Super-capacitors instead of a battery?

[redpoint5]

I keep getting distracted by other projects and then get chicken to just put the darn LiFePo4 in my car... kinda wanted to wait until a battery died to do this.

I've been running just a supercap in the motorcycle since January. Rode it to work tonight, in fact. It will still only go 3 days before draining down too much to electric start. I've noticed zero issues with the charging system, maintaining voltage, etc. Runs as if I have a battery in place.

I'll take your prodding though and get that battery in soon. It's ready to go, just haven't actually installed it yet. I also wanted to put a current limiting resistor in, but maybe I'll skip it and see if I fry a battery. I suppose risking $70 in the name of science (tinkering) is worth it.

I still don't know why this is in the unicorn corral. My motorcycle, and posted videos, prove you can replace a battery with super caps. That said, I'll probably let this thread die and post updates to the thread I started, or the original thread on this subject.

[ConnClark]

Its probably in the unicorn corral because there is no real fuel saving to be achieved by doing so.

[Thenorm]

this has already been done by Mazda i eloop. Don't know why its in the corral

[ConnClark]

Again, without a variable alternator and a dc to dc converter to convert the higher voltage to 12V replacing your battery with a supercap is useless to get any real fuel savings. Also starting with a super cap you risk burning out your starter motor due to an undervolt condition. In the unicorn corral it stays

[redpoint5]

Originally Posted by ConnClark

Its probably in the unicorn corral because there is no real fuel saving to be achieved by doing so.

But it hasn't been shown that there is no fuel savings.

Various sources suggest that lead acid batteries have about a 50% charge efficiency. There is an inverse relationship between charge efficiency and state of charge. At about 50% state of charge, the charge efficiency is over 90%. However, lead acid batteries are normally operated at nearly full charge, which has a charge acceptance efficiency of 50%.

Capacitors have almost a linear charge efficiency of 95+ percent. This should translate into fuel savings, albeit very small.

I'll also note that LiPoFe4 batteries are more efficient than lead at accepting a charge, especially near the full state of charge. I believe they are somewhere around 80% efficient.

No unicorns here, just science.

[ConnClark]

Originally Posted by redpoint5

But it hasn't been shown that there is no fuel savings.

There is no real data that says it has saved any. That is why its here

Various sources suggest that lead acid batteries have about a 50% charge efficiency. There is an inverse relationship between charge efficiency and state of charge. At about 50% state of charge, the charge efficiency is over 90%. However, lead acid batteries are normally operated at nearly full charge, which has a charge acceptance efficiency of 50%.

Capacitors have almost a linear charge efficiency of 95+ percent. This should translate into fuel savings, albeit very small.

I'll also note that LiPoFe4 batteries are more efficient than lead at accepting a charge, especially near the full state of charge. I believe they are somewhere around 80% efficient.

No unicorns here, just science.

Capacitors have an exponential discharge characteristic which leads to I^2 * R losses as they discharge. Batteries have a more linear voltage drop as they discharge. This characteristic becomes very prevalent on starter motor operation. Motor efficiency drops drastically in an undervolt condition (which is why thy tend to burn out when this occurs). In undervolt conditions motors draw significantly more current and I^2 * R losses go through the roof. Also most capacitors are not rated for extreme current discharges required for starting (i.e. you can kiss that 95% efficiency goodbye).

On your typical car trip, the energy used in starting the engine is negligible.

The Mazda system uses the capacitor system in an intelligent manner. It doesn't even try to use it for starting. It charges the supercap under braking which reduces energy wasted on the brake pads and rotors and stores it in the cap. It may also charge the cap up at idle taking advantage to try and boost the break thermal efficiency of the engine. It then releases it reducing alternator load on the engine and thus putting the power to the wheels saving fuel. It is thus a light duty hybrid.

I'm not saying that replacing a battery with a cap might not reduce fuel consumption in some infinitesimal amount, but you will never be able to show it.

[redpoint5]

Originally Posted by ConnClark

I'm not saying that replacing a battery with a cap might not reduce fuel consumption in some infinitesimal amount, but you will never be able to show it.

There is likely an unmeasurable fuel savings by using Ultracaps instead of a conventional battery, but that's beside the point. The question in this thread asks if a battery can be replaced by a supercap. The answer is, yes.

Unicorns don't exist, but supercaps do, and they are capable of replacing a battery. I saved about 10lbs in weight by eliminating the battery in my motorcycle, which isn't much, but if you consider that the bike is only 400lbs, it's 2.5% of the total vehicle weight.

If I could eliminate the 2 enormous batteries in my diesel truck, I could save 80 lbs.

The advantages of eliminating the traditional battery extend beyond the tiny gains in electrical efficiency. We're also talking about weight reduction, better weight distribution (handling), longevity of the energy storage system, and long-term costs. The discussion isn't about perpetual motion or spontaneous creation of energy.

[Cobb]

Thats alright bro, I believe you. I know a few gen 2 insight owners who have seen a change in ima performance and an improvement in mpg when replacing a bad starter battery and upgrading to a slightly bigger battery.

How about you edit all your posts and replace the comments with a few spaces?

[ConnClark]

Originally Posted by redpoint5

There is likely an unmeasurable fuel savings by using Ultracaps instead of a conventional battery, but that's beside the point. The question in this thread asks if a battery can be replaced by a supercap. The answer is, yes.

Well the burden of proof is on you to prove an unmeasurable fuel savings.

Good luck with that.

Until then its a unicorn just like these dimpled car wraps.

[Cobb]

Well Red, with the gen 2 insight it cycles the dc to dc converter from the ima system off and on to charge the 12 volt system under regen and when the voltage falls below 12.5. Ive had some measurable improvement using an agm u1 battery. I added 2 to help firm up the audio system and it had a noticeable negative effect.

I see you can buy small lithium packs in the power sports section of walmart and advance auto and am thinking about giving that a try. Then of course relocating it to the rear by the ima system so it has a smaller window of operating temperature.

A bad 12 volt starter battery will still test good, but cause the gen2 to loose 10-15 mpg and see the ima system dip into regen and little assist.