Hi folks,
I'm working on a project that will control 115VAC power to a hot-water recirculating pump. I intend to use a Arduino Nano Every (the newer Nano, https://store.arduino.cc/usa/nano-every) as the controller. I have a few power-related questions.
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I know the Arduino Nano (original Nano) can take a 12V power input. I cannot find clear documentation on the Arduino Nano Every, though -- the specs just aren't detailed enough. Does anyone know if I can power it off 12V without liberating the magic smoke? I don't know that I can use a 5V power supply for my project, because I'm planning to drive three relays, and with 5V relays, I'd need a power supply that can drive about 3 Amps to accomplish that -- that's a rather big draw. With a 12V supply, I can drive the Arduino and three 12V relays with less than 0.5A, I believe. And anyway, I need 12V for one of the off-board components in the project -- can't escape that.
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Shopping for 115VAC -> 12VDC power supplies, I've found several good (and inexpensive) options. One in particular includes a recommended circuit design for using it safely and efficiently. That one is here: https://www.cui.com/product/resource/psk-s5b-l.pdf. The recommended circuit is in the attached image. My question is: How important are all the components in this recommended circuit? I haven't shopped a lot for discrete components, but the cheapest 120uF electrolytic capacitor I could find at DigiKey was a $47.00 tantalum cap!! That is shocking! The varistor and the ceramic disc cap are cheap enough, as is the TVS diode. But the ecap just torpedoes the project budget. Are there other ways to wire up a power supply like this that don't require so much peripheral circuitry, without hugely compromising the performance and safety of the resulting power supply?
- I know the Arduino Nano (original Nano) can take a 12V power input. I cannot find clear documentation on the Arduino Nano Every, though -- the specs just aren't detailed enough.
The schematic shows a 5V regulator.
The recommended circuit is in the attached image.
My question is: How important are all the components in this recommended circuit?
I don't know... It's odd to require additional components for a "complete" power supply. There used to be some switching supplies that required a minimum load, but I believe most current designs have a small load resistor built-in (if the particular design requires it).
I haven't shopped a lot for discrete components, but the cheapest 120uF electrolytic capacitor I could find at DigiKey was a $47.00 tantalum cap!!
In this kind of application, capacitor values are not critical and you can almost always go higher. (And most electrolytic capacitors have a tolerance of +/- 20%, and they may get worse than that as they age...)
Thanks @DVDdoug and @JCA34F. I guess I'll either do a step-down like the one you suggested or find a dual voltage power supply. The only other alternative I have is a pure 5V supply and current-hungry 5V relays...
I'm curious -- where does one go to look for those schematics? I can't seem to find anywhere on the Arduino website to search for them.
Cheers!
Chris
DVDdoug:
The schematic shows a 5V regulator.
Actually, I'd appreciate another hint on reading the schematic. Or maybe I misunderstood your comment... I see the regulator that provides 5V operating voltage for the Nano Every -- but I don't see constraints on Vin. I'm not knowledgeable enough to know from the schematic what the upper limit on Vin really is -- but I'm sure there is a limit. And that is really the question-- can I put 12V on Vin, and expect the Nano Every to operate normally and safely?
For comparison, the specs for the original Nano (v3.3) are listed here: https://store.arduino.cc/usa/arduino-nano, and they say "Input Voltage: 7-12V". I found the schematic for the original Nano here: https://content.arduino.cc/assets/NanoV3.3_sch.pdf. Like the Nano Every schematic, a 5V regulator is shown, but there is no explicit marking on the schematic that says what the Vin range is. The schematic lists the regulator as LM1117IMPX -- and a quick search for that part finds this page: https://www.mouser.com/ProductDetail/Texas-Instruments/LM1117IMPX-50-NOPB?qs=X1J7HmVL2ZGGwLlD0uGqKQ%3D%3D ... which suggests the max input voltage is really 15V.
Going back to the Nano Every, the schematic shows the regulator with a part number of MPM3610 -- another quick search finds this: https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MPM3610GQV/document_id/2090. This says the max input voltage is 21V.
So, I freely admit there are several logical leaps in my research and thinking here, but it seems to me that the Nano Every should be able to handle a 12V input power supply quite easily. Is my thinking correct? If not, I'd truly be grateful for some hints about where my errors are. 
Thanks in advance!
And.. apologies for the URLs that are not linked -- I couldn't find the markup guide for this forum...
Just in case anyone else has this same question (because neither the Arduino product comparison table nor the table of specs on the Nano Every product page mention Vin at all), I did finally convince myself that I was correct -- Nano Every can take any Vin from 6V-21V. Proof is on the side of the product box:
Thanks all for your help! I really appreciate it. I was able to find the caps I needed for $0.10/ea based on your helpful suggestion that I can always use a larger cap than specified.
Cheers!
