NiMh charger problem or bettery ?

NiMh charger problem or battery ?

Hi,

Have an instrument which has 9 NiMh cell battery pack (10.8 Volts) . The Charger inside the instrument will not do any attemp to charge the battery pack, Voltage of the battery pack is about 0.5V (for all the 9 cells) , it has been in storage for a couple of years and not used.

The charger circuit uses the bq2003 Fast-Charge IC chip : https://www.ti.com/lit/ds/symlink/bq2003.pdf
and according to this document, it says :

If the temperature of the battery is out of range, or the
voltage is too low, the chip enters the charge pending
state and waits for both conditions to fall within their
allowed limits. There is no time limit on the charge
pending state; the charger remains in this state as long
as the voltage or temperature conditons are outside of
the allowed limits.

My assumption is: if the charge controller minimum battery voltage is set above 0.5 (for all 9 cells) , then it will never attempt to charge the battery pack since it suspects it faulty ? am I right ?
Question: what is the minimum working/good 9 cell NiMh battery could have?

Should I suspect a faulty charger?

Thanks!

suspect the batteries they should not go below 1 volt per cell.

Nimh have a shorter shelf life than Nicad therefore if they have been in storage for a while they will have gone below the charging threshold of your charger

I also have a problem related to NiMH batteries and a charger. I will post my question here because I do not want to open another topic.

I have bought 4 AA NiMH batteries recently, 2-3 weeks ago.
A few days ago I charged two of them because they did not work in my camera out of the box. However, despite the fact each of them has a capacity of 2000 mAh and a small label on my old charger reads "NiMH AA-2/4x1.2V = 600 mA max.", the two batteries were apparently charged in less than half an hour. The left green LED on the charger, for the left group of 2 batteries, stopped blinking which indicated they were fully charged. Unfortunately the batteries discharged after less than 20 pictures taken with my camera.

What should I do next? It appears that the charger stops charging the batteries too early (and it does not do like this with other NiMH batteries I have which are charged in a few hours).

I have an AA Ni-MH battery charger that is simply a current source and a timer. It severely overcharges and cooks a cell that still has a charge in it and it will not fully charge a high capacity cell.
A charger with a battery charger IC would not have these problems.

Modern AA Ni-MH cells are sold fully charged and hold their charge for one year.

My charger is not timer based. It stops charging different batteries in various intervals of time.

Anyway, I have continued my experiments and charged all four new batteries and put them in a flashlight which I left switched on till the light produced by its LEDs died out.
At this stage I measured the voltage across each battery and the voltmeter indicated:
1) - 1.29 V
2) - 1.29 V
3) - 1.05 V
4) - 50 mV!!

Battery (4) recovered after being recharged and I repeated the experiment with batteries (1) and (2) and two other old batteries. This time, when the light of the flashlight went off by itself, battery (2) discharged to 70 mV while (1) remained at 1.05 V.

I recharged (1) and (2) in around 10 minutes!! (way too fast) and got 1.3 V across each of them when the green light of the charger stopped blinking.

Regarding my 4 new batteries there is something unusual that tells the charger they are fully charged when in fact this is not the case.

There are a number of reasons why your charger is not charging these batteries

my advice is to build yourself a charger such as this one : https://obrazki.elektroda.pl/6544102100_1428224733.gif

Part Description
R1 56kΩ ¼W, 5% resistor
R2 27kΩ ¼W, 5% resistor
R3 22kΩ ¼W, 5% resistor
R4 47kΩ ¼W, 5% resistor
R5 750Ω ¼W, 5% resistor
R6 220Ω ¼W, resistor
TR1 10kΩ @ 25°C thermistor, approx. 3.7%/C° NTC
C1 0.1µF 10V capacitor
Q1 TIP32C PNP transistor, TO-220 case
Z1 LM393 dual voltage comparator IC, DIP
LED1 Red, green, or yellow LED, 10mA
Other 2-cell AA battery holder
USB cable
Small heatsink

The circuit shown in post #6 is not a Ni-MH battery charger. It simply tries to apply the 5V from the USB directly to the battery without any current limiting and stops charging when the battery gets hot.
Have you ever charged a Ni-Cad and a Ni-MH cell at the same time? The Ni-cad gets cooler[/c] until it is fully charged then gets hot. The Ni-MH cell gets hotter and hotter as it charges. So this battery charger might be fine for a Ni-Cad battery.

I think you should use a modern battery charger IC that does everything correctly.

Hi AudioGuru


Thanks for your comments I have indeed used this circuit many times to charge Ni-mH batteries.
It was merely a suggestion for a method that I have used many times without problems.

Is this forum not here for people who wish to design or make things for themselves as opposed to buying commercial products ??

I have done more tests and I finally separated two batteries out of the group of four, those two that do not discharge to below 100 mV while powering the flash-lamp. I charged and installed them in my camera which unfortunately works for no more than 10 minutes with them.

