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  • joule thief and energy use

    I have read this somewhere:

    A single cell (such as an li-ion) driven by a Joule thief may contain more usable energy than a similar sized multiple cell battery

    Recharging: A single rechargeable cell with output boosted by a Joule thief will be cheaper than multiple rechargeables

    My question is if i connect a dc led to a single cell without boosting will another led boosted with a joule thief have the same burning duration. In other words: i connect a low voltage 5v 5watt led to my powerbank it last lets say 3 hours. Now with a joulethief i connect a 220v ac 5 watt ledbulb. Will it also burn 3 hours?

  • #2
    The terms that you use like "more usable energy" and "output boosted" are somewhat misleading.
    The Joule Thief is a pulsing circuit, much like a PWM Boost Inverter.
    Yes, the output voltage can be higher than the input voltage - ain't no big deal.
    Yes, you can use a JT to drain a little more energy from a non-rechargeable highly drained ( ie "dead" ) battery - again, ain't no big deal.

    But when it comes to rechargeable batteries, no a Joule Thief is not going to make any difference.

    5 Watts continuous consumed by a Low Voltage 5 Volt DC LED vs pulsed 5 Watts (average) consumed by a 220 Volt AC LED, is still 5 Watts.
    So both devices will consume 15 Watt-Hours ( = 5 Watts x 3 Hours ) of energy.

    Also, draining a lithium-ion battery below its Low Cut-off Voltage may do permanent damage to the cell.

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    • #3
      Thank you very much for your clear reply.
      I have one more question. An inverter uses a certain amps or not? How about a joule thief 3-5v to 220v max 9watt?

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      • #4
        Originally posted by Gerard Fivewin View Post
        An inverter uses a certain amps or not?
        I am sorry, I do not understand your question.

        I will reply with this ...
        Watts In = Watts Out

        Therefore,
        Volts-In x Amps-In = Volts-Out x Amps-Out

        The Volts-In and the Amps-In can be, and usually are, very different than the Volts-Out and Amps-Out.


        Originally posted by Gerard Fivewin View Post
        How about a joule thief 3-5v to 220v max 9watt?
        same as above

        The Volts-In will be low (5V) and the Amps-In will be high
        while the Volts-Out will be high ( 220V) and the Amps-Out will be low

        The rule remains "Watts In = Watts Out".
        Last edited by NEOH; 10-09-2017, 01:04 PM.

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        • #5
          A solar system with an inverter (12v to 220v) i always read that the use of an inverter draws also some wattage from the battery. For example, if your total use is 1Kwh per day add 5-10% for the calaculation of the total use cause of the use of the inverter. Ok, there is usually a little fan built-in and some indicators led which use some electricity but thats not so much. Does the boosting uses certain wattage?
          Last edited by Gerard Fivewin; 10-09-2017, 09:49 PM.

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          • #6
            To be more specific. Here is a setup of a joule thief. In my area there is frequent power outages. Enabling me to use excisting lamps i want to use this. You said watts-in=watts-out. So, the joulef thief does not "steel" a little bit watt if i dont use indicators led and/or cooling fan.
            Attached Files

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            • #7
              To be even more accurate ...
              Watts-Out is always less than Watts-In, due to any system losses.
              That is the law on planet earth.

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              • #8
                I appreciate your clear replies. Thank you very much.

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                • #9
                  Just want to thank again for the replies. Ive made another one and integrate all in this lamp so i can bring it and hang it up anywhere i want. Yesterday evening ive tested with 2 li-ions and am satisfied with the result. Turn it on in the living room for 3 hours and 20 minutes and then aprox. 30 minutes in the bedroom, still going strong. Thats in fact was my goal to use one (mobile) 220v lamp for different spaces without grid connection. The li-ions will be charged by a solar panel.
                  Attached Files

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                  • #10
                    Yes, the output voltage can be higher than the input voltage - ain't no big deal.

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                    • #11
                      It can be a big deal hehehe because batteries, rechargeable or not are easy to get but in some areas dc lamps are hard to find.

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                      • #12
                        5 watt 220vac lamp's light output is inferior to 5 watt LED light output. Light output is measured by lumins not by watts.

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                        • #13
                          Originally posted by Gerard Fivewin View Post
                          Just want to thank again for the replies. Ive made another one and integrate all in this lamp so i can bring it and hang it up anywhere i want. Yesterday evening ive tested with 2 li-ions and am satisfied with the result. Turn it on in the living room for 3 hours and 20 minutes and then aprox. 30 minutes in the bedroom, still going strong. Thats in fact was my goal to use one (mobile) 220v lamp for different spaces without grid connection. The li-ions will be charged by a solar panel.
                          What a bunch of mumbo jumbo that means nothing. Light efficiency is measured Lumens/Watt.

                          MSEE, PE

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                          • #14
                            Originally posted by neweclipse View Post
                            5 watt 220vac lamp's light output is inferior to 5 watt LED light output.
                            Hogwash. 5 watts = 5 watts all day long.

                            Light output is measured Lumen/watt. If a light emits 100 l/watt then a 5 watt lamp emits 500 lumens. Does not make a bit of difference what the voltage is or light source is. A watt is a watt and is the measure of heat power. We have the bling leading the blind.

                            MSEE, PE

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                            • #15
                              Good news then. Perhaps i can install some 5 watts 5volt led bulbs using this kind of powerbanks which i will charge with solar panels using stepdown modules and place it as close as possible to the ledbulb. Cheap.

                              Hope i can find 5volt 5watt leds with acceptable lumens.
                              Attached Files

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