Positive Earth ????

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Positive Earth ????

Post  annrubenesque on Sat Oct 30, 2010 8:14 pm

We have got ourselves a project 1969 Worsley Hornet in needs of some tlc....

It needs a battery as wasn't present when picked up...I have been told that we need A POSTIVE EARTH battery, is that correct and does that mean I need to obtain from a specialist battery dealer.

I have been into mini's for years and would like to know what is effected by this POLARITY CHANGE.

I need to replace the rear fuel pump so I guess i need one that is not effected by the polarity change ???

any help will be much appreciated...

Dusty

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Re: Positive Earth ????

Post  RobBFG on Sat Oct 30, 2010 9:07 pm

I believe that all Elf and hornets were built as positive earth. Mine had already been switched when I got it. The battery I bought from Halfords a few years ago had the terminals the wrong way round for negative earth (they're way too close to the clamp bar) so that would be ideal.

Quoteing Lindsay Porter in The Guide to Purchase and DIY Restoration Mini (a usefull book I have found) the clock, electronic ignition, ammeter, air horns, windscreen washer pump, and rev counter are the only polarity sensitive items. None of which is in a standard Elf or Hornet, though I have fitted an air horn to mine and it came to me with an electric washer pump (now replaced with an original hand pump).

If you have an alternator fitted then it is negative earth. If you have a dynamo fitted it is possible to change it's polarity.

I'm sure someone will correct me if I'm wrong.
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Re: Positive Earth ????

Post  superworm on Sun Oct 31, 2010 1:06 am

Rob is correct.....

I have recently converted my Elfie back to "negative" earth (positive as original then changed to Negative Earth and back to Positive earth at restoration) as I had fitted a cigar lighter to drive my (daughter's - when I steal it) Sat Nav. To change the polarity of the Dynamo, you only need to disconnect the field terminal (the smaller of the two "Lucar" spade connecters) and "Flash" that terminal a few times with a wire feed from the battery positive terminal...the starter solenoid is a good place to source some positive power!....just "stroke" the terminal with the bare end of the live wire...it'll spark a little....then reconnect the cable.

The only thing I needed to do was to switch the terminals on my windscreen washer (now electrical) pump so that it pumped water onto my windscreen rather than suck any rain off it!!!!!!! and to switch the terminals on my indicator "bleeper" piezo that I obtained from Maplins (in case I'm driving around with indicators flashing when they shouldn't). Some radios require that you change the polarity switch on their cases whilst other radio's change polarity automatically.....make sure you disconnect the radio feed before you change the polarity in case its not automatically detected....some older ("Period") radios where only ever Positive earth so you'll have to totally isolate it from any surrounding metal structure and provide a separate negative lead wire to the power connection and a positive lead wire to the case.

Standard SU pump doesn't give a monkey's about polarity!!!!!! but note what Rob says about clocks, electronic ignition systems, etc

Cheers

Alan
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Re: Positive Earth ????

Post  annrubenesque on Sun Oct 31, 2010 12:51 pm

Thanks for the advice guys, that hopefully means I can use my mini battery on it and get it running, once i'v obtained a new fuel pump...


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Re: Positive Earth ????

Post  cheleker on Mon Nov 01, 2010 6:34 pm

Another way to answer you question is that there is really no such thing as a positive earth battery. The real issue is the location (and, in some cases) size of the posts on the battery. Your concern should be whether the cables will reach the terminals with the battery in place.

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Re: Positive Earth ????

Post  asahartz on Tue Nov 09, 2010 10:26 pm

I've usually found that the cables will reach. However I also generally use a far higher capacity battery than the original recommendation - currently I have cars with 075, 068 and 027 batteries fitted. Each of these is available with the terminals the other way round - can't remember which is which but a trawl through, for example, tayna.co.uk gives listings with prices, dimensions, capacity and pictures showing which way the terminals are.
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Re: Positive Earth ????

Post  humph on Tue Feb 08, 2011 1:13 am

Interesting thread guys. I haven't picked my Elf up yet, so please excuse the noobie questions I may ask. I am already aware that the Elf is +ve earth, but how can I tell if it has had it's polarity reversed?

Obvious answers would appear to be 1) Ask the current owner, 2) check for an alternator, but anything else? check the battery terminals and cables?

Any advice greatfully received, cheers guys.

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Re: Positive Earth ????

Post  Zef on Tue Feb 08, 2011 1:21 am

Spot on with checking the battery terminals and cables. -ve earth would have the -ve from the battery connected to the body of the car. Very Happy
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Re: Positive Earth ????

Post  humph on Tue Feb 08, 2011 1:31 am

Cheers Zef, just wanted to check really as +ve earth cars are new to me. I suspect the polarity may have been changed, time will tell.

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Re: Positive Earth ????

Post  Zef on Tue Feb 08, 2011 1:35 am

Apparently it's easy to change the dynamo's polarity although I just cheated and fitted an alternator for reliability (I used my Elf year round through winter)
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