I am wrapping up a '57 model 77 restoration & would like to run a fuse to protect the electrical system. I have converted to 12 volts, positive ground, electronic voltage regulator, newly rebuilt generator, no electric starter. Would 10amp be appropriate? Because of positive ground, I assume the fuse goes to the negative battery lead?
Thanks,
Skip Brolund USA
I would use a 35A fuse as…
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Fuses-As this question pop…
Fuses-As this question pops up quite often then perhaps a few rules might help. The best way to look at the fuse and its position is to realize what it is there for in the first place. It is there to stop all the energy in the battery being liberated at once through a short circuit, if this was to happen then wiring would get very hot-melt-catch alight! So you must Fuse one of the battery leads and make sure that all the battery electricity that is going into the bike goes through this fuse. It can be in the earth wire (Triumphs used to do this) but convention says that on the supply side of the battery is usual.
Now value-you need to cover all the needs of your bike with a little bit to spare. Head light? say about 4Amp, you can easily have both beams on 8A and then there is rear light and stop and horn 0.5A+2A+4A-say 15 amp now you need a little head room, as a head lamp when first switched on draws a little more current. So this case would be OK at 20 or 25A . Then you add ignition of 2A so now we are rushing up to 30A (35A is more readily available!)
Hope this helps Al Osborn
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Just to add to to Alan's…
Just to add to to Alan's message. You can get "Anti-Surge" fuses. These allow a momentary surge of current (around double the amperage) they will be less likely to blow when headlights are switched on when you have fuses that are not over large in current rating. The normal workingcurrent rating is the same as normal fuses. They only cost a touch more. Theyof the glass 20 or 25 mm type and you can buy a plastic bayonet type,in line holder for them. If positive earth, then I would choose the negative lead, but cannot see why the positive earth connection could not be used instead.
Les
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Thanks guys, that all help…
Thanks guys, that all helps. I assumed there was a particular amperage that was used from the factory, but mu original schematic does not show a fuse on the circuit. I did upgrade the headlamp bulb to a nice halogen 45/40 watt, pilot is a new LED, tail light is l
LED, speedometer is LED, ignition is from a Lucas Mag. I dont know the wattage on the LEDs but It's tiny.
I amfamiliarwith the "slo-blow" glass automotive fuses, instead of just a "element" it has what looks like a spring. I am considering the newer type automotive fuses (bayonet type) in case I am in need of a replacement fuse on the road, that type would be easier to find (although I would carry a spare).
I heard a rumor that someone makes aresettablecircuit breaker for thisapplication?
Skip Brolund
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Another fuse question, I r…
Another fuse question, I read somewhere that the way that fuses are rated is different in the USA than in England? Any body have thoughts on this?
Skip
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I found the American/Engli…
I found the American/English fuse article! Enjoy:
AutomotiveElectrical Fuses -- British Vs American(Tim Engelâs opinions â use at your own discretion)
British and American standards for rating electricalfuses are different. Both provide anâAmp Ratingâ for very similar looking fuses,but the two ratings mean very different things. The US system rates the fuse based on thecontinuous load it can handle for a specified period of time w/o blowing, whilst the British system expresses the loadat which the fuse will immediately blow.
Thatâs a significant difference! As an example, the 35 Amp fuse called out for many 1950âs/60âs/ 70âs vintage Britcars (Lotus Elan & Europa for sure) is roughly equivalent to a US-spec BUSSAGC 17 Amp fuse. Install a US 35Amp fuse into your LBC fuse box and the wiring harness will melt down beforethe fuse blows.
DO NOTuse a USA rated 35 amp fuse in your vintage British car!
The complete rating for the specified 35amp Lucas fuse isâ?
â17 AMPSCONTINUOUS / 35 AMP SURGEâ
Early British fuses were simply marked with thequick-blow rating, but later fuses aregiven two ratings in an effort to minimize the confusion. For instance, the 35 Amp fuse is often marked as â17 continuous/ 35 blowâ, or simply17/35. In that case, use the lower âcontinuousâ rating as the oneto which you try to match an AmericanBUSS fuse rating. Or, better yet, proper Britishfuses are available from your favorite independent Britcar / Lotus partsdealer. Purchase a supply and keep themin your Lotus' glove box.
The comparison/substitution looks something like this...
British Lucas Fuse ~American BUSS Fuse
Fast Blow DualRating ~ Continuous (AGC) Alternate Opinion (SFE ?)
50 amp 25/50amp ~ 25 amp 25 amp SFE
35amp 17/35 amp ~ 17 amp 20amp SFE
30 amp 15/30amp ~ 15 amp 15 amp SFE (too short ?)
25 amp 12/25amp ~ 12 amp 15 amp SFE (too short ?)
20 amp 10/20amp ~ 10 amp
15 amp7.5/15 amp ~8 amp
10 amp 5 /10 amp ~ 5 amp
5 amp 2.5 / 5 amp ~ _____ 3 amp
2 amp 1 / 2 amp ~ 1 amp
Unfortunately,thereâs no extra data marked on either the fuse body or on the packageto tip-off the user that the ratings are different. Itâs very important that USA owners ofBritish cars be aware of the issue and make wise choices when using USA fuses in them. The best choice is to make the effort tosource proper British fuses for your LBC.In an emergency, the loose Ruleof Thumb is to use a USA BUSS fuse with an Amp rating equal to no more thanone half of the British Lucas fuse rating.
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I would use a 35A fuse as fitted in the Commando, a 10A might leave you with too little tolerance. If it's positive earth then the fuse should be fitted to the negative terminal.
Cheers Paul.