Sine Wave Inverter Anomaly

[SoundGuy]

After following this recent discussion about how to best utilize a sine wave inverter for RV use I decided to go ahead and buy the 1000 watt model mentioned in this discussion since it was on sale for just $199 at Canadian Tire, certainly the lowest price for this size in these parts. My primary use for it is to power 120 vac fans in the camper when dry camping, and based on battery reserve possibly to power our coffee machine, toaster, and my wife's hair dryer, my current limitation of course being the single G27 battery that's presently on the trailer. After musing about it for awhile I decided I'd prefer to wire the inverter "whole house" so I could power the trailer's entire 120 vac system by simply plugging the main service cable into the inverter, the limitation of course being the inverter's maximum 1000 watt rating. I decided to install the inverter on a shelf hung from the joists in the front passthrough compartment where it would be protected from the weather, ventilated, easy to reach, yet occupying otherwise unused space. 6 feet of 4 gauge for both the positive and negative input cables got me to the battery where I ran the positive through an 80 amp fuse. The 120 vac output cable was a few feet of 10 gauge main service cable I happened to have on hand, terminated with a 15 amp Leviton WetGuard connector. For anyone interested, a series of 4 pics starts here.

Time to check everything so although I KNEW everything was wired correctly I proceeded cautiously and before plugging anything in at all decided to check the inverter output with a polarity checker. UH OH ... open ground! :h Hmmm, I never expected that but then I can't say I've ever checked any inverter output with a polarity checker before ... but no question about it, both inverter output receptacles are showing an open ground and indeed if I measure between hot and ground my voltmeter is showing 0 volts rather than a nominal 120 volts as it should and as there is between the hot and neutral. After thinking about it for awhile I decided to go ahead and plug in the main service cable, reasoning the trailer itself would provide the necessary ground ... and bingo, it did. So - it all works just as it should, the inverter easily powers all the aforementioned appliances, BUT I have to wonder why this inverter's output receptacles are not grounded. The inverter does have a chassis stud so it can be grounded to the trailer chassis but that makes no difference at all - it appears the inverter's output is simply lacking ground. Unfortunately the owner's manual is really simplistic and has no schematic so I'd like to ask if those owning a sine wave inverter have ever run into this same situation with their inverter's output not being grounded? :@

[brulaz]

By the way, SoundGuy,
how did you wire that wimpy little case ground post on the inverter. Separate wire to trailer chassis or just a jumper to the inverter's battery neg post (which winds up wired to chassis at the battery).

IIRC a separate wire to chassis is what's recommended?

[brulaz]

SoundGuy wrote:

...
Seems like you're currently between a "rock and a hard place" if your new EMS won't pass the inverter's floating neutral output but the manufacturer warns against bonding. :E
...

By putting the relay (transfer switch) between the EMS and distribution panel, the issue will be resolved to my satisfaction.

The result should be a non-bonded, floating, 120VAC RV, same as it is now, same as EMS likes it, and in agreement with at least some of the commentators here. 🙂

Once installed, I can smell the roses, or swat bugs, but I will not pursue the bonding/non-bonding arguments. I have little tolerance for head banging. :B

[SoundGuy]

brulaz wrote:
Well, the Prog Ind EMS doesn't like this inverter (same as OP's). It refuses to start up with an E2 or "Open Ground" error, but says there's 118VAC present at 60HZ.

And with Prog Ind's strong words against bonding (quoted earlier above), I don't think I'll try that. Have sent Prog Ind an email about it but no response so far.

