It’s been some months, i thought of buying a 9v rechargeable battery for my wireless audio equipments. But from the past experience which i got from the AA rechargable batteries supported by useless chargers made me to do some research which took some months to take a decision.
Upon arriving a closer point of purchase, the decision was to buy a simple and cheap charger controlled by a MC/ MP. with some reviews from here and there from the internet and audio forums, the product which i bought is EBL 840 with 2 pieces of 600mAh battery for $36 inclusive of International shipping to India.
Amazon link for buying EBL 840
Input: 100-240V AC 50/60Hz 120mA
Output: 1.2V DC 200mA;3.6V DC 150mA;9V DC 100mA
No Load Power Consumption: 1W MAX
Full Load power consumption: 5W MAX
Battery Charge Rate: >80%
6F22(9v) li-ion Battery
6F22(9v) Ni-MH/Ni-Cd Battery
After receiving the product, the first impression is the packaging which was good enough to withstand vibration and sudden drops. Preliminary checks are done with voltage readings on both the 6F22 batteries and the charger. The first-worst experience is the one, Needless to say, the 2 page mini user guide which is an absolute crap of no matching information.
Alright, since i have paid more than INR-2k for this product the internal guy inside me was very curious to see the internal circuit and components used. Housing was good with US standard attached power plug at the rear top area. The whole device was secured with just 2 screws which made the disassembly job very easy.
Initial catch was the markings in the PCB which states that the original manufacturer is Beston (BST), a china manufacturer who has some good reputation in European countries among their products. The same circuit model (BST-C818) is also listed on their website. My device is tagged as design version(v1) relesed in the late year of 2014.
The first component which catch’d my eye upon removing the top housing is the transformer. Circuit design is very simple with not much safety components. AC line is directly connected to the SMD Bridge Rectifier via 10 ohms 1/2 watt resistor in series and there is no pre line filter’s. Output from the BD is filtered by a 400v E-Cap and sent to switching transistor with some mega ohms resistor in parallel connected with a zener and 104 ceramic capacitor in between.As asusal in all SMPS circuits, the switched voltage is feeded to mini transformer which isolates the High-low voltage area.
EBL 840 – internal front view
Output stage of the transformer is again stabilized with some resistors and zener’s with a single SMD capacitor. Single comparator for each battery terminal is connected with the LED indicators. But these comparators also sense’s the inflow current to batteries which is under charge. There is a SMD which has 5H5 named on it which is a step down constant DC-DC 600ma IC that controls the entire charging process. It also has an feedback pin which controls the output when the battery is fully charged.
EBL 840 – internal rear view
Overall, this charger is a compact one with a variable voltage from 100v-240v which charges 2 pieces of 6F22 9v li-on/ Ni-MH/ Ni-Cd batteries at a time in parallel. Charging status is identified by the Red color LED indicators. Downside is, the circuit will not withstand sudden spikes and will be noisy for sure.