boost converter fun

[[email protected]]

I tried making a boost converter (as in the pic here:
http://en.wikipedia.org/wiki/Boost_converter ) from a 10V battery pack,
a large inductor (basically, the coil for a 110VAC C-frame motor), a
diode and a 400V 100uF cap.

When manually connecting and disconnecting the coil at say 2-3 times
per second, I was able to get the voltage up to about 100 V. Once I
put a small load on it, though - a 5W night light - the output voltage
dropped considerably.

Then I thought to try something else - have my 100 Hz PWM controller be
the switch. Basically this, but with the inductor in place of the
motor: http://www.cpemma.co.uk/555pwm.html

However, all I got out of it was still 10VDC.

Why would this be?

Is the switching frequency of 100 Hz too high?

What is the typical switching frequency for boost converters, anyway?
I was hoping to get enough juice to run a 5W night light at 100 VDC or
so.

Thanks,

Michael

 

[petrus bitbyter]

I tried making a boost converter (as in the pic here:
http://en.wikipedia.org/wiki/Boost_converter ) from a 10V battery pack,
a large inductor (basically, the coil for a 110VAC C-frame motor), a
diode and a 400V 100uF cap.

When manually connecting and disconnecting the coil at say 2-3 times
per second, I was able to get the voltage up to about 100 V. Once I
put a small load on it, though - a 5W night light - the output voltage
dropped considerably.

Then I thought to try something else - have my 100 Hz PWM controller be
the switch. Basically this, but with the inductor in place of the
motor: http://www.cpemma.co.uk/555pwm.html

However, all I got out of it was still 10VDC.

Why would this be?

Is the switching frequency of 100 Hz too high?

What is the typical switching frequency for boost converters, anyway?
I was hoping to get enough juice to run a 5W night light at 100 VDC or
so.

Thanks,

Michael

The theory is described in wikipedia and I can't do better. Switching
frequency depends largely on the type of the inductor. For the coil of an
110Vac/50Hz motor, 100Hz seems good enough, particularly when there is still
a piece an iron core in the coil.

But... Compare the schematic of wiki and PMW controller carefully,
especially the triple coil, switch and diode. You'll have to see if you ever
want to do electronics.

petrus bitbyter

 

[Chris]

I tried making a boost converter (as in the pic here:
http://en.wikipedia.org/wiki/Boost_converter ) from a 10V battery pack,
a large inductor (basically, the coil for a 110VAC C-frame motor), a
diode and a 400V 100uF cap.

When manually connecting and disconnecting the coil at say 2-3 times
per second, I was able to get the voltage up to about 100 V. Once I
put a small load on it, though - a 5W night light - the output voltage
dropped considerably.

Then I thought to try something else - have my 100 Hz PWM controller be
the switch. Basically this, but with the inductor in place of the
motor: http://www.cpemma.co.uk/555pwm.html

However, all I got out of it was still 10VDC.

Why would this be?

Is the switching frequency of 100 Hz too high?

What is the typical switching frequency for boost converters, anyway?
I was hoping to get enough juice to run a 5W night light at 100 VDC or
so.

Thanks,

Michael

Hi, Michael. Do you still have the diode connected? That will keep
your inductor voltage from going more than 0.7V higher than your power
supply.

Actually, the diode is doing something valuable -- protecting the
transistor. If you've got a standard TIP31, its VCE(max) is only 40V
-- you will probably end up smoking the transistor. If you would like
to do something like this, try the TIP31C -- it will do 100V.

Cheers
Chris

 

[[email protected]]

Hi, Michael. Do you still have the diode connected? That will keep
your inductor voltage from going more than 0.7V higher than your power
supply.

Yes, I do have an NTE587 (I think) it was still connected. That would
explain it then... I didn't think that side would see the high
voltages... hmm...

Actually, the diode is doing something valuable -- protecting the
transistor. If you've got a standard TIP31, its VCE(max) is only 40V
-- you will probably end up smoking the transistor. If you would like
to do something like this, try the TIP31C -- it will do 100V.

