Trickle Charging NiMH LSD AA Cells Test

Hi, AACycler is doing a new test! This time to see the trickle charging effects on NiMH AA LSD cells.

Link to test: http://aacycler.com/post/trickle-charging-lsd-cells/

I'm curious how the lines will progress. Currently it looks like the 100mA trickle charge is even going up in capacity.

Anybody dares to make a prediction?

Perhaps someone also got other test data or papers on the effects of trickle charging LSD cells?

I'll dare to go first, reduced cycles/capacity will be observed, the higher the trickle charge the sooner this will occur. I even expect the 100mA to show its effects as soon as 100 cycles. The 20mA trickle charge effect will be minimal, just a hunch on this one.

Nice! It will be great to see some actual evidence of this, one way or the other.

Trickle charging will eventually deplete the electrolyte. It takes a lot of trickle charging to do it. It requires about 190,000 ampere seconds to convert 18 grams of water into oxygen and hydrogen, so the process is not exactly 'speedy'. The other thing to understand about trickle charging is that if you attempt to charge a NiCd at less than about 1/20th C, it will never fully charge, so while you can maintain charge with a trickle charger, you really cannot actually charge a NiCd with it.

Trickle charging for two days is a lot of manual work because the highest value you can set the "C. rest" for on a MC3000 is 240 minutes. That means you would need to set the trickle time to "end" and manually time it for 2 days then remove the batteries. I too would be very interested in the results and appreciate the time and effort of guys like AA cycler.

Frank

NiMHi said:

[...] I'm curious how the lines will progress. Currently it looks like the 100mA trickle charge is even going up in capacity.

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You need to look at the impedance. Already at 20 cycles it's not looking good for the higher trickle charge rates. For the 100mA trickle, the impedance already rose about 15% vs. his older tests where the impedance rose only 7-11% after 100 cycles (5x as many) with no trickle charging. Likely the impedance will be much higher once these guys hit 100 cycles.

Caveat: possibly these early results could be affected by error tolerances etc, so we'll need more data to be sure.

Bad news: I just noticed that AACycler appears to be using 1kHz AC impedance testing. That's unfortunate since generally there is no simple correlation between that and DC impedance - which is really what matters for most users. In particular, I don't know if there is a linear relationship between the rise in AC impedance and DC impedance as the cell degrades. If not it means that AACycler's tests may be of limited use for understanding degradation as it actually applies in normal use.

NiMHi said:

Hi, AACycler is doing a new test! This time to see the trickle charging effects on NiMH AA LSD cells.

Link to test: http://aacycler.com/post/trickle-charging-lsd-cells/

Click to expand...

Hi NiMHi,

thaks for mentioning my new test here on CPF.

fmc1 said:

Trickle charging for two days is a lot of manual work because the highest value you can set the "C. rest" for on a MC3000 is 240 minutes. That means you would need to set the trickle time to "end" and manually time it for 2 days then remove the batteries. I too would be very interested in the results and appreciate the time and effort of guys like AA cycler.

Frank

Click to expand...

Hi fmc1,

you got it right, I set the trickle time to "end" and I need to remove the cells every 2 days. I programmed my MC3000 to do a "DC" type of CYCLE with COUNT=1, which means it discharges the cells, charges the cells, and then trickle charges them until I remove them 2 days later... So far I've got 24 data points, it is 7 weeks worth of data

Cheers,
AA Cycler

mattheww50 said:

Trickle charging will eventually deplete the electrolyte. It takes a lot of trickle charging to do it. It requires about 190,000 ampere seconds to convert 18 grams of water into oxygen and hydrogen, so the process is not exactly 'speedy'. The other thing to understand about trickle charging is that if you attempt to charge a NiCd at less than about 1/20th C, it will never fully charge, so while you can maintain charge with a trickle charger, you really cannot actually charge a NiCd with it.

Click to expand...

Trickle or bad trickle charge?





In the real world many charger have 20 or 50mA trickle charge, but calculated from pulse current.
This strong pulses have bad effect on small battery (AAA).
The costant current trickle charge have another story.

Gauss163 said:

Bad news: I just noticed that AACycler appears to be using 1kHz AC impedance testing. That's unfortunate since generally there is no simple correlation between that and DC impedance - which is really what matters for most users. In particular, I don't know if there is a linear relationship between the rise in AC impedance and DC impedance as the cell degrades. If not it means that AACycler's tests may be of limited use for understanding degradation as it actually applies in normal use.

