I need a transformer to convert

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chuzzlewit

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mains power to 12V in order to supply a 12V 0.75kW winch. This will pull a small boat on a trailer (total weight 680 kg) into my concrete level drive. There is a hump in the drive like a speed hump : so the maximum current would be about 25A. The winch people suggested keeping an old battery on a trickle charger as a power source.
Does anyone know if (and where) I could get a suitable transformer instead?
 
If it is a 12V DC winch you will need a rectifier as well. One that can easily take the 25A that you expect the transformer to deliver.

You will probably be better off with a 12V battery and a pair of jump leads.

It should be fun. I'd like to know what happens.
 
I'd have thought that a suitable transformer would be quite expensive. The battery option sounds better. Or, how about a spare mainsheet tackle and two bricks as wheel chocks?
 
I know virtually nothing about winches but it seems a strange way to go to run a 12 volt one off the mains. Don't they make mains ones? I would have expected that to have more power. For example, there's one on ebay here for £52 which looks OK for your purpose.
 
A 12 Volt 25 Amp power supply ( which is what you are looking at ) is going to set you back a pretty penny!

Erm why not just use the car battery still in the car you just towed the boat back from the water with? Some Jumper cables will provide thick enough leads for the job.



If you still want to do it stand alone then Airlink transformers will make a transformer for you. I reckon you are in for about £70 or so

You will need a bridge rectifier - 35 Amp at least Less than a fiver from RS Components

A box to stick it all in will cost you a few quid too.

Ideally a BIG capacitor ( 50000uf at at least 16v )

A fuse and switch, a bit of time and you will be £100 out of pocket.

At 12v and 35 amps you can achieve some really nice firework displays/ welding demonstrations if you get something wrong.

Also without regulation the open circuit voltage will be close to 20v or so and could see off the winch as you start it up.

A sterling 35 amp battery charger will set you back over £200

This is perfect, at that price I'd jump in
 
Have you calculated the power requirement to arrive at your 25 amp figure? A 750watt motor could in theory draw 62.5 amps from a 12v supply. A secondhand battery must be the cheapest way of doing it, failing that, a winch which has a 240v motor.
 
Even a highly rated psu may well refuse to start up due to the surge current when you switch the motor on. The PSU's people are directing you to are not simple transformers! I would definitely borrow a battery to provide the current even if I had a meaty charger handy. If you try to run the winch from too weak a supply, you run more risk of burning out the motor. A jump start power pack is another option if there is one handy.
Beware of cables getting hot, I have melted insulation doing this kind of thing, best if there is space around the cables so they don't short if the plastic melts. Some cheap jump leads are poor, some are fine. A car batery and any old charger will be fine if you stop and let the battery recharge as soon as the volts fall, and don't let anything get hot!
Good luck
 
To cope with the fluctuations in demand current, you need a reservoir.
With a transformer and rectifier you will need a bloody big capacitor to act as the reservoir.
Using a float charged battery gives you one hell of a reservoir and you probably already have the battery and charger so no additional expense.
 
What voltage does a cheap cheap DIY welding transformer produce? regardless, battery would be best,'cos you would still have to rectify it, need diodes and big heatsink.
 
Why not remove the speed bump into your driveway and fit a speed camera instead. /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif
 
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