Replace your car battery with capacitors!

[Enki]

Finally found the video I've been meaning to post:

http://www.youtube.com/watch?v=RccLk6NZ5WM

This guy has 12 banks of 6 3k farad caps for a total bank capacitance of 6k farads... I looked up his amps, and at full tilt they are capable of pulling a combined 20k watts @ 14.4 volts. Beefy.

He also talks about the differences between caps and batteries, which is probably the most relevant part of this video as far as this thread goes.

[serialk11r]

Originally Posted by redpoint5

Have you measured the parasitic drain on your car? The Deka ETX12 only has 10Ah, of which probably only 4Ah is usable before you cause damage to it. It also weighs 12 lbs and costs a minimum of $40. I'd go LiFePO4 instead because it's much lighter, costs the same, and you can use most of the capacity without causing damage. It should last longer too.

Wow, at 70A draw for the starter yes a plain lithium sounds like it's probably good enough, certainly. What I was talking about was smaller capacitors however, for an additional layer of surge protection to the battery. For a car an appropriate quantity would be like a 70F bank, but for a motorcycle you could get away with way less.

I haven't measured my car, no. I'm guessing it's low because I don't have remote control key fob and no anti-theft alarm that I know of. Last year I went to Boston, asked my mom to start the car once in a while, which she didn't, and the car ended up sitting for over 2 months. Started up fine.

Sure the lead acid battery has only 10Ah (actually I think it's 14Ah), but an equivalent LiFePO4 battery would still be about 2x the price. Again, I'm trying to take into consideration the fact that batteries are supposed to be dropping in price. If the cost ratio is the same when this flooded battery dies, then I'm going for a small AGM. If lithium is down to 3x the cost for an honest equal nominal Ah rating, I'll buy that.

[redpoint5]

Originally Posted by Enki

As a side note, the 650s have a bank leakage of about 9 mA (as opposed to the 3k farad caps total leakage of 31.2 mA), so adding the cap bank would probably make my drawdown issue worse.

The leakage current isn't constant though (I think). I assume the datasheet lists the leakage at full rated voltage. Even with the balance LEDs on my 350F bank, the voltage only drops 0.07v per day when charged to 13v (2.17v each). I'd bet leakage is logarithmic, and hope to test this at some point.

Originally Posted by Enki

At 14.4v peak, a balancing circuit isn't needed, and here's why I say this:
...
my argument is that a cap bank of identical condition/make/model capacitors will always self balance to a degree; what that degree is, I'm not sure, but the variance on my bank was only 5.186% from most charged to least charged. I'd wager that over time, that number would likely reduce slightly, and that the most charged capacitor(s) could likely hold more voltage before having an issue anyway.

For the caps to not need a balance circuit would mean they self balance, but I haven't seen any evidence of this yet. If they don't self balance at all, then a small difference in voltage could become a significant difference in voltage over time. However, I agree with your assumption that a balance circuit isn't necessary if there is even slight self-balancing at play. This needs to be tested, and the way to test it is to monitor voltage leak on a single cap at various states of charge. If it leaks more at higher charge (likely), then it's self balancing.

Originally Posted by serialk11r

Wow, at 70A draw for the starter yes a plain lithium sounds like it's probably good enough, certainly. What I was talking about was smaller capacitors however, for an additional layer of surge protection to the battery....

I haven't measured my car, no. I'm guessing it's low because I don't have remote control key fob and no anti-theft alarm that I know of.

From a cost perspective, I don't think you will save money overall on batteries by having a capacitor bank. Perhaps the batteries would only live 5% longer.

Since your car doesn't have power doors or an alarm, I think it's even more important to discover what the parasitic draw is. If it's low enough, you could get away with just capacitors and no battery. If you park outside, a very cheap solar maintainer should keep it topped up.

I see the battery as a last resort, when parasitic draw is too great and the vehicle is parked in a garage. Then, if a battery is necessary, and it's capable of supplying the starting amps with plenty to spare, then I don't see the advantage of running the caps.

My TSX takes 290A to start, so it would cost a lot in LiFePO4 batteries to forgo the capacitor bank. This is a situation where the hybrid pack might be the best option. However, I'm now thinking that I might wire up an alternator kill switch and size a LiFePO4 pack large enough to both start the car, and run for 90min, charging in the garage at night. Spending $210 and wiring 3 banks of the LiFePO4 batteries in parallel would give me 30Ah and 300 cranking amps. Now I just need to figure out how to disable my alternator and measure typical power consumption.

[Cobb]

I wonder if your nsx has an eld? Its a "honda" right? I think this replacing bats with caps arguement will have a range of results with the vehicles electrical system they go in. I know many hondas turn the alt off and on as needed. Of course the weight reduction should give a little and the less load on the alt as the charge curve should be rather linear vs parabolic as lead acid takes a while to charge.

[redpoint5]

Originally Posted by Cobb

I wonder if your nsx has an eld? Its a "honda" right? I think this replacing bats with caps arguement will have a range of results with the vehicles electrical system they go in. I know many hondas turn the alt off and on as needed. Of course the weight reduction should give a little and the less load on the alt as the charge curve should be rather linear vs parabolic as lead acid takes a while to charge.

I wish I had an NSX. The TSX is a European Accord (compact, sporty). I'm not sure if the car has an ELD, as a Google search doesn't produce any results. I doubt it has one because voltage is always maintained at ~14v when the engine is on.

The car is a Honda, so I imagine the alternator kill switch and engine kill switch would be similar to other Hondas. Is the crank position sensor the best place to kill a Honda engine? I'm not sure how to go about disabling the alternator.

[Enki]

Figured I'd update this thread with my "jump box" (which has been renamed "DeathBox") progress.

I need to finish the paneling, mount the ballast/drain lights, and then wire it up and then it can be used to jumpstart cars; mostly, it will be used to start-assist my dad's racecar which has no alternator and requires lengthy pit sessions on the charger before it can go back out and make another pass. Hopefully, this will allow for two passes before pitting at the worst.

[serialk11r]

Originally Posted by redpoint5

From a cost perspective, I don't think you will save money overall on batteries by having a capacitor bank. Perhaps the batteries would only live 5% longer.

Since your car doesn't have power doors or an alarm, I think it's even more important to discover what the parasitic draw is. If it's low enough, you could get away with just capacitors and no battery. If you park outside, a very cheap solar maintainer should keep it topped up.

.. Now I just need to figure out how to disable my alternator and measure typical power consumption.

I'm not too familiar with how batteries work, but I always thought that heavy loads cause damage or at least reduce lifespan significantly, which is where the capacitors would help. Aka, it's not heat that kills them, high current draw can do it too. If we're talking lead acid, I feel like caps would increase the battery's lifespan considerably because they're very sensitive to depth of discharge.

Solar panels are definitely in the plans. If the capacitors and car's electronics bleed off 0.5W sitting there, a tiny solar panel sitting on the dash or under the rear window would do the trick. A 15V panel can be wired together from cheapo panels for under 10 dollars. Even so, I feel like a small battery is still a good idea, it's not a big weight penalty for a massive increase in reserve energy storage.

[oldtamiyaphile]

Originally Posted by redpoint5

My TSX takes 290A to start,

Have you measured that? 290A x 12v= 3500W that's nearly 5hp!

About a fifth of that is more typical, if you've seen a 290A inrush current it's only for a fraction of a second and batteries are generally capable of handling those kind of currents in small doses.

[redpoint5]

Originally Posted by serialk11r

I'm not too familiar with how batteries work, but I always thought that heavy loads cause damage or at least reduce lifespan significantly, which is where the capacitors would help. Aka, it's not heat that kills them, high current draw can do it too. If we're talking lead acid, I feel like caps would increase the battery's lifespan considerably because they're very sensitive to depth of discharge.

As you said, it is depth of discharge that kills lead acid batteries. The high cranking amps don't really harm the battery, so caps won't extend battery life.

Originally Posted by oldtamiyaphile

Have you measured that? 290A x 12v= 3500W that's nearly 5hp!

About a fifth of that is more typical, if you've seen a 290A inrush current it's only for a fraction of a second and batteries are generally capable of handling those kind of currents in small doses.

That was measured half a dozen times with little variance, and represents peak amps and not average. The Camry is similar, peaking at 255A. I'm sure lead acid batteries can handle the current, but not so sure a small LiFePO4 pack could.

[Enki]

If that's peak draw, what about overall consumption during start? I'm not sure what peak draw on my Mazda is, but total power consumption to start is somewhere near 570 amps.