I am working on a project where I need to convert DC voltages. I am considering buck converters to reduce the heat over a voltage regulator, and I need to go from 12 VDC down to 5 VDC for sensors and user interfaces, and from 12 VDC up to 24 VDC for a stepper motor (I am considering a 120 VAC to 12 VDC 5 A power block as my power supply for the Arduino and several components).
I have seen a few different types of buck converters, and they seem to be divided into either a buck converter in a simple metal box enclosure and a buck converter embedded into a die-cast aluminum shell with fins on them. I was originally considering the simple box design because they are small and won't take up a lot of space in an enclosure, but I am worried about heat shortening the lifespan of components (I do plan to use a computer fan to cool the system), which has me wondering about the die-cast shells as a potentially better option.
I figured that a heat sink would be a good idea in this situation, especially in an enclosure. However, I am not sure how well the die-cast shells actually radiate heat, with being as thick as they are. The simple metal boxes are thin metal and simply won't have the mass to hold the heat. I have tried finding information about the difference between these two options, but I haven't found much yet. Which would you recommend?
***ETA: I'm asking about the difference between these two types of enclosures.
Since you do not give the wattage for your converters, no comment on heat sinking or heat generation is possible. If you do not know the amount of heat generated, you do not know if any heat sinking is necessary.
I have a box full of the popular LM2596. I often use it to drop 12V to roughly 7V then into a LDO VR to get a clean 5VDC. No boxes, I don't recall much heat either.
That doesn't sound very logical. The stepper motor is likely the biggest power drain. Consider a 24VDC supply and then make 12V and 5V from that for your sensors etc
If you're going to make 5V for sensors etc anyway, might as well feed the Arduino directly off of it too.
The above is subject to a couple of assumptions; you'd have to provide some more details as @Paul_KD7HB suggests if you want more specific advice.
You don't want anything to " hold heat"; you want it to be dissipated away from your device.
What is required in terms of heat dissipation depends on the details you've not yet provided.
Not sure what kind of shells you're referring to. Plastic project enclosures?
Thank you for the detailed breakdown. I'm answer each one accordingly.
Edited
If the data sheets are right, the stepper motor will be one of the smallest draws. The stepper motor draws a max of 1.7 A at 24 V. On the other hand, the 12 V components plus the Arduino Mega 2560 draws between 0.9–1.2 A. The sensors, the user interfaces, the computer fan, and data storage use a combined ~0.8 A at 5 V. There is only one component running 3.3 V, so I was going to run that off of the Arduino. Since 12 V is paired with a large current draw and the power needed for the Arduino, it made more sense to switch up and down from 12 V rather than using a series of buck converters to get the range that I need.
The Arduino Mega 2650 requires 7–12 V, so I can't run it on 5 V.
That's why I am asking this. Aluminum has good thermal conductivity, so it makes sense to use it if you are trying to dissipate heat. However, mass can be used to store heat, and a thick aluminum shell might also hold heat. When enclosed inside of a project box of some type, heat is going to be an issue, and I want to make sure that I am not going to kill electronics.
The aluminum die-cast shells that you can see when you follow the link in my original post:
0.6 A at 24 V is 14.4W.
But anyway, regarding the heat what is important is not the power consumed, but the power wasted into heat. And buck / boost converters are about 90% efficient, so you can do the calculations.
What do you expect that will produce a significant heat? And what are the 12V components that consume so much? and how? all the time?
The arduino consumption alone probably is very low.
Calculate the power consumption of everything in the worst case, and from that calculate the power wasted into heat, approximately, based in the datasheets.
But using switching regulators and maybe LDO's for the last volts, the heat shouldn't be a problem, I think. At least regarding voltage regulation.
And I think that I would choose a 24V power supply and one or two buck converters. You have to convert anyway, and buck is a bit more efficient that boost.
It's a big of a challenge to say what is the wattage of the converters that I am going to use.
The overall power draw of the proposed system is probably in the range of 30 W, but not all of this will be contained in the project box (I am trying to protect some of the components from water). Inside the box, I'm probably going to draw 2.5 W at 5 V, 6 W at 12 V for the various components (no need for converter), and 40 W at 24 V, and I plan to include a computer fan to provide ventilation.
For the converters, it's hard to say exactly what the watts are, as I am going to shop around to find one within the range of what I need for my project, and knowing whether or not I need to use a die-cast enclosure or a thin metal box to narrow down what I am shopping for. For the ones that I linked, one is 15 W, and the other is 50 W, but I don't plan to use the full amperage capacity of those converters.
Sorry, I did my math backwards. You're right that it's 1.7A.
