Inverters and Batteries

We are thinking about buying an inverter and have a couple of questions:

The only thing I can think of that we want to use the inverter for is the TV, VCR, and coffeemaker.  The TV is a 13" color.

What is the highest watt inverter that can be plugged into the cigarette lighter outlet in the TM?

What size would I need to run the coffeemaker, TV and VCR?

What is the recommended number of batteries needed for a three day trip?

I have seen around a thousand different models on the internet from 140 to over 1000 watts.  (We never use a microwave). We are thinking about installing solar panels in the spring before our yearly trek.

Any advise you can offer would be appreciated.

P.S. I've never said I was mechanically inclined or had any previous experience with electricity.  I do know how to install a light bulb though.  ;D

The coffee maker may be your biggest concern. Check the wattage on the coffee maker and size the inverter for it. As far as plugging into the TV lighter socket, it is not wired for a heavy draw. Mine would not pull a 12v air compressor. You should consider mounting the inverter as close to the battery as possible and then run the 120v wiring from there. The 120 volt wiring will require 1/10 the amperage than the inverter and therefore would be much cheaper to run longer distances than the 12 volt inverter leads.
Rule of thumb is appliance/inverter wattage divided by 12 = DC amps.
Example, my bunn o matic coffee maker draws 900 watts. This would require a 1000 watt inverter. This will draw 7.5 amps on the 120 volt ac side (900/120) and a whopping 75 amps on the 12 side dc side (900/12).

Buy a higher wattage inverter than you need. The reserve will reduce heat and inprove inverter life.

You can pick up a 400 watt inverter for around $30 (Sam's club) and it should power any modern 13" TV with no problem (check the TV though). You could then buy a 6 cup 12v dc coffee maker for the coffee.
A 1000 watt inverter will cost $200+.

I just installed a 2000 watt in my 5th wheel and it cost me a little over $300. I purchased it a truck stop/ travel center. I went for the 2000 watt model to power a microwave and small 120 volt air compressor. I installed it next to the battery compartment (it came with 6' cables) and currently use an extension cord to power the desired appliance.

Word of caution, do not try to tie the output of the inverter into the trailer's 120 volt wiring. If you do and plug the trailer in, chances are it will fry the inverter.

a couple of web sites for you to check out:
http://www.outdoor-catalog.com/power/usage_examples.htm
http://www.4wdworld.com.au/products/prowatt/prowatt.htm

Spend some time shopping around as these sites do not have the lowest price, I only include them to give you an idea of what a certain wattage inverter can run.

Hope this helps and happy camping

Chris, If you desire to rustic camp for 3 days at a stretch then you should plan to be frugal with the battery consumption.  You could run a 13" TV and a VCR but not for hours every day.  You could forego a coffee maker and use propane to heat water.  As Chuck points out, a coffee maker would be a heavy draw even though it is short.  I can't imagine using a microwave powered off a single battery.  E.g., 75amps for 10 minutes would take a good chunk of its capacity.

We really enjoyed rustic camping this last summer using a single battery.  Our electric luxuries were a 9" TV and having the water pump.  We would operate only one or two 12v interior lamps when required  -- 3 days without recharge being no problem but the discharge was noticeable per the battery bmonitor.  Of course one could always recharge via the tow vehicle if required.

Thanks for the advice guys. I am going to borrow a 400W inverter for the trip and have ordered 12V coffeemaker.  I realize that we will need to be frugal with the batteries and will limit use of the appliances.  This trip should give me an idea of what we can expect from the batteries and boondocking.  

Thanks again.

Re 12 V coffeemaker....somewhere in these postings, I think someone said their 12 V coffeemaker took so long to heat up that it wasn't worth it.
We heat water on the stove and use a manual drip coffee maker, even when we have 120V available. The water heats in about 5 minutes (never really timed it). We can only put about 1/3 of the water into the coffee pot at one time and wait for it to filter down through the grounds. That takes another five minutes. In about 10 minutes we have some really good coffee.
Opinions are cheap so here is another cheap opinion. Try to stay away from inverters. As pointed out previously they really suck up a lot of battery capacity. If you absolutely have to run stuff off 120 V I'd suggest a generator.

