Arduino Forum

Using Arduino => General Electronics => Topic started by: Qdeathstar on Sep 10, 2019, 05:13 am

Title: 48v to 12v dc converter
Post by: Qdeathstar on Sep 10, 2019, 05:13 am
Hello guys,

i am working on a project to control vast amounts of leds. Due to the long distances and current requirements involved, i plan to distribute 48v and step down to 12v locally.

Originally, i was going to use these

https://www.amazon.com/uxcell-Step-Down-Waterproof-Converter-Transformer/dp/B01ENGOA4S

one for each 5m of led strip.  However, i would like to make the project modular... and easier to install so i found some connectors i can make a pcb to distribute power and make the project modular but for this to work i need to be able to put the converter on my own pcb so i can get rid of all the wiring...

I found these:

https://www.mouser.com/ProductDetail/TDK-Lambda/I3A4W008A033V-001-R?qs=sGAEpiMZZMt6Q9lZSPl3RQsOIly2NLEkmTVN%252BtkV7YUVCu8Gyj6vkQ%3D%3D

But i think in the quantity i need for the project, i can make my own for a better price. What is in the converter from uxcell? Is it just a control chip, diode, mosfet, inductor and capacitors? What determines the current output?  I need a minimum of 80w @ 12v....
Title: Re: 48v to 12v dc converter
Post by: Grumpy_Mike on Sep 10, 2019, 08:45 am
Quote
But i think in the quantity i need for the project, i can make my own for a better price.
Making a buck or boost converter is one of the hardest things to do in electronics. I have managed many specialist power supply engineers in my time and have never had one that could make a successful design in less than three iterations of the design.

The big problem is stability, unless the PCB is "right" they will go unstable at certain currents. This gets more critical as the current increases.

There are cheaper designs on eBay but the ones I have seen and bought claim current capabilities that are totally unrealistic. One could even say a total lie.

Component choice is also critical especially the inductor.
Title: Re: 48v to 12v dc converter
Post by: Wawa on Sep 10, 2019, 11:18 am
Efficiency drops with a larger voltage difference.
48>12 is a 75% drop, and efficiency could drop to ~90%,
meaning 80watt could dissipate about 8watts in the converter.
I doubt a 1" x 3/4" board can handle that with just air cooling.
Leo..
Title: Re: 48v to 12v dc converter
Post by: manveen_singh on Sep 10, 2019, 12:28 pm
The big problem is stability, unless the PCB is "right" they will go unstable at certain currents. This gets more critical as the current increases.
were you making the converter with an IC like lm2596 ? or were you using some mosfter f ,inductor or other passives to make your converter ?
Title: Re: 48v to 12v dc converter
Post by: Grumpy_Mike on Sep 10, 2019, 02:25 pm
Quote
were you making the converter with an IC like lm2596
Yes of course, and following the manufacturer's recommendations as to PCB layout. And remember these were experienced professional engineers.
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 10, 2019, 03:26 pm
I was able to successfully design a 12v to 200v dc dc converter,  but was low current...

It seems like inductor choice is the bigger problem... then keep the tracks short and wide... I was actually able to find a detailed data sheet last night.

Just had to know the right search term "switching voltage regulator"...

Sadly I'm on my phone so I can't post the data sheet, but it has a drawing for a 75 watt power supply which I can make work if I had too by lowering the brightness of the leds a little.. they aren't going to be full white on most of the time anyway.
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 10, 2019, 03:32 pm
Once one design is working, certainly it has gotten posted somewhere on the internet? I don't need to reinvent the wheel...
Title: Re: 48v to 12v dc converter
Post by: wvmarle on Sep 10, 2019, 04:46 pm
There exist constant current LED drivers that take a wide voltage range as input. Those may be suitable for your project as well.

Where does that 48V come from?
Title: Re: 48v to 12v dc converter
Post by: MarkT on Sep 10, 2019, 09:03 pm
48V is the highest standard DC voltage without legal safety issues.  Many systems use 12V, 24V, 36V, 48V, 60V, 72V.  At/above 60V its no longer "low voltage" so various safety regulations apply.  Power over Ethernet uses a nominal 48V for instance.

Note that a multiple of 12V is used due to the availability of 12V lead acid batteries.

