G12 csr voltage

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Peteg
Posts: 32
Joined: Tue Jul 11, 2017 9:00 pm
Location: YORKSHIRE UK

G12 csr voltage

Post by Peteg »

Hi
I have recently bought a g12 csr 1963? none runner and on stripping found a 12volt headlamp bulb and a 6 volt tail lamp it has magneto ignition and alternator power supply there was no battery fitted can some one tell me which is the correct voltage
Thanks
alanengineer
Member
Posts: 1175
Joined: Wed Oct 12, 2005 10:45 pm
Location: KENT UK

Re: G12 csr voltage

Post by alanengineer »

I didnt notice a thank you for the efforts of others from your previous enquiry. Do you think this forum is just for your benefit.
alanengineer
Member
Posts: 1175
Joined: Wed Oct 12, 2005 10:45 pm
Location: KENT UK

Re: G12 csr voltage

Post by alanengineer »

ps.

welcome to the club. Loads of free help normally available
Groily
Member
Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: G12 csr voltage

Post by Groily »

Originally 6v but it's v easy to run at 12 nowadays if you want to (which I and many others do). Probably the best way is by using a combined regulator/rectifier unit, such as an A Reg 1 from Paul Goff, but a zener diode is another way, and there are various other vendors of suitable regulators.
Wiring changes are not hard, but if the alternator is the original it will need two of its leads splicing together to send all power to the regulator (and none via the switch). If it's a more recent 12v single phase one, there won't be three leads, just two and it's dead simple. If (not all that likely I wouldn't think) the PO has fitted a 3 phase unit, though, more wires and slightly fewer choices of regulator I think.
Plenty of info available on here, and if you do some wandering round on the the web.
Original Lucas wiring diagrams for various alternator models are available in lots of places - here's one: http://www.brightsparkmagnetos.com/libr ... agrams.pdf
User avatar
1608
Member
Posts: 2493
Joined: Mon Oct 05, 2009 1:00 am
Location: ESSEX UK

Re: G12 csr voltage

Post by 1608 »

I feel a previous answer to this post was just a little disingenuous, considering that the replies to the previous post referred to were mostly muppet based. Give the bloke ( a member ) chance.
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: G12 csr voltage

Post by Rob Harknett »

Wonder what other items are 6 or 12 v.? pilot and speedo bulb, horn although most still chance a 6 v.
Peteg
Posts: 32
Joined: Tue Jul 11, 2017 9:00 pm
Location: YORKSHIRE UK

Re: G12 csr voltage

Post by Peteg »

Hi Bill
Thanks for the info.just wondered if there's Any way of telling what voltage it's set up for.😀
Alan
Feel free to ignore any requests for help from myself.😡
Groily
Member
Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: G12 csr voltage

Post by Groily »

If there's a rectifier, and no zener diode nor modern regulator lurking somewhere, then it's set for 6 - and one alternator stator lead probably goes to the headlight switch and two others to a rectifier. Things get messed up a bit through the patchwork & piecemeal wiring efforts of owners over the years, but the presence of a simple rectifier would be a big clue.

In reality, it probably doesn't matter much what's there if you don't have a battery and are going to need to go over the wiring anyway - you can choose what suits you best. I like 12 because i) bulbs are easier, ii) there are half the amps floating around, iii) you don't have to worry about any AC wiring at the switch and iv) I like the modern regulator/rectifier boxes that are available. But you can have iv) at 6v too, as the parts also exist.

With a magneto, all the stuff about 'Emergency Ignition' powered directly from the alternator, which matters sometimes to folk with battery/coil igniton, is irrelevant.

Mag & Alternator is, in many people's opinion, the best option on bikes of the day. I like it anyway.
Peteg
Posts: 32
Joined: Tue Jul 11, 2017 9:00 pm
Location: YORKSHIRE UK

Re: G12 csr voltage

Post by Peteg »

Hi Bill
As you say the wiring is a bit of a mess and will require replacing but there is a zener diode and regulator and only two wires from alternator.the rotor measures 76mm so am I right in thinking this is reasonably new type.
Cheers
Groily
Member
Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: G12 csr voltage

Post by Groily »

Not sure about rotor dimensions as a proof of anything Peteg, but it's been running at 12v for sure with the zener (and the 2 wires off the stator tend to support that).

A Zener diode can be good and can last for a long long time - but it does need the heat sink it should be mounted on to dissipate (as heat) all the lectrickery that isn't being used. With mag ignition, that's most of it except when the headlight is on. Permanent magnet alternators chuck out all their juice all the time unless a pair or more of the coils are suppressed (which was the pre-regulator/pre-zener 6v ac-system way of managing loads and not frying batteries).

Not sure what the actual ratings of old zeners are in terms of what they can get rid of continuously, especially if perchance the alternator is an uprated one. On my only machine with a zener and a mag I run with lights on just in case the zener might cook or the battery overcharge!

Best option, just my humble, is to drop the zener and rectifier that's there for an A Reg 1 (or Podtronics, more ££) box connected to the two wires off the stator, with the dc feed to switch/ammeter/battery, and the simplest wiring imaginable. If no flashers fitted, but with horn and brake light, you can get things down to not far off a dozen wires all in, plus a fuse or two if one is wise!.
Cheers!
Locked