Capacitor bank vs dual battery ?

Tested wiring to external terminals tonight for continuity, check. I am golden there. More to come in a few days

 

I haven't had to "mess" with a vehicle battery in f-o-r-e-v-e-r. This appears to be a solution looking for a problem? What's broken here?

 

No kidding. The battery in my car is over 5 years old and is still going strong.

How well is solar going to keep your capacitors charged on cloudy/rainy days, or overnight?

 

I'm still a little skeptical on this... I just don't really see what the cap is going to do for you here. They are great for stereo systems because they help keep the voltage up in quick bursts like when your sub hits hard, but in the long run like winching or starting your engine they will drain so fast that they will basically be useless.

The benefit to capacitors over batteries is batteries discharge slow over time, while capacitors can discharge rapidly (almost instantaneously in fact). Once you go to winch that cap will likely be drained in just a couple seconds or so.

I have two 12" subs in my car with a 5 farad capacitor and when my subs hit hard (peak draw of about 100A) my charged capacitor will go from 14.5V to 11V almost instantly. It literally drains all 5 Farads in less than a second.

Capacitors are designed to prevent instant changes in voltage. Like in this graph, instead of the voltage instantly going to 0V like it shows it will descend down as the capacitor discharges (ie no vertical lines).

On that same note, they also slow the jump in voltage back up, as the capacitor charges.

If you have enough capacitance that the load can't completely drain the capacitor(s) they can actually smooth out the voltage level, but a winch is going to massacre 5 farads, hell your starter will probably be enough to drain it all in one start.

In short, they are good for large, but SHORT draws in current when you need to maintain voltage.

 

So I dug into the math a little. Here's this equation for how much capacitance is needed for a constant current draw.

C = t*I/(V0-V1)

C is capacitance in farads
t is time in seconds
V0 is starting voltage
V1 is end voltage
I is current draw in amps

So say you have a Warn Zeon 8-S, rated at 63 amp draw for no load (ie spooling in the line), which uses far less current than actually pulling a stuck vehicle. Let's say the starting voltage is the 14.5V from the alt and end voltage is 10V since the battery will have easily taken over from there and use 1 second.

C = 1*63/(4.5) = 14 Farads. That is just for your caps to last 1 second while spooling in your line.

If you spooled in all 100 ft at the rated 42 ft/sec that is about 143 seconds. You plug that back in and you now need just over 2000F Sure your alternator will bring that down a lot, but when it comes to pulling a load it won't hardly affect it...

If you are pulling the max rated 8000lbs which is probably pretty reasonable for a 5000-6000lb rig stuck in the mud. You now need a 92F capacitor just to last 1 second and over 5500F to last for just 1 minute...

I think that money is much better spent on a larger alternator than a capacitor bank. Increase the actual power source, not the storage. Just buy a good battery like a red or yellow top.

If you go to a 200A alternator from the 140A you currently have, you could spool that winch in completely on the alternator and not have any draw on the battery. If you had a 540A alternator (unrealistic I know, but some 300A options exist) you could run that winch at full load without touching the energy stored in the battery as well.

 

^^ exactly what I started this thread for.
My idea was to use a huge cap bank IN ADDITION TO a regular battery so that when you use the winch in short bursts, it'll help smooth out those huge spikes.

From what I gather, to make this idea make any practical sense (barely)
The cap bank will have to be wired through a low voltage cutoff that allows it to discharge almost instantly, then isolate itself from the main circuit and charge back slowly through a resistor of a manageable draw so it doesn't demand the same amount of power that it just discharged.
So we need a massive 500 amp diode... And a computer board built specifically for this whole shenanigans.

Fun science project I say.

Switching your main battery for a cap bank is a great start to this though.

If someone does manage to build the above^,
Anyone think it'd have measurable benefits?
Leave "cost effective" out of this argument, as it absolutely is not.

 

Sounds cool, but I don't think you would see any gains, at least in terms of winching. The capacitor bank will disconnect in less than a second from the circuit. I imagine if you measured out the voltage and current graphs on an oscilloscope both with and without the capacitor banks for winching a load, you probably couldn't even tell the capacitors were there.

