| Author | Message | ||
     pat lockyer. Unregistered guest Posted From: 81.135.122.66 |
What is the easy way the faulty know circut is tested to find out the fault when the fuse keeps blowing. I may have a simple way. | ||
| David Gore Moderator Username: david_gore Post Number: 210 Registered: 4-2003 |
Pat, if there is a simple way; we will all be interested in knowing the procedure. My practice is to isolate all the devices in the circuit subject to fusing; if the fuse still blows then there is a fault in the wiring harness. Otherwise I reconnect each device one at a time until the fuse blows to identify the faulty item. However this is not always 100% accurate if more than one device is faulty causing a cumulative overload; in this case a current draw test is necessary for each device to identify which is contributing to the problem. | ||
| Pat Lockyer Unregistered guest Posted From: 81.131.105.85 |
Hi David. As i suspected trial & error. Would like to see more postings in laymans terms before i let on to my simple way of solving the prob and to give everyone a crack @ it. Come on Bob Uk. Pleased that this forum works well. More in due course. | ||
| Martin Taylor Experienced User Username: martin_taylor Post Number: 9 Registered: 11-2003 |
I replace the fuse with a high wattage light bulb, the bulb will glow brightly when the output side is shorted to ground or overloading, If it is a 10A circuit I would use 120 watt bulb in a 12v circuit (both filiaments connected in a high/low headlight bulb). | ||
| Pat Lockyer Unregistered guest Posted From: 81.131.118.74 |
Hi Martin, spot on well done,hopefully there won't be the trial & error resulting in many fuses being used up by [no names no pack drill] | ||
| David Gore Moderator Username: david_gore Post Number: 215 Registered: 4-2003 |
No Names, No Pack Drill [ie myself] doesn't worry about blowing a fuse or two to track down a fault; what is important is to SAFELY find the fault in the first place. The use of a light bulb as a continuity tester is common practice however it does interpose a non-fusible resistance into the circuit which may or may not affect the faulty component[s]. The bulb alone} will not protect faulty components from excessive current draw as a fuse will; a 120W bulb will allow a continuous current of 10A; a dual filament headlight bulb say 65W/120W will allow a current of around 16A to flow in the circuit and possibly destroy the faulty component or burn out the wiring before the fault is identified. After all, the standard Shadow circuits are protected by a 10Amp fuse and this value would have been selected to protect both the wiring harness and the devices in each circuit. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 130 Registered: 4-2003 |
Seconded, David. A light bulb will CONTROL the current to the fuse rating (eg 4.5A for a 55W bulb at 13.8V) on a CONTINUOUS, not fused, basis causing unspecified potential damage. Usually, a 10A fuse will blow because it has been subjected to a potential 80A surge, not just a mild overload. Using a lamp in the circuit, even with the fuse in-line, is the very worst method to use on cars less than 35 years old. All you are doing is pumping a destructive level of current into a faulty device for an unspecified period of time. At best, it's like driving the car flat out with the brakes applied to keep to the speed limit. It won't skid or give you speeding tickets, but how long will the brakes last ? There may be 10 devices for example on each fuse, maybe 1A peak current each forgetting headlamps. As most devices will suffer continuous overload severely after a few fractions of a second (eg seized washer motor or any electronic component), the light bulb method is misleading and definitely not the way to go. Best test the devices individually first on an HRC-fused 13.8V ("12V") supply and work upwards towards the fusebox to find the fault. After eliminating bulb-test methods, fuse-blowing trial-and-error is a last resort. Consider transistorised and microprocessor devices. A true overload for 1/10 second is disasterous. OK, shadows have limited electronics. By comparison, simply jump-starting a mid-series SZ can cause $5,000 damage unless all the unnecessary circuits have their fuses removed (cruise control, ABS, memory seats, turbo ECU, active ride and so on). Fault finding using light bulbs or fuse blowing techniques on these cars is tempting fate and ruin, and I suggest wariness with any post-1969 Shadow too. | ||
| Pat Lockyer Unregistered guest Posted From: 81.131.185.93 |
Hi David & Richard. I feel that maybe the way of useing the bulb system hands on you may be not be quite sure of. Tell me how you would go about useing the bulb on the required blown circuts to damage the fused circut component. It has never hapened to myself with the proceedure that i use. This is for the SS1 SS2. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 131 Registered: 4-2003 |
"Give me a break, and go back to school. This is really boring stuff. Fuses and advance curves for heaven's sakes. Elementary physics please." A bit harsh perhaps. But really, you do not need a University degree to realise that the bulb method is seriously stupid. | ||
| Pat Lockyer Unregistered guest Posted From: 81.131.84.63 |
Hi Dick. I am now sure that you just cannot explain the hands on approach. Maybe the house electrics is your thing,please to see that you are following the great interest in the excellant forum on Shaddow dwell strobe set up. THIS TYPE OF DEROGATORY COMMENT ABOUT ANOTHER PARTICIPANT IS INAPPPROPRIATE AND NOT WELCOME ON THIS FORUM. IT DOES NOT ENHANCE THE CREDIBILITY AND REPUTATION OF THE GUEST PARTICULARLY HIS SELF-INDULGENCE CONCERNING HIS DWELL-STROBE PRACTICE. I HAVE DELIBERATELY NOT DELETED IT BUT LEFT IT AS POSTED SO OTHERS CAN FORM THEIR OWN OPINION ABOUT THE GUEST. FUTURE POSTS OF THIS TYPE WILL BE DELETED. DAVID GORE - MODERATOR (Message edited by david_gore on March 01, 2004) | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 12 Registered: 11-2003 |
