Author Topic: Why positive earth on BSA ?  (Read 3007 times)

Offline Viking

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Why positive earth on BSA ?
« on: 19.08. 2015 09:10 »

Some early manufactures of MC and Car, used positive earth, but why keep this systems on out BSA´s ?

One reason could be originality, but is this enough to stick to this odd system ?

I consider rebuilding my BSA A10 SR to 12VDV, with at Alton generator, and it has a negative earth system.
Later on a digital ignition will be added.

After fettling with weak & feeble dynamos and magnetos for decades, I decided to change to a modern and stronger sparks.
Modern fuel with ethanol is not easy to burn with a magneto system.

And change to a modern power for proper lighting. By law we need to use running light all day in Scandinavia, and it strain the weak dynamo system.

Another benefit with 12V negative earth system, You can fit a AFR gauge and easily monitor if the fuel ration is correct at all throttle and load conditions.

6 Volt is hard on the switches, and getting relayes and bulbs for 6 Volt is getting harder..
6 Volt GPS units are not easy to get, and other electric systemt require 12 V with a negativ earth

So why keep with a positive earth electric system on the BSA ?   

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Re: Why positive earth on BSA ?
« Reply #1 on: 19.08. 2015 09:55 »
 *smile*because we can ;)
Both my A's are 12 volt. E3L>DVR2>12v bat>lights/ignition. But retain +ve.
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Re: Why positive earth on BSA ?
« Reply #2 on: 19.08. 2015 10:31 »
Two of my A10's are 12v, one is pos earth, the other neg, both use dynamos converted to 12v, one has a DVR2, the other has Wassells 12v reg. Lights on both bikes absolutely great and no charging problems, even at tickover. Magneto ignition works well and, of course, doesn't need a charging system to make it work.

The whole point of having a classic bike, in my opinion, is to demonstrate that it is possible to make old stuff work well. If you replace too many parts with modtech you end up with a bike which isn't a classic bike any more. Everybody has their opinion of where to draw the line when improving their classic bike, beyond which it is no longer a classic. This argument will have been done to death so there's no point raising it again but, if you're looking for modern performance, buy a Kawaplastic!

Online terryg

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Re: Why positive earth on BSA ?
« Reply #3 on: 19.08. 2015 12:30 »
I agree it's a matter of personal choice, whether to modify or stay standard. My choice is largely to stay standard but I am using solid state regulators.
I've also added a dc-dc buck convertor that gives me a USB power point for satnav. However, a paper map on top of the tank is easier to read than the satnav screen in sunshine... but the satnav wins at night!
'57 'SR', '59 SR, '63 RGS

Offline stu.andrews

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Re: Why positive earth on BSA ?
« Reply #4 on: 19.08. 2015 13:08 »
Why positive earth?
The answer, from the net explains:-

We’ve all seen the effects of corrosion around electrical terminals, batteries and the like.  However, it was noted that when the ground was Positive, the corrosion effect was greatly reduced.  Now you know.  Faced with imperfect insulation and a wet climate, English auto makers opted for the least corrosive electrical orientation.
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Offline Viking

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Re: Why positive earth on BSA ?
« Reply #5 on: 19.08. 2015 20:40 »
I have been told the same. Positive earth protect the electric wires, but is hard on the frame.

Why change equipment / systems on the old bike ?

To make it usable and perform better.

I fitted taper roller bearings in the steering head, had the crank case re-bored by SRM to correct out of true drilling by BSA, dynamic ball. the crank, fitted modern valves and guides in the cyl. head. New High flow oil pump to prolong engine life.
New Mono Bloc carb. (Messing with old worn out units is a dead end.)

All to improve and to make a bike much more usable and in balance, and to prolong engine life.

Classic style with modern help. And a engine that preforms.
25HP, you are struggling in keeping up with today traffic. 50HP you have plenty of power, even for motorway usage.

I am not convinced that 6 volts it the way to keep the bike on the road.
(I restored the bike to 6 Volt in 1996 to keep it original, with new Lucas regulator, oh Lord, it gave me endless troubles).

Old School batteries keep spilling acid.
I now use GEL batteries.
And I have still not see a bullet prof reason for positive earth.
Just see UK car manufactures changing in the 60ties to negative, to positive and to negative ground again.

No I do not want a “Cow A sock Y”.  Just a usable BSA , and keeping it on the road

Offline morris

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Re: Why positive earth on BSA ?
« Reply #6 on: 19.08. 2015 21:48 »
I also have always understood that it was done to reduce corrosion, mainly on cars.
I have both A10's still +ve ground, plunger on 6v with a modern gel battery (no spills) Boyer regulator and magneto (Brightspark magnetos did a fine job on that), the SA on 12V, V-Reg regulator and electronic ignition. Both are first kick starters and great runners keeping the battery charged even with the lights on.
I keep them +ve earth because it's so much 50's British... *smile*  *smile*
The Morris however has been switched over to -ve earth because I've fitted a radio a couple of years back.
Suppose it's everyone's choice to convert or not?  *dunno*
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Offline saxxmann2200

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Re: Why positive earth on BSA ?
« Reply #7 on: 19.08. 2015 22:45 »
After owning BSA A10s for years, I now have one, but are struggling to decide whether to stay with an original voltage control box, or go with a solid state one.

Its six volt still, and after ringing Dave Lyndsey, I am not sure if changing it to 12v for theuse at night mine has, and also the fact I bought a solid state regulator box from a well know supplier - not Dave, and it lasted a few months, and I ended up in a difficult situation to prove it had malfunctioned, and was nothing I did- nightmare.

Any suggestions ? *smiley4*

Online RichardL

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Re: Why positive earth on BSA ?
« Reply #8 on: 20.08. 2015 05:02 »

Welcome to the forum. *welcome* Please write-up an introductory post as described here:

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Online groily

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Re: Why positive earth on BSA ?
« Reply #9 on: 20.08. 2015 08:07 »
Plenty of threads here saxxmann on the pros and cons of 12 volts, when you get familiar with the site (and welcome!).
With solid state regulators you get what you pay for. There are many options, and one or two very good ones.
I ran a JG unit for 20 years on one machine - Dave Lindsley sells the current versions of the the same make, and they work well. You'll need to modify the dynamo wiring to connect the field coil from F to D, rather than F to earth if you go that way.
Many of us now use the DVR2 units from Dynamo Technologies, which are a straight swap retaining 'field to earth', and work at 6v or 12v - but you have to choose the polarity. (They come with a guarantee of course, but not sure if anyone has ever needed to claim.)
There are those here who are quite brilliant with setting up the mechanical regulators, but I'm not among them, preferring the DVR2 every time.

Offline Viking

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Re: Why positive earth on BSA ?
« Reply #10 on: 20.08. 2015 08:29 »
Engineers discovered that with positive voltage on the copper wires, copper wires age quickly, due to electrolysis. (minus / negative ground/earth)
With negative voltage on the wires, in respect to earth, (called positive ground) the copper is protected from corrosion. This is referred to as cathodic protection.

You can either protect the Cu wires or the steel body.
(It is easier to change wires, then changing the steel body)

Or for our classic bikes, avoid rain, winter and damp conditions   

Offline Guy Wilson

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Re: Why positive earth on BSA ?
« Reply #11 on: 24.08. 2015 11:41 »
I vaguely remember all those really rusty + earth Minis...all with perfect wiring...