Wall Warts

I dunno where it would be ...

Thanks.

Good! :-)

I measure just under 4vdc for the pack. Your opinion is solicited.

Only $150-300. Lordy mercy!

I rambled thru my WW box again and found the following:

ATLINKS USA Telephone power supply Input: AC120V 60hz 4.4w Output: DC 9v 200 mA Class 2 transformer UL etc

but when I measure, I get about 20vdc from my meter. Any idea why the drastic difference from spec?

Thx, P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

the internal impedance of the transformer itself may be the current limiter. That's the way it was in a B&D VersaPack NiCd charger I have.

Just a FYI,I have some Everready NiMH AA cells rated at 2350 mAH(bought at Wal-Mart),and saw some no-name 2800 mAH AA cells for sale on Ebay.

Your battery pack is dead, kaput, eWaste, gone, shorted, etc. That's what probably killed the wall wart and inspired the recall. Charging a shorted cell is a great way to overheat an unprotected transformer. If you simply replace the transformer, you're likely to fry it again.

The requisite computer is not included in the price. I use it to characterize Li-Ion mutations for model airplanes, robotics, cell phones, and general havoc. The energy available is basically the area under the discharge curve.

Sure. You're measuring the voltage without a load. If you load the xformer with a 200ma load: R = 9V / 0.2A = 45 ohms (47 ohms is close enough) and Power = E*I = 9v * 0.2A = 1.8 Watts (so use 5 watt resistor) you should get around 9V DC.

Amazing. I've run tests on some 2200 ma-hr NiMH AA cells using my CBA-II

The results are not very impressive. If I discharge at rediculously low rates, such as 0.01C, I might be able to squeeze 2200 ma-hr out of a cell. I tested one at about twice the estimated self discharge rate, and calculated about 5000 ma-hr out of the cell. I think it took about a week to finish the test. However, when I ran it at a more realistic load of 2C, I was barely able to squeeze out 1000 ma-hr. This was also for a brand new cell, as repeated charge/discharge cycles would also decrease the cell capacity.

See the discharge curves at:

Note how the area under the curve decreases with increasing load.

I keep planning to post some test results, but never seem to have the time to organize anything. Sorry(tm).

Funny, I've always read the opposite with Nimh cells, they need to go through several charge/discharge cycles before they reach full capacity.

This is especially true of the long discharge ones, which come "pre-charged" at about 80% and then at least in my experience take 5-10 cycles to come up to a useable capacity. It also seems in my experience that the lower the charge rate, the more cycles a cell needs.

BTW, if you have any info on charging an Azden HT, please let me know.

Thanks,

Geoff.

This has always been the "conventional wisdom" about nicads, as well.

I wish I knew what the "truth" about rechargeables was. Contrary to the common belief, I've never had problems with rapid self-discharge with NiMHs.

I've never seen that. Nothing similar found with Google or on my favorite sites:

Where I have seen something like this is with cheap Chinese laptop battery packs. The problem is not the battery. It's the charge controller inside the battery. It has to be run up and down in voltage and "trained" before it knows how the pack is going to act. This is usually done at the factory by reputable battery pack manufacturers, but seems to be avoided by others. I've personally only seen this with Li-Ion battery packs, but am told that it's also a problem with older chemistries.

That's probably because NiMH has a rather high self-discharge rate. They may have been at 100% when they left the factory, but have self-discharged in the box. Also, the ideal storage charge level is about 40% for NiMH. None of the NiMH batteries I've tested (Duracell, Rayovac, Sanyo, Energizer, various no-name, and various OEM) have showed anything other than a slow loss of capacity (area under the curve) for repeated charge/discharge cycles.

No experience. This might help if it uses NiMH:

Note that most of my experiments have been on single cells, not battery packs.

Argh. I haven't been paying attention. Duracell 2650 2650 ma-hr Energizer e2 2500 ma-hr Maha Powerex AA 2700 ma-hr Maybe I'll do some shopping and testing (timer permitting).

Here's some result from the RC groups on NiMH packs.

At 0.5A discharge rate, various manufacturers yielded 1700 to 2000 ma-hr.

At 0.25A, this Sanyo battery pack managed to squeeze out 1275 ma-hr:

More of the same for 1900 ma-hr:

This is somewhat better than what I was getting.

Many thanks.

S'l>>

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Most NiMH/NiCd battery manufacturers seem to rate their cells at a discharge rate of 0.05C (20 hour rate) - that would be around 100 mA for those AA cells. Sanyo's charts for their "Eneloop" show about a 10% reduction in useful capacity at a discharge rate of 0.5C (1000 mA).

If you're actually pulling over 4 amps from them (2C discharge rate) I'd expect a significant further loss of capacity.

For comparison, the same Sanyo charts seem to show that an alkaline battery loses about 75% of its useful capacity when you go from 100 mA rates to 1000 mA rates.

I gather that the loss of useful capacity is due in part to the series resistance of the battery, and in part due to inefficiencies in the chemistry under high rates of discharge.

Had these cells been "formed" properly prior to your test (via several slow-charge / slow-discharge cycles)? There seems to be a general agreement that NiMH cells don't achieve their maximum storage capacity unless they've gone through several cycles like this, and that many manufacturers don't take the time to do this during the manufacturing process. I've seen some indication of this in my own testing (using a smart-charger which can cycle the batteries and report the capacities for each cycle).

There seems to be a real tradeoff. In general, the very-high- capacity NiMH cells seem to have a more rapid rate of self-discharge; they're good for "use immediately after charge" applications, but not so good for "charge and store" standby uses.

The low-self-discharge cells (e.g. Sanyo Eneloop, PowerEx Imedion, and similar) seem to run around 10% lower in rated capacity.

