All renewable energy (RE) systems with batteries should include a charge controller. In this article we'll principally be referring to solar charge controllers . Charge controllers prevent battery overcharging and also prevent the batteries from sending their charge back through the system to the charging source (i.e., the solar panels). Think of a solar charge controller as a battery nurse—its job is to monitor the battery bank, feeding it what it needs and checking its vital signs. Since a solar controller does its work in line between the solar panel array and the batteries, it would make sense that its selection and sizing would be influenced by those components. And that's exactly the case.
Voltage and amperage (or current) are the parameters we use in solar charge controller sizing. The solar controller must be capable of accepting the voltage and current produced by the DC source (usually solar panels) and delivering the proper voltage and current to the batteries. This situation might make you think that the DC source, charge controller and batteries must all share a common voltage. While that is one system design strategy used in many installations, it's not the only one. More on the alternatives in another article. For now, it's one voltage for everyone!
Technically speaking, the DC source must always have a higher operating voltage than the battery bank in order for current to flow from one to the other. A handy way to remember this fact is the statement, "curent flows downhill." For the purpose of this discussion, we'll use nominal voltage which means common battery voltages. Nominal voltage in this sense is synonymous with battery voltage. Since batteries (where they are used) are in many ways the heart of an RE system, we can call the bank's voltage the system voltage. The system voltage selected for any given installation is usually, though not always, determined by the battery bank required by the application; the inverter, if one is used, will also influence the choice of system voltage.
Sizing comes down to this: there's the quick method, which will very likely give an acceptable, if perhaps oversized result, but won't describe the why here - we'll just show you the steps.
Short Method for Sizing Solar Charge Controllers
For PWM and PWM shunt solar controllers, select one that is rated at your system voltage (same nominal voltage all the way through the system).
Divide solar panel array total wattage by system voltage.
Add 20% as a safety margin (i.e., (result of Step 2) X 1.2).
Select a solar controller rated at or above the result of Step 3.
Example of the Short Method
Two 125W, 12V nominal modules. System is 250 W, 12 Volt nominal. Solar charge controller will be 12 Volts.
250 ÷ 12 = 20.83
20.83 * 1.2 = 24.996 amps
You could use a Xantrex C35, a 35 amp solar charge controller; or a Morningstar Prostar 30, a 30 amp solar charge controller , for example. Any 12 volt solar controller greater than 25 amps will work.
About the Author
Co-written by Ben Gorman and Sascha Deri.
Founded in 1999, altE, Inc has catered to DIY customers on every continent of the globe. A 2006 Inc. 500 awarded company, altE aims to continue to fulfill its motto, "Making Renewable Do-able," by offering cost competitive, high-quality solar and wind energy related products and educational services to a broad spectrum of the public. For more information visit their website at www.altEstore.com or contact Toll Free (877) 878-4060.
Add-on Accessories To Enhance Your Car - Where To Get Them Online
A power cord from your cell phone to the cigarette lighter socket will keep your phone running without draining its battery. An iceless cooler will conveniently keep a drink cold. A heated mug will keep coffee hot as long as the car is running. Add-on accessories add enjoyment to your ride. Below is information and comments about five types of accessories. To locate the items online, use the link to Leisure ideas at the end of this article.
12-volt heated mug - A mug with a plug for getting power from the cigarette lighter socket. It keeps a liquid such as coffee hot for as long as the vehicle is running. Some models have a thermostat to set the temperature.
Example models:
Wagan Tech Heated Travel Mug, removeable cord plugs into cigarette lighter socket, 16-ounce capacity, double wall vacuum insulation to keep drinks hot up to an hour after you unplug, mug fits cup holders, available for about $30.
New VR3 Stainless Steel Heated Insulated Travel Mug Cup, plugs into cigarette lighter socket, 14-ounce capacity, base sized to fit cup holder, about $10 plus shipping.
Bell & Howell Hot N' Go Heated Car Mug, heats to 145 degrees F in 30 minutes, 16-ounce capacity, priced about $18.
JLR Gear Smart Mug, set the temperature you want, has ready light, 16-ounces, plugs into lighter socket, available online for about $20 plus shipping.
Cooler/warmer - These give the choice of keeping food hot or cold. Can warm food and can cool. Some are sized to hold a can of soda or a mug of coffee, larger units might hold a six pack or more.
Example models:
Coleman 12-Volt 9-Can Console Cooler/Warmer, cools to 40° F and warms to 120° F, 9-can capacity. Available online for about $60.
Vector® Thermoelectric Portable Food Cooler/Warmer Chests, cool to 40° below outside temperature, warm to approximately 130° F, 9-foot cord plugs into lighter plug. Two available, 6- and 12-can capacity, priced $75 and $85.
Koolatron 18-quart Food Cooler/Warmer, cools to 40° F below ambient temperature or warms to 125° F, detachable 10-ft. cord, 3-amp draw, holds 23 12-ounce cans. Available for about $110.
ROADPRO 12-Volt Mini Cooler / Warmer, holds 9 12-ounce cans, about $50.
