Author Topic: MicroSolar 300 Watt Pure Sine Wave Inverter  (Read 7348 times)

Offline Alan Georges

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MicroSolar 300 Watt Pure Sine Wave Inverter
« on: April 24, 2015, 06:33:22 AM »
Pro: Works.  It does deliver clean AC to stereo amp, fans, etc.

Con: Radio Frequency Interference City!  Despite claimed specs, it won’t run a 250 watt refrigerator.

Wow, was this thing a nasty surprise.  To test it, I tapped it onto my micro off-grid solar system’s batteries and snaked a 50’ extension cord through the house to the living room stereo and TV.  And it worked great!  The stereo amp didn’t buzz, which it does when driven by a cheaper modified sine wave inverter, and the rest of the TV and disc player, etc. seemed happy enough.  Then I tried AM radio, and it was totally jammed.  So I switched to FM, and it was jammed too!  Spent a few minutes switching the inverter off and on, changing bands, etc. to make sure.  Yes, this is a very effective RF jammer box.  For comparison, testing with an 800 watt Cobra modified sine wave inverter gave barely-detectable levels of RFI.

The only good news is that the jamming effects are lessened by omitting the long extension cord.  Sort of a hassle, because then I’ll have to haul batteries up to the living room.  Broadcast FM was no longer affected, and AM was improved (but still pretty bad) when I plugged the load directly into the inverter. So it does seem to use its power out line as an RFI radiator.  Also, HF ham frequencies were pretty unusable when this thing is switched on, S9+ noise across the board.  2m FM seemed unaffected.   I tried some snap-on ferrite chokes on all of the lines into and out of the inverter, but they had no effect.  Perhaps a very large choke on the AC out line would help.

I don’t have an oscilloscope.  It would’ve been nice to look at the output waveform, but honestly, the lack of hum when driving fan motors and the lack of buzz when driving the stereo amp told me all I really need to know about its output.  At that level at least, yes, it does work.

About the power rating and what it will drive, the inverter seemed fine with the 200-ish watt load from the stereo and TV.  My refrigerator draws 250 watts when running.  This is a little less than the inverter’s rated 300 watts, and it can supposedly put out twice that for momentary loads, so I gave it a try.  Bottom line is it didn’t work, not enough starting oomph to get the compressor motor rolling.  Oh well.  It would’ve been nice to run the fridge motor off pure sine waves, but it will run on modified sine waves in a pinch.  Not really a surprise, as the aforementioned 800 watt Cobra can't turn it over either.

Well, that pretty well sums it up.  It seemingly delivers clean AC, but its usefulness is limited by the high levels of RFI it puts out.  I’ll be using it very little, but it is good to have at least a limited source of pure sine wave power.  Frankly, I wouldn’t buy this unit again, but since it’s already here I’ll keep it.  Call it 2 stars out of 5.

Offline Carl

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #1 on: April 24, 2015, 07:23:02 AM »
Ferrite beads on the power /extension cord and earth grounding the inverter will help with the radio noise.

Motor startup on typical fridges will be EIGHT TIMES the running watts and I have good results from my 1600 watt inverter and 2200 watt generator (remember that you only get half rated power on the 120 volt generator output) will start the fridge with a struggle.That's why I always suggest over-kill when buying an inverter ,within an economy range' as it allows for easier/cooler running of the inverter and burt capability for motor starting . An inverter does NOT draw it's full power ALL OF THE TIME,it only draws what power it needs so idle/low power use  are nearly the same for small and large inverters (Alan,others may gain from this ,I know ,you know)

Offline FreeLancer

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #2 on: April 24, 2015, 08:42:15 AM »
Is the massive RFI issue an inherent problem with pure sine wave technology in general, or just this particular inverter's implementation?

Offline Carl

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #3 on: April 24, 2015, 11:41:25 AM »
I installed several of the linked unit in campers and boats with little or no reports of RF troubles (one reported noise on his HF radio with the Pre-amp turned on) Xantrex is the U.S. choice for power in many applications.

http://www.amazon.com/Xantrex-806-1210-PROwatt-1000-Inverter/dp/B002I04A74

Offline Alan Georges

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #4 on: April 25, 2015, 07:09:23 PM »
Spent some more time fooling with this inverter today, poking at its innards with a volt-ohm meter, discovered several things.  Remember: All of this poking around was done with the unit turned off and disconnected from everything, for several days even to give any capacitors time to discharge.

OK, first, it has no safety ground, no direct and obvious ways to tie the inverter to some external ground system.  Not a big deal (unless...), but it really is a light-duty unit.

It opens easily.  Four screws on the faceplate, and then the front face is off with a few dangly wires connecting things, and the top panel slides out. 

