Inverters and Batteries

[Chris_Bauer]

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.

[Chris_Bauer]

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.  :D

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

[2swans]

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

[Paul_Heuvelhorst]

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)

[Chris_Bauer]

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.  

:-[ :o :) ;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.

[PopBeavers]

I was glad I found this old thread. I have been considering running a *VERY* small microwave oven off of the batteries via an inverter. It does not appear very feasible.

I just got back from a 24 hour mountain bike race. My TM was the pit area, diner and rest area. The 4 riders were eating cold burritos. I offered to warm them up in the oven, but they didn't want to wait that long.

So I was thinking, if I had a small microwave, I could have fired up the generator.

But what about cooking at 2 AM (this is a all night race)? Could I run the microwave from the batteries and then recharge the batteries from the generator. No generators allowed after 10 pm.

Since this was the first time I was base camp for a 24 hour race I have given up on the idea. If there is ever a next time we need to plan ahead a little more and just use the oven.

However, using the TM as a base for a 24 hour race provided a slightly different perspective on what features are useful.

[B_and_D]

Instead of using the oven, which takes quite a while to heat up, if we're in a hurry, we take some scrunched up layers of tin foil (they work as insulation for the bottom of the pan) and put them on the bottom of a heavy skillet on the propane stove. We then put the food to be warmed on top of the tin foil and put the lid on the skillet. It works very quickly, not quite as fast as a microwave, but you need to check it often or your food can get burned. It's kind of like using a "mini roaster" on the stovetop.

[mjlaupp]

Old cooking trick: Place food to be warmed on lettuce leaves in the skillet, cover and heat. The lettuce prevents burning and provides moisture.
Mike

[jouster]

Question 1: I read that computers should only be powered with sine wave power, the kind your local utility supplies. I was wondering if that applies also to laptops since their juice is always from a transformer? Would using a non sine wave inverter to power a laptop be a no-no?

Question 2: Not being an EE, I wonder if surge protectors are needed just as much for laptops since their juice is always from a transformer?

What's your take on it?

BTW, Xantrex has a 400w sine wave inverter that can be hardwired into TM's 120v and it senses when shore power is present and switches off.

[BobRederick]

I just purchased a Dell laptop & the sales/tech recommended a "golf ball inverter" from SAMs Club. There is also a direct 12V adapter Dell sells for $400 if I heard him correctly.

We have powered a Dell laptop connected to a Go-To computerized telescope off my 400 Watt inverter. It is a Checkers model that is about 4 or 5 years old. -- actually , maybe 10 years old. I have powered everything I can think of with that successfully, cell phone charger, Palm Pilot charger, shaver, model plane charger. I run my Philips Home Theater off it as well. They all work just fine.

Point of interest: I put my cell phone on the Checkers inverter/110V charger and it drew 1.5A. I then tried the 12V charger (small adapter that plugs into the cigar lighter with a cord to the phone) and it drew about half the current.

[pbuck1]

Q1 The answer is of course...it depends.....nothing is black and white.
Both desktop and laptop computers have a power supply which converts 120VAC to low voltage DC and the power supply will contain a transformer (the difference is how much of that power supply is inside or outside the computer case). Size and weight is not so much of a factor in designing a desktop power supply, however, and so these factors do not have to be traded off against other design considerations. This may be why desktop computers are less sensitive to the AC waveform coming in. Below is an extract from DonRowe.com which IMO seems to be a good guide.

Q2 A transformer won't protect against the big transients (surges) which are caused say by lightning. If you run off shore power it is best to add surge protection. If you're running off the TM battery with an inverter and everything is self contained within the TM (an aluminum "faraday cage") maybe you'll get away without surge protection. But why risk it?

Paul

Extract:
Do I need Modified Sine Wave, or Pure Sine Wave?

Advantages of Pure Sine Wave inverters over modified sine wave inverters:

a) Output voltage wave form is pure sine wave with very low harmonic distortion and clean power like utility-supplied electricity.

b) Inductive loads like microwave ovens and motors run faster, quieter and cooler.

c) Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax, and answering machines.

d) Prevents crashes in computers, weird print out, and glitches and noise in monitors.

e) Reliably powers the following devices that will normally not work with modified sine wave inverters:

* Laser printers, photocopiers, magneto-optical hard drives
* Certain laptop computers (you should check with your manufacturer)
* Some fluorescent lights with electronic ballasts
* Power tools employing "solid state" power or variable speed control
* Some battery chargers for cordless tools
* Some new furnaces and pellet stoves with microprocessor control
* Digital clocks with radios
* Sewing machines with speed/microprocessor control
* X-10 home automation system
* Medical equipment such as oxygen concentrators

We carry a full line of Pure Sine Wave Inverters here at DonRowe.com, though most of the inverters we carry are Modified Sine Wave inverters. Modified Sine Wave works well for most uses, and is the most common type of inverter on the market, as well as the most economical. Pure Sine Wave inverters (also called True Sine Wave) are more suited for sensitive electrical or electronic items such as laptop computers, stereos, laser printers, certain specialized applications such as medical equipment, a pellet stove with an internal computer, digital clocks, bread makers with multi-stage timers, and variable speed or rechargeable tools (see "Appliance Cautions" below). If you wish to use those items with an inverter, then choose a Pure Sine Wave inverter. If you mostly want to run lights, TV, microwave oven, tools, etc, a Modified Sine Wave inverter is fine for your needs.

We often are asked if computers will work with Modified Sine Wave. It's been our experience that most (with the exception of some laptops) will work (though some monitors will have interference such as lines or a hum). However, if you have any doubt about any appliance, tool or device, particularly laptop computers and medical equipment such as oxygen concentrators, we recommend that you check with its manufacturer to be sure it is compatible with a Modified Sine Wave inverter. If it is not, choose one of our Pure Sine Inverters instead.

The difference between them is the Pure Sine Wave inverter produces a better and cleaner current. They are also considerably more expensive. You might find it practical to get a small Pure Sine Wave inverter for any "special need" you may have, and also a larger Modified Sine Wave inverter for the rest of your applications.