Originally Posted by eecs

I was discharging it at 0.1A rate. I had the minimum voltage set to 7.0V. Perhaps importantly, I had "Discharge reduce" ON and set to 10%. The discharge started at 0.1A, and progressed normally down to 7.0V. At 7.0V the discharge current started reducing (as expected) down to 0.01A.

Could be a bug related to low currents. Maybe it terminated at 0.01A, but continued to draw a small current from the battery? Try once more and watch what happens.

Fred

Originally Posted by eecs

When it reached 50 degrees C with no termination I gave up and pushed the stop button. The capacity had reached 3.73Ah!

Empty 3.5 Ah NiMH battery should take at least 1.4*3.5 Ah (standard charging).
Have you observed battery voltage on the charger display? At what current value?
Don't forget that you have to consider voltage drop on junctions and wires and it depends directly on current value. If current goes down it follows so you can measure exact battery voltage only in no current state.

Don't expect your battery to stay cool if you quickcharge.

Originally Posted by narpat007

MOSFET whose on resistance is 2.4 milli ohm will have very less dissipation as co mpared with that who has 8 milli ohm.

It is unimportant when you use MOSFETs for "discharge" or "extern discharge". They work as controlled resistances of a few orders higher than 8 mOhm.

Originally Posted by narpat007

What you can make sure that the Electrical isolatior-Thermal Pads of all the MOSFET's are well fixed.

Sure. I put some thermal grease on both sides.

Originally Posted by everydayflyer

Discharge reduce does not control the cutoff voltage point.. Sounds like you failed to set a proper cut off point .

Originally Posted by eecs

Overdischarge problem:
... I had the minimum voltage set to 7.0V.

Is there some other way to set a proper cut off point? I sort of assumed that if I set the minimum discharge voltage to 7.0V then the discharge would not take the battery below 7.0V?!

Also, at higher currents, the minimum voltage does seem to be honored. For example, I discharged the same battery at 0.2A with discharge reduction set to 20% (hence a minimum current of 0.04A) and the charger behaved correctly: a current of 0.2A until the voltage reached 7V, then 7V with reducing current until the current reached 0.04A, then stop.

I wonder if perhaps the problem is that 10% of 0.1A is 0.01A which is the threshold of the charger's current sensitivity? If so then perhaps it would be better to implement discharge reduction by reducing the duty cycle of a full-current discharge pulse rather than attempting to reduce the current?

Originally Posted by flarssen

Could be a bug related to low currents. Maybe it terminated at 0.01A, but continued to draw a small current from the battery? Try once more and watch what happens.

I think you are right about the bug being related to very low currents.

I tried repeating (figured that battery was damaged anyway) and the charge is not terminated until the voltage reaches 0.0V.

Sorry ,I missed that you had set LVC to 7 volts.

Originally Posted by LeszekJ

Empty 3.5 Ah NiMH battery should take at least 1.4*3.5 Ah (standard charging).

True, though this battery is five years old, and has spent most of that time sitting on the shelf with me forgetting to recharge it, so I am not really expecting it to deliver its original capacity!

Have you observed battery voltage on the charger display? At what current value?

The voltages on the display matched the voltages in the log to within 10mV every time I checked them (and I checked them quite frequently).

The entire charge took place at my specified maximum of 2.4A.

Don't expect your battery to stay cool if you quickcharge.

I don't expect the battery to stay cool. But if the charge had terminated when the deltaV/cell reached 5mV then the battery would only have reached 35 degrees C, which is not cool but not hot enough to be a problem. 50 degrees C is getting hot enough to worry me, and in any case the charger did not terminate the charge even then: I had to manually abort the charge...

Originally Posted by eecs

I wonder if perhaps the problem is that 10% of 0.1A is 0.01A which is the threshold of the charger's current sensitivity?

I think 20mA is mentioned as the minimum the charger can handle. That's when it ends charging if balancing trickle is set. Should probably be a minimum discharge current as well.

The battery in question was a small 7S NiMH "9V" 200mAh battery. I was discharging it at 0.1A rate. I had the minimum voltage set to 7.0V. Perhaps importantly, I had "Discharge reduce" ON and set to 10%. The discharge started at 0.1A, and progressed normally down to 7.0V. At 7.0V the discharge current started reducing (as expected) down to 0.01A. This was where I expected it to stop. However, what happened was that the discharge continued, all the way down to 0V, at which point the charger reported "CONNECTION BREAK DOWN" and stopped.

