Hi,
Oscar, as I'm not well up on electrics is there any particular reason that I should be aware of for the Dexta to be Negative Earth??
Brian, should I revert the Dexta to Positive Earth?? would there be any benefit and if I do will I need to replace anything or just re-set the dynamo.
Regards,
Barry
Oscar/Brian
Barry,
As she has a dynamo there is no problem. You must take both wires off the dynamo then run a wire from your output terminal on the battery whether it be positive or negative, to the smaller of the two terminals, the field terminal. Hold it on there for about 10 seconds and the job is done, replace the wires. You may get a small amount of sparking at first but this is normal.
It becomes second nature when you fit dynamos because if you don't you can burn out a lot of electrical systems, so every time we fitted a dynamo, we went through that procedure.
As she has a dynamo there is no problem. You must take both wires off the dynamo then run a wire from your output terminal on the battery whether it be positive or negative, to the smaller of the two terminals, the field terminal. Hold it on there for about 10 seconds and the job is done, replace the wires. You may get a small amount of sparking at first but this is normal.
It becomes second nature when you fit dynamos because if you don't you can burn out a lot of electrical systems, so every time we fitted a dynamo, we went through that procedure.
Fordson Tractor Pages, now officially linked to: Fordson Tractor Club of Australia, Ford and Fordson Association and Blue Force.
Brian
Brian
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Mike Kuscher
- Site Governance Team
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- Joined: Wed Apr 16, 2008 10:18 am
- Location: Worcestershire, England
Hi Barry,
Whilst waiting for Oscar and Brian, here's my 'three penneth'...
This, of course, meant a lot of wiring until some 'bright spark' thought about connecting everything to a 'common feed' and make everything 'live' then just take negative connections to the things you wanted to 'power'. This reduced the wiring needed by 'nearly' 50 per cent.
Why 'common feed'?
Well again, 'logically' it was believed that negative was earth, was ground, was 'common', and that electricity flowed from the positive to the negative so needed to flow 'to' anything you wanted to 'power' and, anyway, it worked so why not?
Later on, electronics research actually showed that current flows from the negative (which is why it is always 'more minus') to the positive (which is why it is always 'more plus' - but let's not 'get heavy' on semi-conductor junctions and the like). More interestingly, they found that because of this, if they reversed the way things were wired, contacts, armature brushes, releys etc., did not 'burn out' as quickly so, in the sixties, manufacturers started to re-wire vehicles with a 'common negative' or 'negative earth'. They also has a 'political' safety 'lever' applied to their decision (explained later).
This also started to allow them to incorporate new advances like diodes (not welsh money lenders) to produce more efficient charging systems (alternators) but, due to costs, these changes were gradually phased in.
For example, my A35, the first 'real' Minis and my 1200 three bearing crank MK1 cortina were all positive earth with dynamo's (generators). The later Mini's and my much missed 1300 GT Escort (I refuse to refer to it as the MK1 because the first 'Escort' was an Anglia Van) were 'negative earth' with alternators.
The Dexta was originally 'positive earth', if you want to keep 'originality' it should be 'positive earth'.
If your Dexta has an alternator fitted, you'll need to replace it with a generator, re-wire and either replace (if it's missing) or rewire your regulator. Approx. 2 hours work.
If your Dexta still has a generator, you'll just have to re-wire then 'flash' the generator to reverse polarity (see Brians earlier post). Approx half hours work.
If you use your Dexta as a 'tool' then, if it 'aint broke, don't fix it.
Little bit of history...
What was the main prompt to change from 'positive earth' to 'negative earth'? A petrol tanker fire!
Originally, with positive earth, everything had a 'live feed' and just needed a negative connection to complete the circuit. Going back to when I was still in short 'leder hosen', a petrol tanker burst tyres whilst crossing a 'metal'd bridge' to a storage depot. The metal rims of the wheels made contact with the bridge and, as everything was wired 'positive', the 'earth' connection to the metal of the bridge completed the circuit with dramatic results. That was the initial prompt for the change, following political pressure.
My Major is 'positive earth', charges the battery 'like a gud un' and stays that way but, as I said, It's personal choice.
Mike
Whilst waiting for Oscar and Brian, here's my 'three penneth'...
When motor vehicles, tractors etc., were first started being built, it was logical to interconnect everything electrical by taking positive and negative wires to each individual item you wanted to 'power'.Oscar, as I'm not well up on electrics is there any particular reason that I should be aware of for the Dexta to be Negative Earth??
This, of course, meant a lot of wiring until some 'bright spark' thought about connecting everything to a 'common feed' and make everything 'live' then just take negative connections to the things you wanted to 'power'. This reduced the wiring needed by 'nearly' 50 per cent.
Why 'common feed'?
Well again, 'logically' it was believed that negative was earth, was ground, was 'common', and that electricity flowed from the positive to the negative so needed to flow 'to' anything you wanted to 'power' and, anyway, it worked so why not?
