Are 30 minute NiMH chargers bad?

[greg_in_canada]

Hi,

In this thread (http://www.candlepowerforums.com/vb/...d.php?t=107554) I was told that using my Energizer 30 minute charger isn't good: the cells don't get fully charged and they get hot. I know that the second point is trun, but don't know about the first.

So am I undercharging my cells with this charger? And maybe more importantly, am I damaging them by charging them in 1/2 and hour?

Are there any better chargers I should be using, that aren't too expensive?

Thanks - Greg

[SilverFox]

Hello Greg,

We need more information...

How hot are the cells getting?
What is the voltage at the end of the charge?
What is the voltage at the end of the charge and after trickle charging for an additional hour?

In general, there are two recommended charge rates for NiMh cells. A slow charge of 0.1C for 14-16 hours that is terminated by a timer. At the end of 16 hours you pull the cells from the charger. The "fast" charge rate is between 0.5C and 1C. During a fast charge, the cells will heat up at the end of the charge, but should stay below around 120F. When you get to 140F and above, you may be doing some damage to the cells. The fast charge gives a end of charge termination signal that can be picked up by a smart charger. Often, a fast charge is followed by a trickle charge to "top off" the cell.

Charging at a rate higher than 1C requires an advanced charging algorithm, and in the case of the Energizer 15 minute charger, forced cooling. I have not checked out the Energizer 30 minute charger, but does it have a fan? If not, you may be able to prop it up a bit for better air circulation. Oh, by the way, the Energizer 15 minute charger charges 2500 mAh cells to 97% of their full capacity in about 20 minutes. The cell temperature gets up to about 130F.

I have charged at 4C with my Schulze charger with good results, but I do not do this on a regular basis. The Schulze uses an advanced charging algorithm and the cells got warm, but not hot. Capacity seemed normal, but I did not formally measure it.

The key to fast charging is to monitor the temperature of the cells. If they heat up, you are going too fast. Keep in mind that different cells have differing internal resistance, and may respond differently to fast charging.

A fully charged cell should come off the charger at around 1.45 volts.

Tom

[Monolith]

Tom,

I've been following the other thread, and I think one point that Miller seemed to be making was that the Energizer 30 minute came with special cells that worked with the 30 minute charger and that using other NiMH cells would not be optimum. Maybe Greg can clarify what cells he was charging.

[Pellidon]

I don't have experince with the Energizer 30 min but I have found with the Duracell 30 minute charger if I don't have the cell snuggled directly on the metal strip at the bottom it won't temperature detect and over heat despite the fan. Other brands detect the heat by monitoring the contact temp at the battery minus terminal. If I seat them correctly they get warm but not hot to the touch when the cell charge light winks off.

When time and space allow it I place a small muffin fan to cool the cells during charging. That additional cooling helps keep the cells happy.

The charger should switch to a trickle charge to top off the cells. Most do this so I would guess that one does as well. Fortunately Silverfox is capable of ferreting out the data that the charger's companies don't seem to put on many of the websites (Duracell--hint--hint) or on the package.

[greg_in_canada]

The cells in question are the Sanyo 900 mAh ones that 4sevens is offering with L0P purchase. The cell I used in my run-time test was just off the charger (but cooled down) and was 1.40V.

I know Eric was suggesting the 30 minute charge needs special cells, but that is not what the packaging or instructions indicate.

This charger has no fan and the cells get fairly warm, but not hot enough to burn you. I don't have a good way of measuring the temp.

The cells are supported in mid air while charging so if there is a temperature sensor it would have to be via the battery contact.

Greg

[onthebeam]

The cells in question are the Sanyo 900 mAh ones that 4sevens is offering with L0P purchase. The cell I used in my run-time test was just off the charger (but cooled down) and was 1.40V.

I know Eric was suggesting the 30 minute charge needs special cells, but that is not what the packaging or instructions indicate.

Greg

One way to solve the problem of the 30 min. charger with no fan: Walgreens has the 15 minute Energizer charger for $23 this week. Coupons for $2 in store may reduce it further. And you get four decent 2200 batts, too. Since I never let them run down all the way in my lights, I don't notice that they don't last quite as long as the 2500s. .

[greg_in_canada]

I'm in Canada so no Walgreens for me.

My understanding of the 15 minute charger was that the special cells are charged in 15 minutes but regular ones are detected somehow and charged pretty slowly (6 hours?). So that wouldn't work well for me since I have close to 100 NiMh AA and AAA cells floating around the house in kids toys.