Dick_B

chris,
we like the heated water approach mentioned in previous post.
a couple more suggestions for the heated water coffee:
   ... use a lexan coffee press--makes coffee almost instantly after water is boiled.
   ...make a delicious latte, espresso, or cappucino using the LARGE-sized(4 shots) GSI brand stove top espresso maker--about 20.00 at good outdoor shops.  we were pleasantly surprised at how fast the espresso trickles through to the metal cup on our TM stovetop--never worked that fast on our other camper stovetop.for a latte, add almost boiling milk, spray real whipped cream on top, and sprinkle some nutmeg/sugar granules on top. voila!

please let us know how your boondocking trips go...thanks, 2swans

Chris,
I tried the 12VDC coffee maker with very poor results. 4 cups took almost a full 60 minutes. :'( By that time I was having double caffeine fits. :P

We bought a Melita Coffee Maker which uses paper filters (easy cleanup) and a glass bottom. Boil water on the stove (3-5 min.) and coffee is done in 7-8 minutes. Far more efficent than an electric, 12VDC or 120VAC. You can buy the paper filters at any grocery store. 8)

Thanks Paul. My brother-in-law showed me his 12V "percolator" which looks like the old stove top with the glass bubble and he says he has a full pot in five minutes. Everyone agrees on the 12V coffeemaker though :-/.  I am getting a stove top while I search for the old-style percolator.

We have run a VCR and a 13" TV on an old 150 watt inverter, but these were old and both had power transformers.  A friend tried to borrow mine and a second one and neither would operate her combination TV\VCR.  It was explained to me that all the newer electronics use a "switching power supply" and prefer power like you have at home, 110 volt 60 cycle sine wave.  If you find someone with a large selection of converters, you will see a price range for units of the same wattage, the difference being "square wave", "modified sine wave" and "pure sine wave", etc. I'd hook up to the vehicle battery and run an extension cord.  That way, each day you drive, you recharge the battery you have been using.  

:-[ ;D

Batteries & inverters could be discussed in length, but the short of it is - think of the battery/batteries as a glass full of water which you cannot use the bottom 20%.  So if you have a standard battery that has 120 amp/hour capacity, you have a MAXIMUM of 96 amp/hour to use. (NOTE: on a standard deep cycle/marine battery, you should only use 50% in order to obtain the typical 30 life cycles)

DO NOT use heavy current drain devices such as coffee makers, hair dryers, etc. for any length of time or your batteries will be discharged very quickly.

EXAMPLE:  Hair dryer for 10 minutes = 1500 watt = 12.5 amps @ 120 volt = 125 amps @ 12 volt = 20.8 amp hours - You now have left 96-20.8=75 amp hours

EXAMPLE:  13" color television W/VCR for 2 hour movie = 70 watts = .58 amps @ 120 volt = 5.8 amps @ 12 volt = 11.6 amp hours - you now have left 96-11.6=84.4

Any device that is designed to turn electricity into heat is generally a higher wattage device (curling irons do not blow air & keep thier heet very concetrated).

Look at the wattage rating & divide by 12 volts - this yields the amperage - Note the amount of time that the device will be used as a portion of an hour & multiple the amperage by this fraction to get the AMP/HOUR.  This AMP/HOUR figure can then be subtracted from your glass of water example showing you how long your batery should last.

Again, do not expect to drain a normal battery more than 50% before recharging it.

The next logical topic would be the inverter.  Size the inverter to be 50% over the maximum wattage of any device you intend to use.  In the case of any device having a motor in it (blender, drill, etc.), you will be best off doubling the size of the inverter over the listed wattage of that device.

A good size to handle most items is a CONTINUOUS 2000 watt inverter.  Do not expect to be able to plug this into the 12Volt socket (or most inverters) because the fuse for that socket will blow.

I wired a 2000 watt inverter under the pull out bed next to the front wall & ran the heavy gauge wires through the floor & connected them directly to the batteries.  I also wired a 120 volt outlet from the inverter along side the refrigerator so that I could plug any devices into it very easily.  With a slight movement of the pull out bed, I can reach my arm down & turn on the inverter when I want to use it & turn it off when I am through.

For good batteries I use 2 Trojan J305H 6 volt 330 amp hour batteries in series with heavy cables connecting them.  This gives me a usable 12 volt with 264 amp hour & will get me & my family through most 4 or 5 day camping trips with (movies).  These batteries have a life cycle of over 800 times compared to typical 15 to 30.  The capacity is also realistic.  

I tested several deep cycle/marine batteries on the market & found thier capacity to actually be less than half of what the manufactuer posted.  The various manufactuers reluctantly stated that they tested the batteries only after controlling the temperature & cycling the batteries through have of thier life to get thier questionable (ONCE IN THE BATTERIES LIFETIME) rating.