I found a 100F car capacitor, but since it is made by Lanzar I seriously doubt it really is 100F... The next size I found was a 50F by Rockford Fosgate. Either way, even that 100F one, will maybe last 1 second at a small winch load, which will barely be a blip on the graph on a 30 second pull...

And then, when you are done winching and that 100F cap switches back on to be recharged it is going to be a large hit on your alternator to charge it back up...

 

Yeah I figured as much.. Well I'll call it case closed for the purpose of the thread being started. There's no magic way to store unlimited power.


Now lets see what happens when you switch your battery out for a cap
Lets see what's in that box dude!!

 

That is literally the million dollar question! You could make millions if you could engineer a way to store huge quantities of power so that you could store excess power produced by power sources during off peak hours, or even harness all of the energy of a lightning strike!



Guess you could always try this! haha


Seriously though! Best bet is a larger alternator. Instead of storing the power just produce more of it when it's needed!
http://www.tacomaworld.com/forum/2n...ce/298108-feeler-high-output-alternators.html

 

I'm sure Nikola Tesla would have solved this thread long ago.

I'll just go with two of the biggest deep cycles I can stuff in there with that bigger alternator and call it a day. Ill leave the Nobel prize for electrical engineering up you you guys.

12TRD come on now! Updates on your project already!

And
Merry Christmas, everyone!

 

Caps are great for short term power smoothing (big amps etc.) but they discharge quickly requiring an immediate recharge from guess what? Yep the battery. There is no such a thing as a free lunch.

 

Super Capacitors, like fuel cells are not quite ready for prime time yet.

 

Wrong

It's what the alternator does. How do you think the system works in a vehicle with no battery?

 

Well sort of. Everything in a car is actually powered off the battery and the alternator is connected to the battery only to recharge it, so all power goes through the battery. That is why it is called an alternator instead of a generator. A generator can run a system without the battery. An alternator cannot. Generators run at 100% power all the time, but as a consequence any unused power is turned into heat, so not only are they not energy efficient and they require cooling so they don't burn up.


Alternators will only supply the needed power by having the ability to ramp the output up and down. The problem is they can't ramp up instantly so the battery can cover that while the alternator is ramping up. Also, in the case of needing more power than the alternator can supply the battery helps make up the difference, at least until it is drained anyway.


Most vehicles that don't have batteries like some dirt bikes and snowmobiles, run generators that are spec'd to handle exactly what the engine needs in stock form, and also have a good air cooling setup for when they aren't using all the power supplied by the generator. That is why you typically have to upgrade the electrical on these vehicles just to add a single light to them a lot of the time.

 

We can simplify this.

Take the alternator out of your car. It will only run until the battery dies.

Now take out the battery. It will run until you cut it off. It just won't start up again.

Yes a battery can help an alternator when needed but your alternator runs any and all electrical until that point.

 

Healthy batteries and vehicle charging systems are co-dependent on each other as Brady pointed out. With engine running, the electrical load is mostly satisfied by the available output from the vehicle's charging system. When the alternator's output is exceed, the difference is made up by the battery until it is drained. Most of the battery recharging occurs when the the alternator's power output exceeds the electrical load of the vehicle. Driving habits will determine if the the battery will fully recharged. If the battery is not periodically fully recharged, lead sulfate will gradually accumulate in the battery reducing it's performance (CCA) and capacity (RC or Amp Hours) until it prematurely fails.

If you make short trips (under 10 miles) or do not dive your vehicle at least every two weeks, it is a good practice to externally "top off" the battery with an external battery charger to prevent the sulfation. IMHO, a better approach is to continually "float" charge the battery with a temperature compensated "smart" charger while the vehicle is not in use to keep the battery fully charged to avoid sulfation or freezing.

The principal job of a starting battery is to start the engine. It also is used to stabilize the DC output of the charging system, so do not ever disconnect a battery from a running vehicle charging system because high voltage and damage the vehicle's electrical or electronic systems. A third function is to provide a source of electrical power when the electrical demand is greater than the vehicle's charging system output. Large aftermarket electrical loads can be satisfied by adding more battery capacity, but this additional battery capacity need to be fully recharged. That usually requires an upgrade to the vehicle's charging system.