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BSA Charging question #736759
05/27/18 10:08 pm
05/27/18 10:08 pm
Joined: May 2018
Posts: 2
MA
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BILL P. Offline OP
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1968 Lightning ammeter reading negative while running....... Headlight on (not running) pegs all the way to the left.

Battery reading 12-14v at idle to 3000 rpm.

Headlight doesn't get brighter with higher revs.

Sounds like an issue?


Any suggestions would be appreciated.

Thanks,
Bill

New to the board.

Last edited by BILL P.; 05/28/18 3:29 am.
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Re: BSA Charging question [Re: BILL P.] #736767
05/28/18 1:24 am
05/28/18 1:24 am
Joined: Aug 2001
Posts: 4,499
Owego, NY, USA
Mark Z Online content
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Mark Z  Online Content
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With the headlight on and the engine not running, the ammeter SHOULD dip to the left, showing that the battery is discharging. I don't know about "pegged" though - the headlamp should draw around 4-5 amps. Was the ignition on too? That could account for another couple amps.

What does the ammeter read when the engine IS running? At idle, the battery should still show slight discharge, more if the headlight is on. When the engine is revved such that the battery voltage reaches 13 volts or more, the ammeter should move to the positive side of zero.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: BSA Charging question [Re: BILL P.] #736810
05/28/18 12:44 pm
05/28/18 12:44 pm
Joined: Jun 2002
Posts: 10,090
Scotland
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Stuart Offline
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Stuart  Offline
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Hi Bill,

Firstly, welcome to the Forum. smile

Originally Posted by BILL P.
ammeter reading negative while running....... Headlight on (not running) pegs all the way to the left.
Battery reading 12-14v at idle to 3000 rpm.
Headlight doesn't get brighter with higher revs.
Sounds like an issue?

From a recent thread on the Triumph Bulletin Board:-

Originally Posted by NickL
The ammeter is functioning as Lucas designed it, it measure machine vibration quite accurately.
Unfortunately, as an instrument for measuring current it is next to bloody useless!

The rotor on your alternator may be a a little tired if it's old, that would account for the poor charging,
but really you should go through the normal tests with a voltmeter and engine running to eliminate
poor connections etc. Like so many of these things it's seldom as easy as 'just fit a new one of these!'

grin

Apart from that, need more information to give you sensible answers:-

. Assuming "pegs all the way to the left" is to the "-" end of the scale, is it an 8A or a 12A scale?

. Points or electronic ignition?

. Standard 45/40 (Watts main/dip) original BPF headlamp bulb or more-powerful upgrade?

To amplify:-

. As Mark suggested, if the engine isn't running, or is only idling, ignition draws ~3.5A, original headlamp dip draws another ~3.5A, standard incandescent tail, pilot, speedo. and tacho. bulbs draw over another Amp between them. That's ~8A total, all coming from the battery so all showing on the Ammeter; if the Ammeter has an 8A scale it's "doing exactly what it says on the tin". bigt If the headlamp has a modern 60/55 bulb, either filament is drawing an additional ~1A more than an original headlamp's filaments did.

. The '68 A65 parts book shows a RM19 alternator as standard (three wires from the stator to the rectifier, two are joined together at one rectifier terminal or somewhere between the engine and the rectifier). If this is what your bike has, regulated to a nominal 12V, when the rotor magnetism was new, it produced about 8.5A/100W @ 5,000 rpm.; however, magnetism attenuates with age, an original rotor is half-a-century old ...

. Otoh, if the stator has only two wires from the black sheathing emerging from the engine, it's likely a later RM21 alternator; nevertheless, even when that was new it only produced 10.5A/120W @ 5,000 rpm.

Originally Posted by Mark Z
When the engine is revved such that the battery voltage reaches 13 volts or more, the ammeter should move to the positive side of zero.

Unfortunately, this is misleading; the Ammeter indicates Amps, nothing to do with Volts.

