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Subject Author Date
AC to DC Converter dgmacq 11-13-2006
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Posted by on November 13, 2006, 8:50 pm


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.


Posted by Tom Kendrick on November 13, 2006, 9:30 pm


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 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, dgmacq@comcast.net wrote:

>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.

Posted by Stormin Mormon on November 14, 2006, 1:39 pm


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.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
.

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 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.




Posted by CJT on November 14, 2006, 3:00 pm


Stormin Mormon wrote:
> Your math doesn't addup. Watts equals amps times volts.

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


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

Posted by mm on November 15, 2006, 1:17 am


wrote:

>650 amps at 12 volts is 6500+1300=7800 watts of power, DC.

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.

...
>
>On 13 Nov 2006 17:50:52 -0800, dgmacq@comcast.net wrote:
>
>>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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