View Full Version : General NiMH Battery Information

04-30-2008, 05:05 PM
This is some nice accumulated info from different charger manuals on NiMH's all rolled into one:

What is the battery’s nominal rated voltage? NEVER guess the rated voltage if not printed on the battery’s label, consult your battery supplier or determine pack voltage as follows:

A. NiCd and NiMH: multiply the total number of cells in the pack by 1.2. A 6-cell pack will have a nominal voltage of 7.2 volts (6 x 1.2). An 8-cell pack will have a nominal voltage of 9.6 volts (8 x 1.2), etc.

• NEVER allow NiMH batteries to overheat, as this could adversely affect their performance. If this happens, disconnect the battery from the charger immediately and allow to cool!
• NEVER deep cycle NiMH batteries as permanent damage could result.
• NEVER attempt to use the NiCd, Pb, or lithium functions with NiMH batteries.
• STORE NiMH packs with some voltage remaining on the cells (refer to battery supplier).

Notes for charging NiCd and NiMH batteries:

• Lower current means it takes longer to charge but it’s less stressful on the batteries, tends to result in more fully charged batteries, and helps to maximize the battery’s lifespan.

• Larger “sub-C” size cells can handle peak charge currents up to 5.0 amps with little heat generation. Smaller “A” and “AA” cells overheat more easily and should be charged at much lower currents. Even smaller “AAA” and “N” cells should be charged at lower rates. Refer to the NiCd AND NiMH CHARGE AND DISCHARGE CURRENTS table for recommended charge currents.

• A battery which is approaching or has reached full charge could become warm to the touch, but never get HOT. If overheated, the battery has likely reached an overcharge condition and should be disconnected from the charger immediately!! Allow the battery to cool before use. And lower the charge current setting for future charges.

• For packs having more than 12 volts, the actual amount of current delivered to the battery might automatically be limited so not to exceed the charger’s maximum rated charge power of 90 watts. See the included MAXIMUM POWER CHART for details.

• To keep NiCd batteries in good operating condition, it’s a good idea to properly discharge them before charging on a regular basis.

• NiMH batteries have a self-discharge rate of about 20-25% (vs. 15% for NiCd). Always recharge NiMH batteries just prior to use.

• After discharge, compare the final capacity measurement displayed to the capacity rating listed on the battery’s label. If a battery provides less than 70% of its rated capacity it may need to be replaced. Additional cycles can be attempted to try and revive the battery, but if capacity measurements fail to improve the battery should be replaced.

• In the “auto” current setting, a charger should automatically set the appropriate discharge current based on the condition of the battery. It is NOT recommended to use the “auto” function if charging smaller electric flight type NiCd / NiMH batteries (smaller than “AA” cells).

Notes for cycling NiCd and NiMH batteries:

• Periodic cycling of NiCd batteries (once every month or two) can be beneficial in keeping them in good operating condition. Excessive cycling (more than once monthly) will unnecessarily shorten the lifespan of the battery.

• A short time delay can be set to occur in-between the charge/discharge functions to allow the battery to cool. This delay period can be adjusted from 1-60 minutes in the Setup Menu (see page 12).

• During cycle mode, the discharge cutoff voltage for NiCd and NiMH batteries is FIXED (not adjustable) at 0.9V per cell.

• See the notes sections for NiCd/NiMH charge and NiCd/NiMH discharge for detailed information regarding charges and discharges.

• Cell manufacturers note three main benefits of cycling NiCd and NiMH batteries:

1. Battery maintenance: NiCd batteries benefit the most from regular cycling to help keep them in good operating condition, and is recommended once monthly. NiMH batteries do not require as much cycling.

2. Determining battery condition: NiCd and NiMH batteries are rated by how much charge energy or “capacity” they can store compared to their rated capacity. A battery that can supply only a small fraction of its rated capacity is likely reaching the end of its useful life and may need to be replaced.

3. Breaking-in batteries: new NiCd and NiMH batteries may need to be broken-in before they will perform to their specifications. Older batteries which have been unused for an extended length of time may require to be broken-in again to regain their usefulness. Repeated cycling is the best way to revive such batteries.

Safety Timer Calculations

For NiCd and NiMH batteries, divide the battery’s rated capacity (mAh) by the fast charge current setting (A). Take that result, and DIVIDE BY 11.1. Set this number of minutes in the safety timer screen. If the charger stops charge at this time limit, approximately 150% of the battery’s rated capacity will have been delivered to the battery.

