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Author Topic: 12v batt polarity swap????  (Read 2170 times)

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Offline Boostinjdm

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12v batt polarity swap????
« on: April 20, 2010, 06:04:56 PM »
Anybody heard of an automotive battery swapping polarity on its own?  I'm workin on a skid loader here and turned the key and got nothin.  So I got out my meter and checked the voltage.  It read -9 volts.  WTF?  Yes my meter was correct, I immediatly checked a known good batt to make sure I saw what I thought I saw.
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Offline fabr

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Re: 12v batt polarity swap????
« Reply #1 on: April 20, 2010, 06:06:32 PM »
Ya got me on that one.
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Offline Boostinjdm

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Re: 12v batt polarity swap????
« Reply #2 on: April 20, 2010, 08:58:19 PM »
A picture's worth a thousand words, but I think "WTF?" sums it up nicely.
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Offline Yummi

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Re: 12v batt polarity swap????
« Reply #3 on: April 20, 2010, 09:39:15 PM »
Quote
If a battery is fully discharged and continues to have a load, for example leaving the headlights on, it is possible for one or more cells to reverse polarity. When the battery has been recharged with reversed polarity the polarity can change. This is referred to as "cell reversal". To change polarity, fully discharge the battery and recharge it with the correct polarity.
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Offline Engineer

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Re: 12v batt polarity swap????
« Reply #4 on: April 21, 2010, 05:42:20 PM »
As Yummi reported it is possible.  Be very careful.  I really don't know how I would proceed with it.  I work in battery plants quite a bit, and trying to charge it could result in it exploding.

I would just suggest not leaving it inside or unattended while charging it.
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Offline fabr

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Re: 12v batt polarity swap????
« Reply #5 on: April 21, 2010, 07:25:32 PM »
A point to consider is this also. A battery once discharged to approx 50% will have it's useful life shortened by approx 50% depending on battery type/construction. A completely drained battery will have it's useful life severely shortened. If it were me I'd replace the thing. I had heard of a battery being able to have it's polarity reversed when fully djscharged but had no idea that there could be a mix of some cells doing so and others not. That's what I didn't understand about the 9 something volt reading.I'm still having a hard time wrapping my head around that! Can anyone explain how that could happen to me? 
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I participate in your fantasy"

Offline fabr

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Re: 12v batt polarity swap????
« Reply #6 on: April 21, 2010, 07:26:35 PM »
Engineer ,next time you talk to the battery people ,check this out OK?
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I participate in your fantasy"

Offline Yummi

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Re: 12v batt polarity swap????
« Reply #7 on: April 21, 2010, 07:30:31 PM »
Quote
Reverse charging

Reverse charging, which damages batteries, is when a rechargeable battery is recharged with its polarity reversed. Reverse charging can occur under a number of circumstances, the three most common being:

    * When a battery is incorrectly inserted into a charger.
    * When an automotive type battery charger is connected in reverse to the battery terminals. This usually occurs when a completely discharged battery is being charged, otherwise sparking will occur.
    * When a series string is deeply discharged.

When one cell completely discharges ahead of the rest, the stronger cells will apply a reverse current to the discharged cell. This is commonly referred to as "cell reversal". Cell reversal significantly shortens the life of the affected cell and therefore shortens the overall life of the battery. In some extreme cases, the reversed cell can begin to emit smoke or catch fire. Some Ni-Cad type cells exhibit a "memory" effect. Some Ni-Cad type cells that are not fully charged and discharged periodically can lose their ability to retain a full charge, i.e. exhibit reduced capacity. Cycling a multicell battery into deep discharge to overcome this memory effect can cause cell reversal and do more harm than good. In critical applications using Ni-Cad batteries, such as in aircraft, each cell is individually discharged by connecting a load clip across the terminals of each cell, thereby avoiding cell reversal, then charging the cells in series.
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Offline fabr

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Re: 12v batt polarity swap????
« Reply #8 on: April 21, 2010, 07:43:30 PM »
Does that apply equally to typical lead/acid as well as to ni-cad?
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I participate in your fantasy"

Offline Yummi

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Re: 12v batt polarity swap????
« Reply #9 on: April 21, 2010, 08:07:13 PM »
It appears the discussion on ni cad was only relevant to memory as a sub set - the discussion on cell reversal was relevant to all batteries.
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I like things that move.   Pretty much limits me to cars and strippers

Did you know I have a blog?  Come on now, it is 2016, everybody does.  http://www.jeepingwithdogs.com

Offline Boostinjdm

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Re: 12v batt polarity swap????
« Reply #10 on: April 21, 2010, 09:30:21 PM »
I figured that to have the polarity reversed, the batt had to be drained down pretty far at some point.  This skid loader came to me with no spark and lot's of wiring issues.  I assumed it had been drained and recharged more than once so I replaced it and fixed the other issues.  Runs like a top and the customer is happy.  This batt is going for scrap, I'm not going to mess with it.
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prana-pete

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Re: 12v batt polarity swap????
« Reply #11 on: April 23, 2010, 04:10:10 PM »
You have the leads pluged in your tester the wrong way round !
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Offline Boostinjdm

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Re: 12v batt polarity swap????
« Reply #12 on: April 23, 2010, 04:30:26 PM »
Quote from: prana-pete on April 23, 2010, 04:10:10 PM
You have the leads pluged in your tester the wrong way round !

I think you got your leads plugged in the wrong way around... 
Mine have been like that for 10 years and are always correct.
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