Greg

[MrAl]

Hi there,

I think i'll wait for some new technology batteries before i invest in any
more charging systems.

Take care,
Al

[SilverFox]

Hello Pellidon,

Are you offering to send me your Duracell charger so I can add it to the Charger Comparison thread?

Tom

[SilverFox]

Hello Greg,

1.40 volts seems a little undercharged to me. Perhaps then need a little time in trickle charge mode to come up to full charge. I suggest you put a set of cells in the charger and let it charge for 4 hours. Measure the voltage as you pull the cells from the charger and let us know what you get.

In order to get a rough idea of temperature, I heated some water in a tea kettle up to 140F. I could hold the kettle in my bare hand for about 1 second before transferring it to my other hand. The old hot potato trick...

There are two 15 minute chargers available. The RayOVac requires IC-3 batteries to charge at a rapid rate. The Energizer 15 minute charger will charge any AA or AAA NiMh cell that does not have a high internal resistance.

There is a disadvantage to using the Energizer 15 minute charger... the cells only get charged to 97% during the fast charge. To get the full 100% charge, you have to let them trickle charge for a while after the main charge.

Tom

[wptski]

I'm in Canada so no Walgreens for me.

My understanding of the 15 minute charger was that the special cells are charged in 15 minutes but regular ones are detected somehow and charged pretty slowly (6 hours?). So that wouldn't work well for me since I have close to 100 NiMh AA and AAA cells floating around the house in kids toys.

Greg

Greg:

I just got the Energizer 15 minute charger. I used C/10 for 16 hours on a special charger just made for a forming charge. I discharged those four 2200mAh cells to .9V/cell and charged them on the Energizer charger. It finished in about 13 minutes. I took four discharged Titanium 2000mAh cells and it charged them in 10 minutes!

I'm now discharging the 2200mAh Energizer cells on a Tritoin to check for capacity. After the forming charge, the capacity was around 2000mAh but that's only the first cycle!

[ks_physicist]

Does anyone know if the Duracell 15 minute charger (CEF15NC, does have built-in fan) continues to trickle charge after the main charging cycle?

It appears to shut completely off. Next time I recharge, I'll use a seperator plate and monitor the charging current (AA max looks to be 8.3 amps, I'm assuming that's net for four cells).

Jim

[wptski]

Does anyone know if the Duracell 15 minute charger (CEF15NC, does have built-in fan) continues to trickle charge after the main charging cycle?

It appears to shut completely off. Next time I recharge, I'll use a seperator plate and monitor the charging current (AA max looks to be 8.3 amps, I'm assuming that's net for four cells).

Jim

Jim:

Don't you mean the Energizer 15 minute charger? I think that Duracell has one coming out in the future!

The bottom of the Energizer 15 states that it puts out 7.5A for AA and 3A for AAA cells. I'll be posting some screen captures of the Energizer 15 in a few days unless somebody else does it first. Charging AA cells I read around 7.3A and around 1.8V per cell. It's PWM like the La Crosse BC-900 and MAHA C808M. I don't remember the frequency/duty cycle of the MAHA but the BC-900 was 51Hz and the Energizer 15 was a bit over 1kHz. Yes, the Energizer 15 does have fan. I think that's all there is to it, a different PWM and higher cell voltage with a good fan.

EDIT: It does trickle charge too!
EDIT: My mistake above, the Energizer 15 isn't a bit over 1kHz, should have look at the trace instead of the value which is wrong becasue the cycle rate is really slow more like the MAHA C808M, 2 seconds!

[noesisdg]

I am brand new to the CP forums although I have popped by here from time to time to see what this learned community had to say about a prospective purchase of mine. Thanks to all of you for your insightful and informative posts.

I just bought the Duracell CEF15NC charger from Costco (item #107292). It came bundled with 6 Duracell 2400mAH AA NiMH and 2 900 mAH AAA NiMH cells for a grand total of $29.99 plus tax. As well as the 120VAC adapter for the charger, the bundle also included the car charger adapter that lets the unit work from a 12VDC supply. The supplied cord plugs into a car cigarette lighter socket.

So far I like the charger. The integral fan seems to do a good job of keeping the cell temperatures down to a tolerable level. I haven't taken a thermometer reading of the the peak temperature they hit, but at no time are they too hot to hold your finger against.

I tried charging some older NiMH and NiCd cells in the charger when attached to its AC adapter and so far I've found that with the exception of some 2300mAH Panasonic AA NiMH cells they all "error out" as unchargeable (the red charge light starts to flash).

