Anyone have a source for good reliable Buck Converter? Checked Digikey, but couldn't find what I wanted. I am looking for 24 to 12 V DC converter.
Thanks.
Try Pololu
Or Oki Murata at Digikey
https://www.digikey.com/en/products/filter/dc-dc-converters/922?s=N4IgjCBcpgrATLKoDGUBmBDANgZwKYA0IA9lANogAcA7DWFSALrEAOALlCAMrsBOASwB2AcxABfYgFp4yEGkj8ArkVIUQSYgE5mbTpBATpO6PKjLVZSJQgsQHLhMkhZ10gGsBAAgC2SvpjsmMziQA
You don't say how much current you need.
Good question however now that we know the voltage what is the current and the input voltage range?
do you want an inexpensive one or a top of the line. You can get them for less then $4.00 from Aliexpress, ebay, and others, depending on current. Many of these are also adjustable. I do not run them at capacity and have several that have been going for over three years.
On Amazon, search: buck converter
I have used two of these for over a year now. About $2.00
LM2596 DC to DC Buck Converter 3.0-40V to 1.5-35V Power
3 amp 92% efficiency
larryd:
On Amazon, search: buck converterI have used two of these for over a year now.
LM2596 DC to DC Buck Converter 3.0-40V to 1.5-35V Power
Saw those, but the reviews scared me off. I was hoping someone here would have tried something like these. Many thanks for the response.
gilshultz:
Good question however now that we know the voltage what is the current and the input voltage range?
do you want an inexpensive one or a top of the line. You can get them for less then $4.00 from Aliexpress, ebay, and others, depending on current. Many of these are also adjustable. I do not run them at capacity and have several that have been going for over three years.
Sorry, should have given a little more information. I am designing a machine to turn fishing rods while the epoxy dries. I will be using steppers because I need to rotate the rod a fixed amount, stop for a period of time, then rotate again. I can program this using a stepper. The voltage for the stepper is 24V and I want to use the same power supply to power the arduino Nano. So buck converter is just the thing.
Pololu units are probably a better quality, however, the ones I posted work okay for me.
A Nano operates at 5V, so you need a 24V to 5V buck converter, not to 12V!
Lots of dirt cheap 2-3A rated buck converters out there (should be perfectly fine for about half the rated current, maybe even more). I've always used the ones with fixed 5V output, cheaper than the adjustable ones and I never had the need for other voltages (always need most power in 5V, a linear regulator can take care of the lesser 3.3V needs).
wvmarle:
A Nano operates at 5V, so you need a 24V to 5V buck converter, not to 12V!
OK if the Op feed the RAW input.
wvmarle:
A Nano operates at 5V, so you need a 24V to 5V buck converter, not to 12V!Lots of dirt cheap 2-3A rated buck converters out there (should be perfectly fine for about half the rated current, maybe even more). I've always used the ones with fixed 5V output, cheaper than the adjustable ones and I never had the need for other voltages (always need most power in 5V, a linear regulator can take care of the lesser 3.3V needs).
Good point. Probably a better idea in the long run. Thanks!
Careful, some of the regulators on those cheapy clones can't tolerate 12V, I would go with 5V to the 5V pin.
Even if they tolerate 12V that's 7V dropped, and the regulators doesn't have much in the way of heat sinking...
Better to have the buck converter, that's gotta be there anyway, to go straight to 5V.
ov10fac:
The voltage for the stepper is 24V and I want to use the same power supply to power the Arduino Nano. So buck converter is just the thing.
Yes, a common misunderstanding fostered by confusing information on the Arduino site and some others.
The point is this:
You have an ATmega328 microprocessor chip.
It is intended to run on 5 V. That is the design voltage, at least to use a 16 MHz clock which is what the Nano has. To use USB, it also has a USB interface chip which is - generally - designed to run on the USB voltage which is 5 V. That is 5 V OK? 
I repeat my "stock" explanation to this question every time. The "Vin" - or "Barrel jack" on a UNO - is nothing more than a legacy "novelty" from the times ten or twenty years ago when 5 V switchmode power supplies were not common as they now are. It allowed you to use unregulated 9 V "plug packs" (US: "Wall warts") which were the common supply for computer "phone" modems and ADSL boxes which contained heat-sinked 7805 regulators. But the regulator on a tiny Nano or even the UNO board has minimal heat-sinking and is only suitable for simple demonstrations of the basic board and a few LEDs.
For protection, there is a diode between the USB connector and the 5 V supply line (which is also the "5V" pin) in the Nano, so plugging 5 V power into the USB jack loses a significant part of a Volt before it gets to the 5 V line. According to the original circuit, this would be a SS1P3L with only 350 mV drop and capable of passing one Amp, but depending on what clone you have, this may be quite different.
So you can simply forget the on-board regulator and "Vin" and when you have a nice regulated supply of 5 V - generally from a switchmode "buck" regulator - you want to convey it to where it is actually required - the "5V" pin and your other modules. 
Many thanks to everyone for the vast array of information. I have changed my mind and will go with the buck converter to 5V output. The more I thought about it the more it made sense to go that way. I don't know why I was thinking 24 to 12 since I really need 5V.
Thanks again and I think a better power supply from a respected company here in the USA is the way to go even though it is a little higher in price. So final design will reflect a 12 or 24 volt (depending on the stepper motor) to 5V buck converter.
Stepper motors are current driven, the voltage you can use depends on your stepper driver, many can take up to 30V or more. Check the datasheet of your specific driver. 24V generally will do fine.
The same sites I linked to, Pololu and Oki Murata at Digikey, offer 5V converters also.
wvmarle:
Stepper motors are current driven, the voltage you can use depends on your stepper driver, many can take up to 30V or more. Check the datasheet of your specific driver. 24V generally will do fine.
Thanks, I have the motor, actually I have about 10 or 20. Most NEMA 17 but a few larger ones. I will use something a little larger for the rod lathe, and the 17s for the rod dryers. Most are 2 to 3 v per coil. I am using an A4988 controller that I have used before. In fact I have a PCB for a nano and the same driver that I designed for another purpose. Only problem is that its designed for 12V power to the VIN pin and to the controller. (which is why I was looking for a 24 to 12 Buck Converter) I may have to do a redesign which would not be much of an issue assuming I can find the original.
Make sure you know the current rating for those steppers. Voltage rating is largely irrelevant.
If you insist on using Vin, feed it 6.5-7V. Not 12V, too much strain on the regulator.
If you don't draw too much current from the Arduino 5V regulator, you might want to reconsider using the Vin pin with 7 volts coming from the SMPS.
Using the Vin pin might give an extra level of confidence as the output of the SMPS might not stay at 5V when set to 5V; whereas 7V ±1 volt to the Vin pin will not damage things.
In any event, I am in the habit of placing a Ferrite bead between the output of SMPS and the Arduino.
On SMPS you may want to remove the adjustment potentiometer and replace with fixed SMD 1206 resistors.
larryd:
If you don't draw too much current from the Arduino 5V regulator, you might want to reconsider using the Vin pin with 7 volts coming from the SMPS.Using the Vin pin might give an extra level of confidence as the output of the SMPS might not stay at 5V when set to 5V; whereas 7V ±1 volt to the Vin pin will not damage things.
In any event, I am in the habit of placing a Ferrite bead between the output of SMPS and the Arduino.
On SMPS you may want to remove the adjustment potentiometer and replace with fixed SMD 1206 resistors.
I have seen that recommendation from other sources. A good idea. Just one question what is "SMPS" not familiar with that acronym.