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ARRAY electronic loads
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saturation:
Congrats on the good price on the eBay item. 
Nice.  Those are great insights, I wasn't entirely clear on the meanders nor the 6 MOSFETS.

Volt adjust is fairly straightforward.   The cal information and software can be downloaded from Array's website.  The software is not well made and unreliable for controlling the device but its fine for data collection.
But if anyone can write a better version!  I'd be happy to test it out  ;)

Note the reverse input protection causes non-stop beeps and a warning on the LCD but it shorts the load rather than cuts it out, so it will draw the full output.  It'll be a shocker if you were testing high current DUT and had reversed the leads in error.



--- Quote from: free_electron on September 21, 2012, 01:07:50 pm ---Yep. Me. Snatched it for less than that :)

I have some 'reverse engineering ' info.
The meanders on the pcb are there for a purpose. The two powerfets at the back have their own 0.1 ohm sense resistor to close the loop. These two resistors share a single trace on the board that is via-stitched between top and bottom layer and comes to the front of the board. The meanders on the front resistors inject the same trace length to the star point. The reason is load balancing. The pcb trace resistance would be different between front and back and the front fets woul pull more current than the back. Deliberate operation. Good design.

The bank of 6 mosfets on the main board is for range switching.
The use either 0.2 ohms for current measuring , in series with 0.02 ohms ( five 0.1 in parallel ). At high current they turn on the bank of six mosfets to short the 0.2 ohms out.

A relay toggles between the sense points. ( strange.. No analog mux ... Probably because there is a post divider protecting against large voltages.. )

My machine is off in the voltage measuring department. The programmed and measured currents are correct. The voltage measured on the terminals is wrong , so it probably needs adjustment.

The sticker said. Cannot adjust , but they didnt even try.... None of the pot seals are broken and this machine has no electronic calibration.... Lazy callabs...

--- End quote ---
free_electron:
Good ! got the info. will hook it to the calibrator over the weekend.
I download the software.... typical national instruments tripe ...  made in CrapWindows or Crapview..
I'll write my own. Just need to find the comms adapter ....
saturation:
I've completed the functional testing.  In a nutshell, I ran 90W for >1 hour and checked the response of the electronics, the load distribution between the modules, and the stability of the readings.  During that time I ran all the modes, CC, CR, and CP but kept to about 90W or more.  I programmed a series of variable loads, going from 0.01A to 2.5A and various level between and ran for 30 min.  Temp was measured with an IR thermometer.

Loads on the power MOSFETs appeared evenly distributed as measured through its voltage across load resistors

the Array can slew far more ~> 1A/1mS as measured to the response to variable loading 

The unit held its calibration as monitored by Fluke 87Vs checking current and voltages 

The fans are a soft hum and not a harsh blowing whine when at full power

The fans engaged at 40C, and keep the unit at a constant 38C.  It shuts off at 35C, the difference being as thermostat hysteresis.  Each load module was only 1 C warmer at the center of the heat sink compared to the end, and -4C at the exhaust end of the vents.

The dual supply linear regulator ICs warm up to 40 50C, while the 5V supply peaks at 64C

The most annoying drawback is the voltage drop across the hook up cables so one will have to compensate for it

The interface is fairly simple, and direct. Rare glitches happened when playing with button and rotary control adjusts, the system would then jump to init mode, which happens quickly so its not a bother, 1 sec or less.  All the saved defaults remain untouched.
T4P:
Good info thanks saturation, so the question still begs ... Maynuo M9712 OR Array 3711A
Both are around the same prices with the Maynuo being newer but the maynuo is only 150V and has battery test feature (Of course my prices are quoted from china directly)
Forget about the CA5030 from precisegauge, i can get a 3711A cheaper than the CA5030
nctnico:
Instead of one 3711A I bought two 3710A devices. They can be parallelled to handle more load or put in series for a higher voltage or used for two different projects at the same time.
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