Hi!

I just tried to duplicate your problem with a 4s 50mAh battery. Disch. red. 10%, LVC 4V, 100mA current.
I tried it with the older and the new firmware, and everytime the charger stopped at precisely 4V. No overdischarge here...

Originally Posted by eecs

this battery is five years old, and has spent most of that time sitting on the shelf with me forgetting to recharge it, so I am not really expecting it to deliver its original capacity!

Trying to evaluate accuracy of -dV detection by quick-charging worn battery is not the best idea. Please, upload a graph from this experiment.
I suggest standard 0.1C or to take a fresh battery for testing.

BTW it's written almost in every manual - use temperature probe and time/charge limit when quick-charging NiMH.

Originally Posted by Julez

I just tried to duplicate your problem with a 4s 50mAh battery. Disch. red. 10%, LVC 4V, 100mA current.
I tried it with the older and the new firmware, and everytime the charger stopped at precisely 4V. No overdischarge here...

Interesting. Are there any settings that affect NiMH discharge apart from the current (0.1A for both of us), the LVC (4V for you, 7V for me) and the discharge reduction (10% for both of us)?

Any other differences? Are you also using a 106B+?

Originally Posted by eecs

Input current display problem:
This is a minor issue. When I look at the input power status screen, and the charger is drawing more than 1.0A, I see a perfectly believable current. I was watching it as my battery approached full charge, and the input current gradually fell from 1.2A to 1.1A to 1.0A to .00A. I was expecting 0.9A, or better .99A, but it just shows .00A for all currents below 1.0A.

Hello eecs,

The screen can show the specific value when the current above 1.0A, but show .00A when all currents below 1.0A.

Originally Posted by eecs

Balance port unused for NiMH batteries:
I understand that NiMH batteries can't be balance-charged the same way lithium batteries can, but where a balance port is available good use could still be made of it. As a minimum I would like to at least be able to monitor the individual cells during a charge or discharge. Better, during a discharge, I would like to stop when the first cell dropped under 1V rather than waiting for the average to be under 1V/cell. Ideally, I would like the charge termination to be based on the first cell that experienced the chosen deltaV rather than the average deltaV/cell.

As you know, the balance port doesn't sopport NiMH batteries, so it fails to monitor the individual cells, and make charge termination to be based on the first cell that experienced the chosen deltaV.

Originally Posted by eecs

Overdischarge problem:
This one is more serious, in that it damaged my battery. The battery in question was a small 7S NiMH "9V" 200mAh battery. I was discharging it at 0.1A rate. I had the minimum voltage set to 7.0V. Perhaps importantly, I had "Discharge reduce" ON and set to 10%. The discharge started at 0.1A, and progressed normally down to 7.0V. At 7.0V the discharge current started reducing (as expected) down to 0.01A. This was where I expected it to stop. However, what happened was that the discharge continued, all the way down to 0V, at which point the charger reported "CONNECTION BREAK DOWN" and stopped.

Our engineers will test again and figure out the problems as you mentioned.

Originally Posted by eecs

Overcharge problem:
This one might have been serious, except that this time I was watching at the critical moment. I was charging a 10S "12V" 3.5Ah NiMH cordless drill battery. I had done a discharge test, measuring the capacity as about 2.4Ah, so I had chosen an "Auto" charge with a 2.4A limit. I had the NiMH Sensitivity DeltaV set to 5mV/Cell. The charge progressed normally, and the voltage peaked at about 15.06V with the capacity about 3.20Ah. At this stage I was watching closely, and measuring the temperature with an infrared thermometer (about 30 degrees C). The charge continued, and as the temperature rose, the voltage decreased.

Did the DeltaV you read via the screen display? The open voltage you read was not correct due to the effection of current. And LeszekJ was right, "Don't forget that you have to consider voltage drop on junctions and wires and it depends directly on current value. If current goes down it follows so you can measure exact battery voltage only in no current state." So the right voltage can be made when the current is zero by disconnecting in a flash, and you can use the Logview and transfer the data then figure out the whole process.

