[RFI] Inverters?

Mon Sep 21 13:24:26 EDT 2020

Adding my 2c.

The makers of inexpensive generators obviously want to advertise the 
maximum power capacity. That means 100% loading of the motor hp, 3600rpm 
operation, maximum power output of the alternator or generator, and 
maximum temperature on all components, windings, and inductors.  And the 
minimum amount of copper, iron, and magnets in the gen/alt.  Hence, 
short life, poor winding balance, no reserve spinning or engine power, 
and high distortion of the AC waveform. I've seen UGLY generator AC 
waveforms and experienced dangerous split phase voltage unbalance.

We did a deep dive test and deconstruction of a inverter Harbor Freight 
3.5kw "Predator" (aptly named) competitor to the Honda EU3000.  Overall 
impressive.  At 3kw load, good output waveform, 60KHz switching IIRC, 
excellent 60Hz stability (why not with a crystal osc clock?), and some 
headroom in the DC filter bank voltage at max load.  Suspect was the 
16ga winding (ampacity) of the 2 toroid output filter, but the cores 
measured about right for the Bmax magnetics needed (we did not destruct 
them).  The electronics are mostly potted. The alternator rotor/stator 
are well constructed, balanced, and uses ferrite magnets.  It is battery 
start and the starter + supplied battery was up to the task.

The plastic injection molding and die cast Al tooling is impressive, but 
we can't speak to the durability/reliability of the engine.  The HF 
manual strongly advises about a proper break in.

The engine went to a friend for teardown to teach his kids about gas 
engines.  Some other parts went into a project we are doing and this was 
the cheapest way to get them.  Everything else went into recycle.

Others have reported on youtube that the HF is slightly quieter than the 
Honda.  I have seen HF advice that maximum continuous output should not 
exceed 2500w.  Seems ok from what was observed, but I would derate most 
any consumer portable gen about 50% for average continuous loading.

A friend also investigated if his EU3000 would start a 14kbtu AC.  It 
did, but every AC is different for max start power and worse for hot 
restart.  So a one off success.  I have not been able to test the HF 
with an 8kbtu RV AC, tbd. (I bought a second one for my RV).  Some day 
I'll test for RFI, but from the AC waveform continuity and minimal 
spikes, think it will be ok.  Still it will have a CM choke and 
commercial line filter. (my first "green wire" CM noise problem was with 
a disk drive I was designing in 1969).

So, this was an interesting experience w.r.t. how Honda is a target.  HF 
Predator 3.5kw about $800, Honda EU3000 about $2100.  Except for the 
starter design, the Honda manual can be used to service the HF.  Also, 
shows how far HF has come up in product quality, perhaps now less 
deserving of the Harbor Fright put-down.

I have no commercial affiliation.

Grant KZ1W

On 9/21/2020 04:57, Hare, Ed W1RFI wrote:
> When QST reviewed generators a few years back, we noticed a wide range in the stability of the motor speed and thus voltage vs load. For some, when we keyed a kW amplifier, the motor speed remained pretty steady. For others, the motor speed dropped significantly, then picked up, but during the drop, the voltage dropped as low as 60V from a 120V generator.  If the amp remained keyed, the motor picked up speed again, but then when unkeyed, the speed and voltage rose.  This would be a show stopper for high-power portable operations.
> 
> 
> ________________________________
> From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of Jim Brown <jim at audiosystemsgroup.com>
> Sent: Sunday, September 20, 2020 11:45 PM
> To: rfi at contesting.com <rfi at contesting.com>
> Subject: Re: [RFI] Inverters?
> 
> Hi Warren,
> 
> Several observations. First, buying ANY generator for anything more than
> FD operation should be done as an engineering project. Some of the
> design criteria are
> 
> 1) what are your loads? Grab a clamp-on Ammeter and measured them --
> don't go by nameplate, which are always worst case. Don't have a
> clamp-on ammeter? It's a VERY important tool to own. Look for one that
> measures relatively SMALL currents -- you want 5-10A full scale, maybe
> 20A or 30A. Unless you're seeing very large loads, nothing more than 50A.
> 
> 2) Our average load 24/7 is less than 1kW; it goes up (a lot) when
> cooking with electricity, running A/C, contesting legal limit, and a
> bit with large fans that are part of an HVAC system.
> 
> 3) Does your gen need to run well motors? My EU6500 Honda (inverter) gen
> does NOT like to run my well motors. A traditional gen half that size will.
> 
> 4) How much of your loads need to be on gen? I found that I could run my
> 22 cu ft fridge, computers, lighting, and moderate size home
> entertainment system on my Honda 2000i in economode. To do that, I had
> to have some of those loads redistributed between legs of 120/240 so
> that all I needed for those functions were on the same leg. Easy to do
> at the breaker panel. Our cooking is propane, so I boil water for coffee
> on the stove when on the gen. Don't try to run the microwave.
> 
> 5) Consider propane. My EU6500 has been converted, W6GJB converted his
> 2000i, and is going to do mine. A $22 can runs 20 hours or more in
> economode, depending on loading.
> 
> 6) Doing county expeditions in very quiet places for CQP and 7QP using
> W6GJB's 2-position contesting trailer with antennas on a pneumatic mast
> and the gen on the back of the pickup it's hitched to, we found that we
> needed a good noise filter. The one that Glen and I came up with was
> added to the Handbook a few years ago. If it's not in yours, you can
> find details in the latest version of k9yc.com/RFI-Ham.pdf  I should
> plug directly into the gen -- it's the AC cable that radiates noise
> common mode, the filter kills that.
> 
> This filter is designed for HF; for 6M and above, see my recent
> recommendations for coax TX chokes for VHF/UHF, using them as a
> guideline for AC cable the size of the coax in those recommendations.
> For 6M, use two turns of RG8 through a Fair-Rite #31 1-in i.d. clamp-on;
> for best suppression, use 2-4 of these 2-turn chokes in series. See the
> photo in the pdf.
> 
> 7) As others have noted, consider duty cycle. Most low cost gens, even
> the good ones, are designed for intermittent operation. My most
> demanding need when on geen is keeping the fridge cold enough to prevent
> spoiling. When running the 2000i, I typically keep the duty cycle below
> 60%.
> 
> 8) It's important to realize that worst case loads are usually starting
> a motor; once the motor is running, the load drops a LOT. It's starting
> my well motors that the EU6500 doesn't like. When in doubt, START your
> gen with no load on it, then connect the load, and once it's stabilized
> (usually under a minute, could be more with well motors), then kick it
> down to economode to save (a lot of) fuel.
> 
> Master DXpeditioner AA7JV, drastically reduced the amount of petrol he
> had to carry on the boat for his trips by using power amps that could
> run on batteries that were float-charged by the generators running in
> economode. George is a VERY smart engineer, and one of my heroes!
> 
> 73, Jim K9YC
> 
> On 9/19/2020 9:23 PM, Warren Wolff via RFI wrote:
>>     I am considering the purchase of an emergency back-upgenerator.  For the first time, I have encountered unitstagged as “inverters”.  Does this mean that some systemsare AC generators while the “Inverter-types” generateDC and then convert it to AC?    “Inverter” immediatelyprecipitates the worry of RFI.  Comments, please.
>> WarrenW7WY
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