Electrical fault

[Superarnie]

Happy New Year everyone.

Please could I seek some advice. Since I finished the restoration of my 1960 Spitfire Scrambler, I have noticed an electrical fault. During the restoration, I have fitted an accessories circuit including lights and horn and converted it to 12volts. (The dynamo has been reconditioned with a 12 volt armature).. The motorcycle has now got a small 12v battery which was necessary when I fitted a Thorsspark electronic ignition. I have noticed that when the ignition switch is turned on all the lights/horn/brake light work perfectly with no issues. I have that circuit protected by a small 5 amp fuse. When I kick the engine over and start it up, the accessories fuse blows. I'm wondering if it might be something linked to the dynamo. Could the yellow and green wires from the dynamo to the regulator be back to front? I'm not too clever with electrics!
Many thanks
Gary

[Klaus]

Hy Garry,
I guess your 5 Amp fuse is to small for this electrical circust. Your dynamo had now 12Volts and an output form 60 Watt are 5 Amps only for this. Do you start with lights on? Try at first a 10 Amp fuse and see what happened. All lights off, start and switch on the lights, do not forget to use the breake and horn, if this works all fine without stopping the ignition the fuse is ok. Otherwise try a 15 Amp and start this procedure again.

Cheers Klaus

[berger]

i seem to remember back in the day on my starfire something like 20amp continuous 35 amp blow, but don't put a 35 amp fuse in there or you might have a fry up

[Rex]

Think you'll find fusing and it's use on bikes has moved on a lot since those days mate.
Keep on upping the fuse rating (as suggested above) isn't the way to go either. Far better to find the fault that's causing the issues, and a Thorspark unit (assuming it's not faulty) isn't going to blow a 5A fuse by itself.

[groily]

Think you'll find fusing and it's use on bikes has moved on a lot since those days mate.
Keep on upping the fuse rating (as suggested above) isn't the way to go either. Far better to find the fault that's causing the issues, and a Thorspark unit (assuming it's not faulty) isn't going to blow a 5A fuse by itself.

Yes, I agree Rex. On the face of it it isn't logical that it would blow the fuse when running if it didn't blow when all loads were switched on with the engine off.
So I think there might be a problem over and above the inadequate fuse rating. (10A is usually good on 12v dynamo bikes, I go with that generally.)

You could check whether D and F are correct at the dynamo (even if they seem to be plugged into the right holes if you've got a plastic / bakelite cover on the end) by whipping the cover off and looking to see: should have D coming off one brush, possibly by way of a terminal blade or post on the brush-plate, and F should be similarly connected to one of the wires coming out of the guts of the dynamo through a hole in the plate. They should obvs go to D and F at the regulator.
However, reversing D and F by mistake won't normally blow a fuse - you just won't get a charge. You'd probably get uncontrolled charging though if there were any connection between D and F on the dynamo.

What does your ammeter tell you though? It should be your friend in this.

[Bsareg]

Could the dynamo rotation have be reversed when rebuilding ?

[Superarnie]

Thanks everyone for your contributions, very much appreciated.
The Thorspark ignition is on a separate fused loop and is not linked to the accessories loop which is again seperately fused.
I will go with a 10 amp fuse and if that blows, I will look closer at the dynamo/wiring setup. I reconditioned the dynamo myself and so know that the wires coming out of it are from the brush and the other is from the coil field. The yellow and green wires then run to a new DVR2 regulator. From the regulator I have one wire going to earth and one is a 12v feed.
My initial thoughts are to disconnect the 2 dynamo wires (I have fitted a weatherseal connector next to the dynamo) and see if the accessories fuse blows when i start the engine. If not blown, reconnect the 2 wires and see if it then blows. That way I think it helps point to a dynamo wiring issue. Do you folks agree with that approach?

[groily]

That sounds sensible to me.
We're assuming that you tucked the white wire on the DVR out of the way for 12v operation (ie didn't join it to brown)!
If the ignition circuit is separately fused, then it wasn't that that caused the fuse to blow.

Where exactly have you put your 5A fuse? Normally, you'd want the main battery cable(s) fused (being sure to cover the horn and brakelight) and one in the A line from the regulator. 10A is recommended there by the makers for 12v use (not everyone bothers with that, but we should).

If the feed (A) from the regulator to switch/ammeter IS going through the 5A fuse you've fitted , then it could well blow with the engine running when you switch on the lights. Because the current required to charge the battery on top of  the surge as you switch all the lights on (which takes a heavy initial current - probably double 'normal' demand - to get the filaments warm enough to light up) may well be too much for it. The dynamo is rated at a max 5A with the 12v windings but there are momentary spikes, which won't don't hurt it but might blow a too-small fuse.

So if that's where your fuse is, then it might be your only problem after all . . . Here's hoping!

[chaterlea25]

Hi All,
I believe most modern fuses are rated as blow rather than the old way when they were rated as continuous?
I think what's happening is that the dynamo is going to full charge and blowing the 5A fuse ?
When I separated the circuits on my SR I put a  fuse on the dynamo output , 
As mentioned I would first try a 10 A fuse

A few months ago the 10 A fuse on the A10 SR starter solenoid circuit popped  for no apparent reason, maybe a surge ?
I replaced it and All fine since.. The modern bike type solenoid do not take big current to operate unlike those used on car starters that have to engage the gear drive

John

[Triton Thrasher]

Start with the easy things.

5A is far too small as a main fuse.  Who recommended that?

15A or 20A are what people use successfully.

You want a fuse that will blow when there’s a short circuit and not at other times.

[Bsareg]

You can reverse dynamo rotation by accidentally swapping the field leads over. If all else fails, might be worth a check.

[JulianS]

The instructions which came with my DVR2 said 10 amp fuse between ammeter and battery for 12 volt circuit.

[muskrat]

G'day Fellas.
I know I'm not that bright (pun intended) when it comes to electricks.
The DVRII with the white wire not connected is to convert the 6v dynamo output to 12v. If the dynamo is converted to 12v would this cause any problems?
Cheers