Later on, electronics research actually showed that current flows from the negative (which is why it is always 'more minus') to the positive (which is why it is always 'more plus' - but let's not 'get heavy' on semi-conductor junctions and the like). More interestingly, they found that because of this, if they reversed the way things were wired, contacts, armature brushes, releys etc., did not 'burn out' as quickly so, in the sixties, manufacturers started to re-wire vehicles with a 'common negative' or 'negative earth'. They also has a 'political' safety 'lever' applied to their decision (explained later).
This also started to allow them to incorporate new advances like diodes (not welsh money lenders) to produce more efficient charging systems (alternators) but, due to costs, these changes were gradually phased in.
For example, my A35, the first 'real' Minis and my 1200 three bearing crank MK1 cortina were all positive earth with dynamo's (generators). The later Mini's and my much missed 1300 GT Escort (I refuse to refer to it as the MK1 because the first 'Escort' was an Anglia Van) were 'negative earth' with alternators.
in my opinion, it's just a matter of logical choice.Brian, should I revert the Dexta to Positive Earth?? would there be any benefit and if I do will I need to replace anything or just re-set the dynamo.
The Dexta was originally 'positive earth', if you want to keep 'originality' it should be 'positive earth'.
If your Dexta has an alternator fitted, you'll need to replace it with a generator, re-wire and either replace (if it's missing) or rewire your regulator. Approx. 2 hours work.
If your Dexta still has a generator, you'll just have to re-wire then 'flash' the generator to reverse polarity (see Brians earlier post). Approx half hours work.
If you use your Dexta as a 'tool' then, if it 'aint broke, don't fix it.
Little bit of history...
What was the main prompt to change from 'positive earth' to 'negative earth'? A petrol tanker fire!
Originally, with positive earth, everything had a 'live feed' and just needed a negative connection to complete the circuit. Going back to when I was still in short 'leder hosen', a petrol tanker burst tyres whilst crossing a 'metal'd bridge' to a storage depot. The metal rims of the wheels made contact with the bridge and, as everything was wired 'positive', the 'earth' connection to the metal of the bridge completed the circuit with dramatic results. That was the initial prompt for the change, following political pressure.
My Major is 'positive earth', charges the battery 'like a gud un' and stays that way but, as I said, It's personal choice.
Mike
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Chris Ivin
- True Blue
- Posts: 149
- Joined: Wed Apr 16, 2008 6:17 pm
- Location: Brailes, Warwickshire, UK
Whilst we are talking electrics, certain French machines are "earth switched".
In other words, instead of breaking the "live" feed with a switch before the bulb or motor, they do it afterwards. This can caused lots of headaches if you are working on a Moreau beet harvester at 10pm in the evening and can't find out why solenoid valves don't work properly.
In other words, instead of breaking the "live" feed with a switch before the bulb or motor, they do it afterwards. This can caused lots of headaches if you are working on a Moreau beet harvester at 10pm in the evening and can't find out why solenoid valves don't work properly.
Fordson Tractor Pages, now officially linked to: Fordson Tractor Club of Australia, Ford and Fordson Association and Blue Force.
Brian
Brian
Brian/Mike,
Thanks for your replies on this subject, so if I have understood correctly there is no need to rewire anything nor change anything within the electrical system such as starter, control box, solenoid etc etc they should work ok with either positive or negative. Therefore all I need do to get her back to original is to follow Brian's explanation on how to re-set the Dynamo.
I'm sure I'm correct in saying that Oscar has rewired the Dexta completely, therefore I was concerned that perhaps it was done as Negative earth for a specific reason?? and if I re-set the Dynamo to Positive earth for originality I would be likely to damage something within the electrical system.
Thanks Guys.
Regards,
Barry
Thanks for your replies on this subject, so if I have understood correctly there is no need to rewire anything nor change anything within the electrical system such as starter, control box, solenoid etc etc they should work ok with either positive or negative. Therefore all I need do to get her back to original is to follow Brian's explanation on how to re-set the Dynamo.
I'm sure I'm correct in saying that Oscar has rewired the Dexta completely, therefore I was concerned that perhaps it was done as Negative earth for a specific reason?? and if I re-set the Dynamo to Positive earth for originality I would be likely to damage something within the electrical system.
Thanks Guys.
Regards,
Barry
Mike,Mike Kuscher wrote:...a petrol tanker burst tyres whilst crossing a 'metal'd bridge' to a storage depot. The metal rims of the wheels made contact with the bridge and, as everything was wired 'positive', the 'earth' connection to the metal of the bridge completed the circuit with dramatic results...
My 2d worth to your 3d!
Forgive me for asking but why should connecting just one battery terminal to ground (via the bridge), be a problem? No current will flow unless the other terminal is also grounded by some means? Is it not the same as a bird sitting on a high voltage cable? The bird's 'chassis' just sits at that potential and the bird comes to no harm.
According to the Rolls Royce owners club from the Silver Cloud onwards, polarity was changed to -ve earth to reduce corrosion.
http://www.rroc.org.au/wiki/index.php?t ... l:Polarity
All the best,
Ben
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Mike Kuscher
- Site Governance Team
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- Joined: Wed Apr 16, 2008 10:18 am
- Location: Worcestershire, England
