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Author Topic: Batteries - the weak link  (Read 448 times)
KE2KB
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Posts: 174




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« on: Today at 08:13:55 AM »

I have been analyzing NiMh batteries, both in a pack of six and individually. To get right to the point, I have found that the batteries in a pack never last as long as those charged individually.
I had purchased an FNB-83xh 7.2V 2500mAh pack for my Yaesu/Vertex VX-150 a few years ago. During most of the life of this pack, I have been using the radio mainly for receiving (railroad band) and not doing much transmitting. So I have not been asking the batteries for much current, and the pack appeared to be working fine.
But over the past six months, the pack would not charge properly on the Yaesu CD-30 desktop (rapid) charger. This charger puts out 400mA, so this is not really a rapid charge - 400mA should be a decent (if not a bit on the low side) charging rate for the 2500mAh pack. The charger was reporting a fully charged pack after only half hour or so. After removing the pack and re-inserting it into the charger, it would charge another hour or so.

When I transmitted on the VX-150 with this pack, the voltage would drop from 8.0 to 5.8V immediately. This was on a supposedly fully charged pack. So I knew that there were a couple of dead cells in the pack.
I decided to cut the pack open and separate the batteries. I found that three of the batteries were labeled Sanyon 2500mAh, with the part number HR-3U. The other three batteries were not labeled.
When I inserted the batteries into my bran-new Maha MH-C9000 charger/conditioner, on the "Refresh/Analyze" mode, four of the batteries failed almost immediately with the "HIGH" reading. This indicates that either the battery is open, and will not take a charge, or it is not a rechargeable battery. It is a feature the charger has to prevent attempting to charge alkaline and other non-rechargeable batteries.
The next step was to discharge the batteries without charging, using the "Discharge" mode on the C9000. The result was pretty much the same, except that the report wasn't HIGH, but the charger reported "Done" after only a few minutes on the discharge cycle.

I was able to get the remaining two batteries from the pack to run on the Refresh/Analyze cycle overnight, but when done, the capacity was less than half of the rated 2500mAh. So it is obvious that the entire battery pack was toast.

I have been using Eneloop batteries for all of my rechargeable battery needs, and am very happy with them. The latest version (Panasonic 3MCCA) have the same capacity (1900 min 2000 typ), but have a maximum cycles of 2100. The problem with these batteries is that the charger they came with charges two in a series, and this is not optimal. That is the reason I purchased the MH-C9000. I have learned a lot in just the week I have owned this charger.
For one thing, the Eneloop batteries come charged, but if you want to get the full capacity from them, you need to run them through a few cycles of charge/discharge/charge. Bran-new Eneloop (Panasonic 3MCCA) placed in the MH-C9000 on Refresh/Analyze (which first charges the battery full, rests for 1 hour, discharges, rests, then recharges), none of the bran-new batteries (I bought a 12-pack) reached their minimum capacity of 1900mAh. Most were very close (1800-1880), but two were significantly lower - 1789.
Older Eneloop (1st gen 3UTG) had lower capacity, most in the 1700-1800 range, but one or two were as low as 1360. These older batteries had been recharged exclusively in the Eneloop NC-MQN06U - 300mA, which charges four batteries in sets of two.
I also have an Eneloop NC-MDR02NU 2-cell charger that will charge AA batteries individually at 550mA, but I used that charger mostly for AAA batteries.

I have been researching NiMh batteries over the past few weeks, and from what I have gleaned, I can safely say that batteries in a series pack cannot be properly charged.
In addition, batteries must be selected to have capacity within 5% of each other in order to get the best performance from the set in a pack.
For this and other reasons, I have resorted to using the AA cell trays for my VX-150 and FT-530, and have built a pack of 10 AA for the FT-530 (requires 12V to produce 5W output) in which I will be using Eneloop AA cells and charging them exclusively on the Maha MH-C9000, following recommended procedures.

