8 kWh Battery pack advice

Good job, looking forward to some pics. Any break-in for the LiPo's :?: You may find +20% capacity after 6 cycles...
 
Xrain said:
We didn't get to test it nearly as much I hoped we would but, we basically pulled all-nighters from the day we got all the parts in, finished it last morning, took it out played around in-front of the building in the snow, brought it back in, made sure everything was rule compliant, crated it and shipped it out.


Not exactly Ideal but you do what you have to.


Thank you guys for all the info you provided, so long as nothing breaks, it should do well to shake up the EV section of the competition!


I'll be sure to post the results, and some pictures and videos of what happens for all of you. (as well as of the machine itself)


Wish us luck!
Click to expand...



Good luck to you and your team! I hope it kicks ass!

Pretty much did everything I advised against doing, from the cell choice, pack arrangement choice, charging choice, etc, lol Yet still, just having the cells be some sort of RC LiPo, and at least having some heat pads in the pack should give you a good advantage over any teams not using LiPo. :)
 
Great news that you got it all together, good luck with the competition! Oh, and I think pics are a must. :mrgreen:
 
liveforphysics said:
Good luck to you and your team! I hope it kicks ass!

Pretty much did everything I advised against doing, from the cell choice, pack arrangement choice, charging choice, etc, lol Yet still, just having the cells be some sort of RC LiPo, and at least having some heat pads in the pack should give you a good advantage over any teams not using LiPo. :)
Click to expand...

Nothing I could do about cell/pack arrangement/ charging. The rules are almost set against people using small/many packs, so it was really the only compromise I could come up with. I'm going to be having a good talking with some of the judges that come up with the rules this year to see if we can come up with a more sensible rule set.

As for breaking in the pack, we did everything we could to get it done early enough to get some time to do it, but no dice. Not what I wanted, but we might be able to get a few discharges in before the competition while we are down in Michigan.

Considering that we managed to take second place with a 700 pound, underpowered 13 kW thunder-sky sled 2 years ago, a <500 pound RC lipo sled should do quite well, extra 20% capacity or not. :wink:
 
Hi Xrain,

I think you may have misinterpreted. You won't get 8 KWh + 20% if you break-in your pack. You may get only 8KWh - 20% if you don't break in the pack, and it's contains some weak/lazy cells. Engineering is also about reducing the unknowns :!:

Should do in the drag race though. I figure your pack can deliver 160 KW (215 hp) continuous. 3 minutes of power at this output level. Or for 20 seconds, it can slam out 240 KW (320 horses) :D

Of course, all this depends on your Controller... I don't think I've seen it yet, have you mentioned what it's max amp rating is :?:

Again, good job and have fun at the event 8)
 
Hi Xrain,

Any news from the SkiDoo races? :)
 
Yes there is! I have a large pile of images and videos that I need to wade through, and I will be posting a proper write up of the events as soon as I get enough free time. Missing that week of school for the competition has made things rather... hectic.

Stay tuned, I'll probably post it in it's own thread. :)
 
Congratulations on being selected "Best Design Winner" at the 2011 SAE Clean Snowmobile Challenge. 8)

I see your Team received a score in the Acceleration event, but not in the Distance event. Did you break :?:

Cheers :!:
 
