Help: Basic Full-Wave Rectification

R

Ravendug

Guest
Hi, I am hoping someone here could help me with what I believe would be a
simple problem
for someone that knows what they are doing (not me), or even with a fairly
basic knowledge of electronics.

I have a 24V DC (6.7W) fan that I would like to power with a transformer
that is rated as:
Prim: 230V 50Hz
Sec: 24V 0.85A

The problem is I have no idea on how to go about rectifying the AC output
from the transformer to be suitable for the DC fan.
I am a 2nd yr Computer Engineering Student but seem to know very little of
building any practical electronic circuits :(.
I know some theory about bridge rectifiers, centre-tap transformers, ripple,
etc not much else on this subject. Pathetic I
know.

I would appreciate any help on finding the correct components and building
the circuit. I am located in the UK so it would be useful to have references
on components from somebody like Maplin (http://www.maplin.co.uk) or
RS-Components (http://rswww.com/).

Any other references or sources of information would be very welcome as
well.
If I have left any other required/useful bits of information please ask and
I will try my best to provide
a suitable answer.

Your help will be greatly appreciated.


Ravendug.
 
"Ravendug
Hi, I am hoping someone here could help me with what I believe would be a
simple problem
for someone that knows what they are doing (not me), or even with a fairly
basic knowledge of electronics.

I have a 24V DC (6.7W) fan that I would like to power with a transformer
that is rated as:
Prim: 230V 50Hz
Sec: 24V 0.85A

The problem is I have no idea on how to go about rectifying the AC output
from the transformer to be suitable for the DC fan.
I am a 2nd yr Computer Engineering Student but seem to know very little of
building any practical electronic circuits :(.
I know some theory about bridge rectifiers, centre-tap transformers, ripple,
etc not much else on this subject. Pathetic I
know.

I would appreciate any help on finding the correct components and building
the circuit. I am located in the UK so it would be useful to have references
on components from somebody like Maplin (http://www.maplin.co.uk) or
RS-Components (http://rswww.com/).

Any other references or sources of information would be very welcome as
well.
If I have left any other required/useful bits of information please ask and
I will try my best to provide
a suitable answer.

Your help will be greatly appreciated.

Ravendug.
Click to expand...
A 4 diode bridge rectifier between the secondary and motor should work
pretty well. No need for a filter capacitor.

http://www.tpub.com/neets/book7/27c.htm

--
John Popelish
 
"Ravendug endug@phreaker.net>" <rav<noSpamPls> wrote in message
news:brnhkr$8i4$1@hercules.btinternet.com...
Hi, I am hoping someone here could help me with what I believe would be a
simple problem
for someone that knows what they are doing (not me), or even with a fairly
basic knowledge of electronics.

I have a 24V DC (6.7W) fan that I would like to power with a transformer
that is rated as:
Prim: 230V 50Hz
Sec: 24V 0.85A

The problem is I have no idea on how to go about rectifying the AC output
from the transformer to be suitable for the DC fan.
I am a 2nd yr Computer Engineering Student but seem to know very little of
building any practical electronic circuits :(.
Click to expand...
Looks like a common 'feature' of nowadays' universities. I'm a Computer
Science student at the Technical University of Berlin and also in the 2nd
yr. Taking a look at my class mates tells me, you're not the only one to
whom the practical part of EE is something rather EErie. So welcome at
S.E.B, you're right here.

I know some theory about bridge rectifiers, centre-tap transformers,
ripple,
etc not much else on this subject. Pathetic I
know.
Click to expand...
<snip>

You will need a classic-style full-bridge rectifier (4 diodes) and a
sufficiently large capacitor. See ASCII schematic below.


.---|>|---x-----x------> + out
| + - | |
------->|<-------x----|>|---' __|__ +
mains <|> 24VAC || _____
------->|<--------x---|<|---. | -
| - + | |
'----|<|---x-----x------> - out


The + and - out connectors is where the motor is to be connected. The cap
should have a rated voltage of 50V and a capacity of (at least) 1000uF. Note
that the output voltage will be higher than 24V. Under no load it will
probably be over 35V (the transformer is rated to provide 24V when loaded,
under no load the voltage increases and the rectifier will further multiply
it by sqrt(2)). Taking into account that the motor will draw a about a third
of the transformer's rated current and the transformer's resistance is
sufficiently far from zero, I would estimate the output voltage somewhere a
little above 30V. Make sure your motor can handle this or use a regulator or
a series zener to cut off the excess voltage. In this case, make sure the
regulator (or zener) does not overheat. P=U*I will reveal the power the
regulator will have to dissipate. Of course, it will not account for the
power dissipated at poweron as the motor is spinning up (changes U and I),
but since the motor is rather small and will probably spin up quickly,
there's no real use in calculating this power either. Do not however leave
out the capacitor. The motor may be an electronic one requiring a constant
voltage. Such a thingy will probably not work off unfiltered DC.

