Battery Chargers » nicad charger

NiCd Battery Charger with Reverse Polarity Protection

eBatteryChargers.com — Wed, 16 Sep 2009 18:47:12 +0000

This NiCd battery Charger can charge up to 7 NiCd batteries connected in series. This number can be increased if the power supply is increased with 1.65V for each supplementary battery. If T2 is mounted on a proper heatsink, the input voltage can be increased at a maximum of 25V.

Unlike most of comercial NiCd chargers available on the market, this charger has a reverse polarity protection. Another great quality is that it does not discharge the battery if the charger is disconnected from the power supply.

Usually , NiCd batteries must be charged in 14 hours at a charging current equal with a tenth percent from battery capacity. For example, a 500 mAh is charged at 50 mA for 14 hours. If the charging current is too high this will damage the battery.

The level of charging current is controlled with P1 between 0 mA – 1000 mA. T1 is opened when the NiCd battery is connected with the right polarity or if the output terminals are empty. T2 must be mounted on a heatsink.

If you cannot obtain a BD679, then replace it with any NPN medium power Darlington having the output parameters at 30V and 2A. By lowering R3 value the maximum output current can be increased up to 1A.

NiCd Battery Charger Circuit Diagram

NiCd Charger PCB Layout

NiCd Charger for 9V Battery

eBatteryChargers.com — Tue, 15 Sep 2009 09:47:48 +0000

This automatic NiCd charger for 9V NiCd batteries is using 555 timer properties and is very easy to build. Why is an automatic 9 volts NiCd battery charger? Because you can leave the battery for charging as much as you like: it will be always completely charged and ready for use when is needed. It wont be overcharged and it will not discharge.

With the values presented in the circuit diagram, the battery charger NiCd circuit is suitable for 6V and 9V batteries. 9 volt types with 6 and 7 cells are charging with 20mA; P1 must be adjusted so that the NiCd charger disconnects after 14 hours. Window inferior level is set at 1V below this value with P2.

5V battery type with 4 or 5 cells are charged at 55mA. Again, with P1 adjust the NiCd charger circuit so it disconnects after 14 hours. Window inferior level must be set at 0.8V below this value.

Automatic 9V Battery NiCd Charger diagram

Automatic NiCad battery charger

eBatteryChargers.com — Sat, 14 Mar 2009 13:54:39 +0000

This circuit is an alternative to expensive battery chargers, the trick to lower the cost is to buy a cheap battery charger and expand it with an automatic charge breaker circuit such as the one presented here.
The heart of this automatic battery charger is the comparator which compares the NiCad battery’s voltage with a referance voltage. When the NiCad battery’s voltage exceeds a certain presettable maximum voltage level, the circuit breaks the charging via the relay and when the NiCad battery’s voltage sinks below the preset minimum level, the circuit closes the relay and the charging resumes.

When the battery voltage level rises, the voltage at the non-inverting input will also rise and by certain level (set with P1) the non-inverting input has a higher level than the inverting input.
The comparator is designed to have a hysteresis that prevents the circuit from “oscillating” (constantly switching on or off the relay) that could be cause by slight changes ti the battery voltage. This hysteresis is set with P2 which also sets the minimum battery voltage level at which the charging resumes.

Automatic battery charger circuit calibration

The best way to calibrate the circuit is to use a variable voltage, regulated power supply. This is connected to the circuit in the place of the NiCad battery. Set the regulated power supply to 14.5 volts and adjust the P1 to a point where the relay snaps open. Newt, set the regulated power supply to 12.4 volts and adjust P2 to a point the relay closes back. You might need to repeat this procedure severals time since P1 and P2 have an effect on each other.

Automatic battery charger circuit diagram

12V NiCd battery charger

eBatteryChargers.com — Sat, 31 Jan 2009 12:46:49 +0000

This NiCad baterry charger regulator circuit can charge 6 volts as well as 12 volts NiCd batteries. It uses a transformer which can deliver 4 to 5 A current between 12.6 and 15 V. Ordinary chargers select the charging voltage through a swith but the circuit featured here uses an automatic current regulator.

The charging current is automatically regulated to 4.2 amperes. Once the charging current reaches 4A, the voltage drop at R1 will be 600 mV. In this case the transistor T1 will conduct and supplies current to T2.

NiCd battery charger circuit schematic

Transistor T2 in turn, shorts the base of T3 to ground thereby reducing or totally cutting off the base bias current of T4. The voltage difference between the collector voltage of T4 and the actual charging voltage of the NiCd battery is dissipated by T4. The power dissipation of T4 is therefore the product of the voltage difference and the charging current. In charging 6 volt batteries, the power dissipation can reach up to 40 watts, therefore you must mount T4 with a cooler.
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Printed circuit layout for battery charger

Parts placement for NiCd battery charger

NiCd portable battery charger

eBatteryChargers.com — Sat, 31 Jan 2009 12:20:02 +0000

The portable battery charger, car adapter and charger has been designed to provide an opportunity to load NiCd batteries even in the outdoors from a 12 V battery of a vehicle. When the circuit is connected to the vehicle battery, D2 lights only if NiCd battery was connected with the correct polarity. Since even on the discarded batteries we have a certain tension, T1 opens and D2 flashes.

As the NiCad battery starts to charge, thru R and D6, lights D6. In the meantime C4 is slowly loading thru P1 and R4. The value of these components determines IC2 monostable period and thus loading time of the NiCd battery. For the components values shown in the schematic, this period can be adjusted with P1 between 26 and 33 minutes. The charghing can be interrupted with the reset button S2.
The loading current thru the NiCd battery is determined by the value of R, which can be calculated with the formula: R = (12 – (0.7 +1.3 x nr of elements) / Ic) Ω where Ic represents current loading – in this case because the duration chosen for loading it is twice the face value of battery capacity. Resistance R must dissipate a power – Ic² xR watt.
Finally do not forget to make sure that your NiCd battery allows rapid loading and be careful when making this operation will not exceed a half hour!
This portable battery charger has not been tested.