Inverter usage

[gschwane]

We have a MH and just purchased a 2500 watt inverter for use while dry camping.  It is a "modified sine wave" inverter.  Everything seems to work well with it (not planning on trying the A/C) except our microwave oven.  Seems that it requires a "true/pure sine wave" type of current.  Does anyone have any suggestions or know of a particular microwave that will work on our type of inverter?
Thanks for any input.

 

[Ned]

Our Sharp MW works on our MSW inverter but makes a bit more noise than when on shore power.  Don't even think of running your A/C on the inverter.

 

[Gary RV_Wizard]

We've run our GE Spacemaker on the inverter in two different rigs. It complains about it but seems to manage to work. The display is often whacky and I'm not sure I would want to rely on any of its numerous automatic functions, but it does cook.

Be aware that a microwave is a power hog, so if you need to run it for more than a few minutes, be sure you have plenty of battery amp-hours.  12-15 amps @120 VAC is a common demand and that means 120+ amps of draw on the battery @12 vdc.

 

[Bob Buchanan]

We have a MH and just purchased a 2500 watt inverter for use while dry camping.

When I bought my first MH I installed a 1500 Statpower inverter. I still have it in my current rig. When it was first installed, I turned on the MW then brewed a pot of coffee to make sure I could do these things when dry camping. However, I didn't have Gary's advice at the time in terms of the down side is that a battery bank charge won't last very long doing those things.

I now never think of MW or Coffee brews while dry camping via the Inverter. I time those so they are done when I have the Genset on recharging the batteries -- and become an Amp Miser otherwise while operating under inverter power.

OTOH, if driving down the freeway and stopping in a rest area for a cup of coffee, I will brew via the inverter as I am now in a Gas Saving mode vs. a Save the Battery Charge mode. My current MW will have nothing to do with my Inverter so that always takes shore or genset power.

 

[Ned]

Schwane,

You didn't tell us how big a battery bank you have.  To drive that 2500W inverter you should have at least 440AH of battery capacity, and 660 would be even better.  That's 4 or 6 6V deep cycle batteries.

 

[gschwane]

Not being very wise in electrical issues, I'm not sure why I would need that much battery power.  Any "large" usage items would only be used for short periods of time, but we simply wanted to make sure that if we needed to use close to the 2500 watts for short periods of time, we would have that power available.  We have two 6 volt Trojan T-105 (I think) batteries.

 

[Ned]

2 T-105s are not enough to power a 2500W inverter.  They have a capacity of 220AH and as you don't want to discharge them more than 50% you actually have about 100AH available.  I would recommend adding at least 2 more T-105s to the bank to give you about 200AH of usable power.  Running the MW will draw 100-125A from batteries as will a coffee maker, depleting them in less than an hour.  Does the inverter also have a charger?  If so, it's probably a 125A charger which may be too much for your small battery bank and you run a risk of boiling the batteries.  Batteries and inverters are generally sized together, matching the AH capacity with the inverter size and charger output.

 

[John From Detroit]

I would suggest a pure sine wave inverter such as a Xantrex Prosine, and I agree with the last poster.. MORE BATTERIES

I use a pair of 130 AH AGM's with my Xantrex Prosine 2.0 and they are just, and I mean JUST big enough

 

[Lou Schneider]

Not being very wise in electrical issues, I'm not sure why I would need that much battery power.  Any "large" usage items would only be used for short periods of time, but we simply wanted to make sure that if we needed to use close to the 2500 watts for short periods of time, we would have that power available.  We have two 6 volt Trojan T-105 (I think) batteries.

The problem is deep cycle batteries cannot supply the large amount of power you need in such a short period of time.  They're optimized for long, gentle discharge cycles, not supplying large amounts of current for a short period of time.  The battery's voltage will drop under the severe load, reducing the voltage output of the inverter or even causing it to shut down from low voltage.

