Battery advice required

5AH does sound a little light for your machine.  But even so, nominally 5Ah at 12 volts gives 60W for an hour. (Check your bulb wattage). 

Your problem sounds like you are depleting the voltage level below the threshold of the  "unknown"  electronic ignition operating range, then she dies.  They can be hungry things and certain types quite sensitive to voltage reduction.

Check your charge level and regulation.  As its non standard already then I would not hesitate in upgrading to a solid state voltage regulator as sold by AO services.

Cheers

J

Yes fit as many Ahr as you can get in the battery box to any of these bikes. 5Ahr is the Minimum. Initially do not blame the regulator, if there is a quantity issue (as there is here) then the alternator is to be investigated for Amps. (aoservices.co.uk has the answer). Along with battery charge voltage 14.4V (if you are lucky!) In this case the 5Ahr could be down to a couple.

To get to root of this problem please get in touch direct. aoservices.co.uk or Electrical on Tech Team.

In the Olden Days, when 6 volts was the norm, the old Lucas PUW7E battery was rated at 12Ah.  A 5Ah battery (the LVW5E) was only recommended for lightweights.  On that basis your battery is seriously underrated.  In any case the battery's capacity is only significant if the load is greater than the alternator's output.  Assuming that's not less than 60 watts at 2000rpm (I would expect more like 100 watts) then you should not need to drain the battery when running normal lighting.

Changing to an AGM battery won't make much difference if the alternator/rectifier system isn't sending enough charge to the battery.  It still needs to be a larger capacity.  Another aspect is that you should not discharge a lead-acid battery below about 50%, which means that a 5Ah battery only gives a usable 30W for an hour - if it's receiving no charge.  Not 60W as Jonathan Newton says.

Except adding weight. Three possible solutions to prolonged night riding.

1. Have charging enough for consumption. First find out how it's wired. Then find out if rotor and stator is ok. Then check rectifier and regulating. There is different ways how this is done. First thing to check.

2. Keep it at high revs. Low revs gives low alternator output. Might be impractical with modern speed limits and dense traffic.

3. Minimize consumption. If ignition is power hungry, replace with a less hungry or fit a magneto. Fit LED bulbs which consumes less. I'm told that there are now head lamp LED bulbs that gives reasonable light, consuming less. First generation which I tried had a lousy light pattern and was not good at night.

Have a BSA B40 with Boyer Mk4 ignition, a rec/reg from Al, probably a RM21 alternator, standard light bulbs, and a 5 Ah battery. To my surprise works well with lights on at moderate revs. Must have a good alternator!

Hi John,

I too have a non standard 650 - I call it a mongrel as it is of unknown parentage. 

When I got it around 24-25 years ago (hadn't run since 1970) there were lots of non original bits on it, rubbishy loom, mag that didn't work etc.

I took the decision to build it up as I wanted, not a 'factory museum piece' and I'm glad I did.

As to the electrics, as my alternator rotor wouldn't hold the weight of a small spanner, I went for a new rotor and 3-phase stator with a Japanese (Kawasaki) regulator, along with all new wiring. I have never regretted it. It balances the load of a 60W headlamp and the electronic ignition (whatever model Boyer was current in 1998) at 18-1900rpm. I run a 7Ah battery on the bike and have no issues there.

Al has offered help with checking your alternator output - I would grab that. 

Only other thing is to go through all connections in the wiring ( and earths) and make sure they are all clean and good.

Good luck,

George 

My 650ss bitsa fits much of your description, John.

I always fit an ammeter to my bikes (8Ah Gel Battery in this case)  and noticed that I had to hit 50 mph in top before the needle went to the middle (Ammeter)  Put the headlight on and discharge all the way. I then thought of my Mk3 Commando and bought an assimulator charge light from Paul Goff. I sine believe that AO sells them too. Anyway, same result. But good to eliminate issues.

The Stator was a new Lucas and so I decided that was not the issue. The Rotor with good magnetism was an old one out of my collection, and guess what? Only by a fraction the air gap was too big. I fitted the correct Rotor and all is charging well.Not all Rotors are the same! 

John, you didn't say if you had an ammeter fitted, did you? Or the charge warning system, I have now both on this bike.

PS: The picture is mostly so Robert T can have a better look at my 2 into 1......

The bike behind is my mates 1961 prize winning ES2. 

PPS: The bigger the battery the better, to an extent, but I doubt a healthy 5AH is your issue. I use one on my Poor Man's Manx....ES2 motor BTW...

With an issue like this do NOT go out buying new alternator or regulator. Find the fault first. You could easily spend £100 or more and still have the same fault. The fault might even be easier, a failed wire in the alternator, if it is an original 6V (RM19) type then the loss of a one set of coils would cause all this. Check DC current after alt/rect and battery charge voltage, then work forward from there. The problem might be with the rotor, but the gap is not that crucial, The quantity of magnetism is. All 6 magnets need to be up to 'scratch'. I can measure magnetism BUT postage can be a 'no no'.Measuring the generated DC as my web site is a short answer. But I will work on a basic magnetism measurer if any one else is interested.

The simplest way to find if the alternator is charging sufficiently is to check the voltage at the battery.  (Lights off) First with the engine off and preferably after standing overnight.  This will indicate if the battery is holding a charge.  Anything below 12 volts means it isn't.  Next check the voltage while running with no load.  Preferably at 1000rpm and at 2000rpm.  You want 13+ volts minimum.  On a car I expect 14+ volts.  See what the variation is at different engine speeds.  It's more difficult to check the AC of the alternator output on any vehicle, as Al Oz will tell you, so I always check at the battery - DC.  I maintain most of my vehicles - a Diesel Motorhome, a petrol Jaguar S-Type and a Skoda Fabia.

1) Lamps At the front, Paul Goff's Daylighter headlamp LEDs are the way to go, regardless of whether you are trying to lighten the electrical load (http://www.norbsa02.freeuk.com/goffyWhyNotLEDs.htm). You might want to consider converting the headlamp to H4 (if necessary) in order to use the Daylighter 2 version — they are brilliant (pun intended). His stop/tail LED is also excellent.

2) Instrumentation I endorse the recommendation of Al's battery status monitor (http://www.aoservices.co.uk/data/bsm.htm). I have one as well as an ammeter; the combination provides a useful cross-check.

Please follow what Alon Osborn says first - he is the club electrical guru!  Don’t spend any money until you’ve checked what’s wrong …. easy with a multimeter for a few pounds from the usual outlets!

But apart from that a cheap digital meter will NOT measure the charge voltage of your battery. As soon as the engine starts the display will jump about, it picks up the ignition. A specific automotive multimeter might do the job or an analogue  'pointer' meter. You don'y need to know the finite number of volts as you are looking for the charging voltage rise of 2V ish. Checking for a non charging fault (low charge voltage) with a Lucas alternator and Regulator/Rectifier will leave confused as to which is faulty. Replace the reg/rect with original bridge rectifier and if the charge is resumed, then reg/rect is suspect (I can test) running the bike for a short test run or even on the road (with lights on) will be ok. Just don't do a long run without the lights!

For what it's worth I use a RM23 single-phase stator with the original rotor, rectification and regulation using a Mosfet Tri spark unit. Voltage at tickover is 14.39V, and stays around this level no matter the revs.

If I use the starter the BSM will indicate green after a minute or so.

Despite the bad press the stators had over the years it seems that they can actually deliver a decent output.