adequate charging for a B40?

[chaz]

with the engine on a reasonably fast tick over Im getting 11.8v returning to the battery. I know on modern bikes Im looking for 13.8v with lights on no difference. as the generator is of unknown vintage I suppose 11.8v isnt bad. probably wont get much better without spending more.

[spaceman]

I assume we are talking about a 12V battery with Zener diode regulator?? If so, the minimum battery voltage you want to see is 12.6V and, with no load and high engine revs, this should go up to about 14.5V.

[chaz]

to clarify
home made loom, H4 bulb headlamp, led rear light, conventional rear brake switch, standard horn, standard 12v generator and rotor, Wassell electronic ignition, 12v coil, Japanese (Honda or Suzuki) CDI, 12v battery.

no zenner, I would think 14.8 isnt possible unless coils and magnets are in as new condition. its not very often that I get to see over 14v on modern Japanese bikes.

[spaceman]

I'm not sure what an alternator made for 6V will give on a B40 12V conversion and how many volts it would push out via an old fashioned rectifier - maybe, it won't get to the ideal 14.5V charging voltage.

If would be useful to know what the battery voltage is with everything turned off - if it was 11.6V then the battery is either in a heavily discharged state or has reached the end of its life. It needs to start off with at least 12.6V and, if this is the case, and it then drops to 11.6V with the engine revved then it would mean that, rather than being charged, it is being discharged - in other words, more current is being drawn from it than the alternator and rectifier is providing.

You didn't mention whether or not the H4 headlight bulb was on when you were getting 11.6V but that would probably draw more current than the generator is capable of providing if it is the original B40 6V unit.

[Colin SS90]

You could fit a LED headlight bulb which uses around 8 watts which is a lot less than the 55 watts that a H4 bulb uses. Gives the charging system a much easier life if you want to ride with lights on. Not cheap, but cheaper than renewing alternator.
I run an Electrex World charging system and found that at low revs the standard 55 watt headlight bulb caused a slight discharge of the battery, so I fitted a LED bulb. This means that I can plod along with the lights on without flattening the battery, and yes, I am aware that the Electrex World ignition system runs independently of battery condition.

[DAVE BRADY]

Hi,

I remember reading something about 6v to 12v with then same alternator and found this.

Dave.

[chaz]

wont be doing any more changes as bike probably wont get ridden, at least not at night. too busy!!
its got a 12v generator, the twin wired version Lucas. its what the bike had when I got it. the H4 is a new headlamp unit so wont get changed either. Flat track bikes dont normally run lights!!
the battery is a new Yuasa YTX9. 8ah sealed one.

[Mike40M]

My B40WD has more than 12.5V at tickover without lights on. On moderate revs it gives more than 13.8 V with lights on.  It's fitted with an A REG ONE rectifier/regulator. Surprises both me and Paul Goff that the old alternator is in so good condition. In my experience the Lucas alternators rarely charge the battery at tickover.