I see the point about finding by disconnecting and isolation of individual circuits. I work with elevators and this is the first method used to trace intermittent faults, if there are 10 circuits being supplied from the same fuse then you would simply feed them from an appropriately rated fuse each while still leaving the origonal fuse in place to protect the supply, the other fuses would then protect each appliance connected. With semiconductors in modern appliances the most dangerous thing can be to replace the fuse without knowing and removing the cause, as stated above the fuse blowing will mean anything above it's current and time rating has been allowed through the circuit for a short time at least. Many modern Radio and amplifier's use a diac or zener across the supply to protect against voltage spikes and reverse polarity, if for example the circuit is connected in reverse the zener will conduct and provide a short circuit causing the correctly rated supply fuse to blow. Repeated applications of reverse power and replacement fuses will in a short time cause the zener to become open circuit and hence allow reverse voltage accross the applince killing it. With the light bulb test mentioned above it is best to start out with a low rated lamp to show the fault to earth without overloading the wiring, even a 5w bulb will show a difference in brightness with a dead short to ground or an appliance attempting to draw over current. I was taught the light bulb method by one of my electrical engineering tutors a few years back, I would call it practical and not stupid, at the time it was more for low impedance AC circuits with more reactance than resistance (cannot be tested with an ohm meter). I may disagree with someone, this does not mean that I do not respect their opinion. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 132 Registered: 4-2003 |
Martin, I agree that a low wattage bulb (1W-5W) is often a useful tool used with discretion. I just feel that any higher rating is asking for trouble. Please excuse my unnecessarily harsh remark in an earlier posting. Some funny results will occur however, especially with semoconductor loads and some other devices. For example, a Silver Shadow (I) impulse clock draws a current spike of maybe 1A for a very short time every few minutes. The bulb test will not work here as the bulb will glow bright as there is not enough current to energise the mechanism but plenty to light the bulb. Leaving the bulb connected for any period of time will be pumping maybe 80-400 mA continuously through the clock coil and will most probably destroy it very quickly indeed. The same applies to servo motors and the like. On a similar subject, often, a partially flat battery may not energise the clock, and this is known to cook the clock and flatten the battery completely. That is one reason why it is best to disconnect the battery if the car is parked for more than a few weeks. Horses for courses, but remember the Electrician's saying "one flash and you¨re ash". I hate blowing fuses: it's probably just a pride thing, though. However, as you say, repeated fuse blowing can only harm the devices being protected. Most automotive applications do not provide fuse discrimination as required by law on safety critical elevators and the like so the dangers are increased. | ||
| John Dare Unregistered guest Posted From: 144.138.194.1 |
It is my sincere hope that the brighter participants in this current debate eventually see the light without blowing a fuse. | ||
| Bob UK Unregistered guest Posted From: 195.93.33.11 |
Using a light bulb in place of a fuse for testing purposes is an old practice. It is not dangerous providing it is done quickly. I have used bulbs to limit amp/volts when I am checking, but never ever permanent. Richard is right about small amps slowly cooking things. A half discharge battery left connected on a lot of modern cars can do similar damage. Not to mention what happens when the starter is tried. Hopefully the car has a good memory. I have known a few body shops muck up because they work 2 weeks on a car with the interior light on because they took the doors off. On Shadows most of the circuits that are joined together on a single fuse come togther on the back of the fuse board. which is good practice -- makes separating the circuits out to find the shorted circuit easier. I worked on a Renault once and found spliced wires inside the main loom to supply circuits from the same fuse that is bad practice. That made finding a short very differcult and expensive. I start with the obvious like bulb holders with displaced connections inside the holder and anything that don't look right. Rear seat bases can cut the loom seen this a few times on various cars, usually caused by work done a few years before. The Shadow has a few not nice areas such as behind the kick plates in the front foot wells. I remember Dave Gore's comment about kick plates --- I do not kick my car I the bulb method in series with the battery to detect leaking. Which very Shadow revelant. My car has just killed the battery.It lasted 3 years which is fair enough nowadays or maybe I should kick the car for being a battery eater. In some parts of the UK the mains was DC and if you connected a car battery in series to a light bulb you could charge a battery direct without a charger. My father being a MOD radar bloke come up with something better. He wound a coil with a brush on it an ampmeter so you could adjust the charge rate. We used to get regular power cuts and we had a bank of batteries ( ex milk float traction batteries ) My pocket money job was to check the SG every day. I would fill in a chart and he would check them at the weekend any cells that were down he would melt the tar around the top pull out the grids and fit spares which he serviced at work. Now all UK mains is 220-240 V AC. and 440V 3 phase. |
