I really don't want to start Another Winch Thread and sorry if I'm hijacking the ops. So here's my questions. I have a 850 cca battery in my tractor. The book says it has a 55 amp alternator. What does that mean and how does it relate to battery draw down by the winch.
Lets discuss your question a bit. What is 850 cca rating you ask? Well it has nothing useful to tell you about rating a battery for use with a winch. What is cca? It is a standard rating. The CCA refers to Cold Cranking Amps. The rating is how many amps can be drawn from the battery for 30 seconds at 0 degrees Farenheight with the battery voltage not to drop lower than 1.2 volts per cell. So in the case of a 12 volt battery with 6 cells, that is 7.2 volts. So if you put one heck of a big load like 850 amps on your battery you could expect it to not drop below 7.2 volts at 0 degrees for up to 30 seconds.
This is not a very useful specification for on how a winch is to be used is it?.. 30 seconds on a winch is about what maybe 2 foot of winch line coming in or less? Of course your winch is not going to draw 855 amps either. These rating are marginally useful in rating how the battery will act in very cold temps and cranking a starter motor that is turning over an engine with thick oil.
There is another rating for your battery, somewhat more useful than CCA and that is its amp hour rating. Your battery is probably about 75 maybe 80 amp hours, which THEORETICALLY means you could draw 80 amps out of it for one hour.. BUT you cant really. What you could do is draw 1 amp out of it for 80 hours though.
So when you start pulling 150 amps out of your battery(a possible real world winch load) for several minutes as you try to drag that log up out of the woods, you can see that the battery is going to go flat in a hurry.. a BIG hurry. If you try to pull 100 to 150 amps out of a 80 amp hour battery it will be below 10 volts in a matter of seconds, or a couple of minutes at best. Dont forget as the voltage drops, the winch will slow.
Now the good news. You have an alternator that is putting power back into the battery. Now the bad news, Your puny 55 amp alternator cannot even begin to keep up with that 150 amp draw from a big winch. So you winch for a few seconds, and charge for a few minutes? Ok you could do that. And the benefit is the winch has a chance to cool down too. But this is going to be a frustrating slow process. Don't forget that alternator is going to get pretty hot too.
Keep in mind that big winches on trucks, are mainly used to get the truck moved a few feet to get it up out of the "hole", and the alternators on even a standard truck is will over 100amps with many around 140 amps, and people who are serious about winching have 2 batteries and 300 amp alternators.
A 55 amp alternator on a CUT tractor is actually a rather large one, as they go, with many somewhat less than 50 amps. But what is the electrical load on a CUT tractor? not a whole lot... just some lights, and recharge the starting battery. On some we have a heater or AC fan or two, and a dashboard, and some computers, but still very small loads. Not huge electrical loads like we would have with all the accessories on a car or truck.
So to sum up.. Is a big electrical winch on a CUT for pulling logs a good idea? NO, not even close. Is it ok for pulling yourself out of a hole? Sure, Just keep in mind the limitations on how long you can pull for and how long you need to recharge and cool.
Is a PTO driven logging winch a good idea? You bet it is. That is why they make them.