The 12 V components include a flow sensor, three solenoid valves, a latching switch, and the Arduino, but only the flow sensor module, latching switch, and Arduino are in the box. The 5 V components include a microSD module, float sensors, use interfaces, pressure sensors, and a few parts, with the user interfaces and microSD module in the box. The only one at 24 V is the stepper motor, but the A4988 modules will be in the box. I figured that it made more sense to go up and down rather than down twice, especially if the quality of the converters end up not being as good as I would like and end up with weird voltages that risk burning out components with the conversions.
I don't expect that many will product significant amounts of heat. However, since several of the components will be enclosed in a box, including the converters, and the system could be running continuously between 6–24 hours, so the heat is going to build up. I plan to ventilate the enclosure to keep things cool during this time.
Honestly, I am just trying to figure out if the thick aluminum shell is going to be as effective or more effective in dissipating heat than a thin metal box. I can't find data sheets for some of these components, some of the components are running only part of the time, some of the components run only under certain settings, so I can't actually tell you how much is going to be waste heat.
To be on the safe side, figure 10% of watts for each device will be heat. Add the up and you will get the heat created by the components in your enclosure. That has to go to the surrounding air outside the box.
You do not want to hold the heat you want to get rid of it. Surface area is your best friend.
I would use a 24V supply then a buck converter to about 8V for Vin on the arduino. Using that will give you some additional filtering which you may need because of the motor. If your 5V load is over 100 mA use a 5V out buck converter as well. When you boost 12V to 24V the current on the 12V side will be at least 2X the 24V side. When reducing it does the same but in the opposite direction. I use about 85% as a rough efficiency, that gives me a bit of cushion.
It's an interesting idea, but dropping to 8 VDC means that I need four different voltages instead of three, which increases components and complexity. The components that I have in mind are rated at 24 VDC, 12 VDC, and 5 VDC (I think that I have eliminated the need for 3.3 VDC). I figured running the Arduino off of the 12 VDC would be the easiest and cleanest, use the same 12 VDC for the few components needing that, increase to 24 VDC for the motor, and drop to 5 VDC for the sensors that need this.
That's essentially what I am trying to figure out with my post. The die-cast aluminum shell has a larger surface area, but it is a lot thicker and has a larger mass that will slow the heat transfer. The smaller box is a lot thinner with a lot less mass, but less surface area. The die-cast shell I think has the components potted that might improve heat transfer compared to the hollow shell of the thinner box.
So the stepper is by far the biggest power draw. 24V @ 1.7A = >40W.
If you were to make the 24V from 12V with a step-up converter, you'd be drawing >3.4A from the 12V rail for just the stepper. You'll incur substantial losses.
It would be best if you specify which modules/components you're going to use. What kind of 12V components are you referring to?
As to the fan: you have a 12V supply, so why not use a 12V fan? A typical computer fan will be in the order of magnitude of 100mA. In your project it may even be run at a lower average current because you're not going to dissipate a huge amount of power in your project box. If you use a 5V fan, you'll just incur further losses in power conversion. Not super harmful, but also not needed.
And now the figures are all different for some reason; 500mA draw from 5V as well as 12V.
That's OK as long as the current draw of that component is not more than 50mA or 100mA or so. What component is it?
No, does not. There reasonable approaches here: use a 24VDC supply and switch down to 12V and 5V for the rest, or use two AC-DC supplies: one 24V and one 12V, and make the 5VDC from the 12VDC supply. The former option (one 24VDC and a couple of step-down converters) is likely to be the most efficient in terms of size, power use and cost.
It's a 5V board. You can supply it with 5V on its 5V pin. The reason it also takes 7-12V is because it has an onboard linear regulator that makes 5V from that external voltage, and the linear regulator needs some headroom to do this. However, you are not obliged to used this regulator and if you're already making 5V for other stuff, you might as well power the Arduino from it anyway. However, if you prefer to feed it with 12V, that's fine, but make sure to only power the Arduino itself from its own onboard 5V regulator, and nothing else because you'll easily overheat the regulator if you feed it 12V. The voltage drop = 7V, so any current draw above 50-70mA or so will be a problem and this includes the Arduino board itself. Better to bypass it so you never un into this problem.
Yeah, sort of, but the questions start with some basic stuff:
How much power dissipation is anticipated in the power supply components?
How big is the project box?
What are the operating conditions for your project; i.e. what kind of ambient temperature will it be working in? Is there airflow around the box?
What will the inside layout of the product box be?
What will the permissible maximum temperature of any component within the box be?
Some of this you will be able to determine with some degree of certainty beforehand. Some of it you'll have to guesstimate, or just plan for a worst case scenario. Some is in your direct control.
As to power dissipation, let's assume you understand my earlier argumentation and you choose to use a AC to 24VDC power supply that you use to make 12V and 5V from. Let's assume the efficiency of your DC-DC converters is around 85%. I'm also going to work with the higher-end figures you gave for your power requirements; note that the uncertainty you've created in this area is pretty massive, so pretty much all bets are off right from the get-go, but still, let's do the napkin exercise.
