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Rechargable Batteries

audioguru

Well-Known Member
Most Helpful Member
You are wasting time discharging batteries and using such a low discharging current. When a battery does not work properly anymore then it can be charged without discharging it more.

Instead of buying a timer, why not buy a good charger instead? My Duracell CEF27NA2 charger works well and came with some of their latest Eneloop-type of batteries.
 

rjenkinsgb

Active Member
You are wasting time discharging batteries and using such a low discharging current. When a battery does not work properly anymore then it can be charged without discharging it more.
This is not discharge-before-charge as with old, timed, chargers.

It is a one-off deep discharge to remove crystallisation in the cell plates - "memory effect".
I've used it many times and it is extremely effective in recovering capacity in cells that stop working (have apparently poor capacity) in high current devices.
 

tvtech

Well-Known Member
Most Helpful Member
Batteries were resting on the desk for 2 hours now voltage has dropped to 1.406 & 1.391

Next time dead batteries need to be charged it looks like they should be charged 14 or 15 hrs that should put final charge closer to 1.5v.

Now I need a 15 hr off timer.

2 hrs later batteries on the decharger are .282v

View attachment 118193
Youve killed them. Discharged them too much. They wont recover.
 

gary350

Well-Known Member
Youve killed them. Discharged them too much. They wont recover.
Batteries did recover and took a very good charge. I put batteries in my camera an took several pictures already. Battery life indicator on camera still shows full charge. Battery indicator is a good indication batteries are better than before after about 40 pictures indicator use to start showing 95% battery. Battery still shows full. I am going to take more pictures today just to put a drain on batteries to see how they do. Already I can see batteries are better than they were.
 
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audioguru

Well-Known Member
Most Helpful Member
Since you are using a cheap charger that does not detect a full charge then shutoff, then it was overcharging the batteries which is bad for Ni-MH cells. Now that you are discharging the batteries completely then charging with your own 14 hours timer, the batteries are working better.
 

rjenkinsgb

Active Member
Youve killed them. Discharged them too much. They wont recover.
The don't-discharge-below-1V restriction is when they are used in a battery pack, as a weak cell may be reverse polarised while others still have charge.

Individual cells have no such restriction, as long as they are not left fully discharged for long periods.

A cell-by-cell deep discharge just eliminates memory effect and restores normal operation.
 

tvtech

Well-Known Member
Most Helpful Member
"2 hrs later batteries on the
decharger are .282v"

What have I missed here?
 

audioguru

Well-Known Member
Most Helpful Member
"2 hrs later batteries on the
decharger are .282v"

What have I missed here?
The lower the battery voltage drops then the lower is the discharge current and the resulting longer time for a complete discharge.

If you try to discharge more than one cell in series then the weakest one becomes completely discharged then the stronger cell discharges more by charging the weak cell in reverse, which is bad for it. Therefore do not discharge series cells below about 1V fore each cell.
 

tvtech

Well-Known Member
Most Helpful Member
Thanks Audioguru. I learned something new today. Im only familiar with little PP3 series cells. So now I understand individual cells better. Ive nevet physically ever worked with or tested one cell at a time. Thats the beauty of Electronics...the learning never stops.

All the best and thanks,
tvtech
 

audioguru

Well-Known Member
Most Helpful Member
Thanks Audioguru. I learned something new today. Im only familiar with little PP3 series cells. So now I understand individual cells better. Ive nevet physically ever worked with or tested one cell at a time. Thats the beauty of Electronics...the learning never stops.

All the best and thanks,
tvtech
A 9V rechargeable battery (PP3) should never be completely discharged because it has 6 or 7 cells in series. If you try to completely discharge it then the weakest cell becomes completely discharged then the remaining cells with power will charge that weak cell backwards while they are still discharging. So do not discharge a 9V rechargeable battery below 6V or 7V.
 

tvtech

Well-Known Member
Most Helpful Member
My little PP3's never discharge below 7.5V. The circuit stops that. I havent lost a PP3 in all the years yet due to overdischarge. In my case, they simply wear out from al the charging cycles.
 

gary350

Well-Known Member
Battery voltage after 53 hrs of discharging = .039v

Maybe it is time to lower the resistance from 100 ohms to about 10 ohms.

118218
 
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gary350

Well-Known Member
Today voltage on each battery is .001v

I soldered a 10 ohm resistor in parallel with the 100 ohm resistor. Tomorrow I solder switch in series with 10 ohm resistor after battery discharges 3 days on 100 ohms then I change to 10 ohms. Maybe 10 ohms is too small maybe 25 ohm is better.


118245
 

rjenkinsgb

Active Member
Today voltage on each battery is .001v
You are getting carried away...

All that matters is the open-circuit voltage after some time to recover is somewhat below 1V. At that, there is no significant charge left.

It probably won't hurt, but do charge the cells after you have finished, don't leave them in the totally discharged state for more than a few days.
 

gary350

Well-Known Member
I notice while testing battery voltage it slowly goes up. When I first tested batteries this morning they test .000v. 2 minutes later they test .001v. Few minutes later they test .002v. Batteries are on the charger now for 14 hours then I test them.
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

Yes that happens. There is a theoretical internal capacitor or capacitors connected to the terminals through a resistance, so when you short the terminals you do not actually short that theoretical capacitor. So when you remove the short that capacitor is not yet discharged all the way and so you see a small terminal voltage rising. So the battery is modeled as a network, and the network has capacitors that do not discharge all the way. That is seen using one of the better models of a real life battery.
Another simpler way of looking at it is that when you short the battery terminals you are shorting the internal battery though it's internal resistance, so you see 0.000 volts while the internal battery still has some voltage left.
Another explanation is that there are still chemical reactions going on inside.
 

gary350

Well-Known Member
These batteries are amazing they have been revived far beyond what they were. I have taken about 100 pictures since I charged the batteries a few days ago. Today I took a 1 hr 15 min video of Educational TV the NPT channel of Wine Making. It took another 20 minutes to download video to the computer. Battery indicator is still not showing low battery. We had a nice 3 day vacation on the lake.

118258
 

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