Reply
 
Thread Tools Display Modes
Old 07-31-2012, 08:29 AM   #1
Senior Member
 
Join Date: Apr 2012
Posts: 3,155
How big an inverter

Quote:
Originally Posted by herk7769 View Post
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:

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

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
__________________

__________________
WolfWhistle is offline   Reply With Quote
Old 07-31-2012, 09:15 AM   #2
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 21,169
Quote:
Originally Posted by WolfWhistle View Post
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.
Attached Thumbnails
Click image for larger version

Name:	battery voltage and capacity Curve vs Discharge Rate.jpg
Views:	144
Size:	44.9 KB
ID:	17344   Click image for larger version

Name:	battery Life as a function of charge discharge cycles.jpg
Views:	120
Size:	28.2 KB
ID:	17345   Click image for larger version

Name:	battery voltage and capacity Curve.jpg
Views:	135
Size:	46.5 KB
ID:	17346  
Attached Files
File Type: pdf Taking care of Deep Discharge Batteries.pdf (7.44 MB, 59 views)
File Type: pdf What is the Peukert Effect.pdf (164.4 KB, 62 views)
__________________

__________________

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 07-31-2012, 11:55 AM   #3
Senior Member
 
Fire Instructor's Avatar
 
Join Date: Jul 2010
Location: Upstate (Albany Area) NY
Posts: 772
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

2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter
Fire Instructor is offline   Reply With Quote
Old 07-31-2012, 11:58 AM   #4
Senior Member
 
Fire Instructor's Avatar
 
Join Date: Jul 2010
Location: Upstate (Albany Area) NY
Posts: 772
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.....
__________________
Fire Instructor

2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter
Fire Instructor is offline   Reply With Quote
Old 07-31-2012, 01:59 PM   #5
Senior Member
 
Join Date: Apr 2012
Posts: 3,155
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?
__________________
WolfWhistle is offline   Reply With Quote
Old 07-31-2012, 02:06 PM   #6
Senior Member
 
Fire Instructor's Avatar
 
Join Date: Jul 2010
Location: Upstate (Albany Area) NY
Posts: 772
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.
__________________
Fire Instructor

2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter
Fire Instructor is offline   Reply With Quote
Old 08-01-2012, 07:48 AM   #7
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 21,169
Quote:
Originally Posted by Fire Instructor View Post
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.
__________________

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 08-01-2012, 07:58 AM   #8
Senior Member
 
Join Date: Apr 2012
Posts: 3,155
Quote:
Originally Posted by Fire Instructor View Post
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.
__________________
WolfWhistle is offline   Reply With Quote
Old 08-01-2012, 08:00 AM   #9
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 21,169
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.
__________________

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 08-01-2012, 08:03 AM   #10
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 21,169
Quote:
Originally Posted by WolfWhistle View Post
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.
__________________

__________________

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Virginia Campgrounds

Reviews provided by




ForestRiverForums.com is not in any way associated with Forest River, Inc. or its associated RV manufacturing divisions.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 11:37 PM.