Math Check Please

Alaska Man · October 2014

If my inverter is using 3Adc at idle * 12V = 36w x 24 hours so my inverter is using 864w a day. That's on the DC side, so I'm using 72Ah out of my 880ah bank just to run the inverter!?!?

Blackcherry04 · October 2014

Re: Math Check Please

That sounds about right, anytime you have a full featured Inverter / Charger with more control options like Transfer relays, remote panels , they all take power. Now when you say " Idle " if you have no load then it should to be able to go into standby. That is sometimes a problem with a modern refrigerator because there are not enough watts to pull it out of standby. Standby threshold is usually adjustable from like 5 w to 50 w or so.

One thing you can do is look for any Parasitic loads, like anything with a remote is always using power. No matter how I try, I can't get mine below 10 amps, It's the cost of having power.

Alaska Man · October 2014

Re: Math Check Please

Thats what I've been going over in my head............ The Fridge requires the larger inverter along with the Toyo heater in the winter. the Heater only runs when we aren't home, but draws a lot of power on warm up. I can do away with the fridge in another few weeks and go to the cold room. After that I think we could get away with a 400W inverter.

Just wondering about setting up some kind of switching so I could go back n forth depending on the season and our needs. Right now about 32% of usuable 220AH stored battery power is going just run the inverter. It seems like I could gain a day or two between cloudy day charges with another more efficient unit.

Blackcherry04 · October 2014

Re: Math Check Please

Alaska Man wrote: »

Thats what I've been going over in my head............ The Fridge requires the larger inverter along with the Toyo heater in the winter. the Heater only runs when we aren't home, but draws a lot of power on warm up. I can do away with the fridge in another few weeks and go to the cold room. After that I think we could away with a 400W inverter.

Just wondering about setting up some kind of switching so I could go back n forth depending on the season and our needs. Right now about 32% of my stored battery power is going just run the inverter. It seems like I could gain a day or two between cloudy day charges with another more efficient unit.

I am sure you could come up with a transfer switch that you could swap the loads over to a smaller Inverter. I have 3 Inverters and I make the change over and do not use 2 of them in the winter. I have mine set up on Range plugs and just plug around the ones I am not using.

One I have dedicated to a A/C and sure not using it in the winter. I like having more than one in a emergency.

Alaska Man · October 2014

Re: Math Check Please

I would have to pick up another battery charger since the Xentrex is a combo. Right now I use the 150Amp that's in the Xentrex. I see a reconditioned Iota 75amp on the front page. Would I see very different charge times going to a smaller charger?

vtmaps · October 2014

Re: Math Check Please

Alaska Man wrote: »

If my inverter is using 3Adc at idle * 12V = 36w x 24 hours so my inverter is using 864w a day. That's on the DC side, so I'm using 72Ah out of my 880ah bank just to run the inverter!?!?

That should be 864 wattHours per day. And yes, that's a lot on a small system. My Outback inverter has a tare loss of 480 watthours/day... that's almost as much as my DC fridge uses.

Generally it makes sense to buy an energystar AC fridge (cheaper than DC fridge) and use the money you save to buy more panels or battery. But that's only if you have a big inverter running 24/7 for other reasons (water pump, HVAC, etc). If the only reason you're running a big inverter is for the fridge, it may make sense to consider DC refrigeration. The Danfoss compressor used in many DC fridges is a variable speed compressor.

Another recent development is the 'inverter refrigerator'. They run on AC and use variable speed compressors and have low startup surges. They seem to be available throughout the world, except for north america. There's another thread about them... I think they will be sold in north america fairly soon.

--vtMaps

Blackcherry04 · October 2014

Re: Math Check Please

Alaska Man wrote: »

I would have to pick up another battery charger since the Xentrex is a combo. Right now I use the 150Amp that's in the Xentrex. I see a reconditioned Iota 75amp on the front page. Would I see very different charge times going to a smaller charger?

