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Product Comparison: Amazon 30 amp switching supply vs. MFJ-4275MV

Moleculo

Administrator
Staff member
Apr 14, 2002
8,942
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A few of the WorldwideDX.com members made me aware of some small, inexpensive switching power supplies being sold on Amazon and eBay and they swore that they were free of hash. After my unbearable experience with the MFJ-4275MV supply (original thread here), I was curious to find out myself if the $30, 30 amp switching supply on Amazon made for a better operating experience.

This is the product that I purchased on Amazon:


And this is the MFJ-4275:

2129-1333519364-916016ac19bf2470323b6d738ed30e0b.jpg



The Amazon unit doesn't come with a power cord, but must of us have those laying around to sacrifice. After wiring up the AC, I also wired up a DC cord for the rig, complete with Anderson power poles.

The first thing I wanted to find out was how bad the hash problem is on the $30 Amazon unit. I turned on the NaP3 Panadapter, used with my Elecraft K3 and took a print screen so you can see the hash present on the MFJ supply:

3173-1411531265-7c4eee4c7b37da920c03edb5d1eb7169.jpg


Note the circled slanted lines - that's the interference you will hear in the RX present on any of those frequency ranges. It sounds like a whistle going by and is quite loud.

This next screen shot was taken only minutes later after changing the rig over the the Amazon 30 amp switching supply:

3174-1411531538-4a011940be627daec3ee1fdf90908bcc.jpg


As you can see, all of the slanted lines are gone. I've been using this supply for about three weeks now, and no matter what band I'm on, I hear no interference from the supply - a night and day difference from the MFJ unit.

I also developed a problem with the MFJ with the voltage varying significantly every time I turned it on. I had set the supply to 14 volts, but found it as low as 11v on occasion and as high as 16v! So far, the Amazon unit has consistently held the voltage I set it at (14v). I do notice about a 1v drop under transmitting at full power with the Amazon unit, but that is about the same as the MFJ supply.

All told, I couldn't be happier with this little, inexpensive supply and haven't found a reason why anyone should spend more money on a more expensive unit.

10/28/14 Update:
I found some hash with this unit and have posted details with a pic later in this thread: http://www.worldwidedx.com/threads/...upply-vs-mfj-4275mv.174465/page-2#post-500387
 
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222DBFL

Sr. Member
Jul 28, 2013
3,300
1,352
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Thanks for the review. My megawatt s400 has performed flawlessly as well! Might have to get one of the units like yours just cause they are so inexpensive! They do work well for the money and I believe megawatt or someone makes the proper part to run 2 or more in parallel. Tallman I believe runs a couple of these In parallel and has had good luck with them, he uses the s400 megawatt units but they are the same unit as what you have minus the power cord. Again thanks for the review Moleculo! God bless.
 

Tallman

W9WDX Amateur Radio Member, KW4YJ EXTRA class
May 1, 2013
5,123
5,953
573
Louisville, KY
Thanks for the review. My megawatt s400 has performed flawlessly as well! Might have to get one of the units like yours just cause they are so inexpensive! They do work well for the money and I believe megawatt or someone makes the proper part to run 2 or more in parallel. Tallman I believe runs a couple of these In parallel and has had good luck with them, he uses the s400 megawatt units but they are the same unit as what you have minus the power cord.

The only switch mode power supplies I have run on my bench is the MegaWatt 400. To run two of these in parallel you need the diode isolator. You have to keep the power supplies from trying to regulate each other.
MegaWatt has higher output units now that they did not have when I bought mine. For the price you pay for these are well worth it in every way you can imagine.
Two years and not a single problem with the power supplies or the diode isolator.
 

Spiderleggs

Member
Oct 1, 2012
27
12
13
The only switch mode power supplies I have run on my bench is the MegaWatt 400. To run two of these in parallel you need the diode isolator. You have to keep the power supplies from trying to regulate each other.
MegaWatt has higher output units now that they did not have when I bought mine. For the price you pay for these are well worth it in every way you can imagine.
Two years and not a single problem with the power supplies or the diode isolator.
 

Spiderleggs

Member
Oct 1, 2012
27
12
13
I also use one of these and haven't had a problem with it in the 1 1/2 years I've had it. I originally ordered two with one for a buddy and one didn't work. I sent it back got another and works nicely with my 98vhp.
 

mr_fx

Sr. Member
Oct 8, 2011
1,537
172
173
Kansas City
I have owned the megawatt 400 watt unit, the first one I had got taken out by lightning, the seller offered to replace it for the cost of shipping, like $10, like any cheapskate ham I took him up on the offer, , then I later sold it when I sold my first HF rig... the new owner says it is still working well

I bought another one when I got my 857d... I love it, works perfect on all bands

it may not have fancy connectors, or voltage readouts or be able to love me long time... but it does the job and it does it VERY well
 

cbradiomagazine.com

2008 - 2014 / Pau Hana
Jan 3, 2007
689
196
53
I'm still on my original Megawatt (2 years now I think or more) and it's worked flawlessly. Can run any 2 pill amp, radios, etc. No voltage drop, no hash, it's amazing to me to have something so small after years of big, heavy power supplies taking up all my desk space.
 
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SuperDave

Active Member
Sep 10, 2012
157
9
28
Luling, La.
Well I ordered one of these units last week friday and it should be here this coming Thursday. What kind of power cord do I need to find for it?
 

tba02

WOOF
Jan 26, 2014
618
403
173
SF Bay Area, CA, USA
I just cut the end off a computer power cable I had laying around. 14Ga or larger depending on the run (I used 2 feet).

[Edit - changed 16ga to 14ga after I got home and double checked - 16ga should still probably work]
 
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SuperDave

Active Member
Sep 10, 2012
157
9
28
Luling, La.
I just cut the end off a computer power cable I had laying around. 14Ga or larger depending on the run (I used 2 feet).

[Edit - changed 16ga to 14ga after I got home and double checked - 16ga should still probably work]

Thanks! I cut the cord off of a broken surge protector the other day and my girlfriend looked at me like I was retarded.. I knew it was going to come in handy, now I just have to remember where I put it!

I have one of those that I use for my 2m Yaesu. I'm very satisfied. I also have the 50 amp one that I use for my Mirage B-1030 and it has no problems with full power on the amp.

Do you have a link to the 50amp?
 

SuperDave

Active Member
Sep 10, 2012
157
9
28
Luling, La.

tba02

WOOF
Jan 26, 2014
618
403
173
SF Bay Area, CA, USA
Singularity35 - can you get that 50 amp version to go to 13.8 volts?

It looks very much like this one (note the description says 12v but the picture is a 24v model)
eBay item #321541229907
.. but not quite, and the specs indicate 12v max.
 
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dxChat
Help Users
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  • @ ButtFuzz:
    on the connector with the green wire, if you short that to a nearby black wire, the power supply will turn on. (for use as a bench supply or whatever)
  • @ ButtFuzz:
    And IIRC, the purple wire is -12VDC, but that is from memory and it does not serve.
  • @ ButtFuzz:
    So if you need, say, 7v, connect + to the Yellow wire and - to the Red wire.
  • @ ButtFuzz:
    or or you need 9v connect + to the yellow wire and - to the orange wire. note: not all PSU's have the orange wire nowadays, as many manufactures had the voltage regulation on the motherboard, and all the power supply gives is 12 vdc
  • @ BJ radionut:
    Thanks ROB will check it out!~!! got to clean the work bench a little make room for that big case :)