BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: Drummie on 27 August, 2017, 20:38:36

Title: Battery flat after riding with lights on
Post by: Drummie on 27 August, 2017, 20:38:36
Hi all,

Out on my bike today for a run.  Decided to use the lights.  Haven't needed to use them yet, so today was the first time.  Rode with them on for around 20 minutes.  Stopped bike and switched it off.  Went to start it again after 5 minutes and it wouldn't start.  Checked the lights and they were almost non existent (a slight glow).   Jumped it with another battery it fired up straightaway and the lights were fine.  Connected multi meter to it while it was running but readings were jumping all over the place so couldn't get any kind of reading from it.

I got the same problem using the multi meter when I got the bike a few months ago.  I've done decent trips on it and it has always been fine until today when I used the lights for the first time.
I've had charging problems with other bikes before but always got a reading to show its not charging
Any idea what the problem could be?

Thanks in advance.  Any help much appreciated.

Title: Re: Battery flat after riding with lights on
Post by: JulianS on 27 August, 2017, 20:41:31
Which bike do you have?
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 27 August, 2017, 20:44:38
sorry forgot that bit. its a a50 royal star.
Title: Re: Battery flat after riding with lights on
Post by: om15 on 27 August, 2017, 20:57:51
Go for the easy fixes first, change the battery and see how you go
Title: Re: Battery flat after riding with lights on
Post by: JulianS on 27 August, 2017, 21:51:51
With engine going does the headlight intensity increase with revs?

Title: Re: Battery flat after riding with lights on
Post by: Drummie on 27 August, 2017, 22:24:10
I've not noticed JulianS, but will check that tomorrow and let you know.

om15 the battery will need replacing. Put it on charge tonight and read fully charged after around an hour. So something definitely wrong there.

Any idea why I cant get a reading from the multi meter. as it fluctuates wildly.
Title: Re: Battery flat after riding with lights on
Post by: STAR TWIN on 28 August, 2017, 07:02:29
If your multimeter if fluctuating, it's either your rectifier/zener diode/powerbox failing on the charging side or an intermittent short circuit somewhere. Your charging side should more than match riding with headlights on so there is something amiss. I would be surprised if it's just a battery problem. 
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 28 August, 2017, 12:36:00
I have checked this morning and the headlight does get brighter when I increase the revs, not to the point bulbs will blow but definitely an increase.
Also noticed a fuse on the lead/wire to the negative terminal on the battery. with the engine off and battery connected i'm getting 12volts from it, but 0volts from positive side. sorry if this is obvious but electrics are not my strong point.

Its a 1966 a50.

Like you said Star Twin I don't think its just the battery, I'm not that lucky.
Title: Re: Battery flat after riding with lights on
Post by: Greybeard on 28 August, 2017, 13:57:46
Whilst I'm happy enough to recreate practically anything mechanical on the lathe or milling machine, electrical stuff leaves me cold. Following a wiring diagram was about the limit  :-[  I bought a copy of Classic Motorcycle Electrics Manual by James Smith. Its a superbly produced book that goes right to the basics and works through from there, basically assuming that the reader knows very little from the outset - unlike many other books on the subject.
It gave me an understanding of how dynamos, alternators and rectifiers etc work, and more importantly, how to test them. It's well worth tracking down a copy. Published price is 35 quid but it can be found for much less than that.

Steve
Title: Re: Battery flat after riding with lights on
Post by: Mike Farmer on 28 August, 2017, 16:23:59
Hi :)

Classic Motorcycle Electrics on Ebay. Item No252989884779. 23.99 +postage.

Mike
Title: Re: Battery flat after riding with lights on
Post by: Greybeard on 28 August, 2017, 18:46:46
That's the one, Mike. Worth every penny. A tad cheaper on Amazon too
https://www.amazon.co.uk/Classic-Motorcycle-Electrics-Manual-James/dp/1847979955/ref=sr_1_1?s=books&ie=UTF8&qid=1503942211&sr=1-1
I couldn't post a link to it earlier as I was using my tablet - there are some things that I've never bothered to find out how to do with it   :-[

Steve
Title: Re: Battery flat after riding with lights on
Post by: JulianS on 29 August, 2017, 10:29:09
It is always worth checking the basics - check all connections are clean and bright, check for frayed or squashed wires, check that all is connected as per the wiring diagram and be suspicious of any bits of wiring which seem to have be crudely added in.

If fitted with zener diode check that the seat of it and heat sink is not corroded, clean if necesary.

The headlamp mounted ammeter can tell you a lot - the charging syatem should easily balance both ignition and headlamp load.

There are some basic checks on the charging system shown in the workshop manual - from the alternator before the rectifier and zener diode - after the rectifier and zener.

If you have a modern solid state regulator/rectifier the makers instructions should tell you how to check the out put from it.

If bike still fitted with the orignal open coil 3 wire alternator stator it could be past its best after over  50 years.
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 29 August, 2017, 22:07:18
Thanks for all your help. I'll have look at it over the weekend. That book does look like a worthwhile buy.
Title: Re: Battery flat after riding with lights on
Post by: EDDIE SIMPSON on 29 August, 2017, 22:31:03
hello drummie,
the quick way i would check your system is with a multimeter on 20volts range dc across the 12.5 volt battery.
14 volts on tickover means its charging. 16 volts overcharging.
12 .5 volts and above at tickover with lights on fairly normal with an old alternator.
play around with lights on / off and if the volts show discharge means short circuit. wire touching frame?
as julian says , zeners can short circuit . cause poor charge or overcharge and boil batterys
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 30 August, 2017, 14:24:06
Hi Eddie Simpson, I have done some tests this morning and first of all found that my first multi-meter was faulty (now changed). When the bike is running at idle it reads 0 on the ammeter. when revved up it increases to just above 0. with the lights on, it drops just below 0 and back to around 0 when revved (headlight gets brighter when revved up).

