Rucksack alternator delete (portable DIY power pack to reduce alternator load) - Fuel Economy, Hypermiling, EcoModding News and Forum

jakobnev · 04-24-2011, 05:40 AM

I've read many threads about people using deep cycle batteries and disconnecting their alternator. But the problem or me is that i live in an apartment and my parking space doesn't have an outlet.

So i got the idea of using batteries - unfortunately, lead-acid would be too heavy and lithium ion-somethings would be too expensive. Luckily (like any tinkerer) i had rescued cells from dead laptop batteries! (typically only one pair or triplet is dead and the other cells are usable - albeit with reduced capacity)

So i built this thing: (all materials free!)

Nominal capacity is 8.8Ah, but unfortunately the combined age of these cells is something like that of the Rolling stones, but otoh i have tried to be nice to them by keeping them at 60% charge and storing them in my refrigerator.

It's not completely finished yet, it needs a lid and a BMS (that's that the little white wires are for) and maybe an amp-meter. The BMS i had planned to implement by having diodes that begin conducting at about 4.1v connected to each parallel set, that would allow the sets with lower voltage to catch up during charging. I have no system planned for discharge balancing as i have yet to come up with a simple system for that. (Maybe you have an idea?)

grswat · 04-24-2011, 07:42 AM

That's good scavenging. If it works pretty well I bet you could contact a couple big companies and talk to their it department and they would sell you dead laptop batteries cheap...or give them away. I have resurrected cordless drill batteries in the same manner.

JethroBodine · 04-25-2011, 05:15 PM

Might be a good idea if you are starting on the large battery already in your car and running on those for your commute, but I'm not sure they will start your car. Might have to check that out before you delete the alternator entirely. Also, you might try one of those battery boost packs with a quick connect, carry it in to work/ home and plug it in when not driving. Added benefit, nobody can steal your car by driving it away.

jakobnev · 04-26-2011, 06:59 AM

Thanks for the replies guys.

Perhaps i should clarify: this battery wasn't intended to result in a complete alt delete where i take off the belt, but rather more of a load reduction, a partial logical alt delete if i may call it that.

Perhaps if i take grswats advice and begin to actively seek used cells i'll get to 100%. But i think someone tested it and found that the additional saving from taking off the belt is only 3%, so even if i reach 100% i may keep the belt on because it is less hassle.

JethroBodine · 04-28-2011, 05:55 PM

jakobnev-
Your question has inspired me to do just what I suggested to you. I have two boost pacs and will be getting a few remaining pieces to complete my swap over( at least testing). I'll document this weekend if i get around to it. Thanks for the inspiration.

FastPlastic · 04-29-2011, 02:34 PM

I always wondered if something like this would work. For the longest time I had to park on the street so I didn't have the option of plugging anything in. If you designed the pack to just drop in like a cordless drill charger, you could go in and out as easy as taking your keys out of the ignition.

jasonck08 · 04-30-2011, 03:42 AM

I'm sorry, but this is a terribly dangerous idea. I'd consider myself some-what of an expert on the Li-ion chemistry.

First off, I've cracked open a number of laptop packs and analyzed them on my Computerized Battery Analyzer. Almost all cells from packs that I've skavenged have been complete junk. Huge increase in internal resistance, and huge decrease in capacity. Many only delivered 25-50% their rated capacity at 1C.

Secondly, Lithium Cobalt cells are only designed to safely deliver currents of up to 2C discharge. I'm guessing that these cells would provide about 25% of their rated capacity at this type of discharge current. It looks like your running maybe a 4s4p configuration. With a car you could very easily try to draw too much current.

Thirdly, Lithium Cobalt cells must be balanced. Each cell must be matched with other cells of similar internal resistance and capacity. I see that you are using at least 2 different types / brands or capacities of 18650 cells in your pack. This is EXTREMELY dangerous, especially for older cells.

If there was a catastrophic failure of this pack, it could be fatal (and no, I'm not joking). I've read stories and seen pictures of people who had un-matched 18650 cells explode. One guy almost lost a finger.

I would urge you for your own safety and for the safety of your car, to abandon this project immediately! This looks like a huge disaster waiting to happen.

jakobnev · 04-30-2011, 06:38 PM

I ran it yesterday in the car and in daytime i only have a 2.5A draw. That's 0.28C at nominal capacity, 0.57C at 50% and 1.1C at 25% - seems safe enough.

As for the batteries being of different types: Each parallel quadruplet consists of one purple, one blue and two green cells, so that evens things out. And the purpose of those little white wires is to be able to keep check on the voltage of each quadruplet.

As for explosions, the whole pack at nominal capacity is only 15grams TNT equivalent..

jasonck08 · 04-30-2011, 07:15 PM

Quote:

Originally Posted by jakobnev

I ran it yesterday in the car and in daytime i only have a 2.5A draw. That's 0.28C at nominal capacity, 0.57C at 50% and 1.1C at 25% - seems safe enough.

As for the batteries being of different types: Each parallel quadruplet consists of one purple, one blue and two green cells, so that evens things out. And the purpose of those little white wires is to be able to keep check on the voltage of each quadruplet.

As for explosions, the whole pack at nominal capacity is only 15grams TNT equivalent..

Here is an explosion that happened from 8x 18650's: Link.

Here is another explosion that happened from just 2x 18650. Link

Don't underestimate what kind of damage Li-ion's can do.

-----------

Also I'm a little confused how you are actually connecting this to your car? Are you also using the Lead Acid battery? What part of your car is this actually powering that your only seeing 2.5A draw? What happens when you turn on the lights or use the horn?

jakobnev · 05-01-2011, 04:43 AM

Ok, i was kidding when i said "only" 15g of TNT

Both those explosions you linked to were cells in sealed metal container tho. (one that draws 10C?) A container that allows a lot of pressure to build up before bursting is going to cause a powerful explosion even from a slowly venting cell. (and provide shrapnel!)

It was connected to the lead acid battery through a long fused wire, i still had the alternator hooked up. The low current is due to the fact that the voltage of this battery isn't much higher than the regulated voltage of the car.