Can a 12 Vdc axial fan be connected to a 15 Vdc or -15 Vdc? - Page 1
Forum section: electronics / projects

author: mike buba
author_rank: Contributor
timestamp: January 19, 2023, 07:20:27 pm
content: I have a +/- 15Vdc source. Most of the axial fans are +12 Vdc (10.8 - 13.2 Vdc). What will happen if the fan is connected to +15 Vdc?What will also happen if the fan is connected to -15 Vdc? DC motors are reversible, and I would expect it to rotate in the opposite direction, but most of the fans have a permanent electrical protection against reverse polarity.

author: mariush
author_rank: Super Contributor
timestamp: January 19, 2023, 07:30:36 pm
content: What would happen? Unknown ... depends on brand, how they made the fan etc etcCould be it will work fine. Could be it works but after xx hours of use, you end up with motor seizing, maybe it overheats and the insulation melts off the coils and kills the motor.A very easy solution would be to add a few diodes in series with the voltage to bring it down to under 13v-ish.A basic 1n4001 .. 1n4007 diode drops around 0.7v so just 3 diodes in series would drop 2v, bringing 15v down to 13v.Alternatively a basic 7812 linear regulator would also work.

author: srb1954
author_rank: Super Contributor
timestamp: January 19, 2023, 08:31:34 pm
content: Quote from: mike buba on January 19, 2023, 07:20:27 pmMost modern fans have internal electronic controllers so connecting in reverse polarity is quite likely to damage them.

author: ajb
author_rank: Super Contributor
timestamp: January 20, 2023, 03:37:18 am
content: Voltage aside, you can run a fan from a -15V supply, as long as you get the polarity correct-- in this case meaning that the fan's negative terminal is connected to -15V and the positive terminal is connected to ground/0V. The fan won't know the difference. Note that PWM input/output, if the fan has those, will be referenced to -15V instead of to ground. Assuming a typical computer-style brushless fan it will NOT run in reverse if you connect it the other way, because it has electronic commutation--instead it will either blow up, or simply not work, depending on whether or not it has reverse polarity protection.

author: DavidKo
author_rank: Frequent Contributor
timestamp: January 20, 2023, 05:49:39 am
content: Since the fan have constant consumption, resistor in series will do the job. You should only care about the power dissipation (with diodes it is the same). If it has automotive qualification, it will probably handle 8-16V without issues.

author: Shay
author_rank: Regular Contributor
timestamp: January 20, 2023, 11:44:00 am
content: I'm going to assume there is a chance of actually connecting it to the -15V, as it is not a one off thing, and you want to know what will happen.There are 2 really possible solutions:1. There is interal diode in series which protects the fan from reverse. So nothing will turn on.2. There is no protection, and it will burn an internal IC.To solve both of the issues of the higher voltage and potential reverse connection, add a simple bridge rectifier. This will make sure the fan will receive +13.8V. Which should be fine.

author: David Hess
author_rank: Super Contributor
timestamp: January 20, 2023, 04:34:58 pm
content: The fan will run somewhat faster on 15 volts rather than 12 volts. Just make sure to get the polarity correct.

author: Zero999
author_rank: Super Contributor
timestamp: January 20, 2023, 06:22:59 pm
content: Do you have the fan's data sheet? Is it specified up to 15V? If you're worried, just the LM7812, or LM317, which can be used to power the fan from either +15V or -15V.