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tahoe healey
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In another post, Stever mentioned inline fused being added. I have some I've added. But I am curious what systems you all have added fuses to and what amperage they each are.
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Inline Fuses [ and Fuse Theory & Application ]
- Thread starter tahoe healey
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Re: inline fuses
The most commonly added & most useful fuse addition is in the wiring going to the side marker, tail, & number plate lamp. Due to the long distances & proximity to the car ends these circuits are particularly vulnerable to minor collisions & wire chafing. The easiest location to fuse this circuit is at the red wires on the back of the lighting switch. Use an inline holder with a 15 amp fuse.
Another popular circuit to fuse is the overdrive circuit. This is easily done by inserting an inline 15 amp fuse in the white wire at the fuse block terminal 3, to the OD circuits.
Another is the fuel pump feed. Another inline fuse in the white wire at fuse terminal 3 with a 15 amp fuse.
You can put 20 amp fuses in the separte high & low beam headlights at the dip switch, if desired, but most people don't like the idea of blowing a headlight fuse.
Lastly, for overall protection, some folks put a 35 amp self resetting circuit breaker in the brown wire from hot starter solenion terminal to the voltage regulator. This is the main feed for all electrical circuits.
D
The most commonly added & most useful fuse addition is in the wiring going to the side marker, tail, & number plate lamp. Due to the long distances & proximity to the car ends these circuits are particularly vulnerable to minor collisions & wire chafing. The easiest location to fuse this circuit is at the red wires on the back of the lighting switch. Use an inline holder with a 15 amp fuse.
Another popular circuit to fuse is the overdrive circuit. This is easily done by inserting an inline 15 amp fuse in the white wire at the fuse block terminal 3, to the OD circuits.
Another is the fuel pump feed. Another inline fuse in the white wire at fuse terminal 3 with a 15 amp fuse.
You can put 20 amp fuses in the separte high & low beam headlights at the dip switch, if desired, but most people don't like the idea of blowing a headlight fuse.
Lastly, for overall protection, some folks put a 35 amp self resetting circuit breaker in the brown wire from hot starter solenion terminal to the voltage regulator. This is the main feed for all electrical circuits.
D
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Re: inline fuses
Gee, I don't know. I think we are more concerned with protecting the wiring from disaster than protecting a single device. Some of the Healey wiring is rather small & a short at the end of longer runs can melt the wire insulation without ever blowing the source fuse which is arranged to handle several different circuits at the same time.
With the small & rather mechanically fragile in line fuses that are generally used, the lighter fuses are noticeably weaker mechanically & more subject to vibration fatigue, thermal fatigue, & failure. A single mechanical shock can fracture the small wire in a one amp fuse.
I doubt if the steady state load current is of much concern in rating a device such as a pulsating inductive load of a fuel pump on which the repetitive peak currents can be considerably higher than the theoretical steady state. A fuse that is subjected to its maximum load rating loses a bit of it's minimum melt rating on each occurance.
The overdrive solenoid can draw something like 20 amps until the pull in coil switches out, then drop to around one amp on it's holding coil. We are really fusing it against the failure of the pull in coil contact to open as can happen if the solenoid doesn't make a full stroke.
Circuits that are under fused only create more reliability problems.
On the other hand, WHY NOT high ratings?
D
Gee, I don't know. I think we are more concerned with protecting the wiring from disaster than protecting a single device. Some of the Healey wiring is rather small & a short at the end of longer runs can melt the wire insulation without ever blowing the source fuse which is arranged to handle several different circuits at the same time.
With the small & rather mechanically fragile in line fuses that are generally used, the lighter fuses are noticeably weaker mechanically & more subject to vibration fatigue, thermal fatigue, & failure. A single mechanical shock can fracture the small wire in a one amp fuse.
I doubt if the steady state load current is of much concern in rating a device such as a pulsating inductive load of a fuel pump on which the repetitive peak currents can be considerably higher than the theoretical steady state. A fuse that is subjected to its maximum load rating loses a bit of it's minimum melt rating on each occurance.
