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++ +Zubi flyer teaches coding to kids with programmable frisbee + + + + + 
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++ +24V input laptop adapter for airplanes, fork lifts, boats and heavy equipment + + + + +
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+ | + | November 17, 2017 | ++ | + |
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+ NiCad Battery Charging Basics |
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+  NiCad/NiMH charger + catalog page |
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+ NiCad (NiCd, Nickel Cadmium) Battery Charging+ +Nickel Battery Charging Basics+NiCad and NiMH batteries are amongst the hardest + batteries to charge. Whereas with lithium ion and lead acid batteries you can + control overcharge by just setting a maximum charge voltage, the nickel based + batteries don't have a "float charge" voltage. So the charging is based on + forcing current through the battery. The voltage to do this is not fixed in + stone like it is for the other batteries. +This makes these cells and batteries especially + difficult to charge in parallel. This is because you can't be sure that each + cell or pack is the same impedance (or resistance), and so some will take more + current than others even when they are full. This means that you need to + use a separate charging circuit for each string in a parallel pack, or balance + the current in some other way, for example by using resistors of such a + resistance that it will dominate the current control. +The coulometric charging + efficiency of nickel cadmium is about 83% for a fast (C/1 to C/0.24) charge, + and 63% for a C/5 charge. This means that at C/1 you must put in 120 amp hours + in for every 100 amp hours you get out. The slower you charge the worse this + gets. At C/10 it is 55%, at C/20 it can get less than 50%. (These numbers are + just to give you an idea, battery manufacturers differ). +When the charge is complete + oxygen starts being generated at the nickel electrode. This oxygen diffuses + through the separator and reacts with the cadmium electrode to form cadmium + hydroxide. This causes a lowering of the cell voltage which can be used to + detect the end of charge. This so-called minus delta V/ delta t bump that is + indicative of end-of-charge is much less pronounced in NiMH than NiCad, and it + is very temperature dependent. Many of the chargers listed here use a + sophisticated algorithm that uses the -deltaV to accurately charge NiMH and + NiCad packs /NiCad-NiMH-Catalog.htm +As the battery reaches + end-of-charge oxygen starts to form at the electrodes, and be recombined at the + catalyst. This new chemical reaction creates heat, which can be easily measured + with a thermistor.. This is the safest way to detect end-of-charge during a + fast charge. This method is often used with multi-cell packs and the 20, 30, + and 40 cell pack chargers here use a thermistor + /NiCad-NiMH-Catalog.htm +Nickel cadmium battery + chargers should cut the charge off when the temperature exceeds the maximum + charging temperature, typically 45 degrees C for a controlled fast charge, and + 50 degrees C for an overnight or fast charge. +Overnight Battery Charging+The cheapest way to charge a nickel cadmium battery + is to charge at C/10 (10% of the rated capacity per hour) for 16 hours.. So a + 100 mAH battery would be charged at 10 mA for 16 hours. This method does not + require an end-of-charge sensor and ensures a full charge. Cells can be charged + at this rate no matter what the initial state of charge is. The minimum voltage + you need to get a full charge varies with temperature--at least 1.41 volts per + cell at 20 degrees C. The best charging practice is to use a timer to prevent + overcharging to continue past 16 hours. An example of this kind of charger is + shown at /Ni-6-200.htm . This charger uses a + microprocessor to report the state of charge via an LED as well as performing + the timing function. +Faster Charging+Some nickel cadmium cells are + designed to be "quick chargeable." This is just a timed charge at C/3 for 5 + hours, or C/5 for 8 hours. This is risky because the battery should be fully + discharged before charging. If the battery still has 90% of its capacity when + the timer starts you would have a good chance of venting the battery. One way + to ensure this doesn't happen is to have the charger automatically discharge + the battery to 1 volt per cell, then turn the charger on for 5 hours. The + advantage of this method is to eliminate any chance of battery memory. + PowerStream does not currently have such a charger, but the microprocessor + board used in the C/10 charger /NiMH-NiCad-solar-charge-controller.htm + could easily be modified to do the discharge. A power dissipating package would + be needed in order to dissipate the energy from a partially charged battery in + a reasonable amount of time. +Fastest Charging+If a temperature or voltage + monitor is used NiCad batteries can be charged at rates up to 1C (in other + words 100% of the battery capacity in amp-hours for 1.5 hours). The PowerStream + battery charge controller shown in /product3.htm + does this, as does the battery management board shown in /product5.htm. The termination can be done + with minus delta V, when the battery voltages drops -10 to -20 mV per cell. To + terminate the charge on temperature requires a temperature slope + measurement.This board also has the ability to sense voltage and + current for more sophisticated algorithms required for ultra-fast charging. + These algorithms require constant monitoring of the voltage, temperature, and + sometimes pressure, to actively determine the amount of current a battery can + take without damage. This is sometimes called a smart charge, or a controlled + fast charge. A cheaper version of the fast charger can be made by just + monitoring absolute temperature. The charge rate is set at C/2 until 45 degrees + C is reached, then switched over to a C/10 charge to complete the charge. This + is the most common NiCd fast charger of the 1960's through the 1980s because it + could be controlled by a simple bi-metallic thermostat switch mounted on the + battery. + Trickle Charging Nickel BatteriesIn a standby mode you + might want to keep a nickel cadmium battery topped up without damaging the + battery. This can be done safely at a current of between 0.05 C and .06 C. The + voltage required for this is dependent on temperature, so be sure to regulate + the current in the charger. + Custom design and manufacture of state-of-the-art + battery chargers, UPS, and power supplies for OEMs in a hurry! |
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