Cheers,
Dimitrij
 
"Dimitrij Klingbeil" <dimitrijklingbeil@arcor.de> wrote in message
news:3fdf96da$0$19080$9b4e6d93@newsread2.arcor-online.net...
"Ravendug endug@phreaker.net>" <rav<noSpamPls> wrote in message
news:brnhkr$8i4$1@hercules.btinternet.com...
Hi, I am hoping someone here could help me with what I believe would be
a
simple problem
for someone that knows what they are doing (not me), or even with a
fairly
basic knowledge of electronics.

I have a 24V DC (6.7W) fan that I would like to power with a transformer
that is rated as:
Prim: 230V 50Hz
Sec: 24V 0.85A

The problem is I have no idea on how to go about rectifying the AC
output
from the transformer to be suitable for the DC fan.
I am a 2nd yr Computer Engineering Student but seem to know very little
of
building any practical electronic circuits :(.

Looks like a common 'feature' of nowadays' universities. I'm a Computer
Science student at the Technical University of Berlin and also in the 2nd
yr. Taking a look at my class mates tells me, you're not the only one to
whom the practical part of EE is something rather EErie. So welcome at
S.E.B, you're right here.

I know some theory about bridge rectifiers, centre-tap transformers,
ripple,
etc not much else on this subject. Pathetic I
know.

snip

You will need a classic-style full-bridge rectifier (4 diodes) and a
sufficiently large capacitor. See ASCII schematic below.


.---|>|---x-----x------> + out
| + - | |
------->|<-------x----|>|---' __|__ +
mains <|> 24VAC || _____
------->|<--------x---|<|---. | -
| - + | |
'----|<|---x-----x------> - out


The + and - out connectors is where the motor is to be connected. The cap
should have a rated voltage of 50V and a capacity of (at least) 1000uF.
Note
that the output voltage will be higher than 24V. Under no load it will
probably be over 35V (the transformer is rated to provide 24V when loaded,
under no load the voltage increases and the rectifier will further
multiply
it by sqrt(2)). Taking into account that the motor will draw a about a
third
of the transformer's rated current and the transformer's resistance is
sufficiently far from zero, I would estimate the output voltage somewhere
a
little above 30V. Make sure your motor can handle this or use a regulator
or
a series zener to cut off the excess voltage. In this case, make sure the
regulator (or zener) does not overheat. P=U*I will reveal the power the
regulator will have to dissipate. Of course, it will not account for the
power dissipated at poweron as the motor is spinning up (changes U and I),
but since the motor is rather small and will probably spin up quickly,
there's no real use in calculating this power either. Do not however leave
out the capacitor. The motor may be an electronic one requiring a constant
voltage. Such a thingy will probably not work off unfiltered DC.

Cheers,
Dimitrij



Your circuit will certainly do the job but....
Click to expand...
I have had some pretty good luck with fans, motors and solenoids on
unfiltered DC....It would be worth a try...If it hums or overheats...filter
it!!!
 
Thanks greatly for your help, I'll give it a go.


"Dimitrij Klingbeil" <dimitrijklingbeil@arcor.de> wrote in message
news:3fdf96da$0$19080$9b4e6d93@newsread2.arcor-online.net...
"Ravendug endug@phreaker.net>" <rav<noSpamPls> wrote in message
news:brnhkr$8i4$1@hercules.btinternet.com...
Hi, I am hoping someone here could help me with what I believe would be
a
simple problem
for someone that knows what they are doing (not me), or even with a
fairly
basic knowledge of electronics.

I have a 24V DC (6.7W) fan that I would like to power with a transformer
that is rated as:
Prim: 230V 50Hz
Sec: 24V 0.85A

The problem is I have no idea on how to go about rectifying the AC
output
from the transformer to be suitable for the DC fan.
I am a 2nd yr Computer Engineering Student but seem to know very little
of
building any practical electronic circuits :(.

Looks like a common 'feature' of nowadays' universities. I'm a Computer
Science student at the Technical University of Berlin and also in the 2nd
yr. Taking a look at my class mates tells me, you're not the only one to
whom the practical part of EE is something rather EErie. So welcome at
S.E.B, you're right here.

I know some theory about bridge rectifiers, centre-tap transformers,
ripple,
etc not much else on this subject. Pathetic I
know.

snip

You will need a classic-style full-bridge rectifier (4 diodes) and a
sufficiently large capacitor. See ASCII schematic below.