Yes, the time would be longer depending on the dod of the batteries. I use a couple different charging schemes depending on what charging source I am using. For me with a Honda EU 2000 I can use a IOTA 30 amp and let it charge for say 7 hours and use the Inverter in by-pass with the charger off and let it Idle. You can cut the charge percentage back on the Inverter and let it charge at a lower level and see what it does to your fuel use with out buying another charger. My other choice is a 20 KW Generator that uses 2 gallons a hour.

Cariboocoot · October 2014

Re: Math Check Please

Note: Outback inverter; 20 Watts running, 6 Watts on standby.

Just one of the many reasons they are better than most.

Alaska Man · October 2014

Re: Math Check Please

I do like the fact that the Xentrex passes AC through to the distribution panel when I am charging. It also makes it easy when I run large power draws like my saws, compressor and such. I plug into the Xentrex and charge while I'm using my tools. The generator is running anyway, might as well charge.

Does the Outback have a similar functionality?

Blackcherry04 · October 2014

Re: Math Check Please

Alaska Man wrote: »

I do like the fact that the Xentrex passes AC through to the distribution panel when I am charging. It also makes it easy when I run large power draws like my saws, compressor and such. I plug into the Xentrex and charge while I'm using my tools. The generator is running anyway, might as well charge.

Does the Outback have a similar functionality?

Having both, I guess I could comment. In principal they are the same, both have about the same features. The Outback is more expensive and has programming that the Xantrex lacked except in the XW series. With the advent of the New SW series has the same XW operational control was put in the new SW Conext Series and the Freedom SW 3012 & 24 , SW 2012 & 24. with the new Operational control system, gone are all the fixed Defaults and algorithms.

Xantrex software is known to be buggy and they are slow to correct it. Outback on the other hand will respond to requests.

Outbacks are easy to field repair and do not require shipment to a repair center.

The Outback tare loss is less, as posted. I like the way you can have two sets of perimeters for two different inputs ( Grid & Gen or Gen1 and Gen2 ) and switch back and forth on the fly.

Rybren · October 2014

Re: Math Check Please

The Inverter Refrigerators are available in Canada - the price is pretty good too. http://www.lowes.ca/refrigerators/samsung-rf220nctaww-216-cubic-ft-french-door-refrigerator_g1340228.html

Alaska Man · October 2014

Re: Math Check Please

Thanks for the help, All.

Alaska Man · October 2014

Re: Math Check Please

New question. I got an 800W Modified Sine Wave Inverter (Cobra) that I want to run for the winter (Draws .005 milliamps) and only turn on the 3,000W (Xentrex)when it's needed. My thought is to hard wire them both into the main breaker on the distribution panel that way no matter which one is on they can both be disconnected or connected with the same breaker.

My question is, since the big inverter is Pure Sine Wave and the little one is Modified Sine Wave, if they are ever both on at the same time and connected to the same breaker is that going to work or will the breaker become some kind of battle ground?

Also since the charger is built into the big PSW inverter is there going to be an issue when the genny feeds power through the Xentrex to the same breaker?

inetdog · October 2014

Re: Math Check Please

Alaska Man wrote: »

New question. I got an 800W Modified Sine Wave Inverter (Cobra) that I want to run for the winter (Draws .005 milliamps) and only turn on the 3,000W (Xentrex)when it's needed. My thought is to hard wire them both into the main breaker on the distribution panel that way no matter which one is on they can both be disconnected or connected with the same breaker.

My question is, since the big inverter is Pure Sine Wave and the little one is Modified Sine Wave, if they are ever both on at the same time and connected to the same breaker is that going to work or will the breaker become some kind of battle ground?

Also since the charger is built into the big PSW inverter is there going to be an issue when the genny feeds power through the Xentrex to the same breaker?

Basic rule of thumb (right up there with "Don't hit it with the hammer!") is that you can never connect two inverter outputs together unless they are both from the same manufacturer and there is an official stacking function, probably with a sync cable, to enable that operation.
Beyond that, even from the same manufacturer, there is no way to stack a PSW and an MSW inverter to connect them in parallel.
You need to either use a transfer switch, a pair of breakers with a mechanical lockout to keep both from ever being closed, or a plug-in cord connection on both generators so that you can only plug in one of them at a time.
Now if you wire the two inverter outputs directly to separate loads (or to separate load panels even), you can use them both at the same time.

