Honda 6v coils

[jjc839]

Hi all,

Just finishing up the restoration of a '78 CB125T. This bike has a 6v system, 3 phase alternator and regulator rectifier. The RR is shot, and a 6v replacement looks near impossible to find. I'm thinking this is a good time to switch to 12v, since 12v 6 wire RR's are a dime a dozen.

I know I have to change the RR, battery and lights, but since the 6v coils are in good shape, can I run a resistor in line and keep the 6 volt coils? The resistance of the primary windings on each coil are 3.2 ohms. If I run a 3 ohm 50 watt resistor in line, will this work?

Thanks for any advice.

[cb1rocket]

Loads of 6v RR on ebay. The generator will be more than 6v anyway. So you could simply wire in a 12v rr easily enough. No need to mess with resistors as the 6v coil works on it own, although i stand to be corrected.
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[jjc839]

Thanks for the reply. Problem is, I don't think the coils 'act on their own'. There is a 6v ignition wire that runs to the coils, that excites the field for starting. It's a kick-start only bike, but it requires a battery for spark.

Unless I'm missing something obvious, I don't see why I can't just put in a 2.5 - 3 ohm resistor in the 50w range and call it good. Seems too easy!!

[stinkwheel]

First hit on google for "6v 3 phase regulator rectifier"

https://www.rexs-speedshop.com/epages/es143131.sf/en_GB/?ObjectPath=/Shops/es143131/Products/RR12V-8
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jjc839]

Cheers, but that's a 5 wire 12v.

[stinkwheel]

[stinkwheel]

Actually, thinking about it. I don't see what would be wrong with using a standard zennor-based 12v reg/rec then adding a 6v voltage regulator.

The reg/rec will still rectify the alternator output and will regulate output down to 12v. The 6v regulator will then regulate anything between 6 and 12v.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Teflon-Mike]

Curiousely I dont have the book readily to hand, BUT, all the other CB125's, CD's & CM's have a independent 'self-exited' ignition..

Three windings in the magneto aren't neceserily three 'phases'; one coil is dedicated to the sparks, then other two, get 'regulated' for charge & lights. & on your bike, I believe it's "AC-Direct" lighting, fed from one of the two 'spare' windings, other providing charge through a big zenner diode, which just clips the -ve pulses off the waves, rather than inverting them for full-wave rectification & clips voltage of +v pulses at 6v... the head-lamp switch back-feeding current from the AC lighting circuit to the Zenner in the lights 'off' position, or the circuit bridged, so that th charge * light coils feed the zenner, but lighting circuit takes direct unregulated current off one winding....

Various perms on the arrangement; hence would need book to check....

The 6v CD 200 Benley, I believe has a full-wave rectified charge circuit, but ISTR still runs AC-Direct lights... I have a CD200 loom knocking about some-where & definitely has full wave reg/rect on it,

ANYWAY... obvious 'solution' to 12-volting a 6v CB125 Twin Engine..... use the 12v system from later 125 Super-Dream!

Cases bolt for bolt interchangeable on the mag-side, and have the twin pick-ups needed for 180 timed sparks; use Super-Dream CDI's & Coils & you get the beefier & more reliable points-less CDI ignition. You would need the Super-Dream Rotor to 'match' and the 12v Super-Deam Reg-Rect; but system would work pretty much as per the book.. just not for that bike! Only niggle is that the later S-D mag-casing isn't so 'period' to the rest of the bike.

Hybridising the T's 6v system? I haven't done it to a 6v Benley, I have to confess... Super-Dream cases & wiring looms are too many a penny round here to be bothered! But I did 12v the 6v Yamaha.

Most 6v systems are as described; three windings in the mag; one for the sparks, one for the lights, one for the battery, with simple zenner regulation.

