Interesting behavior from PowerSonic battery

I have two 6 volt and one 2 volt PowerSonic cells in series to make a 14 volt pack for one of my sailplanes. I had one of the batteries go bad, so I did a little checking to see which one. All showed appropriate charge voltage when not loaded, however, one battery went from 6.2 volts no load, to showing -3.8 or so volts when loaded by turning on a S-Nav and GPS-Nav. Now, I have seen an individual battery go to very nearly zero volts, but never negative voltage! Turn everything off, and it slowly recovers back to showing about 6.2 volts no load.

Anyone else ever seen a battery do that before? And please, no comments about 14 volt battery packs or old technology batteries. Age of battery unknown, as I do not remember when I built up the pack.

Just curious.

I had one 12V SLA that showed full voltage unloaded but when selected in the glider caused all avionics to cycle on/off with a 1-2 sec period. Don't remember what the loaded volage was but I think it was close to zero. The unloaded voltage was, if anything, higher than normal.

Andy

On Monday, May 6, 2013 3:31:41 PM UTC-4, Steve Leonard wrote:
I have two 6 volt and one 2 volt PowerSonic cells in series to make a 14 volt pack for one of my sailplanes. I had one of the batteries go bad, so I did a little checking to see which one. All showed appropriate charge voltage when not loaded, however, one battery went from 6.2 volts no load, to showing -3.8 or so volts when loaded by turning on a S-Nav and GPS-Nav. Now, I have seen an individual battery go to very nearly zero volts, but never negative voltage! Turn everything off, and it slowly recovers back to showing about 6.2 volts no load.



Anyone else ever seen a battery do that before? And please, no comments about 14 volt battery packs or old technology batteries. Age of battery unknown, as I do not remember when I built up the pack.



Just curious.

Since you have all the batteries in series with the load the voltage drop across the bad battery it appears like the bad battery is being reverse-biased by the good ones. You would see the same kind of result if you replaced the bad battery with a resistor and measured the voltage across it. The bad battery obviously has what is called "High internal resistance".

-PC

On 5/6/2013 1:31 PM, Steve Leonard wrote:
I have two 6 volt and one 2 volt PowerSonic cells in series to make a 14
volt pack for one of my sailplanes. I had one of the batteries go bad, so
I did a little checking to see which one. All showed appropriate charge
voltage when not loaded, however, one battery went from 6.2 volts no load,
to showing -3.8 or so volts when loaded by turning on a S-Nav and GPS-Nav.
Now, I have seen an individual battery go to very nearly zero volts, but
never negative voltage! Turn everything off, and it slowly recovers back
to showing about 6.2 volts no load.

Anyone else ever seen a battery do that before?

I've not seen that, but - digital VOM attached - I've seen a new/under full
replacement warranty standard 12V car battery intermittently become a 6V
battery, engine running & engine off, battery connected to the system. The
vehicle wouldn't run in "6V mode." It took some persuasion for the lady owner
of the vehicle to get the chain to honor their battery warranty, but her
vehicle hasn't suffered a "mystery engine stoppage" since flaky battery
replacement several years ago.

Bob W.

On Monday, May 6, 2013 5:14:28 PM UTC-5, Jim wrote:
Since you have all the batteries in series with the load the voltage drop across the bad battery it appears like the bad battery is being reverse-biased by the good ones. You would see the same kind of result if you replaced the bad battery with a resistor and measured the voltage across it. The bad battery obviously has what is called "High internal resistance". -PC

Yep. And the guy at All Pack gave the battery the highly scientific "shake test". Apparently, the innerds dried up and came apart. Sounded like shaking a box of rocks. 5 years of service from the battery, and $23 to replace it in the pack. Will be good to be able to secure the battery in the intended box again rather than having a smaller one out on the shelf behind me.

On Monday, May 6, 2013 3:31:41 PM UTC-4, Steve Leonard wrote:
I have two 6 volt and one 2 volt PowerSonic cells in series to make a 14 volt pack for one of my sailplanes. I had one of the batteries go bad, so I did a little checking to see which one. All showed appropriate charge voltage when not loaded, however, one battery went from 6.2 volts no load, to showing -3.8 or so volts when loaded by turning on a S-Nav and GPS-Nav. Now, I have seen an individual battery go to very nearly zero volts, but never negative voltage! Turn everything off, and it slowly recovers back to showing about 6.2 volts no load.


Flip the meter around and you can measure the voltage drop of that battery which is now just a big resistor

On Monday, May 6, 2013 12:31:41 PM UTC-7, Steve Leonard wrote:
I have two 6 volt and one 2 volt PowerSonic cells in series to make a 14 volt pack for one of my sailplanes. I had one of the batteries go bad, so I did a little checking to see which one. All showed appropriate charge voltage when not loaded, however, one battery went from 6.2 volts no load, to showing -3.8 or so volts when loaded by turning on a S-Nav and GPS-Nav. Now, I have seen an individual battery go to very nearly zero volts, but never negative voltage! Turn everything off, and it slowly recovers back to showing about 6.2 volts no load.



Anyone else ever seen a battery do that before? And please, no comments about 14 volt battery packs or old technology batteries. Age of battery unknown, as I do not remember when I built up the pack.



Just curious.

This is called "cell reversal" and does occassionally happen.

My question is why do you think that you need a 14V battery? All modern aviation electronics is designed to operate on a wide range of input voltage. This is accomplished by a circuit called a "dc-dc converter" that boosts the input voltage to a higher, regulated, internal voltage.

Tom

On May 21, 2:32 pm, 2G wrote:

...My question is why do you think that you need a 14V
battery? All modern aviation electronics is...

My suspicion is that Steve has a collection of vintage avionics that
is not even in the same zip code as "modern," and that said devices
start crapping out at around 11 volts. With the 14v pack, you have
three volts of margin between nominal and nordo; with the 12v pack you
have only one volt of margin.

Thanks, Bob K.

On Tue, 21 May 2013 15:20:17 -0700 (PDT), Bob Kuykendall
wrote:

On May 21, 2:32 pm, 2G wrote:

...My question is why do you think that you need a 14V
battery? All modern aviation electronics is...

My suspicion is that Steve has a collection of vintage avionics that
is not even in the same zip code as "modern," and that said devices
start crapping out at around 11 volts. With the 14v pack, you have
three volts of margin between nominal and nordo; with the 12v pack you
have only one volt of margin.

Quite so. Traditional avionics are designed to run on the 13.8V you
get from the voltage regulator in a "12 volt" system.

rj

On Tuesday, May 21, 2013 4:32:29 PM UTC-5, 2G wrote:
This is called "cell reversal" and does occassionally happen. My question is why do you think that you need a 14V battery? All modern aviation electronics is designed to operate on a wide range of input voltage. This is accomplished by a circuit called a "dc-dc converter" that boosts the input voltage to a higher, regulated, internal voltage. Tom

Well, 2G, where do you draw the line on "Modern" avionics? MicroAir radio? Becker 3201 radio? Becker 4201 radio? Filser ATR500? I have seen all of the above "crap out" on a 12 volt battery when my Cambridge computer and nav keep on working.

Be happy with your 12 volt system, and don't be diss-ing on me for my 14 volt system, OK?

And, yes. I am aware of cell reversal. I just hadn't seen it "self recover" when the load is removed.