Then I got curious as the instructions said that when operating from the 12V car adapter that the charge rate was going to be slower. I looked at the AC adapter and its rated output is 16VDC at 4A. The charger itself is marked as accepting 12-16VDC input.

So, I got a 3A 13.6VDC power supply (the one I used was a Radio Shack 22-503 switching power supply I have had around for years) and ran the Duracell charger off that. Now all of a sudden all the older, lower capacity (650mAH-1100mAH) NiCd cells that "failed" will charge OK. I even managed to resurrect some cells that I had given up on - they would charge in other chargers but then quickly self-discharge after a few hours. I carefully monitored the temperature of the older, low-capacity cells when they were charging as I didn't fancy scraping "cell-guts" out of the charger if they overheated and exploded, but I was relieved when they stayed quite cool to the touch throughout the charging cycle. Careful though, your mileage may vary and I have no idea how the charger deals with older cells in various states of decline, and especially since Duracell says that you must only charge NiMH cells in the charger.

It seems therefore that the 15-minute "screaming fast" charge rate requires an input voltage to the charger of 16VDC, which also makes it a bit temperamental about which batteries it will accept for charging. I would guess that the chip that they use in the charge controller circuit watches the rate of climb of cell voltage after the start of the charge cycle, and if it comes up too quickly, then it rejects that cell as too low a capacity for charging at the high rate.

I haven't done any benchmark tests yet on the rate of charge with 13.6VDC (or 12VDC) applied, but I would roughly estimate that it takes about 2 to 3 times as long to charge when running the charger from 13.6VDC.

So, if you want to be "kinder" to your AA and AAA cells when you are using this charger, and charge them at a slower rate, all you need to do is use a lower input voltage that is in the range of 12-16VDC. According to the usual rules of charging and NiCd/NiMH cell chemistry the slower you charge a cell and the cooler it remains while charging, the greater the number of recharge cycles you will get from it.

I would be curious to hear from other forum members what experiences they have had with this charger.

Dave

[kitelights]

Excellent find. I believe that the Energizer 15 minute charger is identical to the Duracell and I've been having the same problems - it's rejecting most all of my cells. I didn't get the DC cord and I've got to dig out an old PS and see if the amperage is adequate.

Thanks for all the detailed info. I'll check with my local Costco and find out if they have that item # coming in. If so, I'll return the Energizer and get the Duracell. I think that you've solved the mystery and it makes perfect sense.

[Brighteyez]

Have you tried using the AC adapter that came in the package with the charger? If so, what kind of results did you have with that one?

I bought this package about a week or so ago, and quite honestly, have just not gotten around to opening it yet.

It seems therefore that the 15-minute "screaming fast" charge rate requires an input voltage to the charger of 16VDC, which also makes it a bit temperamental about which batteries it will accept for charging.

I haven't done any benchmark tests yet on the rate of charge with 13.6VDC (or 12VDC) applied, but I would roughly estimate that it takes about 2 to 3 times as long to charge when running the charger from 13.6VDC.

Dave

[ciam]

Hi,

In this thread (http://www.candlepowerforums.com/vb/...d.php?t=107554) I was told that using my Energizer 30 minute charger isn't good: the cells don't get fully charged and they get hot. I know that the second point is trun, but don't know about the first.

So am I undercharging my cells with this charger? And maybe more importantly, am I damaging them by charging them in 1/2 and hour?

Are there any better chargers I should be using, that aren't too expensive?

Thanks - Greg

Energizer's 30-minute charger is only rated at 750 mAh for AAAs and 2100 mAh for AAs.

[wptski]

Excellent find. I believe that the Energizer 15 minute charger is identical to the Duracell and I've been having the same problems - it's rejecting most all of my cells. I didn't get the DC cord and I've got to dig out an old PS and see if the amperage is adequate.

Thanks for all the detailed info. I'll check with my local Costco and find out if they have that item # coming in. If so, I'll return the Energizer and get the Duracell. I think that you've solved the mystery and it makes perfect sense.

The only thing identical about the E/D 15 chargers is the so-called 15 minute charging. The Duracell has a arched bottom allowing more air flow and it does appear to have more air.

Both use pulse width modulated current. The E-15 charges then trickle charges, Energizer's site states trickle for 24 hrs but at times it will give it a short pulse at 4A. The D-15 charges, with the LED still lit, it pauses for a few minutes, resumes at a reduced charging current till the LED shuts off. When the fan shuts off, it trickles at one rate for about 30 minutes, then the reduces the trickle lower for another 30 minutes and then stops completly.