Author Topic: my '61 BSA super rocket is negative earth... really?  (Read 2154 times)

Offline mikeb

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Hello
my first post...
I've just bought a 61 SR which is said to have been off the road for while and has a very old dead 6V exide battery (includes white lumps on the inside). Weird thing is the earth wire to frame (checked by my multimeter) is red but goes to the negative battery terminal. So i removed the battery and added a 6v power source and when the power negative goes to frame and the lights are on then the amp meter shows current drawn (like -ve amps, draining) - hence confirming its negative earth... right?
All I've seen on the forums is they are positive earth. but there are wiring diagrams around also showing negative earth. would someone actually bother to change the polarity from +ve to -ve earth? before I put in the new battery I'd like to be sure i get it in the right way around.

BTW is it safe to run without a battery? Its not running yet tho maybe soon i could test polarity by getting it running and measuring with a volt meter

Any advice? 

thanks

Mike
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Offline duTch

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #1 on: 13.12. 2014 09:36 »

 G'day Mike, yeah could well be positive earth to frame- I'm actually in the midst of a battery issue, and seriously considering a change to -ve Earth to frame (or otherwise)...not that I care if it's + or -, but personally to save confusion.

  So long as you know what is going on, and everything is connected appropriately I think it's nothing other than a matter of choice and polarizing- but allow those more knowledgeable (geez that spellin' took a few goes), than I to get it right....

 Where you at..??
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online Triton Thrasher

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #2 on: 13.12. 2014 13:54 »
Polarity is up to you.

+ earth is original, some people change it to -.

You can run without a battery, if you want. Some say it burns the regulator contacts, but I've never seen that happen.

Offline muskrat

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #3 on: 13.12. 2014 22:49 »
G'day Mike,  *welcome* to the forum.
As both duTch and TT said it doesn't matter much ass long ass you flash the dynamo. Use the search on the left, next to Home Help Search for flash dynamo. Also the same for battery, there's a few discussions going on.
Go to Bikes Pictures & Members start a new post and tell us about yourself and bike.
Cheers
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Offline duTch

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #4 on: 14.12. 2014 00:16 »

 I'm also having another thought as to whether or not the brushes /'D'/'F' configuration changes.....for change of polarity...?? I'm sure I can find that with some research .......or think about it..??

 I think I want to change to -ve earth, just for simplicity, and uhoh-I just realized I already said that..... *conf*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online Triton Thrasher

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #5 on: 14.12. 2014 02:30 »
Wires don't change for change of polarity.


Offline mikeb

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #6 on: 14.12. 2014 03:29 »
thanks for the replies.
ok so increasingly looking like negative earth.
I've got the bike running (!!) without a battery but its not generating any voltage at the battery leads. So I can't test polarity this way and may have other problems.
is this likely to be the revs are too low? is there a cut-it point for the regulator?
looks like i may be reading up some other threads re the generator or regulator

any tips appreciated!

cheers

Mike
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Online beezermacc

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #7 on: 14.12. 2014 09:19 »
The first thing to do is check what is coming out of your dynamo, i.e. voltage and +/- earth. The two leads connected to the dynamo are usually yellow (D) and green (F). If you twist these two leads together so that you are connecting the two terminals together and connect a 12v bulb to the joint where the leads are twisted together and the other side of the bulb to earth, start the bike you should get a healthy glow from the bulb. The dynamo can deliver 20v. so don't rev the bike. If the dynamo is producing a charge you can test the output with a multimeter to find if it is +ve or -ve earth or you can determine which way you want the dynamo to deliver by 'flashing' the 'F' terminal with your selected live lead off a battery.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline duTch

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #8 on: 14.12. 2014 10:00 »

 
Quote
Wires don't change for change of polarity.

 TT, if that's for my benefit, I'm not that friggin' dumb- I said ...'...brushes /'D'/'F' configuration changes'...maybe I just had a moment, but at least I gave it consideration....didn't think my English was that bad, sorry!

 I think B-Macc has answered the call- so it's that simple as I would've otherwise expected, just change the polarity of the FLASH,(software) but not any wiring 'configuration' (hardware).?? how about the amps guage- no, I'm ok to work that out myself...if I get stuck, I'll holla.....!!