Eventually I may switch to Lithium battery packs, but until then I believe that individually charging/conditioning the Eneloop AA cells and selecting them for capacity within 5% to place in the AA cell holder will result in optimal performance and life.

It is unfortunate that our radio technology has advanced in leaps and bounds, while battery technology is still in the "dark ages" of technology.
I believe that within the next few years, more advanced battery technology will be available, giving us much better performance from our portable equipment. But as is always the case, new technology must go through a period of trial and error before it is perfected, and is reasonably priced.

Lastly, I want to warn you that rapid charging of any NiMh or NiCd battery will ruin it. The recommended charge rate varies depending on the battery. Here is an excellent thread on Eneloop and other NiMh batteries in the CandlePower forum. Please note that the reference to "C" as in 1C, 0.5C, etc has nothing to do with temperature. "C" referrs to capacity of the battery. Charge rates are in fractions of C.

http://www.candlepowerforums.com/vb/showthread.php?190625-Eneloop-Charging-Rate

Frank - KE2KB
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N3QE
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Posts: 2356




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« Reply #1 on: Today at 08:38:23 AM »

One way around the series-cell imbalances dragging down the life of the pack, is to use only a single large mAH cell.

With NiMH this nets only a nominal 1.2V and there's not a lot of general purpose electronics that can get by with that low of a supply.

With Li-ion a single cell nets a nominal 3.6V. Many consumer devices (cameras, cellphones) engineer the whole device to run off a single Li-ion cell (built in step-up converter where necessary). I don't know of any ham handie-talkies engineered to run off a single 3.6V Li-ion cell but I betcha there will be soon.
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K0BG
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« Reply #2 on: Today at 08:48:27 AM »

The real issue is cost. All batteries have an ESR, and although batteries in series packages may be selected to have the same ≈ESR, over time the ESR changes, resulting in the issues you outlined.

It is possible to build a battery pack with built in equalizing, but you no doubt wouldn't want to pay the price for the requisite circuitry.

I'm taken aback by the statement that rapid charging will destroy a NiCad et. al. That's an over-reaching statement. If there is but one thing which limits charging rates it's temperature. Here too, circuitry is available to limit the issue.
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W8JX
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« Reply #3 on: Today at 09:02:45 AM »

This charger puts out 400mA, so this is not really a rapid charge - 400mA should be a decent (if not a bit on the low side) charging rate for the 2500mAh pack. The charger was reporting a fully charged pack after only half hour or so. After removing the pack and re-inserting it into the charger, it would charge another hour or so.

Optimal rate for a full charge is .1c or less which means you want to charge at 250ma or less. The charger cuts off when it sees a certain voltage across battery. I would strongly suggest that you fully discharge pack with a 20 ohm 5 watt resistor over night to discharge all cells fully. Then when you charge it in Yaesu charger when it shows charged, remove it for a few hours them place it back on charge. This should give you more run time
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N6PG
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Posts: 61




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« Reply #4 on: Today at 02:33:46 PM »

This charger puts out 400mA, so this is not really a rapid charge - 400mA should be a decent (if not a bit on the low side) charging rate for the 2500mAh pack. The charger was reporting a fully charged pack after only half hour or so. After removing the pack and re-inserting it into the charger, it would charge another hour or so.

Optimal rate for a full charge is .1c or less which means you want to charge at 250ma or less. The charger cuts off when it sees a certain voltage across battery. I would strongly suggest that you fully discharge pack with a 20 ohm 5 watt resistor over night to discharge all cells fully. Then when you charge it in Yaesu charger when it shows charged, remove it for a few hours them place it back on charge. This should give you more run time

I can't find it now, but there was a great study done with eneloop a at different charge rates. It was interesting to see the temperature become a problem, and the charge termination at certain charge rates. The conclusion was that at .5c you actually get a relatively rapid charge, don't damage tge battery... But also give up just a bit of capacity. It seemed a good balance. .1c was also good, but took a long time. I think the internal charger of the kx3 is a very low rate to protect against heat and battery damage. It's also not a balanced charger, so better with .1c.

