Generator/AC Shootout 2017 v0.7

Copyright (C) 2017 by padgett, all rights reserved



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Note: Weasle words: This is a limited experience. The AC and generators are all single examples purchased at retail and sometimes below (I get a 10% discount at Lowes including sale items) & free shipping with Amazon Prime. It is possible that one or more may not be a representative example. The purpose of these tests is to solve a personal problem. Being a Floridian I need AC while camping.

Electrical and Mechanical concepts expressed are from observation and experience & would be glad to discuss. Can contact me at app1 at 6007 dot us.

2017 Testing

My life is like this. I begin looking for something and usually find it. Since this series began I gave away to family members the Honda and the Predator & kept the two Westinghouses which can be paralleled (but mainly just use the WH2400i when camping - is light and has a good reserve when running the AC).

To Californians and others used to reliable power a note: when I was growing up in south Florida just about everyone either had a generator and a shortwave radio (my introduction to Zenith TransOceanics). Today is is not much different. In the years I've been in this house, I have lost power for short periods every year, once for over 24 hours. I have UPSs on just about everything (Office Depot just had a sale so I bought two more) and surge protectors on everything else. Since 2004 I've had enough backup power to run the refigerators, a portable room AC, and some electronics. So a generator as a gift is not unusual.

I travel mainly "stage 3" camping, dry for up to a week but that is about the longest so my combination of two GC2s, 200W solar, and the gen for AC & coffee is "enough". Last year I proved that the single WH2400i was "enough"

However new devices appear constantly and while two years ago few thought a single 2KW class generator could run a camper AC, today it is commonplace and the market is full of products in this arena. In 2015 I proved that with simple mods a 2KW class 50 lb generator/inverter like the Honda EU2000i could reliably start a common 13,500 btuh RV AC. In 2016 I was looking for something the same size with more reserve & found the WH2400i (2400w starting/2100W continuous) that was fine for my camping that year.

2017 is different. Was thinking about the new Coleman CG3500i which appears to be a newer version of the Harbor Freight Predator 2500 (now discontinued) I tested earlier but now with 3500W starting/3000W continuous, 149.5cc engine, with a new Economy switch (possible only with inverters - see below), & the same 70 lbs but have already gone about as far with small generator/inverters as needful.

Then in early March I heard of a new version of the common open frame generator that was quiet, 3750W starting/3250W continuous & was designed specifically for RV use and had less than 5% THD (total harmonic distortion). This means able to run the AC and power sensitive electronics like laptops or a HDTV. My thought was to determine if this was true despite being out of the size/weight limits I had established before. However on Amazon for less than half the price of the CG3500i, this I had to see.

Pulling the specs out was not easy at first (better now) but the technology is quite different/simpler than the generator/inverters I had used before. Where g/is use a small, light, high speed (5000-5500 rpm), this is more like an American V8 - slow turning (3600 rpm) big (208cc), heavy (100 lbs), and with a big gas tank (4 gallons) but with a lot of modern improvements to achieve the low THD. However needs the 4 gallon tank to be able to run over 12 hours at a 50% load (1625W - enough for the AC) so is considerably thirstier than the 2400 (runs almost all night with AC on 1.3 gallons). Does have a fuel gauge though.

Additionally EPA, CARB, and USDA Forest Service approvals are good to have.

Not entirely new since the WH3250C - WH7500E series has been around for a while but those were contracter grade and not directed at the RV market so while a new model Westpro can be expected to have a lot of experience with the design.

Like the earlier models it starts by the second pull if you give it a few seconds for the bowl to fill after turning on the gas and like other units with CDI ignition, a gentle pull is all it takes. This is good since the frame makes it necessary to pull the rope at an angle.

Should also mention the packaging: the box is of the same construction as that for the 2400 but at more than twice the weight it really needs more protection

Mine was found on my stoop with "this side up" on the bottom, probably because all of the statples on the bottom were no loner connected & the bottom was open. The dent on the end cap (Westpro immediately sent a new one) probably resulted from the system falling out of the carton). I am not the only person to have this happen. Fortunately examination proved that the damage was cosmetic only

OTOH I have found Westpro to be very responsive to problems, I can usually reach a human and they usually know what is going on. They recently came under new ownership (MWE Investments, LLC) and have replaced an external service organization with their own, I hope they maintain the quality I have seen from their products (in fact I had more issues with the Honda EU2000i than the westies. Of course there is much more Honda knowlege on the Internet than for these).

Note: these are Chinese made generators but are from a major supplier (on emissions sticker) and to American design specifications. While I wish they were made in this country, at the moment there is not a lot of choice.

The major test device is a 15,100 conventional room AC I bought to cool the garage. Like the Coleman on my trailer, this is a self contained 115VAC unit. Being about a decade newer, this unit has about the same SLA and RLA as the '06 13,500. I plan to install a switchable soft start unit on it also but the 3250 has no problem starting it as is despite a momentary 53A (maximum seen) surge. Before I had to parallel the 2000 and the 2400 together to start the Frigidaire.

I also used a dual power (800/1500W) heat gun and a second 5,000 btuh portable AC at different times in an attempt to find the load limit.

