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BSA B40 12V conversion #740289
06/30/18 5:18 am
06/30/18 5:18 am
Joined: Jun 2018
Posts: 11
Salt Lake City, UT
L
LandoLando Offline OP
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LandoLando  Offline OP
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Joined: Jun 2018
Posts: 11
Salt Lake City, UT
I’ve searched around quite a bit and found two prevailing methods of upgrading to a 12V system but I have a few questions about each.

Method one: podtronics module

Install podtronics module, remove capacitor and change light bulbs. My concern with this method is, I don’t like the look of the module and I don’t want to stuff everything behind the side cover. Also, I read that without changing the alternator it will lose charge at idle.

Method two: later parts retrofit

Install Lucas 12V regulator and 12V alternator. Remove capacitor and install 12V battery. Change bulbs.

Are the later 12V alternators a clean swap?
Has anyone rewound their alternators for 12V instead of buying the 12V?
Has anyone required their regulator for 12V?
Do I need a new ignition coil and/or plug for 12V?
Is it a good idea to switch to negative ground with 12V?

Last edited by LandoLando; 06/30/18 5:24 am.
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Re: BSA B40 12V conversion [Re: LandoLando] #740291
06/30/18 5:25 am
06/30/18 5:25 am
Joined: Dec 2004
Posts: 9,375
Scotland
kommando Online content
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kommando  Online Content
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Scotland
Your current alternator voltage is determined by the regulator/system its in, it will provide 12V and if you use LED bulbs the output will be sufficient.

Re: BSA B40 12V conversion [Re: LandoLando] #740297
06/30/18 9:36 am
06/30/18 9:36 am
Joined: Jun 2002
Posts: 9,957
Scotland
S
Stuart Offline
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Stuart  Offline
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Joined: Jun 2002
Posts: 9,957
Scotland
Hi,

Firstly, what system does your B40 have now? What you've posted assumes it already has a rectifier converting alternator AC to DC; if it currently has ET, the change is a bit more complicated ...

Assuming DC already, 'fraid you're confused:-

. To echo "kommando", the nominal DC - 6V or 12V - is determined by the regulation of the alternator's AC output. 6V "regulation" is in inverted commas because it's determined solely by the battery, some switching of alternator coils by the ignition and lighting switches hoping the alternator output wouldn't boil said battery ... facepalm

. There isn't really a recommendable "Lucas 12V regulator". It was originally a Zener diode but the currently-available are proportionally shonky and expensive. thumbsdown

. The Podtronics is a long-time reliable regulator and rectifier. thumbsup

. If not the Pod, "NickL" has been recommending the Chinese-made pattern Honda 3-phase reg./rec. (e.g. https://www.eBay.com/itm/Motorcycle...-for-Honda-CB250-Hornet-250/162708739867) for years (the linked one is reg./rec. and plug together; if you buy separately, they can be had cheaper; yes, you can use a 3-phase reg./rec. with a (the existing Lucas) single-phase alternator smile ). thumbsup

. If that doesn't appeal, entering "honda regulator rectifier" into eBay's Search will turn up both single- (4-wire) and 3-phase reg./rec. in innumerable shapes and sizes.

Originally Posted by LandoLando
I read that without changing the alternator it will lose charge at idle.

The bike's existing single-phase alternator doesn't "charge at idle" anyway. At very-best, the high-output single- or 3-phase might show a small charge at idle but, even then, I wouldn't expect it to be capable of much.

Assuming your bike is '62-on and has a 74 mm. o.d. rotor and 3-wire RM19 stator, regulated to 12V instead of 6V, it produces less at all rpm; Lucas rated it for about 8.5 Amps/100 Watts @ 5,000 rpm.

Otoh, if your bike is '62-on and has the RM19 bits, it's well over fifty years old, so about 8.5 Amps/100 Watts @ 5,000 rpm could well be hopeful rather than realistic. "kommando's" suggestion of LED 'bulbs' doesn't fix the age of the alternator bits; otoh, a new (high-output?) 3-phase alternator and bog-standard bulbs might be a better investment?

Originally Posted by LandoLando
Are the later 12V alternators a clean swap?

Assuming your bike is '62-on, "clean"-ish ... The vast majority of the different stators available today are patterns of the Lucas '62-on stators by Wassell ("Genuine Lucas" laughing ), Sparx and various eBay chancers, all having ... errr ... different ... views of 'quality' ... whistle

I prefer to pay the little extra for what's known in the trade/listed as the "Made In England"/"Made In UK" stator - if you click here and scroll down 'til you see "/UK" in the "Code" column, you'll see what I mean. TMS is in GB but afaik some US dealers (e.g. Mitch Klempf) stock them.

Originally Posted by LandoLando
Has anyone rewound their alternators for 12V instead of buying the 12V?

As both "kommando" and I have posted, the alternator is nothing to do with the DC Volts. Later stators simply produce more Amps at given rpm and are 'potted' for greater vibe protection. Watching paint dry or grass grow will be more-rewarding than attempting to rewind a half-a-century-old stator.

Originally Posted by LandoLando
Has anyone required their regulator for 12V?

confused "rewired their regulator"? Not possible. 6V "regulation" was/is the battery, 12V regulation was a Zener diode.

Originally Posted by LandoLando
Do I need a new ignition coil and/or plug for 12V?

Ignition coil, yes. Plug is HT so unaffected by any change in LT system Volts.

Originally Posted by LandoLando
Is it a good idea to switch to negative ground with 12V?