 My dumb sounding questions are as much for the benefit of any future similar inquisitions (FAQ's).....*beer*

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #9 on: 14.12. 2014 13:24 »
OK brush and field connections don't change when you change polarity.


Online bsa-bill

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #10 on: 14.12. 2014 13:49 »
Strange old day today
I just read a Dutch fella from New Zealand and a Scot discussing the intricacies of the English language, now me being a pretty died in the wool adopted Geordie like (like is obligatory at the end of any Geordie speak like) I don't feel I could add much of use but as I look out my living room window for inspiration a double decker red bus passes by, we are four miles from the nearest bus service, (the last bus service that passed anywhere near here was phased out in the sixties).
This has little to do with  mikeb's problem (sorry Mike) unless Red double deckers had positive earth systems, but it's is email so careful how you read it

Sandwich and a cuppa then off back to the shed where sanity will be restored
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline RichardL

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #11 on: 14.12. 2014 16:34 »
If you were also curious...

From separate research and through the forum, I've known about flashing a non-working dynamo, or one in need of polarity change, for some time. What I just admitted to myself was that I didn't understand what magnet was being magnetized, since the dynamo doesn't really have a dedicated permanent magnet. After more research, I now see that the soft iron pole pieces in the centers of the field coils (which also hold the field coils in place) serve as weak permanent magnets that control the direction of the very small current flow from the armature just as the dynamo begins to spin. Once spinning, part (I think it's just "part") of the generated current is sent back through the field coil. This intensifies the strength of the magnetic field through the field pole piece, hence increasing the current generated through the armature until equilibrium is reached for a given engine speed. The routing of generated current through the field coils keeps their iron pole pieces weakly magnetized after the dynamo stops spinning, therefore, maintaining polarization for + or - earth.

More specialized forum members (I could name a few, including posters to this thread) could probably explain this better or in more depth. I just hadn't seen this magnet issue explained, so I thought I'd throw it out there.

Finally, just for reference, in case someone is about to flash their dynamo, I thought this was a really clear set of instructions: http://www.dynamoregulatorconversions.com/polarising-a-dynamo.php

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

Online bsa-bill

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #12 on: 14.12. 2014 16:53 »
Thanks for that Richard, one of those things I just accepted without wondering too much about how a coil held a residual charge, just assumed it was kind of like those can things
(scuse the techno talk)
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online groily

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #13 on: 14.12. 2014 17:50 »
This is also regarded as a useful and 'bookmarkable' place by many people in the parallel universe of AMC machinery  . . . http://matchlessclueless.com/electrical/lucas/testing-lucas-dynamo/#reading

and this is my simplified  take on it  . . . with apologies to those who know this stuff better than I do anyway. An important point being that D gives everything (rather than part of itself) to F at pre-cut-in rpm.

There are five stages in a system comprising a (two brush) dynamo and voltage regulator: Static (ie dynamo at rest); excitation; avalanche; unregulated charging; and regulated charging.

With the engine stopped (static stage)
1. The cut-out is open.
The battery can not permanently be connected to the dynamo. If it were, it would try to make it turn like a motor.  So, in ‘FADE’ terminology, wire A (to ammeter, switch and battery) is only connected to D when the cut-out is shut. A and D are never connected at rest or at low dynamo rpm.
2. The contacts on the voltage regulator are closed. So D is connected to F through the voltage regulator contacts. Their default position is ‘Shut’. When the revs are high enough for voltage regulation to be required the connection switches off and on rapidly - but at rest and low- to mid-rpm the contacts are closed firmly.

The ammeter shows nothing because Nothing’s Happening unless you've left the lights on.

From Start-up to Cut-in (excitation and avalanche stages)
The dynamo starts by turning slowly.
The dynamo’s body contains a small amount of residual or remanent magnetism from the last time it ran (Richard's point). The armature is therefore turning in a very  weak magnetic field.
The armature uses that weak field in the initial ‘excitation’ phase to produce a very small amount (like ½ a volt) between D and E.
This very small amount is fed from the D terminal straight back to F the field through the closed points on the voltage regulator.
With the extra electro-magnetism now available in the field, power builds up fast at D. This is the ‘avalanche’ phase.
 
