Wylex fuse wire / repairing old style Lucas fuses ?

[Durango2k]

Now you MUST think "the dreaded german has finally gone totally nuts", yet I just had the idea of repairing my old original 1/66 marked Lucas fuses (I have a few spares with the 35A paper still inside).

Googling brought up the british Wylex system, for which you can still buy cheap wire cards on ebay.

Has anyone ever tried that ?

Carsten

(Now writing a mail to Blend-a-med for a new empty toothpaste tube because one blew and a tip how to fill the white stuff over into the new one...)

P.S. - yes I know these:

http://www.sngbarratt.com/ProductDetail ... 1e3402&l=7

[Heuer]

You used to be able to buy fuse wire very easily but you would have difficulty in finding any nowadays. The other problem is the replaceable wire in the plug in fuses was rated at a maximum of 30 amps and you need 35amps in most cases:



Besides the cost of the fuse wire will be more than buying the replacement fuses!

[Durango2k]

Hello David,

These cards sell for 1.25 pounds on ebay.co.uk, so thats ok.

Then, 35 is impossible to achieve, you're correct, because any parallel wiring inside would lower the total ohm value.

Hm.......

Have you seen for how much original Lucas Fuses sell ? I have seen single blue 35 ones for 15 pounds, or 5 for 25 and so on.

'bit like Cheneys methinks...

Carsten

[Heuer]

I use the SNGB ones at 25p each. Even the most avid concours guys don't go as far as using original fuses as far as I know. Besides, when correctly mounted with wire facing out, you can't see the Lucas script. I will see if I can calculate the correct swg wire to carry 35amps which should make it easy for you to source some.

[christopher storey]

David :It's now some 54 years since my A level physics, so I hope I'm not getting this completely wrong , but I think that V divided by I = R should still apply . So for 35 amps capacity, the resistance of the fuse should be 12/35 ohms = 0.34 ohms. In practice , bearing in mind that the Lucas ratings (unlike modern fuses) were blow ratings rather than continuous ratings, I suppose one wants the wire to carry rather less than 35 amps so that the resistance of the wire length should perhaps be more like 0.4 ohms . This does not help with the swg thickness, but I have some fuse wire so I'll measure its resistance and report back

Edit : Unfortunately, the residual resistance in my multimeter leads appears to be about 0.4 ohms, so my readings are rather suspect, but a 35 amp lucas fuse I just measured gave a resistance of 0.6 ohms, and the 30 amp fuse wire I measured was 0.79mm diameter, so 35 amp would presumably be slightly thicker than this

[Heuer]

There are two things to consider - 'Fuse Rating' which is printed on the fuse and 'Fusing Current' which is the point at which it blows. Conventionally fuse ratings are assumed to be half fusing current. So for a 35amp rated fuse its fusing current would be ~68 amps which in turn requires 19 swg tinned copper wire. Wire rating would be 8.4 amps. This stuff should do it:

"TINNED COPPER WIRE - FUSE WIRE - 500grams (1mm 35amp 19 SWG) FUSING CURRENT WILL BE HIGHER THAN THE STATED CURRENT CARRYING CAPACITY"

And before you ask, the 50amp rated fuse would require 18swg wire. :D

[christopher storey]

David - your point about rating was the one I referred to. Lucas ratings are the blow rating, and so a Lucas 35 amp fuse should blow at 35 amps. It is modern fuses where the blow rating is twice the nominal rating, which is why typically one sees a maximum of 17 amp fuses for most applications with one or two heavy applications having e.g. 25 amp fuses and the heaviest being 30 amps, which would blow at a flow level of about 60 amps. Also, the 30 amp wire I measured is 21 swg

It is this oddity ( by modern conventions ) of the Lucas rating which causes a good deal of anxiety, ( not to mention the possibility of fire if a modern 35 amp fuse is used to replace a 35 amp Lucas fuse ) but it is perhaps easiest to visualise whether a fuse is reasonable in its context by considering the watts it will pass at 12 volts, so 35 amps Lucas will pass 35 X 12 = 420 watts

A rather good exposition of the problem is here

http://www.groups.tr-register.co.uk/nen ... 20BUSS.pdf

and I think the same problem may arise with the Amazon reference you have given i.e. one needs to be absolutely clear whether their wire is 35 amp blow rating or 35 amp continuous rating - it looks to be the latter, which is too high a rating for Carsten's purposes

[Heuer]

Christopher

Resistance will depend on length of the wire. 19swg wire would have a resistance of 21.3 Ω/km. To measure the resistance of a short length would require a very accurate meter indeed. A 1 ft length would be 0.008Ω, 1" would be 0.001Ω.

