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Old 11-11-2011, 08:16   #1
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Modified Sine Wave, Buzzing GFIs and Electrical Damage

I have been cruising for 15 years with a Heart Interface 1KW modified sine wave inverter / charger with no problems other than poor microwave efficiency. I recently purchased a 2008 boat with Freedom 30 3KW modified sine wave inverter. When under inverter power all systems operate but my GFIs make an obnoxious buzzing sound that was not present on the other boat. I plan to try replacing the GFIs to eliminate the sound but may also consider pitching the current inverter. My question rather simple, how many folks have actually had AC electronics gear damaged by the modified sine wave? My experience to date has been quite good so I'd rather not pitch a perfectly good inverter, but thought I would get some new insight. Thanks.
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Old 11-11-2011, 08:35   #2
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Re: Modified Sine wave, buzzing GFIs and Electrical Damage

Replace the GFI. The new GFI dont buzz, at least mine dont with a 3000 watt MSW inverter. My GFI are totally silent. I bought them on Ebay. And remember reading the standards changed and older style ones will buzz with a MSW invertor.

If you get one that meets this then should be good.
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Meets or exceeds 2008 UL 943 class A, UL 498. Protects from miswired line-load connection. Increased surge immunity. More resistance to electrical noise and to moisture corrosion.
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Old 11-11-2011, 08:44   #3
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Re: Modified Sine wave, buzzing GFIs and Electrical Damage

I used to have an older inverter with a modified square wave (more technically correct term ). It destroyed a couple wall warts. Electric motors such as in power tools never quite worked right either.

I now have a 3000 watt inverter with a true sine wave. It creates no electrical noise, the microwave works normally and it also runs some pretty power sensitive oceanographic equipment controllers.

If money is not an issue, it is probably worth getting a true sine wave inverter.
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Old 11-11-2011, 08:45   #4
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Re: Modified Sine wave, buzzing GFIs and Electrical Damage

My solution 15 years ago was to dump the GFI's. I've never damaged anything running it on the MSW inverter. However, some newer appliances don't use enough power in standby mode to turn the inverter on, so I have to plug in a small load like a cell-phone charger to trigger the inverter. I also find a separate 150 watt inverter is much more efficient for small loads like the cell-phone charger.
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Old 11-11-2011, 12:03   #5
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

Le Tour-
Check the Owner's manual for a list of GFCIs that Xantrex has tested and found to work with the MSW (good one David M!!) inverter/charger.

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Old 11-11-2011, 19:59   #6
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

Quote:
Originally Posted by Le Tour View Post
My question rather simple, how many folks have actually had AC electronics gear damaged by the modified sine wave?
Modified sine waves are perfectly idea for all electronics. At greatest risk are motorized appliances.

Usually coils are sealed in a varnish type material. Higher frequency anomalies (ie modified sine waves) do not vibrate that wire. Apparently your GFI coils are not sufficiently sealed. Vibration is not harmful; just annoying. At greater risk are motorized appliances and any power strip protectors.
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Old 11-11-2011, 20:12   #7
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

I installed one of these last year.
Perfectly happy with it.

OSP 1500W PURE SINE WAVE POWER INVERTER 1500 3000 WATT | eBay

The first thing I did was add a remote switch and LEDS at the galley.
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Old 11-11-2011, 22:18   #8
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Many thanks for the good replies. I purchased a newer 2010 Leviton GFCI ( could not determine if it conformed to the newer UL standard as suggested), unfortunately the buzzing was actually worse. I also noticed some buzzing coming out of the stereo receiver and TV while on inverter power but not shore power. I suppose it's decision time, drop $1200 on a pure sine wave replacement or live with the buzz. Thanks.
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Old 11-11-2011, 22:31   #9
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

A couple of months ago I purchased a Xantrex pure sine wave inverter from West Marine.

A 1000 watt continuous, 3000 watt surge pure sine wave inverter for $300 US including shipping. It was on sale, so I'll look to see which one I purchased and what the regular price might be.

edit,... this one. Still the same price, maybe not on sale when I purchased one. http://www.westmarine.com/webapp/wcs...classNum=50539

I was considering the Morningstar 300w unit for the same price until I saw the Xantrex.
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Old 12-11-2011, 00:31   #10
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

Well, here's some more anecdotal hoo-haa:

We are still using the Heart Interface MSW 600 W inverter that I bought in 1988 or thereabouts. Has never caused any damage to devices plugged into it. Variable speed tools have jerky "throttle response", but seem to reach full speed and torque. Everything else that I have plugged into it has worked fine. I've never looked at its waveform on a scope, so don't know really what is happening, but 20+ years of faultless usage is hard to criticize. It also has very low idle current which I appreciate. Many of the true sine wave jobs draw a couple of amps at zero load, and that would be unacceptable to me, 'cause I like to leave it on 24/7.

I know that this sort of data isn't statistically important, but hey, it works for me!

Good luck and cheers,

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Old 12-11-2011, 04:05   #11
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

I’ve burned up 2 Dell computer plug/chargers in the last 5-6 years--they do get hotter with the modified sine wave- and both times i forgot to unplug them for many hours- so now I plug them for 1 hour max. at a time-let them cool for 15 min and plug back in= I have a vacuum cleaner, blender, food processor and power tools I’ve been using with no trouble
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Old 12-11-2011, 06:23   #12
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

Mobile Power Outlets

I have a Peak 3000w MSW inverter shown here.
The GFCI does not buzz.
Perhaps differnet MSW inverters have differing wave patterns on the output.
This one runs everything. So far starts midsize fridge, 1300 watt microwave, all variable speed tools and fans. The microwave is louder than on utility power and the fan has a slightly different sound.


I wired in a remote switch and used a computer plug for a quick disconnect.




I also wired this into the boat outlet circuit using a 20 amp DPDT switch on-off-on to flip the hots and neutrals.
So I have a shore-gen switch to select between shore and genset. Then on the outlet circuit from the breaker panel I can select shore-gen power OR inverter power. So right next to each other, I have 2 switches and 2 LED. The LED lights up when the inverter puts out 120 volts. The other LED lights up when the outlet circuit is powered.

This inverter shuts down if the load exceeds the 6000 watt surge capacity

This is the GFCI I got off ebay and works with no buzz.

http://www.ebay.com/itm/GFCI-Outlets...ht_1161wt_1066

110 volt LED lights, good deal here. Also they have 12 volt led look the same.
http://www.ebay.com/itm/290571856826#ht_3221wt_1216
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Old 12-11-2011, 06:53   #13
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

Get the pure sine inverter. Do not compare the old Heart Interface units with current Xantrax cr*p. There's plenty of threads on this forum to find out the reasoning behind this.

I would stay far away from any new Xantrex units for the time being. I took my loss a year ago and replaced the 3kW Xantrex with a Victron unit. Completely cures the situation.

cheers,
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Old 12-11-2011, 12:26   #14
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Re: Modified Sine Wave, Buzzing GFIs and Electrical Damage

Some inverters use the old c-form transformer, and they buzz.

Newer better quality inverters use a toroidal transformer, and they don't buzz....as bad, if at all.

MSW, or Pure SW, will buzz if they use the c-form transformer.

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