Britbike forum Forums British motorcycles in general British motorcycles in general RM21 Alternator Wiring

I managed to damage the green yellow/ wire on the stretch from my alternator to the rectifier whilst trying to remove the harness tape. I have cut only two strands of the copper wire inside.

Could I leave this and put a bit of heatshrink on it ?

Or could I strip back the insulation slightly and run some solder over the damage and then use heat shrink?

Lastly I have some thinwall green/ yellow wire rated 16.5 amps with which I could replace it. Is this an adequate rating for this point?

Thanks

The 16.5amp thin wall is more than adequete. the standard RM21 is only about 10.5amp at total output.

Depending on where the break is along the wire, If its in a visible area after it has exited the crank case for example, I would fit some terminals and then wire upto the rectifier.

If you check the stator (and other harness) wires then you should find they contain 14 strands of 0.0108"/0.274mm copper wire (14/32 SWG) that has a rating of approximately 8 (8.3?) Amps.

The modern metric equivalent standard PVC is 14/0.30 (14 strands of 0.30mm diameter) 1 sq. mm., 8.75 Amp.

https://www.vehiclewiringproducts.co.uk/p-1020-8-75amp-1mm-sq-14-0-30

The thin wall wire which Dave already has at 16.5amp will be roughly the same total thickness of the 8.75 amp wiring. Since he already has it (and I assume in the correct colours) he isn't hurting anything by using it)

I agree. You posted as I was typing so I wasn't suggesting he use 14/0.30mm only that the original and modern equivalent amp rating was/is considerably lower than 16.5A (thin wall).

Thanks Allan and LAB. I suppose it would be most sensible to change the whole wire as you say that the new stuff is adequate for the job. It would be the stretch from the bullet connector under the engine to the rectifier.

I have now gathered my earth leads from the zener, rectifier, frame and headlamp,etc, to a common point at the mounting for the rectifier as suggested on R F Whatley's site. When it comes from going from this point to the battery via the 35a fuse is 16 amp wire ok? I could use two together. When the fuse was on the negative side the original single wire was ok.

Dave

Yes. The fuse must be the 35A blow (17.5A continuous) type and the 35A blow fuse is used with original 14/32 8A wiring.



The modern equivalent fuses (blade fuses etc.) are 15A or 20A as they are continuous rated.



The side of the battery the fuse is on makes no difference to the amp rating.

Thanks L.A.B.
I suppose it was a bit of a silly question as the current must be the same on both negative and positive sides of the battery. If the old negative wire has always taken it then the single 16 amp will certainly be ok.
Dave

If your putting a fresh fuse lead in (say a bladed type) these often come with a red wire attached. Feel safe putting this on the “earth” side fro my out common grounding point back to your battery. A 15amp fuse is
More than adequate for the most complex of wiring.

If you have a reg/Rec with inbuilt capacitor ie the Boyer power box, this will need fusing also between that and the next thing the wire touches.

You also won’t go far wrong with a 3amp fuse for you electronic ignition if you are fitting one of those. This will protect that unit at a lower amp rate without effecting other components which require more current draw.

Allan- Thanks. My fuse is a glass one with metal ends and a single wire inside marked 35 amp similar to the one in LAB's photo but without a continuous rating marked. Is this fuse ok? It is the type that has always been in there. I have noticed that the paper rating label inside has looked a bit scorched sometimes in the past but the fuse hasn't blown in normal use.

I will be re wiring my old original type fuse holder with the thin wall 16.5 amp wire. I have points, zener and one of those little square solid state rectifiers so I don't think I need any extra fuses.

Dave

Yes, but the fuse holder it uses is prone to faults so all of mine are now modern blade fuse holders. 15 amp fuse in a 3 phase equipped Commando worked even with 60W halogen bulb,

Not all 'Blow' rated fuses show the continuous rating, unfortunately.

https://www.vehiclewiringproducts.c...breakers/p-675-glass-cartridge-fuse-30mm


The fuse wire thickness should give you an idea if compared to a known 35A blow fuse. If in doubt, replace or change to a blade type fuse and holder as kommando says.

I respectfully disagree



Agreed. If it only has one value, then this will might be the continuous rating or the blow. If unsure, get one that says 15amp. If it pops when you turn the lights on then it’s either too small or more likely you have a short. 15amp is More than ample. As Kommando said with the rest of his comment.


Those glass fuse holders can work well for years then let you down at the last minute. (Mine failed just as I loaned the bike to a mate, not his fault
But the poor fellow got stranded) I switched to a blade immediately after.

Also if you get one with the red wiring (check the rating on the wires, no point if it’s got wiring capable of 5amp, that’ll fail before the fuse will.) it’ll fit happily on the return side and also cut down on bits of joined up wiring on the live side.

No, that wasn't what I said. A 1 1/4"/31mm glass fuse marked 35A can certainly be the blow rating.

The fuse rating can also be stamped on the metal end cap .

https://www.ebay.ie/itm/2x-35A-BLOW...-CAR-MOTOR-FUSE-6-3-x-31mm-/382856091018
"These 35A fuses are marked according to the modern Lucas regime (metric / post decimalisation) system whereby the marked rating is the BLOW rating and the continuous rating is half that marked (17/17.5A (Amp) CONTINUOUS)"

https://www.triumph-spares.co.uk/35-amp-glass-fuse-fuse35
https://rrsl.co.uk/product/fuse35a-1-1-4-glass-fuse-35a-blow/

Sorry buddy, I’ll amend that.

Changes in regulation don’t help, the ones you can pickup from almost any fuel station (least in the UK) will indicate the continuous rating. You may find some stated otherwise in such places. But again I’d Stick the 15 amp in and see if anything blows immediately.

I try and stress using the lower rating due to my own experiences. Having had a bike where the PO used a 35 amp (blade in this case) fuse.

old stock Lucas fuses used colour coded paper along with printed ratings .
the 17.5/35 A was white , ( the instantaneous blow rating was 40 amps )


if i was concerned with reliability i would not use an old fuse ... or old fuseholder .
.

Lots of good info from all about fuses. I hope mine is a blow at 35 with a continuous rating of half that. It does have a white label. Anyway, no damage done caused by the fuse but I had better get some more to make sure.

Dave