Originally Posted by eecs

The temperature kept climbing. When it reached 50 degrees C with no termination I gave up and pushed the stop button.

When the temperature kept climbing, you can try to reduce the voltage to below 3mV/cell.

Regards,
Junsi

Originally Posted by LeszekJ

Trying to evaluate accuracy of -dV detection by quick-charging worn battery is not the best idea.

Relying on there being a clear -dV with a worn NiMH battery is certainly not a good idea. However, in my case, the battery did show a clear -dV (36mV/cell), so the question is why the charger did not recognize this?

Please, upload a graph from this experiment.

OK, here it is:

Note that the vertical axis is in mV, and the horizontal axis is just whatever time base the charger uses when sending data out its USB port (just under one sample per second). These are the values being reported by the 106B+, so it certainly saw the -dV.

I suggest standard 0.1C or to take a fresh battery for testing.

Speaking of which, is the 106B+ capable of giving a NiMH battery a 0.1C 14 hour charge? I suppose if I use a charge limit of 0.1C and a time limit of 14 hours then I will probably get what I want, unless it detects a -dV when I don't want it to and stops early!

BTW it's written almost in every manual - use temperature probe and time/charge limit when quick-charging NiMH.

Very true. I didn't want to use a time/charge limit until I finished working out what the true capacity was (though in hindsight I could probably have assumed the old battery wouldn't do better than its nameplate 3.5Ah capacity). I should certainly have connected the temperature probe, and will do so in future.

However, I would like temperature, time and capacity limits to be secondary charge termination, reserved for when I am charging a battery that does not exhibit a clear -dV. My complaint is not that an old, strange battery fooled the charger by not exhibiting a clear -dV; my complaint is that my battery did exhibit a clear -dV and the charger ignored it.

Originally Posted by junsi

The screen can show the specific value when the current above 1.0A, but show .00A when all currents below 1.0A.

OK, no problem. However, if you don't choose to show currents below 1A, I would suggest a display of <1A rather than .00A to avoid confusion.

As you know, the balance port doesn't sopport NiMH batteries, so it fails to monitor the individual cells, and make charge termination to be based on the first cell that experienced the chosen deltaV.

I know it doesn't support NiMH batteries, but the hardware is certainly capable of doing so, so it would be possible to add it in a firmware update. However maybe there is not much interest in NiMH batteries in your market for this charger?

Did the DeltaV you read via the screen display?

The values I am quoting come from the data the 106B+ sends out its USB port. However, I was watching these during the charge, and they matched the LCD to within +/- 10mV. So yes, it is fair to say that the 36mV/cell -dV (360mV for my battery) was what was shown on the charger's LCD.

When the temperature kept climbing, you can try to reduce the voltage to below 3mV/cell.

If a setting of 5mV/cell did not terminate the charge when the battery voltage was down by 36mV/cell then I can't see why a setting of below 3mV/cell would help, but I will give it a try!

Originally Posted by eecs

If a setting of 5mV/cell did not terminate the charge when the battery voltage was down by 36mV/cell then I can't see why a setting of below 3mV/cell would help, but I will give it a try!

OK, just finished trying a charge with the following settings:

NiMH Auto 2.4A
NiMH Sensitivity DeltaV 1mV/Cell
NiMH/NiCd Check Delay 5min
Temp. Cut-Off ON 40 C
Safety timer OFF
Capacity Cut-Off OFF
Buzzer OFF

and all other settings at factory default. Here is the graph of the charge:


Note that the battery was already partially charged. However, the peak occurs well after the 5 minute mark (300 seconds), so the charger should have been looking for it.

The current for the entire charge shown was 2.4A.

The peak voltage was about 15.25V.

I terminated the charge manually when the voltage had dropped to about 15.05V, a drop of about 0.2V (200mV) below the peak. This is a drop of 20mV/cell.

Originally Posted by eecs

in my case, the battery did show a clear -dV (36mV/cell), so the question is why the charger did not recognize this?

I'm not sure that you've seen -dV. It might be necessary to look at the current value also.
I can see no graphs as yet (only picture placeholders). Don't forget to present every sample (no decimation).

Edit: please, show also the current and the charger input voltage.