The overdrive solenoid can draw something like 20 amps until the pull in coil switches out, then drop to around one amp on it's holding coil. We are really fusing it against the failure of the pull in coil contact to open as can happen if the solenoid doesn't make a full stroke.
Circuits that are under fused only create more reliability problems.
On the other hand, WHY NOT high ratings?
D
Keoke
Great Pumpkin
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Re: inline fuses
/ubbthreads/images/graemlins/savewave.gif the circuits being discussed are long and the wiring will current limit the fuse. In the case of the overdrive the 19 amp current lasts for 3 milliseconds so why the big fuse given its steady state running current is less thn 2 amps???---Keok amps>???Keole /ubbthreads/images/graemlins/confused.gif
/ubbthreads/images/graemlins/savewave.gif the circuits being discussed are long and the wiring will current limit the fuse. In the case of the overdrive the 19 amp current lasts for 3 milliseconds so why the big fuse given its steady state running current is less thn 2 amps???---Keok amps>???Keole /ubbthreads/images/graemlins/confused.gif
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Re: inline fuses
Keoke,
I don't think the wiring current limits the fuse as much as you think.
The typical British wire for side marker & other light duty circuits consists of 14 strands of .03mm diameter wire. It is rated at 8 amps & is equivilent to 18 gage US wire. It has a resistance of about .019 ohms per meter. At a worst case of 20 ft of wire or 6.14 meters, shorted at the far end, this is .117 ohms. At 12 volts, there would be 103 amps flowing.
Since this represents 1240 watts dissipated in the wire which is tightly bundled with others & reduces heat dissipation, the insulation can melt in spots. As I said, we are protecting the wiring, not the device that it feeds. If the short happens at a critical location & the sparks create an arc near the exposed gas tank with it's inevitable small vapor leaks, there is a potential bang. this is most likely in the event of a minor rearend impact. If a device shorts solid, it is gone anyway, save the wiring but don't sacrifice reliability by using fuses that are too small. You havent addressed the shorter mechanical fatigue life & thermal rating reduction of using light fuses. Do you not believe it or just consider it trivial?
As far as the OD solenoid the most frequent problem is the contacts don't shut off the 19 amps, due to a mis adjusted solenoid or defective switching contact in the solenoid, & the 19 amps remains on continuously. this fries the solenoid when only a small adjustment is really needed to prevent it.
The fuel pump protection is mainly because the pump end of the feed wire is vulnerable & sometimes gets grounded by pinching or coming loose.
I only gave some of the reasons that folks add extra fuses. Not wishing to start an extended debate on the pros & cons of the practice. We can do this off line if you wish. Or maybe you are just trying to draw me out?
Each person will have to decide for themselves wheter extra fuses are needed & what size.
D
Keoke,
I don't think the wiring current limits the fuse as much as you think.
The typical British wire for side marker & other light duty circuits consists of 14 strands of .03mm diameter wire. It is rated at 8 amps & is equivilent to 18 gage US wire. It has a resistance of about .019 ohms per meter. At a worst case of 20 ft of wire or 6.14 meters, shorted at the far end, this is .117 ohms. At 12 volts, there would be 103 amps flowing.
Since this represents 1240 watts dissipated in the wire which is tightly bundled with others & reduces heat dissipation, the insulation can melt in spots. As I said, we are protecting the wiring, not the device that it feeds. If the short happens at a critical location & the sparks create an arc near the exposed gas tank with it's inevitable small vapor leaks, there is a potential bang. this is most likely in the event of a minor rearend impact. If a device shorts solid, it is gone anyway, save the wiring but don't sacrifice reliability by using fuses that are too small. You havent addressed the shorter mechanical fatigue life & thermal rating reduction of using light fuses. Do you not believe it or just consider it trivial?
As far as the OD solenoid the most frequent problem is the contacts don't shut off the 19 amps, due to a mis adjusted solenoid or defective switching contact in the solenoid, & the 19 amps remains on continuously. this fries the solenoid when only a small adjustment is really needed to prevent it.
