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-   -   DPS5020 dual power supply build (https://www.badcaps.net/forum/showthread.php?t=76581)

Dannyx 05-13-2019 12:22 PM

DPS5020 dual power supply build
 
2 Attachment(s)
Good day folks. A while back, in a different topic of mine about how I was trying to build my own adjustable power supply from scratch, someone suggested I should just scrap that idea and not bother and just get a pre-made power supply module which would be infinitely better and save me a lot of trouble and so I did: I got myself the DPS5015 of Ali after it was recommended to me, for which I built a nice little enclosure and powered it off a rather beefy UPS transformer. Granted, it was a bit pricey for my taste, but I realise now it was money worth spending because it does everything I need and more and I would have never achieved the same level of functionality and stability with my own attempt at building one.

So now it's time for a new project, bigger, better, stronger :D Being very satisfied with the overall performance of these little power supplies, I of course turned to them again as the heart for my new supply and noticed an improved version came out in the meantime, the DPS5020, which can not only take an additional 5A which was already overkill :D but also includes a piece of software which allows the board to communicate with an app on a PC or phone so you can view and adjust your values from your PC or device. Now I must admit, although I try to call myself a semi-professional, I AM a sucker for eye-candy like this, so I had to get myself one. Again, expensive ! For my budget at least, especially since I went all-out and got the BT version which I'll probably never use :D Actually, the project calls for TWO of them, but I didn't have the necessary funds at the time. It has now arrived and with it sitting on my desk, it's time to start building: same two chunky UPS transformers, two 50a rectifiers, some fuses, two filter caps (more on that later), a ton of wires, enclosure....etc.

I laid down a wiring diagram, although it's very simple: there's two circuits side by side, perfectly identical, to form a dual-output bench supply. This way I can have two completely isolated supplies or I can join their GNDs together to have a common-GND dual-output supply which is handy for testing devices which require more than one power rail (12v-5v for instance). That's the theory at least.

There are some things I still need to work out.

1) Let's start with the very beginning: notice how I wired the two transformers straight to the 230VAC input - should I look for some sort of EMI filtering there ? If so, what should this be ?

2) For C1 and C2 I found some caps on Ali which CLAIM to be 10000uF/80V....is bulk capacitance a generally good idea on the input of the DC-DC modules there or should I look for some inductors as well ?

3) ZD1 and ZD2 - 51v zener diodes. 50v is the maximum input the modules can tolerate. If the 230v input swings too high, the secondary voltage will also increase, possibly past the 50v margin, so supposedly those zeners will become biased and blow F3/F4. Good idea/bad idea ? I fear they may false-trigger often :|

4) feel free to suggest stuff and improve on my design :D

I'll keep you guys posted along the way with pictures of the build :D Cheers and thanks.

megaraider 05-13-2019 01:35 PM

Re: DPS5020 dual power supply build
 
wth 10000uF...??? Have you done the peak current maths upon power up :crying:
Not to mention EMI filters needed, chokes, ..., and the total cost amount...!!!
imo, keep it simple, functional, clean and... much cheaper
use DC laptop adapters (eg: 19V~3.5A, 30V~3A) to power the DPS50xx modules.

Dannyx 05-13-2019 01:39 PM

Re: DPS5020 dual power supply build
 
Inrush current might be a problem indeed, so I'm trying to come up with something like a soft-start....

The modules themselves are the most expensive part of the build - the transformers were scored for free out of the junk pile and I already have them, so no money lost there :D

stj 05-14-2019 01:44 AM

Re: DPS5020 dual power supply build
 
i wouldnt worry about chokes, the DP units run at very high frequency and without a scope you would have trouble pinning down any noise to suppress.

Dannyx 05-14-2019 01:57 AM

Re: DPS5020 dual power supply build
 
Quote:

Originally Posted by stj (Post 896313)
i wouldnt worry about chokes, the DP units run at very high frequency and without a scope you would have trouble pinning down any noise to suppress.

Are you referring to a possible choke between the bridge rectifier and the input of the modules ? My current build also doesn't have any of those - it's straight off the diode bridge, with two capacitors in parallel there.

