Choosing Rheostat and Schematics

[polanskiman]

Hello everyone,

As you will see I'm brand new to this forum, so please be toleratnt with me...

My project has nothing to do with overclocking but does involve a fan, a power source, a rheostat, some cabling, screews and glue... I'm in fact building a magnetic stirrer.

So, first of all I would like to say that I've already read the Guide provided by greenman100 on "How to Choose a Rheostat/Variable Resistor". So far so good. I've applied the formulas provided and so I now know what rheostat I need...

Now I've read some of the posts in reaction to that guide and they are talking about adding transistors, voltage regulators.... All this looks cool but since I ain't an electronic engineer I have no idea what we are talking about. Could that improve my setup and provide me with a more stable and precise circuit? If yes, I would be honestly thanksful to those who can help by providing a schematic of the circuit (simplified if possible to the ignorant that I am).

Here is the material that I already have in hands:

- Viariable Power supply: min 3.5v max 12v (for convenience purposes I'll leave it at 12v all the time, reason why I needed to add a rheostat further in the circuit again)
- Fan: 12v - 1.2A
- Rehostat/variable resistor: 14ohms - 3.5W (still haven't purchased it)

Any help would be appreciated.

Thanks in advance.

 

[m0r7if3r]

As long as you're running just one fan on this thing, there's no reason that you need anything in addition to your pot (potentiometer, yet another name for a variable resistor, but its the shortest). What you DO need to look at is to make sure that your pot can handle about an amp of current (less depending on your fan...but 1amp is a good ceiling). If you're not setting this up as a voltage divider, be careful near the bottom because i've gotten arcing on them before. I haven't run the numbers, but I don't think 14ohm is the right resistor value, without the current your fan draws and the minimum voltage you plan on running it at I really can't say though...

 

[polanskiman]

As long as you're running just one fan on this thing, there's no reason that you need anything in addition to your pot (potentiometer, yet another name for a variable resistor, but its the shortest). What you DO need to look at is to make sure that your pot can handle about an amp of current (less depending on your fan...but 1amp is a good ceiling). If you're not setting this up as a voltage divider, be careful near the bottom because i've gotten arcing on them before. I haven't run the numbers, but I don't think 14ohm is the right resistor value, without the current your fan draws and the minimum voltage you plan on running it at I really can't say though...

Thanks for the advise.

Not sure what you mean when you talk about voltage divider... Sorry but I'm no electronic expert...

14ohm was calculated through the Ohms law under the assumption that the lowest voltage at which the fan can operate is 5V...

 

[m0r7if3r]

I figured that was how it was calculated, but when i worked it backwards the ampherage it output was a bit low (though I guess you could be going for a lower rpm fan...I hadn't really considered that since the blueprint for this stirrer in my mind is capable of like 5k rpm...). Something you may want to think about, sleeve bearing fans die quicker when they are used in a horizontal orientation, which is how I assume you're placing your fan, so be careful with what kind of fan you buy.

 

[polanskiman]

I figured that was how it was calculated, but when i worked it backwards the ampherage it output was a bit low (though I guess you could be going for a lower rpm fan...I hadn't really considered that since the blueprint for this stirrer in my mind is capable of like 5k rpm...). Something you may want to think about, sleeve bearing fans die quicker when they are used in a horizontal orientation, which is how I assume you're placing your fan, so be careful with what kind of fan you buy.

Thank you very much for this very useful information. I guess I shall reconsider the fan I'll use. The fan has indeed a high rpm and may not be appropriate for magnetic stirring. What amperage would you recommend for such use ?

 

[rainless]

I need a micro rheostat. No idea where I can get one.

 

[Jolly-Swagman]

I need a micro rheostat. No idea where I can get one.

Have you tried Radio Shack or similar outlet

 

[m0r7if3r]

Thank you very much for this very useful information. I guess I shall reconsider the fan I'll use. The fan has indeed a high rpm and may not be appropriate for magnetic stirring. What amperage would you recommend for such use ?

Well if you've got one that'll do high rpm at low ampherage, by all means, use it, I was just going off what I've seen (which, admittedly, is primarily bigger, 38mm thickness fans).