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Portable Power
HOW TO DESIGN A PORTABLE POWER SOLUTION THAT'S RIGHT FOR YOU

So you've always fancied yourself as a bit of an adventurer? Sure. As long as the adventure includes warm meals, hot showers, and a good entertainment system! When caravanning you might have some of those, but you'd need to find powered sites - until now...

Portable power has come in various forms of petrol generators, dynamos, and even the vehicle you're traveling in. But now you can utilise the latest in solar power to keep those creature comforts running! Solar power is certainly not a new concept. A report from late 2015 shows more than one in seven households in Australia now have solar Photovoltaic (PV) systems installed on their roofs*. While government incentives played a hand in the rapid uptake of solar in homes, solar adoption for motorhomes, caravans, and camping has been much slower. Many new caravans and motorhomes do come with one or more solar panels to keep things running a little longer. However, if your vehicle is a little older, or if you want a mightier system capable of running anything and everything, then we can tell you how to design the right system.

Building Your Own System

It's a relatively straightforward process to design and install your own portable power system. Especially with a little assistance from your friendly local Jaycar store! There are some fundamental principles you need to adhere to, but you can essentially make it as large or as small as you like (or have space for). You'll need to calculate your expected power usage, how you're going generate that power, where you're going to store the power and how you're going to deliver that power to your appliances.

How Big is Big?

Well, when it comes to portable power you can never really have too much. But due to budget and space constraints, building a system specific to your power usage is optimal. You need to look at what equipment you need to run, and what voltage that equipment requires. Some appliances will run straight from batteries (12V), others (especially if they were intended for home use) will require mains power (240V). The biggest ones you want to look at are electric coolers, cooking appliances, TVs, and lighting. Of course gas power will take care of many power-hungry things like hot water, larger fridges, and of course - a nice BBQ for cooking - but an adequate system can do those things too! More commonly, your biggest power-consumers will probably be lighting and entertainment - especially because they aren't just used for a short time. Often they'll be running between sundown and bedtime. As a good starting point, look at all the appliances you'd like to run at night.

Working Out Your Power Usage

The simplest way to calculate this is to find out the overall power consumption (expressed in watts, or simply W). Many devices will specify their wattage. If they don't, you can work it out yourself using the following formula:

Volts x Amps = Watts. Therefore, if your appliance says 12V at 2-amps, it will use 24-watts of power.

Once everything is converted to watts, you simply add the numbers together to find your required system wattage. For example, to take care of basic lighting and entertainment at night you might add together 2 x 25W lights, a portable media player at 40W, and a phone charger at 10W. If you're running everything together you need at least 100W of power at any given time. That's not a whole lot of power to run from the grid at home, but in a portable scenario it can add up fast! Then you need to consider how long you'll need 100W of power. From sundown to bedtime, it can easily be 6hrs a night in winter. 100W x 6hrs = 600-watt-hours (expressed as Wh). That's how much power you'll need to generate and store to keep everything running for the night. We recommend you should at least double this amount for unexpected contingencies (though tripling or quadrupling will allow for far more over-indulgence of your power!).

TIP: If there's no current-usage rating written on your appliance, you can often use the fuse rating as a good guide to its upper-limit of power usage.

Working Out Your Power Storage

Now you need to work out the amps that you need your battery to store. Watts divided by voltage = amps. Assuming you have a 12VDC battery system, and are using the scenario of 600Wh at night, you would need 50-amps of power (600 / 12 = 50). That's quite a lot of power for even a large battery, but certainly not a problem you can't solve! The trick is then to make sure you're charging fast enough to recharge that battery throughout the day - even in poor weather.

If you've decided to double your expected power requirements (better to be safe than sorry!) then you would need a 100Ah battery, an inverter large enough to run all your devices, and solar panels large enough to recharge everything in half a day (in case of poor weather, you'll have a better chance of a full recharge).

Now that you have your basic requirements for the overall system, you can start looking further into individual components.

The Power Source

Unlike home installations where you can utilise grid power when the sun's down, solar panels alone aren't going to help you much in the dark. You need somewhere to store all that energy, so you can use it at night! The most common way to do this is by using large batteries. They come in various forms, each with their own pros and cons, but the biggest thing we're interested in here is capacity. Expressed in Ampere Hours (Ah for short), capacity is easily compared across batteries using this value. Basically the bigger, the better! More accurately, the higher the Ampere Hour capacity, the more charge it can store for later use.

Most commonly, solar systems will provide 12 or 24-volts to recharge your batteries. 12-volts are more common, but higher-capacity systems will often be 24-volt (often running 12V batteries together to form a 24-volt system). If your system is designed purely for mains-power with the use of an inverter, it won't likely matter much - just make sure all of your components run on the same voltage. If you're integrating it into your vehicle or another system, ensure they're the same voltage first.

Power Generation & Recharging

Solar panels are the cleanest, simplest, and most set-and-forget method of power generation. Unlike petrol generators or wind-turbines - aside from checking they're clean and the sun is shining - they'll require virtually no maintenance over their usable life. Even in cloudy weather, solar panels will still receive UV rays (albeit somewhat diminished over a sunny day). Wind generators are great in some areas, but unless there's a persistent strong breeze, you might find yourself having difficulty. A good Wind Generator is also more of a fixed-installation device due to weight and setup challenges. Petrol generators are noisy, smelly, and require fuel to be added regularly. Of course a petrol generator makes for an excellent backup, but solar is usually best when it comes to reliable power generation. It's renewable too!

