Splitting up wiring with new fuse box - what fuses to use?

[tinweevil]

Perhaps somebody with a storage scope could measure this ?
Thanks,
Tony.

Nice work Tony. I can pop round with a picoscope sometime if you like? I'm in Woking these days.

[MIG Wielder]

Hi Julian, Thanks for that. Guess what I've got ! A storage scope ! Not state of the art but still a good bit of kit.
Yes, I know the Picoscope range. Amazing value for all the whizzy functions.
I'll do some measurements perhaps tomorrow on a Halogen set-up and a sealed beam set-up for comparison.
Cheers All,
Tony.

[Jon Tilson]

To add a further comment to this on contemporary cars that were wired up with a bit more effort than we got on Dollies

(Rover P6 and Stag) use a fuse box which pretty much separates all individual bits and peices and I think you get 10 x 1-A fuses
and a nice little labelled cover too....

So they could have done it properly..... They just chose not to bother.

Jonners

[Toledo Man]

You can blame the bean counters at BL trying to save a few pence here and there.

[GTS290N]

If there were a bit more space............

http://www.ebay.co.uk/itm/CIRCUIT-BREAK ... 1635208176

[tony g]

Circuit breaker blade fuses

http://www.ebay.co.uk/itm/Circuit-Break ... 2042887955

[Mahesh]

Circuit breaker blade fuses, been looking all over for them.,

Thanks Tony,

[GTS290N]

Circuit breaker blade fuses

http://www.ebay.co.uk/itm/Circuit-Break ... 2042887955

They are the dog's danglies, didn't know they existed.

[MIG Wielder]

I promised a couple of weeks ago that I'd have a look at the Dolomite headlamp peak current surge, having got the use of a storage scope.

Some results;

55W sealed beam outer unit.

Peak current = 35.2 A at 12.4 V
Drops by ~ 63.5% in 5mS ( Five thousandths of a second )
Drops to normal running current of 4.28A in 138mS ( Just over 1/10th second )
So multiply these numbers by 4 for main beam .
Potential Peak current = 140.8A
Running current = 17A for 4 main beam lights.

A 25A ATOF blade fuse would be fine here.

60W H4 Halogen bulb ( outer).

Peak current = 50.7 A at 12.4 V
Drops by ~ 63.5% in 9mS ( Nine thousandths of a second )
Drops to normal running current of 5.16A in 134mS ( Just over 1/10th second )
Again multiply these numbers by 4 for main beam .
Potential Peak current = 201 A
Running current = 20.5 A for 4 main beam lights.
A 30 A ATOF blade fuse would be fine here.

References: " Littlefuse ATOF data sheet.

If you would like some scope traces drop me a P.M. but I need to find out why the download isn't working yet.

The most interesting thing was the scope traces using different switches. If you use a small, low current switch there are lots of switch contact bounce each one being a make / break action and each time you get an arcy-sparky, so quite quickly the switch will burn out. I used a high current electric window-motor switch with large clunky contacts. This showed just 2 bounces of the switch contacts during the switching on sequence. This would be much more reliable. I'd like to try a Dolomite headlamp stalk switch sometime.
Moral. Definately use a relay !
Note that these peak currents were measured with thick, low resistance wiring. In practice the resistance of the wiring loom would limit these peak currents to something rather less.
HTH,
Tony.

[Jon Tilson]

Great work Tony and does indeed show the need of a relay....

I think the doly headlight switch has some sort of internal spring effort to minimise bounce but as we all know
the world's greatest switch it is most certainly not.....

Jonners

[Mahesh]

Those potential peaks are in the ranges that I did not envisage, more electrical work to feed my paranoia.