Discharge or not?
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Fallingwater
Flashlight Enthusiast
No.
Every discharge takes some life out of the cells.
In your place, I'd never use it at all. The so-called memory effect is largely a myth.
It could be useful to recondition old or tired cells in an attempt to give them a last bit of life, but in ordinary use it'll only kill the cells faster.
Every discharge takes some life out of the cells.
In your place, I'd never use it at all. The so-called memory effect is largely a myth.
It could be useful to recondition old or tired cells in an attempt to give them a last bit of life, but in ordinary use it'll only kill the cells faster.
SilverFox
Flashaholic
Fallingwater
Flashlight Enthusiast
You choose to call memory effect and voltage depression the same thing, while I don't. 
At any rate, as you say, voltage depression happens if a cell is discharged at the same level multiple times. This almost never happens in normal household use.
http://www.dansdata.com/gz011.htm
At any rate, as you say, voltage depression happens if a cell is discharged at the same level multiple times. This almost never happens in normal household use.
http://www.dansdata.com/gz011.htm
SilverFox
Flashaholic
Hello Fallingwater,
Terminology aside, it is not a myth... it is just very difficult to produce.
Tom
Terminology aside, it is not a myth... it is just very difficult to produce.
Tom
Fallingwater
Flashlight Enthusiast
Well I did say "largely", implying not absolutely completely a myth.
Anyway, my point is: ok, voltage depression does exist, but the vast majority of people who buy and use discharging chargers don't need them and are only damaging their cells.
Anyway, my point is: ok, voltage depression does exist, but the vast majority of people who buy and use discharging chargers don't need them and are only damaging their cells.
SilverFox
Flashaholic
Hello Fallingwater,
Just because someone doesn't understand how and when to use the discharge function on their charger doesn't mean that they don't need it...
Just so everyone understands...
A complete discharge down to 0.9 volts per cell is not required on every cycle for either NiCd or NiMh chemistries. A complete discharge every 20 cycles, or so, will improve the performance and cycle life of both NiCd and NiMh chemistries.
I agree that people get carried away using the discharge function, but still believe that it is a very valuable feature on a charger.
Tom
Just because someone doesn't understand how and when to use the discharge function on their charger doesn't mean that they don't need it...
Just so everyone understands...
A complete discharge down to 0.9 volts per cell is not required on every cycle for either NiCd or NiMh chemistries. A complete discharge every 20 cycles, or so, will improve the performance and cycle life of both NiCd and NiMh chemistries.
I agree that people get carried away using the discharge function, but still believe that it is a very valuable feature on a charger.
Tom
jrmcferren
Enlightened
Thanks for the tip, I was just going to recycle those 2500's, I'm going to try a few charge/discharge cycles first to see if that helps.
radellaf
Flashlight Enthusiast
I'm observing voltage depression aka colloquial memory effect right now.
Have a UBA4 discharging a 9Ah (ostensibly) NEXcell D NiMH. At it's maximum load of about 3A the cell did over 6Ah. At .9-1 Volt
We ain't running much more at the 800mA level now.
Hoping that will improve with a few cycles.
Problem I have with the discharge function on chargers is that .9V doesn't really cut it for reconditioning cells...depending on current and cell capacity of course. I have two discharging chargers that hang it up at 1V, and are running a good bit more than C/10 current for most cells.
I can see .9 on a pack. 1V at C/5 though, I don't think that's really helping.
Have a UBA4 discharging a 9Ah (ostensibly) NEXcell D NiMH. At it's maximum load of about 3A the cell did over 6Ah. At .9-1 Volt
We ain't running much more at the 800mA level now.
Hoping that will improve with a few cycles.
Problem I have with the discharge function on chargers is that .9V doesn't really cut it for reconditioning cells...depending on current and cell capacity of course. I have two discharging chargers that hang it up at 1V, and are running a good bit more than C/10 current for most cells.
I can see .9 on a pack. 1V at C/5 though, I don't think that's really helping.
SilverFox
Flashaholic
Hello Radellaf,
You are correct. If you are trying to "bring back from the dead" a crap cell, you may need to go below 0.9 volts.
However, if you are simply trying to keep your cells in excellent condition, a discharge to 0.9 volts does a very good job of emptying them. It is an interesting test to take a healthy cell, discharge it to 0.9 volts, then discharge it again. There is very little capacity left. If you greatly reduce the drain current, the test will last for an extended period of time, but you will not show much capacity at all.
With normal and healthy cells, a discharge every now and again helps keep everything vibrant. With crap cells, more drastic measures are needed.
Tom
You are correct. If you are trying to "bring back from the dead" a crap cell, you may need to go below 0.9 volts.