I see our posts crossed. In which case a Lucas 35 amp fuse (17 AMPS CONTINUOUS / 35 AMP SURGE) would use 23swg wire and have a modern fuse rating of 17amps; wire would be 0.574mm in diameter with a resistance of 0.002Ω/inch. This one would work for you Carsten:

It seems American and British ratings are different. They work on 'continuous load' and we work on 'blow rating'. Probably a good idea not to use US manufactured fuses in British classic cars then! Thanks for pointing that out Christopher - I never realised the difference.

[christopher storey]

David : sorry, I have amended my post several times, and I hope this will not cause confusion . Thank you also for the specific resistances - no wonder I could not read the fuse resistance with any accuracy !

[cactusman]

The fuse wire is still easily found. Frankly 30 amp or 35 amp really makes no difference. I very much doubt any original Lucas fuse would fail at precisely 30 amps and in any case A fuse will carry its rated current for many hours and requires several times it rated current to fail promptly.

Car fuses are far from precision items so 30 amp wire would do just fine. Fuses 1 and 2 run the main lights and I fit a 35 amp. Fuse 3 does the horn and again fit a 35 amp fuse. Fuse 4 runs the fuel pump and I fit a 5 amp here. Fuse 5 runs the side lights, panel lights and rear lights. 15 amps is fine. Fuse 6 does the screen washer, horn relay, brake lights and cooling fan. 20 amps would be fine. Fuse 7 runs the instruments and wipers, the reverse light and the indicators. 20 amps is fine. Fuse 8 does the interior lights and cigar lighter and also flashes main beam. So 20 amps is really fine. All these are for a series 1 3.8 so later cars may differ.

[cactusman]

If anyone wants glass fuses in all sorts of ratings up to 25 amp then Rapid Electronics sell packs of 10 (same rating) for around ?2 for all except the very low fuse rating... either quick blow up to 16 amp or time lag up to 25 amp ( 25 amp time lag would be good for head lights and the horn). Get a pack of 5, 10, 16, 20 and ,25 and you are sorted. Better quality than any fuse from a motor factor and cheaper too!

[Heuer]

One of the more practical aspects of owning an E-Type is its simplicity. All, bar one 50A fuse, are 35A rating (17A continuous) so spares are easy to replace even in the dark. They are there to protect the wiring which is rated at 17A or above continuous which means there is no need to mess about with a range of different fuses. The fuse holders even have storage capacity for spare fuses so simply buy a bag of the 35A ones (plus a 50A one) from SNGB and leave them in the holder.

Carsten - you could indeed use the mains style fuse wire that is available on the cards as long as you use the right one. Simply a matter of measuring the diameter of the wire. If the wire is ~0.5mm it will have a fusing current of 30A, 17A continuous. It will be the wire marked as 15A on the card. I just measured it.


Good luck and let us know how you get on.

[cactusman]

Not strictly true about just two fuse values as 3.8 cars have the fuel pump fused at five amps. The 4.2 litre cars have no fuse for the fuel pump. Folly in my view but there we go.

Yes. You can stick 35 amp fuses in most places. Personally I would prefer to use a lower value where it is sensible to do so to ensure the fuse fails as rapidly as poss in case of a short.

Electrical fires are rapid and spectacular and reduce your car to ash in minutes and given the less than easy access to the fuses in an E type, manually pulling one if smoke appears somewhere it should not is far from easy. Err on the side of caution and reduce the fuse value if you can. Each 12 watts of load uses an amp. Then double just in case. So two 60 watt head light bulbs. 120 watts. Or 10 amps. Really a 17 amp continuous is more than sufficient even allowing for the surge at switch on. Only the head lights horn and cooling fan are likely to pull currents above 10 amps. Hence in my view wise to reduce others where possible for increase safety margins. Pretty empirical but good enough unless you want to calculate circuit resistances and fault currents. Life is too short for that!

