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Old 07-11-2009, 10:07 AM   #1
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Inverter Question

I'm looking to install an inverter to my coach to run the big flatscreen, the satellite receiver, the digital converter, and some other light electronics (laptop, etc.) My manuals leave much to be desired for information on wattages. Does anyone know or have a rule of thumb as to the size of inverter I'll need? Does it need to be pure sine or can it be modified sine? Any info is much appreciated.
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Old 07-11-2009, 10:34 AM   #2
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You should see a sticker on the flat screen indicating how many watts of power it consumes. If not, it should be in your owners manual that of course you kept and can find.

If your going to be running the flat screen, you really want a pure sine. Modified sine wave converters are more for things like the coffee pot, battery chargers, etc. Anything that could be compromised by the interference that modified sine wave converters might generate should be put on a pure sine wave converter, which is also fine for the other things that wouldn't be bothered by the interference.

Add up the wattage ratings of everything you think you might be using the converter for (at the same time), and then get as much above that total as your wallet will allow. If you load it too close to its rating, some devices may draw a surge when you tuen them on, causing a bogus fault condition that could be avoided with a bigger innverter.

Pure sine wave inverters are expensive, but that is the cost of having the TV on while travelling, I guess. The good part is that the bigger inverters are really not that much more expensive than the smaller ones. In proportion the price increase vs. load capacity is pretty low, up to a point. You should be able to find a sweet spot without going overboard.

Hope this helps you make the right choice, it's a sizeable investment.
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Old 07-11-2009, 10:56 AM   #3
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As was stated, every product has a a sticker on it, DOUBLE the reading for start up on electronics (So if it says 100 watts, you need at least 250 to kick start it)

Why not just do it right,, ,Have Camping world, or another installer, drop a Xantrex Prosine 2.0 into a handy spot.

This is about 2,000 watts, and 2,000 dollars (installed) worth of TRUE sine wave inverter/charger, The charger is a top line 3-stage charger with some very nice features (My opinion is that though you can do as well with other products, it don't get better period, I say the same of several makes and models however) The unit has an automatic transfer switch built in so if you loose shore power during "Days of our lives" the wife may well never notice, and it has enough power to run the microwave along with the television/home theater stuff.

NOTE: you can save big time by buying one at the REFURB store.

Install is simple if you choose to do it yoruself. the 120 volt line is this

Main breaker box 30 amp------Prosine----Sub Panel (2nd breaker box) smaller breakers to loads.

12 volt negative side Prosine====Battery (Big cable)
10 volt positive side Prosine====fuse====battery (Big cables)

And that's it,, Make sure there is a wall between prosine and batteries
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Old 07-11-2009, 03:54 PM   #4
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I think that 2000W is too light, and that a 3000W would be a betterchoice. But a more serious question wuold be how many batteries he will be pulling from to run all that equipment. I have three pairs of 6V and a 2000W inverter and wish I had more. a 1200w microwave will take almost the whole 2000w om the initial start up, and big color televisions are notoriously greedy when it comes to power usage. Add the satellite receiver loads, etc. and it will suck a lot of power.
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Old 07-11-2009, 05:07 PM   #5
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My LCDs run fine an a modified sine inverter. Most of them only need 100w or so. If he only wants to do what he says (tv, computer and "light electronics"), a 600-1000w inverter should work fine, with plenty of margin.
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Old 07-12-2009, 04:29 AM   #6
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Modified sine wave as Gary has said is fine. You may want to consider one that has a built in three stage charger as well. If so I would go with a 2000 watt, then you can run what you want other than the air conditioners. Check out the classified ads of this website as there are a couple listed.
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Old 07-12-2009, 10:03 AM   #7
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Since you are looking for s rule of thumb, you will find your LCD TV probably runs about 120W at 'standard backligtht setting' <more on this later>. Thats what my 26" does. My 46" Sony at home is 275W. My Sat reciever is aboyt 20W and is also a dtv converter although I do not need it now.