Thought it was only fair to post in here, as i'm new to the team and didn't know this thread had been started and kept up for so many posts. To answer a couple of questions that i didn't see answered yet: we didn't get to compete in the range event because they didn't like a bunch of our wiring etiquette. The biggest one was "no high voltage outside the sealed/vented battery box." we had the bm6's all stuck up on the dashboard, and they didn't like that. had to hack a big hole in the side of the machine and place them inside, looking out through a little window. i think there was a couple of other wires they dind't like, too...but i can't remember what they were. they REALLY didn't like that our contactors didn't seem to be disconnecting the charging leads from the pack. turns out the pre-charge resistor had been damaged in shipping, and the batteries happily supplied the 10,000+ amps for a few millisecond to rapid charge the cap bank in the motor controller. spent a day replacing contactors (and a couple of vaporized battery box studs that happened when we were getting to the contactors) and fixing the pre-charge. got it back together just in time for the drawbar, drove it out the door of the shop to head to the event.... and the motor controller caps that we'd previously tortured turned into fireballs. the big buss bar inside the logisystems controller decided to turn into plasma and make a nice fireball out the side. replaced the motor controller with a lower voltage one we had brought with us, rewired the pack for a 30s5p pack, and managed to compete in the acceleration test and the objective handling event. AND we got the pheonix award, for coming back from the ashes. i was un-aware of the discussion that had taken place on here, looks like the nano-techs are a good buy even if only for the fact that they are more reliable.

a bunch of our pictures are up on facebook. http://www.facebook.com/saeuaf

try not to laugh too much at how many times we broke stuff! i wasn't actually a part of the team until two days before the competition started, so it's not my fault ;)

i know i have a ton more pictures somewhere, i'm not sure where they're at right now though

trying to start much earlier this year so we can get some ACTUAL tests in before the competition. pretty sure the pack wasn't cycled even once last year...

i'm also trying to organize building our own motor controller based off of the open revolt, but using IGBT's and a ring capacitor. i'm thinking we should get another logisystems for some early battery testing though, as the homebuilt controller probably won't be done for another month or so =/ as a side note, what controller do most people on here use? I'd love to have a Soliton 1, but we're still looking for funding ;)
 
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
 
perhaps this shall be the new thread of the uaf CSC attempt each year. i finally have a phone with a camera on it, so i can post more pics as we go along. would be very interested in finding a charger that can handle the voltage, just as a single unit. i certainly agree that the server supplies are the best bang for the buck, but i think they are pretty opposed to having chargers in series. we had two UL listed chargers last year that were each good for half the pack, and one non-UL listed that could do the whole pack. they were like OMGWTF you can't series chargers, and made us use the non-ul one. prolly just gonna use it again this year i guess.

also uploading pics of the new build to imageshack, i'll link as soon as their done


*edit*
finished already.

http://imageshack.us/homepage/?user=isaac_alaska
 
Sucks. "real" high powered chargers are real expensive. and having only one would make me nervous because they fail easily. I just built a 5kw charger out of server power supplies and a meanwell power supply for like $100. It's modular so if anyone unit fails I can't swap it out.

sick looking machine btw
 
just posted a pic of the charger we used last year to my imageshack account-i linked to it earlier in this thread.

http://evolveelectrics.com/Elcon Chargers.html

this is their website. not sure what we paid for the charger. looks like they dont offer one specific to lipo but the voltage can be set correctly if you lie about how many cells you are using. not sure about the AH rating though. seems like that would be important to get an accurate charge. our pack was 45 AH, and they offer 40 and 50 AH versions

*edit*

this just came in the mail today
http://img840.imageshack.us/i/imagekmj.jpg/

most of the parts to build a 48 channel BMS :)
 
so i know it's been said before that the nano-techs are the way to go, but since the rest of our components can't support nearly that high of a current, it's hard to justify spending the extra $1,000.

Right now we're looking at the zippy flightmax 6s 5ah, and trying to choose between the 15C and 25C. my vote is for the 25C, because of the increased electrical efficiency related to lower internal resistance. The argument for the 15C is that they are slightly smaller and lighter weight.

physical specs:
15C: 145x52x46 mm, 346840 mm^3, 715grams
25C: 148x51x51 mm, 384948 mm^3, 770grams
30C: 146x53x53 mm, 410114 mm^3, 784grams

either their numbers aren't perfect or the different tech used to produce different C-rates results in different densities.

