Boost 150mV to 1.5V

[Nursyukriah Idris]

If you can get (or even build) an alternator, you can use a transformer to increase the voltage.

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current (AC) right? But, in my project, the output from the wind turbine was Direct Current (DC).

How can I use an alternator?

 

[spec]

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current (AC) right? But, in my project, the output from the wind turbine was Direct Current (DC).

How can I use an alternator?

You would convert the alternating voltage from the alternator into a direct voltage. Then you would convert the direct voltage into any form you want within reason. For example if you got 2V RMS at 1A RMS from the alternator you could convert that into a stable 5V DC at a current of 400mA less conversion losses of about 20% which would mean you would end up with 5V with a current capability of 320mA.

spec

UPDATE: 2016_03_25 A generator produces electrical power from mechanical power. There are two types of generators, AC and DC. The former is known as an alternator and the later is known as a dynamo. You could use either depending on what output you want.

 

[Nursyukriah Idris]

You would convert the alternating voltage from the alternator into a direct voltage. Then you would convert the direct voltage into any form you want within reason. For example if you got 2V RMS at 1A RMS from the alternator you could convert that into a stable 5V DC at a current of 400mA less conversion losses of about 20% which would mean you would end up with 5V with a current capability of 320mA.

Thank you for your explanation. I will try..

 

[ChrisP58]

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current (AC) right? But, in my project, the output from the wind turbine was Direct Current (DC).

How can I use an alternator?

The alternator would have to replace the DC generator that you now have. The reason for an AC output is that it can drive a transformer to step up the voltage. That would work at any input voltage level.

You could use an inverter to drive the transformer from DC, but that would have the same limitation on input voltage that a DC converter would have. And it would not get around the problem of you needing more power out, than you have available to put in.

 

[Nursyukriah Idris]

Do you have control over the air speed hitting the turbine? Is the turbine separate from the generator? Can you use a gearing mechanism to increase the speed of the generator shaft?

Sorry for late reply..

Actually, I didn't use any control over the air speed hitting the turbine.

I'm use a DC motor not a generator. The DC motor was connected to the shaft of the blade rotor.

 

[BobW]

I haven't read all of the posts here, but it is possible to build a boost converter that takes an input in the millivolt range. Here is an example that works down to 60mV:
https://www.aldinc.com/pdf/EH4200Brochure.pdf
I seem to recall that ALD also has a technote that describes the complete circuit, but I didn't go looking for it.

 

[audioguru]

We explained that you cannot boost 0.15V/30mA to 1.5V/300mA to light an incandescent light bulb. If you boost the voltage 10 times then your current will decrease 10 times to only 3mA minus losses, then what will you use the 1.5V/3mA for?

 

[JonSea]

I think you need to drop back and make some aerodynamic calculations on the turbine. Given the stated airflow, how much power can you theoretically get from the turbine?

You absolutely can not exceed this power output, but in reality, it's worse than that.

You need to consider the efficiency of converting this mechanical energy to electrical energy. This is where you evaluate permanent-magnet motors verses a purpose-built generator verses an alternator. The output power from this conversion will be less than the mechanical power generated by the turbine. This is called efficiency and it CAN NOT exceed a factor of 1.

Only after this point can you consider the conversion of electrical energy to a useful form. Again, you need to consider the efficiency of this step, and again, the efficiency WILL BE LESS THAN 100%. There are losses in each conversion, and it's not possible to get more power out than power in. All you can do is maximize the efficiency at each step of the conversion process.

I think I just outlined your project for you...at least what it needs to be even if it's not what you want it to be.

 

[spec]

I haven't read all of the posts here, but it is possible to build a boost converter that takes an input in the millivolt range. Here is an example that works down to 60mV:
https://www.aldinc.com/pdf/EH4200Brochure.pdf
I seem to recall that ALD also has a technote that describes the complete circuit, but I didn't go looking for it.

Hi Bob,
Aside from the requirements of this application and the impossibility of having more power out than in, those low voltage/current inverters are very interesting. As a matter of interest I have been trying to figure ways of using a very low voltage. The only thing I came up with was a nano motor driving a nano alternator.
spec

 

[audioguru]

I think an "energy harvesting circuit" can be used for charging a capacitor for weeks from a feeble source then use the charge on the capacitor to blink a dim LED one time.

