Boost 150mV to 1.5V

spec said:

The biggest shock I had was a highly respected and long time analogue designer, complete with pipe and patches on his jacket elbows (sure signs of intellectual gravity and integrity in the UK at the time). I did a design review on his stuff for a particular system. He was trying to sum two analogue voltages by joining them with two resistors and feeding the junction into the non inverting input of a parallel feedback opamp. He also thought it was OK when the flaw was pointed out. Then he didn't know about long tailed pairs either.

Another engineer was asked to design a 10Mhz Xtal oscillator. He kept complaining that he could not get the circuit to work. He had copied a low frequency Xtal oscillator circuit from a 4000 CMOS data book. Also the leads on the Xtal were around 5 inches long.

Another engineer built a switch mode buck PSU with the first capacitor he found laying around the lab. He kept complaining that the data sheet for the chip he was using was a lie, because he could only get 55% efficiency. When I told him that he needed a low ESR capacitor and that the equivalent circuit of a capacitor is quite complex he would not accept it and more or less called me an idiot.

spec

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The cap thing is funny. We had a 1 MHz low power switcher chip and we got dozens of calls from people who kept using Tantalum caps with them (despite data sheet warnings to only use ceramic). Amazingly enough, they were functional with the tant caps despite the fact the resonant frequency was an order of magnitude lower than the switch frequency, they just didn't put out much load current.

I had to knock heads with our marketing guys when I published an article explaining some of the facts about capacitors, like how Z5U and Y5F ceramics should be thrown directly in the garbage because they only provide about 20% of rated capacitance...... and make our parts oscillate when they need a minimum capacitance value for stability. I specified X7R on the data sheets for my parts and they didn't like it because they cost a couple of cents more. The funny thing is I have noticed some of my text on ceramic caps quoted verbatim on competitor data sheets.... we all got a really good laugh when competitors copied our errors and typos which happened sometimes.

bountyhunter said:

The cap thing is funny. We had a 1 MHz low power switcher chip and we got dozens of calls from people who kept using Tantalum caps with them (despite data sheet warnings to only use ceramic). Amazingly enough, they were functional with the tant caps despite the fact the resonant frequency was an order of magnitude lower than the switch frequency, they just didn't put out much load current.

I had to knock heads with our marketing guys when I published an article explaining some of the facts about capacitors, like how Z5U and Y5F ceramics should be thrown directly in the garbage because they only provide about 20% of rated capacitance...... and make our parts oscillate when they need a minimum capacitance value for stability. I specified X7R on the data sheets for my parts and they didn't like it because they cost a couple of cents more. The funny thing is I have noticed some of my text on ceramic caps quoted verbatim on competitor data sheets.... we all got a really good laugh when competitors copied our errors and typos which happened sometimes.

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I must have read your stuff bounty

What was your nom de guerre? If you don't want to publish it, please PM me.

I had a constant battle with capacitors and it is still going on now- along the lines of what you say. I had a chap from the buying office telling me to buy cheaper capacitors because they were the same value.

spec

spec said:

In front of our flat in KL there was this huge 10 feet deep drain and as it only ever had a trickle of water in the bottom I thought it was overkill big time, until the monsoon came that is. The drain turned from a trickle to a raging torrent and filled right up.

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They kinda call this the design for the 100 yr event or the 400 year event at least when your designing drainage, In this case, it's the yearly event, but you may need capacity for the 100 or 400 year event. The "overkill" part.

KeepItSimpleStupid said:

They kinda call this the design for the 100 yr event or the 400 year event at least when your designing drainage, In this case, it's the yearly event, but you may need capacity for the 100 or 400 year event. The "overkill" part.

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Plenty of that in the USA as well, load's of films with cars racing in storm 'drains' in Los Angeles

From a UK perspective it's quite surprising.

spec said:

If you don't want to publish it, please PM me.

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How do you send a PM here? I can't find it anywhere.

bountyhunter said:

How do you send a PM here? I can't find it anywhere.

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Click on a member's avatar and you will get a window with 'start conversation' or similar

Hi,

Wow, lots of posts already.

To the OP:
There are various tricks you can use to boost very low inputs like 0.5v or under up to something usable, but the power requirement has to be met no matter how you do it. If you have 1 watt in put you cant not get 2 watts output for example.

The most common trick is to use bootstrapping. That's where you use some other trick to get the boost circuit going, then feed the output back to the input drive stage and that provides an extra voltage to work with. If you use a transistor driver though you need a transistor with a very low sat voltage or a MOSFET with low Rds.

One technique would involve a start up battery that is used just for starting the converter. You can charge the battery once it starts.
Another idea is to use a reed relay as the startup switch, then switch to the low sat transistor after the converter starts, again using bootstrap.
In slightly higher voltage applications a germanium transistor might fill in either for all the conversion time or just for startup.
A hand crank startup is possible too, and is even a little comical
A push button single shot startup is possible too with a coil and push button. The back emf of the coil provides enough voltage to start up.
Many possibilities here, including a solar array or thermoelectric generator pile which may operate full time or just to start up.

Nursyukriah

Although there are ways to boost low input voltges up to a more usable voltage, they all require some alternate method of getting the converter started with a higher voltage, or some other bootstrapping method.

But, in looking over the power source that you were given, I think that the real problem is with the previous students choice of trying to use a brushless motor as a generator.

