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Voltage Inverters & Converters non-technical information for fellow travellers

October 22, 2009
Voltage Inverters & Converters  non-technical information for fellow travellers

The following information has been prepared by Phil Jones aka Ozzie_Traveller for the benefit of GoSee supporters.

Phil Jones has acquired much of this information via the university of life.

In a previous life he was an adult-education lecturer in Canberra; now he offers Tag Along Tours and Learn Digital Photography workshops to fellow travellers. See his web site (below) for more details.

12-Volt Transformers / Converters Inverters

There are lots of discussions in the caravanning community regarding inverters, sometimes voltage transformers/converters. This text is designed to assist newbies to understand a bit more about it without becoming at all technical.

Voltage Transformers / converters:-

A transformer changes voltage downwards.

The battery in your mobile phone camera - torch or trannie radio is recharged by a small black box thing that you plug into the household power point and it then connects into the phone camera - torch or trannie radio. This device is often called a battery saver, really it is a voltage converter or a power transformer.

If you look at the tiny writing on it, it will say something like Input = 240 volts, Output = 3 volts.

The biggest problem with these things is that the makers of your electrical stuff often have different plugs on them, meaning that you end up with 1/2-dozen devices all doing the same sort of thing for 1/2-dozen things in your caravan.

You can replace these 1/2 dozen devices via a single black box gizmo converter from someone like Jaycar Electronics or Dick Smith Electronics. It costs about $40 and goes from 240volts down to 3v, 6v, 9v,12v etc x 1Amp of power, and comes with 6 or 8 plugs of differing sizes to fit many different devices ... ie:- 1 device takes over from many others.

You can also buy an almost identical device that plugs into the car's cigarette-lighter, also for about $40 and goes from 12volts to 3v, 6v, 9v etc and powers lots of little things just the same way.

It also comes with 6 or 8 differing plugs to suit lots of things. [see figure-1]

Many caravanners fit a 12-volt multi-socket costing about $30 into their caravan - it may have 2 or 3 sockets for the cig-lighter gizmos to fit into it, and with this socket you can have multiple things going at once. The device is connected to the battery via a fused lead for electrical safety thing.

<!--mo1####mo2-->Figure-1, JAYCAR 12v to 9v-6v-3v  voltage converter, $30<!--mo3-->
Figure-1, JAYCAR 12v to 9v-6v-3v voltage converter, $30

Voltage inverters:-

An inverter changes voltage upwards.

Small inverters, costing about $75 can plug into the cigarette-lighter socket, and can change the voltage from 12v up to 15v, 18v or 21volts to run a laptop computer etc. [see figure-2]

Other, bigger inverters, costing from $150 upwards can change the voltage from 12v to 240 volts for household electrical devices. [see figure-3 figure-4]

Any inverter producing 240volts needs to be correctly wired for electrical safety - 240volts from an inverter can electrocute you just as easily as 240volts at home if you start fiddling and get it wrong.

Let's invent some items that may be around your campsite ...

- you have a small personal fan the small writing on its base says

240volts x 40 watts; and

- you have a small bed light, using a 25 watt bulb; and

- you want to hang a mirror-reflector lamp from a tree for some night-time use, the lamp having a 150 watt bulb.

Okay ~ add up the watts ... 40 + 25 + 150 = 215 watts.

With electricity you always lose a bit as it goes through the wires, so for our arithmetic let's call it 240 watts, so therefore, a 250watt or a 300watt inverter could operate all three things at the same time and have a little bit of spare capacity. And you can run all these things from a regular household 240volt x 4-way power board plugged into the inverter.

<!--mo1####mo2-->Figure-2 JAYCAR 12v to 24v x 150w inverter, $75<!--mo3-->
Figure-2 JAYCAR 12v to 24v x 150w inverter, $75

The how is it done the but however it may not work now comes along.

Many 4wd people get an auto electrician to permanently wire a second battery into the tow vehicle, and it gets charged as you run the engine.

Also fitted is some smart circuitry to let you use the second battery without affecting the engine-starting battery.

Many caravans have a battery (sometimes two batteries) in the caravans storage boot, and connected to the tow vehicle via a special plug (called an Anderson plug) ~ the normal plug for blinker brake lights etc cannot carry the power (called amps) needed to recharge a battery, thus the need for a special plug and suitable (thick) wiring to allow lots of power to flow from the motor to this battery.

When thinking of inverters powering up your electrical stuff, keep in mind your car headlights ...

Your cars headlights are probably 2 x 75watt bulbs, ie: totalling 150watts.

Im sure that you well know what happens when you leave the headlights ON while the engine if OFF ~ its something that all of us have experienced in our lifetime So how long can you run a 300watt inverter before the battery supplying that power also goes flat? ~ ie: NOT all-day or all-night ...

The battery is probably labelled as 12volts x 90AmpHours capacity ... ie: it will theoretically deliver 1Amp for 90 Hours, or 90Amps for 1 Hour. However, experience tells us that only about half of the theoretical battery power is really available to us. Im not going into the reasons, its just the way it is. So lets presume that weve got 50AmpHours available.

<!--mo1####mo2-->Figure-3 JAYCAR 12v to 240v x 150w inverter, $160<!--mo3-->
Figure-3 JAYCAR 12v to 240v x 150w inverter, $160

Earlier on we calculated that our campsite devices totalled 215 watts, and we presumed 240watts as our usage. Now, if we do some simple sums ... 240watts divided by 12volts gives us 20Amps (following schoolboy science days of E=I/R ... amps = watts/volts). Therefore our 50AmpHours of battery will give you 2-1/2 hours of power before it goes flat.

The battery power being provided to you is in the form of Amp-hours and the easiest way we can work out how many amps are left in the battery are via the volts remaining. Sound a bit odd, but thats they way it is.

As the battery power is used, the voltage drops from 12 to 11 to 10volts ~ at which stage the battery is flat. If you continue to use it, and the voltage drops to 9 - 8 - 7 the internal circuitry of the battery will be destroyed. To save you unnecessary expense in replacing expensive batteries, you are recommended to install a $5 Low-Voltage warning buzzer into the wiring.

The battery Low-Voltage alarm is set for 10.5 volts, and it goes off like a smoke alarm at home ~ if/when it starts, you will know all about it.

Recharging your battery:-

In some bush-camp settings, I have myself, and I have seen plenty of others just run the cars motor for 1/2-hour every 2nd day to recharge the battery. Works okay, but a bit inconvenient.

Another way of recharging your 12volt battery is via a portable solar panel ~ often called a floater. Editors Note: See the chat with Battery World expert Tom Spence on the GoSee Home Page on the subject of solar power.

These panels are about 400-500mm wide x 700-1000mm high and create between 40watts to 80watts of power when in full sunlight, and are connected to the battery being recharged.

As the sun moves through the day, you need to reposition the solar panel towards the sun in order to get maximum advantage from sunlight, (so the name floater). PS: you can also have them fitted permanently to the roof of your caravan, though not all caravans (ie: some pop-tops) can do this.

And yet another way is via a petrol generator ~ these come in various shapes and sizes, cost $1500 upwards for a nice quiet one (cheapies sound like a motor mower), but it means you lose storage space for the genny and the can of fuel has to be considered as well.

Disclaimer: Phil Jones has no commercial alliance between himself and any of the businesses named here as supplying equipment to the caravanner marketplace.

Author: Phil Jones

<!--mo1####mo2-->Figure-4 JAYCAR 12v to 240v x 600w inverter, $250<!--mo3-->
Figure-4 JAYCAR 12v to 240v x 600w inverter, $250

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