polarity

[single]

I reckon some of the 12v sockets are reverse polarity but how do i check.Most stuff works but things like strip lights don't.

 

[bedouin]

I think a cheap multi-meter is an essential part of a boat's tool kit - you can pick them up for a fiver.

Other than that pretty much anything with an LED indicator in will tell you. LEDs require the correct polarity so in most cases the LED will only light up if the polarity is correct - I have for example a 12V socket splitter that also provides USB power that has an LED indicator that would show.

 

[single]

Cheers....forgot about that.

 

[chasroberts]

I managed to find a 12v testlight probe that looks like a standard 240V test screwdriver but has a long cable and a crocodile clip. Attach the clip to the -ve terminal on your battery and than probe away to find any positive you like. Also works the other way round and is good for checking earth connections etc. etc. A great piece of simple kit that is always in use. If you can't find one to buy there is a fascinating (and easy) set of instructions to build one yourself using an old biro case:

http://www.electronics-tutorials.com/test-equip/led-test-lamp.htm

Good luck

Chas

 

[VicS]

Or the simple way is to dip a piece of red litmus paper in some salt solution. Touch the two wires onto it.

The litmus will turn blue around the negative wire and be bleached around the positive wire

 

[lustyd]

Or the simple way is to dip a piece of red litmus paper in some salt solution. Touch the two wires onto it.

The litmus will turn blue around the negative wire and be bleached around the positive wire

You're a very clever man but that has to be the most complicated solution to a problem I've ever seen on these forums! well done for thinking outside the box though

 

[pappaecho]

If you have a LED bulb, it will not work if the polarity is reversed

 

[VicS]

You're a very clever man but that has to be the most complicated solution to a problem I've ever seen on these forums! well done for thinking outside the box though

Hardly complicated ! Every school kid can use litmus paper, although I suppose these days they all use universal pH paper but that would work just as well.


I claim no credit for the idea! It predates digital multimeters by many decades. Predates me as well I should think.

 

[viago]

Or the simple way is to dip a piece of red litmus paper in some salt solution. Touch the two wires onto it.

The litmus will turn blue around the negative wire and be bleached around the positive wire

very interesting. im not sure exactly how that works but im guessing that he would use the salty litmus paper to bridge the socket wiring. would the different reactions then be caused by a cathodic/anodic type event?
should the positive feed wire be red or brown?
also, if electrons are negatively charged particles then how come they flow to the negative terminal of the battery? opposites attract as i remember.

 

[neil1967]

LED would work, but perhaps not an LED bulb - many have built in regulators which mean they are not polarity sensitive.

Neil

 

[VicS]

very interesting. im not sure exactly how that works but im guessing that he would use the salty litmus paper to bridge the socket wiring. would the different reactions then be caused by a cathodic/anodic type event?
should the positive feed wire be red or brown?
also, if electrons are negatively charged particles then how come they flow to the negative terminal of the battery? opposites attract as i remember.

It works by electrolysis of the salt solution.

Just hold the two wires onto opposite ends of the salt soaked litmus.

Positive sodium ions migrate to the negative end. They form sodium hydroxide which turns red litmus blue. The negative chloride ions go to the positive end. You'll get some hydrochloric acid formed ( which would turn blue litmus red) and chlorine which bleaches the litmus.

There's a you-tube video if you Google http://www.youtube.com/watch?v=TaeDg9cgjTU

You went to school presumably so you will almost ceratinly have seen the same thing with a Hoffman Voltameter filled with brine and some litmus solution. One arm goes blue, the other red before being bleached.

Electrons flow FROM the negative terminal of a battery etc to the positive.

That's the opposite way to the conventional way in which electricity flow is usually represented ....... Physicists are like Engineers ... a bit slow to understand things properly!