When I put in an inverter for the entertainment stuff and laptop (the wife sometimes must work 'remotely' using her laptop when we sneak off early on a trip), I found a good 600W pure sinewave converter that had a built in transfer switch for the 110v side. You probably could go with a 400W inverter, but I went for a bit more capacity with the WFCO 600TG and its been working without problems for 3 years.

The pure sinewave is probably not a requirement, but I have had issues with radio noise the modified sine wave converter I used to have (Xantrex 400w) generated. I have also heard of some people having issues with electronics and modified sine wave inverter power. BTW - it has been reported that a modified sinewave inverters 110v output wil fry a "Kill-a-Watt" meter so if you have one, do not use it with with a modified sinewave inverter.

One thing to consider is where you will put the inverter. I have a Class-C and my inverter is in the overhead < I do not have a bed - I have an entertainment center> near the 110v load and I ran ~15ft of #4 wire to the battery which is a longer run than I wanted. It would be better for the inverter to be closer to the battery, but that was not an option for me. 600W at 110VAC is ~50A at 12V and wire size/length makes a difference at 12V. The good news is that you or I will not likely go over ~250W and so far, voltage drop under load has not been a problem. The transfer switch also acts like a UPS so the TV and stuff are powered by shore power/generator and when that gets turned off, switches to inverter/battery automatically if the inverter is turned on.

Depending on your battery configuration (I have a pair of 6V batts for about 220AH), conservation can be important. I will suggest you can cut the current draw of your LCD TV WAY down by turning the backlight to the lowest setting. I keep mine on 1 or 0 (off) at night which is when I typically would be watching TV on inverter power when traveling.

SO - what I have said is a general approximation - 400-600W is the sweet spot for what you want to do. However, if you want to consider a larger inverter to power most 110V loads in your rig, forget what I have said - you will need to do a lot more planning.

Hope this Helps!
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Old 07-12-2009, 10:23 AM   #8
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Wow! Thanks for all the info. So many things to consider. I see our primary use as being only used for TV/ satellite use on the main TV while boondocking. We hate the generator running in the evening while watching TV. I'm now concerned about the batteries. I had planned on hooking this up to the 2 12volt coach batteries currently in the rig. See any issues with this?
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Old 07-12-2009, 01:06 PM   #9
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Think of your batteries as a water tank. It has a finite capacity and unless you replace what you use, you will run out of water. However, unlike your water tank which will not be damaged by being completely drained, batteries do not like to be repeatedly discharged much past 50% of their capacity and they must be recharged fairly soon or they will be will damaged a bit every time and will have a shorter life and diminished capacity.

If you have 2 typical 12v batteries, you probably have around 210 amp hours of total capacity which gives you a 'safe' capacity of 105ah. That capacity is shared with all 12 volt loads. During the summer, you should be ok as long as you re-charge your batteries daily. During the winter, you may need to watch your 12 volt power usage more depending on how much your heater (furnace) runs as they draw a lot of current when running. If yout TV and sat recieved draw 150w total, that is about 15 amps including the inverters overhead load. That means if you run the TV and receiver for 4 hours, you are using 60AH.

We have about the same battery capacity as you and we do not have any issues as long as we _fully_ recharge our batteries daily and conserve power usage in the winter. It takes about 4 to 5 hours of generator run to recharge our batteries when we run the heater and TV on batteries during the winter in addition to the lights, water pump and all the other little stuff that is always using 12v power. You will also need to be dilligent about checking and maintaining your batterys electrolite level.

If we could, we would have at least 4 batteries instead of 2, but there is no place to put two more wet batteries in our gig and I can not afford AGM batteries right now. I am still waiting for my stimulus money ;-)
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Old 07-12-2009, 02:19 PM   #10
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My response was based on actual experience. You've had a couple responses that have said they are certain a modified sine wave inverter would be fine for you, but without knowing more details, I can't say for sure one way or another.