Mains supplies producing these voltages are fairly commonly available, I assume that's the original power source,
and that there's a reason to not supply mains cables everywhere within the project.  Low voltage wiring can be
much thinner for instance since the insulation doesn't have to be so thick.
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 10, 2019, 11:32 pm
I am powering ws2812b leds so I don't think a constant current driver will be suitable. I'm just a little surprised there isn't a board layout that works laying around the internet somewhere. Seems like it would be fairly standard..

I am getting the 48v from a meanwell power supply dropping the power for the reasons MarkT has illustrated
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 11, 2019, 04:36 am
datasheet for the chip i'm considering using, it has a nice drawing for 75w...

https://www.analog.com/media/en/technical-documentation/data-sheets/3845fd.pdf
Title: Re: 48v to 12v dc converter
Post by: wvmarle on Sep 11, 2019, 05:01 am
I am powering ws2812b leds so I don't think a constant current driver will be suitable.
Neither would be a 12V supply... Those things need 5V, and the standard flexible strips a bit more than one power point every 5 meters, you will have to place 5V wires in parallel and connect them every meter or so. If you have the 30 LED/m strips you may get away with powering it from the middle but still not a good idea. With any higher numbers of LEDs, no chance with a single power point per 5m strip.

By the way, remember to connect the GND and DI/DO between the strips, NOT the 5V.

datasheet for the chip i'm considering using, it has a nice drawing for 75w...
You're never going to replicate anything near that with a home-built circuit.
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 11, 2019, 01:52 pm
i have got 12v strips :P. Google it brah.

Why can't i replicate it? It's very detailed even down the the component choice. Only they they didn't specifically list is the model inductor but they did give a value, and elsewhere in the datasheet it has some detailed information about picking inductors...
Title: Re: 48v to 12v dc converter
Post by: wvmarle on Sep 11, 2019, 02:37 pm
I am powering ws2812b leds
Have you checked the datasheet (https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf)? It clearly states supply voltage maximum 5.3V.

i have got 12v strips
One of these two is false. WS2812B LEDs can NOT handle 12V.

I'll take your word on the 12V and direct addressable part, but the LEDs are certainly not WS2812B. Maybe your strips are outfitted with WS2815 LEDs (http://www.normandled.com/upload/201808/WS2815%20LED%20Datasheet.pdf). Those are in fact designed for 12V supply, and I've seen quite some places falsely selling them as "12V WS2812B".

Why can't i replicate it? It's very detailed even down the the component choice. Only they they didn't specifically list is the model inductor but they did give a value, and elsewhere in the datasheet it has some detailed information about picking inductors...
Good luck getting the PCB just right for it to work with reasonable efficiency.
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 11, 2019, 03:49 pm
I see you googled it, congrats ;)

The also have/had led strips with dc/dc converters built into the strip bu said can't find them anymore... probably they didn't work too well...
Title: Re: 48v to 12v dc converter
Post by: MarkT on Sep 11, 2019, 06:35 pm
I can imagine linear regulators built into a strip, not DC-DC converters.
Title: Re: 48v to 12v dc converter
Post by: wvmarle on Sep 11, 2019, 06:49 pm
From the Chinglish datasheet of the WS2812b:

Quote
Also include a precision internal oscillator and a 12V voltage programmable constant current control part, effectively ensuring the pixel point light color height consistent.
This sounds like a constant current supply AND a boost converter (supply voltage is 5V, here they appear to say the constant current supply runs at 12V) built into each LED?!
Title: Re: 48v to 12v dc converter
Post by: MarkT on Sep 11, 2019, 07:00 pm
Quote
Also include a precision internal oscillator and a 12V voltage programmable constant current control part, effectively ensuring the pixel point light color height consistent.
I think that means each chip has an undocumented program option to correct for LED variations - this 12V is definitely not in normal use, I expect this is done once on manufacture - they are just boasting that they get better consistency of brightness than the LED dies they incorporate into the thing.
Title: Re: 48v to 12v dc converter
Post by: Qdeathstar on Sep 11, 2019, 08:23 pm
@markT I am not sure what it had exactly but a linear regulator to drop from 12v to 5v at high current seems unlikely. (To work).. I think they had one every meter and the strip was about twice has wide...