Hello once again, Forums...
I have made numerous projects and yet feel really stupid asking these questions.
I have a 24V Cooling fan that I would like to control On/Off with a temp sensor. I have the temp sensor figured out. However, when powering the Arduino UNO that I have with a 9V Battery, how do I ramp that power up to the required 24V? Also, how do I figure out Amp etc. to know how to properly run it without burning stuff up ( 
)?
Here is the fan Brand and number if you would like to take a look...
WINSINN B0757RPCN9
Thanks for your help and time!
Let me know if stepping up the power from a battery is impossible without expensive equipment/modules.... 
OK your 9V battery is likely a PP# type battery. This is not going to go well. Your 24 VDC fan draws about 80 mA or simply 0.080 amp of current. Even using a boost converter to get 24 volts from a 9 volt source your 9 volt battery will be dead or flat for those across the pond in very short order. A nine volt PP3 battery simply is a poor choice for most applications including powering an Arduino let alone a 24 volt fan drawing about 80 mA. We can do all the math if you would like but take my word for it, not a good idea.
Keep in mind when using a boost converter there is, like most things, a trade off. You go from 9.0 volts to 24.0 volts DC the trade off is more current draw on the low side to get higher voltage on the high side. Nine to twenty-four volts will eat your battery alive.
A better solution would be a 12 volt battery source.
Ron
I don't really have anything good for a 12V power source, unless there is a certain battery that outputs 12V... Which would be fairly massive and heavy.
It would take about 8 AAA's just to get to 12V, which, although feasible, still takes up a fair amount of room. About how long do you think 8 AAA's hooked in parallel would last?
OK we do a little batteries 101 lesson. Eight AA batteries in parallel would be 1.5 volts. Eight AA Batteries in series would be 12 volts. Earlier I mentioned a "trade off". So here is how batteries play out. When we place batteries in parallel we get the voltage of a single battery but we get more current capability. The typical and I say "typical" AA battery is about a 1500 AH (Amp Hour) battery depending on chemistry. That in theory means the battery fully charged at 1.5 volts should deliver 1.5 amps for one hour till discharged at 0.9 volts. The same battery should deliver 0.750 amps (750 mA) for two hours and .375 amp for four hours, see how this is going? A Google will bring up a dozen graphs from a dozen manufacturers.
You can also Google a PP3 common 9.0 volt battery and see the AH ratings.
If you absolutely need battery power the new rechargeable 12 v lipo batteries are a good option.
To get to what you want/need start by looking at how much current you need, You know your fan current draw, figure in the current efficiency for your boost converter and your uC current draw. Next look at the AH rating of a choice in batteries. I can't change the rules of power. Tried in my younger days but never could change the laws.
Ron
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Hey Ron,
So my bad there... I have the general concept of the parallel/series idea, I just keep getting the names mixed up, my bad.
I meant series, that's why I chose 8 batteries, to get to 12V. I will likely consider those lipo batts, except I'll need to buy a charger too.
Can I use a MOSFET transistor, to control the on/off, do you think?
Yeah, unfortunately the laws of power don't like to budge 
OK since this is battery powered I can buy q 12 volt SLA battery for about $21 USD. I van power my Arduino off that sems battery using the external DC jack. Then I but a boost converter like this one. pack for $13 USD. Finally an inexpensive 12 volt battery maintainer which charges and maintains yoy SLA battery anytime not in use. About $9.00 USD. With that 8 AH battery yoy get an easy 8 hoursof runtime.
Ron
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