mymahdi digital mp3 player wont recharge why

MYMAHDI DIGITAL MP3 PLAYER WONT RECHARGE WHY FULL

MYMAHDI DIGITAL MP3 PLAYER WONT RECHARGE WHY FULL

The cells are full when the voltage peaks, and the charger shuts off shortly thereafter.Īs the temperature rises above 33☌, Vtmp will become less than Vref, and the open-collector output of Z1a will float high. This will fully charge a pair of 2500mAh cells in just over 5 hours.īattery voltage versus time. Q1 has a beta of about 90, so about 470mA will flow through into the two AA cells being charged. While charging, the output is pulled low by an internal transistor, drawing about 5.2mA of current through Q1 and R5. The output (pin 1) can be in one of two states, floating or low. The heart of this charger is Z1a, one half of an LM393 dual voltage comparator. Power Source: Desktop, Laptop, or Hub USB port.Charge Termination Method: Battery Temperature (33☌).This charger has the following specifications: The charger incorporates an automatic charge cut-off circuit based on cell temperature, and the cells can be left in the charger indefinitely after cut-off. It will charge 700mAh NiCds in about 1.5 hours, 1500mAh NiMHs in about 3.5 hours, and 2500mAh NiMHs in about 5.5 hours.

The charger in this project is designed to charge two AA NiMH or NiCd cells of any capacity (as long as they are the same) at about 470mA. Different ones can be found here and here, but these take 10 to 12 hours to charge 2500mAh cells. I found a 2/4 cell charger that can be powered by a USB port, auto adapter, or wall wart, but it is as large as the wall charger I’m trying to replace. The distributor calls it an “overnight charger”, but at 100mA, a 2500mA cell would take about 40 hours to charge (40 instead of 25 due to the inefficiencies of charging at low currents). There is a two cell USB powered AA charger available, sold under a variety of names, but it charges at a very low 100mA rate. Unfortunately, the cell capacity is very low (most NiMH AA cells are 2500mAh these days), and each cell requires its own port. The USBCell is a 1300mAh AA NiMH cell with a removable top that allows it to be plugged directly into a USB port. There are commercially available USB AA charging solutions available, but they each have some drawbacks: This makes the USB port a convenient source of power for devices such as this charger. The USB standard specifies that a device may not use more than 100mA until it has negotiated the right to use 500mA, but apparently no USB ports enforce that requirement. (By the way, if you want to lighten your laptop load, take a look at the MoGo Mouse.)Īny USB port can supply 5V at up to 500mA. This project, which can charge a pair of AA Nickel Metal Hydride (NiMH) or Nickel Cadmium (NiCd) cells using a laptop’s USB port for power, arose to address part of that problem. I’m always complaining about all the chargers and wall warts I need to carry with me when going on a trip.

Mymahdi digital mp3 player wont recharge why