Author Topic: - or + Earth  (Read 803 times)

Offline Slymo

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- or + Earth
« on: 04.11. 2018 03:02 »
About to start wiring my 58 SR and have come across both positive and negative earth diagrams. My incination is to go negative earth but want to know if it is incompatible with the year?
NZ

Offline muskrat

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Re: - or + Earth
« Reply #1 on: 04.11. 2018 03:50 »
G'day Slymo.
Positive earth from 51 to 63.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Online beezermacc

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Re: - or + Earth
« Reply #2 on: 04.11. 2018 07:05 »
I find it easier to wire +ve earth as some of the regulators on the market require you to alter the dynamo wiring if using negative earth.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline mikeb

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Re: - or + Earth
« Reply #3 on: 04.11. 2018 09:43 »
its easier to wire negative earth if you ever want modern kit like bright LED lights (yes you do - you live in a rainy country).
decent electronic regulators can be got for either +ve or -ve and no dynamo rewiring needed (just re-flashing - 5 min job)
the rivet counters will only grumble if they can see which way the electrons are traveling
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Offline Slymo

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Re: - or + Earth
« Reply #4 on: 04.11. 2018 09:51 »
Ah I thought as much. I suppose I should stick with originality. They do sell LEDs both for positive and negative earth although I agree negative earth ones are likely to be more easily aquired. The last ones I purchased were from a vintage car site in the states and they were not cheap.  Ive thought about using an led as the pilot light which can run all day and keepingnthe headlamp bulb traditional as I do prefer the colour of a tungsten bulb whenndrivig at night.
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Online groily

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Re: - or + Earth
« Reply #5 on: 04.11. 2018 12:01 »
Just to elaborate a tad on the regulator question in relation to choice of earth, as it can be confusing.

The commonly-admired DVR series and the V Reg 2 from AO Services (Alan Osborne)  come in Pos or Neg earth at 6 or 12v and don't require changes at the dynamo. I think the same goes for the Podtronics 6v units too.
The two to watch on this are, first, the Neg earth Wassell 6v item, and also  JG units. They both require the field coil to be connected between F and D at the dynamo, with just a brush to earth.

Why the Wassell Neg earth unit isn't designed to regulate on the same side as the Pos earth one I don't really know. What I do know is that these particular items have been known to struggle to maintain a decent system voltage; many would say 'you get what you pay for'.
The explanation for the JG units is simpler  because were designed to work on Miller systems back in the 80s, and Miller wired their dynamos with the field between F and D, not the Lucas way of F to E. Most or all continental dynamos are also wired F to D.

So as Beezermacc says, you gotta be careful here. I also have my own machines on Pos earth just so I don't muddle myself up!
Bill

Offline Slymo

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Re: - or + Earth
« Reply #6 on: 04.11. 2018 18:47 »
I have two new copies of the original lucas buzzing coil regulator with the metal lift off lid which I guess are made in India or China although there is no identification of any sort on them . Always a pretty trouble free unit in my experience. I'll run them both up on the bench and see if they work as they should. Guess its a Positive earth set up for the sake of originality.
NZ

Offline trevinoz

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Re: - or + Earth
« Reply #7 on: 04.11. 2018 19:59 »
Good luck trying to accurately set the pattern regulators.
The adjusting screws are too coarse and it takes a lot of patience  to  get a good result.

Online duTch

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Re: - or + Earth
« Reply #8 on: 04.11. 2018 21:13 »
 Slymo, I bought one of those and it seems to work ok, but be aware that the cover was (is) shorter than the original and the reg.frame is a bit taller, so the cover was rubbing on the frame and causing me grief.
 I used my old Brass cover instead, but still had to  *work* carve some material from the corners of the frame to stop it earthing out, and re-shape the cut-out in addition to insulation (cereal packet- uprated to modified plastic yoghurt container lid *conf*) in the top of the cover (it was obvious where it was rubbing), which I also have packed up with small SS screws in the cover seats......also the mounts were out-of-whack so re-riveted those....

 You may have better.......but it works ok 6 years later, though of late have had an occasional erratic meter which may be the meter as the battery charge is ok.... *conf2*

 edit PS- I was sticking to +ve earth, but went to -ve earth to save myself confusion- I'm mechanically dysliexic enough already  *eek*

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Online Greybeard

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Re: - or + Earth
« Reply #9 on: 05.11. 2018 09:12 »
Re problems with voltage regulators: I have a DVR2 inside a genuine old reg case. It looks original and requires no attention. I'm still on 6v POS earth.

Online Rex

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Re: - or + Earth
« Reply #10 on: 05.11. 2018 09:33 »
The two to watch on this are, first, the Neg earth Wassell 6v item, and also  JG units. They both require the field coil to be connected between F and D at the dynamo, with just a brush to earth.

