Friday, 23 October 2015

PowerTech MP-3800 0-24 volt power supply - a quick review

I have been powering my RepRap 3D printer with a hacked ATX power supply - it has been working OK, but I was finding that it could be a bit slow getting the heat bed up to a stable temperature, especially if I want to print ABS (which needs a very hot heat-bed to stick properly). When I hooked up my multimeter, I found the supply voltage was dropping a bit under heavy load, so I guess my power supply really wasn't 100% up to its rated capacity. I started thinking about getting a proper desktop variable voltage power supply.

Luckily for me, JayCar recently had a special on several power supplies, including the MP-3800, which they were offering for only AUD$119 (usually $149) - not bad for a 0-24 volt power supply, with a load rating of 15 amps continuous at 12 volts (18 amps peak). It is rated to better than 9 mV ripple voltage, and has thermal and overload protection, so it ticks all of my boxes.

Note that the rated output current capacity depends on the selected output voltage, so check your needs if you plan to run at other voltages:

So I grabbed one, hooked it up to my RepRap, and it works great - highly recommended!

The power supply has back-lit analogue gauges for volts and amps, which seem to be pretty accurate when I test against my multi-meter. The RepRap pulls a maximum load of about 12 amps during the heat-up phase, but this drops to around 5 - 6 amps during normal printing. The power supply handles this admirably, with no detectable fluctuation in supply voltage, even when the load is fluctuating rapidly, such as when the heat-bed is cycling on and off.

The voltage control knob has a central detent position, at which it delivers 13.2 volts, which is where I normally run the RepRap. (The RAMPS 1.4 card is nominally a 12 volt board, but it can happily take a little bit of over-voltage, and the extra supply voltage gives faster and more stable heat control.) However, I need to be sure to not accidentally overload the RAMPS by giving it 24 volts - I really wanted a digital display to give a crystal-clear voltage display, to make sure I don't over-power my RAMPS 1.4.

I bought a cheap 0-30 volt LED voltmeter on eBay for less than $3 including postage (search for "0.36" LED Digital Voltmeter", and make sure to pick one which has the right voltage range for your power supply, as they come in 10V, 30V, 100V and 200V variants). Hook up the red and blue wires to the positive terminal and the black wire to the ground terminal, and you have a nice bright digital voltage display.

I then printed a voltmeter bracket which I came across on Thingiverse, and it works great - now I get a brilliant indication of supply voltage as soon as I power up, greatly reducing the risk of blowing the RAMPS electronics. (And of course it works just as well when I am using the power supply for my other electronics projects.)