8 kWh Battery pack advice

[auraslip]

These won't be nearly as neat, but they might be allright price wise. http://epbuddy.com/index.php?main_page=index&cPath=26_14&zenid=5c7t59kbs4mf1lpuope0i0kvl1

dirty fuses! dirty dirty!

by "smaller packs" i meant it would get confusing building enough of those to parallel 9 strings of 8 packs.

So I guess you're not going to put them in parallel first?

 

[isaac_alaska]

i'm not paralleling the power leads, only the balance leads. this picture should explain it

the extra leads coming in from the right hand side of the screen are an artifact of the copypasta

actually, there should be nine vertical strings total, but they don't all show up in the picture. i think if you open the image in a new tab it will show them all. There is a parallel board per three strings because i basically have 3 sub packs, each containing three strings. (they are all physically next to each other in the box, just arrangement wise. my box is only 12 inches wide, so the pack layout looks like.....) *i'm drawing this right now*

this is how the battery box will be layed out, top down view. each color represents a separate string

 

[isaac_alaska]

after deciding to get the 25C zippyflightmax packs and submitting the purchase order i get an email from hobby king saying the Turnigy 20C's are back in stock. (literally six minutes apart, from me submitting the purchase order, to getting the update email.)

Anybody have any real-world comparison tests between the two? it seems like everyone on here uses the Turnigys instead of the Zippy Flightmax packs. Is that just cause the Turnigy are usually cheaper?

 

[Xrain]

Awesome! I was bummed that we didn't get any follow up videos.

Yay for the pheonix award. Competitions sound like a lot of stress. I was going to go to the race in california at the end of the month, but seeing as my bike won't be finished until near then I think it'd be out of the question. I think a couple hundred miles with out a problem before a race is a good plan. Road tested (or snow tested) = no stress'd

I knew I was forgetting something, the videos!

They did take a few of them of the events we completed.

The first two were from the Subjective handling event,

[youtube]8updG5fUFJg[/youtube]

[youtube]6wKo3ZSJOtU[/youtube]

The reason it stopped was our GFI (ground fault interrupt) has been known to have false faults, and our 12V system was rather... "special" and so the GFI tripped and cut out the main pack. It has a reset button on it but the first time it quit I didn't think about it. We were on track for getting first in the event before it cut out, as my teammates timed me a few seconds quicker than the person in first place.

The second time I used the reset, and got it going again, but we lost quite a few seconds, we still did get third however!

These videos are on the Sled pull

[youtube]RwDZHK6Ygk0[/youtube]

[youtube]6TbRHrGU4AQ[/youtube]

We got second in the event , and that squealing you start to hear is our belts protesting the significantly more HP than the 20 they were rated going through them.


Overall the lipo's you guys recommended were quite amazing. We only weighed 479lbs vs. the 742 lbs of the team that won. Granted we didn't have our entire pack, but we estimated we would come in at 550 lbs with the full 8 kWh.

Here is the results page if anyone is interested in more.

http://www.mtukrc.org/csc2011_download.htm

However, all this said about the old sled, the new sled Isaac and the team are working on this year is looking like it will blow the doors off of last years entry. (Just hopefully with less fire this time around)

 

[isaac_alaska]

hey guys, little update here:
we totally blew the competition away this year. first place in all but two of the nine categories. one of those was weight, which we lost by 30 lbs. but we had an 8kwh pack, and the lightest team only had 3.2kwh. we also "lost" the range event, because our motor decided to explode the night before, so since we were 15 minutes late rebuilding it, we didn't get points for competing in range. we did drive 15.1 miles though, and the next best team only got 9.8 miles.

here's some pictures...the machine looks a little better this year than last year.

also some pictures!
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[Kin]

Nice! Congratz! Pretty sweet battery. Would be nice to have a 4k battery grant . Also, certainly amusing that the person with a lighter battery had less than half the capacity.

 

[isaac_alaska]

i really want to try to find a larger cell for next year, to reduce the number of parallel strings. probably going to run higher voltage, too, maybe 310 volts instead of 177. all in an effort to keep the wire count lower haha

 

[adrian_sm]

Maybe A123 20 Ah Prismatic ?

http://endless-sphere.com/forums/viewtopic.php?f=31&t=37401

 

[isaac_alaska]

thanks! that may be a good way to go about it, as it would reduce my series strings from 9 strings, to only 2. (it could be done in one string, and ideally it would be, but competition rules limit us to 300 volts nominal, 400 volts off the charger.)

did a few calculations and the a123 batteries are pretty closely matched as far as energy density and size goes. i'll have to see if i can fit a pack as long as this into the machine though.
waiting for a company to start producing custom-sized cells....it's not like it's difficult to set up a machine to produce cells in pretty much any format you want. even at double the cell cost, it would be worth it to not have to worry about ever paralleling cells.

on the other hand....for about 50 grand i can buy every machine i need to produce cells of any chemistry and any format. anyone interested in a "group buy"?

 

[Kin]

a123 will be relatively comparable with wh/kg, but somewhat substantially more volume. Forget the exact calcs, but I want to say maybe ~30%. This is as compared to LiPo, and I apologize if your pack is not actually made from LiPo (i thought that was the pack chemistry).

 

[isaac_alaska]

You're right on all counts, the A123 are definitely a more bulky cell. Part of it depends on what numbers you go by though, at least from what i can see. because going by the numbers on the data sheet from their website, the A123 cells are only a little tiny bit bigger. i think the difference is that some numbers include the extra inch for the tabs, and other numbers quote only the cell dimensions.
Our pack is indeed LiPo, and i'd like to continue using them. they have not yet let me down in the slightest.

also, check out these videos! The only limit here is traction and Rev limit on the DC motor, both of which we are planning to fix for next year. (studded track, and trying to find a permanent magnet synchronous motor)


[youtube]poVdxFoeack[/youtube]

[youtube]-YQG54ZKW8g[/youtube]

[youtube]6-CD05OIT4s[/youtube]