Reversed Polarity

[crandall]

I've an odd problem here. I've just fitted a new loom to my 18s 1952. Everything fitted fine and it corresponded to the wiring diagram and it all worked too.

I then took the battery out, 2 cells wired in parallel, to charge it up. But when I connected the charger I got a big spark. I placed a multimeter on the battery and noticed the battery had reversed its polarity.

Apparently this can happen when a battery gets completely flat and is then charged up with the with the charger leads around the wrong way. I've also heard that although it'll work it will shag the battery out pretty quickly as its not designed to work that way around.

So my question is how do I set it right? Is it a simple matter of swapping dynamo wires over to make it charge the right way? Or do I have to flash the dynamo?

It's a positive earth and the new loom was made as a positive earth. It has an electronic regulator.

I'd really appreciate any help you chaps can give me as I'd love to sort this out before the summer.

Thanks in anticipation

Clint

[Rob Harknett]

How are you going to change the polarity of your brand new electronic regualtor?
I think I'd play safe and go for a cheaper option of getting a new battery, rather than buy another a new regulator, as you intend to change the porlarity ?????? Just get a new battery is the simple answer and may work out by far the cheapest. The battery may not be that good anyway having been left flat for ???? time

[en7jos]

Hi Clint,

Sounds like you should first check what polarity the dynamo is working at to ensure this is also giving a positive earth output (to match your loom and regulator). Also, you're sure the electronic regulator is +'ive earth right?

I don't quite follow what happened with charging the battery. Do you think it had already reversed polarity before charging, or was this during charging? Not quite sure how a battery (lead-acid type?) can reverse polarity as would have thought this was fixed by the chemistry and plates in the cells. I once had a battery (admittedly back in India where anything is possible!) where the terminals were incorrectly labelled - culd that be teh case with your battery too?

In case it helps, there's some instructions for flashing / repolarising a dynamo on my website:
http://matchlessclueless.com/electrical ... as-dynamo/

Regards, James

[GSAX1]

In my youth I worked in a auto electric workshop, and one day a truck came in that had the charging light on after the owners had charged the (two) batteries overnight. Suspecting a dynamo fault I took it out and tested it in our bench, however there was nothing wrong with it. The regulator was also OK. I then checked the batteries, and to my surprise the polarity was opposite to what it should have been. The owners had charged them the wrong way! I then discharged the batteries completely overnight, and recharged them the right way the next days. The truck then started right up and charged normally.

Some months later the owners told us that the batteries still were functioning normally, so I guess the operation was a success .

[en7jos]

Found this which would seem to answer the various questions:
http://www.batterystuff.com/blog/batter ... arity.html

Didn't think this would be possible, but you learn something new everyday, hey. James

[crandall]

Thanks fellas, I think the route to head down is the dynamo polarity. The electronic regulator is a positive earth one and it was working fine before I fitted the new loom, although the loom was brittle and cracked, so I suspect that isn't the problem. I tried a new battery this morning and and soon as I connect it the correct way, ie positive to earth, I get sparking at the terminal and blowing of the main fuse, when I reverse connection it's fine. So sadly I don't think I'm going to be as lucky as GSAX1 on this occasion.

James, may I take this opportunity to commend you on your excellent website, it's an excellent resource, good job and well done, cheers.

So my next move is to flash the dynamo to positive earth and see what happens. I'll let you know how it goes.

Cheers

Clint

[crandall]

UPDATE - Just checked the output from the dynamo, using James' website on the ipad down in the garage which was brilliant, and it is generating current correctly as a positive earth unit. So I then checked the wiring of the Wassel 6v + earth electronic regulator, the instructions use different colours to the original wiring diagram, but with a bit of deduction I think I might be on to something; the F & D wires from the dynamo are definitely connected correctly, I've checked continuity and they are good, but the 2 others are so obvious, so I've swapped them around and when I connected the new battery positive to earth, no sparks.

I'll report after a test run.

Clint

[crandall]

I'm pleased to report that it's sorted. The problem was that the A and the E wires were around the wrong way, the ammeter was also reading backwards, but I swapped the wires around on that too and all seems well.

Many thanks for all your help, especially James and that brilliant website.

Clint

[en7jos]

Glad you've found the solution Clint and pleased you found my website useful.

Regards, James