I wish I could find the other thread. Someone went to a lot of trouble plotting temps, voltages, etc and compared them with eneloop data sheets.

Scott N6PG

http://www.candlepowerforums.com/vb/showthread.php?190625-Eneloop-Charging-Rate
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KE2KB
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Posts: 174




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« Reply #5 on: Today at 04:53:25 PM »

The real issue is cost. All batteries have an ESR, and although batteries in series packages may be selected to have the same ≈ESR, over time the ESR changes, resulting in the issues you outlined.

It is possible to build a battery pack with built in equalizing, but you no doubt wouldn't want to pay the price for the requisite circuitry.

I'm taken aback by the statement that rapid charging will destroy a NiCad et. al. That's an over-reaching statement. If there is but one thing which limits charging rates it's temperature. Here too, circuitry is available to limit the issue.
The problem with rapid charging is that, when done in inexpensive (non-smart) chargers, the battery will overheat and life will be greatly reduced. However, I suppose that if one charges these batteries in the Maha MH-C9000 or other smart charger at 1C (2.0A for the Eneloop AA cells), the charger will monitor the current and temperature, and prevent overheating. That said, the battery temperature will still rise, and heat will eventually damage the battery.
There is an argument over at CandlePower over whether charging at a low rate for a long time is less damaging than a higher rate for a shorter time. That would depend on whether the battery can withstand a higher temperature for a short period better than it can withstand a moderate temperature for a prolonged period.

It has been proven that most of these smart chargers get a stronger termination signal from the battery at a higher charge rate (0.5C and above), and thus terminate properly. If the charge current is too low, the signal may not be sufficient for the charger to terminate, thus causing overcharging.

I have been charging/discharging my Eneloops in the MH-C9000 at 500mA, which is 0.25C. The charger instructions recommend not charging at rates below 0.33C due to the termination signal strength issue, but so far I have not had any trouble with this low rate.
I have some older Eneloop cells I want to experiment on. I'll try different charging rates, and compare the results.
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KE2KB
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Posts: 174




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« Reply #6 on: Today at 04:59:14 PM »

This charger puts out 400mA, so this is not really a rapid charge - 400mA should be a decent (if not a bit on the low side) charging rate for the 2500mAh pack. The charger was reporting a fully charged pack after only half hour or so. After removing the pack and re-inserting it into the charger, it would charge another hour or so.

Optimal rate for a full charge is .1c or less which means you want to charge at 250ma or less. The charger cuts off when it sees a certain voltage across battery. I would strongly suggest that you fully discharge pack with a 20 ohm 5 watt resistor over night to discharge all cells fully. Then when you charge it in Yaesu charger when it shows charged, remove it for a few hours them place it back on charge. This should give you more run time

I can't find it now, but there was a great study done with eneloop a at different charge rates. It was interesting to see the temperature become a problem, and the charge termination at certain charge rates. The conclusion was that at .5c you actually get a relatively rapid charge, don't damage tge battery... But also give up just a bit of capacity. It seemed a good balance. .1c was also good, but took a long time. I think the internal charger of the kx3 is a very low rate to protect against heat and battery damage. It's also not a balanced charger, so better with .1c.

I wish I could find the other thread. Someone went to a lot of trouble plotting temps, voltages, etc and compared them with eneloop data sheets.

Scott N6PG

http://www.candlepowerforums.com/vb/showthread.php?190625-Eneloop-Charging-Rate
The MH-C9000 has a "Break-In" mode which will charge at 0.1C for 16 hours, wait one hour, discharge at 0.2C, then recharge at 0.1C. I read that new Eneloops do not benefit from this "forming charge", and so far I have not used it. I really can't afford the time, but perhaps on my next purchase of Eneloops I will run at least some of them through the break-in cycle.
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KE2KB
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Posts: 174




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« Reply #7 on: Today at 05:03:30 PM »

This charger puts out 400mA, so this is not really a rapid charge - 400mA should be a decent (if not a bit on the low side) charging rate for the 2500mAh pack. The charger was reporting a fully charged pack after only half hour or so. After removing the pack and re-inserting it into the charger, it would charge another hour or so.

