12 volt conversion - G3 with alternator

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McMaz
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Joined: Tue Jun 02, 2015 4:57 pm
Location: Wales

12 volt conversion - G3 with alternator

Post by McMaz »

I'm restoring a 1962 350 short-stroke and am about to make a start on the electrics. Testing the stator shows that one set of windings is dead and it would seem that the rotor will be no longer fit for purpose after lying in a box of bits for many years. So I've decided to convert to a 12 volt setup with an AGM battery but leaving the points in place.

I've looked at the info/advice on the forum and elsewhere and just want to check that I'm right in believing that the following items are correct/suitable in order to carry out the conversion.

Lucas Stator - RM21 2 lead single phase 10 amp, LU47205
Lucas RM20 Rotor, LU54202299
Lucas 12 volt coil, LU45276
Single phase solid state rectifier regulator
12 volt AGM battery
Appropriately rated inline fuse situated immediately off the battery
Replace bulbs with 12v bulbs

Any corrections, reassurance or words of wisdom will be most welcome.
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kernow kid
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Joined: Wed Feb 14, 2007 3:55 pm
Location: CORNWALL UK

Re: 12 volt conversion - G3 with alternator

Post by kernow kid »

Hi Maz,
I did this conversion to Dads 59 16MS about twenty years ago, but we used a seperate rectifier and zener diode to regulate. It has been very reliable, but technology has moved on, so a combined rectifier/regulator would be good. If you look online for single phase rec/regs, there are lots available, some very cheap. Personally, Id stick to a UK supplier and one thats recognised in the classic bike world over a cheap Ebay/Amazon option. May cost a little more but you will have tech support and Id like to think improved reliability. Several companies offer these units, but I havent got first hand experience. Others have and hopefully they will pitch in with their experiences. I would say that you should take particular notice of the mounting instructions for any rec/reg , regarding air flow, heat dissipation, etc.
The new winding and rotor should be all good, but be careful when youve mounted the windings and rotor to try and check the clearance between the rotor and the windings to see that the rotor is central. Its not easy to do as the winding is mounted in the cover. Some owners have modified this by making up pillars to mount the winding on the back plate, allowing you to accurately centre the rotor in the middle of the winding, but its a bit of an engineering job.
Im not sure of the benefits of the AGM batteries...in theory they should put up with periods of no charge and survive and not leak, but they can be a bit fussy about the charging side. Ive used a Cyclon unit in the AJ that was actually second hand from a ride on lawn mower, and that worked very well for about ten years including periods of 4 or 5 months of inactivity, and put up with the relatively harsh charging that a zener offers.
If you like to keep the bike looking original, Vehicle Wiring Products offer a kit of the British crimps with the tool that will allow you to wire it all up with connectors the same as originally fitted, rather than red/blue/yellow pre-insulated that may or may not offend your eye!
Hope this helps.
Regards kk
Ohh! Regarding in line fuse, whilst not particularly original, Id go for an inline splashproof blade fuse holder. These are robust and securely hold a blade fuse that is readily available and have cover that presses over the fuse. Tucked in the toolbox it wont be on view.
Top tip - if it needs more than 2 bolts to hold it on, its probably important...
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kernow kid
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Joined: Wed Feb 14, 2007 3:55 pm
Location: CORNWALL UK

Re: 12 volt conversion - G3 with alternator

Post by kernow kid »

Just to add to your thoughts, you could actually fit a 3 phase rotor and winding and suitable rec/reg that would give you up to 200w of power for lots of light!
Dont forget the horn...you can use a 6v but it screeches and recent posts have raised concerns about a fire/overheating risk, but personally my AJ has survived for twenty years with a 6v squeaker!
Also I ve seen comments about fake Lucas parts, so again, a reputable supplier probably safest!
Regards kk
Top tip - if it needs more than 2 bolts to hold it on, its probably important...
McMaz
Posts: 48
Joined: Tue Jun 02, 2015 4:57 pm
Location: Wales

Re: 12 volt conversion - G3 with alternator

Post by McMaz »

kk – thank you, very helpful and informative – auto electrics are not a strong point of mine!

Re. 3 phase rotor and stator – just been doing some googling and from what I can gather the lucas RM24 LU47244 3 lead, 3 phase 14.5 amp stator in conjunction with the Lucas RM20 Rotor would be OK. Apparently 3 phase also gives better output at lower revs.

Do you know if the 3 leads from the RM24 stator would simply marry up with the existing original wiring loom without the need to modify anything with the lighting switch set up?

Sean
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kernow kid
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Joined: Wed Feb 14, 2007 3:55 pm
Location: CORNWALL UK

Re: 12 volt conversion - G3 with alternator

Post by kernow kid »

Hi Sean,
Yes, once the three phase output has gone through a three phase rec/reg, you've got two wires producing 12v but with the extra capacity, so it's only between the windings and rec/reg that you have any extra wires. The only other thought I had was about earthing. I'm pretty sure by 62 your bike was negative earth from the factory, but it's worth checking. Just see which terminal on the battery went to the frame. All modern vehicles are negative earth and it just makes life a bit easier if you buy modern parts to add to the bike, like LED lights, which are often polarity concious and neg earth ones much easier to source.
Regards Tony
Top tip - if it needs more than 2 bolts to hold it on, its probably important...
McMaz
Posts: 48
Joined: Tue Jun 02, 2015 4:57 pm
Location: Wales

Re: 12 volt conversion - G3 with alternator

Post by McMaz »

Hi Tony,
Checked the earth and it's still positive in 1962.
Re. info about the horn in your previous post – came across a tip to use disconnected original horn a dummy to keep bike looking original but install a 12v one hidden away.

Thanks again, Sean
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