the results are not pretty! | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 877 Registered: 9-2004 |
When a fuse blows, do you blindly put a larger one in its place ? I think not. Richard, no you you never fit a higher rated fuse if it blows or get hot, you also never ever fit a circut breaker as a bodge to get over a confirmed makers fault. With the makers update proceedure in place if you still have a prob check for the real cause. As Jan states" when a car catches fire and the results are not pretty!" And the traces of fire cause with the circut breaker failings if fitted was rarly found by investigators however things are different now. You have so far been very lucky with your turbo r your LUCK may run out. Do make sure that your insurance is notified of your mod as insurance companys have stipulations applied maybe same as the UK regarding ANY mod. Hope this may help you with your prob. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1152 Registered: 6-2006 |
When a fuse blows, do you blindly put a larger one in its place ? I think not. Correct and I would not. Richard you may hammer away at problems and fashion a crude and frankly ridiculous answer from your hammering. I prefer to use a magnifying glass. inspect the problem, and find a cure. Fortunately we are not attempting to tunnel through a mountain without even looking at what's on the other side. There is a perfectly safe route to what we want out cars (and my clients cars) to do in a SAFE way. You earlier tried to justify using a circuit breaker by saying that it is just protecting a mechanical load and not electronics. That shows how blindly you are hammering. The item you describe as a relay is in fact an ECU. Protect an ECU with a self setting circuit breaker (SSCB). Frankly that is ridiculous. Think further on to the consequences of that - burnt out circuit boards etc if you are lucky and the fault is on the board. If you are really lucky the circuit breaker may break when you are in a petrol station or parked and will keep on breaking so you are aware of and can repair the problem. OR You try putting it in neutral, Back in park. You scratch your head - by then the SSCB has cooled and a few seconds later your car starts perfectly again, you shrug, you carry on. 5 minutes later it breaks again - this time you are going around a sharp mountain bend at 50 mph with your nicely filled tank of petrol. Nice engineering solution you've hammered out. If my engine does cut out I want as many chances as possible to know about it and cure the fault. I certainly do not want to have somebodies design 'hiding' the problem. A manually reset circuit breaker in this circuit would be complete overkill but infinitely more acceptable from a safety standpoint. A SSCB on this safety critical circuit - ridiculous. SSCB are perfect for an electric window motor where the kids keep playing with them and they are getting hot due to a load.  Your Electric seats that have too fat a passenger on that can't get comfortable after the lovely meal you've just had - fine. Maybe even headlights - if an overload due to a blowing bulb puts them out for a minute and then the good one comes back on by itself, nice. safer These are not due to faults, these are not dangerous. These are ALSO protected by a fuse. Perfect applications for a SSCB. But an engine cutting out and then "designed" to be able to run again without curing the problem - Ridiculous - certainly . . . criminally dangerous - very possibly.  Richard, as a professional design engineer , why does this circuit require a self setting circuit breaker? | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2981 Registered: 4-2003 |
Wow. Paul, the ECU has it own fuse mounted on the PI relay as shown in the diagramme above. The fuel pump, a mechanical device, is quite happy with slower protection even if a suitable breaker is no slower than an open fuse. No luck involved here. Just the prudent choice of a suitably-rated device whilst observing the fuse discrimination offered by the crude Littel fuse on the PI relay. Originally, two similar fuses were run in series to the ECU. That is just nonsense. The Crewe bulletin applied to this design fault is a very poor patch. Had I any concerns about alarmist hypotheses I would fit an HRC fuse. Old houses use fuses. Breakers have come a long way to improve domestic safety compared to hot wires. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1154 Registered: 6-2006 |
"The Crewe bulletin applied to this design fault is a very poor patch." Why is it poor when it cured the fault? Marginally increasing the fuse rating also cures the fault. The PI "relay" as you describe it is not a "Relay". It is an ECU that monitors system voltage and breaks a circuit if the voltage is out of range. It is the Motronic electronic control unit for over-voltage protection. These ECU's give enough spurious and intermittent problems without a SSCB being added to the circuit. Circuit breakers are a brilliant device. This I would not even want to argue against. When used correctly. Your Bentley is neither a new house or an old house. No matter, because both use circuit protection that involves manually resetting that protection. For SAFETY reasons. Have you fitted SSCB in your house as well? There are a million different good applications for circuit breakers. But even if every one is quoted it does not make any good argument for using a SSCB in this circuit. Richard, as a professional design engineer , why does this circuit require a self setting circuit breaker? | ||
| Ernest Carty Experienced User Username: edcarty Post Number: 39 Registered: 12-2012 |
Paul you like several others including Myself on this thread have already stated the obvious regarding the use of circuit breakers and the DIRE consequences and as Patrick rightly points out I do indeed hope that Richard has informed his insurance Company of this Modification.But as I said earlier he is at his own Peril and can we please have an end to this BORING Topic when the obvious has been already STATED.Best Wishes for Xmas and 2014. | ||
| David Gore Moderator Username: david_gore Post Number: 1357 Registered: 4-2003 |
Unfortunately this thread is becoming repetitious due to the different perspectives of the major experienced contributors in relation to the problem first raised namely overheating of a fuse carrying a current close to its rated capacity - this heating is to be expected and is normal as the heating eventually functions to melt the fuse wire and break the circuit once the current exceeds the rated capacity of the fuse. The time for this to happen is a function of the type of fuse/circuit breaker installed [fast blow/slow blow; fast acting/slow acting] to match the components requiring protection. I respect the experience and expertise of Paul and Richard and I commend their advice and comments as being relevant, applicable and valid with respect to their different perspectives relating to the original request for advice. Regarding Paul's enquiry re the use of a "self setting circuit breaker", I suggest this would be the same reason for this type of breaker being used in headlamp circuits - purely for convenience in on-road situations where the driver only has to wait for the breaker to cool and reset itself without having to find the owners manual to find the location of the breaker [usually in a difficult-to-access location] before it can be reset manually. I have closed this thread. |