The fuel pump protection is mainly because the pump end of the feed wire is vulnerable & sometimes gets grounded by pinching or coming loose.
I only gave some of the reasons that folks add extra fuses. Not wishing to start an extended debate on the pros & cons of the practice. We can do this off line if you wish. Or maybe you are just trying to draw me out?
Each person will have to decide for themselves wheter extra fuses are needed & what size.
D
Keoke
Great Pumpkin
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Re: inline fuses
/ubbthreads/images/graemlins/savewave.gif
Thats great if the overdrive circuit fault causes 19 amps of steady state curent to flow it sure will blow a 5 amp fuse presto don't you agree??---Keoke---The minute that wire starts drawing heavy currebt its resistasnce also begins to rise the current in the circuit decreases and the voltage drop accours across the wire. the total power dissapated in the circuit is essentially constant.Bundling wires in the harness adds to the themal problem due to proximity effect. Good Night All.
/ubbthreads/images/graemlins/savewave.gif
Thats great if the overdrive circuit fault causes 19 amps of steady state curent to flow it sure will blow a 5 amp fuse presto don't you agree??---Keoke---The minute that wire starts drawing heavy currebt its resistasnce also begins to rise the current in the circuit decreases and the voltage drop accours across the wire. the total power dissapated in the circuit is essentially constant.Bundling wires in the harness adds to the themal problem due to proximity effect. Good Night All.
fordhealey
Jedi Hopeful
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Re: inline fuses
regrounded all of the gauges. solved the problem. noted
some blistered spots in wire running from the dash to ground.thought it was easier just to replace it all.
thanks
gregg
regrounded all of the gauges. solved the problem. noted
some blistered spots in wire running from the dash to ground.thought it was easier just to replace it all.
thanks
gregg
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Re: inline fuses
Keoke,
For the third time, unnecessarily light fuses present their own reliability problems. Maybe this can be demonstrared to you by the following quote;
"If, however, the fuse is subjected repetitive high current overloads, the temperature in the fusible link will fluctuate causing two types of fatigue - mechanical fatigue and thermal fatigue.
Mechanical fatigue is precipitated by overloads of longer duration while the current stays below the fuse current rating. The periodic heating and cooling of the fusible link will weaken it and the mechanical stresses will eventually cause the link to open. Thermal fatigue is more likely the result when switched higher temperatures in the fusible link caused by the short duration, high energy pulses will lead to grain growth within the molecular structure of the fusible link. This grain growth, which is permanent, weakens the element and will ultimately cause premature opening of the fuse and unnecessary equipment down time."
This would be the case witht the OD fuse if it were set at 5 amps. note the last two sentences.
D
Keoke,
For the third time, unnecessarily light fuses present their own reliability problems. Maybe this can be demonstrared to you by the following quote;
"If, however, the fuse is subjected repetitive high current overloads, the temperature in the fusible link will fluctuate causing two types of fatigue - mechanical fatigue and thermal fatigue.
Mechanical fatigue is precipitated by overloads of longer duration while the current stays below the fuse current rating. The periodic heating and cooling of the fusible link will weaken it and the mechanical stresses will eventually cause the link to open. Thermal fatigue is more likely the result when switched higher temperatures in the fusible link caused by the short duration, high energy pulses will lead to grain growth within the molecular structure of the fusible link. This grain growth, which is permanent, weakens the element and will ultimately cause premature opening of the fuse and unnecessary equipment down time."
This would be the case witht the OD fuse if it were set at 5 amps. note the last two sentences.
D
Re: inline fuses
Hello all,
I'm with Dave Russell on the fuse sizing. However, one thing concerns me and that is putting something like a 35 amp fuse or circuit breaker in the main brown feed. Unless ALL the sub circuits are suitably fused, then a short in a minor circuit could shut down the car; not very nice in busy traffic and multi lane roads, not to mention if it happens at night.
