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Charging NiMH Battery Pack: 7.2 V, 2200 mAh, 3x2 AA Cells, JR Connector with iMAX B6AC V2 Balance Charger and Discharger

Hello, I have this battery product ( Pololu - Rechargeable NiMH Battery Pack: 7.2 V, 2200 mAh, 3x2 AA Cells, JR Connector ) driving the dual TB905 motor controller shield ( Pololu - Dual TB9051FTG Motor Driver Shield for Arduino ) . I am trying to recharge it with SkyRC iMAX B6AC V2 ( Pololu - iMAX B6AC V2 Balance Charger and Discharger ) and have gotten the voltage back up after charging for about 5-6 hours.

It seems this charger operates by regulating current into the battery back to charge the battery then provides you a GUI to see what the state of the voltage is.

I have gotten the voltage back up to the recommended 8.4V, but am curious to know if this is a sufficient criterion to end charging.

I was reading a WikiHow article about charging NiMH batteries ( How to Charge NiMH Batteries: 12 Steps (with Pictures) - wikiHow ) and it seemed like you want to apply C/10 into the battery ( 2200mAH /10) = ~0.2A which was what I used.

Their time recommendation was to charge for C/3.33 time (not sure what units nor how they exactly did their calculation.) Watching a Youtube video, the guy suggested a number in the 12-16 hour range ( SkyRC Imax B6 LIPO BALLANCE CHARGER-How to charger NI-MH, NC-ID, Lipo Tutorial - YouTube )

Do you have any suggestions given your team seems to have extensive experience with this product used in my exact application?

Hello.

The fully-charged voltage of a NiMH cell should be around 1.4V, so your six-cell pack charging to 8.4V sounds good.

The iMAX has a lot of features and settings to decide when to stop charging the battery. For NiMH, it uses a technique called delta-peak detection where it monitors the battery’s voltage and stops charging automatically when the battery’s voltage peaks and then drops past a certain threshold. So the charger should take care of deciding when to end charging, and the only option you should really need to set is the maximum allowed charging current. You can find more details in the iMAX B6AC V2 instruction manual, which can be found under the “Resources” tab of its product page. The amount of time it takes to charge a battery pack can depend on several factors (including how discharged it is when you start). In general, C/10 is a good rule-of-thumb for slow charging (or trickle charging), and 1C is usually fine for quick-charging (which is also mentioned in the WikiHow article you linked to).

Brandon

It looked like when I was charging it, and I was using the Windows GUI over USB, that the thing cut off at 3 hours and I ended up rerunning charging 3 times for a total of 9 hours. Is there any way to turn on delta-peak detection from the GUI Windows Application?

It sounds like you probably running into the safety timer. You can disable or adjust the safety timer length in charger’s system settings. Note that there is also a capacity cut-off that automatically stops the charging process if the configured capacity is supplied before the delta peak voltage is detected or the safety timer has expired. As far as we know, there is no way to disable the delta peak detection for the charger.

Brandon