Enclosed trailer wiring

just a quick question .... what is the reason for it, you have the "post" as enclosed trailer wiring but want to drop 240 down to 12v ...
Maybe a bit of detail on what you want out of it and what it will be on ???
In a sorta nutshell it will work fine, probally add a battery and the "transformer" will be simply a charger then no need for changover switch ect
Cheers
Joe

Sorry i should have put more detail.

The trailer is a enclosed race car trailer, the reason for keeping both 240 and 12volt is i will be using both on a mixture of occasions and didn't want to have a battery within the trailer to worry about. When i can run the lighting from the tow vehicle under 12v and when connected to mains power at race meetings i can then select the power supply to 240volt.

In my mind it all seems to work but am unsure about what size transformer to use and is a normal battrey switch ok?

Thanks

The diagram you have would not work.
You need a 12Volt DC power supply (240Volt AC input) rather than a transformer which outputs AC.
You can probably buy one of these at Jaycar (maybe Dick Smith). These would look similar to a mobile phone charger
There is an inconsistency in the power consumption figures on the bottom right; the current of 0.6mA is incorrect it should read 0.6A or 600mA for 7.2 W power consumption. (or else the power consumption is 7.2mW)

Don't use a transformer but rather a battery charger that has power supply mode.

This way you will also have a battery charger for the race car :-)

You could even consider fitting a battery into the circuit, that way you can have lights and radio without 240V and without needing to connect the trailer to the car.

Use something like our ACDC-DC 15A charger with auto input, that way you don't need the master switch. It also has power supply mode so you don't need a battery connected at all times. Looking at you pictures 15A would be fine.

What you have in the diagram will basically work, as long as you use a power supply (outputs DC) rather than a transformer (outputs AC).

The kind of power supply you need outputs 12 to 14 volts at a handful of amps. "12 volt" power supplies are easy to find and they usually output exactly 12 volts. You can get some with outputs of say 13.5 or 13.8 volts, which is closer to what a car electrical system actually runs at. Either kind will run your lights and stereo OK.

For the "handful of amps": the stereo is going to be the biggest current draw you have; the lights will take 0.1 (rounded up) + 0.1 + 0.6 + 0.6 = 1.4 A. The stereo will probably be fused at 10 A but it won't draw that much all the time; maybe 1 A at a minimum to 7 or 8 A if you really crank it up. A 12 V 10 A power supply would probably do it, but maybe 12 A or 15 A would be better.

Sometimes power supplies like this are sold to run mobile CB or HF radios on mains power. These will be well-filtered so as not to cause a whine in the audio. Jaycar MP3079 or MP3097 are in the right direction, but these are probably not very well filtered - the lights won't care but there might be a slight whine or buzz in the sound from the stereo.

One optimization is to put an Anderson plug on the output of the power supply; that way you don't need the battery switch. You plug the trailer into *either* the tow vehicle *or* the power supply, not both at once.

Another suggestion: include a cigarette lighter socket in the trailer. Maybe not with a lighter element, but as a place to plug in your mobile phone charger, 12 volt air compressor, or similar.

Having said all that... I'm gonna add my voice to the "are you *sure* you don't want a battery in the trailer?" chorus. Having worked with a race car trailer before (it had both 12 V and mains lights from the factory, and we installed a 12 V battery), it was *nice* to be able to open the trailer door and click on the 12 V lights even without the tow vehicle there. You can look for your tools or luggage or whatever without having to hold a flashlight (torch).

If you are concerned about weight and space, and are willing to not run the stereo on the battery, you could install a smallish gel-cell. The 7 amp-hour size is about as big as your two fists together, weighs 3 kg, and would run all your lights for about 3 hours. If you want to run the stereo for any length of time on the battery, you are looking at maybe a 20 amp-hour size on up.

If you do install a battery, there is a little more wiring to do to get it to charge from the tow vehicle and not feed back juice where you don't want it; this is where a gadget like the charger+power supply that ABR posted about is handy.

A final suggestion: Before buying a battery, install the lights you think you need, and make sure they give enough light under all conditions. If you decide to install a few more lights, then you can buy a slightly bigger battery if needed.

I hope this helps!

Matt R.

Guys thanks alot for your replies. it all seems abit clearer now.

I have thought about the battrey and i will now need it as I am installing 2x winches one for the car and one for the back door!

How would the battrey charger option work abr sidewinder with your diagram?

If i didnt want to spend that kind of money on the smart charger is there any other options? in regards to charging the battrey i have a normal battrey charger which i would just plug in at home...

Thanks
Nick