The dynamo is working away now, but nothing’s yet showing on the ammeter. That happens when the voltage being supplied from D becomes greater than the battery voltage already present at A. At that moment, the cut-out closes. D and A are now connected. Power from D is now allowed out to play.
So D, F and A are now connected – F  to D through the still-closed regulator contacts, D to A through the now-closed cut-out. Because the ammeter is in the A line to the battery, we can now start to see what’s happening for real. This is the end of the ‘avalanche’ and the start of a phase of unregulated charging.

As Dynamo rpm gradually increase in this unregulated stage, so does the power generated by the armature.
D is connected to A as we’ve seen ( via the cut-out) and always has been to F (voltage regulator contacts).
The system voltage rises a little but not much – the battery, a chunky resistor now in play, prevents that (even when it’s state of charge is low) - so the voltage into the field doesn’t increase much and nor does the power it is consuming.
The system’s working fine, but at this intermediate stage the voltage is still not being regulated (D is connected to F solidly by those points on the regulator).
But it gets closer to needing to be regulated with every extra engine/dynamo rpm, as the voltage rises.

As Dynamo rpm rise further (regulated stage)  . . .
With D, A and F all still firmly connected, voltage has risen to the point where the voltage regulator says ‘Enough, I’m at my pre-set limit, and I’m going to start regulating’. We’ve arrived (probably around 1800-2000 engine rpm ) at the regulated phase.

(In reality it all happens darn fast – a mere blip of the throttle gets you through most of this in the blink of an eye.)
 
The voltage regulator is pre-set to prevent D from feeding the field with more current than is necessary for it to enable D to support it (the field) and the electrical needs of the machine at that moment (A). F’s feeding programme and other calls on the dynamo all depend on what’s switched on – and the state of charge of the battery.
If F isn’t overfed, then D can’t overproduce and fry itself or anything else; if F isn’t underfed, then D will produce enough to balance the load and maintain the battery.
The trick is in making sure that F is adequately fed when the electrical load requires lots of support and/or the battery needs a charge, and is not overfed when the load is light and the battery only needs a trickle to keep it up.

How does the regulator regulate?
When it cries ‘Enough’, those voltage regulator contact-breaker points open for the first time so far and F is disconnected from D (and therefore from A).
Immediately, the current to the field drops, so the armature’s output drops and so the current from A to the battery also obviously drops. So does the voltage. A split second later the control box decides the voltage is no longer excessive after all, countermands the order, and the regulator closes and reconnects F to D and A. Next instance the cycle repeats – too high a voltage - disconnection. Then, the voltage drops – reconnection. And so on and so forth, depending on revs and load. The contact-breaker is now in ‘trembling’ mode and we’re regulating.

It’s the relative amount of time the regulator points stay shut versus open that determines the average voltage at A. The higher the proportion of time the points are open the lower the voltage, and vice-versa. Thus the voltage at A is maintained at about what it should be to avoid overcharging the battery, to trickle-charge it once it’s fully-charged and to protect any electrical components that are in use from blowing.

As dynamo revs drop off (or as the electrical load increases to the point that the dynamo can’t sustain the prescribed regulation voltage) the regulator switch stops trembling and closes to let the full output from D go to F once again. D and A remain connected through the cut-out. The dynamo is running unregulated once more.

As the revs drop off even further, the point will be reached where the cut-out senses that the battery needs to be disconnected – and opens to prevent the battery trying to drive the dynamo as a motor.
A is disconnected from D, while D and F remain fully connected at the regulator.

This is precisely where we started.

Cheers, Bill
Bill

Offline RichardL

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Re: my '61 BSA super rocket is negative earth... really?
« Reply #14 on: 14.12. 2014 18:41 »
Groily (being one of those names I could think of),

Great post. I must confess that I plagiarized one sentence in my post from a different matchlessclueless page. Specifically, "equilibrium is reached for a given engine speed. " http://matchlessclueless.com/electrical/lucas/repolarising-lucas-dynamo/
I would have gotten away with it until you stepped in.  *smile* *smile*

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.