To determine what size solar panels you need, determine what you need to be able to recharge your batteries in an average day. The maths is quite simple. Say you have a single 20Ah/12V battery, that's about 240 watt-hours (just multiply them together). To charge that battery, you need to figure out how many hours of sun you expect to get (let's assume 10), by the required charging power. 24 watts per hour would theoretically recharge that battery from empty.

24W x 10hrs = 240 watt-hours - just enough to charge your battery. Of course, the sun is never "perfect", and pesky things like clouds will get in the way. So multiply your solar panels by 2-4, and you'll be set.

Now all this power can't just go around flailing in the wind... you need to make sure it's managed appropriately. That's the job of the Charge Controller. It provides a few primary functions. They are to:

■  Regulate the output of the solar panels.
■  Manage charging of the batteries.
■  Stop reverse-charging (where your battery can actually discharge through the solar panels).
■  Electrically isolate components when something goes wrong (like a short circuit).

The main selection criteria for a charge controller is its rated current. To find your required current, add up the wattage of all your solar panels (eg 2 x 200W panels = 400W), then divide it by the system voltage (400W / 12V = 33.3A). In this example, you would require a charge controller with a capacity of 40A or greater, to ensure it can adequately handle everything when the sun is bright, and the battery is flat.

Power Delivery

Only using 12V appliances? Awesome, you're all set! However, most commonly power will be converted from battery (12-24V) to mains power (240V) so you can run just about anything. Inverters come in all shapes and sizes, and also varying qualities. Most notably, "modified sine wave", and "pure sine wave". As it sounds, they're differences in the quality of mains waveform produced. For many appliances, this doesn't matter a great deal. However, for sensitive electronics such as laptop computers or televisions, Pure Sine Wave is far superior. We won't go into the depths of why here, but if you're looking for versatility, Pure Sine Wave will power just about anything up to its rated power.

Keep in mind, if you need to use power tools, or any appliance with a large motor (a refrigerator or large electric water pump), you will need an inverter much larger than the rated power of the appliance. This is due to what's called "startup current". It can require many multiples of the rated power, for even just a fraction of a second. This is enough to throw your inverter into overload protection mode.

Wiring it all Together

If you've ever completed a "join the dots" activity (who hasn't!), you'll probably recall that the final image is only as good as the carefully crafted lines between those dots. The same rule applies to wiring any power system. You need to use heavy duty cables and quality connectors that are suitably sized and rated for your system. High power cables feature current-ratings, so you can easily select the cable thickness for your system. If you need to be able to detach part of your system while you're on the road, high current Anderson connectors provide a reliable and safe way to connect and disconnect high power cables with little fuss.

For safety, all electrical systems should have fuses or circuit breakers on all heavy-duty wiring (and even the smaller stuff via a fuse box or distribution board). It's imperative to prevent electrical fires in the event of a short circuit. Those batteries can push quite a lot of current into your wiring when something goes wrong, turning your heavy cables into a large heater. A fuse or circuit breaker trips the instant anything like that happens, preventing any damage. Use appropriate mounting hardware, heat-shrink, and soldering for solid connections. A blown fuse might be inconvenient, but an electrical fire could be fatal.

Sounds like a lot? Don't worry - our team know everything there is to know about it, so just ask them!

Just a few more tips to go...

Efficiency

One of the reasons we "round up" on the numbers is due to efficiency. In the course of generating, regulating, and monitoring all this power, there's a certain amount of efficiency loss. It can be anywhere between 2% and 30% of your power. So it's always better to have more solar panels than you think you'll need, a larger battery than you calculated you require, and a larger inverter than the numbers say you'll need. Then you can be extra-confident your system is capable of everything you want to use it for.

The Math...

It's somewhat necessary to work backwards to get accurate numbers. To ensure everything is clear, here are the basic mathematical steps to follow, when planning your system:

1. Add up the wattage for all your appliances that will run at night.
2. Consider how long you want to run those together for to get your total wattage - you'll need an inverter at least that large.
3. Calculate your total watt-hours (total wattage multipied by the number of hours of use).
4. Divide your total watt-hours by your system voltage (eg - 12VDC) to get your amps. You'll need a battery with at least that many ampere-hours of storage capacity to run things for the night. Ideally, double the capacity will ensure your battery is never completely drained.
5. Select solar panels that total at least 2x your total watt-hours (to ensure you can charge them in sub-optimal conditions).
6. Lastly, ensure your wiring can handle all charging and power delivery, with room to spare.

In practical terms, using 1000Wh overnight usage as an example:

Total Wattage - 1000Wh (200W total, over 5 hours).
Inverter - 1000Wh / 5hrs = minimum 200W - ideally, 500W.
Battery - 1000Wh / 12VDC = minimum 83Ah / 12VDC - ideally 150Ah.
Solar Panels - 1000Wh / 10hrs = minimum 100W / 12VDC - ideally 200W+.

Pre-Built Portable Power Kits

If all of this seems a little overwhelming, even after chatting with your local Jaycar store - perhaps a pre-wired, pre-made kit is the answer for you! We have several quality kits that include ultra-efficient LED lighting, mains power, and USB charging ports - all neatly wrapped up in a tidy-unit and stored in a back-pack!

If you have any questions or would like further advice, our sales staff are always ready to help.
Drop into your local store, or contact us and we'll make sure you get the right equipment for your needs!

*Source: http://reneweconomy.com.au/2015/australia-leads-world-on-household-solar-and-on-coal-89654