With the engine switched off I got a reading of 12.25 volts across the battery terminals. when I switched the lights on for around 20 secs the voltage dropped to around 11.25 volts. When I started and ran the engine for a couple of mins then switch it off, it jumps up to around 12.80v.

I also found that when running i'm getting 14.30v at idle which increases to 16v at 3000 rpm, when connected across the battery terminals.

I was thinking rectifier, but then thought it would of blown the bulbs by now.
Title: Re: Battery flat after riding with lights on
Post by: Editor on 30 August, 2017, 15:42:08
Hi Drummie,
Try that again with the engine running at about 3000 revs with the lights on. If its showing more than 15.5V then it could be the Zener that's the problem. It may be just the earth on the Zener, not earthing.
Good luck!
Chris

Title: Re: Battery flat after riding with lights on
Post by: EDDIE SIMPSON on 30 August, 2017, 16:34:41
figures given  shows its charging [ possibly a little high] but the original fault was lights on=flat battery. it could have been the old battery causing the problem. the way forward is simple. ride with your lights on during the day and see if the faults gone.
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 31 August, 2017, 08:25:08
Thanks for all the help. I'll ride it around and see how it goes.
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 01 September, 2017, 13:48:08
Hi again, I've done another voltage check at the the battery and at idle with lights off i'm getting around 14.3v this increases to 16.2v at 3000 rpm.
With the lights on i'm getting 11.2v at idle increasing to 14.5v at 3000rpm. Also Its fitted with a boyer mirco III ignition, if this makes a difference. How do these readings seem to you all. I've also cleaned all the earth points.
Title: Re: Battery flat after riding with lights on
Post by: JulianS on 01 September, 2017, 14:26:36
My A10 on 12 volts.

With lights off battery show 12.9 volts.

Switch lights on - H4 headlight bulb - volts drop to 12.4 after about 30 seconds. Lights off after that short time then volts back up.

I think the drop you are experiencing suggests battery past its best.
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 03 September, 2017, 09:38:05
I'll  change the battery and see how it goes. Thanks again.
Title: Re: Battery flat after riding with lights on
Post by: Editor on 03 September, 2017, 17:34:24
Based on what you said, the charging rate is fine with the lights on. Most likely the Battery
Chris
Title: Re: Battery flat after riding with lights on
Post by: EDDIE SIMPSON on 03 September, 2017, 22:29:49
hi, i would suggest there is a large power drain with the lights on at idle. it could be the battery, but could also be a poor lighting switch or a large watt halogen headlamp bulb ? maybe remove the headlamp bulb and recheck the voltage on idle with the lights on. a very common fault is a live wire touching the handlebars in the light switches. remove the switches and remeasure.
another way of checking for a short is by removing the battery connections and  bellout with the multimeter between live and earth, lights on and off. should be no buzzer on either.
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 13 September, 2017, 14:33:15
Thanks Guys. I believe the battery has had it. I was out on the bike yesterday and after around 20 minutes stopped, and still with the engine running switched the lights on. The bike cut out after about 10 seconds, which is a lot worse than before. Switched them off and she started first kick and rode perfectly. I will have a look at the switches and wiring and also the headlight bulb. That rang a bell, as I remember that being a fault on a Honda 400 four I had a few years ago. I was thinking of a possible conversion with a boyer bransden powerbox if need be. Do any of you know of them or better still used/use one. Thanks again Drummie.
Title: Re: Battery flat after riding with lights on
Post by: LIONELSMITH on 18 September, 2017, 20:21:38
Drummie, with those voltages I agree the rectifier sounds faulty, but that does not explain why the battery discharges so quickly, The only thing that makes sense is the faulty rectifier has damaged the Battery and its capacity is shot. I would replace the rectifier, I would go solid state, and try another borrowed battery for a brief test. Otherwise I agree with Julian, you have a wire that is earthing out. If you want an original rectifier I like many have taken off a working rectifier.
Title: Re: Battery flat after riding with lights on
Post by: Editor on 19 September, 2017, 18:41:01
Re Boyer Bransden ign, I've had one on my Thunderbolt for the past 11 yrs, and it was already fitted when I bought the bike so its really old. I've never had any problems with it and the beauty of them is, once fitted and set up, they don't need any adjustment or maintenance, in fact its a fit and forget job. Highly recommended by me!
Chris
Title: Re: Battery flat after riding with lights on
Post by: Caulky on 25 September, 2017, 10:30:01
Hi Drummie
You said "With the engine switched off I got a reading of 12.25 volts across the battery terminals."
At this voltage, your battery is less than 50% charged.
Fully charged it should read 12.6V (6 cells at 2.1V).
After a charge, the voltage may be 13V plus.
This is the 'surface charge' which disappears after time or loaded.
When buying a new battery, get the vendor to load test it, I had two bad battery's in a row. 
Title: Re: Battery flat after riding with lights on
Post by: Drummie on 10 October, 2017, 17:32:17
Thanks again for all the help. Took the bike to the Glasgow Distinguished Gentleman's Ride Out, and without the lights on it didn't miss a beat, even riding through the monsoon type rain we get here. I've taken it off the road now for the winter, and will be going through everything and changing a few bits ie the rectifier over the coming months. Caulky, I checked the battery a couple of days ago straight after a short run, and it was showing 13.3 volts. I'm going to change it though, and get the new one checked as you suggest. Thanks again.