Normally the AC switching built into the Xantrex takes care of all of the issues with generator and charger, but adding the MSW inverter into the mix will not work in that context either.

jcheil · October 2014

Re: Math Check Please

inetdog wrote: »

Basic rule of thumb (right up there with "Don't hit it with the hammer!") is that you can never connect two inverter outputs together unless they are both from the same manufacturer and there is an official stacking function, probably with a sync cable, to enable that operation.
Beyond that, even from the same manufacturer, there is no way to stack a PSW and an MSW inverter to connect them in parallel.
You need to either use a transfer switch, a pair of breakers with a mechanical lockout to keep both from ever being closed, or a plug-in cord connection on both generators so that you can only plug in one of them at a time.
Now if you wire the two inverter outputs directly to separate loads (or to separate load panels even), you can use them both at the same time.

Normally the AC switching built into the Xantrex takes care of all of the issues with generator and charger, but adding the MSW inverter into the mix will not work in that context either.

And he might have issues with the neutrals since on the PSW they are not bonded and require the bond at the panel and the MSW will blow up/fault if the there is a NG bond at the panel. So I think idea of a "cord" that only one could be plugged into at one time is safest, but still will have the NG bond issue at the main panel.

Alaska Man · October 2014

Re: Math Check Please

Sounds like it was a good thing I asked.

So if I understand this correctly, I can draw from the same battery bank to power two different inverters, but can't ever power the same loads with two different inverters unless they are stacked inverters of the same make?

Not sure I understand the grounding issue, I was just going to ground the new inverter to the same ground as everything else. Is that a problem too?

Cariboocoot · October 2014

Re: Math Check Please

It's a matter of connecting outputs together. Without the inverters being designed to have their AC out coupled (either serial or parallel) it is a no go. Their waveforms will not be in synch. A MSW inverter and a PSW inverter can never be in synch because the wave forms are very different.

Further to that most MSW inverters do not create their 120 VAC output the same way as PSW units do, which results in it being impossible to connect one side of the MSW's AC to ground at all regardless of circumstances. If the co-wiring of the PSW inverter creates such a path the MSW inverter will burn up. This can even be an issue with shared neutral on a service if the PSW has an N-G bond and the MSW is also grounded; the PSW unit's bond will create the same condition of the MSW's neutral being bonded, and out comes the smoke.

The only certain way to use the two different inverters for the same load is to make sure all three AC connections are isolated from each other.

The MSW's attraction of lower tare draw is not so appealing when you look at its limitations.

Alaska Man · October 2014

Re: Math Check Please

I will say this, a conversation with you all will lead me to some strange places............. Wave form:

Had I known putting up those Pv's would lead to an Electrical Engineering education I might have thought twice. ;-)

I thought it best to learn more about Wave form:

An alternating function or AC Waveform on the other hand is defined as one that varies in both magnitude and direction in more or less an even manner with respect to time making it a "Bi-directional" waveform. An AC function can represent either a power source or a signal source with the shape of an AC waveform generally following that of a mathematical sinusoid as defined by:- A(t) = Amax x sin(2πƒt).

The term AC or to give it its full description of Alternating Current, generally refers to a time-varying waveform with the most common of all being called a Sinusoid better known as a Sinusoidal Waveform. Sinusoidal waveforms are more generally called by their short description as Sine Waves. Sine waves are by far one of the most important types of AC waveform used in electrical engineering.

The shape obtained by plotting the instantaneous ordinate values of either voltage or current against time is called an AC Waveform. An AC waveform is constantly changing its polarity every half cycle alternating between a positive maximum value and a negative maximum value respectively with regards to time with a common example of this being the domestic mains voltage supply we use in our homes.

This means then that the AC Waveform is a "time-dependent signal" with the most common type of time-dependent signal being that of the Periodic Waveform. The periodic or AC waveform is the resulting product of a rotating electrical generator. Generally, the shape of any periodic waveform can be generated using a fundamental frequency and superimposing it with harmonic signals of varying frequencies and amplitudes but that's for another tutorial.