It has been 29 years since I graduated with a degree in electrical engineering, but certain things have not changed even since then. A modified sine wave is rich in odd harmonics. It's a noise generator. Mine was very close to my TV, and I had interference...horizontal lines in the image. It bothered me enough to not want to watch it. It also interfered with my CB and AM radio, even though neither of those items ran off the inverter. You may not even use either one of those items.

My experience could have been due to the fact that the inverter that came in my rig was a piece of crap in the first place. When I would turn on the TV, the inverter would fault, and I had to play a game of switching it on and off until it would finally stay on.

I'm not the type of person who runs out and willey nilley buys the most expensive items, thinking because it costs more it would be better. In fact, I'm just the opposite. But personally, I would never own another modified sine wave inverter. Based on my experience, in this case, it's worth the difference in cost to get the better technology.
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Old 07-15-2009, 03:20 PM   #11
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I have a 3000 watt modified sine wave inverter and both my flat screens run fine. All that said however MSW inverters are noisy and on things like battery chargers, they do not work well. As was mentioned before most do not have enough battery power to use a large inverter. I have 6 T105 batteries for a total of about 720 amp hours available but even with this capacity it takes forever running the generator to charge them back up and that is with an 80 amp converter and the 20 amp charger built into the gen set. The other thing with a large inverter is to locate it as close as possible to the battery string and use 4/0 cables no longer then 16 inches from the battery to the inverter. Remember at 120 volts 12 amps is = to about 120 amps at 12 volts and inverters are not 100% efficient so figure more in the neighborhood of 150 amps at 12 volts to maybe run your microwave. Add in the DVR, TV sound system, etc, and other assorted draws you are close to 200 amps being pulled out of the batteries. Keep those inverter leads short and stout and have a very good battery string with an equally good charging system connected to your gen set.
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Old 07-16-2009, 10:37 AM   #12
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Interesting thread - if I can ask 2 questions:

1) What do most people do with large inverters - install them so they run the whole 110V system in the coach? Or wire them to specific outlets only?

2) I've heard that MSW inverters are better for running things with bricks (laptops etc), and that pure sine inverters can fry bricks but are better for more sensitive electronics. True/false?

Thanks,

- Clay
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Old 07-19-2009, 10:00 PM   #13
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Clay,

There are those like me that have battery bank limitations and simply use an inverter to power entertainment equipment. Most of the other folks replying have 4 to 8 batteries and run large inverters power all 110 v electrical loads except the air conditioner and probably water heater.

Then there are some extreme cases - I have a friend with a 42ft Super-C with two 4KW pure sinewave inverters that power _everything_ in the coach including a pair of 15KBtu heat pumps, his fridge and stove - he has no propane in the rig. He has two 48V AGM battery banks (one per inverter) and can run AC all night without going down past about 50-60% on his batteries. That is SO extreme it is not even funny, but he also has a 48CH recording studio built into the rig and a 20KW generator. He runs the AC on inverter because the generator is under his bed and the noise/vibration bothers his sleep. He and his rig are quite unique and he also has a lot of antennas on the rig for both commercial, broadcast, and ham radio.

As far as a sure sinewave inverter damaging any equipment, I think you may have things reversed. A pure sinewave inverter is the closet thing to the power from your generator or shore power you can get. On the otherhand, a MSW inverter puts out a stepped squarwave not a sine wave. Square waves cause clocks to run at the wrong speed, most microwave ovens to put out less power than normal and can be very rough on alot of equipment. My computer power supply (brick) runs hotter on a MSW inverter than a pure sinewave inverter. MSW inverters also cause TV and radio interference..

I am like others that have posted, I will not have a MSW inverter in my coach. Yes, they work and I tried it once but quickly learned that for me, it is not an option due to radio and TV interference.
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Old 07-20-2009, 09:11 AM   #14
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Hi Randy -

Thanks for the clarification - I've often been known to have things reversed! I appreciate it. I checked the "other" BBS and that's indeed what someone had me, that MSW inverters are better for brick-power electronics, but a web search showed that you're indeed correct!

Best,

- Clay
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