Monday, December 30, 2013

Jaycar MP3086 30 Volt PSU Teardown and testing

Old MP3086
Okay so I bought a 30VDC Variable 3 amp PSU from Jaycar a few weeks ago. It is model MP3086 with CV and CC modes. I was expecting the one shown above with 3 pots, one for amps, and coarse and fine ones for volts.. Instead I got a new improved model, unless you like the coarse/fine pots!

New MP3086
So of course with anything new you need to follow Dave from EEVBlog's advice.. Don't turn it on tear it apart so that's what i did..
Cover off, transformer looks nice doesn't it ?
Okay so first impressions from the photo above.. Nice secure soldering on the mains connections, shake proof washers on the earth wire and extra covering on the mains feed, see that black rectangle on the right centre ? Here it is closer up...

Switch Close-up
It is a real clunking power switch on the mains, so no standby current usage, Yay a thumbs up..

IEC socket with integrated fuse holder, nice one !

Shake proof washer a point for Jaycar

Spring washers on transformer mounts with intake vent for fan, there is also vents on the sides with exhaust at the rear of the unit

Terminal block for permanent connections say a bench Multimeter and banana sockets
Okay now for the close-up internal shots, there are five boards
  • Rectifier board Power transistor board with Relays to switch taps from transformer to transistors
  • LCD Display board
  • Keyboard Board for buttons
  • CV/CC Control board
  • Connection board for front panel outputs with current shunt for amps readings

Rectifier Board with room for two more transistors
Is this a real Japanese Rubycon or a copy ? 
The Main Power board looks like it has a real Rubycon capacitor, the screen printing looks good and it does not look like a rip off

LCD Control Board all SMD, the bodge wires on the right run to the back light, keyboard board bottom left with ten turn pot for volts selection underneath

The Voltage and Current control board, there is nothing on the other side apart from a few through hole caps and a voltage regulator on a small heat-sink, notice the flux residue on the through hole hand soldered joints, not good how hard is it to clean a a board ? Here are some close ups of the cruft left behind after soldering. But hey the Ningbo QJE company gave us their phone number if you want to call and complain to them about it :p

NXP Chips a counter IC and a logic gate, some more quality parts to go with the Rubycon cap...

Nice SMD soldering, re-flowed not hand done ! This is one of the trimmers to calibrate it all

Nice thick bus bars to the connections on the front panel with shake proof washers as well, excellent job.

Thermal switch for the fan, wired in series with fan it is rated at 5 amps and 50 C cut in temperature but cuts in before that, 

Okay now for some testing.... 
The test set-up consisted of the following.
  • RS232 connected DMM logging temperature
  • Galaxy Note 2 Smartphone for dB readings (Not real accurate but okay) 
  • Incandescent 12V globe as resistive load
  • Digitech QC1932 25MHz DSO
  • Supply set at 6.9 Volts, this just switched to the second tap (6.8V) so max heat from transistors

12 Volt Light globe pulling 1.33 amps at 6.9 volts, this tested at about half of the maximum amps and the second tap on the transformer had just switched in at 6.8 volts so I was dissipating the most heat for this amperage in to the heat-sink. 

The test set-up, I connected the scope probe to the terminal block on the front directly, I just hadn't done it here yet

Below is the capture of power on unloaded, there is a small HF ripple at power on then ramp up to full voltage (5VDC) with no overshoot, there is a small amount of ringing when it reaches the set voltage, from power on to stable voltage is about 10 milliseconds.

This is a close up of the spike at power up unloaded, about .5-.75 volts lasting 206 microseconds

Here is a capture of a loaded supply at 7VDC from turn on to full output is 76 milliseconds with no overshoot to speak of.

1.6mV ripple at 7 volts under loaded conditions

dB levels with phone acting as meter with smart tools app. The first bump is me pressing the power switch, the second is the mechanical temp switch clicking in, then you can see the fan ramp up to 69dB. the phone was sitting 10cm behind the PSU with the microphone sideways to the fan, the power switch click is quieter as it is at the front while the temp switch was closer to the rear. The ripples in the graph is just background noise in the shack.

