BC-9009 pauses when charging Duraloops: what should I do?

[JazzMan]

I have many packages of AA Duraloops (white-top LSD Duracells manufactured in April '09) that I just recently opened.

When I put 4 of them in my La Crosse BC-9009 and set it to charge at .5C (1000mA), the charger momentarily pauses charging on a couple cells towards the end of the charging process. All the cells are also very hot to the touch, to the point that I can only hold my finger on them for a couple seconds. I have tried this with multiple packs, and it happens on all of them. It also happened with older non-LSD Rayovacs, but I figured it was caused by the old batteries and didn't expect it to keep happening when I switched to the new Duraloops.

Is this normal, or might it damage the batteries over time? I can think of several ways to handle this issue:

1) Do nothing (if it poses no real problem)
2) Direct a fan at the charger
3) Reduce current below .5C
4) Limit charging to 2 batteries at a time (although this is significantly less convenient)

Thanks for any advice!

 

[Bullzeyebill]

They are probably quite warm toward the end of the cycle because they were not discharged enough before you applied the 1A charge. Would have been easier on the cells if you topped them off with a more gentle charge, not that you hurt them, by the way. What was their voltage prior to charging?

Bill

 

[LED_Thrift]

Have you tried two at a time? It may be less convenient, but if the cells are too hot to hold that doesn't sound good or very safe.

 

[TakeTheActive]

...When I put 4 of them in my La Crosse BC-9009 and set it to charge at .5C (1000mAh), the charger pauses charging on a couple cells towards the end of the charging process. All the cells are also very hot to the touch, to the point that I can only hold my finger on them for a couple seconds...

Pausing during CHARGE mode is not good because the charger is detecting greater than 127°F.

• Run a TEST @ 1000/500 with cells in slots 1 & 4.
  .
• If those cells don't get too hot, run another TEST @ 1000/500 with different cells in slots 1, 2, & 4. The idea is to give EACH cell additional airflow and that no cell is SURROUNDED.
  .
• Run a DISCHARGE @ 500 and remove each cell when the charger switches back to CHARGE mode. After all cells are discharged, run a CHARGE @ 700 with cells in all 4 slots and check that:
  1. The cells terminate properly at less than 0.5C
     .
  2. The cells still don't get too hot at the reduced current.

During all of the above CHARGE modes, monitor the VOLTAGE and CAPACITY when the cells begin to heat up. This will give you some clues as to the health of the cells.

 

[JazzMan]

They are probably quite warm toward the end of the cycle because they were not discharged enough before you applied the 1A charge. Would have been easier on the cells if you topped them off with a more gentle charge, not that you hurt them, by the way. What was their voltage prior to charging?

Well, this has happened in both the "Discharge" and "Test" modes, so the cells would have been fully discharged before the charge was applied.

Have you tried two at a time? It may be less convenient, but if the cells are too hot to hold that doesn't sound good or very safe.

Yeah, I have tried two at a time, and there was no pausing then. But you're right, if the charger can only be used as a two-battery charger, it's a lot less convenient.

During all of the above CHARGE modes, monitor the VOLTAGE and CAPACITY when the cells begin to heat up. This will give you some clues as to the health of the cells.

I'm in the middle of performing the steps you suggested. If the cells terminate properly when charging at 700 this time, does that mean I can safely assume they will continue to do so during future charges? I can monitor the charger this time, but that won't always be the case (and it would be even less convenient than charging only 2 cells at a time).

Is this a common problem with the BC-9009 charger, or do I have a sketchy unit? I'm skeptical that it's a problem with the batteries, since they're fresh and it's occuring with multiple packs.

 

[Mr Happy]

Charge at 700 mA instead of 1000 mA. Even consider charging at 500 mA.

It is normal for batteries to get hot at the end of charge when using higher charge rates, but if they get too hot you should reduce the charge rate.

Some chargers are better than others in this regard. The better chargers allow some ventilation space around the cells, and also have a design that keeps hot parts of the charger away from the charging bays.

I think (though I don't own one) that the BC-9009 has a very compact battery compartment and also has hot charger components right underneath the battery bay. This is not ideal for keeping batteries cool during charging.

 

[JazzMan]

Charge at 700 mA instead of 1000 mA. Even consider charging at 500 mA.

It is normal for batteries to get hot at the end of charge when using higher charge rates, but if they get too hot you should reduce the charge rate.

Some chargers are better than others in this regard. The better chargers allow some ventilation space around the cells, and also have a design that keeps hot parts of the charger away from the charging bays.

I think (though I don't own one) that the BC-9009 has a very compact battery compartment and also has hot charger components right underneath the battery bay. This is not ideal for keeping batteries cool during charging.

Yes, the BC-9009 does have a very compact battery compartment. There are only a couple millimeters between each battery. However, I haven't noticed a lot of reports of this problem with the BC-9009 when searching the forums, so I'm not sure if my specific unit is just behaving differently.

It wouldn't be a big inconvenience for me to charge at the slower rate of 500 or 700, but I've read a ton of threads where the consensus seems to be that charging at 1,000-2,000 is best. The next best option seems to be charging at a very low current for a specific period of time (and not relying on the charger to terminate at all), but this is highly inconvenient. The worst option, according to the general opinion on the forums, is the middle ground of the 500-700mA charge, because the charger may miss the relatively weak termination signal and cook the batteries. That's what scared me away from just going with 500-700mA, and why I posted this question.

Thanks to all four of you who have responded so far!

 

[Mr Happy]

It's OK. That 1000 - 2000 mA charging recommendation is one of those "perfect world, ideal situation, all other things being equal" kind of recommendations. It's not terrible to deviate from it, and in fact many BC-900 users seem to charge at 700 mA as standard.