Certainly as standard, the way the wiring is connected is Amps from the battery flow through the Ammeter to reach the ignition switch and then the users - ignition coils, bulbs, etc. So the Ammeter indicates the Amps being supplied by/drawn from the battery.

When the engine is running, it's spinning the alternator rotor, the alternator stator supplies Amps through the rectifier to the ignition switch and then the users. Alternator/rectifier Amps increasing with engine rpm decreases draw from the battery, meaning the Ammeter needle should move from "-" towards zero.

When the ammeter needle reaches zero, the alternator is supplying all the users, nothing is being drawn from the battery. When the Ammeter needle passes zero towards "+", not only is the alternator supplying all the users, it's also charging the battery.

Finally here, a potential issue with old Lucas alternator rotors is the metal around the magnets and the central hex. can come loose, allowing the central hex. to push the magnets outwards. There's (should be) only 8-12 thou clearance between rotor outer and stator inner, so the magnets don't have to move far before they start mullering the stator. frown

Just for peace-of-mind, maybe have the primary chaincase and stator off to check?

. Check for 0.008"-0.012" clearance all round, with the rotor in different positions relative to the stator.

. When pulling the stator off its mounting studs, be aware hot oil stiffens the old cable.

. If the rotor can be exposed sufficiently, grab the outside tightly and see if you can discern movement between the magnets, surrounding metal and central hex. when you attempt to rotate it and the engine back-and-forth?

. According to the parts book, an original rotor was "54213901"; also possibly stamped on it will be a date, in two-figure-week-number-two-figure-year format?

Hth.

Regards,

Re: BSA Charging question [Re: BILL P.] #736830
05/28/18 3:37 pm
05/28/18 3:37 pm
Joined: Sep 2015
Posts: 313
Kent, England
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John Alexander Offline
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Simple reply, if your bike is charging the lights should glow brighter when revs rise from tick over.

Re: BSA Charging question [Re: John Alexander] #736850
05/28/18 7:31 pm
05/28/18 7:31 pm
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Posts: 10,090
Scotland
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Stuart Offline
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Hi John,

Originally Posted by John Alexander
Simple reply, if your bike is charging the lights should glow brighter when revs rise from tick over.

Possibly. However, ime lights glowing brighter, or not, on its own isn't a reliable pointer to a particular conclusion.

Hth.

Regards,

Re: BSA Charging question [Re: BILL P.] #736851
05/28/18 7:41 pm
05/28/18 7:41 pm
Joined: Feb 2008
Posts: 4,387
New Jersey USA
Tridentman Offline

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IME if the lights go brighter as you rev the engine then it proves that the charging system is charging.
Think about it--the brighter lights come from a higher voltage.
The higher voltage does not come from the battery in isolation so must come from the charging system.
Note however that while brighter lights if the engine is revved prove that the charging system is working--if the lights do not go brighter if you rev the engine then all it is telling you is that the charging system is not charging.
To find which one of the umpteen different possible causes of the non charging you have to dig deeper.
HTH

Re: BSA Charging question [Re: BILL P.] #736854
05/28/18 8:29 pm
05/28/18 8:29 pm
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Posts: 1,450
melbourne florida
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bodine031 Online content
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For the record my 64 SF-Hornet went out this morning. I have a LED battery monitor on it. (bike is wired neg grd.) Tympanium reg/rectifier. A time tested stator and rotor no history and a BB EI.
At idle head lamp off 14.2V, running done the road in 4th gear lights on 13.5 -14.0V
I would check with RF Wobbley as he does this daily to have weekend $$$ for runs around the moutains!!!

Re: BSA Charging question [Re: Tridentman] #736894
05/29/18 2:39 am
05/29/18 2:39 am
Joined: Aug 2001
Posts: 4,499
Owego, NY, USA
Mark Z Online content
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Mark Z  Online Content
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Originally Posted by Stuart

Originally Posted by Mark Z
When the engine is revved such that the battery voltage reaches 13 volts or more, the ammeter should move to the positive side of zero.