Dannyx 05-14-2019 05:19 AM

Re: DPS5020 dual power supply build
 
Also I remember I have this in my junk box as well. I ripped it from a plasma TV before tossing it out. Might make a nice addition to out project maybe ?

stj 05-14-2019 05:39 AM

Re: DPS5020 dual power supply build
 
well with regular transformers and rectifiers you have no noise to suppress because your following the sinewave.

the DP modules may create noise - but maybe not - they have good caps on them.
and if they do create switching noise, any filter would have to be selected for the frequency you want to block.

Dannyx 05-14-2019 12:02 PM

Re: DPS5020 dual power supply build
 
4 Attachment(s)
Here's some pictures of the case that just arrived today and how I plan to lay it all out. Only one PSU module for now as you can see, but I shall prepare the second location as well for when I'll finally get the other one too. I'm actually planning to take the front panel to a CNC or router to have it machined professionally because that's 3mm thick aluminium there...sawing through that and hoping to achieve some precise cutouts would not be fun or easy. This project has gone way overboard already, so might as well go all out. Not sure if those DPS supplies deserve such a nice case, but hey...YOLO :D

stj 05-14-2019 12:52 PM

Re: DPS5020 dual power supply build
 
oh nice, an oldskool rack case!!

Dannyx 05-14-2019 01:57 PM

Re: DPS5020 dual power supply build
 
Quote:

Originally Posted by stj (Post 896420)
oh nice, an oldskool rack case!!

Glad you like it :D

redwire 05-14-2019 10:38 PM

Re: DPS5020 dual power supply build
 
I love enclosures like that, could build a power amplifier...

With the DPS modules I add (Y-caps 2,200pF or more) from (-) and (+) to chassis GND, to limit HF noise.
Once I did try add an output choke and cap, noise was gone but the extra DC resistance ruined the regulation. A clamp-on ferrite could work. It's mainly if you want to power radios or need quiet power with little noise, I add an extra filter on the DPS output.

Add a resistor from the bridge rectifier (-) to earth ground to limit the stray voltage due to the power transformer's leakage.

Most DPS modules have a low-side N-ch mosfet, so they disconnect output (-) when you command it off. You can check with ohmmeter, there is no continuity from module input (-) to output (-). This can make them confusing.
I think the mosfet allows the units to not blow up when charging batteries.

I would rotate the bottom so air from the ventilation holes can go by the DPS for cooling.
I also use big 10,000uF filter caps with no problems, the modules like that and RuTech recommends several 1000's uF so AC ripple does not stress the module. An 8A bridge or better, with heatsink can take the inrush and steady 5A.

Serial comms will be an issue if both DPS modules are floating.

Dannyx 05-15-2019 01:20 AM

Re: DPS5020 dual power supply build
 
Thanks for the great tips. That's the sort of pointers I like to hear :)

Quote:

Originally Posted by redwire (Post 896477)
With the DPS modules I add (Y-caps 2,200pF or more) from (-) and (+) to chassis GND, to limit HF noise.

Should those caps be on the input or output of the DPS module ? I assume the output. So one cap on the negative leg and the cap on positive, then the remaining legs of the caps tied to chassis GND. Trouble is, although I'll use an IEC 13 connector to power the whole box, which has an earth terminal which I shall tie to the metal case, most buildings aren't actually earthed here :D
Keeping the two modules separate kinda goes out the window, since they now share a common GND.

Quote:

Originally Posted by redwire (Post 896477)
A clamp-on ferrite could work.

Something like this ? I actually have these after ordering some a while back. Again, should these go on the output or input ? Or perhaps both ?

Quote:

Originally Posted by redwire (Post 896477)
Add a resistor from the bridge rectifier (-) to earth ground to limit the stray voltage due to the power transformer's leakage.

What value should this have ? Just like with the Y caps, this will just sit there probably doing nothing, since there's technically no earth :D Also, it removes any chance of the two supplies floating...which may not actually be a bad thing in the long run now that I think of it.

Quote:

Originally Posted by redwire (Post 896477)
Serial comms will be an issue if both DPS modules are floating.