Optimal rate for a full charge is .1c or less which means you want to charge at 250ma or less. The charger cuts off when it sees a certain voltage across battery. I would strongly suggest that you fully discharge pack with a 20 ohm 5 watt resistor over night to discharge all cells fully. Then when you charge it in Yaesu charger when it shows charged, remove it for a few hours them place it back on charge. This should give you more run time
You're probably right about the discharge. I believe the MH-C9000 shuts down the discharge cycle when the battery voltage falls below around 0.8V for a 1.2V cell. But how far down do you want to run the cells? Leaving them connected to a 20 ohm resistor overnight may discharge so completely that you get the polarity reversal, and damage the battery.
I would want to use at least a diode in series to limit the minimum voltage to around 0.6V.
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N6PG
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« Reply #8 on: Today at 05:28:02 PM »


It has been proven that most of these smart chargers get a stronger termination signal from the battery at a higher charge rate (0.5C and above), and thus terminate properly. If the charge current is too low, the signal may not be sufficient for the charger to terminate, thus causing overcharging.

I have been charging/discharging my Eneloops in the MH-C9000 at 500mA, which is 0.25C. The charger instructions recommend not charging at rates below 0.33C due to the termination signal strength issue, but so far I have not had any trouble with this low rate.
I have some older Eneloop cells I want to experiment on. I'll try different charging rates, and compare the results.

The termination signal is an important point. I charge at .5c, as I think it's the best balance for time, capacity, and longevity. If time weren't a factor, I think .1c would be fine. It's between .1c and .4 c I avoid because I want to be sure the termination signal is clear.
Scott N6PG
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W8JX
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« Reply #9 on: Today at 07:54:42 PM »


You're probably right about the discharge. I believe the MH-C9000 shuts down the discharge cycle when the battery voltage falls below around 0.8V for a 1.2V cell. But how far down do you want to run the cells? Leaving them connected to a 20 ohm resistor overnight may discharge so completely that you get the polarity reversal, and damage the battery.
I would want to use at least a diode in series to limit the minimum voltage to around 0.6V.


Cell reversal is not likely with a shunt discharging battery fully. When shunt is removed place it on charge immediately. The reason you discharge like this is so cells can be at a different stat of charge causing charger to shut off too soon as voltage goes high on fully charged cells. The stunt takes all cell to same state to start over.
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KE2KB
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Posts: 174




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« Reply #10 on: Today at 08:13:14 PM »


You're probably right about the discharge. I believe the MH-C9000 shuts down the discharge cycle when the battery voltage falls below around 0.8V for a 1.2V cell. But how far down do you want to run the cells? Leaving them connected to a 20 ohm resistor overnight may discharge so completely that you get the polarity reversal, and damage the battery.
I would want to use at least a diode in series to limit the minimum voltage to around 0.6V.


Cell reversal is not likely with a shunt discharging battery fully. When shunt is removed place it on charge immediately. The reason you discharge like this is so cells can be at a different stat of charge causing charger to shut off too soon as voltage goes high on fully charged cells. The stunt takes all cell to same state to start over.
Don't have the 20 ohm 5W resistor or a single cell holder, so I have put 4 cells into an led flashlight and let it burn. Maybe not the best option, but I want to do something now.
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W8JX
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« Reply #11 on: Today at 08:32:15 PM »

Don't have the 20 ohm 5W resistor or a single cell holder, so I have put 4 cells into an led flashlight and let it burn. Maybe not the best option, but I want to do something now.

You can improvise some. Flashlight can work.
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