Hello,
My 1930 Ford has a 6v battery.
But there are no markings showing which terminal is + or -
I know this is hard to believe. But there are no markings.
Is there a way of finding out which is which using a multimeter or such like?
THanks
Edited by Dynamic Dave on 13/05/2009 at 19:48
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Put the multimeter on the highest DC range possible. Briefly connect to battery.
If the meter is analogue and the needle doesn't try to go backwards, you've got it right.
If the needle tries to go backwards, you've got it wrong.
Put the meter on the range closest to, and above the battery voltage (say 0 - 10V) to confirm.
If it's a digital meter, again use the highest possible DC range.
If it gives you some stupid reading, you've got it wrong.
Always use the highest possible DC range initially, and you shouldn't damage the meter (hopefully)!
I've never broken my meters, except by dropping them. ;>(
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The positive terminal is usually larger in size than the negative.
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Have you got flat post terminals that are identical or round post which may well be different diameters. The meter test will confirm the polarity. Regards Peter
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Connect two wires to your battery. Obtain a potato. Cut it in half and stick the ends of the wires 1/2" apart in the cut face of the potato.
The potato will turn black around the positive lead.
659.
Always at the cutting edge of technology.
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Thanks to everyone.
Can't wait to get my spud out!
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I think that they were all positive earth, my pre war Ford was anyway. It wont do a great deal of harm if you connect it up back to front as there is nothing electronic on it - unless you have installed something, unlikely with 6 volts. The dynamo can be made to charge the other way round simply by touching a live lead on the large terminal briefly, that will re polarise it.
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To re polarise an earthed-field DC machine (dynamo), the battery live lead should be momentarily connected to the machine field terminal which is the smaller of the two.
This procedure should only be undertaken if you are sure of the charging circuit wiring. In any event, it's very desirable to disconnect the regulator when re polarising a machine. Running up an incorrectly polarised machine risks welding the cutout contacts.
659.
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Unlikely to have a regulator at that age-just a cut-out.
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Some digital multimeters,like mine (Fluke),tell you what polarity you have.The potato idea sounds more in keeping with a 1930s flivver though.
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The potato will turn black around the positive lead.
I am actually going to try that this weekend! :-)
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I saw the potato method on "How" in the sixties.
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Sorry - the small terminal is correct.
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