The case looks like raw sandblasted aluminum, but it seems to have a non-conductive clear coat.  The case is electrically isolated from the inner chassis, but the four side-wall screws are connected to the chassis and isolated from the case.  One of those screws might make a fine ground lug attach point in the near future.

There's an internal 40 amp ATO fuse.  Good to know, I'll have to pick up some spares.

Here's the *ahem* shocker: The AC outlet's safety ground wire is simply clipped off inside the box!  Might as well put a cheater plug on things.

For the next step in trying to reduce RFI, I'll run a safety ground from a cheater plug to the solar system's ground bus, and maybe with a jumper to one of the afore-mentioned chassis screws.  Would've gotten to it today, except that the solar power system was in actual use during a power outage and I didn't want to start running experiments while this was going on.

Thanks for the commentary Carl.  I had no idea that refrigerators pulled 8x running amps during startup; I was thinking more 2-3x.  No wonder it takes a 1500 continuous / 3000 peak inverter to drive the thing.  Normally, the fridge pulls 190 to 250 watts, depending on how cool it is, so even that big inverter is getting a good workout.

Research on reducing RFI continues, but may be on the back burner for a couple of days.... or weeks.

ps: it just occurred to me that perhaps not everyone is familiar with the term "cheater plug."  Doing a search turned up what I'm talking about, and then there's the body jewelry.  In other words, this:
https://en.wikipedia.org/wiki/Cheater_plug
not this:
http://www.bodycandy.com/cgi-bin/category/cheaterplugs
Under no circumstances should you ever electrify your body jewelry!  Not even if you have an emergency inflatable goat at the ready.
« Last Edit: April 25, 2015, 07:22:53 PM by Alan Georges »

Offline TexasGirl

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #5 on: April 25, 2015, 10:52:01 PM »
Yeah, just now reading your post, I say it's grounding issue.  Technically, the green ground wire needs to be connected to "earth" as well as the neutral.  But some Chinese designs use a push-pull as if both the neutral and hot are each a hot (as in foreign 200v systems) and will not tolerate properly grounding the neutral.

I've seen similar issues with larger "bargain" solar system inverters.  There's a push to have more and more efficient specs, smaller size, weight.  Eliminating the isolation transformer adds about 1% efficiency, with the tradeoffs of RF coupling and "ungroundedness".



One alternative is to use an isolation transformer (1:1 transformer) on the output.  Then you can properly ground the neutral, transformer case, and outlet green wire.  The extension cord should cease to be a radiator.  The inverter and transformer could also be placed within a grounded enclosure to reduce radiated RF.

http://solarprofessional.com/articles/design-installation/ungrounded-pv-power-systems-in-the-nec/page/0/2


~TG

Offline Alan Georges

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #6 on: April 26, 2015, 07:39:19 AM »
Yeah, just now reading your post, I say it's grounding issue.  Technically, the green ground wire needs to be connected to "earth" as well as the neutral.  But some Chinese designs use a push-pull as if both the neutral and hot are each a hot (as in foreign 200v systems) and will not tolerate properly grounding the neutral.
I'm pretty sure that's what's going on.  Sub-$100, made in China, lots of RFI – those are all good hints.

I think a friend in town has an isolation transformer.  If so, we'll try that next.  A decent isolation transformer is out of the budget on this project, but if there's one handy it's something to try. 

If he can't locate that transformer easily, the next step will be to test the load (stereo, TV, etc. all on one power strip) to see if there's a DC path between neutral and safety ground.  Shouldn't be, and if there is not, I'll jumper a safety ground between a cheater plug at the inverter to the solar power system's DC ground.

Remember, this quest for a 300w source of pure sine wave power is very much a "nice to have."  For emergency power, all of the major bases are already covered.  All I really want to do here is drive the stereo's amplifier without its internal power supply transformer freaking out.  The thing actually buzzes when fed modified sine waves.  Not "audio signal buzz through the speakers," I mean "raspy electromechanical buzz from the device."  And to be fair, this little inverter works great for that.  It's just that it jams every radio in the household, and maybe farther, and that's a problem.

So, in order, (1) iso transformer, (2) safety ground, (3) RF chokes.  After that, or if I manage to fry the inverter along the way, one way or the other the project will be concluded.

Anyway, thanks TG, and Carl.  Will keep y'all posted.

Offline Carl

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #7 on: April 26, 2015, 07:55:05 AM »

Offline TexasGirl

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Re: MicroSolar 300 Watt Pure Sine Wave Inverter
« Reply #8 on: April 26, 2015, 09:58:55 AM »
Here ya go, Alan:

http://ebay.com/itm/231542287275?nav=SEARCH




3.5Amps, $39.95 or best offer.  Simply ground the green ground and neutral white of the output receptacle to earth ground.  (Actually, you may only need to ground the green wire.)

~TG