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5v to 12v convert Answered

I want to connect a portable solar powered rechargeable to 2 DC fans of 12v to cool my car.
1. I have 2 options of portable solar powered: (A) 1500mAh, outputs: 5.5V / 800mA (B) 2000mAh, outputs: 5V 500mA
    which one is preffered to connect to those PC fans?
2. most of the PC fans are working at 12v. I don't quite sure if I'll build simple 5v to 12v regulator it will works and produce enough airflow.


You will not be able to use "just" a regulator in order to boost voltage.

It is simple enough to double or triple AC voltages, using a step up transformer,  DC is a different animal and would require either special ic's or conversion to AC, and then back rectified back to DC again. All that will waste precious power (you're amperage from the source will decrease as you increase voltage, forgetting even about losses due to heat and other factors, etc).

Without knowing the power draw (amperage) of the fans, it would not be possible to even start a suggestion here.

most regular 8cm fans are 12V 0.15-0.3A.
What you offer is waste of a lot of power.
some fans can work under 5v but the airflow is low, so I don't know if it will breeze out hot air from my car.

reducing DC voltages is easy enough, stepping it up is much more complicated. AC is easy to step up or down.