Certainly the electrical system of cars of the era we are interested in is pretty basic, but given routine maintenace is reliable. (Less so in cars that are driven only on rare occasions.) Fuse rating were selected to give reliability, hence seemingly high ratings but sufficient to protect in the event of a short circuit.
Alec
Hello all,
I'm with Dave Russell on the fuse sizing. However, one thing concerns me and that is putting something like a 35 amp fuse or circuit breaker in the main brown feed. Unless ALL the sub circuits are suitably fused, then a short in a minor circuit could shut down the car; not very nice in busy traffic and multi lane roads, not to mention if it happens at night.
Certainly the electrical system of cars of the era we are interested in is pretty basic, but given routine maintenace is reliable. (Less so in cars that are driven only on rare occasions.) Fuse rating were selected to give reliability, hence seemingly high ratings but sufficient to protect in the event of a short circuit.
Alec
mvanderploeg
Senior Member
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Re: inline fuses
Keoke, I'm not sure if you're being serious about a wire's ability to limit current flow during a fault, but if so, I've disproven your electrical theories on several occasions through inadvertant experimentation in my garage. Fault current will melt the wires in a Healey or on a 230kV Transmission line running along the highway. I've seen both happen on a variety of occasions. High current will not increase a conductor's resistance nearly enough to have an impact on the current flowing to a fault. Heat will result (current squared times resistance) and the wire will most definitely melt unless protected by an appropriately size circuit breaker or fuse. Fuses in Healeys are sized from the factory to protect multiple circuits, not individual wires, thus the need to add in-line fuses. I guess you could size the fuse anywhere from just above continuous load current to just below the ampacity of the wire, but, as Dave mentioned, the fuse is typically there to protect the wire in the event of a fault, not to protect the load.
Keoke, I'm not sure if you're being serious about a wire's ability to limit current flow during a fault, but if so, I've disproven your electrical theories on several occasions through inadvertant experimentation in my garage. Fault current will melt the wires in a Healey or on a 230kV Transmission line running along the highway. I've seen both happen on a variety of occasions. High current will not increase a conductor's resistance nearly enough to have an impact on the current flowing to a fault. Heat will result (current squared times resistance) and the wire will most definitely melt unless protected by an appropriately size circuit breaker or fuse. Fuses in Healeys are sized from the factory to protect multiple circuits, not individual wires, thus the need to add in-line fuses. I guess you could size the fuse anywhere from just above continuous load current to just below the ampacity of the wire, but, as Dave mentioned, the fuse is typically there to protect the wire in the event of a fault, not to protect the load.
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Re: inline fuses
[ QUOTE ]
Mick ,This is time related if the wire resistance increases where does the fuse get it current to blow???-Yes I am serious and garage experiments can be missleading.-Regards ---Keoke
[/ QUOTE ]
Keoke,
The energy contained in a short circuit follows the rule of current squared times time. Or I^2 T seconds. The fuse element follows the same rule. Thus a 10 amp fault lasting for .5 seconds has the same energy as a 100 amp fault lasting for .005 seconds. the fuse heat increases much faster with current increase than it does with time increase. Further, the wire resistance only increases by about 0.4% per degree C increase in wire temperature.
Alec,
The typical 35 amp self resetting circuit breaker actuall requires about twice this current to trip. It is only a last ditch device to prevent complete wiring harness burn out.
D
[ QUOTE ]
Mick ,This is time related if the wire resistance increases where does the fuse get it current to blow???-Yes I am serious and garage experiments can be missleading.-Regards ---Keoke
[/ QUOTE ]
Keoke,
The energy contained in a short circuit follows the rule of current squared times time. Or I^2 T seconds. The fuse element follows the same rule. Thus a 10 amp fault lasting for .5 seconds has the same energy as a 100 amp fault lasting for .005 seconds. the fuse heat increases much faster with current increase than it does with time increase. Further, the wire resistance only increases by about 0.4% per degree C increase in wire temperature.
