OK, it’s been almost 20 years since I took this stuff in college.
I am building a fan system for a set of goggles to keep the lenses from fogging up. I have two little 25mm laptop fans, each runs at 5v, 0.06 amps.
I’d like to run them both off a single 9v battery.
If I hook them up in parallel (that is, connect both “hot” lines from the two fans to the positive terminal of the battery, and likewise with both neutrals to the negative of the battery), the voltage drop over each fan will be the same, thus 9v, correct? Total current will be (0.06+0.06) = 0.12 amps. This means I’d be running 9v into a 5v fan which could cause overheating/fan failure/my head catching on fire.
If I hook them up in series - that is, positive terminal of battery->hot of fan 1, neutral of fan1->hot of fan2, neutral of fan2->negative of battery, then the total voltage drop across both fans together will be 9v, so 4.5v each, and the total current flow will be the same across each fan, 0.06amps.
Am I missing anything? It seems to me that running them in series is the way to go - I don’t run too much voltage through either fan and the total current is lower as well (so my battery will last longer).