AC to DC Converter

[dgmacq]

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.

[Tom Kendrick]

650 amps at 12 volts is 6500+1300=7800 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 >Hello, I use a 12 volt winch to pull my boat up on a marine railway at

[CJT]

If it really draws 650 amps, or a significant fraction thereof, you 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.

[Mark Lloyd]

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).

[hallerb]

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

[hallerb]

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

[Richard J Kinch]

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.

[lwasserm]

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.

[krw]

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.

[Bennett Price]

As others have pointed out, the CCA rating doesn't help. I suggest you buy a cheap ammeter at the auto parts store and measure the current draw of your new winch, (including when it is locked - trying to pull something that simply won't move.) Then you can consider whether to buy a battery charger, extra battery, or AC->DC converter.

[e-mail] wrote:

[Goedjn]

Seems to me that that would be an excellent place to store a manual winch. How big is this boat?

[George]

Why not go the simple route and open your hood and use your vehicle battery when you need to do this.

[Stormin Mormon]

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.

[Stormin Mormon]

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.

[CJT]

I think that's what he did. 650*12=650*(10+2)=6500+1300=7800

[Mark Lloyd]

For a limited time, just enough time to start an engine.

[CJT]

How long does it take to winch a boat?

[mm]

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.

...

[Chris Lewis]

According to mm :

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.

[Chris Lewis]

According to [e-mail] :

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.