Mega Watt S-400-12 Power Supply

Power supplies that convert 120 volt AC power to 12 volt DC power are large, heavy, cumbersome electronics devices that take up a bunch of room on your desk right? Well all that has changed with the introduction of the switching power supply. Switching power supplies are small and light and are able to provide the same amounts of amperage without hogging up all the space.

They aren’t without their problems though and many of the 1st generation of switching power supplies weren’t the best for use with Ham radio or CB gear as they generated a lot of noise in receivers. I know from experience the radio shack switching power supply I had made a lot of noise and also an early MFJ supply made noise in my receive (a MFJ switching supply I purchased more recently worked much better).

All of this leads me to a strange purchase I made three month ago. I was in the market for a new power supply to replace the Pyramid PS-36K that I had sold to a friend and I was considering getting an Iota power supply as I’d heard good things about them but I decided to be cheap and look for something less expensive.

After some random searching on eBay I found the Mega Watt S-400-12 being sold by someone who was importing them in from China. He has a couple of websites online where he sells these and other products but other than that he isn’t really a storefront or company. He accepts payments by paypal and shipping fees were quite reasonable at $5.00.

He sells two versions of this switching power supply on his website – a 33 amp version for $50 and a 36 amp version for $65. In blue below I’m going to post their advertisement text they use on their eBay ads.

“This Unit is designed for powering mobile CB radios and Linear Amplifiers. The output section of the power supply is highly filtered to eliminate RF in the output voltage. Yes, it is possible to properly filter a switching power supply. Please read my feedback for reviews from all the happy CB radio operators. Great upgrade power supply for RCI 2995dx and the General Stonewall Jackson bases.

The power supply is rated at 36 Amps, 90% duty cycle (not peak power) Peak power means full power for only a split second burst. A 90% duty cycle means 30 minutes at 36 amps and 3 minutes at 30 amps to cool down for another run at 36 amps. It is conservatively rated at 30 amps continuous 24-hour service. Handles spikes up to 41 amps. Great for Shortwave radios where the transmitter draws most of the power but is only in use 1/2 the time the radio is on.

Full 2 year factory warranty. This unit will hold up to a 36 amp load, see pictures above. It will cold start with a 36 amp load connected.

This is not your typical inexpensive power supply. Poorly or unregulated power supplies will cause your sound or radio equipment to hum while in use. Awesome for powering your high-powered Shortwave radio equipment in the house. This unit has a built in cooling fan on a thermostat to control fan speed and over voltage/short circuit protection. It operates on 120 volts AC or 220 volts AC, 47Hz to 63Hz, 747 Watts. It’s fully shielded for use in a computer or radio environment. It’s brand new, never used, not refurbished, not returned. It is a nice small package, 9 X 4 5/8 X 2 inches. This is a “switching” power supply, which uses solid state electronics to produce the output voltage. This makes this unit much lighter, smaller and less likely to malfunction than the old fashion transformer type power supply. This item is guaranteed to be brand new and arrive as described in this auction. I have lots of these for anyone looking for more than one. Combined shipping is available on multiple purchases. A free 110 volt power cord for testing the unit right out of the box is included with each unit. ”

So now that you’ve read the claims let me give you my experience and review of the unit. The power supply arrived within a couple of days of orders and was well packaged. It can be set up for 115V or 230 V operation by adjusting a switch on the side.

It also arrived with a AC power cord that has an in-line switch so you can plug it directly in to the wall socket.

The unit is small and light – 9 X 4 5/8 X 2 inches as advertised. It’s about the size of a DVD drive you’d have in your computer. Weight around 2 lbs I’d guess. Within a couple of minutes I had hooked up the AC power cord, attached my CB radio + Cobra 350 XL 2 x 2879 transistor amplifier and plugged it into the wall.

My radio and amp powered on and in my receive I found no hiss, hash or other interference whatsoever. Their sales pitch was correct, this switching power supply has enough filtering that I did not encounter any adverse noise.

Next I used my multi meter to test the voltage and found it was just a hair under 12.6 volts so I made a slight adjustment to the power supply (it has a voltage control pot exposed that can be adjusted with a screwdriver) and set the voltage where I wanted it.

Within minutes I was talking on my radio and the power supply had no problems powering the CB. I then turned on the amp (which does just under 300 watts output with the CB driving it) and ran the combo into a dummy load. I was able to achieve full power with no difficulties and the power supply didn’t even seem to flinch. To put this in perspective – with the Pyramid PS-36K using the same combo at full output the power supply would start to work pretty hard and I could hear the fan speed change inside the power supply. The amperage meter on the front would almost peg out at max. This new power supply certainly seemed to be doing the job.

Now – the ad claims this power supply can handle 36 amps for 30 minutes and then with a small rest can do it all over again. The beauty with CB radio is that because you most likely won’t be talking for 30 minutes straight you won’t be hitting the maximum ratings for this power supply. I haven’t yet tested it with my Xforce 2 x 2879 which pulls more amperage than the Cobra 350 XL I used for this test so I might find myself pushing the 36 amp rating on peak but I have a feeling this power supply can handle it. The little fan seems to run most of the time but doesn’t make a whole lot of noise.

After 3 months of use I’ve had zero problems. I turn it on when I go into the shack, leave it on for a couple of hours and then turn it off when I leave. It’s been powering multiple devices and radios over that time and I haven’t noticed any problems, interference, etc during use.

So is this little switching supply the ultimate deal? Well it does have it’s faults. It’s cheaply made, and of course made in China. The power supply doesn’t have the nicest finishing to it; it’s basically just a circuit board with a case attached to it. The actual locations for connecting your wires are mounted right on to the circuit board so as you push down and tighten with your screwdriver make sure not to push too hard or your could crack the board. So it’s very bare bones, and again it seems cheaply made but it’s inexpensive and made in China so it’s kind of what you’d expect.

The seller says there is a 2 year warranty from the factory, but how long he will be importing these or around to answer questions could be up in the air. So if you spend $65 on one of these you might be taking your chances.

As of right now though, none of the above is bothering me one bit. The power supply is doing what it’s supposed to, it’s quiet, has a fan to keep it cool, runs my radio equipment efficiently and I have no complaints.

I’m not 100% sure on the quality or how long these things will last, but for the price and with my experience so far I’d have no problem recommending these as a cheap and effective buy for a power supply. I love the space I’ve gotten back on my desk.

Now if I can only talk them into importing and selling a 75amp version for $80.