Primary concerns are killing the battery if the vehicle is off and over-stressing the electrical system if the battery begins to run low. In addition to that I would like to keep power to the winch at an optimum voltage to maximize the performance and prevent strain on the winch itself.
So being that I like to pick the road less traveled whenever making these considerations, both to explore new ground and inspire others... rather than simply add a battery in parallel with my existing one I want to take advantage of some new technology which has become increasingly more affordable... and dangerously more powerful of the last 5 years or so!
Behold... a few examples of 50 Farad Capacitors! (All typically priced under 200$)
I personally am no stranger to capacitors. I used to be a big buff on car audio about 10 years ago; running cars that often won trophy's at SPL competitions. The only difference is back then to run sytems that drew well over 200 amps we used to use a couple of 0.5 or 1 farad capacitors... yes there was no such thing as a 50 farad capacitor, it is even hard for me to fathom how giant and powerful these things must be. The price is also amazing, back then we would pay sometimes close to 400$ for just a single farad capacitor.
Anyway, using some quick "beer theory" I want to give you an idea of how this would work. Basically the difference between running a second battery and a capacitor is the delivery and response of the system.
A second battery in parallel would work in conjunction with your existing battery to deliver a higher rate of amperage, a sufficient way to gain that increase in power but a bit overkill and also pricey. One of the downfalls of battery power alone is the voltage, often battery voltage can vary depending on the condition and load placed upon it, low voltage can be a dangerous thing both for your winch and also for your vehicles electronics as they are designed to operate within a range... running with low voltage can cause performance problems or sometimes even damage. The advantage of a battery of course is time, you can operate a winch much longer on a battery than a capacitor.
Consider now running a 50 farad capacitor; first and foremost I want to touch on safety. You can electrocute yourself in a split second with a capacitor of this size... capacitors can discharge their load nearly instantaneously... a connection without resistance between the terminals would result in a large explosion and poof of smoke, it would output much more power than even an arc welder. With a capacitor of this size I cannot stress how careful you need to be!
The function of the capacitor however is what gives it the advantage in providing a stable load. With a capacitor it charges very quickly, often only minutes are needed. Similar to a battery you would hook it up in parallel... it will charge automatically until something draws current that is beyond the charging capacity of the alternator. As soon as the system begins to experience a deficit it begins to discharge... instantly and much faster than a battery. It would continue to supplement power for the deficit until empty, then the system would default back to the battery.
Going back to my beer math for some example numbers; a winch under full load would draw roughly 400 amps at peak. Your alternator could provide as much as 100 amps, but the battery would need to supply the rest... unless you have a capacitor. Then that 300 amps would come from there; I did some calculations and found that a 50 farad capacitor could supply 300 amps for just under 2 minutes. Looking at the specs for the winch I have been considering that would be a pull of about 12,500lbs for 8.6 feet.
But being more realistic, winches are usually used at 70% or less. That means a draw of about 200 to 300 amps... which if you consider an 8000lb pull on the same winch would translate into closer to 3.5 minutes of pull time before it ever even started to drain the battery. Being that the winch would pull at a higher line speed that translates into over a 25 foot pull.
Now consider that unlike drawing on a battery it would be operating at a solid and optimum voltage with no variance for that time, also the second you stop pulling the capacitor goes back into a charging mode. You would get the maximum performance out of your winch during the pull minimizing the risk of damaging your equipment and not stressing your trucks electrical system.
Another nice feature of most of these capacitors is they often have a digital readout for voltage and capacitance. They also generally have a remote, which means you can activate them when you head out onto the trails and then deactivate them when coming off; It doesn't need to charge or stay charged. With a dual battery setup your vehicles electrical system is always teeming with a higher available amperage on tap than it needs unless you disconnect one battery.... although then you get into the issue of how to keep it charged.
Anyway, this is just my crazy idea. Let me know what you think!
