Conditioning on a MH-C940

[Dimt]

Just got a Powerex MH-C940 yesterday and started to test it by conditioning 8 AA Eneloops at about 11am. Later in the afternoon I took a battery out of the 8th position because it showed a high 2100+ mAH. Kept glancing at it until just before going to bed at 1am. At 1am the batteries status was:
1. 1936 mAH and Done
2. 1935 mAH and Done
3. 1963 mAH and Done
4. 1940 mAH and Done
5. 1754 mAH and Done
6. 2033 mAH and still charging
7. 1987 mAH and Done

I stayed and watched expecting #6 to post done at any time. After 10-15 minutes #6 had climbed to 2051 mAH and was still going, so I went to bed. At 6am I woke and found #6 at 2054 mAH and done as I expected and all the other batteries at the same status I saw at 1am. Except #5. To my surprise I found #5 at 3073 mAH and charging again. At this point I took #5 off the charger and the cell was hot. Not sure what to think about this. I wanted the MH-C940 to charge my cells at a gentle 500 mAH rate instead of the 1000 & 2000 rate of the MH-C810d I have, but wonder if the termination was missed at the 500 charge rate. At 1am #5 showed 1754 and done, so I assume termination was registered. So I expected that cell was finished and was surprised to see it at 3073 and charging 5hrs later.
I have another batch of cells conditioning today so lets see what happens.

 

[MidnightDistortions]

What I would do next time, I figured these Eneloops are the 2000mAh ones is to pull them out if they exceed 2200mA or they get about 140°F / 60°C. You were fine to charge them at a slower rate if they haven't been used at all. I would make sure to record that one cell as questionable and keep an eye on the one slot for the next one.

I use this to estimate how long it should to take to charge and use 0% charging inefficiency. When any battery exceeds that timeframe monitor it for heat and I'd pull it out after 2200mAh charge as it would exceed the charge time. Either it missed the charge or cell has developed higher internal resistance.

Battery Charge Time Variable Efficiency Calculator

You can also use this to discharge time the batteries if you're using the conditioner.

https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-battery-life

 

[Monocrom]

....I don't want to spend much more but also don't want bottom of the barrel.

One, Welcome to CPF. We love getting new members.
Two, never buy the cheapest option.
Best way to save money is buy the mid.-tier option(s).
You'll get some good quality that won't make your wallet cry out in pain.

 

[Dimt]

I have been going thru my stash of standard Eneloops and running them thru the conditioning option on the Powerex MH-C940. So far I have conditioned 103 cells. Eight cells at a time. Some batches end with one or two cells showing very low capacity numbers. When I drain and charge those cells on my Zanflare C4 they show a large capacity. For example on my last batch a cell showed a capacity of 8. This cell was part of a set of 3 AA's used to keep the memory alive of a shortwave radio I have not used for years. It was drained so low, by the radio, the MH-C940 did not recognize the cell when I first put it in. I had to charge it on the Zanflare C4 for a couple minutes to get enough juice in it so the MH-C940 would recognize it.

After trying to condition that cell on the MH-C940 it ended up with a capacity of 8. I drained that cell using a single cell AA flashlight then recharged it on the Zanflare C4. That cell then showed a capacity of 2320 on the Zanflare C4.

The only thing in common with these low capacity cells is that they have been sitting unused for a long time. Any explanation of why the conditioning process of the MH-C940 show these cells at such a low capacity, yet when I charge them on another charger they take a large charge?

 

[sbj]

............
The only thing in common with these low capacity cells is that they have been sitting unused for a long time. Any explanation of why the conditioning process of the MH-C940 show these cells at such a low capacity, yet when I charge them on another charger they take a large charge?

The explanation is that the charger has switched off the charging process prematurely.

In my experience, this can happen with all chargers with older NiMh cells. Although sometimes my cheap chargers from the discount store seem to be less susceptible to this.
Even for my MC-3000, where I can change a lot of charging parameters, I have not yet found a setting for such cells to reliably prevent this.

This usually occurs within the first quarter of an hour. When this happens, I quickly check the temperature of the cell. If it is not noticeably increased, I simply restart the charging process. With a bit of luck, the charging process then runs normally. But it can also be that it switches off prematurely again. That's why it's always good to be nearby and be able to check the temperature immediately.

Conversely, with older cells it can also happen that the charger does not recognize the end of charging. As you already found out in your first post. The cell then gets hot and is only switched off by a temperature sensor or a previously specified maximum capacity value.

Interestingly, I have never had this problem with the original Eneloop cells. Even after more than ten years of use, they do not seem to show any signs of aging.

 

[Dimt]

You are probably right. I have not bought Eneloops for years I'm sure some are older than ten years. I never had this problem with the MH-C810d that charged at the default rate of 2000mAH and the gentler rate of 1000. I wanted the MH-C940 to charge my cells at a gentle 500 rate. Seems this 500 rate may not be enough to accurately determine end of charge.

I still have six cells (in a trail cam) that I want to run thru the conditioning process. I'm going to condition them with the MH-C940 at the 1000 rate and see what happens.