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Old 09-05-2012, 12:40 PM   #1
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Controlling Fans for Fridge.

Recently I was involved in the (long) discussion about fans for the
fridge and had some off line chats with Lou on the subject. Since I
have a bank of four fans to install, I took some of what I learned
for ya'll and made a circuit to control the speed of the fans and
to assure the fans are OFF when the fridge is OFF. Lou had
indicated that it was a good idea to be certain the fans were off
when using solar to drive the fan(s)and the fridge was OFF.
(storage etc???) . Since I will be running off the TT battery for the
present and left my brain at the office when I retired, I will want to
have something to "remember" for me also. Dead batteries are NOT
my friend!

I created an archive of the design (and some variations) and put it
at: ADrive | Online Storage, Online Backup, Cloud Storage.

So I made a board that contains two circuits:
1- A MOSFET switch that controls the Minus of the fans to
shut them down when the fridge is off. The MOSFET
means that no current will be drawn from the TT battery
when the fridge is OFF and only 105 microamps when the
fridge is ON. That is current required by the MOSFET switch,
the fans will draw whatever current they need from solar
or TT battery.
2- A 6V voltage regulator to control the Plus of the fans
to provide a slower speed for the fans.
They can run full speed at 12V or slow at 6V. I use
two speed switches to control two fans each. I included in
the archive, versions with one speed switch and four speed
switches to control four fans or one fan each, respectively.
{My fans draw <0.8A at 12V and <0.065A at 6V.}

If any of this can be of use to you, you are free to use it in
any (non-commercial) way you choose..........

Happy camping to all.

cheers,
johnd

My board looks like this:
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Old 09-05-2012, 12:53 PM   #2
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I guess that's all fine and kudos to you for designing your board to control your fans.

I'm just not sure why you or anybody just don't hook fans to the on / off switch for fridge ? My three fans draw a total of 1.01 amps .

Turn the fridge on fans turn on.
Turn the fridge off fans go off .

Help me understand why you made it complicated .
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Old 09-05-2012, 01:10 PM   #3
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Quote:
Originally Posted by f1100turbo View Post
I guess that's all fine and kudos to you for designing your board to control your fans.

I'm just not sure why you or anybody just don't hook fans to the on / off switch for fridge ? My three fans draw a total of 1.01 amps .

Turn the fridge on fans turn on.
Turn the fridge off fans go off .

Help me understand why you made it complicated .
My fridge came with a factory fan that you can't control at all.There is a thermal switch that is temp. activated on a line that is always powered.If the fridge is turned off and it is a warm day you will hear the fan running.This is a definite battery killer so I take the in line fuse out when not using the trailer.I also wondered why the factory wouldn't have powered the fridge fan off the on off switch for the fridge.Makes sense to not need the fan running if the fridge is off.
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Old 09-05-2012, 01:19 PM   #4
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Quote:
Originally Posted by Malco

My fridge came with a factory fan that you can't control at all.There is a thermal switch that is temp. activated on a line that is always powered.If the fridge is turned off and it is a warm day you will hear the fan running.This is a definite battery killer so I take the in line fuse out when not using the trailer.I also wondered why the factory wouldn't have powered the fridge fan off the on off switch for the fridge.Makes sense to not need the fan running if the fridge is off.
Malco,
Can you not wire it as I did ?
The junction point for switched power on a dometic fridge is just inside the outside fridge cover on the lower left.
There's a black cover over all the junction points.
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Old 09-05-2012, 01:25 PM   #5
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Thanks for the VERY comprehensive write-up, including copper trace photos.

Real nice design, however....

The data sheet for the four-fan All Electronics assembly shows the operating range for the fans to be 7.0 to 13.8 volts.

Your regulated voltage for half-speed falls outside that range, so results may be less-than-reliable.

Just an FYI.

See:
http://html.alldatasheet.com/html-pd...FBA09A12M.html

Pop
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Old 09-05-2012, 01:27 PM   #6
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The line with the fuse in it comes from that corner of the fridge.So if I get what your telling me I suppose the live line is already coming from that junction box and would just have to be reconnected to the switched line.But once again wouldn't it have made sense to do this from the factory.
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Old 09-05-2012, 01:29 PM   #7
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Quote:
Originally Posted by Malco
The line with the fuse in it comes from that corner of the fridge.So if I get what your telling me I suppose the live line is already coming from that junction box and would just have to be reconnected to the switched line.But once again wouldn't it have made sense to do this from the factory.
Yes it would have !
I'll take some pics tonight.
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Old 09-05-2012, 01:29 PM   #8
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Quote:
Originally Posted by f1100turbo View Post
I guess that's all fine and kudos to you for designing your board to control your fans.

I'm just not sure why you or anybody just don't hook fans to the on / off switch for fridge ? My three fans draw a total of 1.01 amps .

Turn the fridge on fans turn on.
Turn the fridge off fans go off .

That's exactly what the MOSFET switch does. Slaves the fans
to the fridge. But without drawing more than microamps
from the fridge. Hooking the fans to the fridge power switch
will, of course, work fine - if you are using TT battery, rather
than solar. And my future plans are solar to run the fans.
A separate toggle switch for the fans will do the
same using solar....if you remember; my memory....well,
not so good.

And I DO want the speed control, regardless........

Help me understand why you made it complicated .
Which complication? The Speed Control or the MOSFET
switch?

And if it doesn't fit your needs, it doesn't fit your
needs. That's kewl.......

cheers,
johnd
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Old 09-05-2012, 01:36 PM   #9
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Quote:
Originally Posted by SpringerPop View Post
Real nice design, however....

The data sheet for the four-fan All Electronics assembly shows the operating range for the fans to be 7.0 to 13.8 volts.

Your regulated voltage for half-speed falls outside that range, so results may be less-than-reliable.

Just an FYI.

See:
FBA09A12M datasheet(1/7 Pages) PANASONIC | Locked rotor protection circuits Automatically restarts in a few seconds Reverse voltage protection

Pop
True!
I pushed the envelope, but checked mine down to 5.25 volts.
If a problem occurs, the 7806 can be replaced with a higher voltage
regulator..........

Edit: Or a forward-biased diode(s) placed in the common line of the 7806 will
raise the output by .6V for each diode.

cheers,
johnd
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Old 09-05-2012, 01:42 PM   #10
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John - nice work. I'm curious why you chose 4 fans. Is it based on what you had or did you run some tests?

Thanks
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