In addition, this kind of rapid discharge will reduce the life of a deep cycle battery.  Having multiple batteries (or multiple pairs of 6 volt batteries) not only gives you more running time, but reduces the current drawn from each battery so it does not exceed what the battery can safely deliver.

 

[Karl]

They're optimized for long, gentle discharge cycles, not supplying large amounts of current for a short period of time.  The battery's voltage will drop under the severe load, reducing the voltage output of the inverter or even causing it to shut down from low voltage.

I can give a good example: My 1500W microwave would run, but barely, on the inverter powered by two T125's. My initial thought was that it didn't like the modified sine wave. Wrong. Added two more T-125's and now it's happy Of course, it's only used for a few minutes at a time; not for cooking dinners. Maybe 5 minutes max. for defrosting a chunk of meat.

 

[gschwane]

Sounds like adding two more batteries may help a lot and allow us to use the MW on the inverter.  Thanks for everyone's input.  This has helped a lot.

 

[quiethunter]

I run an auto-tracking (2) 125 Watt solar panel unit with 10 6V batteries, and a 3000 Watt Sine Wave Inverter. All we do here in Idaho is dry camp. Not many current bushes here. Mounted on a 30 ft 5er. Works great. I had to keep adding storage batteries unil I had plenty for our usage. But the auto-tracker is the key with keeping everything charged. My panels are in the sun's face from sun-up until sun-down, and it is ready for the sun rise the next morning. For you that already have panels this frame will accomadate (2) 165 panels or (3) 100 watt panels or (2) 125 or (2) 130 watt panels. If you want further information send me a msg. Happy camping.

 

[Finn]

I now never think of MW or Coffee brews while dry camping via the Inverter. I time those so they are done when I have the Genset on recharging the batteries -- and become an Amp Miser otherwise while operating under inverter power.

Here's a simple answer to your coffee woes.... http://www.coleman.com/coleman/colemancom/detail.asp?product_id=5008C700&categoryid=27400

I've got one and it works great.

 

[terrylmichaels]

Really, new MW's should be able to accept inverted power. even the worst MSW inverter produces cleaner power than any of the current GENs on the market. The staff writers are correct. battery size is critical.  With modern appliance now day any of them should respond OK to a MSW including the new plasmas. I work in the industry and have to evaluate this type of performace all the time. The only appliance that has issues is the residential Amana how ever it is just the solenoid for the ice door flap that burns out. It is under rated. Your MSW inverter must be able to handle the surge from the start up of any appliance. If you you use Toshiba 27" flat screen tubed TV's they require degaussing and that is a big surge so it could throw a smaller inverter into a failure mode.

 

[Karl]

Terry,

even the worst MSW inverter produces cleaner power than any of the current GENs on the market.

I'm not sure what you mean by "cleaner". There are some devices (electric blankets, coffee makers/grinders, clocks/clock radios, fans) with electronic controls that absolutely refuse to work or work properly on MSW or will actually burn out, but are perfectly happy with genset power. Could you explain?

 

[Ned]

The Onan Quiet Diesel generators use an inverter and produce power as clean and well regulated as any shore power.  Our coffee maker clock runs at double speed on our MSW power too.

 

[John From Detroit]

I recently read a post regarding use of a Kill-A-Watt device with inverters... The poster said something I'm going to have to check out (When I get the famous round-tuit that is)

Part of what he said I can verify one way or another  I can state at this time "IT IS POSSIBLE", (I can not say it is true, just possible) I have seen other devices which use this type of system.

He said the Kill-a-watt gets it's power by using a capacitor to pass a portion of the 120vac to a rectifier power supply.  As i said, I've seen this done in the past, Do they do it that way now... Kill-A-Watt says they are making changes.

He said that Capacitors pass more current at higher frequencies (This is true, 100% true, In fact I know the formulas)

The capacitor that was used was chosen for 60hz operation.