Unfortunately, this is misleading; the Ammeter indicates Amps, nothing to do with Volts.
Regards,


It's sort of related; certainly if the current draw of the system were sufficiently large, the alternator could be putting out 13V and still not charging the battery. But with a healthy battery and charging system and a normal electrical system with no faults, it happens to be true. But you're right, I shouldn't have mentioned voltage; I should have just said, when you rev the engine, the ammeter should move to the positive side.


Originally Posted by Tridentman
IME if the lights go brighter as you rev the engine then it proves that the charging system is charging.


Not always. Since I started running an AGM battery with a Tympanium rectifier/regulator, I've noticed that my headlamp no longer dims at idle speed. I attribute this to the battery maintaining voltage for a longer period of time when the charging stops. I'm sure if I idled long enough, the voltage would drop, but I'm careful not to do that, and I live in an area where I don't have to stop much for traffic or traffic controls. And yes, my charging system works. I've noticed too that batteries, as they start to age, don't hold a charge for as long. I installed the Tympanium and then the battery about one year ago. (I keep mentioning the Tympanium because I believe it's key to maintaining an AGM battery, but that's another discussion.)


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: BSA Charging question [Re: Tridentman] #736912
05/29/18 9:26 am
05/29/18 9:26 am
Joined: Jun 2002
Posts: 10,090
Scotland
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Stuart Offline
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Hi,

Originally Posted by Tridentman
IME if the lights go brighter as you rev the engine then it proves that the charging system is charging.
Think about it--the brighter lights come from a higher voltage.

'Course ... the alternator rotor spinning faster isn't generating any more Amps ... whistle all of the rpm vs. Amps graphs produced by Lucas for their alternators are completely wrong (all graphs stating one regulated Volts figure) ...

When you rev the engine of your car, the lights get brighter? Or it has a large modern battery with a very high potential Amp-hour rate? When the electrical use is low, the rotor's magnetic strength is reduced to generate less Amps, or less Volts?

When the magnetic strength of an old Lucas rotor is reduced, it generates less Amps, or less Volts?

All those constructing "it isn't charging" theories based just on "Headlight doesn't get brighter with higher revs" in Bill The O.P.'s post are ignoring the line above ... "Battery reading 12-14v at idle to 3000 rpm." ... Given Lucas, BSA and Triumph workshop manuals all say greater than 15.2V or 15.3V DC is too high, which bit of "higher voltage" is missing?

Moreover, the first line of Bill The O.P.'s post says, "ammeter ... Headlight on (not running) pegs all the way to the left"; one of the Ammeters fitted as standard to Britbikes is +/- 8A, I laid out the consumption figures for standard electrical components in my first post ... God forbid Bill The O.P. might have something as simple as a bike with standard electrics and a good battery?

Imho, it's better to construct a theory based on all the evidence, rather than constructing a theory and ignoring evidence that inconveniently doesn't fit the theory. wink Nevertheless, afaict 'til Bill The O.P. supplies more information, we don't have all the evidence.

For instance, where in Bill The O.P.'s post does he say the battery isn't being charged? ... whistle

Hth.

Regards,

Re: BSA Charging question [Re: BILL P.] #737655
06/04/18 4:41 pm
06/04/18 4:41 pm
Joined: Aug 2008
Posts: 85
Burlington VT
mikelucas Offline
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Just throwing this into the mix as I didn't see this mentioned and it's a quick check. Although the phrase "healthy battery" came up a few times

What's the batter voltage when the engine isn't running?

Poor battery can cause all sorts of issues. I had a running issue/ammeter issue from a weak battery once. When running the voltage was fine....took me a few minutes to figure it out but made sense when I was done.

Re: BSA Charging question [Re: mikelucas] #737656
06/04/18 4:57 pm
06/04/18 4:57 pm
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Posts: 12,901
Central Virginia
Lannis Offline

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Originally Posted by mikelucas
Just throwing this into the mix as I didn't see this mentioned and it's a quick check. Although the phrase "healthy battery" came up a few times

What's the batter voltage when the engine isn't running?