I inherited one of these units from a friend after doing some work for him on his bike, and although unused it had no instructions with it. Can you expand on what changes (if any) I would need to make to the dynamo wiring configuration on my 1951 A7?
I would normally spring for a DVR2 unit as I've had good service from them (but not the dire AO unit!!) but in this instance I thought I might as well give this unit a try first.
It also helps that I have an Indian-made control box for gutting....and that was about all it was ever any good for. Utter rubbish!

Offline Slymo

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Re: - or + Earth
« Reply #11 on: 05.11. 2018 09:55 »
I have to admit to having a friend who is a mechanical and electrical savant. He has made a superb capacitor discharge remagnitiser with which I will ensure maximum output from my K2F and he is a extremely skilled at adjusting the regulators so they produce 8 volts. With regard to the shorting cover I had that problem with an original Lucas one on an early Redditch RE Bullet I had and I found that lining it with cardboard cut from a cerial packet sorted the shorting out a treat.
NZ

Offline cyclobutch

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Re: - or + Earth
« Reply #12 on: 05.11. 2018 13:03 »
Re problems with voltage regulators: I have a DVR2 inside a genuine old reg case. It looks original and requires no attention. I'm still on 6v POS earth.

Ditto apart from sticking in an old case. My bike is mongrel enough not to worry on that score.
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Online Greybeard

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Re: - or + Earth
« Reply #13 on: 05.11. 2018 13:18 »
Re problems with voltage regulators: I have a DVR2 inside a genuine old reg case. It looks original and requires no attention. I'm still on 6v POS earth.

Ditto apart from sticking in an old case. My bike is mongrel enough not to worry on that score.
I even soldered the DVR2 connections to the original reg internal connectors so it looks exactly original.

Online groily

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Re: - or + Earth
« Reply #14 on: 05.11. 2018 14:02 »
Hi Rex: not sure whether you have inherited a JG unit or a Wassell neg earth one? The JG is a good unit for going 12v. One I had for many years had just three wires off (DF&A) as the box was earthed - not sure if that is still the same as haven't got a more recent one to look at. The Wassell thing has 4 wires, same as went to the Lucas box. Black I think is earth on them. Without wanting to be unduly critical, not such a good thing maybe.

The dynamo change is really quite simple.
If you look at the brush end of the dynamo, you'll see 2 wires coming through from behind the mica insulating plate that the brushes are mounted on. They are the wires from the field coil. Both are probably black, may well be a bit frayed - and not easy to tell apart.
One of them will be attached to the F terminal of the dynamo (either to a brass plug-in bit on the brush-plate, or by a 4BA nut to the rear of the bakelite/plastic end cover, depending on which exact model you have). The other will be earthed, and probably secured by the same little screw as the earthed brush. (The other brush goes to the dynamo D terminal.) So - there is one wire from the field coil and one brush, both to earth. There is one wire from the field coil to the F terminal, and there is one brush to the D terminal. This was the way Lucas did it, and works with DVR2s etc as discussed.

The Wassell thing and the JG work differently. Any dynamo just about can be regulated either way - the difference simply being that the field coil must be connected between F and D inside the dynamo end cover, not between F and earth. So really, as long as the wires are long enough and the routing is OK, it's a quick job to change over. The result is one brush earthed all on its own, the field coil wires to F and D, and the other brush also on D.

(Note that the standard standalone test for dynamo output by bridging F and D and putting a meter or bulb from bridge to earth won't work now - the equivalent test is done by bridging F to E, and putting the meter or bulb between D and E. Testing for regulated output on the A lead from the regulator to ammeter/switch/battery remains the same.)

If you get muddled about which field coil wire went where/ goes where, then you'll need to check the rotation is still correct by driving it to see which way it needs to turn to produce lectrickery. If the 'wrong' way, then the wires now at F and D need swapping over. (Or you could swap the brushes over for that matter on E3Ls, for the same result - but don't swap both or you end up where you started.)
Sometimes it can be more elegant to swap things around a bit to get nice easy routes for the brush leads and the field wires and their connecting tags, but mostly there's no hassle.

If in doubt as to whether the polarity of the dynamo has been messed up - it shouldn't have, but things happen! - then flashing the field will confirm it's whichever way you want. Neg earth presumably if it's the Wassell thing you have inherited.

No changes are needed to any of the bike's wiring. F and D plug into the dynamo as before.

As an aside, I occasionally find that Lucas dynamos where I am in France have been wired with the field from F to D because that is how continental folk look at these things   . . . so then we have to go through the opposite routine if they want to fit a DVR or similar . . .

Bill