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AUSTIN 301 LORRY/POLARITY CHANGE
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holdfast



Joined: 30 Dec 2009
Posts: 5
Location: north east worcestershire.

PostPosted: Wed Dec 30, 2009 11:47 am    Post subject: AUSTIN 301 LORRY/POLARITY CHANGE Reply with quote

Hello
i wish to change the polarity of my 50's lorry. it is positive earth with a dynamo.
i know the starter motor is not polarity sensitive, but i am afeared that something else will short out or explode if i change anything else.

where do i start?

who will hold my hand?
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Phil - Nottingham



Joined: 01 Jan 2008
Posts: 1252
Location: Nottingham

PostPosted: Wed Dec 30, 2009 12:31 pm    Post subject: Reply with quote

Unless its got a radio and possibly a clock - nothing really.

If it has ammeter then leads will need swapping as will coil.

Dynamo may need polarising if does not charge by touching jump lead a couple of times on the D (small) terminal.

Note also that battery terminals are different sizes so may not fit well after just swapping over leads especially if helmet type so will need renewing
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Wed Dec 30, 2009 12:44 pm    Post subject: Reply with quote

We changed lots of vehicles battery polarities to enable the use of solid state two way radios. There are absolutely no problems except with solid state (transistor) components or motors with permanent magnets for the field magnetism (instead of windings). Wound-field motors, like your starter motor will run in the same direction. It is very unlikely that any motors on a 1950s vehicle will have field magnets or solid state electronics.

The procedure is simple. Fit the battery with the polarity reversed and remove the field (small terminal) wire from the dynamo. Connect a jump wire to the +ve battery terminal and hold it on the dynamo field terminal for 5 to 10 seconds. That will reverse the polarity of the residual magnetism in the field poles and the dynamo will charge with positive live.

Job done! But if your regulator makes buzzing noises you did not hold the jump wire on long enough.

There is one exception I know of which is the Daimler DR450 range. There may be others. But if so they will have an alternator WITH POSITIVE EARTH. As long as you have a dynamo there are no problems.

While I was typing this Phil from Nottingham beat me to the posting. He rightly mentions the ignition coil connections. I over looked that, but the small dynamo terminal is the "F".
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are ever likely to want". Computers had not been invented then!


Last edited by Jim.Walker on Wed Dec 30, 2009 2:04 pm; edited 1 time in total
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holdfast



Joined: 30 Dec 2009
Posts: 5
Location: north east worcestershire.

PostPosted: Wed Dec 30, 2009 12:57 pm    Post subject: AUSTIN 301 Reply with quote

Many thanks for advice, i have wanted to fit a radio for years as 30 mph journeys are a bit tedious!

if you hear a BANG over Bromsgrove i havent been paying attention!
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First Bedford



Joined: 11 Dec 2009
Posts: 107
Location: Darlington, Durham

PostPosted: Wed Dec 30, 2009 8:31 pm    Post subject: Reply with quote

I have a 52 Bedford, same positive earth. Is there a benefit to changing Polarity?
Pete
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Wed Dec 30, 2009 11:08 pm    Post subject: Reply with quote

I would say "no", First Bedford, unless you wish to add modern electronics such as things with transistors or diodes etc.

Just my opinion. I have 3 +ve earth machines and I see no point in changing them from original (authenticity?).
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!
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Phil - Nottingham



Joined: 01 Jan 2008
Posts: 1252
Location: Nottingham

PostPosted: Wed Dec 30, 2009 11:09 pm    Post subject: Reply with quote

The only benefit is that modern electronic equipment can be used without having to make arrangments to ensure it casing polarity is negative earth togther with anything connected to it eg radio aerials.
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First Bedford



Joined: 11 Dec 2009
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PostPosted: Thu Dec 31, 2009 12:46 am    Post subject: Reply with quote

Sorted, it will stay as original.
Pete
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