Poor battery can cause all sorts of issues. I had a running issue/ammeter issue from a weak battery once. When running the voltage was fine....took me a few minutes to figure it out but made sense when I was done.



The very very very first thing to do in this sort of situation is to load-test the battery. Everything else could be working splendidly, but if the battery is failing, sinking too much current, not able to supply current, etc, then the whole thing doesn't work, and it can make it look like something else has failed.

Load-test, not just voltage-test. If you don't have a load-tester, take it out and let your local discount auto parts place do it for you ....

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: BSA Charging question [Re: BILL P.] #737692
06/04/18 9:52 pm
06/04/18 9:52 pm
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NickL Offline
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quote
'When you rev the engine of your car, the lights get brighter? Or it has a large modern battery with a very high potential Amp-hour rate? When the electrical use is low, the rotor's magnetic strength is reduced to generate less Amps, or less Volts?'



With the typically huge Field Excited Alternator fitted to most cars now, they will put out 14.2 - 14.4v with the headlights on at 800RPM. Increasing engine speed will not change it . You cannot really compare the two alternator types.
It is a general guide that by revving the bike if the lights get brighter the alternator is at least working. It is not a definitive test as to it's output, either voltage or current.

Last edited by NickL; 06/04/18 9:53 pm.

Lamas are bigger than frogs.
No room for sanity here.
Re: BSA Charging question [Re: BILL P.] #737832
06/06/18 5:49 am
06/06/18 5:49 am
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Anchorage Alaska USA
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Mitch Offline
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things that affect the generation of electrical power are: number of poles on the generator (alternator), number of windings on the poles, strength of the inducing magnetic field, and the number of flux changes per unit of time (RPM). once the design is set, the only variables are RPM, and strength of the inducing field (sometimes). if the generator has a permanent magnet to induce current in the stator (armature), then the only variable is the RPM. this is a typical motorcycle charging system that simply makes whatever it can based on RPM.... the faster you turn it, the more power it makes.... like a magneto. it is "full on" all the time. vehicles with this system simply dump the excess to ground in order to keep from going over system voltage. thats what the big Zener diode does, and thats why it is mounted in a heat sink. these systems make 100% of whatever they can make at a given RPM, anything not needed is turned into heat in order to control voltage. automotive systems (and some Motorcycles) have a regulator that varies the rotor (field) current to maintain system voltage.this change the inducing magnetic field so that the alternator only makes as much power as it needs to in order to keep the system at set voltage. current increases or decreases with changes in the applied load.

and amps/volts/ohms can not be separated.... they interact. designers of charging systems have to pick something, and voltage makes to most sense. too high, the bulbs burn out, too low they are dim. that kind of thing. so, if you hold voltage steady, the amperage will be proportional to load. turn on a lot of things and the load is high (but low ohms). since voltage must stay the same, the amperage must increase to meet demand. that is accomplished in automotive systems by increasing (or decreasing) the "exciter" field strength. in permanent magnet systems excess power is dumped to ground... allowing more to be used in the lighting or whatever systems.

when equipment is turned off, the resistance in the system (ohms) increases. with the regulator at a steady state, this would cause the voltage to rise if unchecked, so the output must be reduced to keep voltage constant (and current is reduced). all this is done by the regulator.... in automotive systems, the inducing (exciter) field is diminished. in (most) motorcycle systems, the excess output is run to ground and turned into heat

Last edited by Mitch; 06/06/18 7:50 am.
Re: BSA Charging question [Re: BILL P.] #737921
06/07/18 2:00 am
06/07/18 2:00 am
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BILL P. Offline OP
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Thanks everyone, I greatly appreciate all the insight and info. I will absolutely dig a little deeper this weekend and try to shed a little more light (pun) on the issue/s. Again, greatly appreciate the responses. Thanks, Bill P.


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