Your 5V draw will be around 5W/1A. This means around 750mW of power conversion loss during moments of peak power draw.
Your 12V supply will have to supply maybe 15W, which means roughly 2.25W power conversion loss, again on peak moments.
Your 24VDC supply will have to supply 1.7A (peak) for the stepper and ca. 23W (peak) for the 12V and 5V supplies, so let's round up to 65W. We can assume an AC-DC SMPS to run at around 90% efficiency, so this means a 6.5W loss.
The total dissipation of your entire power supply will thus be a little less than 10W, most of which is handled by the AC-DC SMPS.
Your buck converters don't really need any particular encasing etc. as long as they're properly dimensioned. Pick modules with a rating of >=2A (output) for both and you'll be fine. The critical components will be heatsinked already, either through the PCB itself (thermal plane, thermal vias) or using a small radiator heatsink. If you supply airflow, they'll be perfectly happy. The same goes for the AC-DC converter, but you want that to be rated for 4A or so (24V 4A supplies are common and cheap; I use quite a few of them). Again, if you supply airflow, it'll be perfectly happy.
The long and short of it is that it doesn't really matter whether you pick open frame/bare PCB modules, encased ones etc. as long as they're somewhat conservatively rated, and you provide airflow if they're going to be locked up together in a tiny space.
If you run the exercise above for the scenario you planned (24V and 5V both made from a 12V AC-DC supply), you'll see that you'll just end up with more losses and overall higher cost due to higher demands on the 12V supply. There's very little sense to doing it that way even though it will in principle work.
As always, the more specific the information is that you provide, the better your answers will be. As it stands, the power requirements you specify vary wildly and there's otherwise virtually no specific data on your project. That's OK; it just means that you need to figure it out yourself and I hope to have shown above in part how you can approach that. It involves some data, some assumptions, some conservatism and some logical thought. Experience helps a lot, too, but lacking that, you'll just have to be a bit more conservative and probably do some testing to see if your assumptions pan out.
Really? What type of stepper motor is this? Can you provide a link to the datasheet? If the coil current is 1.7A, the current from the PSU is much less, because the A4988 works very similar to a buck converter. And 1.7A is really a lot for the A4988, maybe another driver ( e.g. DRV8825) is a better choice
Can you please post a link to data/specs of the stepper?
From your previous thread, Liquid flow sensor questions you say you are new to Arduino.
Can you please tell us your electronics, programming, arduino, hardware experience?
In that last thread you pointed out you could not see any code for using the analog outputs of some of the flow sensors you looked at.
Sorry. but can I suggest you get down and dirty and start to do some physical experiments in Arduino and evaluate what you have available.
If you are going to use Arduino, then you need to learn how to use it.
Using other peoples code is wrought with problems when you don't understand the basics.
Especially when you need to detail it in a PhD project.
Please list all the hardware you are aiming to use, with links to data/specs, if possible, so we can better advice you.
If you are at an educational institution, use those resources, you are or will be paying for your education whether you use them or not.
There must be lecturers/tutors who can help code in Arduino, advise on sensor selection and other peripherals.
Since you need to convert 120VAC to DC, you might consider also something like this:
You should not try to compare two enclosures when the internals are different.
If the internals were the same, that thicker radiator enclosure would be better. There is a reason why heat sinks are not made of aluminum foil. To spread the heat to the whole surface area you need good conductivity. Within the same material, thicker it is, better it is.
Thanks for the suggestion. I spent a bunch of time searching DigiKey yesterday for power supplies like this, but you end up having to enter all the permutations of the voltages to see all the options (it seems that it can't convert it to combination) and I was struggling to find ones with suitable current for the voltages. This one looks like it might work.
I do have some experience with Arduino as well as coding, so I am not a complete novice, though I don't have as much experience with electronics as I do coding.
I do have a basic grasp of the coding, but some of the parts are more complicated than what I have encountered before with more simple coding. I am not copying code from others wholesale but rather using it to actually understand the code and then write my own (copying code wouldn't be useful when trying to create custom programs). It's not a perfect solution, but it's better than nothing.
I also have friends who are computer engineers, computer scientists, and electrical engineers who have offered to help me with this when I am ready to start testing, but I am not expecting them to teach me everything. I am having to research a lot of stuff myself to try to learn and understand this stuff. When I exhaust my research (Google and academic search engines get you only so far), I ask questions here where people have more specific knowledge than I can sometimes find elsewhere (e.g., my question about flow sensors was because I had found possible options, shared the specs of what I had found, and was wondering if anyone has experience with those components because I wasn't finding any reviews, tutorials, or even some basic details about some of the components, and in the process, I got other helpful information).
I am not willing to share my entire project at this time though as it is a major part of my research and might result in publications. Until I have results published, I can't exactly give out all the details. Once I get things published, I will likely put it all on GitHub for others to use.