I would also recommend the battery be isolated (negative lead) with a proprietary switch or removable screw when unattended. A fused bridge across the isolator at 3 amps is more than enough to keep a clock running and the courtesy lights operational but will instantly fail should something untoward happen while you are not around. They can be had for a few pounds off the internet. Take five mins to fit.
Just my thoughts really as I suspect Jag kept the fuses mostly the same for parts simplicity and not for sound electrical engineering reasons!

[Heuer]

My point is the fuses are ultimately there to protect the wiring which itself is rated higher than the fuse. About the only thing that will cause an overload is a direct short to earth which will kill the fuse before the wiring. The fire risk is the wiring not the component. In fact this happened to me last Thursday when my wife and I decided to head to Wetwang for some superb fish 'n chips from Harpers, a round trip of about 200 miles. We were almost there and I was waiting to turn right when the engine abruptly cut-out. We pushed the car to the side and I suspected the fuel pump but it was working OK. I then noticed the choke light was off and the indicators were not working properly so I checked the fuses. Lo and behold it was a 35A Fuse #7 which also had the ignition on it. I guessed it was the indicator can that was the problem so decided to replace the fuse and continue on our pilgrimage without using the indicators for the rest of the day.

Checked the indicator can on my return and sure enough it had failed and shorted to earth.


It was an evetful shake down day. Also had a leaking hose (clip needed tightening) and a water temp gauge that went up to 70c and then began to gradually descend back to zero (loose spade connector on temp sensor). Hopefully that's my three for the season!

[cactusman]

Nasty!! At least the fuse went. Hope the fish and chips were good?

Fuses......so deceptively simple a device.
As you say. They are there to protect the wiring and not the load. Trouble is that to effectively protect they need to fail fast and to fail fast they need a big overload and to do that the intrinsic resistance of the circuit must be low at its farthest point to ensure a high short current and rapid fail. With just 12 volts nominal the resistance of the cable and not just its current carry can be significant. I measured the resistance from the brake switch to the farthest bulb holder on my car using a precision fluke meter with the test lead resistance removed. 0.21 ohms. Add to that the resistance from the battery to the fuse to the switch and you are probably at almost twice that accounting for contact resistance etc. So a short in the boot would cause about 28.5 amps and maybe a bit more to flow assuming a good solid short. Not really enough in my humble opinion. A 35 amp fuse would fail...eventually. Just an example and obviously brake lights are not permanently live but within reason it makes sense to me to have a fuse that is high enough not to fail without reason but low enough that it will fail pronto in case of fault. For some circuits a 35 amp or 17 amp continuous is really higher than is desirable in my view.

[Duckham]

Some time ago I had a puzzling electrical problem. It turned out to be a fuse that would pass enough current to fool a multimeter but as soon as a few amps were going through it would fail. When I looked at it carefully I could see the crack in the conductor - as it heated up it they must have been flicking sideways to cause a gap.
That caused me to think about fuses for the first time ever and a googling session told me that like most subjects it is a lot more complicated than I ever imagined!

Among others I remember heat dissipation is a factor in fuse design.
A 1A fuse will fail correctly in still air but if cooled (blow air with a fan or an accidental heat sink) it may never blow at that current.
So I wonder if the carded fuse wire is designed for a lot of still-air dissipation but when put inside a glass cylinder will actually blow at a much lower current as the heat builds more?

I can't imagine it matters in the real world but it is interesting to speculate.

Joe

[cactusman]

Indeed Joe. You are quite right....a simple piece of wire yet it's operation is actually very complex. Hence the vast array of fuses. Slow blow, quick blow, anti surge, time delay. Arc suppressed....the list is very long. The humble glass fuse with its piece of wire is not as simple as one assumes. My advice would be choose a good quality fuse with the wire welded to the end caps.....many a car fuse just has the wire folded over the tube ends and then the cap friction fitted...and dimension the fuse appropriate to both the current capacity of the wire and the expected load present in the circuit.