Alec,
The typical 35 amp self resetting circuit breaker actuall requires about twice this current to trip. It is only a last ditch device to prevent complete wiring harness burn out.
D
mvanderploeg
Senior Member
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Re: inline fuses
Keoke, you had argued that the wire resistance increases, not me. See your quote below:
[ QUOTE ]
The minute that wire starts drawing heavy currebt its resistasnce also begins to rise the current in the circuit decreases and the voltage drop accours across the wire. the total power dissapated in the circuit is essentially constant.Bundling wires in the harness adds to the themal problem due to proximity effect. Good Night All.
[/ QUOTE ]
My point was that wire resistance doesn't increase, it doesn't limit the fault current, and therefore, the fuse has plenty of current available to blow or the wire has plenty of current to melt if there's no in-line fuse installed. Your last post now seems to argue this same point, which is contrary to your quote above.
We're making this a lot more complicated than it is. A fault will draw current depending on the resistance (impedance in an AC circuit) of the fault. The increased current will either cause the wire to melt, a fuse to blow (melt), or a circuit breaker to interrupt the current. Size the fuse less than the continuous current rating of the wire, & the fuse will melt first. How much less is up to you, but Dave makes some good points for not going too small. If the fuse (or circuit breaker) is sized appropriately, time will be irrelavent. Yes, low fault current will take longer to melt a fuse than high fault current and a fuse rated at lower amperage will blow quicker than a fuse rated at higher amperage for the same fault current, but either way, if it's sized correctly, it'll always melt sooner than the wire it's protecting.
Keoke, you had argued that the wire resistance increases, not me. See your quote below:
[ QUOTE ]
The minute that wire starts drawing heavy currebt its resistasnce also begins to rise the current in the circuit decreases and the voltage drop accours across the wire. the total power dissapated in the circuit is essentially constant.Bundling wires in the harness adds to the themal problem due to proximity effect. Good Night All.
[/ QUOTE ]
My point was that wire resistance doesn't increase, it doesn't limit the fault current, and therefore, the fuse has plenty of current available to blow or the wire has plenty of current to melt if there's no in-line fuse installed. Your last post now seems to argue this same point, which is contrary to your quote above.
We're making this a lot more complicated than it is. A fault will draw current depending on the resistance (impedance in an AC circuit) of the fault. The increased current will either cause the wire to melt, a fuse to blow (melt), or a circuit breaker to interrupt the current. Size the fuse less than the continuous current rating of the wire, & the fuse will melt first. How much less is up to you, but Dave makes some good points for not going too small. If the fuse (or circuit breaker) is sized appropriately, time will be irrelavent. Yes, low fault current will take longer to melt a fuse than high fault current and a fuse rated at lower amperage will blow quicker than a fuse rated at higher amperage for the same fault current, but either way, if it's sized correctly, it'll always melt sooner than the wire it's protecting.
Re: inline fuses
Fuse values are often selected by expereience. Keoke, if your experience shows 5 amps is good; enjoy.
As for the wires being self limiting; you just need to check the spot in my boot where the D.P.O. nearley burned the car to the ground to know that the wire isn't safely self limiting.... If that isn't enough "experience", you can also observe the left over bits of red vinyl under my dash to add to the knowledge base. Yes, the wires heat, turn cherry red, decompose the vinyl and open; the resistance is then significantly higher! Unfortunately, that sequence doesn't always occur fast enough to prevent fire.
Fuse values are often selected by expereience. Keoke, if your experience shows 5 amps is good; enjoy.
As for the wires being self limiting; you just need to check the spot in my boot where the D.P.O. nearley burned the car to the ground to know that the wire isn't safely self limiting.... If that isn't enough "experience", you can also observe the left over bits of red vinyl under my dash to add to the knowledge base. Yes, the wires heat, turn cherry red, decompose the vinyl and open; the resistance is then significantly higher! Unfortunately, that sequence doesn't always occur fast enough to prevent fire.
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Re: inline fuses
---- That's all for me folks -------
D
---- That's all for me folks -------
D
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