Pyle - Automotive Travel Cooler/Warmer - PLCOOL6, holds two 12-ounce bottles, 9-foot detachable cord, 12 volt/120 volt/220-volt, about $40 online.
Rubbermaid® Cooler/Warmer 289377 1.1-gallon capacity, holds 6 12-ounce cans, plugs into cigarette lighter socket, in warming mode, warms to 120-degrees F., tie-down strap and buckle strap for fastening to seat back. 7' long 12v cord. Available online for $80 plus shipping.
Cell phone charger - Plugs into the cigarette lighter socket to power or charge your cell phone.
Example models:
Virgin Mobile Silver Dolphin Car Charger, for Kyocera phones, plugs into car's power outlet and charges phone in 2.5- to 3.5-hours, http://www.radioshack.com can locate the stores nearest you where you can get this charger, about $15.
Phoenix Wireless Vehicle Power Adapter for Samsung M300/M510, has coiled cord that plugs into cigarette lighter socket, about $25.
Quick Cell 3900 Car Charger Nokia, web site lists stores nearest you that stock this charger, about $15.
Phoenix Vehicle Power Adapter for Samsung Phones, has coiled cord that plugs into cigarette lighter socket, 3.5-mm plug, for many Samsung phones, for about $25.
Generic Car Charger for Nokia N91, N90, N80, 770, 7370, 6282, 6265i, 6165i, 6155i, 6126, 6103, 6102i, 6102, 6101, 3155i. Available for about $5.
Power inverter - Plugs into the cigarette lighter socket, clips to battery, or wire it in. The vehicle's 12-volts dc is changed to 120-volts ac to power things like laptop computers, coffee makers, cell phones, camcorder battery chargers and other small appliances. Don't go bigger than 400 watts unless you want to go directly to the battery with heavy wire. Even then, high power devices will drain your battery quickly and could fry the alternator if the engine is running.
example models:
Xantrex X Power Mobile Plug 75, only 75 watts, very light duty, for about $30 online.
Whistler 400-watt Power Inverter with Circuit Pro, will run TV/DVD combos, laptops, cooling fans, $30 plus shipping.
Xantrex Technologies XPower Plus 400-Watt Inverter #851-0400, 400 watts for 5-minutes, 600-watts surge for easy startups, and 300-watts continuous power, plugs into car cigarette lighter, automatic shutdown mechanism protects against overload, over-temperature and low battery conditions, two 3-prong grounded AC outlets, and a DC outlet. Available online for about $30.
mp3 player - Down load music or other audio content onto either the player's memory or a separate flash drive. Hours of audio can be stored in a single memory device. Some content can be downloaded for free. Listen to the program any time you choose.
example models:
VR3 MP3/WMA FM Modulator w/USB Port and Audio, VRFM8BLN, plug a flash drive into its USB port and use Play, Pause, Volume, Shuffle, and Track Selection controls to play MP3 and WMA files, has a mini jack to use a mp3 player or other audio source, has cigarette lighter plug, priced about $35.
DLO TransCast FM Transmiter for MP3 Players, 0092007, use to play audio from an MP3 player through a car's radio. Gets power from cigarette lighter jack or batteries, 3-foot cord for connecting an audio source, compatible with MP3 players, PSP, and iPod. Available from radioshack.com for about $40 plus shipping. Radio shack will ship free to the store nearest you.
USB Car MP3/WMA FM Modulator Player W/Audio Input, will accept a standard USB drive to play MP3 files with car's FM radio, plugs in cigarette lighter jack, input jack for audio from CD, DVD or MP3 player. Available online for about $25.
Belkin TuneCast II Mobile FM Transmitter, will except audio from a MP3 player's headphone jack and transmit it to a car's radio to be played through the car's existing speaker system, powered by batteries or through car's cigarette lighter jack, available for about $24.
Other accessories that can be used to enhance your car include seat covers, floor mats, steering wheel covers, sun shades, head rest covers, litter bags, can and cup holders, inside/outside thermometer, gps/map device, extra loud or novelty sound horns.
Items to keep in your car for repair, emergency, safety and miscellaneous - Jack, lug wrench, trouble light, flares, jumper cables, maps, cell phone and phone numbers, coolant for radiator, drinking water, long storage food, empty container for gasoline, various hand tools, gloves, coat, hat, blanket, rain poncho, and a first aid kit.
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Rv inverters I am getting a 24 volt reading in my 12 volt RV, do I have a bad inverter?
I have 24 volts showing on my volt meter when I check my voltage. I have disconnected both batteries and only hooked the battery back that cranks the motor home. Still I get 24 volts. Could the inverter be the problem?
I don't see how. That's the wrong end of the inverter. That takes AC and makes DC out of it. I don't it's even connected to the electrical circuit. Are you sure you're measuring correctly? You'd be burning out light bulbs and our turn signals would be fast. Your dash lights and headlights would be very bright as well. Where are you measuring and what happened to make you check it in the first place?
