Curly battery problem for nerds

[Expert]

got a curly battery problem. well, not me, my dad in the uk.

he emailed me this morning about a bike he's had in for repair with an electrical fault.
the bike seemed to be refusing to charge and was and was blowing fuses.

after going through everything and much head scratching he disconnects the battery and checks the battery voltage and finds that the battery polarity is reversed, so positive is negative.

the owner of the bike had put a new battery on it before father picked it up.
dad fits a new battery and the bike is all good.

how can this happen? what dictates the polarity of a battery?

i remember in school we made batteries in science class, bolted lead strips to the inside of plastic coffee jar lids and filled the jars with acid and then screwed the lids on so the lead was in the acid and that's a battery. give it a charge and it worked.
i dont remember though what dictated the polarity. was it the first charge? was it some difference in the lead strips which appeared the same? divine intervention?
all lead acid batteries work on the same principle so....

Can a battery receive it's first charge at reversed polarity and forever be stuck with that orientation?

any input? it's got me scratching my head.

maybe the manufacturer of the battery got the symbols the wrong way around in the factory? unlikely i would guess. a rookie mistake even for the worst chinese battery company.

[avgas]

To reverse it would require some effort as your effectively changing the anode tank to a cathode tank and vice versa. This is dictated by what charge is floating in the tank - the thing connecting the 2 tanks (lead strip?) loops the circuit.

To put this into a real world application - imagine changing ice cream into water and water into ice cream. Not impossible - but not likely.

I imagine it was around the wrong way to start......or......

what he was seeing was the LOSS across the battery. e.g. -12v means the battery is consuming 12v of the source (meter or capacitor?) across it. Which means is fucked.......and effective a big bit of carbon.

I am assuming it was a lead acid battery? What was the exact voltage he measured?
Did he try hooking up the battery back to front and seeing if it started the bike?

I would be surprised if someone hooks up a new battery, finds the bike doesn't start then doesn't instantly assume the battery is a problem

[unstuck]

:scratch::scratch::blank::no:

[bogan]

Depends on the age of the bike a lot, older bikes would still potentially run with reverse polarity wouldn't they? points/coil might take a bit of damage, but still work in theory, even start motor and relays would still spin correctly as both the armature and stator windings would be reversed. Only the charging system would be blowing fuses, or discharging the battery if the fuse didn't blow. Course you wouldn't expect one with a CDI or transistor points to run at all...

[Laava]

Prob be a huge improvement on Italian bikes?:bleh:

[avgas]

Depends on the age of the bike a lot, older bikes would still potentially run with reverse polarity wouldn't they? points/coil might take a bit of damage, but still work in theory, even start motor and relays would still spin correctly as both the armature and stator windings would be reversed. Only the charging system would be blowing fuses, or discharging the battery if the fuse didn't blow. Course you wouldn't expect one with a CDI or transistor points to run at all...
Good point.

May be he had an AC battery :facepalm::laugh:

Expert - get him to put the battery back in and see if the lights turn on.........I suspect they won't which means the battery polarity isn't reversed, its stuffed.

[NinjaNanna]

http://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery


Initial Charge
Initial charging establishes which plate will be the anode, and which the cathode. The process is driven by the forcible removal of electrons from the cathode and the forcible introduction of them to the cathode. This splits the water into Hydrogen (which bubbles and is drawn off) and Oxygen, which binds with the lead on the cathode, producing lead (II) oxide.

Anode Reaction: 2H+(aq) + 2e− → H2(g)
Cathode Reaction: Pb(s) + 2H2O(l) → PbO2(s) + 2H+(aq) + 2e−


my money is on "the battery was supplied dry and whoever added the acid and performed the intial charge fucked up" that person could have been a shop or the previous owner

[Expert]

http://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery



my money is on "the battery was supplied dry and whoever added the acid and performed the intial charge fucked up" that person could have been a shop or the previous owner


That's what i thought, the first person to do the charge fucked it up.

In all honesty Polarity of the battery is probably the last thing i would check, and when you connect a digital multimeter it reads a voltage regardless of which way you have it connected with a only a little minus sign in the corner if it's the wrong way around. lots of modern bikes have diodes in the loom or in the fuse box to prevent reverse polarity problems from wrongly fitted batteries.

I think it was an italian bike, he gets some strange stuff to work on, he had a little 125cc ducati in the other day.