12V mini fridge

[N.O.Y.B.]

Hi,

I have a 12V 50watt power supply (designed for halogen downlights).

It's a heavy blocky thing, so it's definatley not a switchmode.

Would these run a 12V mini fridge (below is a link to the fridge I have)?

http://www1.jaycar.com.au/productView.asp?ID=GH1376&CATID=45&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=739

The fridge wattage is 50watts cooling and 40watts warming, it's one of those
little fridges that have both cooling/heating functions by way of a peltier
semiconductor.

I was told that I'd need a bridge rectifier to convert the AC current to a
DC current, is this necessary with my 50watt transformer?

Any advice would be appreciated,

noyb

 

[Geoff C]

"N.O.Y.B." <mslava04@hotmail.com> wrote in
news:2ntjjhF4kdhdU1@uni-berlin.de:

Hi,

I have a 12V 50watt power supply (designed for halogen downlights).

It's a heavy blocky thing, so it's definatley not a switchmode.

Would these run a 12V mini fridge (below is a link to the fridge I
have)?

http://www1.jaycar.com.au/productView.asp?ID=GH1376&CATID=45&keywords=&
SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMi
n=&priceMax=&SUBCATID=739

The fridge wattage is 50watts cooling and 40watts warming, it's one of
those little fridges that have both cooling/heating functions by way
of a peltier semiconductor.

I was told that I'd need a bridge rectifier to convert the AC current
to a DC current, is this necessary with my 50watt transformer?

Any advice would be appreciated,

noyb

Definitely you would need a bridge rectifier since AC will only cause
heating due to polarity reversals.

The peltier device is an inefficient heat pump and will waste nearly 1
watt of heat for every watt pumped.

Also, it is probably preferable to smooth the rectified AC with an
electrolytic capacitor. from what I have read, the peltier device will
suffer from long term damage if low frequencies are used to power it eg.
pulse width modulation controllers with low frequency output. Probably
because current causes small physical movement in the thermocouples. I
don't know if 100 Hz is regarded as fast or slow in this respect but a
cap is cheap.

 

[N.O.Y.B.]

What about this cap?

http://www1.jaycar.com.au/productView.asp?ID=RE6245&CATID=33&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=798

For about $5. It's a 4700uF 50V RB Electrolytic Capacitor

Going by specs, it's 50 volts at 2,280mA (2.28A), so going by this it would
be able to handle 114watts of throughput?

Cheers
noyb

"Geoff C" <notinterestedin@spa.comm> wrote in message
news:wyhSc.24385$%r.255283@nasal.pacific.net.au...

"N.O.Y.B." <mslava04@hotmail.com> wrote in
news:2ntjjhF4kdhdU1@uni-berlin.de:

Hi,

I have a 12V 50watt power supply (designed for halogen downlights).

It's a heavy blocky thing, so it's definatley not a switchmode.

Would these run a 12V mini fridge (below is a link to the fridge I
have)?

http://www1.jaycar.com.au/productView.asp?ID=GH1376&CATID=45&keywords=&
SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMi
n=&priceMax=&SUBCATID=739

The fridge wattage is 50watts cooling and 40watts warming, it's one of
those little fridges that have both cooling/heating functions by way
of a peltier semiconductor.

I was told that I'd need a bridge rectifier to convert the AC current
to a DC current, is this necessary with my 50watt transformer?

Any advice would be appreciated,

noyb


Definitely you would need a bridge rectifier since AC will only cause
heating due to polarity reversals.

The peltier device is an inefficient heat pump and will waste nearly 1
watt of heat for every watt pumped.

Also, it is probably preferable to smooth the rectified AC with an
electrolytic capacitor. from what I have read, the peltier device will
suffer from long term damage if low frequencies are used to power it eg.
pulse width modulation controllers with low frequency output. Probably
because current causes small physical movement in the thermocouples. I
don't know if 100 Hz is regarded as fast or slow in this respect but a
cap is cheap.

 

[Phil Allison]

"N.O.Y.B."

