My NiMH cells reversed polarity! Oh no!

[[email protected]]

Is this bad? Or will re-charging them fix the problem?

The situation: I have 16 of them powering my laptop (18.5VDC input
required, using my battery pack in lieu of the external switching power
supply running on mains power). The pack lasts about 2 hours.

Lately, though, I noticed my battery pack cuts out early. I measured
the voltage with my AMM, and the needle pegged NEGATIVE.

Is this bad? Must I throw the batteries away? Or will charging fix
the problem?

Michael

 

[John Woodgate]

Is this bad?

Yes. Several cells have failed and have been charged in reverse by the
others.

Must I throw the batteries away?

Yes; they should be recycled.

Or will charging fix the problem?

No; it is likely to make matters worse, by causing further cells to
fail.

 

[vasile]

Is this bad? Or will re-charging them fix the problem?

The situation: I have 16 of them powering my laptop (18.5VDC input
required, using my battery pack in lieu of the external switching power
supply running on mains power). The pack lasts about 2 hours.

Lately, though, I noticed my battery pack cuts out early. I measured
the voltage with my AMM, and the needle pegged NEGATIVE.

Is this bad? Must I throw the batteries away? Or will charging fix
the problem?

You have opened the batery pack and have full access to any of the
NI-Mh cell terminals ? If yes, charge seprately cell by cell, using a
fast charging algorithm.
Then discharge separately every cell using nominal load (the same
current which is discharging the battery your laptop) and measure
discharging time. You'll discover there are cells which have a long
discharge time and cells with very short discharge time. Probably some
cells does not charge almost at all. So, replace defective cells with
new ones, charge the whole pack with small current (0.1*C to 0.4*C
untill the C=1.2*I*t equation is true (I is the charging current, t is
the charging time, C is the cell capacity measured in amperes*hours and
written on every cell).
In 80% from those situations, only one or two cells are deffective, or
the laptop charging circuit is broken.
In the other 20%, the battery pack is very old (more than 2-3years of
usage) and need to be replaced.

greetings,
Vasile

 

[Phil Allison]

"John Woodgate"

Yes. Several cells have failed and have been charged in reverse by the
others.

** Failed ???

No need for cell *failure* to ocurr for the polarity to go reverse during
the discharge of a battery. When a cell is fully discharged, the internal
impedance goes very high so it can easily take up a small reverse voltage.

While not desirable, it takes a lot more to kill a rechargeable cell than
this.

No; it is likely to make matters worse, by causing further cells to fail.

** Rediculous nonsense !!

The reverse voltage cells will recover normal polarity when charged as usual
and there is NO bad effect on the cells that have not reversed.

The Wood Duck is quacked.



........ Phil

 

[John Woodgate]

The reverse voltage cells will recover normal polarity when charged as
usual and there is NO bad effect on the cells that have not reversed.

The Wood Duck is quacked.

Phil, he's measuring the TOTAL voltage as negative, so there are more
reverse-charged cells than good ones. Unless he can charge the cells
individually, which means breaking open the pack, that situation is
unrecoverable.

 

[Phil Allison]

"John Woodgate"

Yes. Several cells have failed and have been charged in reverse by the
others.

** Failed ???

No need for cell *failure* to occur for the polarity to go reverse during
the discharge of a battery. When a cell is fully discharged, the internal
impedance goes very high so it can easily take up a small reverse voltage.

While not desirable, it takes a lot more to kill a rechargeable cell than
this.

No; it is likely to make matters worse, by causing further cells to fail.


Phil, he's measuring the TOTAL voltage as negative,

** WRONG - that is simply quite impossible.

so there are more reverse-charged cells than good ones.

** Not possible in the scenario as described.

The PC cuts out the battery load at a positive voltage.

The Wood Duck is more Quacked than I thought.






......... Phil

 

[John Woodgate]

** WRONG - that is simply quite impossible.

It's what he told us. If it's wrong, it's not my error.

 

[Phil Allison]

"John Woodgate SNIPPING MANIAC "

Yes. Several cells have failed and have been charged in reverse by the
others.

