How about a 4 pound "battery"?

[CTScott]

Last week James (Jerkratt) sent me a video via Facebook of a guy demonstrating the use of a bank of supercapacitors as a super light weight replacement for the battery on his Scion xA. I have used supercaps for various engineering projects in the past, but have never considered using them to completely replace a car battery. After watching the video I immediately ordered six Maxwell 650 Farad 2.7V ultracapacitors. These supercaps are 2" tall by 2.5" in diameter. The weight just under half a pound each, so six weigh in at under 3 lbs.

For comparison, the OEM battery weighs 33.2 lbs:


Capacitors behave very differently than batteries because of their low internal resistance, so they can charge and discharge extremely quickly, without the large losses that occur with a battery (due to the much higher internal resistance of a battery). With the supercaps having a voltage rating of 2.7V, they must be connected together in series, so that the sum of the ratings is greater than the maximum voltage of the system. With a car, the alternator can output up to about 14.8 volts, so six of the supercaps connected in series provides a safe margin with a 16.2 V limit. Supercaps can be extremely dangerous, as they may explode if connected in reverse polarity or are connected to a voltage source over their limit.

To experiment with the supercaps that I purchased, I made some strips of bus bar out of aluminum to connect them together and used some fire resistant ABS plastic to make top and bottom covers to prevent accidental shorting.

Here is one of the SuperCaps:



Here are six of them connected in series:



This was my first pack configuration. I was trying to make it as small as possible, but didn't really think about the correct location for the terminals. This configuration weighed just under 4 lbs:



After doing some bench testing with the pack (charging it with a bench power supply and then driving a large 12V DC motor), I was ready to test it in Crashy. I immediately realized that my choice of shape and output connection locations were not optimal, but it would be fine for my initial testing.



I charged the pack to 14.2 Volts, installed the pack in Crashy and turned the key. To my amazement she started with no problem. The voltage sagged to about 11 volts during cranking, but within a few seconds of starting, the pack charged back up to 14.1 volts. I started and immediately shut her off about 20 times, and each time the pack had charged back up so fast that I could have repeated this all day without a problem. A normal battery takes quite a few minutes to charge all the way back up, so this demonstrated one of the advantages of the supercaps.

To test the amount of "reserve" the supercap pack had I then unplugged the EFI fuse (which powers the injectors) to prevent the engine from starting. I then cranked the starter for four seconds and then stopped. I was able to repeat this nine times before the pack had discharged enough to no longer be able to crank the starter.

Impressed with the results, I decided to reconfigure the pack to better match the OEM battery. I just loosened the bus bars and shifted them so that the ends would be along the long direction of the pack. I added two more pieces of bus bar and connected those from the two end caps to 12mm bolts that I decided to use to simulate battery posts. The reconfigured pack measured 9" long x 5" wide x 3.5" tall. With the extra two pieces of bus bar and the two large bolt I increased the weight to 4.4 lbs. Using thinner bus bar and a lighter weight plastic would easily get me back under 4 lbs.



I mounted it back in Crashy to continue my testing, but the new configuration will allow me to easily use the pack on the road in Crashy2. I will leave it in Crashy until tomorrow, as I want to see where it discharges to overnight, with the Yaris' significant static draw of about 150 mA. Once I verify that it holds enough charge after 12 hours of sitting to still easily start the car I will move it over to Crashy2 to begin some road testing.



I took a few videos, and once I get around to editing them I will post them as well.

[RedRide]

Interesting .

The Lead/acid battery has been around forever it seems but, who knows what the future will bring?
Perhaps combo of a smaller battery and caps? Maybe some sort of an integrated cap/battery combo?

[UberSilver]

Thats cool! Now make a Sun blocking dash cover out of solar panels, and your golden.

[CrankyOldMan]

What?? 650F?!?!



All silliness aside, how do you think it will hold up in the heat/cold? I would assume that they have a relatively low self-discharge, otherwise it would be a moot point, no?

[CTScott]

Originally Posted by CrankyOldMan

All silliness aside, how do you think it will hold up in the heat/cold? I would assume that they have a relatively low self-discharge, otherwise it would be a moot point, no?

Because of the crazy low internal resistance, the self discharge is extremely low. They are rated for millions of charge/discharge cycles and they have excellent temperature ratings, so it will definitely be interesting to see how they hold up. The dude from the video that Jerkrat sent me has been using them in cars for quite some time. These are actually used in most hybrid vehicles to quickly accept the energy produced from braking.

[CTScott]

And, 16 hours later, I turned the key and she started with no problem. The voltage had dropped to 10.85 V during that time (due to the large static drain of the Yaris {~105 mA}).

[Golddeenoh]

cool but would it still hold a charge over the weekend i.e. drive home Friday and don't go to drive it again until Monday?

[CTScott]

Originally Posted by Golddeenoh

cool but would it still hold a charge over the weekend i.e. drive home Friday and don't go to drive it again until Monday?

I'll let you know as I do further experimentation. Maxwell makes them in 650, 1200, 1500, 2000, and 3000 Farad sizes, where the 650 F weigh just under 1/2 lb each and the 3000 F weigh about 1.5 lbs each, so even if the 650 F don't have enough stand-by capacity for the Yaris, one of the larger sizes likely would.

The problem is cost though, as the 650s are about $140 for 6 and the 3000s are about $390 for 6.

[Shinare]

not much listening to the radio or runnin the fan with the car off I guess, hehe. I like to listen to my radio for about an hour over lunch every day while I eat lunch in my car. This probably would not be good for that.

I guess one could keep one of those "cigarette lighter jumper batteries" (like this one) on hand if you ever needed it.

[CTScott]

Originally Posted by Shinare

not much listening to the radio or runnin the fan with the car off I guess, hehe. I like to listen to my radio for about an hour over lunch every day while I eat lunch in my car. This probably would not be good for that.

I guess one could keep one of those "cigarette lighter jumper batteries" on hand if you ever needed it.

The {stock} radio doesn't draw much. I ran the radio for about an hour yesterday with the engine off and only dropped about 1 volt.

[Amdkt7]

Very cool! One of my concerns would be the possible overloading of the alternator due to the very low internal resistance (fast charging rate) of the caps. I don't know if the alternator is self limited in peak output, or if the battery holds it back.

The biggest concern is the possibility of having to charge it after not using the car for a few days. Since mine rarely gets even one day off this should not be a problem.

One other concern would be the possibilities of voltage surges exceeding 16.2 volts. I might consider placing an appropriate sized zener across the caps, but the super caps themselves should help prevent such surges anyways.

I will follow your results with a great deal of interest.

If this seems to pan out I will replace my own battery in a couple of years this way. I'd just as soon get all the use out of the original battery that I can.

Perhaps a much smaller standard battery along with the caps could keep the charge up for several weeks and still start the car.

[CTScott]

Originally Posted by Amdkt7

Very cool! One of my concerns would be the possible overloading of the alternator due to the very low internal resistance (fast charging rate) of the caps. I don't know if the alternator is self limited in peak output, or if the battery holds it back.

The biggest concern is the possibility of having to charge it after not using the car for a few days. Since mine rarely gets even one day off this should not be a problem.

One other concern would be the possibilities of voltage surges exceeding 16.2 volts. I might consider placing an appropriate sized zener across the caps, but the super caps themselves should help prevent such surges anyways.

I will follow your results with a great deal of interest.

If this seems to pan out I will replace my own battery in a couple of years this way. I'd just as soon get all the use out of the original battery that I can.

Perhaps a much smaller standard battery along with the caps could keep the charge up for several weeks and still start the car.

The voltage regulator module, within the alternator, would be the first to fail if the current draw by the caps is too much. Thus far I have seen a peak current draw of 45A, which is well within the 70A rating of the stock alternator.

The zener diode is not a bad idea to prevent damage from over voltage, but there again the voltage regulators in modern cars generally prevent that type of failure mode. I will eventually add a large rectifier diode to the pack to prevent the possibility of reverse polarity, as that would result in the most catastrophic failure.

[Amdkt7]

I was thinking about using a different type of connector for the battery connection. There is no need to use the standard lead connection due to the absence of battery acid. I would put some type of female connections on the "battery" so that no one could short it out. Further, make the two connectors different to prevent reverse hookup.

I'd sure love the comments from the service tech who never seen anything like that.

[CTScott]

Originally Posted by Amdkt7

I was thinking about using a different type of connector for the battery connection. There is no need to use the standard lead connection due to the absence of battery acid. I would put some type of female connections on the "battery" so that no one could short it out. Further, make the two connectors different to prevent reverse hookup.

I'd sure love the comments from the service tech who never seen anything like that.

The OEM connectors are not lead, but it would make sense to eliminate them to further reduce weight. That way you also would not need my "bolt posts" which also add unnecessary weight.

[RedRide]

Here is a related story about a new cap invention that I saw over at "Major Geeks" and is said to have possible future automotive apps.

http://www.majorgeeks.com/news/story...n_seconds.html

[tooter]

CT, you really do have quite the curious innovative streak in you, don't you?

One of these little "cigarette lighter" plug in voltmeters would make a handy gauge to monitor your status. They're only $5 with free shipping. The other blue thing is a $5 rechargeable flashlight from HoDePo. I'm a sucker for cheap stuff.

[CTScott]

Originally Posted by tooter

CT, you really do have quite the curious innovative streak in you, don't you?

One of these little "cigarette lighter" plug in voltmeters would make a handy gauge to monitor your status. They're only $5 with free shipping. The other blue thing is a $5 rechargeable flashlight from HoDePo. I'm a sucker for cheap stuff.

Those are definitely a handy thing for people experimenting with things like this. I actually run a handheld oscilloscope, rather than a voltmeter, as it allows me to see what is happening "in between" the readings that a digital voltmeter would capture.

[mr_miles]

This is interesting. I wonder how something like this would hold up with my minor sound system upgrades and such. I still need to order my braille lol.