.---|>|---x-----x------> + out
| + - | |
------->|<-------x----|>|---' __|__ +
mains <|> 24VAC || _____
------->|<--------x---|<|---. | -
| - + | |
'----|<|---x-----x------> - out


The + and - out connectors is where the motor is to be connected. The cap
should have a rated voltage of 50V and a capacity of (at least) 1000uF.
Note
that the output voltage will be higher than 24V. Under no load it will
probably be over 35V (the transformer is rated to provide 24V when loaded,
under no load the voltage increases and the rectifier will further
multiply
it by sqrt(2)). Taking into account that the motor will draw a about a
third
of the transformer's rated current and the transformer's resistance is
sufficiently far from zero, I would estimate the output voltage somewhere
a
little above 30V. Make sure your motor can handle this or use a regulator
or
a series zener to cut off the excess voltage. In this case, make sure the
regulator (or zener) does not overheat. P=U*I will reveal the power the
regulator will have to dissipate. Of course, it will not account for the
power dissipated at poweron as the motor is spinning up (changes U and I),
but since the motor is rather small and will probably spin up quickly,
there's no real use in calculating this power either. Do not however leave
out the capacitor. The motor may be an electronic one requiring a constant
voltage. Such a thingy will probably not work off unfiltered DC.

Cheers,
Dimitrij
Click to expand...
 
Another question for further clarification.
Which diodes would be suitable/ (How would I determine if is suitable?)

i.e. Would something like the 1N4001 be ok?

"Ross Mac" <this.is.a.mung@example.invalid> wrote in message
news:dRpEb.212841$Ec1.7668497@bgtnsc05-news.ops.worldnet.att.net...
"Dimitrij Klingbeil" <dimitrijklingbeil@arcor.de> wrote in message
news:3fdf96da$0$19080$9b4e6d93@newsread2.arcor-online.net...
"Ravendug endug@phreaker.net>" <rav<noSpamPls> wrote in message
news:brnhkr$8i4$1@hercules.btinternet.com...
Hi, I am hoping someone here could help me with what I believe would
be
a
simple problem
for someone that knows what they are doing (not me), or even with a
fairly
basic knowledge of electronics.

I have a 24V DC (6.7W) fan that I would like to power with a
transformer
that is rated as:
Prim: 230V 50Hz
Sec: 24V 0.85A

The problem is I have no idea on how to go about rectifying the AC
output
from the transformer to be suitable for the DC fan.
I am a 2nd yr Computer Engineering Student but seem to know very
little
of
building any practical electronic circuits :(.

Looks like a common 'feature' of nowadays' universities. I'm a Computer
Science student at the Technical University of Berlin and also in the
2nd
yr. Taking a look at my class mates tells me, you're not the only one to
whom the practical part of EE is something rather EErie. So welcome at
S.E.B, you're right here.

I know some theory about bridge rectifiers, centre-tap transformers,
ripple,
etc not much else on this subject. Pathetic I
know.

snip

You will need a classic-style full-bridge rectifier (4 diodes) and a
sufficiently large capacitor. See ASCII schematic below.


.---|>|---x-----x------> + out
| + - | |
------->|<-------x----|>|---' __|__ +
mains <|> 24VAC || _____
------->|<--------x---|<|---. | -
| - + | |
'----|<|---x-----x------> - out


The + and - out connectors is where the motor is to be connected. The
cap
should have a rated voltage of 50V and a capacity of (at least) 1000uF.
Note
that the output voltage will be higher than 24V. Under no load it will
probably be over 35V (the transformer is rated to provide 24V when
loaded,
under no load the voltage increases and the rectifier will further
multiply
it by sqrt(2)). Taking into account that the motor will draw a about a
third
of the transformer's rated current and the transformer's resistance is
sufficiently far from zero, I would estimate the output voltage
somewhere
a
little above 30V. Make sure your motor can handle this or use a
regulator
or
a series zener to cut off the excess voltage. In this case, make sure
the
regulator (or zener) does not overheat. P=U*I will reveal the power the
regulator will have to dissipate. Of course, it will not account for the
power dissipated at poweron as the motor is spinning up (changes U and
I),
but since the motor is rather small and will probably spin up quickly,
there's no real use in calculating this power either. Do not however
leave
out the capacitor. The motor may be an electronic one requiring a
constant
voltage. Such a thingy will probably not work off unfiltered DC.

Cheers,
Dimitrij



Your circuit will certainly do the job but....
I have had some pretty good luck with fans, motors and solenoids on
unfiltered DC....It would be worth a try...If it hums or
overheats...filter
it!!!
Click to expand...
 
"Ravendug endug@phreaker.net>" <rav<noSpamPls> wrote in message
news:brv9er$krf$1@hercules.btinternet.com...
Another question for further clarification.
Which diodes would be suitable/ (How would I determine if is suitable?)

i.e. Would something like the 1N4001 be ok?
Click to expand...
Yes
 
"Ravendug" <rav<noSpamPls>endug@phreaker.net> wrote in message news:<brv97b$asu$1@sparta.btinternet.com>...
Thanks greatly for your help, I'll give it a go.
Click to expand...
dont, youll fry the fan. Your 24v transformer will give you about 35v
on load, and even higher with a load less than its max rating. This is
much too high for a 24v fan.

Try a 16v transformer for about 24v dc.


Regards, NT
 
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