However, if you are simply trying to keep your cells in excellent condition, a discharge to 0.9 volts does a very good job of emptying them. It is an interesting test to take a healthy cell, discharge it to 0.9 volts, then discharge it again. There is very little capacity left. If you greatly reduce the drain current, the test will last for an extended period of time, but you will not show much capacity at all.
With normal and healthy cells, a discharge every now and again helps keep everything vibrant. With crap cells, more drastic measures are needed.
Tom
radellaf
Flashlight Enthusiast
It's an OK feature, but esp. a 1V cutoff without programmable current (if the current is too high) I've not been that thrilled with it.
Still, I'd prefer a charger with rather than without.
Just think they should set the cutoff for single-cell chargers down a good bit further. Cells become at least temporary "crap" so very quickly.
---
As for capacity left, I did get this result off a mag charger pack:
One Hour Discharge
Duration (h:m:s): 01:02:13
Load current: 2.205A.
Cut-off voltage: 900mV.
Battery discharged: 2.285Ah.
Exit condition: Battery cut-off voltage reached.
Recondition Discharge
Duration (h:m:s): 02:34:05
Load current: 216.5mA.
Cut-off voltage: 500mV.
Battery discharged: 556.0mAh.
Still, I'd prefer a charger with rather than without.
Just think they should set the cutoff for single-cell chargers down a good bit further. Cells become at least temporary "crap" so very quickly.
---
As for capacity left, I did get this result off a mag charger pack:
One Hour Discharge
Duration (h:m:s): 01:02:13
Load current: 2.205A.
Cut-off voltage: 900mV.
Battery discharged: 2.285Ah.
Exit condition: Battery cut-off voltage reached.
Recondition Discharge
Duration (h:m:s): 02:34:05
Load current: 216.5mA.
Cut-off voltage: 500mV.
Battery discharged: 556.0mAh.
SilverFox
Flashaholic
Hello Eugene,
The low self discharge cells are new. I have only been using my Eneloop cells for about a year and a half now. They are going strong with only a couple of complete discharges in that time. It will be interesting to see how these cells age, and what happens when they move toward "crap" status.
The Maha C9000 seems to do a good job discharging to 0.9 volts, as does the CBA.
Tom
The low self discharge cells are new. I have only been using my Eneloop cells for about a year and a half now. They are going strong with only a couple of complete discharges in that time. It will be interesting to see how these cells age, and what happens when they move toward "crap" status.
The Maha C9000 seems to do a good job discharging to 0.9 volts, as does the CBA.
Tom
N162E
Enlightened
You can check out the "CBA" at http://westmountainradio.com/CBA.htmThe CBA is a useful device that a lot of us use to check capacity of our cells and packs.
N162E
Enlightened
Hi Tom, when using my CBA I only discharge to 1.1 volts. The difference to .9 volts is only 2 or 3 percent of total capacity. This was a rule of thumb back in my RC days when we used nicads. Considering that memory is not really a factor with NIMH, why beat them up any harder than necessary?
Ahh, I recognize west mountain radio, I've seen their powerpole gear. I'm switching all my stuff over to 12v powered and went searching for power connectors when I found the powerpoles. running all 12v though prevents use of the maha c9000 since its line powered.
SilverFox
Flashaholic
Hello Fred,
Standard capacity tests for NiMh cells is based on discharging to 0.9 volts. I believe this goes for both NiCd and NiMh cells. When we join several cells together to form a pack, this changes. With packs, 1 - 1.1 volts per cell is considered a safe low voltage cut off.
Tom
Standard capacity tests for NiMh cells is based on discharging to 0.9 volts. I believe this goes for both NiCd and NiMh cells. When we join several cells together to form a pack, this changes. With packs, 1 - 1.1 volts per cell is considered a safe low voltage cut off.
Tom
SilverFox
Flashaholic
Hello Eugene,
The C9000 runs very nicely on 12 volts.
Tom
The C9000 runs very nicely on 12 volts.
Tom
N162E
Enlightened
Hi again Tom,
I understand the concept of widely accepted standard capacity tests. This testing is dictated by or results funded by the battery manufacturers. These are the same people that recommend c/1 or c/2 charging. These are also the same people that sell the product that really don't want them to last forever and conducted their capacity tests at 50 or 100 ma drains.
Many of the devices I use will not operate much below 1.1 volts, my gps and two cameras will not operate below 1.1 volts.
If I'm testing for comparison I'll use comparable parameters. For my own use I'll discharge to 1.1 volts and charge at 500 or 700 ma.
I'll keep a light on!!:candle:
