How big an inverter

[WolfWhistle]

Originally Posted by herk7769

Solar Cell, Solar Panel, Solar PV, Solar Products, Charge Controllers, Solar Trackers

About a buck a watt.

Herk,
I have a 2012 21RR... haven't checked for available roof space... got to give her a bath, so I will check today. I see this 40" x 60" (roughly) panel for $202.40x (Not sure the shipping cost to FL) same retailer:

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We don't use much power and already have all LEDs. Only the 'scare' light is standard, but don't use it much. To be able to run fridge, TV, Dish receiver, microwave, maybe a coffee pot, would this work. I understand that we might have to do microwaving and coffee potting, one at a time. Water heater is gas only. It might make better sense to only use gas for fridge. Essentially most things not including the AC unit. Would this work? I guess I am asking how much inverter capacity? Can this be done using that single panel and two batteries? What controller would you use that might allow for future growth? I think (just read it) it might be better to install batteries over axle on left (driver's) side. I really appreciated the info.

Clint

[Herk7769]

Originally Posted by WolfWhistle

To be able to run fridge, TV, Dish receiver, microwave, maybe a coffee pot, would this work. I understand that we might have to do microwaving and coffee potting, one at a time. *** I guess I am asking how much inverter capacity? Can this be done using that single panel and two batteries? What controller would you use that might allow for future growth? I think (just read it) it might be better to install batteries over axle on left (driver's) side. I really appreciated the info.
Clint

This is a big request for an open forum. If I could design Solar systems I would go into business () I also do not have a solar panel installed (yet) but I have done some research. I will also make this a new thread.

So some thoughts:

When boondocking you should realize that ALL your power will be coming out of your battery bank (regardless of how it is replaced - generator; wind power or solar). All 12VDC items must be powered by 12VDC because it will use less amps overall by using DC directly rather than being converted to AC for use. The fridge will also cool better on propane than the 120 VAC heater coil.

ALL your 120VAC will be coming from your Inverter. The bigger your AC load in watts, the bigger your battery bank needs to be.

Lets take JUST the coffee pot for example. A coffee maker uses a "resistance" load (heating coils) so a cheaper modified sine inverter would work just fine.

How big an inverter and battery bank do you need JUST to run that coffee maker (and nothing else).

Say your coffee maker uses 1600 watts to run the hot plate and the percolator water heater. To MAKE 1600 watts AC you will need to draw 1600 watts through the inverter. Since the inverter is not 100% efficient converting DC watts into AC watts (about 95%) you will need about 1700 watts of DC to "make" that 1600 watts of AC.

1700 divided by "about" 12 volts (12.5 fully charged dropping to about 11.5 when near death) equals 141 amps drawn from the battery bank while making coffee. If the coffee maker runs for 15 minutes to make coffee it will consume 141 amps/15 minutes or 35 amp hours from your battery bank. A typical OEM battery has 75 amp hour capacity when fully charged. So making coffee will suck 50% of your fully charged battery's capacity out (all things being equal - which they are not).

This assumes you can actually PULL 141 amps from your battery without reducing the battery's ability to deliver said load. (See what happens when current demands get big using the attached battery charts.)

A 100 amp hour capacity battery's TOTAL fully charged capacity will be reduced when trying to yank electrons out of those thick plates. This is by design. Deep Discharge batteries have thick plates that make it hard to pull power out so it lasts a long time at small loads (starting battery plates are thin so they give up and receive large amounts of amps very quickly but have NO staying power at all). Deep cycle batteries also take a LONG time to recharge for the same reason.

Pulling 140 amps all at once will reduce that 100 amp hour capacity to about 40% (OR LESS) or 40 amp hours (OR LESS) while the coffee pot is running. So, with just one battery making coffee with a 2000 watt inverter and a 70 AH OEM battery will kill a fully charged battery.

By adding a second 70 AH battery the load is shared across the two batteries (140 AH total) AND the amps required from each is halved. With 4 batteries the amps required drops to 1/4 with a resultant increase in individual battery capacity.

Worse yet if you use a microwave. Most microwaves, computers, and digital TVs require PURE SINE power and not modified (square wave) power. This will increase the cost of your inverter by a factor of 3.

Solar panels and wind generators replace power drawn from your batteries over time. As you can see, you will never be able to "run your camper off of solar" or wind.

[Fire Instructor]

Last Summer, I did 10 days in Assateague Island SP (MD) with no electricity, other than starting the generator to run the microwave or to run the Margaritta maker. All of my other 12v and 120v use came from a small inverter (it was before I installed the 2000w Xantrax) off of my two 6v GC batteries. Last Fall (less sun at a steeper angle), I did similar in Dover for 5 nights for the NA$CAR Race, with the Xantrax, only running the generator for the MW. Before I go on another long boondocking trip, I'll likely add a second pair of batteries, so that I can make better iuse of the abailable slar charging. My panels usually have my batteries charged, and back on "float" by 11 am, so I can take advantage of the aftrenoon sun, and use more battery in the evening and morning.

BTW - I make my daily pot of coffee with a Coleman drip coffee maker that sits on a propane burner.

[Fire Instructor]

And BTW, Herk - Most TT's are equipped with digital televisions, but they are 12v operated. You don't need a pure sine-wave inverter to recharge DC batteries that supply one of these. the microwave, and OTHER 120v home appliances, on the other hand.....

[WolfWhistle]

Not to answer my own question, but to add to the discussion; I found this:

Examples:
A 19" TV uses 100 watts for 4 hours uses 36.4 AH
A coffee maker 1000 watts for .5 hours uses 45.9 AH
A microwave 1200 watts for .17 hours uses 18.7 AH,
A hair dryer uses 1600 watts for .17 hours uses 24.9

Total AH = 125.9
Total Watts = 3900

Watts / 12 * 1.1A * 4 = AH

When sizing your inverter, calculate the total wattage required at any one time and choose the inverter with a slightly higher power output. (Start up surge should be considered for compressive loads.

*Since deep cycle batteries should only be discharged to 50% total capacity, the total amp hours consumed between charge cycles should be multiplied by 2.
Example:
amp hours consumed between charge cycle = 126
amp hour rating of battery = 90 (Group 27)
(126X2) / 90 = 2.8
(Round up to the nearest whole number.)
Therefore, the minimum number of batteries required is three with the above values."

Typical Battery Amp Hour Rating Battery Size Amp Hour Rating
Group 27- 90AH
Group 31 - 105AH
4D - 160AH
8D - 220AH
6V Golf Cart - 225AH

So, the inverter needs to be of higher capacity than the total load that can be presented to it. I am slightly confused at those numbers since I can run AC, microwave, TV and lights while only served by 20 Amp.. I've done it many times. The standard electric capacity of the trailer is 30 Amps... so the total watts the trailer can handle is only use 3600 watts. Why wouldn't 4000 watt inverter be plenty? As far as how many batteries you would need depends what you run and how long your run it. Based on the above example and that usage, as stated, three group 27 batteries would work. So, lets say I get four group 27 batteries, that would give me 180 AH used between charge; a 4000 watt inverter would exceed the total 'at one time' usage. Next, how many solar panels at what watt rating would we need to bring the batteries back up during day light hours, and how long will it take. I don't know the inefficiency of controller, if there is any, but to replace the 126 AH depleted from the batteries (in the example) depends on how many watts the panels generate per hour, how many panels, and for how many hours of sun available per day. I have found a rule of thumb to calculate how many Amps a panel can makes in a day, "For solar panals (sic) the usual rule of thumb is 0.3 x Rated watts = Amp-hours/day. So, for a 100 W solar panel expect 30 amp-hours per day." To replace the 126 AH (amp-hour) in the example, that was depleted we get: 126/30= 4.2, so it would take 420 watt of array to do it. The rule of thumb (30 AH / day) might be on the low side based on what I've read, "a Kyocera 135 watt panel is seen to produce from 8 to 40 AH". That statement, if true does equate to a 24 AH average... so the 30 AH per day sounds right on. So, three 135 watt panels could work but four would be better. I haven't checked but I don't think there's room for four 30" x 60" panels on the roof. Does my numbers seem about right?

[Fire Instructor]

I don't think that my cardiologist would let me LOOK at the sticker price of a 4000w PSW inverter!!! The 200w unit was bad enough! (about $350, now) And if I survived the heart palpatations, the beating from my wife would be a sure painful death....

And I can't imagine the battery-bank that one would need to power same!

In an RV you can be a lot more frugel with power use than we tend to be at home. You learn not to run high-draw appliances simultainiously. Additionally, you do as much with propane vs. electric as you can.

[Herk7769]

Originally Posted by Fire Instructor

And BTW, Herk - Most TT's are equipped with digital televisions, but they are 12v operated. You don't need a pure sine-wave inverter to recharge DC batteries that supply one of these. the microwave, and OTHER 120v home appliances, on the other hand.....

Both my OEM digital TVs are 120VAC.

[WolfWhistle]

Originally Posted by Fire Instructor

I don't think that my cardiologist would let me LOOK at the sticker price of a 4000w PSW inverter!!! The 200w unit was bad enough! (about $350, now) And if I survived the heart palpatations, the beating from my wife would be a sure painful death....

And I can't imagine the battery-bank that one would need to power same!

In an RV you can be a lot more frugel with power use than we tend to be at home. You learn not to run high-draw appliances simultainiously. Additionally, you do as much with propane vs. electric as you can.

I found this (12V) 5000W inverter. Its called a modified sine wave...

5000 Watt Power Inverter 12 volt DC by AIMS

at the same site is a 5000W pure sine wave... it is pricy...

5000 Watt Pure Sine Power Inverter 12 volt by AIMS - Free wireless remote

I was thinking if I bought 24volt panels I would need 24Volt inverter.

To reduce the price... I could go with 3000W, which I think is still big enough (based on 25A *120VAC = 3000W)... here is a pure sine wave at same site....

http://www.theinverterstore.com/3000...-inverter.html

It might not be feasible to be able to everything in the trailer "off grid"... because of cost, but the costs have come down considerably.

[Herk7769]

You are missing the point made in the graphs about amp draw and battery capacity. The more amps you try to draw from a deep cycle battery; the LESS capacity they have.

While 30 amps at 120 volts = 3600 watts, 3600 watts (plus inverter loss at that high wattage requires 4000 watts of DC input.

4000 watts of DC divided by 11.5 volts (average battery voltage 12.5 Full - 10.5 dead) is 350 amps demand from your battery system.

While not impossible, it would take a battery bank of 14 batteries (that weighs several thousand pounds) to deliver that wattage at that amp draw and keep the individual battery amp load to less than 25 amps (see the capacity vs amp draw charts).

There is not enough roof area to supplement that with solar. Most likely all available roof would be required to replace ONE of those batteries.

Like I said, I am NO expert. There are experts on the Solar forums and I highly recommend if you plan on an installation that large that you contact an expert.

[Herk7769]

Originally Posted by WolfWhistle

I was thinking if I bought 24volt panels I would need 24Volt inverter.

Not true as the solar panel controller will regulate output to 13.5 -14 volts even with 24 volt (or higher) panel inputs. In fact, if you intend to maximize your wattage, most solar installations do it by sending higher voltages down to the controller where it is converted to 13 volts at a higher charging amperage.

[WolfWhistle]

Originally Posted by herk7769

You are missing the point made in the graphs about amp draw and battery capacity. The more amps you try to draw from a deep cycle battery; the LESS capacity they have.

While 30 amps at 120 volts = 3600 watts, 3600 watts (plus inverter loss at that high wattage requires 4000 watts of DC input.

4000 watts of DC divided by 11.5 volts (average battery voltage 12.5 Full - 10.5 dead) is 350 amps demand from your battery system.

While not impossible, it would take a battery bank of 14 batteries (that weighs several thousand pounds) to deliver that wattage at that amp draw and keep the individual battery amp load to less than 25 amps (see the capacity vs amp draw charts).

There is not enough roof area to supplement that with solar. Most likely all available roof would be required to replace ONE of those batteries.

Like I said, I am NO expert. There are experts on the Solar forums and I highly recommend if you plan on an installation that large that you contact an expert.

Herk, I appreciate it, by the way, clearly I am no expert, but there is something wrong with your numbers, how can (in the example) running a the devices (in the example) for the hours (of fractions of hour) shown, could it possibly require 14 batteries. The total depleted is 126AH. I was trying to figure how many batteries would be required so not to deplete 50% (no more)... and further how many watts of panel(s) to be able to bring the batteries to float during a single day. With fourteen group 27 batteries at 50% the available AH is 630! or five times the amount in the example. Do you see what I mean? Based on your numbers I would need a 60KW generator to run an 120V alarm clock and a TV (joke!).

[Herk7769]

Originally Posted by WolfWhistle

Herk, I appreciate it, by the way, clearly I am no expert, but there is something wrong with your numbers, how can (in the example) running a the devices (in the example) for the hours (of fractions of hour) shown, could it possibly require 14 batteries. The total depleted is 126AH. I was trying to figure how many batteries would be required so not to deplete 50% (no more)... and further how many watts of panel(s) to be able to bring the batteries to float during a single day. With fourteen group 27 batteries at 50% the available AH is 630! or five times the amount in the example. Do you see what I mean? Based on your numbers I would need a 60KW generator to run an 120V alarm clock and a TV (joke!).

<sigh> I can see I am going no where with this.
Since you clearly are not getting the impact of the discharge graphs I am attaching a document on the Peukert Effect of discharge and battery capacity.

If after reading it (I did attach it previously) you still think it is possible to feed and water a 4000 (or even 3000) watt inverter in an RV, I can only wish you a great amount of luck in your endeavor.

[n1joh]

hi all i hve a solar system on my coach 2009 georgetown 373 ds. i have two 110 panels on the roof and a gp-25 regulator with 4 trojan t-105 plus batteres(I think) I install a 3000 watt inverter with the remote. i will be at the rally on Aug 11 Sat. feel free to stop by. i am new to solar too and still learning. I have tested it and i can run the air when i go shoping at wally world to keep the watch dog cool.

[Fire Instructor]

Originally Posted by herk7769

Both my OEM digital TVs are 120VAC.

Wow! I installed a small flatscreen in the bedroom that I got from Wally World, and that is 120v, but my factory flatscreen has a 120v plug and adapter brick (that I store in a cabinet) but it plugs into a 12v power source.

[Herk7769]

Originally Posted by n1joh

hi all i hve a solar system on my coach 2009 georgetown 373 ds. i have two 110 panels on the roof and a gp-25 regulator with 4 trojan t-105 plus batteres(I think) I install a 3000 watt inverter with the remote. i will be at the rally on Aug 11 Sat. feel free to stop by. i am new to solar too and still learning. I have tested it and i can run the air when i go shoping at wally world to keep the watch dog cool.

Those 4 batteries (a double bank of 2 x 6volts) have an amp hour rating of 450 amp hours capacity (225 each) http://www.trojanbattery.com/Products/T-1056V.aspx. The graph below is for a 100AH battery.

Not sure what the amp draw on compressor start up is for your air conditioner, but say it is 15 amps and it is the only draw on your entire system. That is 1800 watts. This is well under the 3000 watts (most likely 3500 peak) your inverter is capable of producing.

1800 watts at an average voltage of 11.5 volts means you are taking 160 amps out of your battery bank (buffed with 15 amps solar support [2x110 watt panels = 220 watts/12 volts = 15 amps] or 145 amps tasked to the batteries).

With 4 batteries providing that 145 amps each bank is tasked to provide 1/2 of the electrons or 72 amps per hour out of the 225 available to the bank.

Since the graph is based on 100AH batteries we will need to "normalize" for the graph. (72/225)=(X/100) solve for X = 32 amps out of a 100 AH battery.

Plotted that on the graph says those batteries will reduce the effective capacity of your banks 50% to 225 AH for the 4 battery system fully charged.

Delivering 145 amps out of a 245AH bank will deplete your batteries from fully charged to 10.5 volts inverter cutout in 1 hour and 40 minutes (or so).

Obviously this assumes the compressor runs the entire time (which it does not).

That is how I understand how the calculations work.
How does that match up with your experience?

Oh, and I am totally jealous of your battery bank. I have two 70AH Deka DC-24s (140AH when they were new) pushing a 2400 Watt inverter.
My AC would most likely run about 30 minutes before my batteries died.

When I had only 1 battery my coffee maker would kill my battery by the time the coffee was done.

[n1joh]

you are correct. it will run for about 1 and 1/2 hour. my inverter is a go power sw3000 which is 3000 watts with 6000 surge. i am thinking of adding more batteries.but because of cost have to wait. Are you going to the rally (Lou)

[Herk7769]

Originally Posted by n1joh

you are correct. it will run for about 1 and 1/2 hour. my inverter is a go power sw3000 which is 3000 watts with 6000 surge. i am thinking of adding more batteries.but because of cost have to wait. Are you going to the rally (Lou)

Not this year.

DW health problems and house maintenance expenses have really put a crimp in our travels this year. I have only one 10 day camping trip scheduled end of September (to add 3 more state stickers) and we are done for the year.

I hope the DW will be back on her feet (literally) by the first of the year so we can head to Phillies Spring Training next year.

[Herk7769]

Originally Posted by n1joh

you are correct. it will run for about 1 and 1/2 hour. my inverter is a go power sw3000 which is 3000 watts with 6000 surge. i am thinking of adding more batteries.but because of cost have to wait. Are you going to the rally (Lou)

This makes total sense since the AC is not the only draw on the batterys and the compressor/fan does not run continuously. Also your batteries may not be at 100% capacity at the start of your shopping trip.