Going by specs, it's 50 volts at 2,280mA (2.28A), so going by this it
would
be able to handle 114watts of throughput?

** NO !!

The ripple current spec is just that - the voltage has no effect on it.

At 12 volts that cap is good for about 20 watts of DC power.




........... Phil

 

[N.O.Y.B.]

Okay, so which cap would I need?

Cheers
noyb

** NO !!

The ripple current spec is just that - the voltage has no effect on
it.

At 12 volts that cap is good for about 20 watts of DC power.




.......... Phil

 

[N.O.Y.B.]

What I really cannt understand is why these damn fridges didn't come with
their own power supply unit. Would have solved all these issues

noyb.

"N.O.Y.B." <mslava04@hotmail.com> wrote in message
news:2ntjjhF4kdhdU1@uni-berlin.de...

Hi,

I have a 12V 50watt power supply (designed for halogen downlights).

It's a heavy blocky thing, so it's definatley not a switchmode.

Would these run a 12V mini fridge (below is a link to the fridge I have)?


http://www1.jaycar.com.au/productView.asp?ID=GH1376&CATID=45&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=739

The fridge wattage is 50watts cooling and 40watts warming, it's one of
those
little fridges that have both cooling/heating functions by way of a
peltier
semiconductor.

I was told that I'd need a bridge rectifier to convert the AC current to a
DC current, is this necessary with my 50watt transformer?

Any advice would be appreciated,

noyb

 

[Phil Allison]

"N.O.Y.B."

Okay, so which cap would I need?

** Just use two or three of them.

The ripple ratings add up.



.......... Phil

 

[Brian Goldsmith]

"N.O.Y.B." <mslava04@hotmail.com> wrote

What I really cannt understand is why these damn fridges didn't come with
their own power supply unit. Would have solved all these issues

noyb.

****Er,did it ever occur to you the fridges were designed to operate from a
12 Volt battery,and
not require connection to mains power!!

Brian Goldsmith.

 

[KLR]

On Wed, 11 Aug 2004 18:35:59 +1000, "N.O.Y.B." <mslava04@hotmail.com>
wrote:

What I really cannt understand is why these damn fridges didn't come with
their own power supply unit. Would have solved all these issues

These fridges are normally intended to operate from a car battery, and

are more suitable for small capacity mobile applications where there
isn't any mains power available.

If they did supply a power supply of that capacity - it would simply
add to the cost to you anyway.

For home (240v) use its expected most likely that you would buy a
mains powered compressor type fridge. In my experience they run a
hell of a lot colder than those peltier units, as well as having
freezing space.

noyb.

"N.O.Y.B." <mslava04@hotmail.com> wrote in message
news:2ntjjhF4kdhdU1@uni-berlin.de...
Hi,

I have a 12V 50watt power supply (designed for halogen downlights).

It's a heavy blocky thing, so it's definatley not a switchmode.

Would these run a 12V mini fridge (below is a link to the fridge I have)?


http://www1.jaycar.com.au/productView.asp?ID=GH1376&CATID=45&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=739

The fridge wattage is 50watts cooling and 40watts warming, it's one of
those
little fridges that have both cooling/heating functions by way of a
peltier
semiconductor.

I was told that I'd need a bridge rectifier to convert the AC current to a
DC current, is this necessary with my 50watt transformer?

Any advice would be appreciated,

noyb

 

[KLR]

On Wed, 11 Aug 2004 18:10:17 +1000, "N.O.Y.B." <mslava04@hotmail.com>
wrote:

What about this cap?

http://www1.jaycar.com.au/productView.asp?ID=RE6245&CATID=33&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=798

For about $5. It's a 4700uF 50V RB Electrolytic Capacitor

Although a 50v rated cap will work fine, you don't need to go to as

high as a 50v rating, 25v would be more than adequate and should be
much smaller and cheaper too.

If I was building this for my own use I would be looking though at
12,000UF for this - as I recall the old rule of thumb was approx
2200UF per amp at 50hz..