For comparison, the Maha Powerex AA are rated at 2700 mAh, while the Maha Powerex "Imedion" AA are rated at 2400 mAh.

I've read that this is due to difference the structure/alloy of the metal hydride used for the electrodes... varities which can bind more hydrogen, also tend to suffer from more spontaneous de-binding and leakage (or so my crude understanding goes... I probably have the details wrong).

I've had reasonably good results with the Imedion and Eleloop types for my radio go-kit... I can charge them up after use, and depend on finding plenty of power available even six months later. Never could do that with standard NiMH types, when I tried a few years ago... I couldn't trust them to be useful even 3 months after charging.

Why should they, when it would add to the cells' cost? Given the relatively low price of uP-controlleed chargers, there's no point.

That hasn't been my experience. My 2200mAh and 2700mAh MAHAs hold up very well -- months, in fact. I've never made a study of the actual capacity, but they /do not/ "fall flat" shortly after being put into use.

Nope. They came directly out of the box. I didn't record how long they had been sitting on the shelf. I must admit my ritual was rather sloppy.

I would initially charge the battery in a Radio Shock 23-1305 charger.

Not the best, but I have 3 of them, so they get used. One big advantage for me is that it will independently charge a single AA cell. Also, it runs off 12VDC. It came with 4ea NiMH cells, but I killed them long ago.

After charging, I would leave the battery sit for anywhere between 1 and 8 hrs to let it cool down and supply sufficient time to charge up more cells. I vaguely recall that they were Sanyo cells, but as I have several types on the bench, I can't tell which one was used.

I would then connect the battery to the CBA-II tester, plug in the desired test settings, and generate a graph. Repeat for several cells. I would usually try to discharge it until the "knee" is visible, which my guess(tm) is down to about 15% of capacity.

I haven't done much NiMH testing (mostly because Li-Ion is my current interest), but I do recall seeing a drop in capacity with every cycle. There was no evidence of any "conditioning" effects. Incidentally, until I see numerical or personal evidence of such a "conditioning" requirement for NiMH batteries, I prefer to ignore it. To me, it's the same as NiCd "memory effect", which I have yet to experience, and which I have spent considerable time attempting to demonstrate.

I'll believe it when I see it demonstrated, documented, or chemically explained. I just wasted some time searching Google Scholar for any references to NiMH conditioning, training, pre-charging, etc. Zilch.

I was watching some TV show (How it's made???) showing how batteries are manufactured. "Testing" the batteries was done on a high speed conveyor and lasted about 1/2 second per cell. I don't think this is enough time to "condition" the battery.

As far as I have been able to guess (Yeah, I know, I should have measured), the typical NiMH cell arrives out of the box at about 30% charge. I don't know if this is intentional, an artifact of the manufacturing process, or some safety requirement. There are quite a few battery vendors proclaiming that they ship NiMH and other batteries discharged for safety reasons. Anyway, if they ship them discharged, then the "conditioning" cycle would need to be: Full -> discharge -> Full again -> test -> discharge I wouldn't expect such an exercise for consumer products.

Sanyo Eneloop.

LSD doesn't have lower capacity. It's roughly the same as other NiMH. LSD NiMH batteries have a higher terminal voltage. The energy capacity is the area under the discharge curve, which is close to identical for types with the same chemistry. However, the higher terminal voltage will cause the curve to drop earlier for the LSD NiMH, so they appear to not last as long.

Lots of vendors of LSD batteries:

Dunno. I've read some on battery chemistry, but have generally ignored NiMH as a marginal idea. Sorry(tm).

Are you running an electric airplane, using the battery pack to run a glow plug, igniting a squib, or running telemetry electronics? All would benefit from a switch to Li-Ion.

The reason I bought a CBA-II battery tester was because of my inability to properly guess actual battery capacity.

Most of my experience with NiMH batteries was with Metricom radios and various Motorola and Kenwood handheld radios. It doesn't take much to kill them. For example, you don't even need to discharge them to a NiMH battery pack. The country distributed Motorola MTS2000 radios to all the hospitals as part of the HEARNET (Hospital Emergency Administrative Radio Network) system. The radios were permanently planted in charger with power on 24x7. Some radios were turned on, but most were left off. There would be a short test roughly twice per month. After about a years, not one of the radios were functional because all the NiMH batteries were dead.

I'm having a similar experience in my palatial office, where I use a Motorola HT600 and several NTN7016A NiMH battery packs. Unlike the hospital example, I make it a point of not leaving the battery in the charger after it reaches full charge. I also use the radio in a normal manner, charging the battery only when the xmitter craps out. The result is that I charge the battery approximately 3 times per week. Despite this care, I manage to kill about one battery every 2 years (that's after only about 150 charge cycles).

I also use NiMH batteries in my various cameras (Canon S5IS etc) all of which use AA cells. I'm seeing the typical 1%/day self-discharge rate. I keep two sets of batteries in the bag. It's not unusual for me to find the spares to be nearly dead after about 2 months.

Your NiMH milage may vary, but mine sucks.

Weird. Which brands do you use? I use mostly MAHA (PowerEx).

Interesting... one of Sanyo's pages shows different results. See

They compare alkaline, Sanyo Eneloop, and the Sanyo "high capacity" NiMH cells. The latter have a definite advantage in capacity, and the terminal voltages under load look almost identical in the "100 mA discharge" graph.

Hmmm... the graphs on the page cited above seem to suggest differently... what do you think?

Nope... typical ham-radio handheld radio use (about 80% receive, 20% transmit).

I do have several such radios which run on LiIon batteries. My preferred "field assignment" radio is still a NiCd/NiMH type... with the auxiliary six-AA-cell battery pack, and a bunch of charged Imedions and some alkaline AA cells as last-ditch backup, I could be deployed for a couple of days before I'd be in immediate need of a recharge.