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I have multiple (9v 1500mA to 9v 3500mA) LED light fixtures that I have tested chaining a single fan (12v 5.2w and 12v 0.16A fans) and they seem to work under the brief test with enough air flow for my needs.

Anything I should be careful about while doing this and any direction to better understand if there are concerns or how to calculate? I am a software engineer, just getting into electronics via raspberry pi projects, so still learning as I go. The actual project right now is regulating / climate control of multiple dart frog terrariums.

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    \$\begingroup\$ It will just rotate slower and blow less air compared to 12V nominal voltage. Nothing to worry about. \$\endgroup\$ Jul 15, 2017 at 23:08
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    \$\begingroup\$ They ought to run down to 1/3 V but may a bit more to start. The current is fairly constant, regulated internally while the RPM increases with V+ \$\endgroup\$ Jul 15, 2017 at 23:16

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There is generally no harm in running a fan or any DC motor on lower voltage.

If the voltage is too low, then the motor will not run (or continue running if already spinning but not start), because there is not enough torque generated to oppose the “cogging” effect of the layout of magnets inside the motor. (This effect is why when a fan is turned off you will see it bounce and stop at a particular angle, and you can feel it by pushing the blades around). In this case, the motor is stalled and in principle this could burn out the motor just like any other stall, but that is less likely as the voltage and therefore the stall current is lower.

If you find that a fan promptly starts up at a given lower voltage, then you should feel free to use that lower voltage.


If you need a fan to operate at a wide range of speeds including very slow ones, then rather than changing the supply voltage, it is better to use a fan which has a PWM (pulse-width modulation) input, which is driven by a microcontroller or other oscillator (e.g. a 555 chip) you provide and tells the brushless motor controller inside the fan what speed to run at. Because the controller has access to the full supply voltage when needed, it can start up and run at much lower speeds.

Since you're interested in climate control, this might be a good future project — a temperature-controlled fan. It can be done with a single-purpose fan control IC, a microcontroller, or even with separate chips (an oscillator and a comparator at minimum).


Finally, I'm guessing that you don't have this problem, but just to avoid any confusion for other readers: from context, when you say "LED power supply" I assume you mean a regular (constant-voltage) 9 V power supply, not a constant-current LED driver. You should not run a fan off the output of a LED driver.

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Your fan will operate. It will make less noise. It will waste less power. It will last longer. Because it turns slower it will shift less air and it will have less back pressure. All you should do is check your heatsink temperature and deduce the junction temperature. If the junction temperature is low then you are good to go.

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    \$\begingroup\$ AFAIK dart frogs don't have heatsinks or junction temperatures \$\endgroup\$
    – anna328p
    Jul 16, 2017 at 9:46

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