Super capacitor replacement of lead battery

I saw goldmine electronics (link below) had a sale on 3000F 2.7v maxwell super capacitors so I picked up 6 of them and a balance board and some other odds and ends to see if I can replace my 7 year old stock mazda battery and shave about 30 pounds out of the top side of the engine bay.


http://www.goldmine-elec-products.com/prodinfo.asp?number=G17930

Considering my dash cam is likely going to discharge my capacitors in a hurry I also found a 12v solar panel with an integrated diode that will fit nicely in the dimple on the rear cargo cover. If it all works out I may try adding a small LiFePO4 battery (link below) and removing the solar panel to keep the capacitors charged up and sufficient power for the dash cam.

https://hobbyking.com/en_us/zippy-flightmax-4200mah-4s2p-30c-lifepo4-pack.html

 

Highly interested how this turns out. I've been waiting for these to reach a price point where I could do the same.

 

This has always been a project I wanted to try but needed the really big capacitors to make it worth while.

A sealed lead acid battery is still about half the cost of this project, but where is the fun in that!

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Check mine and enki's thread for info about both super caps and lifepo4 batteries.

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Those were actually my inspiration for doing this! I think I can address the shortcomings of the super cap bank by supplementing it with lifepo4 or solar charging

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So the caps arrived today so i started doing layout on my 1/8" copper plate and found my supplier shorted me 1/4" on one of the critical dimensions so now I won't be able to get the 5 straps I need out of it *facepalm*. Decided to go for some pre-made aluminum straps from Mathews Engineering and add a small tap to each for the balancing circuit. For sake of future proofing, I've attached some images and dimensions of the straps in question.

 

Capacitor straps arrived along with some 2 gauge wire and 1/2" lugs to help make the connection between the capacitor bank and the stock battery terminals. All that's left before I can start charging and testing things is a balance board that's still en-route from china.

Side note, the straps are sold in packs of 1 or 12 and priced such that if you buy 7 of them you could get 12 so I opted to double them up for half the resistance.

 

It's verking! Or at least charging anyway. I got the balance board hooked up tonight and let it charge up to just shy of 16v and verified the balancing board worked as intended. Next up is to test the temperature and overvoltage alarm on the balance board to make sure it's relatively safe. If all goes well I should be able to start constructing the case for the capacitors and the balance board this week.

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I hate to have to tell you this but that bank will drain in short order without something to prop it up; these cars have high parasitic load even when completely shut down (to the tune of ~250ma sustained). This is why I built a badass LiFePo4 pack and am not using either my 500 farad bank (like yours) or my smaller bank that I never finished making due to size issues.

 

I totally agree! Although when I measured the standby current on mine (left it sitting for an hour with the hood up) I got about 130ma using an extech multimeter between the battery negative and chassis ground. This was after finding out that my phone charger was drawing 80ma with no phone connected to it!

In any case, my first try at it will be to extend the standby time with a small 5w solar panel. If I can get it up to 24 hours with that, I may count it successful and stop there.

If I need to go for a second try I'll add in a small sealed lead acid battery (12v home alarm battery backup variety). If that fails I'll add a small motorcycle lithium battery and go that route.

Lots of options and having a blast tinkering... oh and I picked up a lithium boost pack so I wouldn't be that guy trying to wave down cars with jumper cables while I was doing this development.

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