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Electronics => Beginners => Topic started by: THATguy on October 16, 2016, 10:25:02 am

Title: Energy harvesting?
Post by: THATguy on October 16, 2016, 10:25:02 am

I'm really into free energy! hehehe, okay seriously the low voltage kind.

Just a quick intro:
Electrical novice, though I have done part of an Electrical Engineering course at University.
I'm not good with Amp, Volt, Watts formulae, but can do them. Just haven't had the practice.
I know my capacitors, and can read a resistor, sort of understand the differences between PNP & NPN resistors.
I've done some soldering, can use a multimetre and am experimenting with making metal detecting coils.
I found this because of a youtube video on metal detector pointer tear down, or was it zener diodes?

My question:
I have some small kinetic generators - millivolts, and an energy harvesting antenna.
(or is even less than that).
Anyway, I want to save it up to 5v so I can add that to a battery.

Right, here is how I imagine doing that:
[correct me if I'm wrong]
Have a tiny little capacitor attached to each kinetic generator and the antenna.
Have a resistor on each of these capacitors, the voltages add up, then go into next stage.

Now do I repeat the capacitor resistor setup, or have a small transformer?
Eventually I want this to become 5v that feeds a battery. The battery will be small 3.7v lithium.

Just a disclaimer, I'm not expecting any instant charge up of the battery or anything "magical."
I realise this will take a long time to charge up my tiny battery.
I also know that perhaps I will need more than one transformer and they might be bulky components and inefficient at charge conversion (the small amount of charge I have may be lost).

Oh and for the sake of my schematic (pretend the circuit board is off, ie not draining the battery).

Title: Re: Energy harvesting?
Post by: Ammar on October 16, 2016, 11:26:42 am

First step is to determine how much power you expect each generator to create and then go from there. Are you expecting nanowatts? microwatts? milliwatts?

Let's use some round numbers to get an idea. Suppose your generator provides 10 microwatts and your battery is 5V. P = IV so that is 2 microamps. Suppose your battery has a 2 Amp-hours of capacity. At 2 microamps that would take a million hours to charge. You can work out how many years that is.

This does not take into account losses in your system and I am simplifying how a battery is charged a great deal, but I hope it gives you an idea. Dave has quite a few good videos on battery charging and energy harvesting that may be useful.

Title: Re: Energy harvesting?
Post by: THATguy on October 16, 2016, 12:08:15 pm

Thanks.
My battery is 220mAh

Yes I'll need to test my Antenna & Kinetic gernerators to see what they are outputing.
I hope my multimeter can measure it  :-[

Title: Re: Energy harvesting?
Post by: 2N3055 on October 16, 2016, 12:34:37 pm

http://www.linear.com/products/energy_harvesting (http://www.linear.com/products/energy_harvesting)

Take a look...
Read whitepapers, look for other manufacturers, it's all the rage now...

Title: Re: Energy harvesting?
Post by: THATguy on October 16, 2016, 12:57:40 pm

Thats awesome. I was considering using a peltier. And also piezio buttons, I have some around I'll test them next to my wifi router and other large powerboards & crazy washing machine. That will give me an idea for the capacitor/resistor ratings.

Title: Re: Energy harvesting?
Post by: Ammar on October 16, 2016, 09:17:31 pm

Quote from: THATguy on October 16, 2016, 12:08:15 pm

Thanks.
My battery is 220mAh

Yes I'll need to test my Antenna & Kinetic gernerators to see what they are outputing.
I hope my multimeter can measure it  :-[

Yes, you can by placing a load on the device. If you place a resistor across the terminals and measure the voltage, you can use V^2/R to get the power. This is one of many ways. A data sheet should tell you too.

Title: Re: Energy harvesting?
Post by: IanB on October 16, 2016, 09:22:13 pm

Also check out Shahriar's blog on the subject here:

http://thesignalpath.com/blogs/2013/01/03/tutorial-and-experiments-on-energy-harvesting-ics/ (http://thesignalpath.com/blogs/2013/01/03/tutorial-and-experiments-on-energy-harvesting-ics/)

Title: Re: Energy harvesting?
Post by: Audioguru on October 17, 2016, 02:58:04 am

First you must learn about the dangers of a Lithium battery. Charging with 5V will cause it to explode and burn with a very hot fire.
But luckily your parallel generators and antenna do not add their voltages because they must be in series to add. If the generators are AC (the antenna is AC) then their small voltages will cancel and the battery needs DC anyway. A transformer cannot be used with DC.

Title: Re: Energy harvesting?
Post by: THATguy on October 17, 2016, 06:48:35 am

That antenna will probably be a piezo button.
Oh that transformer, I probably meant step up converter - I'm not familiar with many of the terms.
Yeah, I probably only need 3.5v or something. Which is even better.

I'll let you guys know how I get on.