It is well known, generally speaking, that a brushless motor is more efficient than a brushed motor. But, those reasons apply only when it is acting as a motor. But, they do not apply when trying to use it as a generator.

A brushless motor uses electronics to drive the field coils to make the motor run. The electronics will consist of a IC that uses a position detector (Hall effect switch) to decide which field coils to turn on and off, and when to do so. But, that IC needs to be powered with IT'S minimum operating voltage (3volts?) before it can wake up and make intelligent decisions. That IC will contain output drivers, either mosfets or BJTs, to actually switch power into the coils. But again, without power to that IC, nothing is going to happen. Also, I suspect that the polarity of those output switches is going to be in the wrong direction for generator vs. motor current.

Now, I suspect that the coils within the motor are generating a voltage high enough that leakage currents are getting through the power switches and the IC. And the 0.15 volts you are seeing is from that leakage current.

Now, if your assignment is that you must use the turbine/brushless motor combo as it is, then you need to boost the voltage. And the knowledge you will learn on that path will be valuable, even if the project is, in the end, a waste of time.

But, if the the end goal is to create a useful power source, then I suggest that you replace the brushless motor with a brushed motor that is known to function well as a generator. My guess is that you will have much more voltage and current from such a combination than what you now have.

ChrisP58 said:

But, in looking over the power source that you were given, I think that the real problem is with the previous students choice of trying to use a brushless motor as a generator.

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Actually, my previous student's project use a gearless DC motor as a generator.
Gearless DC motor is a reversible right? It can convert mechanical energy/power to electrical energy/power or vise versa.
But, until now, I don't know why her input voltage was too low.

I want to replace a DC motor to a DC generator. Is it by using DC generator the input voltage can be increased?

So, by "gearless", do you mean a normal DC motor that has brushes? Or do you mean brushless? I have to ask because "gearless" isn't a word we normally use.

A bicycle dynamo would work much better for this project - although I believe it's actually an alternator so you would have to rectify the output.

Nursyukriah Idris said:

I want to replace a DC motor to a DC generator. Is it by using DC generator the input voltage can be increased?

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Hi Nursyukriah,

It is almost certain that if you replace the motor with a generator that you will have more power output but we can't be sure. Can you give answers to the following questions.
(1) how fast is the turbine turning when you measure the motor (generator) output power?
(2) can you tell us what the motor is: description, part number, picture would all help.
(3) can you post a picture/ pictures of the turbine/motor set-up.

spec

throbscottle said:

So, by "gearless", do you mean a normal DC motor that has brushes? Or do you mean brushless? I have to ask because "gearless" isn't a word we normally use.

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I have been assuming that gearless means that the motor and the turbine shaft rotate at the same speed.
spec

The OP needs to provide FULL details of the motor that he is using as a generator. (I.E. Voltage rating. RPM at rated voltage. Current or power rating.) He also needs to say at how many RPM the turbine rotates the motor. If he is using the term "gearless" correctly then a gearbox on the end of the motor does not change weather the motor is reversible or not. As most of the motors with a gearbox on the end have reduction gearboxes I do not think the very small turbine would provide enough torque to drive the motor through a gearbox. As well as the motor ratings we also need to know the TYPE of motor. Is it brushless, If it has brushes is it permanent magnet, shunt wound, or series (Universal) wound.) ?

Les.

The attach file is my previous student's finalize report.

Chapter 3 - Methodology

Chapter 5 - Results

Pictures of real Existing Micro - Savonius Vertical Axis Wind Turbine (VAWT).

Les Jones said:

The OP needs to provide FULL details of the motor that he is using as a generator. (I.E. Voltage rating. RPM at rated voltage. Current or power rating.) He also needs to say at how many RPM the turbine rotates the motor. If he is using the term "gearless" correctly then a gearbox on the end of the motor does not change weather the motor is reversible or not. As most of the motors with a gearbox on the end have reduction gearboxes I do not think the very small turbine would provide enough torque to drive the motor through a gearbox. As well as the motor ratings we also need to know the TYPE of motor. Is it brushless, If it has brushes is it permanent magnet, shunt wound, or series (Universal) wound.) ?

Les.

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err, he is a she.
spec

Sorry for getting the gender wrong. From the picture of the motor in chapter 3 and the partial data it looks like it is a permanent magnet brushed motor. This is probably the best type of motor to use as a generator. The data in table 5.2 seems a bit odd as the load resistance is different in each test. I cannot see any mention if the load resistance was varied intentionally to maximise the power output so this is something that should have been mentioned.
Test 1 Load resistance 2.64 ohm
Test 2 Load resistance 2.34 ohm
Test 3 Load resistance 1.93 ohm
Test 4 Load resistance 1.76 ohm

If you wanted to get a higher voltage output (But at less current.) then choosing a motor with a higher voltage rating and a lower RPM rating would help. From the figures in table 5.2 I think the motor would run at about 20000 RPM on 3 volts.

Les.

It looks pretty obvious to me.

The motor chosen to be the generator was a low voltage high RPM type and the rotor design is a low-speed high torque design.

Simply put to get better power and efficiency out of the device a larger low RPM higher voltage motor should have been used.

Nursyukriah Idris said:

The attach file is my previous student's finalize report.

Chapter 3 - Methodology

Chapter 5 - Results

Click to expand...

Nursyukriah Idris said:

Pictures of real Existing Micro - Savonius Vertical Axis Wind Turbine (VAWT).

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Hi Nursyukriah,

Thanks for the above posts. They are very informative

spec