ToothDoc

So I made version 2.0 and it's essentially identical to the first one except that I have 5 cells in parallel first and then in series so each individual cells will balance each other out. In addition, I have a "balancer" that makes sure each pack of 5 in parallel are balanced voltage wise with the other 3. The only thing I need is a low voltage alarm. I didn't go with a low voltage cutoff switch because it weighs almost as much as the battery itself!

This one has been in operation since August without a SINGLE glitch and every battery is the exact same voltage. When I top it off to make sure the cells are fully charged, they were about 95% charged as before.

I still have enough batteries to make 2 more of these LOL. I thought initially I needed to make a huge 15 pounder or something.

megomaniac

Nice update. I liked it so much I've started my own project.
It's coming along slowly, I have 8 groups of 4 in series so far. I'm waiting for more deans pro 3.0 solder bars to connect my cells in parallel. I got a battery brain gold on ebay for 2.25$ lol, I hope it works.

As of now, I'm not planning to connect any balance device, but, I haven't seen one like the one you have before. I'm new at this. From what I've read online, a balance device thats always installed on a battery reduces the batterys capacity. I'm hoping that with the low voltage disconnect and over kill with # of cells, I won't be anywhere near the battery's peak, not puting to much strain on each group of 4 in series, keeping them all fairly closely balanced. My uneducated theory.

I went with 8 parallel for the extra amp hours, thinking that the parasitic draw will take longer to run down the voltage.

Still undecided on what gauge wire to go with. I might try a 6awg for each 2 parallel.


top side


bottom

FD3SISF

iTrader: (2)

Looks good. Might try doing this mod when my battery craps out.

ToothDoc

Important thing to do - Now that you have 8 in parallel of 4 in series, you want to make each cell in each pack parallel with the other packs. I do strongly recommend the balancer - it'll keep your batteries lasting forever! On a side note, I decided to charge my battery last night and only .7 amps went in before it was fully charged. That means the alternator is keeping the batteries charged at over 90% at all times. The balancer from Astroflight (you can get them on ebay - but make sure they're for LiFePO4s and NOT lipolys) draws really slowly.

If you don't add a balancer, you'll notice that some cells will get really high voltage and some will go really low voltage and the pack will eventually fail after a few years.

You're getting a low voltage cutoff? I don't have one of those...

Oh, make sure you do a FINAL polarity check before plugging it into your car. Those A123 cells always seem backwards to me with the positive being the flush side and the negative being the little round button side. I don't want to hear that you blew up your ECU by reversing polarity.

Good luck!

megomaniac

okay I'm convinced, thanks for the advice.
Found the balancer,
http://www.astroflight.com/pdfs/106_123_BALANCER.pdf

seems easy enough to install from the pdf.

where did you get the little 4s balance connector with leads? I think I know which one to order...

edit: Did some more reading, connector I need to order is JST-XH with pin spacing of .1in (2.5mm) 5pin (4S)
http://www.tjinguytech.com/charging-...nce-connectors

budget balance setup on order.

ToothDoc

Okay, since Dirtdig asked.. here's are some pictures. I've come to the conclusion that it's a good idea to have the cells in PARALLEL and then have them in series. One way to accomplish this is to simply solder all the cells like I have done.

This way, each group of cells in parallel has the SAME voltage.

Oh, before I forget, these cells are VERY sensitive to overheating so if you're NOT good at soldering, do NOT do this project and simply order some "Green LiFePO4" cells from maxamps.com instead.

Anyways, keep the voltage of every cell the same is critical for LONG term success of the batteries and when I say LONG term, I'm talking about the LIFETIME of your car!

ToothDoc

The configuration of this particular pack is 6p4s so 6 cells in parallel and then they are in series. So, if you order them pre-welded, ask them for 5 or 6 or even more in parallel first and then have them in series. Ask them for wire taps so you can attach a balancer to it.

megomaniac

nice work!
Looks just like what I'm trying to do. I'm going to use more bars instead of wire to get them all parallel though.

Are you planning to put it in an enclosure? I was thinking some clear shrink wrap would look cool.
I ordered some blue shrink wrap, but miscalculated some how, way to big fml...

ToothDoc

Since the parallel ones are only used basically for equilibrating, bars are not necessary - they carry very little current.

I was going to put it into an empty drained stock battery and utilize the terminals and the standard battery tray/holder/etc. Make it into a sleeper but decided to K.I.S.S. and just duct taped the thing to the bottom tray. LOL

PSJ

Y, your custom solution was pretty impressive. In all my years of car modding I've never seen someone make their own car battery setup.

If you ever feel like making another, holla my email is john@motorsports-media.com.

My stock battery is 44 lbs and I was planning to get the 17 lb Braille next year.

John

ToothDoc

The 17 pound braille probably has less power output than my new 4 pound battery. Seriously, if you're interested, let me know - pm me. If you read the whole thread, you'll see the slow evolution over time. I have a new one in the works that's got 6 in parallel and I was planning on putting it INSIDE an old lead acid battery so it looks completely stock! I just finished the wiring, balancing right now, I got rid of one cell that was self-discharging too rapidly (must have cooked it during soldering). This new slightly larger version should easily start up a 6 liter engine. The only thing that worries me is that you got that underdrive pulley. As long as your alternator is over 13.5 volts you should be good. As long as you drive it once a week, you won't have any problems and if you keep your car outside and it gets into the single digits - it gets a little weak. But otherwise, I've been running this setup for years now.

ToothDoc

So it'll save you 40 pounds and in your vehicle. That's like having an extra 6 gallons of fuel in your tank!

PSJ

I'll pm you, I'd like to learn more.

My UD setup charges anywhere from 12.8 to 14.5. Car sleeps inside.

ToothDoc

The harness that comes out is a tap to the individual batteries so if need be, they could be charged individually (well, the cells in parallel). His comes with a built in balancer so if you got his, you wouldn't have to do all the soldering etc.

When I first started this project, I didn't know if it was going to work or last. Now, over 3 years later, I no longer even carry a jumper or backup battery anymore. I'm pretty confident that I won't be stranded. At first, I wouldn't even let my wife drive the car around for fear of stranding her. Now I just tell her that so she doesn't drive it as an excuse. LOL

High PSI

iTrader: (1)

Any more info on the setup that doesn't require soldering? I went to maxamps.com and got confused with all the options regarding Green LiFePO4 batteries. How do we calculate what cranking amps these will give us?

Side note - did some research on google and it appears that "battman" has his own website selling these:

http://www.lithiumaviationbattery.com/

He has a 440A 3.3lb unit for $290. How much does it cost to build the latest design yourself?