Seems like you're currently between a "rock and a hard place" if your new EMS won't pass the inverter's floating neutral output but the manufacturer warns against bonding. :E FWIW, TRC now offers an upgraded Surge Guard 34830 model which also won't pass power if it detects what it believes is an "open ground", unlike my earlier version Surge Guard 34730 which ignores it and does pass power. While you're waiting for a response from Progressive I'd suggest you grab a coffee, sit down and take l-o-n-g hard read of that bonding discussion linked to earlier. Heck, I've been at it twice now and I'm still only at Page 15! If nothing else, because of what has been brought up I may add a GFCI to both my genset and inverter outputs ... but because of all the "professional", yet heated arguments in support of either view, I'm still not convinced whether to bond or not to bond. :h

[brulaz]

Well, the Prog Ind EMS doesn't like this inverter (same as OP's). It refuses to start up with an E2 or "Open Ground" error, but says there's 118VAC present at 60HZ.

And with Prog Ind's strong words against bonding (quoted earlier above), I don't think I'll try that. Have sent Prog Ind an email about it but no response so far.

With both my VOMs (digital), I get similar results at the inverter output as the OP. And testing my trailer 120VAC wiring with the ohmmeter shows no bonding there.

So, the transfer relay has arrived and will be going in between the EMS and 120VAC distribution panel, eventually. And the trailer's 120VAC will remain floating (unbonded).

[SoundGuy]

road-runner wrote:
A lot of debate on this thread: 406 posts about floating output, grounding, and bonding.

Holy (*%(^&){*) Batman! "Debate" is an understatement ... I'm only on Page 4 and the boxing gloves are out! :E That was back in 2008 and now 7 years later we're still debating ... guess I'll just have to forage through all 41 pages in hopes I may find some clarity on the subject! :S

Thanks for the link ... I think. :W

[MEXICOWANDERER]

I clip a 3 meter lead onto an exposed metal part of the converter and use a commercial voltage non contact detection device to determine leakage if any. It is my understanding thirty volts is the detection threshold of many of the detectors. By scanning the tip if the stretched-out wire, a good idea of voltage leakage exists. Curiously I have detected voltage in this manner, but insignificant voltage measuring voltage with a meter from case to inverter neutral.

[MrWizard]

406 post bonding generator bonding thread

yes.. i made the same logical statements in that thread

i'll add one more statement
there have been numerous posts in these forums about, shocking or tingling, at home or in the CG when touching the RV skin , door etc while standing outside when rv is plugged into shore power
it always leads back to a grounding issue, or power leakage
in the RV or at the power source

i DO not remember any such posts,,regarding this happening while dry camping and using an inverter

if anyone has had this happen with an inverter turned on, NO shore power please post it.. or a link to the post

[SoundGuy]

MrWizard wrote:
try a different Fan..

this might be specific to the windings in the fans motors
or specific to this inverter

I have tried several different fans, they all squeal, objectionably so when powered with an MSW inverter, only slightly with this 1000 watt sine wave inverter I now have ... on 120 vac shore power no squeal at all.

i myself do not want a bonded electrical system when dry camping, NOT connected to shore power, i do not desire having the frame or metal skin of my RV, as part of the active hot electrical system, by being tied to the neutral , even more so for a portable generator sitting on the ground, possibly creating a circuit path between damp ground and the rv body
i prefer to keep the real power between neutral and hot, not body frame and hot,, with a floating neutral,, the perceived 60v to grd/frame is induced phantom voltage with NO current potential because it is not electrically connected to the power producing inverter

Good point ... thanks for the input!

[MEXICOWANDERER]

SoundGuy wrote:

BurbMan wrote:
I guess when you're retired you have time to endlessly ponder such things...

Ha Ha! I guess you're right, 'though as I mentioned in another discussion I'm not totally retired and still do put in ~ 20 hrs week ... helps keep me clear of the Honey Do list! 😉

When refrigerator honey-do sticky notes graduate to 8-1/2 X 14"

You in trouble

[road-runner]

Regardless of what is causing this it's evident that bonding the inverter's output makes this "problem" of errant voltage readings disappear ... whether that's preferable or not I guess is the question I still haven't been able to answer.

I believe the several posts that have put forth an opinion have agreed that (1) It's not a problem, and (2) There's no strong argument toward bonding or not bonding. IMO, there's no strong argument because it's not a problem. For myself I wouldn't bother bonding it, but if it makes you more comfortable, add the bond.

