I'm going to build a humidifier. The mist maker uses a 24VDc input, the rest of the components I'm going to use (computer fan and Arduino nano + DHT 22) use 12VDc. So my question is which of the following power supply is preferable and why:
a) 24VDc PSU and a step down converter 24V to 12V
b) 12VDc PSU and a step up converter 12V to 24V.
Thanks in advance!
What power is used at each voltage? Better to drive the lower power rail from the higher power rail then
the converter can be cheaper/smaller.
Well, converters are equally cheap (from Ali). So the question is more from performance / best practice perspective.
As for power:
24V: mist maker: 0.2-0.8A (haven't selected one yet)
12V: arduino ca.0.04A (ok, let's put it even 0.06A) and fan up to 0.25A, total 0.3A
So PSU would be either 1A or 2A depending on mist maker, since I haven't figured out the difference, most of them are 0.2A, but there are some 0.8A ones.
24V might be up to 20W, 12V is 4W. I'd suggest 24V to 12V converter rated at 5W or so.
Unless you find a 12V mist maker of course...
Got it, thanks!
Well, converters are equally cheap (from Ali). So the question is more from performance / best practice perspective.
Actually, Mark's point is that they won't be equally cheap if one rail has much higher power requirements than the other. In your case, a 20W converter is going to be significantly bigger and more expensive than a 4W converter.
I wouldn't throw 12V at a Nano. It'll probably make some smoke instead of mist.
Jiggy-Ninja:
Actually, Mark's point is that they won't be equally cheap if one rail has much higher power requirements than the other. In your case, a 20W converter is going to be significantly bigger and more expensive than a 4W converter.
I'm currently looking at these two: step down (LM2596) and step up (LM2577), both seem to have necessary capacity for me and price is the same.
INTP:
I wouldn't throw 12V at a Nano. It'll probably make some smoke instead of mist.
Why not? According to specs, it's fine with 12V, googling also proved that people didn't have any problems with feeding it with 12V. So could you please elaborate?
12V is the maximum voltage - the higher the Vin the less current you can draw from 5V without
overheating/cutting out the regulator. That may not be "fine"... Its a small board so the power
handling of the on-board regulator is necessarily limited. Are you drawing any current from 5V
for external sensors/devices?
Yes: 4-digit-7-segment display, DHT22 + 2 x IFR540 to control the fan and switch the mist maker on/off.
antti_s:
I'm currently looking at these two: step down (LM2596) and step up (LM2577), both seem to have necessary capacity for me and price is the same.Why not? According to specs, it's fine with 12V, googling also proved that people didn't have any problems with feeding it with 12V. So could you please elaborate?
I would not trust sub-$1 modules to do 20W of voltage doubling well. You have no idea what the specs of that inductor are, and that's by far the most critical component for switching regulator.
antti_s:
Why not? According to specs, it's fine with 12V, googling also proved that people didn't have any problems with feeding it with 12V. So could you please elaborate?
According to specs, 12V is a max. According to common sense, running things at max tends to be a bad idea. According to actually reading many cases of fried Nanos, your Google proof is dubious. According to your desire to live and learn, go ahead and just ignore what I said.
Jiggy-Ninja:
I would not trust sub-$1 modules to do 20W of voltage doubling well. You have no idea what the specs of that inductor are, and that's by far the most critical component for switching regulator.
Let's set price & quality question aside:) (after all, I can make converters on my own with LM7812 and LM7805, should I need 5V as well). I think the general idea is that in my case it's better to use the step-down one, right?
INTP:
According to specs, 12V is a max. According to common sense, running things at max tends to be a bad idea. According to actually reading many cases of fried Nanos, your Google proof is dubious. According to your desire to live and learn, go ahead and just ignore what I said.
Thanks, for elaborating, however I still don't understand why it's a bad idea if it's within the specs limit, even though on the border. If the issue here is what MarkT mentioned or something else, that has technical explanation, I'd be grateful if you could explain.
MarkT already gave the technical explanation. If you're refusing to believe it, that's all you.
Use a separate buck converter and spare your tiny smd regulator. Or go spend a few years learning about electronics so that what MarkT said will make sense to you instead of questioning solid help just because it currently doesn't make sense to you.
INTP:
MarkT already gave the technical explanation. If you're refusing to believe it, that's all you.
Use a separate buck converter and spare your tiny smd regulator. Or go spend a few years learning about electronics so that what MarkT said will make sense to you instead of questioning solid help just because it currently doesn't make sense to you.
Where do I mention that I'm refusing to believe what MarkT wrote?
Let's go and try to read what MarkT wrote, shall we? He says that it might not be fine and the way I see it, the key aspect is how much current I will draw from nano. Please correct me if I'm wrong in my assumption.
I see that you're trying to make a point not to feed nano with 12V, but instead of answering why you're just being arrogant for no clear reason.
The "arrogance" started on your side when you think Google corroborates your faith in the datasheet spec as if your baseless ignorance supersedes advice coming from real understanding and experience. That's fine, nothing unusual really, so I do encourage you to go with your plan and share your results. You may single handedly declare all of those who have fried their Nanos as complete liars because yours didn't.
I'm sorry if you took my google-comment as arrogant, nothing like that was intended. However, since you're just continuing with the arrogance on your behalf and ignore my comments there's really nothing I can add.
And back to technical aspects.
@MarkT, could you please clarify, if I got your message correct: 12v to nano isn't ok if I draw current from nano at all or there's some kind of threshold value?
I'm fine with adding (or not adding) LM7805 between 12V and nano if that makes sense in my case.