(You can parallel as many caps as you want across the 12v DC to
achieve this value if you cant buy a single unit. The total UF's must
add up to the required amount though.)


Note also that when you put a bridge across a 12vac transformer - you
will likely end up with about 15-16v of DC, and you must make sure
that this isnt too much overvoltage for the peltier unit.

(to make matters worse - many "12vac" transformers in the real world
tend to push out more like 13vac and possibly more if your mains
voltage is higher than the nominal 240v in your location.)

At full load (50w) however this may drop a volt or 2 and is probably
fine for this application. Also if said fridge is intended for car
use - car electrics tend to sit about 14v anyway.


--------------------------
Finally peltier units dont like being turned on and off at low
frequencies. After so many on-off cycles of low frequency they fail
- so DONT go running a standard mechanical switch type fridge
thermostat on this unit - or go turning it on and off frequently.



As I remember if the temp needs to be varied then they should be run
at a fairly high frequency and the pulse width varied to alter the
temperature if needed)

Going by specs, it's 50 volts at 2,280mA (2.28A), so going by this it would
be able to handle 114watts of throughput?

Cheers
noyb

"Geoff C" <notinterestedin@spa.comm> wrote in message
news:wyhSc.24385$%r.255283@nasal.pacific.net.au...
"N.O.Y.B." <mslava04@hotmail.com> wrote in
news:2ntjjhF4kdhdU1@uni-berlin.de:

Hi,

I have a 12V 50watt power supply (designed for halogen downlights).

It's a heavy blocky thing, so it's definatley not a switchmode.

Would these run a 12V mini fridge (below is a link to the fridge I
have)?

http://www1.jaycar.com.au/productView.asp?ID=GH1376&CATID=45&keywords=&
SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMi
n=&priceMax=&SUBCATID=739

The fridge wattage is 50watts cooling and 40watts warming, it's one of
those little fridges that have both cooling/heating functions by way
of a peltier semiconductor.

I was told that I'd need a bridge rectifier to convert the AC current
to a DC current, is this necessary with my 50watt transformer?

Any advice would be appreciated,

noyb


Definitely you would need a bridge rectifier since AC will only cause
heating due to polarity reversals.

The peltier device is an inefficient heat pump and will waste nearly 1
watt of heat for every watt pumped.

Also, it is probably preferable to smooth the rectified AC with an
electrolytic capacitor. from what I have read, the peltier device will
suffer from long term damage if low frequencies are used to power it eg.
pulse width modulation controllers with low frequency output. Probably
because current causes small physical movement in the thermocouples. I
don't know if 100 Hz is regarded as fast or slow in this respect but a
cap is cheap.

 

[Patrick Dunford]

In article <pjilh0lmad1picvr3uvhgvt24uv74kutqf@4ax.com> in
aus.electronics on Thu, 12 Aug 2004 11:40:13 +1000, KLR
<kenreed@yahoo.com> says...

On Wed, 11 Aug 2004 18:10:17 +1000, "N.O.Y.B." <mslava04@hotmail.com
wrote:
What about this cap?

http://www1.jaycar.com.au/productView.asp?ID=RE6245&CATID=33&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=798

For about $5. It's a 4700uF 50V RB Electrolytic Capacitor

Although a 50v rated cap will work fine, you don't need to go to as
high as a 50v rating, 25v would be more than adequate and should be
much smaller and cheaper too.

If I was building this for my own use I would be looking though at
12,000UF for this - as I recall the old rule of thumb was approx
2200UF per amp at 50hz..

(You can parallel as many caps as you want across the 12v DC to
achieve this value if you cant buy a single unit. The total UF's must
add up to the required amount though.)


Note also that when you put a bridge across a 12vac transformer - you
will likely end up with about 15-16v of DC, and you must make sure
that this isnt too much overvoltage for the peltier unit.

It will peak at this, but the average voltage will be closer to 12V.
Since you can get up to 13.8 volts out of the car's electrical system, it
may be OK.