I've actually got the IRF530 there... good to 100V I think. But now I
don't want to fry my 555...

Cheers
Chris

Yep, it's pretty obvious that this isn't my main area of expertise.
Just found a couple of coils in the garage, and thought, hmm... maybe I
can make a boost converter.

I'll have to dig out my old electronics book... I remember the part
about V = L dI/dT, but determining L and deltaI would be a bit tough
for me... (any suggestions?)

Michael

 

[default]

Yes, I do have an NTE587 (I think) it was still connected. That would
explain it then... I didn't think that side would see the high
voltages... hmm...




I've actually got the IRF530 there... good to 100V I think. But now I
don't want to fry my 555...



Yep, it's pretty obvious that this isn't my main area of expertise.
Just found a couple of coils in the garage, and thought, hmm... maybe I
can make a boost converter.

I'll have to dig out my old electronics book... I remember the part
about V = L dI/dT, but determining L and deltaI would be a bit tough
for me... (any suggestions?)

Michael

Boost converters aren't that difficult to make even with some pretty
unusual parts (like motor windings for inductors).

Typically they use very small inductors and very high switching
frequencies. The frequency goes up as the amount of energy stored in
the inductor goes down. 100 HZ is reasonable for using a motor or
transformer as the inductor since that represents a large inductance.

A motor might be less than ideal if you are talking about a shaded
pole or other induction motor - They have shorted turns to simulate a
rotating filed to start the motor turning.

The 555 cost you 20 cents? The transistor probably costs $1 - worry
about blowing the transistor - it takes the brunt of the abuse and
costs more.

DIODES - pay attention to your diodes in switchers. ordinary
rectifiers are nearly useless in some switching supply applications.
Rectifier diodes like the 1N4000 series are too slow - once they start
conducting they conduct in the reverse direction for a time before
they turn off - square waves and fast rise time pulses require high
speed rectifiers. With ordinary rectifiers some of your power will be
wasted as heat or the switching transistor will self-destruct due to a
slow diode - or the diode will short and take out other parts.

If you only need tens of milliamps at less than 100 V a fast signal
diode like the 1N4148 will work - great for little battery projects
like LED boosters to work 3.5 V leds with 1.5 volt supplies. Lots of
stuff on the web for that and it is an inexpensive way to learn about
switchers.

 

[default]

I tried making a boost converter (as in the pic here:
http://en.wikipedia.org/wiki/Boost_converter ) from a 10V battery pack,
a large inductor (basically, the coil for a 110VAC C-frame motor), a
diode and a 400V 100uF cap.

When manually connecting and disconnecting the coil at say 2-3 times
per second, I was able to get the voltage up to about 100 V. Once I
put a small load on it, though - a 5W night light - the output voltage
dropped considerably.

Then I thought to try something else - have my 100 Hz PWM controller be
the switch. Basically this, but with the inductor in place of the
motor: http://www.cpemma.co.uk/555pwm.html

However, all I got out of it was still 10VDC.

Why would this be?

Is the switching frequency of 100 Hz too high?

What is the typical switching frequency for boost converters, anyway?
I was hoping to get enough juice to run a 5W night light at 100 VDC or
so.

Thanks,

Michael

http://www.daycounter.com/Calculators/Switching-Converter-Calculator.phtml

 

[[email protected]]

Hi, Michael. Do you still have the diode connected? That will keep
your inductor voltage from going more than 0.7V higher than your power
supply.

Actually, the diode is doing something valuable -- protecting the
transistor. If you've got a standard TIP31, its VCE(max) is only 40V
-- you will probably end up smoking the transistor. If you would like
to do something like this, try the TIP31C -- it will do 100V.

Cheers
Chris

You were absolutely right. I removed the diode from the PWM circuit,
and got around 50V before I chickened out and cut the power. I also
removed the two capacitors from the PWM circuit; they're only rated at
about 10V or so.

Hooked up my 5W night light, and the New Improved boost converter
topped out at around 35V. Enough to make the night light glow
slightly. This was at about 80% duty cycle.

Fun stuff.

Thanks everyone,

Michael