Recharging Ni-MH batteries from the sun

Greetings, radio amateurs- DIY !
 Recharging Ni-MH batteries from the sun Topic alternative energy sources among those who like to do something do it yourself popular is not easy – after all, it has a lot of practical benefits. The simplest and at the same time actual example is charging batteries from light using solar panels. Every year solar panels are becoming more and more available, it is now easy to buy a copy with a small area. Options with a larger area are much more expensive, and therefore generate much more power – they are quite often used in sunny countries for autonomous power supply of entire houses. To recharge small-capacity batteries, which will be discussed in the article, a panel with dimensions from 4×4 cm to 10×10 cm will be enough, with an increase in size, it will be possible to accelerate the charging process, or charge several batteries at the same time, but the size of the structure will also increase. As rechargeable batteries can be used types Ni-MH or Ni-Cd AA or AAA, despite the appearance of lithium-ion batteries, these types are still used. In this case, they have the advantage of being easy to charge and resistant to over-discharge, thus making it easy to use in combination with solar panels. The following scheme is used to connect batteries:
Recharging Ni-MH batteries from the sun The solar panel itself is shown on the left, the voltage given to it in the light should be about 3V. Please note that the panel has polarity – it is important not to mix it up, otherwise the battery will not charge. As you know, the voltage at the output of the panel directly depends on the luminous flux that hits its surface, thus, at dusk, the voltage at the output can drop to zero and the voltage on the battery will become more than on the panel. In order to prevent the battery from starting to give the accumulated charge back to the panel, the VD1 diode is present in the circuit, it passes the charging current only in one direction. To reduce losses, either germanium diodes, for example, D311, or Schottky diodes, for example, BAT42, can be used here. The diode used must be rated for a voltage of at least 20 volts and a current of 100 mA. On the contrary, when the sun is bright, the voltage on the panel rises significantly, and can exceed the maximum battery voltage. In order to limit the voltage on the circuit, the VD2 LED is present, firstly, by its glow, it indicates that the solar panel is working, and secondly, it acts as a zener diode, preventing the voltage from increasing above a certain threshold. This threshold depends on the color of the LED – LEDs of different colors have different voltage drops. In this case, a value of about 1.6V would be ideal, this corresponds to a red or infrared LED. A rechargeable battery is connected in parallel to the LED; polarity must be observed when connecting. The charge current will depend only on the power of the solar panel and the luminous flux from the sun, when using large panels it makes sense to connect the same batteries in parallel and charge at the same time, in this case, you should take the VD1 diode with a higher current.
 Recharging Ni-MH batteries from the sun The whole structure can be mounted on a small plywood base; the solar panel itself and the battery holder are fixed next to it. The author uses a solar panel 4×4 cm in size, it provides a very small charging current and the time to fully charge the battery is quite long. But even in this case, the design can be used in practice, for example, to power some very low-power load that consumes current continuously. For example, it can be any temperature, light, humidity, etc. sensor used as part of an automated system. Another application is to power devices that turn on for just a few seconds a day, for example, for a video intercom in a country house. The video intercom circuit, powered by a solar panel battery, will only draw current when someone calls the intercom, so the rest of the time during the day the solar panel will recharge the battery, keeping it charged. Happy build!


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