Click to expand...

Hi Gauss163,

yes, I measure AC impedance at 1kHz with ALL-SUN EM3610, because it gives me more consistent readings than DC resistance measured by various analyzing chargers. And as a bonus, measuring AC impedance of a discharged cell is possible while measuring DC resistance is not.

The AC impedance correlates pretty well with DC resistance, check my internal resistance meters test to see how EM3610's AC results compare to other analyzers' DC results. The rule of thumb for AA NiMH cells would be DC resistance = AC impedance + 25 mOhm.

Cheers,
AA Cycler

AA Cycler said:

Hi Gauss163,

yes, I measure AC impedance at 1kHz with ALL-SUN EM3610, because it gives me more consistent readings than DC resistance measured by various analyzing chargers. And as a bonus, measuring AC impedance of a discharged cell is possible while measuring DC resistance is not.

Click to expand...

Unfortunately AC impedance values are of little use for almost all users.

AA Cycler;5256377 The AC impedance correlates pretty well with DC resistance said:

internal resistance meters[/URL] test to see how EM3610's AC results compare to other analyzers' DC results. The rule of thumb for AA NiMH cells would be DC resistance = AC impedance + 25 mOhm.

Click to expand...

There are reports of AC impedance differing from DC resistance by 3x to 4x in certain contexts. They are measuring very different things (google "Nyquist curve" to learn more), so it is not surprising that they may not correlate well.

I am not aware of any such "rule of thumb" that works well under all conditions. Alas, there is far too little data in the linked chart to asses its claims. That would require a precise enough description of the tests that they could be independently verified.

If you are able to do so I highly encourage you to measure DC resistance since that is what really matters to users, and this is what all common analyzing chargers use (so your numbers will correlate much better with the IR numbers from the charger - assuming it has a decent IR test).

Yes, perhaps the DC method is better for determining the internal resistance. This article from Energizer also mentions that DC is more accurate than AC: http://data.energizer.com/pdfs/batteryir.pdf

But! to be honest, the test is good as it is. In my eyes it is mostly about comparing the effects of trickle charging and a more accurate IR value will not improve this comparison much.

NiMHi said:

But! to be honest, the test is good as it is. In my eyes it is mostly about comparing the effects of trickle charging and a more accurate IR value will not improve this comparison much.

Click to expand...

IR is the primary indicator of degradation. If you don't measure that correctly there is little point in doing the tests.

The important thing is to notice the change in IR over the duration of the test. You can argue direct is better than alternate, but the absolute values aren't the point of the test. And, if he can measure alternate more accurately or consistently, even if it's not the best method, then that's far more useful than an inaccurate/random measurement of DC resistance.

^^^ Both absolute and relative numbers matter. And the numbers aren't very useful if they measure attributes that don't reflect actual usage conditions, i.e. high-frequency AC vs. DC. I quoted leading experts here before on these matters, e.g. in this post.

Gauss163 said:

^^^ Both absolute and relative numbers matter. And the numbers aren't very useful if they measure attributes that don't reflect actual usage conditions, i.e. high-frequency AC vs. DC. I quoted leading experts here before on these matters, e.g. in this post.

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Okay, I'm looking forward to your own NiMH cycle tests, using the method you state. When are you going to publish your results?

^^^ What's the point of the above snarky reply? I'm trying to help AACycler to choose methods that will be most useful to the community, and to help others learn about what methods are best to measure battery health. If your aren't interested in such then please simply ignore my posts.

Because AACycler is actually doing something useful. All you're doing is crapping all over him for it. If you don't like what he's doing, why don't you do it yourself the way you want to?

I, for one, really appreciate AACycler's testing. It's great information, and however he chooses to do it is way better than not doing it at all.

WalkIntoTheLight said:

ll you're doing is crapping all over him [...] however he chooses to do it is way better than not doing it at all.

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So you don't give your friends advice when it could lead to improvements? If a friend boasted about what a great deal he got on 10000mAh ultrafire cells would you not tell him the truth for fear of "crapping all over him"?

See image/development above. Something or somebody is smoothing the curves...