If you look between the cursor marks on the timebase below you can see two little ripples lasting about a second, this was when the fan switched in but was brief and low in amplitude. It may have just been induced noise from the arcing in the mechanical temperature switch for the fan as its contacts closed.

Here is the temperature run at 7VDC 1.33 amps from cold (I did this test first after leaving it off overnight) Starts at about 26c the shack temp, ramps up to 43.9c in about 2 minutes then settles to around 34c and stays there. I ran it longer then this graph loaded and the temp was stable and didn't run away at all which it shouldn't pulling 9 watts from a 90 watt supply.

 All in all for the price I am very happy with it, well built steel case, the front panel is plastic but has steel rails running from it to the back panel for support.

So what don't I like ? Well not much the only things are as follows.

  • Earth Connection is in the centre, so I cant plug a standard spaced dual banana plug adaptor in to the - and + rails, I may re arrange the banana sockets and move the earth to one side.
  • You need to short the rails to set the required amperage for CC mode, I am going to put a NO momentary switch on the front so i don't need a lead to do it
  • Switching on CC mode is a bit hit and miss, I dont know if it is key bounce or a slow micro but you have to press the CC button a few times before it locks in to CC mode, it is a soft switch
Apart from that i really like it and it actually goes to 31.5 Volts

MP3086 Regulated lab Power Supply 30VDC at 3 AMPS

List price $199 AUD

Tuesday, December 24, 2013

Photos of the shack all setup

The Twisted Shack
The twisted Professor

Shack mascot Tux and Mr Bean teddy

My Pulse Jet

Tools in filing cabinet

Power tools in Filing Cabinet

Close up of my books

More books

Even More Books

Bits and bobs on display

A few more knick knacks and a dummy load project DC-1GHZ 250W

VIC Royal mail Service Morse Key circa late 1800's

Small hand tools

More Small hand tools

Pocket Digital Scope and Function Gen from Velleman

Keyboard and mixinf desk at workstation side

Fishtank and tablet

Loose tools behind Drillpress

Storage bins

12VDC Shack battery backup

Gas storage Mapp/propane

Microscope, ultrasonic cleaner battery Charger, Pestle & Mortor and telescope optics

Flatbed scanner I get out as needed and storage draws


Labeller, tacho and camera

Dremel and Hot Snot

Gaming PC in old 19inch Rack case and Fan/heater on top under the desk 
Air COmpressor Oiless with water trap for dusting electronics

Tool Bag for field work

Inside tool bag, I add the pocket scope and sig gen when i go out with the bag

Swing out lead rack

Test leads for field bag

Network cable tester and resistor/capacitor sub boxes

2nd Dremel and drillpress stand

Air tools

Measuring and scraping draw


Metal Working, files snips reams



Hammers clamps and random tools

larger pliers, side cutters allen keys


Handmade clock from old 240VAC clock that had broken glass and burnt out Mistral Desk fan

More Sockets Taps/Dies Drifts Wad punches

Under workbench storage and solder dispensper Atten Digital iron and Compressed air outlet

Digitech 2 Chan DSO, Powertech 30VDC 3A PSU Tek 314 Scope GW Freq Counter DMM with Cap/Ind/Tran test and cordless power screwdriver

Main Shelving with video feed from driveway and frontdoor so i dont miss the postie with goodies from eBay

Atten Iron (Base under desk) Digitech SMD rework station (air and iron) and small PCB hand tools in old makeup case with USB outlets to left and Power fail torch (Comes on when power goes out)

Drill press and visitor chair with storage bins, resistors in drawers to left

Asst small parts Caps/Semis/Screws etc

Overview of workbench side

Panning to left of workbench

Workstation, Desktop PC at top laptop with 2nd screen center and tough book laptop right, all linked with synergy remote software to use one keyboard and mouse to run it all as one virtual PC

Ham radios Mindisc recorder, 10 band graphic equalizer transmatch and 13.8PSU with 24VAC for weller iron (So I can solder power etc at radio side)

Sign my son made me for Christmas, just hung it up for the pics :)

The entry to the shack

Old fridge outside shack to use for chemical storage

The 2.4x2.4Mt (8x8 foot) garden shed that is the shack

The wire bin for scrap wire

Around the back of the unit is bins of larger parts and some tools