Re: Maha MH-C9000 SUPPORT Thread
MH-C9000 Frequently Asked Questions
Updated Jan. 5, 2007
Using the BREAK-IN mode, I am seeing a charging capacity much higher than the capacity I programmed. Why is the battery overcharged?
When using the BREAK-IN mode, the charger puts in 1.6 times the capacity of the battery (entered at the start of the charge). This does not cause any harm to the battery as the charging rate is very low (only 10% of the battery capacity). The increased total charging capacity compensates for energy lost as heat. This is the charging scheme recommended by International Electrotechnical Commission (IEC).
I am charging some older batteries and see that the charging capacity is much higher than the capacity I programmed. Why doesn't the charger terminate correctly?
The charger terminates by voltage and by temperature simultaneously. For certain older (and low quality) batteries, they do not produce the proper negative delta V signal (a small voltage drop at the conclusion of the charge) needed for the charger to stop. At the same time, the battery temperature failed to reach the termination limit as the charging rate was probably too low.
To address this issue, you should attempt to perform a BREAK-IN mode on the batteries first. You should also use a higher charging rate.
When using higher charging current, the charging capacity seems to reduce. Is this normal?
When charging at higher current, the charge completeness reduces thereby lowering the charging capacity. This is to prevent battery overheating. This typically occurs at a rate greater than 1500mA. Generally speaking, 1000mA achieves nearly full charge completeness for AA batteries.
Even after the charge ends (DONE appears on screen), the charger will apply a topoff charge and continuous maintenance charge. Despite that the capacity on the screen no longer increases, the batteries are being topped off.
If you would like to achieve better charge completeness at higher currents, a small fan can be added to cool the batteries externally.
Why is it not recommended to charge battery below 0.33C?
When charging below 0.33C (except in BREAK-IN) mode, the batteries may not produce a sufficient end-of-charge signal for the charger to terminate correctly. Although the temperature sensors will safeguard battery overheating, lower charging rate might not cause enough heating in the batteries to trip the sensors.
If low charging rate is desired, you should use the BREAK-IN mode. Charging in that mode is terminated by only time (1.6 times battery capacity) and temperature.
After the charge begins, why do I see an abnormally high voltage (~ 1.6V to 2.0V) on the screen?
In the first few seconds, the MH-C9000 performs a proprietary "high impedance" check to filter out batteries unsafe to charge including non-rechargeable batteries. During this time, a high current is applied and voltage measured to determine the impedance of the battery.
The voltage will return to normal by the second time voltage data is displayed on the screen.
Why doesn't the charging and discharging current reach the set values exactly? I thought the charger is supposed to be precise.
The charging and discharging current are pulsed, thereby causing the displayed current to go up and down. The capacity calculation is based on the actual current rather than the set current so capacity calculation remains accurate.
I am using the CHARGE mode. Why is the capacity different than my battery capacity?
The capacity displayed in any charging process is called the "charging capacity." This is the amount of energy put into the batteries. This number does not equal to the battery's capacity as it is dependent on the amount of charge already in the battery as well as the battery's internal resistance.
For example, a half used 2000mAh battery may only show a charging capacity of 1000mAh since the battery is half full.
It is normal for the charging capacity to exceed battery capacity by as much as 30% depending on battery brand and charging rate.
To determine the battery's useful capacity, you must look at the "discharge capacity." Such information is available in the REFRESH & ANALYZE, BREAK-IN, DISCHARGE, and CYCLE modes. Note that the battery is not recharged in the DISCHARGE mode.
How do I tell if the capacity displayed on the screen is charging or discharging capacity?
If charging or discharging is in-progress, a blackbox contain either CHARGE or DISCHG will be displayed on the screen. The capacity shown during charging is always the charging capacity. Similarly, the capacity shown during discharging is the discharging capacity.
In the CHARGE mode, the final capacity displayed (after DONE appears) is the charging capacity.
In the REFRESH & ANALYZE and BREAK-IN mode, the final capacity displayed is the discharging capacity. The battery have also been recharged after the discharge.
In the DISCHARGE mode, the final capacity displayed is also the discharging capacity. However, the battery is not recharged.
In the CYLCE mode, the capacities saved in memory always refer to the discharging capacity.
When I discharge certain batteries, the current seem to taper off near the end of the discharge and seems to take very long to finish. Why and does this affect the capacity of the battery?
This is normal for batteries that exhibt high internal resistsance. MH-C9000 measures the voltage of the batteries while briefly pausing the discharge (every few seconds). For high resistance battery, this voltage might differ from the actual voltage of the battery. For the MH-C9000, it is not designed to maintain set current when battery is below 0.9V.
This does not affect the calculated capacity as the realtime current is used in the capacity integration.
Using the CYCLE mode, why do I see a "0 mAh" capacity on the screen? What happened to the saved battery capacity?
A CYCLE is consisted of:
Charge > 1 Hour Rest > Discharge > 1 Hour Rest (repeats for programmed number of times)
The discharge capacity is saved into the memory at completion of discharge but cannot be reviewed until that cycle is completed (after the 1 hour rest). During the rest, a zero capacity is displayed.
During this period, all previously completed cycle data can be viewed, but not the most recent cycle. It will become available after that particular cycle is completed.
Cycle data can be accessed anytime after completion of the first cycle by using the "UP" and "DOWN" keys.
There is an arrow that moves below the slot number. What does it mean?
The LCD screen displays information a slot at a time. The information (capacity, current, time, voltage) is displayed twice before moving on to the next slot. The arrow points to the slot reporting.
Is it normal for the batteries to get warm during charging?
Yes, batteries do get warm during the charge due to both internal heat and heat produced by the charger. Lower charging rate can yield lower battery temperature, but it is not recommended to go below 0.33C or 0.33 times the battery capacity.
Adding an external fan can also cool the battery.
The manual makes recommendations for charging rates. How about discharging rate
Most NiMH batteries can accept discharge rate up to 3 times its capacity. A higher discharge rate will yield lower capacity.
For accurate capacity measurement, use the BREAK-IN mode which complies with IEC standards (0.2C discharge rate).
Is the MH-C9000 compatible with the new "low self-discharge" batteries (e.g. Sanyo Eneloop)?
Yes. Follow the same charging rate recommendations for general NiMH batteries.
What is the maximum capacity supported by the MH-C9000?
The maximum capacity supported is 20,000mAh making it compatible with future technologies.
The charger cannot detect my battery. What can be done?
Virtually all batteries can be detected by the charger. Therefore, if a battery cannot be detected, it is likely not making good contact with the charger. This can be caused by improper seating of the battery or battery not meeting the IEC dimension standard. Try rotating the battery or placing it in another slot.
There is a faint noise emanating from the charger. Is this normal?
The charger can produce some high frequency hum, which is generated by the high frequency pulse charging and switchers.