can someone confirm if the 15C packs are really that much lighter than the 25C packs? it's a small difference but adds up to about 8 lbs difference on an 8kwh pack.
pros and cons would be greatly appreciated. personally i think the higher C rate is worth the 8 lbs. the batteries are almost identically priced. 30C is more expensive but i included it for physical comparison
 
my thoughts

a) make sure they have enough in stock. i'd e-mail them personally. maybe you can even get sponsored ;)
b) 4s hard packs are more work, but 2/3 the price right now per wh.
c) with regards to the difference in Ri I would ask/research in the rcforum. They usually do more in depth testing. Or just order samples and have them rushed to you for testing.
d) I made this spreadsheetto help run some pack building numbers. You can see how Ri loses importance with the more packs in parallel. I can't remember if the spreadsheet still predicts voltage drop and I^2R losses.
 
i made a similar spreadsheet that lists a bunch of the same info yours does. mine doesn't have Ri listed though. the problems with 4s hardcases are they are more work (although, with my new design i'm planning, not THAT much more soldering) and take up more space. could remove the hard cases, but that's probably a good ammount of work by itself. plus the extra wires from having a series connection every fourth cell instead of every sixth cell. the upside would be, if a single cell goes bad and you want to change the whole pack, you're only replacing 4 cells instead of six.

Bottom line right now is,i don't see them in stock in any of the warehouses =/
it seems like the 15C and 25C are in stock cause not as many people are using them, but also more expensive (supply and demand)

i'll try to post my spread sheet here
 
Yeah.. it's a lot more work. As I said, I think I've got this stripboard plan down, so it shouldn't be too much more work. I'm going to parallel by soldering the leads to ANL fuses and wrapping them in heat shrink. This gives each parallel group fuses, and it means you don't have to use rare (do they exist?) 100v DC rated fuses.

BTW I updated my spreadsheet to show voltage sag and I^2R power losses. Yay!
 
so you're using fuses between each cell? i thought you were using the circuit board as a fuse. maybe post a picture? (anl makes a TON of different fuse sizes, so i'm not sure where you're putting it.) i'll post up a pic of a BIG fuse here in a bit, i'm heading back to the lab in a few minutes. we have some 100 amp fuses and a couple of 500 amp fuses. they're impressive. (and dc rated)

a agree your stripboard is a genius idea. i came up with the same idea about six months ago, but i hadn't thought of stripboard, i was picturing having to mill my own circuit strips
 
fuse.jpg


Like this basically.
 
imagert.jpg

this is our main fuse, it's purpose is what you would expect a fuse to be used for: protect things like the motor and motor controller

imagesfu.jpg

same fuse, this is the negative bus bar. all the negative leads tie to the bus bar, and from there the bus bar ties to the +side of the fuse. - side of the fuse goes to the motor controller.

imagecdrx.jpg

these are 100 amp fuses, rated to break 200kA 600V AC or 20kA 300V dc
their purpose was purely for rule compliance. (if someone can tell me a possible situation where they would help, i'm open to suggestions)
we used these at the top of each string, so the string attaches to a fuse, and the fuse bolted to the positive bus bar.
a couple of them are a bit melted cause we shorted the negative bus to the bottom edge of the fuse trying to take the battery box apart. no flames, but some copper fumes and a big arc flash (think: an arc welder turned all the way up and you forgot to close your welding hood)

i like your fuse idea, looks like it would great for smaller packs. might have to do that on our eco-trike this year!
 
Holy sh*t those fuses are huge... though at my work this summer, there was a foot long one with tabs that were at least a 1/8 inch thick being used as a doorstop... I always wondered what it was :lol:
 
wait till you see the SBE ring caps i have coming...they're a smidgin over 9 inches diameter and 2 inches tall :) (trying to build a motor controller, also)
 
haha no, those are actually the same fuses i used on the shell eco-marathon trike. well, same brand, i think i used 75 amps per string and a 150 amp main. (two strings of 12 cells)

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

the really nice anl fuses come with a gold plating on all the metal parts, and the product line is "golden"
(i say this only cause it makes me laugh when the box says "golden ANL fuse block")
 
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