 

[SilverFox]

Hello Mr Happy,

I beg to disagree...

The 0.5C - 1.0C charging rate recommendation comes from the battery manufacturers. It is the best charging rate when utilizing change in temperature or -dV termination.

The charger manufacturers often don't bother to read the battery specification sheets, and are constrained by cost to produce a charger that "will mostly work." This does not mean that you will get the best performance or life by ignoring what the battery manufacturers say.

Tom

 

[TakeTheActive]

...I'm in the middle of performing the steps you suggested. If the cells terminate properly when charging at 700 this time, does that mean I can safely assume they will continue to do so during future charges?...

No. As the cells age, they will need more and more current to develop the necessary -DeltaV for the charger to detect Charge Termination. What I do, and suggest others do, is periodically monitor the CHARGE put into the cell (as opposed to the CAPACITY). As you lower the Charge Rate, the efficiency decreases and it takes more mAh to fully recharge the cell. CLICK on my Sig Line LINK and read the theory article by jtr1962 to get an idea of the 'Percent of Efficiency' at different Charge Rates.

UPDATE: Just to expand a bit on this - with rough approximations - if you CHARGE @:

• ~1.0C, you may need to put ~110% back into the cell
• ~0.5C, you may need to put ~120% back into the cell
• ~0.3C, you may need to put ~140% back into the cell
• ~0.1C, you may need to put ~160% back into the cell

Thus, if you're Charging @ ~0.3C and you see ~160% going back into the cell, it missed the -DeltaV termination and then has to rely on MAX VOLTAGE or MAX TEMP or MAX TIME.

Maha got around this -DeltaV 'problem' by lowering MAX VOLTAGE to 1.47VDC and then adding on a '100mA for 2 hours Topoff', so most cells terminate on MAX VOLTAGE on the Maha MH-C9000 while I see most of my VIBRANT and SEMI-VIBRANT cells terminating at -DeltaV and ~1.55VDC on my BC-900.

...Is this a common problem with the BC-9009 charger, or do I have a sketchy unit? I'm skeptical that it's a problem with the batteries, since they're fresh and it's occurring with multiple packs.

The BC-9009 is basically a BC-900 v35 with a different wallwart. And, although CPF is primarily Maha MH-C9000 country, I haven't seen many complaints about 'Charging 4 new Eneloop 2000mAh AAs @ 1000mA in my La Crosse BC-xxx and Pausing Due to Overtemp'. I know that I recently recharged an 8-year-old set of Sanyo 1700mAh non-LSD NiMH AAs with low ICV @ 700mA in my BC-900 and THEY overheated, which puzzled me. I haven't pursued it further, yet.

For improved airflow, I have my BC-900 sitting on 2 hexagonal wooden pencils. You may give that a try.

How did charging 3 cells @ 1000mA work out?

 

[Turbo DV8]

My experience with the BC-xxx chargers has rendered reliable, consistent termination using 500 mA/700 mA charge rate when using 'Loops. So far they have aged very gracefully and continue to terminate just fine at these rates. I cannot say the same for 'Brids. I've had lots of lesser cells pause to cool off on the BC-900 when attempting to charge at 1 amp. Those cells are packed in there so tight, it's really not a suitable charger for charging four AA cells at 1 amp.

One thing different I might stress is to discourage the use of any forced cooling. Thinking cooler is always better, I went through a phase with the BX-xxx of having a fan suspended over the chargers, and I noticed multiple failed charge terminations as long as the fan was running. Within two minutes of turning the fan off, the charge on all the cells terminated. This happened time and time again. The cells need to be allowed to build up a certain amount of heat which creates a stronger -dV signal at end of charge.

 

[JazzMan]

OK, here are the results of my tests.

When charging in slots 1 & 4, there is no issue. (But I already knew that from previous uses.)

When charging in slots 1, 2, & 4, there doesn't seem to be a significant issue. None of the cells paused charging. Of course, cells in slots 1 & 2 were warmer than the one in 4, but not overly so.

When charging in all four slots but with the charger sitting on a surface with greater air flow (which happened to be a metal cooking rack--no fan was used), the issue seems to be mitigated. None of the cells paused, although the cells in slots 2 & 3 were somewhat hot. But not so hot that it would hurt to hold my finger on them, and slightly (but noticeably) less hot than when I've used the charger with it sitting on a table.

After this, I tried charging in all four slots with the charger on a table again. The cells in 2 & 3 were noticeably hotter to the touch than when the charger was on the cooking rack, and the cell in slot 2 paused again. This occurred at a voltage of 1.44 and a capacity of 1,990mAh (the cell ended up taking 2,060mAh for the complete charge, and the other three all took 2,040-2,060 as well). The pause only occurred once, although in the past there sometimes were two pauses in slots 2 & 3 before the charge was completed.

So, it seems like I have a reasonable workaround for the issue, although I'm still curious if something is up with my particular BC-9009. There will be situations where it might not be convenient to setup the charger on a surface with great air flow. Or, more likely, times when the ambient air temperature is higher than it was during my recent tests (they were at about 68 Fahrenheit, 20 Celsius) and therefore the increased air flow wouldn't help enough to avoid the problem. If replacing my charger would alleviate the issue (since other BC-9009 owners don't seem to have many problems with this), I'd certainly do it.

Thanks again to everyone who responded! I GREATLY appreciate it!! :thumbsup:

 

[Turbo DV8]

That reminds me of another thing I've done to all my BC-xxx chargers from the get-go. I installed thick rubber footsies on the bottom to raise the chargers about 3/8". Another solution would be to at least rest them on pencils. The factory zits on the bottom are simply insufficient.