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Old 03-18-2016, 12:17 PM
TAT TAT is offline
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Battery Voltage question

Ok here is the deal, I am not understanding battery voltage issue. I am using a Tenergy Tb6B charger, So far I have charged 4 different kinds of batteries.

1) Elite Force Lipo 7.4 V 1500 mAH NiMh battery. Fully charged ( Alarm went off) reads 8.39 V

2) Elite Force Crane stock 9.6 V 1600 mAH NiMh battery. Fully Charged (Alarm went off) reads 12.7 V (P.S doesn't hold charged, maybe 2 140 rounds Elite force Mid Caps and battery is DEAD)

3) Shuangao Crane Stock 8.4 V 1500 mAH NiCd battery. Fully Charged ( Alarm went off) reads 11.63 V

4) Shuangao Crane Stock 9.6 V 1500 mAH NiCd battery. Fully Charged ( Alarm went off reads 14.38 V ( P.S gray looking metal dust at the ends where the wires are going into the battery Think that might be a problem)

I just not understanding why the volt reading are so different. Any input with this issues would help.

Elite Force 7.4 Lipo is used in a CA Scar Sportline

Elite Force 9.6 is used in a JG R36

Shuangao 8.4 is the battery that came in the JG R36

Shuangoa 9.6 is a back up battery I got in a trade

I dont know if using the batteries in different guns makes a difference.
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Old 03-18-2016, 01:24 PM
TAT TAT is offline
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update charged a intellect 9.6 2000 mAH Ni Mh and when charged it read 12.01 Volts
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Old 03-20-2016, 08:28 AM
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theone theone is offline
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In order for a battery to charge, the input voltage going to it has to be greater than the voltage of the battery.It sounds like battery number 2 has a bad cell causing all the other cells to drain. This is common with cell batteries, nicad,nmhd. Right after you unplug the battery you will see that the voltage is still high with a volt meter. Although you will see on the meter the voltage will begin to slowly drop. It will drop after a period of time, maybe 20 minutes, to the given battery voltage.
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Last edited by theone; 03-20-2016 at 08:31 AM.
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Old 03-20-2016, 10:21 AM
RotaryProphet RotaryProphet is offline
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NIMH and NICD batteries should charge to 1.5v per cell, and are rated at 1.2v per cell.

Some of the readings in your first list are way over, which would indicate to me one or more bad cells. I'd double check the settings on your smart charger, but generally it's safe to set the smart charger and let it do it's thing -- It's not necessary to worry about the charged voltage of the pack unless you're trying to diagnose a bad battery.

For a slightly more in-depth answer, NIMH and NICD batteries don't hold volts, they hold amps (So for instance, your 2000mah 9.6 has 8 cells which each hold 2000mah of current). At their full capacity, they -create- voltage of between 1.2 and 1.5v. The problem is that the voltage part is a bit fuzzy, and it changes with the battery's remaining charge. We use voltage as a rough indicator of remaining charge because we can't directly measure amps without actually pulling the current, and that would discharge the battery. We consider the battery dead when we try to pull amps from it and as a result the low current causes the voltage to drop to a point where it's no longer capable of doing any work.

The battery charger works similarly -- Voltage is a side effect of current introduced offset by resistance, and so the charger may fiddle the voltage up or down to get the battery to accept more amps. (The charger actually works by measuring the amp draw on the charging line, and changing the voltage up or down until that current matches the settings you input. When the current drops to 0 for a long enough time while the voltage is within acceptable levels, the battery is considered "charged") A worn out battery has more internal resistance, so it takes more input voltage to get it to accept it's rated charge. Typically when these begin discharging, the voltage output drops off much more quickly than a fresh battery.

So, the short version of the long answer is: Let your battery charger do it's thing, and when the battery is no longer capable of running the gun for long it's time to pitch the battery.

Last edited by RotaryProphet; 03-20-2016 at 10:24 AM.
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Old 03-21-2016, 08:14 PM
TAT TAT is offline
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Thank you both for the input, I am trying my best to do the research myself but I have started to get back into playing. I know lipos are the way to go but I need to do some major upgrades to the guns before I put lipos into them,
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Old 03-21-2016, 09:31 PM
2tall 2tall is offline
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Quote:
Originally Posted by TAT View Post
I know lipos are the way to go but I need to do some major upgrades to the guns before I put lipos into them,
I am no expert but in my experience ( someone correct me I am wrong) but a 7.4 lipo Is pretty much the same as running a 9.6 NIMH battery, that I see you mentioned above you were having issues with.. Trigger response is better as well IMO
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Old 03-22-2016, 10:28 AM
RotaryProphet RotaryProphet is offline
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That's sort of true, but for misleading reasons -- NIMH batteries are actually fairly poor at running high-amp draw devices like airsoft motors. When you try to draw ~15-20 amps from a 1500mah NIMH battery the 9.6-12v battery pack drops down to ~6-8v under the load. LiPo batteries are rated to much higher discharge rates, and don't suffer the same problems. The 7.4 will run about like a 9.6, but it's far more efficient, and it tends to lead to less heat buildup in the motor (And thus a longer motor life).

It comes down to the "C" rate of the battery -- A relatively modest 11.1v 2000mah battery with a 20c rate is rated to pull 40 amps at a time -- Plenty to run an airsoft motor without voltage drop. (The formula is Capacity * C Rate = Max Amps)

I started my lawn mower from a 5800mah 11.1 Lipo with a 40c rate -- 232 Amp draw is plenty to run the starter motor, and it did a better job than the big lead acid battery that came with it.

For those interested, you can measure the current draw for your airsoft gun -- Just unplug the battery from the gun, hold the trigger down (A little clamp helps), and use a multimeter to measure the resistance of the two terminals inside the gun side battery connector. Then use the multimeter to measure the voltage from the two terminals on the battery itself. Divide voltage by resistance, and you get current draw (In amps). On the gun I have sitting nearby, I get about 0.75 Ohm resistance from the gun, and the battery is an 11.1 lipo charged to 12.5v -- 12.5/0.75 = ~16.6 Amps.

Last edited by RotaryProphet; 03-22-2016 at 10:30 AM.
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