DPS5020 dual power supply build

[stj]

Re: DPS5020 dual power supply build

the metal of the usb is frame-ground - it should be seperate from the 0v pin.
but that's not important, what matters is the side that plugs into the psu - that's opto-isolated from the usb side.

so you should be o.k.
check it - plug the adapter in and ohm between the usb socket and the ground on the psu module

[Dannyx]

Re: DPS5020 dual power supply build

One side of the front panel is done. My old man, God bless him, did his best with the modest tools he had on hand, but it's not quite 100% despite his best efforts...some things just don't line up properly as you can see, but hey...beggars can't be choosers. He could really use a better drill press to unlock his full potential. The chuck on this one is a bit wobbly so the drill bit tends to slip off the intended target, hence why some of the holes are slightly offset there...

[stj]

Re: DPS5020 dual power supply build

strip the chuck and clean and grease it.
it's just 2 halves with the jaws seperated by springs in it.
maybe a spring cracked.

[Dannyx]

Re: DPS5020 dual power supply build

Ehh...no, it's actually the whole shaft that's wobbly. There's no actual bearing in there - the shaft just spins on the plastic shell of the drill, relying only on some grease to reduce wear, so after so much abuse, the plastic has started giving in, causing play in the shaft and chuck assembly. It's a cheap nasty thing anyway, no need to bother with it...

[megaraider]

Re: DPS5020 dual power supply build

no, the usb to serial boards are optically isolated.
as long as they are not touching the metal case the pc wont be referenced to the psu's

@Dannyx
Did you forgot our previous discussion here...?
Plus stj post i've quoted gave you another hint (psu metal case)
and a relief concerning usb port to serial boards being optically isolated.

WTH how did you manage to forgot the main power switch at the psu front panel...???

[Your father, besides being good craftsman (my congratulations to him )
is a good guy to put up with his son laziness (shame on you )]

[Dannyx]

Re: DPS5020 dual power supply build

@Dannyx
Did you forgot our previous discussion here...?
Plus stj post i've quoted gave you another hint (psu metal case)
and a relief concerning usb port to serial boards being optically isolated.

No, I didn't forget that. I went over the thread several times, since I was still a bit confused as to whether or not I should connect anything to the case. Running the two modules in series is not a priority to me ATM and I'm not even sure it could be done....can DC-DC converters like these even be wired in series ? However, keeping them separate to allow for a split-supply IS important, otherwise I would've just had a common GND at all times, including on the case.

WTH how did you manage to forgot the main power switch at the psu front panel...???

I didn't forget it, I just don't have it yet, so I don't know where it should go or what size hole it should have

[Dannyx]

Re: DPS5020 dual power supply build

I figured it would be wise to have some sort of short circuit protection on both the AC input to the two transformers and on their outputs. I was going to go with glass fuses, but then I thought THESE might be a good idea. They're adequate for the mains side no problem and I was planning to use them for the secondary as well, where I would of course up the current rating to around 20A, but then I noticed they can only hold 50v of DC , which is right on the edge of what the secondary outputs and I'm not sure it's ideal to push them to the limit like that, even though they'd probably never trip, unless the bridge rectifier becomes shorted somehow.

Then I though I'd go with THESE instead which can take an extra 10v of DC which would put them within the range of the transformer's output. Yeah, I know you're more likely to see those used on mains circuits, but they would be within spec for the low voltage side as well. They would be a PAIN to install though, since they would require cutting a BIG rectangle in the already thick and hard to machine metal, whereas with those pop-out thingies, I could just attack it with a 10mm drill bit, so that's another aspect to consider

[stj]

Re: DPS5020 dual power supply build

just remember that unlike fuses, most circuit breakers only work on AC - or atleast they only trip where they say on AC.

[Dannyx]

Re: DPS5020 dual power supply build

I was thinking of placing the secondary one before the bridge rectifier, so it's technically still AC. That is to protect the transformer in case the rectifier itself fails, which is unlikely, but NVM...

[stj]

Re: DPS5020 dual power supply build

actually rectifiers can short out - i'v seen it a number of times.

[Dannyx]

Re: DPS5020 dual power supply build

Second side done

[redwire]

Re: DPS5020 dual power supply build

Second side done

Looks really good. I add a PE GND green binding post in case I need it.

The DPS5020-USB board has two opto-isolators, so the USB should be OK. The shell can touch chassis PE ground or float unconnected.

[Dannyx]

Re: DPS5020 dual power supply build

I just remembered I faced another intricacy of transformers when I built my first supply: the transformer got rather warm (to hot) when unloaded and seemed to stay cool when actually LOADED, ironically....I suppose it's got something to do with induction, but again: transformers to me are one of the most complex electronics parts, with all their particularities and physics they involve, so I'm not really sure why. I left it plugged into the mains on the workbench without anything attached to the secondary (I think I simply forgot about it) and when I came back after an hour or so, it was too hot to touch...Yeouch !....so that got me working on designing some sort of cooling system, especially since the first case is wood...not the best design idea, but it was the best we could build from absolute scratch. This one is metal and has plenty of space inside, plus ventilation holes, so it should be OK to go fanless.

For my first one, so the fan wouldn't be on all the time, I modified a car mobile phone charger that normally plugs into the lighter socket to increase/decrease its output based on heat. I replaced one of the feedback resistors with an NTC and tacked that down to the top of the transformer, so as it got hotter, the NTC's resistance dropped and increased the output voltage, making the fan spin faster...don't think I'll go through that trouble with this one though, at least not yet.

[Dannyx]

Re: DPS5020 dual power supply build

Yes, you are right: the metal shell of the micro USB connector does not contact the GND of that output header which plugs into the PSU module itself. I checked it today.

[Dannyx]

Re: DPS5020 dual power supply build

Still on the topic of PSUs in general, since I didn't want to open a whole new thread just for this, I thought I might as well ask here: when you've got a mechanical switch/relay and a load, particularly an inductive one, should you place:
A) a capacitor across the switch
B) a diode across the load
C) both ?

Obviously in AC circuits you can't put a diode across the load, but what about DC ? This PSU will use a couple of relays and I want to make sure it's as industry-standard as possible.

[stj]

Re: DPS5020 dual power supply build

it's good to put a film cap across the contacts, but you want a resistor in series to limit the current.
you can buy caps with the resistor built in for use as snubbers.

[megaraider]

Re: DPS5020 dual power supply build

C) both ?

Yes, both.

[Dannyx]

Re: DPS5020 dual power supply build

Question then is what value should the cap/resistor have and what should the cap be ? One of those yellow "X" caps ? I reckon it's dependent on the voltage/current you're expecting to see there, though I think a higher voltage rating for the cap would work on a 12v system too.

[stj]

Re: DPS5020 dual power supply build

that question depends on the inrush of the load.

the idea is to supress any contact arcing while keeping leakage across open contacts to a minimum.

[Dannyx]

Re: DPS5020 dual power supply build

that question depends on the inrush of the load.

the idea is to supress any contact arcing while keeping leakage across open contacts to a minimum.

Yeah, that's tough to determine.....say a beefy transformer in my case, though that's not really helping much.