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Step down transformer

Discussion in 'General Electronics Discussion' started by BGT, Nov 27, 2020.

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  1. BGT


    Oct 22, 2020
    I recently bought one of these
    ebay link
    to power some solar garden lights (not enough daylight this far north) I removed the recharable 1.2v battery and connected them to this power supply set to 1.25v instead. A month on it is working perfectly. I was now going to connect a few more and have a couple of questions.

    Should I be leaving the batteries in so as they work as some sort of buffer ?

    During the day when the sun is out the solar panels generate up to about 3v. what effect does this have flowing back to the 'step down transformer'? I can't disconnect the solar cell as this switches the lights on and off for daylight/night)

    I know it has worked fine with just one set connected, but now I am going to have 4 sets and wondered if something could go wrong.
  2. Audioguru


    Sep 24, 2016
    The solar garden lights are designed to be charged from a low current solar panel. Remove the batteries to avoid the external unlimited current from exploding them then connect the voltage converter set to 1.25V directly to the battery contacts on the circuit with the correct polarity.
    The circuit will have a diode to prevent back current in the solar panel when it is dark.

    You have a voltage converter, not a transformer. What DC voltage do you feed the voltage converter?
  3. Nanren888


    Nov 8, 2015
    I presume the circuit will be similar to that shown as the figure after "Detecting Darkness" of
    Yes, the solar cell during the day will attempt to charge the downconverter.
    Not my area, sorry. Someone else may be able to comment on this.
    The down-converter will presumably see this as overvoltage and scale back it's own efferts to provide the output voltage. Whether this looks like excessive load to the solar cell and any effect on the solar cell, sorry, I don't know.
    One answer on this page https://electronics.stackexchange.c...ll not damage,short circuited into an ammeter.
    suggests that solar cells don't mind being shorted.
  4. Audioguru


    Sep 24, 2016
    The solar panel on a cheap solar garden light is a weak little thing. A dead battery (after a week of clouds) shorts it for a while as it slowly charges the battery.
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