Initial Tests

First I broke in the 3250 as usual running over five hours with the enclosed oil then draining and refilling with Mobil 1 10W-30 suitable for my mild climate. No problems experienced, started on first or second pull every time as long as I remembered to use the choke, drained oil was clear of any particles.

Must admit I had my doubts, years ago I had an American 3K class generator that was louder even than my 800W 2-stroke from Harbor Freight. Muffler was for a lawn mower. Gave it away as a housewarming gift to a friend.

The WH3250RVC surprised me, really could not tell any difference between it and the WH2400i or the Honda EU2000i (both very quiet). Meter showed less than 2 db difference which I attribute to the open frame/mechanical sounds. Put a scope on the output both at idle and under AC load. Noisier than the other two Inverter/generators mentioned but within 5% (see traces below).

Tried with the 800/1500W heat gun and a Portable 5,000 btuh AC. Barely grunted on start with a 200 ms transient. Connected the 15,100 btuh AC with about a 300ms transient & a 53A meaured peak current. No problem. If anything the waveform was smoother under load. 4800 Hz harmonic. No higher transients seen, looks exactly the same with a 20kHz low pass RLC filter.

Also tried with both the heat gun and the 15.1 AC to simulate AC starting while making coffee. No problem

So bottom line, if you can handle the size (17" wide without wheels) and weight (100 lbs dry) this looks to me as a very good value for the camper who occasionally "dry camps" without power but needs AC and cannot afford one or two generator/inverters and/or soft start devices. What really surprised me was how fast modern systems were able to respond. Handling 50A surges in milliseconds and with very little overshoot while maintaining +/-1 hz at 60 is impressive. Have about 20 hours on it now and no problems. If there are it does have a one year full warrenty and two more years "limited" (essentially parts but all I really need).

I still plan to fit the Frigidaire with a soft-start device to see if the inverter/generators can then start the big AC but the 3250 needs no such help, it just works.

Sidebar: Inverter Generator vs Generator

Since the end of the last century there has been a general acceptance that to have truely clean power for sensitive electroics you needed to use an Inverter Generator. Unlike a normal generator that provides AC power directly from an alternator and which may contain multiple harmonics into the RF spectrum, the inverter generator is a three stage device producing AC which is rectified into DC which is fed into an inverter to produce AC with much "cleaner" power. The measure of the "dirtiness" of power is THD or Total Harmonic Distortion. This is the square root of the sum of the squares of all of the harmonics divided by the measured voltage. If only a single harmonic then it is simply the harmonic voltage divided by the measured voltage. For example this is an example of home AC power:

Next, the output of an inverter/generator with under 3% THD:

And finally the plain generator showing less than 5% THD. Can see the difference but seems even the old and sensitive electronic devices I tried were not visibly affected

If anything, the home power is the ugliest wave. The important thing is that anything under about 6% THD is considered safe for sensitive electronics. It is clear that the generator is below this point and has a single major harmonic at about 4800 hz (well below the RF spectrum). I have asked Westpro if they can explain the 4800 (estimated) hz noise.

One major difference between a generator/inverter and a generator is a g/i can run at any speed since the output is rectified to DC then inverted back to AC. This allows most g/i machins to have an "ECO" or economy mode which slows the engine to just enough to maintain the load and stretch a tank of gas. Commony such a machine will slow from 5500 rpm (rated power) to 2000 rpm. As we saw in the initial tests some machines had difficulty ramping up to a sudden surge like an AC starting. Adding a soft-start device slowed the intial surge and gave the g/i devices more time to come up to speed.

Generators are different. To maintain 60hz the generator must hold exactly 3600 rpm so an ECO mode is impossible.Secondly they must maintain that exact speed when a surge occurs so modern generators use microcontrollers and servo throttles to respond very quickly to any change in demand. Second, very precise AVR (automatic voltage regulation) systems are needed to avoid under and over-shoots. This is where new devices have an advantage, even a decade ago such regulation was expensive and the province of 10KW and larger generators. This year is the first I have seen this capability in an inexpensive 3KW class device.

Note: waveforms were taken on a laptop using a SainSmart DDS-120 "oscilloscope", a 100X1 probe, and its enclosed software.

A very good writeup on THD can be found here.

Addendum: 1 April, 2017

Amazing how fast things change. Way back in 2014 when I realized I needed AC when dry camping, many did not think it possible. Proved it was and that resulted in the 2015 "shootout". Since then the manufacurers have been busy. 2016 was the year just about everyone had a 2KW class portable inverter generator and I said that that was enough for the AC but no reserve for much else and moved up to a 2400W/2100W continuous.

2017 seems to be the year of the "RV-Ready" 3K-4KW gensets, some loud others quiet, some <3% THD, others <5% THD, and a few more claiming RV with no THD rating atol. In February the Westpro was pretty much the only one (and still the only one with all of the features I wanted) now there are at least 4 others, expect a dozen by summer. And so it goes.

Original 2015 Shootout

2016 Update

Brief History of Generators with Low THD

Copyright (C) 2017 by padgett, all rights reserved


This page was written using Windows 10 Notepad. Some habits die hard.
All photos taken locally. I have never been very good at graphcs.