voltage out on raspberry pi or arduino   - Page 1
Forum section: electronics / beginners

author: silviasol
author_rank: Regular Contributor
timestamp: July 29, 2017, 09:38:43 pm
content: Is there a 3v out on raspberry pi and arduino? I had these 15mm mini fans that I sold on ebay quite well. I was going to buy some micro 10/12/15mm sunon fans from alibaba to sell. The 15mm fan was off brand and was 5v, these sunon are 3v. Wouldn't want to waste my money if 3v is not supported. Would 3v be any problems on them using a fan?

author: alm
author_rank: Super Contributor
timestamp: July 29, 2017, 09:44:29 pm
content: What does the pinout for their extension connectors show? Also, which of the half a dozen Raspberry Pi versions and hundreds of Arduino variants that are available are you considering?

author: silviasol
author_rank: Regular Contributor
timestamp: July 29, 2017, 09:51:36 pm
content: Quote from: alm on July 29, 2017, 09:44:29 pmI won't be doing anything with arduino or raspberry pi's, just selling fans that can be used with them.http://imgur.com/a/RnwHCThey are 3v, no one sells the mini fans in 3v, only 5v. So before spending the $9 price for each fan I just want to make sure it will work with 3v. If not on all versions of arduino or pi, atleast the most commonly used. Sorry I really am kind of a nub at arduino stuff, I used the fans I had to cool a 1w led thing I made then I stopped using it so sold the fans.

author: Ian.M
author_rank: Super Contributor
timestamp: July 29, 2017, 09:57:40 pm
content: Thee usually isn't enough spare current capability on the Pi or Arduino 3.3V regulator for a fan and the startup surge of the fan can brownout the 3.3V rail and crash the Pi, or Arduino models that use a 3.3V MCU.

author: wraper
author_rank: Unknown
timestamp: July 29, 2017, 10:22:06 pm
content: There is 3.3V voltage regulator in Raspberry pi. However even if it appears to work fine, you may overload it by attaching fan. Buck converter IC itself should be able to handle it but inductor might we too weak and saturate causing failure.

author: silviasol
author_rank: Regular Contributor
timestamp: July 31, 2017, 11:21:22 pm
content: Ok glad I researched. Thanks alot for the help. Sounds like I would have some unhappy people returning them after it crashes leaving nasty feedback.Here is the specs of the fans. So probably best not to use 3v fans? They have some side vent blower style fans in 5v but no axial in 5v.

author: Ian.M
author_rank: Super Contributor
timestamp: July 31, 2017, 11:59:03 pm
content: For the Pi, you'd probably get away with 3x 1N4001 diodes in series to drop 5V to 3V for the 3V fans.Powering a fan off an Arduino is more problematic as there's limited spare current from the 5V regulator if the DC in jack is being used so even using a diode dropper to move the load from the 3.3V rail to the 5V rail may not help. E.g. for a Uno, if the input voltage is 7V and the board is in open air it will be fine, but at 12V in even 40mA is an extra 0.28W dissipation in the LM1117 regulator which will be marginal in a case at high ambient temperatures.

author: silviasol
author_rank: Regular Contributor
timestamp: August 04, 2017, 03:11:32 am
content: Hmm. So are 5v fans also problematic, or would it just be 3v? Maybe people know this and are routing power directly from the power source thru a separate converter board.

author: Ian.M
author_rank: Super Contributor
timestamp: August 04, 2017, 04:46:01 am
content: A typical Pi is usually powered by fairly beefy 5V SMPSU and due to the limited current available on earlier models for USB peripherals, users are used to doing power budget calculations so there's no problem with 5V fans on a Pi.How often do you see a fan-cooled Arduino project? By the time one realises the need for active thermal management, one probably needs a beefier 5V supply as well, and hopefully the developer has the skills to implement an energy efficient solution to providing 5V.

author: GarthyD
author_rank: Regular Contributor
timestamp: August 04, 2017, 04:54:22 am
content: Re the Raspberry Pi:There is no 3V. There is 3.3V, but the current limit may be as low as 50mA for some models, and may be much lower depending on how you use them. Much is undocumented. I wouldn't rely on the 3.3V rail powering anything unless it uses well under 50mA. The 3.3V GPIO pin limits are much lower too- I'm not sure how low but there are interacting restrictions. What sort of current do you need?If you can't use 3.3V, you'll need to use the 5V. This'll give you a *rough* idea as to what the various models can power:https://www.raspberrypi.org/help/faqs/#powerReqsThere is also a polyfuse, and I think it differs between models. You'll need to watch the current going through that.I don't know enough about Arduinos to answer the other part of your question.