NiMhy conditioning...?

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chiphead

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I've been using NiMHy cells for some time and just like my NiCads I preconditon them. That is to say that I charge them then run time down a few times before I put them in general use. Is this really something I need to do for Nickel Metal Hydride cells?

chiphead...walking through life at DEFCON-3.
 
In my experience, mart chargers terminates prematurely with new cells and I find charging new cells on an overnight charger to be helpful.
 
Just keep in mind each charge and discharge cycle hastens the demise of any battery made. That being said I have read NIMH do take several charge/discharge cycles to attain full charge capacity. Myself I would rather use the batteries for their assigned task than to just waste all that power doing a task that normal use will accomplish but takes a bit longer. I always have freshly recharged batteries with me for when my power source starts dropping off during use
 
smokinbasser said:
Just keep in mind each charge and discharge cycle hastens the demise of any battery made. That being said I have read NIMH do take several charge/discharge cycles to attain full charge capacity. Myself I would rather use the batteries for their assigned task than to just waste all that power doing a task that normal use will accomplish but takes a bit longer. I always have freshly recharged batteries with me for when my power source starts dropping off during use
Click to expand...

That's sort of like saying you add scratches everytime you wash your car.
 
Hello Chiphead,

To get the best performance from you NiMh cells:

1 - Do a 16 hour 0.1C forming charge. A 2500 mAh cell would be charged at 250 mA for 16 hours. This is a slight overcharge designed to evenly spread the electrolyte throughout the cell.

2 - Cycle the cell around 5 times, charging at 0.5C to 1C (for a 2500 mAh cell that works out to 1250 - 2500 mA), and discharging at 0.5C down to 0.9 - 1.0 volts.

3 - Every 20 - 40 cycles of partial use, do a discharge down to 0.9 - 1.0 volts per cell, followed by a 12 hour 0.1C charge.

4 - On the odd chance that the cell is not used for a period of time, do a discharge/charge cycle every 30 days.

On the other hand, if peak performance is not that important, just charge them up and use them. :)

Tom
 
Tom,

Is 0.5C considered fast charging? If so does it mean it will deteriorate cell lifespan. I know you did a test regarding fast charging vs slow charging, I need to go digest it.

Secondly, would superfast charging enchance performance? For example, reducing the cell voltage sag. I am trying to 'prime' some cheap cells so I get best performance out of them knowing they won't last long.

Vince.
 
Hello Vince,

0.5C charging was picked because it is about the slowest of the fast charge rates where the end of charge termination signal is prominent. Charging at slower rates may end up over charging the cell because the end of charge signal is slight and may be missed.

Most cycle life testing involves 0.1C charging with a timed shut off, so I would assume that rate would give you the best cycle life.

To get the best performance from cells, use them hot. Cells at 120F perform better than those at room temperature.

Tom
 
SilverFox said:
Hello Vince,

0.5C charging was picked because it is about the slowest of the fast charge rates where the end of charge termination signal is prominent. Charging at slower rates may end up over charging the cell because the end of charge signal is slight and may be missed.

Most cycle life testing involves 0.1C charging with a timed shut off, so I would assume that rate would give you the best cycle life.

To get the best performance from cells, use them hot. Cells at 120F perform better than those at room temperature.

Tom
Click to expand...

Sanyo rates their capacity based on 0.1C x 16 hr and 0.2C discharge, but rates cycle life based on C rate charge -10mV delta V charge and C rate discharage to 1.0v.

I don't know about other mfrs.
 
Tom,

Please forgive me if the extreme thickness of my skull is showing, but how would the conditioning cycle of the Maha c808m compare to your above advice about forming charges and conditioning cycles? I've read your review of the c808m (thanks so much) and some of your other great work but I am really at a loss to quantify what's going on most of the time.

I've been wringing out my new c808m 24/7 for over a week now and I'm happy with it -- I just wish I understood more.

Sub
 
Sub_Umbra said:
Tom,

Please forgive me if the extreme thickness of my skull is showing, but how would the conditioning cycle of the Maha c808m compare to your above advice about forming charges and conditioning cycles? I've read your review of the c808m (thanks so much) and some of your other great work but I am really at a loss to quantify what's going on most of the time.

I've been wringing out my new c808m 24/7 for over a week now and I'm happy with it -- I just wish I understood more.

Sub
Click to expand...
Smart chargers can not charge unconditionally and they tend to misdetect end of charge with new cells. Dumb chargers will unconditioanlly push the current until unplugged or timer expires.
 
Hello Sub_Umbra,

The Maha 808 will do a slow discharge down to around 1.0 volts, but it will not do a "forming" charge. With the 808 you need to just use the cells and every 20-40 cycles of use, hit the condition button. In active use NiMh cells will usually "form" in around 10 cycles.

Tom
 
Tom:

I just happened to test a C808M low voltage point for the condition cycle! It was 1.06V.
 
I charge my cells slow at 0.1C - 0.2C (200mA to 300mA) when I have the time and seldom do fast charge at 0.5C when I need it quick. I don't go beyond 1C even though my equipment can support up to 3Amps of charging current.

So far my equipments (ICE, Maha C401FS, BC-900) are all doing very well at detecting end of charge -dV voltage when doing slow charging. On the ICE I set it -3mV. Except a couple of times when BC-900 terminated earlier than expected when priming new cells at 200mA.


vince.
 
I think all new batteries come partially charged so before doing the forming charge, should I discharge the battery first or go straight with the forming charge?

I only have the La Crosse charger. Can I adapt its charging characteristics in some way to simulate a forming charge. Since it stops charging when it detects full, can I restart it again and again at 200ma until it totals 16 hours or am I damaging the batteries this way? Does it help any if I just leave trickle charging when it reads full until it reaches 16 hours?

Thanks.
 
Hi there,

Duracell states that they charge and discharge every one of their cells
50 times before shipping. If this is really the case, these cells dont
need any kind of pre-conditioning.
 
Billson,
Forming charge (say on BC900 at 200 mamps) doesn't have to last exactly 16 hours. You could use the Discharge mode to drain cells first before charger starts forming charge. My new Energizer 2500 charged as little as 1 amp the 1st time. After several forming charges you'll get close to 16 hours at which point you can move up to faster rates.
 
"SilverFox
0.5C charging was picked because it is about the slowest of the fast charge rates where the end of charge termination signal is prominent."

Is this still correct or out of date info? Despite some metldowns many BC900 users use 200 mamp rate which for current capacities of 2500 is 0.08C, without any problems. Even if the signal is not prominent at 0.1C does it not become prominent before 0.5C? I thought that 0.3C is sufficient for a prominent signal.
 
Hello Bob Ninja,

In general, the 0.5C rate is still stated as the slowest of the fast charge rates required to repeatedly and reliably give a strong end of charge signal. You can charge at lower rates and it will "probably" work fine, but it depends on your charger.

I believe the 0.3C rate is a carry over from NiCd charging.

Tom
 
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