After being discharged by the camera, the voltage shown by the voltmeter for each battery is around 1.28 V and after I charge them again the voltage goes to 1.38 V. Why they discharge in less than 10 minutes in my camera remains a mystery.

Are you measuring the batteries with a load applied?

tempos said:

After being discharged by the camera, the voltage shown by the voltmeter for each battery is around 1.28 V and after I charge them again the voltage goes to 1.38 V.

Click to expand...

These are figures I also see in my rechargeables.

There is another measurement you can try. Namely what voltage develops on the battery as you start charging. This indicates its internal resistance. A low figure means the battery has low internal resistance. This is a good sign (within limits).

My charger is not smart. It sends 100mA through any battery, continually, until I remove it. My rechargables are in various states of decline. A deteriorating battery shows a high voltage when charging, above 1.8 V, say. This indicates a chemical makeup with high internal resistance.

But there are bad batteries with very low internal resistance. The electro-chemical makeup does not take a charge.

There are different charging algorithms too.

Why they discharge in less than 10 minutes in my camera remains a mystery.

Click to expand...

Some digital cameras are hungry that way. Perhaps they have some feature that makes up for it.

I find if I disable the flash on my camera, it extends the time a charge lasts.

kam1787 said:

Are you measuring the batteries with a load applied?

Click to expand...

No, without a load.

BradtheRad said:

Some digital cameras are hungry

Click to expand...

In the past, using two AA 1.2V "ENERGIZER" batteries, I was able to take at least 100 pictures, each time also firing the flash.
My old batteries, 3 years plus, can still power the camera for a time longer than 10 minutes. They are still superior to my new batteries which, it is true, are of a little known brand called "PERSONNELLE".

Whats the Mah of the batteries as this plays a big part in how long they last mine are 2200mah and last long time in my camera. Cheap batteries do not perform as good and the best ones

The capacity written on these batteries is 2000 mAh.

I test the remaining quality of my 2300mAh Energizer AA Ni-MH battery cells by shorting a charged one with my multimeter. A good cell shows 9A and some that have been charged and discharged 500 times and are about 4 years old show only 0.6A. They are guaranteed for 5 years and I have made a few warranty claims and got coupons to replace them.

I recently bought a stash of them from a Target store. Target made a big mistake coming to Canada, spent a fortune building huge stores, could not compete with Wal-Mart and are leaving Canada so I bought Energizer 2300mAh premium cells at 40% off the cost of Energizer 1400mAh cheaper cells (Target made a mistake and showed the same price for the premium cells as for the cheaper cells).

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I test the remaining quality of my 2300mAh Energizer AA Ni-MH battery cells by shorting a charged one with my multimeter. A good cell shows 9A and some that have been charged and discharged 500 times and are about 4 years old show only 0.6A. They are guaranteed for 5 years and I have made a few warranty claims and got coupons to replace them.

I recently bought a stash of them from a Target store. Target made a big mistake coming to Canada, spent a fortune building huge stores, could not compete with Wal-Mart and are leaving Canada so I bought Energizer 2300mAh premium cells at 40% off the cost of Energizer 1400mAh cheaper cells (Target made a mistake and showed the same price for the premium cells as for the cheaper cells).

Fully charged, my new "PERSONNELLE" brand batteries have a short circuit current between 3.5 and 3.8 A while the voltage with no load is 1.37 - 1.38 V.

The old ENERGIZER cells generate roughly the same short circuit current (~ 3.9 A) and also the voltage across them is the same, 1.37 - 1.38 V. However, they last a considerable longer time in my camera as compared to the PERSONNELLE batteries.

My advice for everybody would be "Do not buy Personnelle"!

Rechargeables are in large consumption by the public. However their specs are not easy to measure by most people. It gives manufacturers room to finagle.

From this thread (as well as my experience), I suspect that manufacturers have been cheapening the quality of their rechargeables, until they have shorter useful life. Only for a brief time when they are new do they live up to the labelled Amp-Hr specs.

BradtheRad said:

Rechargeables are in large consumption by the public. However their specs are not easy to measure by most people. It gives manufacturers room to finagle.

Click to expand...

I have found a review about a battery charger and power analyzer for NiMH and NiCd batteries that seems interesting. The device is a bit expensive (over 50 dollars) but it can measure the real capacity of any AAA or AA cell. I believe it can be useful to people having a lot of batteries, of different brands, quality and ages, that have to be sorted out to separate the best cells suitable for various application.
I suspect that my "PERSONNELLE" batteries have capacities below 400 mAh instead of 2000 mAh.

Charger Powerex MH-C9000




See: https://www.candlepowerforums.com/v...-Review-of-Analyzing-Charger-Powerex-MH-C9000

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"The memory effect is when you charge your battery until full, but after using it for a short period, it goes dead. However, if you have nickel-based batteries that have gone bad, it's likely you can revive them."

Click to expand...

Source: https://www.ehow.com/how_8060746_revive-bad-rechargeable-batteries.html

My batteries have this "memory effect" like comportment. They charge and discharge quickly.