A lot of debate on this thread: 406 posts about floating output, grounding, and bonding.

[MrWizard]

we have (4) 6" fans, (1) 10" fan, and (1) 20" box fan
that we run from inverter power, NONE of them squeal, not on the 300w go power psw , or on the 1250w tripp lite power verter msw

the 10" is 7yrs old and ran two summers on a vector 400w msw from pep boys
and did not squeal then either (that i remember)

try a different Fan..

this might be specific to the windings in the fans motors
or specific to this inverter

as far as Anomaly..
there is NO anomaly
most inverters today are built with a floating neutral
aka not bonded..it is normal and it is safe in the RV

i myself do not want a bonded electrical system when dry camping, NOT connected to shore power, i do not desire having the frame or metal skin of my RV, as part of the active hot electrical system, by being tied to the neutral , even more so for a portable generator sitting on the ground, possibly creating a circuit path between damp ground and the rv body
i prefer to keep the real power between neutral and hot, not body frame and hot,, with a floating neutral,, the perceived 60v to grd/frame is induced phantom voltage with NO current potential because it is not electrically connected to the power producing inverter

[SoundGuy]

Salvo wrote:
The 60V from hot to ground and from neutral to ground are caused by capacitive voltage divider, not inductive coupling. Some electronics (like the converter) have emi capacitors from hot to ground and from neutral to ground. The sum of these two voltages will add up to 120V.

Even though the 60V seems daunting, it is harmless. If you were to measure this voltage with an analog meter you would get about 5V, not 60V. The analog meter has lower input resistance, similar to what the human body has.

Although I'll pass on the human body test I did compare DVM to analogue voltmeter readings and the analogue reading was significantly lower in each case ... the only reading that remains consistent is the hot > neutral, which one would expect. Interesting also is if I reverse the probe polarity for either meter the neutral > ground readings change to something completely different. Regardless of what is causing this it's evident that bonding the inverter's output makes this "problem" of errant voltage readings disappear ... whether that's preferable or not I guess is the question I still haven't been able to answer.

[SoundGuy]

BurbMan wrote:
I guess when you're retired you have time to endlessly ponder such things...

Ha Ha! I guess you're right, 'though as I mentioned in another discussion I'm not totally retired and still do put in ~ 20 hrs week ... helps keep me clear of the Honey Do list! 😉

[SoundGuy]

road-runner wrote:
Does the fan even have a connection to the ground wire?

No, it doesn't, nor does the table fan, but other devices such as the toaster, coffee machine, and hair dryer are wired to ground with a 3-prong plug. The fan squeal isn't so much of an issue as it is a curiosity because it is so slight, yet nonetheless distinguishable from when the fan is running on 120 vac shore power. Rather, I'm more interested in these unusual voltage readings between neutral and ground when the inverter output is not bonded.

The quality of the filtering varies from inverter to inverter, possibly related to "you get what you pay for".

That certainly seems to be the case here ... unfortunately I don't have access to a premium quality sine wave inverter so I can compare the results but it wouldn't surprise me if this slight squeal disappeared entirely.

[SoundGuy]

Salvo wrote:
Even though the 60V seems daunting, it is harmless. If you were to measure this voltage with an analog meter you would get about 5V, not 60V.

As it happens I still have a Heathkit analogue voltmeter I built many, many moons ago :E so thanks for that tip, I'll have to go dig it out and see what difference in readings there may be between it and my DVM.

FWIW, I did try those tests suggested by vermilye ... indeed, when I load the circuit with my wife's hair dryer (on low ~ 300 watts) that fan squealing noise almost completely disappears. However, when I tried to measure current flow between neutral and ground the Surge Guard immediately decided to not play nice and turned off ... I'll have to try this another time with the SG out of the system. Great suggestions, I really appreciate all the ideas being presented! :B