So the sparks circuit can be ignored; you'll often get a healthy 13+v 'peak' off the charge & lighting coils at slightly higer than idle revs, though, SO, you 'may'.. feed both lighting and charge windings into a Honda C50 or pit-bike 'four-wire' regulator, (lights, charge, earth & reglated +ve feed) which can be picked up off the bay for about a tenner... that's the cheap bit...... and easy enough to wire in.

Wiring ought to be 'good' for 12v, as P=IV, so for the same wattage, going 12v halves the amps, which is handy.... BUT, if you have AC-Direct lighting, you need to sort out the feed and switching so that its takng regulated current off the battery, and not back-feeding regulated current back to the regulator through the AC 'bridge' ... this is where it can start to get expensive or difficult, buying appropriate switch clusters or trying to mod the ones you have.....

THEN.. you need a 12v battery... the same size to fit in original battery box.... A-N-D... a whole new set of 12v bulbs... head-lamp, tail-lamp, indicators, warning-lamps & back-lights n the clocks etc.... indicator flasher unit will need switching out for a 12v item, then the horn.... an I think you may be OK, not having an electric boot and having to worry about the starter solenoid or starter motor!

CAN be 'done'.. but knock-on's to the deal start to compound, and to avoid the 'ugly' non-orignal Super-Dream mag-casing, you get lots of alternatve 'ugly' not original 'features', like the switches.. and possiby the head-lams, where gettig a 12v ulb in the same fitting as an old 6 may beg changing the head-lamp for one that takes a 'standard' H5 bulb!

On the Yamie I did, there was no electrics bar the ignition to start with worth the keeping, so it was all going to have to be bought in anyway; & once 'done', it was a definte improvement over most 6v systems... BUT.. generator out-put was marginal, and I would't have wanted to try running it as an every-day rider through the winter & expecting the battery to stay charged 'just' on the out-put of the magneto with the lights in almost constant use! And I had made savigs there, LED-ing the indies & tail and clocks, and using a 35W HID head-lamp for max lighting... THAT was pretty impressive for a light-weight, I'll confess, BUT, big chunk of the difference accounted for not by the 12v conversion, or even the high-out-put HID bulb, but simply having a brand new, and actually shiny reflector behind it, and a similarly new, clear, un-etched, ad accurately moulded lens in front

However... cutting to the chase... all things is possible, with a little ow-how, a little ingenuity and the wiring diagrams i the back of the Pains Manual.... BUT.....

For the sake of finding the correct 'bit' you need, or suitable like-for-like substitute; and if needs be, paying the apparently exorbitant price that may be asked to get it..... this idea is one that is likely to MAKE you a heck of a lot more problems than it's likely to solve..... believe me!

Actually should have checked this first, but CSML.... CB125T, Regulator, Part No; 31600399008 .. Only niggle is 270Euro price tag, but they have them on the shelf ready to ship..... Dave Silvers are often more sensible, but they day 'discontinued'..

Where-Used cross ref to see what else it's used on chucked up nowt on CMSL. but then they didn't list any of the CD Benleys of any capacity... which I suspect the 6v variants use the same part on.....

But if the CMSL price of OE replacement is too exhorbitant; then, be down to suck-it-and-see 2nd hand regulators of the bay or from breakers, and hping one suits, possibly with ust a little splicing to match the wiring loom's plug for it.... OR, given that its reletively simple electronics.. simple Bridge circuit with four high amp diodes and a smoothing capacitor..... I'd be tempted to get handy with the soldering iron and some power diodes from RS spares on a hobby-board from maplins, and an old Computer heat-sink, if I couldn't burn the 'old' gubbins out the original and fit in the new.

Few resources on DIY regulators on the Net, for part codes and component selection, as well as tracking diagrams... chap at work used to what he called 'bread-board' reg/rects for folk in his lunch-break, like that, without even the hobby-board, just loose cable soldered direct to the diode legs, after ans were soldered to the old reg casing!

Its all skinning cats, my friend, BUT.. my 4-penneth for what its worth.... yours is not the way I would go about the problem.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'