Supercapacitor Battery Replacement

[Enki]

Sorry about that. Should be fixed now.

[redpoint5]

My trucks 2 group 27 batteries are on their absolute last leg. With a solar panel keeping them topped up, the truck barely starts on a cold day.

I wanted to see if it would be safe to run 5x of the BCAP3400 supercaps in series considering they have an individual voltage rating of 2.85v, and a series rating of 14.25v. My concern is that the alternator might over-volt the caps and cause premature deterioration or even perhaps catastrophic failure.

I started the truck, connected a small bank of 6x 350 farad capacitors, and disconnected the lead acid batteries. This tested the trucks output when only supercaps are connected. One thing I noticed is that almost no current flows into, or out of the caps. The voltage seemed to be tightly regulated and the alternator supplied just enough to meet the electrical demands. At idle with all electrical loads turned off, the alternator maintained an average of 14.17 V. It very briefly peaked at 14.37 v when I revved the engine with no load, and had a minimum of 13.88 when all electrical loads were turned on.

I measured individual cell voltages of all 6 caps and found a 2% difference between the highest and lowest value cells. Since my truck has a peak of 14.37v, that would make the average cell voltage of 5 cells 2.874v. 1% more than that would be 2.903 v.

Since the caps have an absolute peak of 3v each (15v total), it seems I could just barely make them work in this application.

I could buy 2 group 27 batteries for $250, or I could experiment with 5x BCAP3400 for $340. My trucks extremely low 5.7 mA parasitic draw would not be a problem, and the caps would be kept topped up with a small solar panel. They would be balanced and trimmed by either LEDs or a Zener diode circuit.

What do you think? I'm leaning towards the caps because I think there is a good chance they will work, and will at least satisfy my curiosity if they don't work so well. I could re-purpose them if I find them regularly operating outside of their design envelope.

Oh, and I already purchased the aluminum z-strap bus bars. You can tell me I'm crazy and I won't be offended.

[Enki]

Sounds like it's worth a shot to me. Let us know!

[mikeyjd]

Following with interest.

[ECONORAM]

So, I found this by Google today. Looks like this is a 3000F capacitor kit, if I am reading correctly? iKIT60MM2V7A2S Ioxus | Mouser

[redpoint5]

Originally Posted by ECONORAM

So, I found this by Google today. Looks like this is a 3000F capacitor kit, if I am reading correctly? iKIT60MM2V7A2S Ioxus | Mouser

It's a kit which is compatible with up to 3000 farad capacitors. You still have to buy the caps. The kit comes with the bus bars and the balance circuits. Supercaps are still super-expensive.

I should have another post on replacing a battery with supercaps this Tuesday 4/7/15. I've got a bank of 5x 3400 farad caps in series now.

[Nautilus]

Hello everyone. I've registered my account here firstly and foremostly to reply to this matter.

Having found out Laserhacker's experiment back in 2014, I've tried to replicate it myself. The foremost purpose was weight balance in the car - as the battery, originally 60Ah and over 15kg / 33lbs, is at the extreme front end, outside the wheelbase, and any sizable weight reduction here decreases the polar moment on inertia and therefore the understeering.

Parts used:

6 x 700F Nippon DLCAP supercapacitors
6 x CSDWell balacing boards in parallel to each supercap
1 x 10Ah AGM motorcycle battery for current reserve
16 sq mm (5 AWG) welding cable connections
Brass / copper bolts and fittings for better conductivity
Brass battery posts

Everything fitted inside a wooden box I've made myself to fit on the original clamps inside plastic battery box.

Starter motor is rated to 1.1kW, as as any brushed single-speed electric motor are only about 60% efficient, means it needs to draw over 1800 watts to turn the engine, which translate into a bit over 140 A at 12.6 volts.

Assembled package is about 5kgs in weight. This equals removal of 10kgs (22lbs) from the extreme front end of the car. (Adding some small, non-essential parts already moved to rear, front/rear weight distribution changed by more than 36kg, or from 59:41 to roughly 56:44, which helps to limit understeer). The system fits invisibly inside of the car's battery box.

Results: starts much quicker at 0°C compared to lead-acid battery alone, voltage with engine running is stable at 14.2 volts engine hot, 14.4 volts engine warm, 14.6 volts engine cold, idle a bit smoother. Rpms climb a little bit faster, as the alternator hardly does any effort after the first few seconds needed to recharge the capacitors.

I'm happy my little experiment worked and a HAPPY NEW YEAR for everyone

[serialk11r]

I think I didn't point this out here, but a guy on Spyderchat discovered this battery going on Amazon for what is I believe an unprecendented price for lithium ion:
https://www.batterystuff.com/batteries/ss51913.html

It is approximately 10Ah for 150 bucks, which is a great deal. A bit more powerful and higher capacity all things considered than a typical 30lb battery found in a Corolla or Civic or something, and only barely cheaper.

That alone should be quite adequate for most climates, but if you're in freezing temps some supercaps might help the car start since lithium ion doesn't do very well at low temps.

My car battery is probably on its way out so I am going to buy one of these soon.

[Nautilus]

The fact lithium ion doesn't do very well at low temps in terms of power is a minor problem. We can always use a bigger one. The worst thing is lithium-ion doesn't charge properly at low temps, it gets damaged if you try. Lead / gel / AGMs love freezing temps, the colder the better. They die at temps over 35°C (95°F), which are pretty usual even under the insulation layers used in modern cars (fiber battery blanket + plastic battery box).

So for someone living in warmer climates, as in the Mediterranean or Southern US, lithium may be best option to get a lightweight (2-5kg) battery for a reasonable price. A small AGM + capacitors cope better with climates where temps may jump from -15°C in winter to 35°C in the summer.

There is also a pretty easy way to cool your battery in the summer, if the car has a battery box from factory. As the engine draws a huge amount of air, thousands of cfm at 6000 rpm, we fit two pieces of wire-wound hose. One from front grill to a hole drilled in the battery box; the other from a hole on the opposite side of the box to the engine air filter. It makes the strongest air flow one can get, throughout the battery box.

[Harlan]

I've been running a bank of 3000F 2.7v Super Caps in place of my battery for a while on my car. The only issue is the standby drain is so high that it will only last a few days on the capacitor alone, so as such I do have an auxiliary battery in the trunk. I don't have a balancing circuit, but I have checked the individual caps every few months and there is very little imbalance.

The car doesn't care and cranks instantly regardless of weather. I also connected the capacitor with a Anderson disconnect, and have the aux battery wired separately to maintain the ECU/clock/radio.

My original intent was to have it available for a jump start kit by connecting alligator leads to the disconnect, but I've been too lazy to finish it.