Yes, I just realized that myself. As soon as you try to connect both USBs to a PC, the ground becomes common. One workaround would be to use the BT functionality. The trade-off of course is that you can't have both connected at the same time, unless you use two PCs, each running an instance of the software. I doubt it can run multi-instance on the same machine to allow controlling two or more supplies in real time. Haven't tried that yet. It would be interesting to find out.

stj 05-15-2019 03:19 AM

Re: DPS5020 dual power supply build
 
dont link anything after the transformers to ground.
it will cause problems if you want to tie the 2 channels together as a split-rail output.

you can get usb isolators from china for beer money.
why not put a dirt-cheap hub in too - so you only need one external connector.

btw, how does the usb know which module your addressing? do they have configurable i.d.'s??

Dannyx 05-15-2019 03:42 AM

Re: DPS5020 dual power supply build
 
Quote:

Originally Posted by stj (Post 896501)
dont link anything after the transformers to ground.
it will cause problems if you want to tie the 2 channels together as a split-rail output.

So you're saying the Y capacitor idea wouldn't work in this case ? I should just leave the case itself floating, only connected to earth and nothing else then ?
Split-rail refers to +15v and -15v for instance ? If so, wouldn't the GNDs of the two supplies be the 0v point and the output of each module represent each of the +/- output ? I forgot how this worked :D

Quote:

Originally Posted by stj (Post 896501)
why not put a dirt-cheap hub in too - so you only need one external connector.

I considered that as well, given that there's no speed concern here. Still, it would have to be used in conjunction with the isolators you suggested.

Quote:

Originally Posted by stj (Post 896501)
btw, how does the usb know which module your addressing? do they have configurable i.d.'s??

Yes, if you check out the manual I posted, you'll see further down that they are addressable. The software itself has a drop-down list in which you select which one you wish to "talk" to. Here's the link to the whole archive if someone's interested and doesn't feel like hunting it down.

stj 05-15-2019 08:25 AM

Re: DPS5020 dual power supply build
 
earthing, earth the rack case and the transformer bodies - although that will happen through the bolts anyway.

split-rail,
you connect the - of one channel to the + of the other channel.

so instead of [0v +15v] [ 0v +15v]
you have [-15v 0v-0v +15v]

if you did that and there was common ground you would short out the first channel.

Dannyx 05-15-2019 10:13 AM

Re: DPS5020 dual power supply build
 
I could use a switch which would toggle between tying the GNDs together in one orientation and tying the + of one to the - of the other in the other position, how's that ? That's more of a convenience, since a piece of wire would work just as well :D

stj 05-15-2019 11:09 AM

Re: DPS5020 dual power supply build
 
you could - and hit it by mistake!!

btw, i was looking at the pdf pictures.
the unit uses a serial port.
the interface is a serial>usb adapter with a WinChipHead chipset (a damned good chip)
now here is the interesting bit, in the picture it looks like it's already opto-isolated!!!!!

Dannyx 05-15-2019 11:32 AM

Re: DPS5020 dual power supply build
 
Quote:

Originally Posted by stj (Post 896565)
the interface is a serial>usb adapter with a WinChipHead chipset (a damned good chip)
now here is the interesting bit, in the picture it looks like it's already opto-isolated!!!!!

Yes, there is a serial>USB adapter included in the box. It's got a CH340 chip on it which I'm familiar with since it's present on my SPI programmer, though it's a CH341 there - same thing.
How did you determine what it is and that it's isolated ?

stj 05-15-2019 12:48 PM

Re: DPS5020 dual power supply build
 
look at the end with the 4pin connector - below are 2 4pin packages.

i know the chipset because of the driver they are using. :)

redwire 05-15-2019 03:16 PM

Re: DPS5020 dual power supply build
 
If you leave the secondary-side floating, there will be stray voltage - it can be as bad as a SMPS brick Y-cap floating to 60-90VAC but even a 1MEG can lower it so nothing gets zapped. The Y-cap in this case is the transformer's pri-sec capacitance. You can measure it if you don't believe me, it can be a 100nF on toroids.
There is no cap across the on/off switch so a large arc happens and switch-off spike can hit the secondary side, it can kick up 100's of volts.
So I use a 1MEG/10nF cap on the secondary to earth ground just so it can't float or spike up. It's still considered floating for stacking power supplies.

stj, do these have the low-side N-ch mosfet? It was why RdTech said some DPS modules can/cannot charge batteries.

The Bluetooth add on module might be better, to go wireless? But I think the firmware is different or something makes it a hassle to add.


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