Excuse my bad memory, but where can the fuse for my M20 best be placed: in the "-" lead or the "+" lead
Or perhaps in both leads

email (option): viaconsu [at] planet [dot] nl

It depends if you're running -ve or +ve earth, Hans...

Assuming normal -ve earth , then fuse in the battery +ve.

email (option): 79x100(at)gmail.com

When we do a rewire we put in 3 fuses.
Both sides of the battery and on the feed wire from the regulator to the switch.
The logic behind this is a start insie the headlamp shell will do alot of damage to the wiring and depending upon how well the regulator is working, the dynamo which will see a very heavy load an go to full power mode till the solder melts or the regulator packs it in.

email (option): wariron@tpg,com,au

Only girly men use fuses! If it's wired correctly who needs them?

That's a very manly thing to do Douglas
I'm sure all the bikes are wired correctly when being used. The problem is when wires get older and rub on metal or electrical components fail, creating a dead short. I've seen wiring looms melt, and trying to get a battery off with the wires melting isn't much fun.

email (option): horror@blueyonder.co.uk

Yes men were men when they made these bikes without fuses!

And I have seen more than 1 bike burned because of a short in the headlamp shell setting fire to "foreign" objects that the owners kept inside the headlamp.
This is of course on the extreme end. however a badly burned hand from trying to rip a red hot wire with melted insulation off the battery is fairly common as is a paint job ruined from globs of molten insulation.

Of course if you are using cloth over clay wires then no problem, the wires will eventually melt and loose contact and all it will cost is a £ 30.00 battery and some new £ 2.50 / foot wire.
OTOH a 50p fuse if nothing else is a lot lot cheaper.

PS most of my fuses end up being donated to modern bikes on club runs, Usually forgotten about then I spend hours wondering why the candle in the headlamp is not glowing.

email (option): wariron@tpg,com,au

email (option): Grumpy.moran@gmail.com

Hi Hans,

It does not matter if you fit the fuse on the main (+) or (-) lead to the battery,
Or if your system is negative or positive body. what goes out from (+) returns to the (-)

[Actually, it is really the other way round, but that doesn't matter now...]

In every electrical system, the current (I) is equal in every point you will measure it along the mail line,
Just like the flow is equal in every point you probe in a working water line.
(Of course, it would be lower at the "branches" - to bulbs and so on)

If you would like to protect one of the branches especially, and not wait
For the rated value of the only main fuse to be reached before it blows,
As the main fuse should be some 20% over the maximum normal current consumption,
So it does not blow at every normal current spike, like when turning on the lights,
You can fit a smaller / lower rated fuse to a particular branch you wish to protect,
Such as light/s, regulator feed or outlet, and so on

Noam

email (option): noam10@gmail.com

Noam can you remind us. What would be the normal fuse rate for our 6 volt bike systems.

Ron

email (option): ronpier@talk21.com

There is even more need for fuses in this day and age, you may have used immaculately soldered joints and the best wire you can get your hands on, but don't forget that your switch is 70 years old and may not make as good a contact as it did originally, so it's easier to get a dead short on the switch than you think. I always fit one but just one of the new blade type ones and I sit it in the battery box. The reason I use a blade type one is because you can make a better connection as most of the glass type fuse holders are a little bit cheap and nasty and also how many petrol stations sell glass fuses compared to flat blade ones?

email (option): davmax@ntlworld.com

Hi Ron,

The formula is P(Watt)=I(Amp) x V(Volt)

So I(Current in Amps)=P(Watts) / V(Volts)

For example-
If you use a 6V system, then 6Watt Bulb would take 1Amp,(6W/6V)
Whilst on 12V system it would take only 1/2 Amp (6W/12V)

So it is very easy to calculate the Amp for the fuse, according to your system:

For example:

5 Watt tail light
+21 Watt brake light
+18 Watt headlamp (We do not calculate the low cause it is not working with the normal or high beam)
So the total is 44Watt.
44W/6V (For 6V system) is 7.34 Amp, so I would use a 10A fuse here.

There is a reason I did not include the horn:
The horn, at peak, can take as mush as the entire system, or close to it,
So I do not think it would be wise to install a 15A fuse just because of the horn..
I think it will make the fuse miss its cause, if one would have to wait
For a 15A short circuit in order for fuse to blow..

I would leave it with no fuse, and connect the feed line of the horn
Directly to the battery, OR install a 5A fuse just for the horn,
Again, to a separate line to the battery, not via the other (Lights) fuse.

Anyway, if one has another rating for the headlamp,
Or using LED lamps with almost no current consumption, or has a sidecar lamp,
Just add all into the formula, and you are done !

Of course, put the next amp rating of fuse available.
~7A max consumption > 10A fuse.
~12A max consumption > 10A fuse and so on..

Cheers,
Noam.

email (option): noam10@gmail.com

Thanks Noam. Based on your formula, a 10 amp fuse it is.

Ron

email (option): ronpier@talk21.com

My pleasure, Ron.

By the way,
Now I see that I had a mistake in my last example.
I meant ~12A > 15A fuse, and not 10A as I wrote,
But I cannot edit anymore...

Good luck!
Noam.

email (option): noam10@gmail.com

Noted. Cheers Noam.

Ron

email (option): ronpier@talk21.com

Is this something for an entry in the Technical Section: "Fuses"

email (option): viaconsu [at] planet [dot] nl

Hi Hans,

The rumour goes that your BSA is for sale, is it really?

Henk

email (option): ahum@quicknet.nl

Not yet

email (option): viaconsu [at] planet [dot] nl

Good to hear that

email (option): ahum@quicknet.nl