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18v to 12v conversion question

88.jessen

Nov 10, 2022
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Hello everybody.

I'm working on a project where I need to power a 12v cooling fan, from an 18v power supply. Will this little guy do the trick for me?

I'm pretty new to electronics, so forgive me if it's a stupid question.

Ideally I am looking for something with a switch, that will allow me to alternate between having 12v/18v as PSU, but always powering a 12v unit.

Greetings from Denmark.

Michael.
 

kellys_eye

Jun 25, 2010
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Bit of 'overkill' but yes, it will work.

There are many other types of buck (down) converter available and one with a lower power capacity would be smaller and cheaper. Your cooling fan is possibly rated at well under 1A (?) so something like this will do:


As for switching, any small toggle switch on the input side of the converter will suffice.
 

Harald Kapp

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Nov 17, 2011
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This converter is suitable - if it fulfills on the promised technical data. It is rated 4 A, but often this is a very "optimistic" rating. Probably good for <= 3 A.
The switch can easily added externally:
1668069917424.png
 

88.jessen

Nov 10, 2022
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Bit of 'overkill' but yes, it will work.

There are many other types of buck (down) converter available and one with a lower power capacity would be smaller and cheaper. Your cooling fan is possibly rated at well under 1A (?) so something like this will do:


As for switching, any small toggle switch on the input side of the converter will suffice.
That looks nice. My fan uses 0.48w, and operates between 7-12v, so that gives me 0.04A right?

I need the fan to run with 12v/18v Li-Ion batteries (like this makita one) and they are typically rated between 2.0Ah and 5.0Ah
 

88.jessen

Nov 10, 2022
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I have an update in this matter, that I need some help to understand.

I am now at a place in my prototyping, where I want to power a vacuum motor with an 18v 5A battery.

Specs for motor:

7.5V
40 W
Around 5A

Is it possible for me to step down the voltage, and have enough headroom on my batteries to power the motor safely? And, what kind og dc-dc converter would do the trick? I've looked at a lot of different types, but can't seem to find any that steps down from 18v to 7.5v. All help is appreciated :)
 

Harald Kapp

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Such converters can be found on the internet easily.
Here's just one example, here's another one.
(These pages are in German, but they give you an idea. You can also switch the language to e.g. English.)
 

88.jessen

Nov 10, 2022
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Such converters can be found on the internet easily.
Here's just one example, here's another one.
(These pages are in German, but they give you an idea. You can also switch the language to e.g. English.)

Great, thank you! I found this one that looks good for my project. But when it says the input voltage is 12/24v (9v-35v) does that mean that it can handle as much as 35v for a short period of time, when starting a machine for example?
 

Harald Kapp

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does that mean that it can handle as much as 35v for a short period of time
Supposedly yes, but the technical data of such cheap components usually have to be taken with a grain of salt. They are "optimistic".
The converter from my second link is spec'd for an input voltage of up to 90 V, much more headroom there.
 
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