# Boost 150mV to 1.5V

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Nursyukriah Idris, Mar 24, 2016.

1. ### specWell-Known MemberMost Helpful Member

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Hi Nursyukriah,

You have asked to light an incandescent lamp with a 150mV 30mA = 4.5mW power source. While all the information posted here about different generators etc would no doubt improve the electrical power output of the wind turbine, it seems that it is not your job to change the existing design of turbine and generator.

The trouble is that an incandescent lamp to operate at such a low voltage and power is not available, so would any of these options suit you:
(1) Moving coil meter to indicate power.
(2) Light emitting diode (LED) which illuminates to indicate power output.

The moving coil meter would be by far the simplest to implement and could give a reasonable indication of power output over quite a wide range. It is thus, the approach that I would recommend.

The LED approach would require an energy harvesting boost switching regulator using complex circuit techniques in view of the very low voltage. The boost regulator would then generate a constant current to power a LED. The math looks like this.

Power input = 4.5mW.
Assume a converter efficiency of 65% this gives an output power of , 0.65* 4.5mW= 2.93mW
The forward voltage of a red LED is 1.2V, so the current through the LED would be 2.93mW/1.2V = 2.44mA which would be sufficient to illuminate a small high efficiency red LED.

Would you like to give this some thought.

spec

Last edited: Mar 28, 2016
2. ### Nursyukriah IdrisNew Member

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Yes. I know, it is not my job to change the existing design of turbine and generator.

But, my lecturer give a task to me to use a Boost Converter to step up the output voltage of the Existing Micro - Savonius Vertical Axis Wind Turbine (VAWT) and then light up the considered load (Miniature Light Bulb - 1.5 V and 0.3 A).

I've made some research that Boost Converter doesn't suitable to use to step up a very low voltage. That's why I made a decision to replace my previous student's DC motor to DC generator.

3. ### Nursyukriah IdrisNew Member

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It is these options for the considered load?

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5. ### specWell-Known MemberMost Helpful Member

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With the meter option you would do a simple calculation and put resistors in series and parallel with the meter to present the required load to the generator (motor).

With the LED approach no, the inverter would simply take a constant power as would your original bulb approach.

spec

Last edited: Mar 28, 2016
6. ### specWell-Known MemberMost Helpful Member

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Last edited: Mar 28, 2016
7. ### JonSeaWell-Known Member

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Chapter 3 of the report shows the motor. It's a common permanent magnet DC toy motor drawing 200mA at 3 volts. Radio Shack has similar motors for a few bucks. The rated speed of the motor is not given but the speed of this type of motor is typically 5000 - 6000 rpm.

Chapter 5 of the report lists the test results, including the motor rotational speed ranging from 270 - 650 rpm.

A quick plot of speed vs. output voltage shows the expected linear relationship. Output voltage is directly proportional to speed.

If the motor speed is increased to the normal operational range, a useful voltage in the range of 1 - 3 volts will be produced. How much current (and power) is available depends on the power the turbine can produce. Increasing the motor speed with pulleys and a rubber-band belt gets the voltage up to the level where lighting an LED might be possible.

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8. ### specWell-Known MemberMost Helpful Member

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9. ### Nigel GoodwinSuper ModeratorMost Helpful Member

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Of course he could, his problem is in not spinning the motor at any kind of reasonable speed - small DC motors work pretty well as generators, but you have to make them rotate

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10. ### tcmtechWell-Known MemberMost Helpful Member

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80+ posts and just now people are figuring out that the motor used was a poor choice (high RPM low voltage rather than low RPM high voltage unit) for a generator for the experiment?

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11. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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I'll "comment too". A permanent magnet DC brushed motor will work as a generator.

When generating a voltage at "No load", voltage will be proportional to RPM. That application is called a tachometer.

Some "speed controllers" use the following transfer function: V = Vm-Im*Rm where Vm is Vmotor, Im is I motor and Rm is the resistance of the motor. Vm you really can't measure directly. What is does say, is that you loose voltage as you load it.

The incandescent lamp has yet another problem. The cold resistance could be 10x less than the hot resistance, so you need more VA to get it lit initially. A LED would be better. It normalizes your power requirements.

As a motor, torque is proportional to current. Voltage is only proportional speed if non-loaded.

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12. ### JonSeaWell-Known Member

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No, actually I said this in my second post in the thread. It's been lost in a sea of...let's go with...far-fetched ideas.

13. ### audioguruWell-Known MemberMost Helpful Member

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The little DC motor with brushes is running at an RPM that is much too low. It needs gears or pulleys to make it spin faster but then the windmill might be too small to drive it.
Maybe the windmill needs to be held out the window of a car that is driving very fast?

14. ### tcmtechWell-Known MemberMost Helpful Member

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Yes you did but nobody ever reads anything anyone says that has any common or rational sense behind it anyway.

At any point in time there are around half a Billion people online yet for the most part all of us are just typing to ourselves.

15. ### JonSeaWell-Known Member

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Sadly true. My experience is, the more replies to a post, the less information there is.

16. ### audioguruWell-Known MemberMost Helpful Member

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The boats on the huge lake near me use a propeller or something like a fan directly connected to a generator and they spin at a high RPM like crazy. They know that when there is no wind (rarely) then there is no electricity to charge their battery.
But in Malaysia there is almost no wind, they are using a low RPM small windmill and a high RPM, low voltage motor.

17. ### JonSeaWell-Known Member

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I pity the poor kid trying to sort the tiny bit of useful information from the noise in this thread.

[Note to moderators: delete this if you must, but consident my point. Ban me if you wish.]

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18. ### audioguruWell-Known MemberMost Helpful Member

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Isn't it sunny in Malaysia? Then wouldn't a solar panel be appropriate for producing electricity?

19. ### ChrisP58Well-Known Member

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Does a university project have to be for local use only? A few years ago, my company supplied materials and technology to support a local university for a project to be deployed in Ghana.

20. ### audioguruWell-Known MemberMost Helpful Member

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I was thinking the same. Use a continuously variable speed belt drive on the generator (like some cars have) and set it for your country's wind speed.

21. ### tcmtechWell-Known MemberMost Helpful Member

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I take it you have not looked at the linked reports on the unit. It's maybe 4 - 5 inches in diameter and 10 - 12 inches high plus the wind source is the exhaust fan of the outdoor half of an air conditioner unit.

Neat design but painfully obvious that no math relating to matching any of the components to each other or the working environment was done. ~4 milliwatts of output from a central air conditioner condenser fan that is likely 200 - 300 watts in itself.

My off my head numbers say that given the rotor size and driving source of air that at least a 1 - 2 watts output should be expected and maybe double that with the air concentrator device in place . 4 mW?