** Failed ???

No need for cell *failure* to occur for the polarity to go reverse during
the discharge of a battery. When a cell is fully discharged, the internal
impedance goes very high so it can easily take up a small reverse voltage.

While not desirable, it takes a lot more to kill a rechargeable cell than
this.

No; it is likely to make matters worse, by causing further cells to fail.


Phil, he's measuring the TOTAL voltage as negative,

** WRONG - that is simply quite impossible.

so there are more reverse-charged cells than good ones.

** Not possible in the scenario as described.

The PC cuts out the battery load at a positive voltage.

The Wood Duck is more Quacked than I thought.

It's what he told us

** The OP's heading say "cells" .

The OP's text alone is ambiguous.

You failed to exclude the impossible.

That is a massive blunder.

If it's wrong, it's not my error.

** Believing impossible things is your error.

Your claims about cell failure are in error.


Quack, quack, quack ......





......... Phil

 

[John - KD5YI]

Is this bad? Or will re-charging them fix the problem?

The situation: I have 16 of them powering my laptop (18.5VDC input
required, using my battery pack in lieu of the external switching power
supply running on mains power). The pack lasts about 2 hours.

Lately, though, I noticed my battery pack cuts out early. I measured
the voltage with my AMM, and the needle pegged NEGATIVE.

Is this bad? Must I throw the batteries away? Or will charging fix
the problem?

Michael

Make sure your "AMM" test leads are connected properly. Put the red lead
into the AMM's + (plus) hole. Put the black lead into the AMM's - (minus)
hole. Set the AMM for 20 or more volts. Touch the red probe to the battery +
terminal and touch the black probe to the battery - terminal.

Is "the needle pegged NEGATIVE"?

John

 

[Phil Allison]

"John - KD5YI"

Make sure your "AMM" test leads are connected properly. Put the red lead
into the AMM's + (plus) hole. Put the black lead into the AMM's - (minus)
hole. Set the AMM for 20 or more volts. Touch the red probe to the battery
+ terminal and touch the black probe to the battery - terminal.

Is "the needle pegged NEGATIVE"?

** It won't be - as that is simply impossible.

The get whole pack reversal, you would have to charge it in reverse.

The OP may have one or two reversed cells - or else he is an utter idiot.




........ Phil

 

[John Woodgate]

Quack, quack, quack ......

Go on. You just want me to call you Phyllis Alison again.

 

[[email protected]]

It's what he told us. If it's wrong, it's not my error.

Oh, sorry, meant to say that 4 batteries out of the 16 had negative
voltage. Sorry I didn't clarify this. (Whoa... if the *whole*
battery pack came out as negative, that would be weird!)

I tried this: I put one bad one in a flashlight (in series with the
"wrong" polarity with another good battery, to ensure the batteries
drained), then charged. Curious, I took the bad one out, and it
registered a positive voltage of about 0.3V.

So, is it fixed, or is it ruined forever?

thanks,

Michael

 

[John Woodgate]

Curious, I took the bad one out, and it registered a positive voltage
of about 0.3V.

So, is it fixed, or is it ruined forever?

It may be OK. Charge it slowly by itself, being careful to control the
current to C/20 or so, and stop when it shows 1.2 V. It won't be fully
charged, but if it holds that 1.2 V above 1 V overnight you stand a
chance. Do that with each one that shows a negative voltage. Then charge
the whole string.

 

[John - KD5YI]

"John - KD5YI"





** It won't be - as that is simply impossible.

The get whole pack reversal, you would have to charge it in reverse.

The OP may have one or two reversed cells - or else he is an utter idiot.




....... Phil

Yeah. I just saw his most recent post. Sorry to bother.

Thanks, Phil.

John

 

[Michael A. Terrell]

Go on. You just want me to call you Phyllis Alison again.

Go ahead. It makes her day.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Bobo The Chimp]

Go ahead. It makes her day.

Face it, Michael. You're in love with Phalluson.