 

[JonSea]

I think we've missed a key point here. If a permanent-magnet motor is rotating at its rated speed, the output voltage should be nearly its rated voltage (i.e., a motor rated at 6000 rpm with a 3 volt supply will generate nearly 3 volts when spun at 6000 rpm).

Since the motor/generator is only producing 0.15v, it must be running far below its rated speed. I suppose the motor is being driven directly by the turbine rotor at slow speed, so the output voltage is low.

The turbine may be capable of delivering much more power than is being delivered right now, but not at an optimal speed for the motor.

This gets back to those aerodynamic calculations. How much power can the turbine deliver at what speed ? How efficiently can the motor convert energy at that speed? Some kind of a speed increaser (think pulleys and a rubber band) may save the day.

A quick&dirty test would be to measure the speed of the turbine open circuit and again with the motor leads shorted together. If the turbine speed is virtually identical, the motor isn't generating anywhere near the power the turbine is capable of producing.

I know. Damned engineers take the fun out of everything - always wanting calculations and math.

 

[JimB]

JonSea
Well done, I was wondering how long it would be before someone would realise that.
JimB

 

[JonSea]

I wasn't quite awake when I wrote my first post

 

[JonSea]

This thread actually illustrates a common problem. Both the original poster and almost everyone who has replied fell into this trap - starting with a solution before the problem is understood and defined.

The first problem is to determine how much power the turbine can produce at what speed. Only then should the conversion from mechanical to electrical energy be considered. What devices are available and at what speed are they most efficient. With a micro-power turbine, efficiency is the #1 priority.

Everyone who replied fell into the trap of providing a solution without unserstanding the problem. Why is the motor-turned-generator only putting out 0.15 volts (or is it a tenth of that?)? Have you ever seen a DC motor designed to run at 0.15 volts? That should have been a big red flag addressed before any soluion or lack of solution was offered.

This is a common problem I get into with my clients. "I bought these micro-controller boards and started laying out a circuit to do this (totally undefined thing where the goals aren't even defined yet). I've worn out a few pairs of shoes dragging my feet in the sand on stuff like that!

 

[audioguru]

Replace the generator or replace the load?
He took the very low power wind turbine designed by somebody else and decided to "boost" its output power 100 times without understanding that energy cannot be increased.
Knowing that the output from the wind turbine generator was very low power he selected a much higher power incandescent light bulb as its load instead of selecting something that uses the low power properly.

 

[JonSea]

AudioGuru, you've totally missed the point.

The motor output voltage is very low because it's spinning below its design speed.

From the given information, we don't have any clue how much power this micro-turbine can produce. We do know the motor is turning too slowly to produce useful power, but we don't know if it's using the availabe turbine power as efficently as possible.

It's likely that if a speed increaser is used, the motor will make more effective use of the generator's output power.

 

[JimB]

He took the very low power wind turbine designed by somebody else

Actually, if you look at the link provided earlier, you will see that "he" is actually a "she".
The word BINTI gives the game away. If my knowledge of Malay is up to scratch it means "daughter of", whereas BIN means "son of".

JimB

 

[audioguru]

I would notice the girl if she walked past me but I did not notice her avatar.
It seems she has no clue about power or boosting power. She selected a micro wind turbine, designed a converter with an output of 1.25V and 250mA without noticing how much input current it needed. Then she selected a 1/2W load.

 

[JonSea]

Admittedly, I did not look at the PDF.

The project is flawed starting with the low output voltage of the generator. The turbine speed is too slow to turn the motor at a high enough speed to produce useful power.

If this project is to be useful, the speed the motor is turning at has to be increased. That is a given no matter how much you want to argue about it.

Is the turbine capable of producing more output power? At this point we know nothing about this. I described a simple measurement to take to get a feel for this already. Measure the turbine speed with no load. Then measure the turbine speed with the motor shorted - the max possible load under the present arrangement. If the speed doesn't change much, the turbine isn't delivering much power to the motor because of how slowly it's turning.

Sure, this may be outside the scope of the project but so is developing an over-unity solution!

 

[audioguru]

Her next project might be a vehicle powered by an electric motor fed "juice" from a computer fan in the airflow. Not enough power? Then drive into the wind or go faster.