Hi everybody, I have a question regarding step down converters. I found this one on amazon capable of transforming 24V DC to 12V DC. Are they any good? Do you have experience with them? The other ones I found have a giant heatsink. So my best guess is the difference is heat dissipation through that giant heat sink vs heat dissipation through thin air. Thoughts on this?
Read up on switching DC to DC converters. The one you show is a boost (increases voltage) buck (decreases voltage) converter. They also come in boost only (output higher than input) and buck (output lower than input) versions. The magic is in the high frequency switching, which is like it sounds. It switches the input on and off at a high rate. Google search is your friend, look for a non-math heavy description, not one full of differential equations for (no offense intended) grad students. If you’re interested you can also read up on the less efficient but usually cheaper linear voltage regulators.
Like all cheap parts they come in an uncertain range of quality. Big heatsinks mean cooler operating temps and potentially longer life.
I use these extensively. (I also work with the people who designed the guts of the chip used for this.) They work fine. They’re pretty hard to kill unless you run them way over their rated current limit for quite a while. The chinese manufacturers who make this really skimp on the input and output capacitors: this thing is supposed to provide 35v out, but the cap is only rated to 35v. That’s not a good idea. But if you derate the input and output voltages, they’ll do a good job for you.
By the way, I don’t know what other ones you’re referring to. If they have a heatsink they are probably a linear regulator, which converts, say, 40V to 12V by literally burning 28V as heat. This is a switching regulator, which converts 40V to 12V by switching on 30% of the time, and switching off 70% of the time, and using that big inductor and those capacitors to (I’m summarizing here) average out those pulses and produce the voltage you want. The result is that the only heat it has to dissipate is very small inefficiencies in some of the switching process. The problem with switchers is that they generally inject a fair amount of noise at the switching frequency into whatever’s running off their output, but for most uses that’s not a problem.
what do you want to use it for?
Actually I want to use them to convert the voltage from 24v PSU to 12v for the Mainboard. @Kirk_Yarina didn’t feel offended, just wanted to know the difference. @John_Bump thanks for the heads up!
i would think it works assuming you do not have some special display or other 5v devices (fans, servos etc). arduino and such boards have a voltage regulator from 12v down to 5v so the spikes should be handled there.
Amps. This one is limited to 3 amps, at the very best. I wouldn’t use it if you want to draw more then 2 amps continues.
My local dutch shop sells these, which is where I found the specs: https://www.tinytronics.nl/shop/nl/spanning-converters/step-down/dc-dc-verstelbare-step-down-buck-converter-lm2596-3a
If you are planning to run motors or a hotend. This is not your solution. If it’s only board power, and the motors/heaters are ran from the 24V, then it’s fine.
@Daid_Braam the one I posted is rated 3A also. Depends on the motors if it works or not right? So actually a linear step down converter would be more desirable. The one I found is rated 20A.
Linear waste a lot of power. At a full rated load of 20 amps, from 24v to 12v it would waste 240watts of power, which is insane if you even found a linear voltage regulator like that.
Why do you want to go to 12v anyways? Why do you use a 24v power supply if you want 12v.
Most motor controllers can handle up to 35v, and most control boards too.
it would probably be cheaper to buy another supply… make sure you have common ground if you mix currents.
@Stephanie_A The initial idea is to power a 300x300mm (~2 ohm) bed from a 24V PSU to get 12A for heating it. The printer has a 12V board though and I actually don’t want to change the board and compile/configure a new firmware for it. So I thought it might be a good idea to step down the voltage for the board so it gets the desired 12V.
@Daniel_Stauffer what you want is a buck converter. Make sure it is a buck and not boost. They work pretty well. Most control boards have them onboard to drive the controller
For what you want it for a buck converter should work fine.
@Daniel_Stauffer motors are generally 0.8A to 1.2A, and that’s average current, not peak. So, no, you cannot run motors on that regulator.
Boards running on only 12V are odd, generally most of them are designed to run anything between 24V and 12V. Running motors from 12V supplies is actually a bad thing for certain motors.
If you want to run drivers, no. But if it’s just the IC, it should be fine. Most are good for around an amp
If you’re pushing that much power you might as well go 120v ac power with an SSR. 12 amps is a huge amount of current, and likely to cause a fire unless you have proper overrated connectors and wires.
(terminology: buck switcher reduces voltage, boost increases it. buck/boost usually can run its output either above or below its input, although some of them are inverting, as in they turn 12V into -4V, and SEPIC and Ćuk converters are likewise able to provide an output either above or below their input, with different topologies and usually higher efficiency than a buck/boost. Usually boost/buck is used to specifically identify a boost switcher driving a buck switcher, where a buck/boost is usually an integrated unit.)
@Stephanie_A The connection goes from the PSU to a 24V/30A mosfet and from there directly to the bed. So 2.5mm2 cables should do it, I only want 12A so I have about 20A left. The connections are going to be crimped, the only modification I have to make on the bed is a terminal connector instead of soldering the wires directly to it I think.
@John_Bump the ones I mentioned can do both I think… Right now I am thinking of failure due to vibrations in the machine. They could loosen the voltage adjustment.
Actually this discussion makes wonder a little bit. The printer is a kit and the parts are driven by a 12V board along with it’s psu. So if the board takes 12V from an actual 12V rated PSU, why shouldn’t it take 12V from a 24V PSU? It is able to run motors, heaters etc. from the original PSU, so it should run them from the bigger PSU also.
Something not mentioned here is that some of these boards have different ground (the - side on the in/out) voltages. If there’s not a direct short between IN- and OUT- I wouldn’t use it with any of the standard controller boards.
The issue here is that if you’re running the PCB heater and the electronics off the same supply (but bringing the voltage down for the electronics), then it’s expecting ground to be ground everywhere. If it’s not, you might get weird results, such as a fluctuating output that isn’t clean or useful for what you want.
Good point Cristian/Stuart! If the input and output grounds on the switcher are different potentials, I’d expect a dramatic release of some magic smoke.
I use 24V for steppers and hot end, 12V (via the exact same buck regulator pictured above) for fans (much wider fan selection for 12V than 24V), and 120V (line voltage) + SSR for heated bed. Not using 12V or 24V for bed allows for much smaller (and more importantly fanless=silent) 24V supply. That combination gives you the best system power efficiency, stepper performance, fan selection, and lowest noise increase (the SSR clicking is the loudest part of the power supplysystem) I can imagine. Also 24V means 1/2 the current to the hot end heater vs 12V, so I can just get away with 2 CAT-5 cables for all my hot end wiring.
And this was basically explained already, but linear regulators need a huge heat sink because the voltage difference between the input and the output is multiplied by the output current and dissipated as heat. Waste heat = (Vin - Vout)*ILoad. Switching power supplies use magnetics to store energy so there is much less waste heat regardless of output current or I/O voltage difference. They’re typically >90% efficient nowadays, so they don’t need a large/any heatsink (often the wasted heat is so low that the PCB itself is the only heatsink needed, as shown in the regulator photo above).
I think I get it now. Thanks so far for the good input. Is there actually any PSU available of providing both 12 and 24V at 300W? And how do you separate the Mainboard from the motors/drivers to use 24V on them?