AC to DC Converter

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Hello, I use a 12 volt winch to pull my boat up on a marine railway at my seasonal cottage in Canada. I do not have permanent AC power to the location, but can get a big enough extension cord to it if need be. I want to buy a more powerful winch which requires a battery rated at "12 VDC - 650 Cold Cranking Amps" which is not a problem. I would like to buy a back-up 12 volt AC to DC converter to power the winch if the battery fails. Please advise on how to rate the converter based on the battery requirement. Much thanks! D. MacQueen.
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650 amps at 12 volts is 6500+1300x00 watts of power, DC. The rectifier (converting AC to DC) as well as a transformer (step down from AC power voltage to 12 volts DC) will have some losses as well. I believe that you will find such a rectifier to be impossibly expensive for such an application. So costly that several alternatives become affordable: - Another battery, kept charged - A small winch driven by a suitably geared gasoline engine - A suitable tow line capable of attachment to a vehicle
There is no information regarding the anticipated current drawn by the winch at stall speed, nor is the effective load of the boat (including both friction drag and angle of incline on the railway). Surely the winch does not demand maximum battery current along the entire hauling path.
On 13 Nov 2006 17:50:52 -0800, snipped-for-privacy@comcast.net wrote:

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Your math doesn't addup. Watts equals amps times volts.
Be nice to know the actual current draw of the winch under full load. The battery charger with the 12 volt boost setting sounds like one good answer. Spare battery sounds even better.
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Stormin Mormon wrote:

I think that's what he did. 650*12e0*(10+2)e00+1300x00

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wrote:

I don't think a 650 CCA battery puts out 650 amps at one time. Everything would melt.
To the OP, I don't think it is called a converter unless it goes from DC to AC. From AC to DC it is called a rectifier, even if that is only part of it.
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It _can_, more or less. Whether it'll melt is up to how you've connected it.

The OP is using informal terminology. "Converting 120VAC to 12VDC" is what he's trying to do. A rectifier converts AC to DC, but without a voltage change.
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snipped-for-privacy@comcast.net wrote:

might as well forget it. The power supply will cost much more than the winch (and I seriously doubt your extension cord will be up to the task). Buy a backup battery instead.
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On 13 Nov 2006 17:50:52 -0800, snipped-for-privacy@comcast.net wrote:

Does any of the documentation with that winch tell how much current it uses? Probably a lot less than that CCA rating (which is for a few seconds).
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buy a large battery charger. I have one with 200 amp boost. My 200 amp boost charger will start my van with a stone dead battery. cranking my caravans engine at zero degrees a winch will be childs play
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buy a large battery charger. I have one with 200 amp boost. My 200 amp boost charger will start my van with a stone dead battery. cranking my caravans engine at zero degrees a winch will be childs play
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I seem to recall somewhere reading that 12V winches draw anywhere from 50 to 200A. Boost chargers are rated for highly intermittent operation, after which they have to cool down. A practically small boost charger for 100-200A will only be able to deliver that for a matter of seconds. For the cost of a boost charger capable of running for longer than that, you can buy several spare car batteries, and the batteries would weigh less.
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On Fri, 17 Nov 2006 03:37:06 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

Yes, get some batteries. Store them charged.
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batteries large enough limit it to lead acid, which have a finite life with declining poer over time, shouldnt be stored discharged and they go dead just sitting around and after such discharge dont recover their previous capacity......
probably better off with a 12 volt generator.
you could buy a large battery charger and try it in use. if its not good enough return to store.
my 200 amp boost says it supplies 60 amps at 12
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snipped-for-privacy@aol.com wrote:

Someone had the best idea. Just jump from your car battery if necessary.
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Rich256 wrote:

That can also have a couple of downsides, though --
if you're not careful, you can discharge your car battery and strand yourself
it's not always possible to move a car into a suitable position to use it that way
Maybe one could use the BOAT's battery (if it has one)?
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snipped-for-privacy@aol.com wrote:

Generators can also deteriorate if not run regularly, and cost more than batteries.

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The battery doesn't tell you the motor requirements. All you know is that it exceeds them.
DC power supplies are expensive. Upwards of $1 per watt, and you need many hundreds of watts.
Why bother at all? Just borrow a battery from another vehicle if yours fails. Even a spare battery would be far cheaper than a DC power supply.
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Unfortunately, Cold Cranking Amps is a measure of battery capacity to store energy, not an indication of how much current it can supply at any given time. See if you can find an actual current requirement on the winch, i.e. number of amps.
If not, you would be better off buying an automotive battery recharger. One that is capable of 'boosting' or starting a vehicle, would have no problem running a 12V winch. For that matter, if you can get your car close enough, you could use a good set of jumper cables from the car battery to power the winch.
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snipped-for-privacy@fellspt.charm.net says...

No, "Cold Cranking Amps" is the maximum current the battery will supply at some given (low) temperature. This is the current it will supply to a locked-rotor starter. The "Amp Hour" rating is the measure of the capacity of the battery to store energy.

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Oddly enough, cold cranking amps *IS* a measure of how much amperage it can supply.
If you want the total battery capacity, you want the "reserve capacity" which is often expressed as 90 minutes at 25 amps.
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