Author Topic: WD B40 Fuse  (Read 1099 times)

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DWS

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WD B40 Fuse
« on: 10 March, 2017, 09:04:31 »
Not being very clued up on electrics, I am trying to find out what fuse I should use on my WD B40, it has a Boyer electronic ignition and, being ex-RAF, is fitted with indicators.

A new wiring harness I bought has a 35 amp glass fuse (the amp rate is printed on blue paper inside the glass tube) however, I have read somewhere that a modern glass tube fuses of 35 amp 'blow' fuse is equivalent to a 17 amp 'continuous' fuse.

Can someone please explain all this please and recommend which fuse I should fit.   ???

Arthur

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Re: WD B40 Fuse
« Reply #1 on: 10 March, 2017, 09:19:42 »
You need to use the lowest fuse rating possible to give maximum protection to the wiring harness. Normally, on a 6V classic bike, 15/16A fuses should be ok with half that rating needed for a 12V system. The particular type of fuse used (glass, continental, blade etc) doesn't matter very much since you're basically just protecting the wiring harness from damage.

DWS

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Re: WD B40 Fuse
« Reply #2 on: 10 March, 2017, 10:38:56 »
Sorry for being 'electrically dumb' but when you say "..on a 6V classic bike, 15/16A fuses should be ok with half that rating needed for a 12V system..." what amp fuse should I use?

Bess

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Re: WD B40 Fuse
« Reply #3 on: 10 March, 2017, 13:15:16 »
Hi,

Try using this formula to calculate fuse ... Fuse Amps = Total Watts of equipment Voltage

As Arthur stated you are protecting the wiring so ensure the cable rating will be ok with the Watts consumed. Modern cables with more strands carry greater loads.

If the fuse is running close to max then it will heat, reducing its effectiveness hence blowing prematurely, glass fuses are delicate. I use automotive blade fuses as they are robust in situ.

Best wishes....

Arthur

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Re: WD B40 Fuse
« Reply #4 on: 10 March, 2017, 13:50:00 »
Sorry for being 'electrically dumb' but when you say "..on a 6V classic bike, 15/16A fuses should be ok with half that rating needed for a 12V system..." what amp fuse should I use?
I would go for 15A fuse whether it is a 6V or a 12V electrical system since it is basically protecting the wiring which is rated the same for both.

DWS

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Re: WD B40 Fuse
« Reply #5 on: 10 March, 2017, 14:14:33 »
Thanks for the responses,

I still have to wonder why the brand new WD B40 wiring harness I purchased recently from Burton Bike Bits has a 35 Amp fuse in it?

Bess

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Re: WD B40 Fuse
« Reply #6 on: 10 March, 2017, 15:15:14 »
Handlebar warmers? lol

My cals say they are giving you 420 available watts and using 10 gauge or 2.6mm cable, hope nothing develops a fault.

Best advice is to total your consumption in watts use the formula add 10% and select the nearest fuse.


Bess

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Re: WD B40 Fuse
« Reply #7 on: 10 March, 2017, 15:43:56 »
Hi,
      For 12 volt my calc gives:

Boyer ignition - 21 Watt max (that's at fault level)
Coil                 -50 Watt
Headlight        - 60/55 Watt max
Stop/Tail light -21/5 Watt
Indicators       - 23 Watt each
Pilot Lights     - 4 Watt x 2
Speedo/Rev    - 2.2 Watt each

Total max 194.4 Watts. Assume horn and stop light straight from battery without fuse.

194.4Watt/12volts = 16.2 amps.. Maybe


DWS

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Re: WD B40 Fuse
« Reply #8 on: 10 March, 2017, 15:46:14 »
You would think that someone like BBB would supply a harness for a specific motorcycle model to the correct specification?

DWS

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Re: WD B40 Fuse
« Reply #9 on: 10 March, 2017, 15:48:13 »
Hi,
      For 12 volt my calc gives:

Boyer ignition - 21 Watt max (that's at fault level)
Coil                 -50 Watt
Headlight        - 60/55 Watt max
Stop/Tail light -21/5 Watt
Indicators       - 23 Watt each
Pilot Lights     - 4 Watt x 2
Speedo/Rev    - 2.2 Watt each

Total max 194.4 Watts. Assume horn and stop light straight from battery without fuse.

194.4Watt/12volts = 16.2 amps.. Maybe

And don't forget the Blue Flashing Light!
 :)

Bess

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Re: WD B40 Fuse
« Reply #10 on: 10 March, 2017, 15:59:35 »
lol, yep forgot that...

I guess if it was a 6 volt system it equates to 32.3 amps. However, usually headlamp for a 6 volt is less and indicators are possibly not used.

STAR TWIN

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Re: WD B40 Fuse
« Reply #11 on: 18 March, 2017, 17:36:07 »
The fuse, as mentioned, is to stop wires burning out in the event of a short circuit. So a 35A glass fuse is OK for that. It's what I have in my bikes.
You can get all sophisticated and have fuses for various circuits and relays for the headlight for example but that's not how they came out of the factory.
As an indicator of electrical sophistication, my 1951 Land Rover has just one fuse. The workshop manual states that in event of fuses blowing, fit a higher rated fuse. Things have moved on since then.

DWS

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Re: WD B40 Fuse
« Reply #12 on: 18 March, 2017, 21:03:59 »
The fuse, as mentioned, is to stop wires burning out in the event of a short circuit. So a 35A glass fuse is OK for that. It's what I have in my bikes.
You can get all sophisticated and have fuses for various circuits and relays for the headlight for example but that's not how they came out of the factory.
As an indicator of electrical sophistication, my 1951 Land Rover has just one fuse. The workshop manual states that in event of fuses blowing, fit a higher rated fuse. Things have moved on since then.

Thanks for that Star Twin, I find it so annoying to be 'electrically challenged'  :)