Alternating voltages and currents can not be stored in batteries or cells like direct current can, it is much easier and cheaper to generate them using alternators and waveform generators when needed. The type and shape of an AC waveform depends upon the generator or device producing them, but all AC waveforms consist of a zero voltage line that divides the waveform into two symmetrical halves.

vtmaps · October 2014

Re: Math Check Please

Alaska Man wrote: »

Sine waves are by far one of the most important types of AC waveform used in electrical engineering.

Actually, they are the only waveform. Fourier analysis shows that all other wave forms, including just a single pulse, are composed of superimposed sine waves.

--vtMaps

BB. · October 2014

Re: Math Check Please

The world of AC power is actually quite wild and deep... This article gives a good idea of AC inverter's and their output:

https://lib.store.yahoo.net/lib/wind-sun/Pump-Inverter.pdf

Many of the old assumptions and rules for DC and AC power have been blown out of the water with the advent of modern electronics and power systems... The basics still apply--But it is much more difficult to make statements of "fact" without some quibbling.

For example:

Alternating voltages and currents can not be stored in batteries or cells like direct current can, it is much easier and cheaper to generate them using alternators and waveform generators when needed.

Yes--You cannot (at least today) store AC power directly in chemical batteries... But Grid Tied AC Inverters (solar panels => GT inverter => home's Main AC power panel) looks for all the world like the GT AC inverters are recharging a giant AC battery bank. The loads (lights+appliances) and GT inverter and Utility generators all sit on the same "power bus"... Just like your car's power system (headlights, radio, alternator, 12 volt battery). The "voltage" (or voltage+frequency) is set by the "battery". Loads and Alternator/GT inverter simply share the wiring--And the direction of power flow depends on if the Loads-GT inverter power is less than zero (utility supplies some power) or greater than zero (utility "sinks" or "stores" power--All using the utility meter as the "referee").

An old car's generator is really similar to an "alternator" with a mechanical rectifier (brushes and commutator). An alternator, more or less, replaces the brushes with diodes to rectify to DC power.

And first large scale utility power systems where DC distribution... But where quickly replaced by AC power (easier to use transformers and send higher voltage power long distances and down convert to low voltage AC power for use in the home). Today, we have quite a few high voltage DC power transmission lines because it is "electrically" easier to send DC power very long distances and does not need the AC Frequency to be "matched" between the two ends of the transmission line.

And the rule that you cannot connect the output of two AC inverters or two AC generators together... A good rule to live by with the typical Off Grid AC inverter and standard small consumer grade gensets.

However, you can parallel GT AC Inverters together, and you can parallel some Honda and Yamaha (and other brands) inverter-generator AC outputs together (within certain rules).

You can even connect an GT AC inverter's output the the output of an Off Grid AC inverter... In this case, the GT inverter will pump energy "backwards" through the Off Grid AC inverter and recharge the battery bank (and you can put your AC loads on the same AC bus--The two inverters+battery bank will work very much like your car's power system with DC loads+generator+battery). There are a bunch of details (don't just jam them together--Terrible things can happen).

At least at the beginning--I like to talk about the things that "matter" to your system/needs. Once you have a handle on that, then we can branch out and talk about other options/interesting facts.

-Bill

Alaska Man · October 2014

Re: Math Check Please

Good stuff, thanks. My education continues. :cool:

inetdog · October 2014

Re: Math Check Please

BB. wrote: »

You can even connect an GT AC inverter's output the the output of an Off Grid AC inverter... In this case, the GT inverter will pump energy "backwards" through the Off Grid AC inverter and recharge the battery bank (and you can put your AC loads on the same AC bus--The two inverters+battery bank will work very much like your car's power system with DC loads+generator+battery). There are a bunch of details (don't just jam them together--Terrible things can happen).

Not just any off grid inverter will do. AC coupling with backfeed will only work for an inverter that works bidirectionally in the first place, like some of the hybrid inverters from Xantrex or Outback or even SMA's Sunny Island. Your typical off-grid inverter will either cause the GT to shut down by failing to regulate the voltage or will fry itself.

Math Check Please

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