Small CC Honda - Converting from 6v to 12v...

Hey all,

Seeing the jump in the little honda's of late and given our numbers are getting stronger, I wanted to create a one-stop thread for modernising the charging system.
Problem is, I've got some gaping knowledge gaps with the whole thing, but that phase of my build is fast approaching.

My CB125, for example, uses a sealed beam 6v headlight, 6v bulbs, and a 6v coil. It charges from 500rpm according to literature, and uses the old selenium rectifier but no regulator.

From my understanding, converting to 12v in this case just needs all bulbs, coils, and battery changed to a 12v item. The use of a 12v regulator/rectifier such as the radioshack job in the $50 thread seems perfect too.

Have I got anything wrong so far?

Below is the schematic for an SL125 - most small CC 6v hondas will be the same.


First question I have is, how many Ah should a 12v battery have to run in this system?

S, My 1st thought would be if stator had enough output to support a 12v system. luck G

I have an 82 125s with electronic ignition,,,,,,,,,,,,,,,,6V the bike might barely exceed the head light at speed(74 mph..of a cliff,,no rider),,,spend the $ on a better carb, the stock keihin is junk

I've got a 75 CB125s seems to go alright with the 6V, however can't get a spark at the moment so I spose you shouldn't listen to me!

I was always told that I'd have to change the flasher relay, points, condenser, coil, bulbs, rectifier and battery and couldn't ever be bothered doing it.

Which model do you have?

JD

I don't want to discourage you, but the 6v stator probably doesn't put out enough juice to charge the 12v battery; especially if the bike didn't have a regulator stock. to convert to 12v you'd have to change all the bulbs, the coils, condenser, flasher relay, regulator/rectifier, battery, and electric starter & solenoid if so equipped.

If the stator doesn't put out enough juice it will have to be rewound. If the bike is running and you have a volt/ohm meter I can help you test how much it puts out.

Also the 'Radio Shack' rectifier from the $50 mod thread is not a magic bullet. It is not always the best rectifier for the job and most certainly IS NOT a voltage regulator. don't get me wrong I put a new silicon rectifier on every bike I wire; they are much better then the old selenium ones. The particular rectifier mentioned in that thread works great in any application where the alternator puts out single phase and either the bike never needed a regulator or you install a new regulator to match. These rectifiers are available in any configuration you could ever need on a motorcycle and are comparably priced to the RS one.

If you do decide to go forward with this I'd love to help you out.

Edit: After looking at your diagram the RS rectifier will work fine for you, but your bike never had a regulator so it probably has a weak alternator.

Mr evinude hit the nail on the head 8)