For example: NiCd battery’s Fast charge Safety timer rated capacity current setting calculated setting:

1500mAh 2.5A (1500 divided by 2.5) = 600, divided by 11.1 = 54 minutes
3800mAh 2.3A (3800 divided by 2.3) = 1652, divided by 11.1 = 149 minutes
1000mAh 0.9A (1000 divided by 0.9) = 1111, divided by 11.1 = 100 minutes

For NiMH and NiCd 1.5 hours (90 min) is good safety time cut off

The following features apply to NiCd and NiMH batteries only

PEAK DELAY AT START: At the beginning of charge the voltage of NiCd and NiMH batteries can be somewhat unstable. This could cause the peak detection circuitry to accidentally stop charge far too early, which would cause the battery to NOT become fully charged. This peak delay function will temporarily turn off the peak detection circuit only during the very early stages of charge to prevent this from happening. Select the number of minutes to temporarily shut off the peak detector at the
beginning of charge. A 3 to 5 minute delay is usually enough. Setting a delay time of 0 minutes turns this function off. Note: Charge current will likely be lower than the setting during this time, which is normal.

DELAY BETWEEN CHARGE/DISCHARGE: This is a time delay designed to allow a battery to cool between charge and discharge portions of a cycle. Select from 1 to 60 minutes. If the battery becomes too warm during a cycle, increase the number of minutes on this screen to a higher value.

PEAK SENSITIVITY: When peak charging NiCd/MH batteries, charger should see the battery’s voltage increase to a maximum level – or “peak”. Then, the battery’s voltage should actually drop very slightly. When the charger sees this, it should stop charge completely. You can customize how closely it will try to detect this peak, which is called “peak sensitivity”. This value is set in milli-volts per cell in the pack. A higher mV number can result in less precise peak detections. A lower mV number can result in more precise peak detections, but very low values (under 5mV) can sometimes result in erratic operation (depending on the quality of the input power source, input and output connections, battery, etc.). Recommended settings are 8-10mV for NiCd batteries, and 5-8mV for NiMH batteries.

NiMH MAX. CHARGE INPUT: This is another backup safety feature to protect NiMH packs. During charge, IF peak voltage is not detected and the safety timer has not expired, this function will automatically stop charge when the amount of capacity delivered to the battery matches the value set in this screen. Setting this number to 110% of the rated capacity of your battery is recommended. For a 650mAh battery, 110% would be (650 x 1.1) 715mAh. The 110% value of a battery rated at 1800mAh would be (1800 x 1.1) 1980mAh, etc. Setting a value of 9900mAh will effectively turn this feature off.

TOP-OFF CHARGE: When peak charge ends, delivering another short burst of charge will help to quickly maximize a NiMH battery’s voltage before trickle charge starts. Charger should deliver the amount of current set in this screen for 20 minutes only before trickle charge starts. Set this screen to somewhere near 7% of the current set in the “NiMH CHARGE” screen. For example: if the “NiMH CHARGE” current is set at 3.5 amps, set this screen to (3.5A x 0.07 = 0.245A) 200mA or 300mA. If the “NiMH CHARGE” current is set to 850mA, set this screen to (850mA x 0.07 = 59mA) 100mA, etc. It’s not critical to set this value with extreme accuracy. This feature can be turned off by setting this screen to “None”. “Top-off” will show on the display during top off charge, and “END” will show when complete (now in trickle charge).

05-10-2008, 07:51 AM
This is great info, two questions on Nimhs and Nicads:

How does the discharge rate affect the performance of an ESC?

Anyone had experience with 7.2V Venom or Trinity 5000mah packs and whats their discharge rate?

Whats the best pack with highest discharge rate?

05-10-2008, 09:17 PM
How the discharge rate affects the performance of an ESC depends on what kind of ESC you are referring to, and what it's specs are, how it's wired, and how you are using it. Also, "how the discharge rate affects the performance of a ESC" is the same thing as asking, "How well will an ESC will perform using a good quality vs. low quality batteries?"; clearly that would be less than desirable.

A good quality NiMH pack will generally outperform a Nicad in every category.

The Trinity NiMH's are really good quality-you won't be disappointed if utilized correctly. As for the Trinity 5000 series I can't say don't have any but I have the Trinity EP and Reference 4600's and can't complain. I will be hard for the price to find a better NiMH.

I can say this, for the price today of a 5000mah NiMH pack you are better off going Lipo for any application.

What is the best pack with the highest discharge rate? You may have to find some packs that you are interested in and compare which have the highest. At the time I was researching, the Trinity EP held true to their raings of 35A.

Hope that helps.

05-11-2008, 10:18 AM
Thanks for the info, I guess i am trying to grt the low down on packs. I have tenergy 4500's that have a discharge rate of 45amps per pack. I was wondering if the trinity or venom 5000's has a higher discharge rate. Well lipos are another option, but a very pricy option. You should do a lipo section info thread. What you do from purchaseing the right packs, the correct usage,connectors,charging and charger. The works am thinking about lipo but have seen mixed reveiws.

05-11-2008, 01:10 PM
I'm not 100% sure, but I think the Tenergy post over rated discharge ratings from what I think I have read somewhere on this board.


I have not gone to Lipo as yet, all the NiMH's packs I have are still new, some have not even been used as yet so I'm jut watching the prices fall. For example: