Supercapacitor Battery Replacement

[Enki]

The weight savings is very real, but minor. The load on the electrical system would actually be higher until fully charged, and then it would be about the same as a battery.

What you could potentially do, however, is build a controller so that while pulse and gliding, is have the alternator only deliver current while engine braking, using the capacitors to power the vehicle while accelerating.

How you'd implement such a thing I'm not sure, but I am sure that the gains would be measurable, if disabling load on the alt does, in fact, have an impact on economy.

[redpoint5]

The price of the 3400 farad supercapacitors have dropped again on Mouser. You can now buy a quantity of 5 for $68 each ($340 total).

Maxwell has provided tons more literature on the technology with topics such as sizing the system, estimating usable lifetime, and cell balancing.

I'm getting pretty close to purchasing 5 and seeing how they do combined with a 1.5 watt solar maintainer in my truck. I have confidence I could eliminate the 2 huge batteries and run just this supercapacitor "boostpack".

Originally Posted by 2000mc

looking at $209 for just the capacitors, what are the advantages against just running a big lifepo4 battery?

I'm coming around to your way of thinking. These 20Ah LiFePO4 cells go for $35 each, and you only need 4 of them to get 12.8v. That's a total cost of $140, and maybe $10 more for the various straps to connect them together. The total weight is only 6.6 pounds.

There is also a ready made 20Ah battery for $189

The main drawback is that they get damaged if charged below 32 degrees F. If the battery could be relocated to the passenger cabin, then that probably isn't a concern.

What I'd really like to do is purchase 4 of the 60Ah cells for about $400, and then install an alternator disable switch. I would grid charge the battery using a proper LiFePO4 charger, and have the option to turn on the alternator on longer trips. By grid charging, I could eliminate charging in sub-freezing environments.

The reason I'm still interested in capacitors for the truck is because it requires upwards of 400 cranking amps, and it has very low parasitic draw. Perfect for a supercapacitor.

I still think running a bank of 650 farad supercapacitors in parallel with a battery is a good idea. It will prolong the life of the battery, and provide extra cranking amps even after the battery becomes weak. It's not a bad deal at $70.

[Enki]

I think there's feedback issues with disabling the alt outright. What you might have to do is set up a small cap bank (using the 300 farad caps maybe?) to take on the role of allowing current through so there's no feedback on the system.

It's my understanding that if you just straight disconnect the alt from the battery during operation it can seriously screw up the diodes/regulator, and that an alt that doesn't have a charging load doesn't take any power to run, so this might be the best way.

[changzuki]

Originally Posted by redpoint5

I'm coming around to your way of thinking. These 20Ah LiFePO4 cells go for $35 each, and you only need 4 of them to get 12.8v. That's a total cost of $140, and maybe $10 more for the various straps to connect them together. The total weight is only 6.6 pounds.

Those batteries look amazingly similar to the ones I've used in the "Aurora Project":
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~CrazyJerry

[ECONORAM]

To make sure I'm thinking right, I could use 12 super caps at 350F each, in a series parallel setup with balance circuits as a battery assist, yes? I've been watching this: Ultracapacitor Module Kit Battery Eliminator Car Audio Starting Remote Solar | eBay
The 2000F capacitors look good, but I don't want to spend $300 on a capacitor set...

[Enki]

You could, but the effective bank capacitance would be 116.66F (farads; two banks of 6), vs 108.3F for a single bank of 650s, 250F for 1500s, or 333.3F for a bank of 2000s. It will help a little, but maybe not as much as it should, depending on how much draw there is for your particular vehicle at start up.

[redpoint5]

I've read through all of Maxwell's literature on the supercaps, and among the things I read is that leakage occurs at a faster rate as the voltage increases.

This means that capacitors will self balance as long as they aren't continuously held on a charge. Whenever the vehicle is turned off, the capacitors will slowly bleed off voltage due to leakage, and it will do so at a more rapid rate for the highest voltage caps.

I don't believe it's necessary to have a balance circuit for vehicle applications as long as the total voltage doesn't get too close to the maximum allowable bank voltage of the capacitors.

For a 14.4v alternator output charging 6x 2.7v capacitors, that amounts to only 2.4v per cell, leaving 0.3v headroom for some capacitors to be a little higher than others. This seems acceptable to me.

Originally Posted by ECONORAM

To make sure I'm thinking right, I could use 12 super caps at 350F each, in a series parallel setup with balance circuits as a battery assist, yes? I've been watching this: Ultracapacitor Module Kit Battery Eliminator Car Audio Starting Remote Solar | eBay
The 2000F capacitors look good, but I don't want to spend $300 on a capacitor set...

Yes, it works, but I wouldn't do it that way. It's not space or cost effective. Buying higher farad capacitors is cheaper than trying to parallel the capacitance you want, and they will take up less space and likely last longer since there are fewer points of failure.

The same seller has 6x 1500 farad caps for $180, which is just a little more than buying 2 of his 350 farad kits. As Enki points out, the 1500s would give you more than twice the capacity.

[Enki]

I agree. The leakage is really, really bad on the initial charge, but subsequent charges to "top up" the bank result in significant lengths of time required to drop a full volt (on the 3k farad caps anyways).

[ECONORAM]

I was looking at All Electronics today, and found they have 2.7Vdc Maxwell 1500 Farad capacitors for $25 each. All Electronics | Electronic and Electro-Mechanical Parts and Supplies at Discount Prices

[Enki]

This link: ULTRACAPACITOR 1500 FARADS - 2.7 VDC | All Electronics Corp.