I'm intending to display my car at Minishow 2008 in July and was wondering if there was a way to have the 'accessory' electrics in the car (lights, horn, radio, etc.) operating all day without flattening the battery. The obvious way is to hook up a battery charger permanently connected to the battery and rely on the trickle charge to maintain the charge to a suitable level. But I'm not sure if there are any safety implications.
Has anyone done this successfully in the past?

I would've said go the charger.
They only pump in as much juice as the battery will take.
Alternately, take another battery (like a big one) and drain it till its flat.

No real safety implications with leaving a charger on (if an outlet is available) but if the load exceeds the supply (as is very common with cheap chargers) then you will only put off the innevitable.

Work out the load the accessories are drawing and make sure you can match the charging level to the current drain. Alternately you could put a spare battery under the car and have it supply the accessories discretely while the main battery is disconnected, and swap it out with a charged one from time to time.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

You can get 240V power adaptors, not sure where from though. That's how all the big audio guys run their sound systems all day

You can get what they call an intelligent charger that's suitable for long term use (according to autobarns catalogue anyway ...) but the main thing is make sure your mini has an accesories position in the ign switch and you aren't just leaving the ignition on as it can burn out your points or keep your fuel pump (electric) running the whole time .

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The intelligent chargers detect when the battery has reached it's peak charge by watching the voltage level and the current going into the battery. Then it stops charging.
If the battery charger has an open circuit voltage of 15 volts, and chemically the battery will not charge any more above 14 volts, then the extra charge the charger tries to stick into the battery will be boiled off as gas and heat.

The smart chargers are the better option if you are going to let the battery get to full charge over long periods, but a cheapie will be fine if there is a consistant load.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

the couple of batterie ideas doesnt work, and gets really annoying, especially when you flatten 2 batteries, and have to clutch start your car after a show

i am also in teh same vote, trying to work out whta i want to do for minishow!

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-jamie-
1963morris 850
1965 solid side van
1994 rover racecar

We have a similar problem with solar power on one of our properties.

We have twelve volt controller to the battery, a thirty amp battery charger and we bump up the power with a generator.

The controller was off ebay for about $60, the charger was off ebay for $99 and the generator is a $99 two stroke at .75 kva from Mitre 10. The generator pumps out about 20 amps all day an is very quiet.

You do need a controller as the cheaper generators do give varying voltages.

Yes we also have solar panels but you dont always have good sun.

I decided to go the transformer route for Minishow power.
I bought a 240v unit from Jaycar for $40 that puts out a handsome 8 amps at 12v dc and has a single cigarette lighter socket output. Add a 3 lighter socket adapter that also includes a USB socket (to power an MP3 player) purchased on eBay for $12.50 (incl. postage from Hong Kong), plus a few lighter sockets from Jaycar at $4 each to put on the end of the items needing power and I'm away.

Is this being held in a caravan park? Will you be able to get to a power point to plug it in??

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Power is available to display cars on a first come basis. Minishow is inside a pavilion at the Melbourne Showgrounds.

So there will be plugs in the floor then?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I haven't seen the venue so don't know if there are plugs in the floor, leads from the roof, a long extension cord with a fifty way plugboard, dozens of petrol generators, solar panels, or whatever. Maybe it's just power points around the wall. So long as I get one 240v outlet I'll be happy.
Seriously Mick, if you need to know contact Krystian (KJ on this forum).
Oh, and if you are considering displaying you need to request power on the entry form.

Nope, not I. Nope, no radio will be in my car. I can barely hear a conversation with a passenger in my minis, let alone a hi-fidelity stereo.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

No (dumb ar$e), its indoors at the royal melbourne show grounds and yes there is power available but you need to contact "KJ" about this. There are some power outlets from the roof and down the walls from memory but best to contact the person that knows 100%

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http://www.youtube.com/watch?v=nDMkVq1jRGU