This is the part I can only partially confirm

Modified sine wave inverters output frequencies not only at 60hz, but at other frequencies as well, (higher frequencies) because of the somewhat "Square" nature of the wave form

But what he said is that TRUE SINE WAVE inverters atcually are the same as MSW inverters only instead of just 2 or 3 or 4 "Steps" they have hundreds of steps.

To test this all I need to do is plug in the venerable heathkit and hook it to my inverter (It is a 'scope) but I do know how to make a true sine wave and have worked with devices that do just that.

What I don't know is if Xantrex did it analog or digital

 

[Karl]

John,
Maybe you could post a link, because we can't figure out exactly what he's trying to say with regards to the Kill-A-Watt.

He said the Kill-a-watt gets it's power by using a capacitor to pass a portion of the 120vac to a rectifier power supply.  As i said, I've seen this done in the past, Do they do it that way now... Kill-A-Watt says they are making changes.

Heck, all you need is a resistor and a diode (or 4 for fullwave rectification). Maybe add a capacitor for filtering, but not necessary.

He said that Capacitors pass more current at higher frequencies (This is true, 100% true, In fact I know the formulas)

Depends. A large capacitor will pass greater amounts of current at low frequencies; small capacitors pass more current at high frequencies.

But what he said is that TRUE SINE WAVE inverters atcually are the same as MSW inverters only instead of just 2 or 3 or 4 "Steps" they have hundreds of steps.

Unless the manufacturer is lying about it being a pure sine wave inverter, the sine wave is not stepped, but a true sine wave. I've already proven that on both my inverter and Terry's. We looked at 1/2 cycle on the 'scope and could see no 'steps' at all.

Modified sine wave inverters output frequencies not only at 60hz, but at other frequencies as well, (higher frequencies) because of the somewhat "Square" nature of the wave form

Any source of power will put out harmonics; not just modified sine wave inverters, and it has nothing to do with the "square" nature of the wave (whatever that means). Usually these harmonics are down -60, -90 or more dB's and are of no consequence and filtering them out is not necessary except for some critical applications such as MRI's and radio astronomy.

 

[John From Detroit]

Karl.. I don't know if I can find a link to his post.. But I think we are actually on the same page.

My reaction to what he said was kind of "SAY WHAT?" 

He was claiming that a true sine wave is just micro steps, where a modified sine wave was big steps.

Frankly.  I do not believe him.. But I still have not scoped my inverter to be sure

I do know it is possible to make a pure sine wave.  I do it all the time

I also know this.. I have listened to ham radio receivers when a MSW inverter was operated nearby (To rotate the beam) and let me tell you it was bad,  Electronic hash all over the place

My Kenwood TS-2000 does not even notice my True Sine Inverter. It's not there, can't hear it at all, nothing

So if this guy was right about "All the harmonics" Should I not hear the inverter every sixty hertz as I tune the bands?

I will check with the scope, But I wished to pass on what he said along with the feeling that it is that which makes the roses to grow (Male Bovine Organic Fertilizer)

 

[Karl]

John,
I know you've got the Prosine, and I believe that's what Terry has too. Like I said, we scoped 1/2 of one cycle of the 60hZ output, both positive and negative, expanded 10X, and could see nothing but pure sine wave. Mine is a small 600W Samlex and it too was clean except for a slight bulge of about 2.5 volts that lasted for less than 2.5msec on both the upward swing of the positive half cycle, and the downward swing of the negative going half cycle at exactly the same place. That I can live with

So if this guy was right about "All the harmonics" Should I not hear the inverter every sixty hertz as I tune the bands?

Generally speaking that's true if they were present, but you know that you're tuning your receiver to a fundamental frequency and it has various high pass, low pass, band pass, and notch filters to keep unwanted signals and harmonics out. Besides, the harmonics are c(e,g,etc.)sin2w0t or b(d,f,etc.)cos2w0t where the fundamental frequency is f0=w0/2pi, and therefore have much less power than the fundamental frequency (60Hz). 

(Male Bovine Organic Fertilizer)

Boy, you got that right! ;D