No. Unless you really can't deal with 'positive ground'.

Hth.

Regards,

Re: BSA B40 12V conversion [Re: LandoLando] #740301
06/30/18 11:26 am
06/30/18 11:26 am
Joined: Aug 2001
Posts: 7,455
scotland
triton thrasher Online content
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triton thrasher  Online Content
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scotland
The “rewinding for 12V” and “losing charge at idle” may be the result of confusing your alternator system with the older dynamo DC generator.


Amateur Loctite enthusiast.
Re: BSA B40 12V conversion [Re: LandoLando] #740312
06/30/18 1:58 pm
06/30/18 1:58 pm
Joined: Jun 2018
Posts: 11
Salt Lake City, UT
L
LandoLando Offline OP
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LandoLando  Offline OP
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Joined: Jun 2018
Posts: 11
Salt Lake City, UT
Thanks for the replies guys. Clearly I am new at this so bear with me. My bike is a 1964 B40 with a 1961 B40 B 951 motor swapped in because the old one had a spin bearing. I don’t know what size the alternator is because I haven’t pulled the primary. It does have three wires though. It’s got a blue capacitor and a little round heat sink looking thing under the seat. I assumed that was a regulator. Apparently it’s a rectifier?

So you guys recommend the podtronics?

Re: BSA B40 12V conversion [Re: LandoLando] #740323
06/30/18 4:43 pm
06/30/18 4:43 pm
Joined: Jun 2002
Posts: 9,957
Scotland
S
Stuart Offline
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Stuart  Offline
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Hi,

Originally Posted by LandoLando
1964 B40 with a 1961 B40 B 951 motor
I don’t know what size the alternator is because I haven’t pulled the primary. It does have three wires though.

So did the aforementioned RM19. However, the engine would've been fitted originally with a smaller (70 mm. o.d. rotor and even more feeble) RM13 or RM15. It's possible to convert some bikes to later, larger alternators (rotor and stator) but I'm not sure about a B40 so I'll leave answering that to someone more-knowledgeable. However, if it's possible to upgrade, at least it's a no-brainer.

Originally Posted by LandoLando
It’s got a blue capacitor and a little round heat sink looking thing under the seat. I assumed that was a regulator. Apparently it’s a rectifier?

First look at the wires coming out of the engine from the alternator - an educated guess says they're Light Green, Dark Green and Green-with-a-Yellow stripe? If the Light Green and Dark Green wires are attached to the upper and lower terminals on the "little round heat sink looking thing under the seat", with a Brown-'n'-White-striped wire off the middle terminal, that's the rectifier.

Hth.

Regards,

Re: BSA B40 12V conversion [Re: Stuart] #740328
06/30/18 5:18 pm
06/30/18 5:18 pm
Joined: Jun 2018
Posts: 11
Salt Lake City, UT
L
LandoLando Offline OP
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LandoLando  Offline OP
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Joined: Jun 2018
Posts: 11
Salt Lake City, UT
That’s correct on the wire colors. So no chance what ever alt that’s in there has the current to run everything at 12V?

Re: BSA B40 12V conversion [Re: LandoLando] #740329
06/30/18 5:31 pm
06/30/18 5:31 pm
Joined: Dec 2004
Posts: 9,375
Scotland
kommando Online content
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kommando  Online Content
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Scotland
Quote
So no chance what ever alt that’s in there has the current to run everything at 12V?


Can't tell until you open up the primary, and it really depends as much on the load as the output, the rotor magnetism will have dropped reducing the potential output but the blue capacitor says someone has already been upgrading the electrics for batteryless running so maybe it has a later alternator, does it have a 6v battery fitted ? .

If you do not plan running at night then a good pilot bulb at 23W halogen or a high lumens 5w led pilot bulb are good daytime running lights, this gives a wide spread unfocused beam that can be seen from side roads to hopefully stop them coming out. During daylight a focused beam is best seen by traffic in front of you, not to the sides. For the odd night time a 35/35W bulb would work and not drain a battery.

Re: BSA B40 12V conversion [Re: LandoLando] #740372
07/01/18 2:51 am
07/01/18 2:51 am
Joined: Jun 2018
Posts: 11
Salt Lake City, UT
L
LandoLando Offline OP
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LandoLando  Offline OP
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Joined: Jun 2018
Posts: 11
Salt Lake City, UT
I just took out the capacitor and installed a 6V battery. This thing really runs. I don’t want to waste time with it apart over the summer. I’ll do the 12V swap over the winter. Thanks for all the help guys!

Last edited by LandoLando; 07/01/18 2:52 am.
Re: BSA B40 12V conversion [Re: LandoLando] #740459
07/01/18 10:51 pm
07/01/18 10:51 pm
Joined: Feb 2014
Posts: 1,096
Lancaster, California
C.B.S Offline

Parts Dealer
C.B.S  Offline

Parts Dealer
Joined: Feb 2014
Posts: 1,096
Lancaster, California
install an electrex world with alternator, then use a capacitor and run all LED lights.... works for me!

Re: BSA B40 12V conversion [Re: C.B.S] #740538
07/02/18 7:59 pm
07/02/18 7:59 pm
Joined: Jun 2002
Posts: 9,957
Scotland
S
Stuart Offline
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Stuart  Offline
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Scotland
Hi,

Originally Posted by C.B.S
install an electrex world with alternator, then use a capacitor and run all LED lights.... works for me!

Sadly, Electrex doesn't seem to work for everybody ... frown

Regards,


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