# Lipo Pack Build



## DIYguy (Sep 18, 2008)

winzeracer said:


> . Hi all,
> 
> I am building a small lipo pack for my E-kart (build log here http://www.diyelectriccar.com/forums/showthread.php/silent-scream-build-thread-75205.html )
> 
> ...


Well, I think you have figured out one of the keys. Managing heat at wire connections is key for a pack that will have to perform for 20 minutes. If it were 10 seconds or so for drag racing, I would say copy John Metric's and use both terminals of a Deans connector (real Deans only, not copies) for each wire. But for longer run times and high current draws, I think Steve (Jozzer) has a lot of experience and know how about such things.... way more than most. . with a lot of packs on the track to prove it. This is why he developed those connectors.. . to wick away the heat. I would definitely look closer at this part of your build and see what can be done. I know John Metric tested his lipo to failure. . . at around 100+C and at that point, the wire solder joint failed. This is where the heat is focused. 
Additionally, I thing you need to look further into a BMS. (BTW, I'm a non-BMS guy for lifepo4) I know Olly (Black Current) was setting his pack on fire every run for a while there because he had the balance wires connected together and hitting these lipo cells hard caused imbalances that the wires could not handle . . as they were too light. Perhaps a slight over-build of the pack is necessary and not joining the balance wires. I would speak with Olly and Steve about this.
Derek Barger at High Tech Systems is another great resource for racing batteries. One of the best. I think Thomas Cook at Lithiumstart did John's battery.


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## winzeracer (Apr 3, 2012)

DIYguy,

I can see how the heat buildup at connections is an issue, I may have to machine some solid copper male bullet connectors with threads so that I could basically make what Steve sells. I wanted to get around all that work, but it is not worth burning up batts over. As far as BMS, I am planning to run Methods HVC/LVC system, and I have ordered a few different types of battery medics to test and see which works best. Which I will mount in view of driver so that voltages and temps can be monitored on the fly. As for balancing, I will always balance charge at home, and at the track I will bulk charge with the 10kw EMW charger, I will also have a couple cell balancers with me at the track to balance if something is out of balance. It will only get charged a max of 5 times at the track without getting balance charged, however I will balance if needed. How does this sound? This is just what I have come up with from reading lots, no real experince, but you gotta start somewhere.

I will look into the other resources that you mentioned, thank you for the referals.


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## winzeracer (Apr 3, 2012)

After emailing with Steve, he suggested that wrapping of individual cells in fiberglass would probably not work as the heat would still get to the nearby cells and burn them up too, so he suggested to make 5 modules that were fireproof. So I am considering each 5 cell parralell module be separate, that way if one goes up I only loose that 5 cell module.
As for bussbars I will be mating 6.5mm bullet connector to the copper bussbars. I will be using methods HVC/LVC, but still looking/researching at a BMS. I was looking at the ATICA in the classifieds but the guy stopped responding to PM's. 

I will recess each module into the plastic side pods on the kart, this will give a bit more room on the kart, and I will make it so that the side pods with battery modules will be removable from kart for transporting and possible extra pack.

Steve also recommended a larger pack but I do not believe I have enough weight to spare.


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## winzeracer (Apr 3, 2012)

The beginings of some kickass bussbars


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## lithiumlogic (Aug 24, 2011)

I think if you wrap every brick in fibreglass, not only are you slowing down the rate at which a brick gains heat from a neighbour in thermal runaway, you are slowing down the rate at which it can disippate the heat it has aquired. The fibreglass traps heat , so an overheated cell is more likely to go into runaway, and when it does , it stays hot for longer. 

So overall it might slow the process down, but won't by iteslf stop the even propagating throughout your entire pack.

My ideal layout would be -


Brick - Air Gap - Fibreglass sheet - Air Gap - Brick - etc.

Each brick has an air gap around it, where natural convection currents can carry heat away / flames propagate upward / but a fibreglass lies beyond the air gap to prevent flames from one brick directly impinging upon its neigbour. 

This implies a pack that is one brick high pack that is wide and long and flat in the floor of the vehicle (like a tesla model s). It also gives early warning of potential problems, as your butt starts getting hot.


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## Ziggythewiz (May 16, 2010)

Save the car, flame the driver!


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## winzeracer (Apr 3, 2012)

Ziggythewiz said:


> Save the car, flame the driver!


Ya after all the fussing about fireproof and heat, it is just not worth it. I was also reading over at Endless Sphere and these batteries have lots of bad press about how dangerous they are. I watched a video where a guy put a torch on so Li-poly and it was not very exciting. http://youtu.be/YbI6EmL5GJ8

On his page here he talks about it a bit, so i am not really going to mess with fiberglass.
http://evmc2.wordpress.com/category/lipo-batteries/


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## sunworksco (Sep 8, 2008)

I wouldn't trust the Turnigy battery low quality.
I have used there products and it is similar to Russian Roulette .
I would feel safer using Hyperion batteries.


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## winzeracer (Apr 3, 2012)

sunworksco said:


> I wouldn't trust the Turnigy battery low quality.
> I have used there products and it is similar to Russian Roulette .
> I would feel safer using Hyperion batteries.


Sun,

Hyperion would be nice but at over 3X cost I will play Roulette 
http://www.allerc.com/hyperion-g3-vx-5000-mah-10s-37-0v-35c-65c-lipoly-split-pack-p-5118.html


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## sunworksco (Sep 8, 2008)

winzeracer said:


> Sun,
> 
> Hyperion would be nice but at over 3X cost I will play Roulette
> http://www.allerc.com/hyperion-g3-vx-5000-mah-10s-37-0v-35c-65c-lipoly-split-pack-p-5118.html


You get what you pay for.


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## winzeracer (Apr 3, 2012)

Ya I hear ya just can't see spending over 5k on batts for a Kart.

Anyway... I have been cycling my 6s Turnigy bricks and have found that they are doing well. IR ( calculated by PL8) is always between 1.7mOhm 1.9mOhm.
I just discharged at 5+C and set to LVC to 3.4v, this let 4.7Ah out of the pack and after resting for 5 min the High Cell was at 3.602v and low cell was at 3.482v which I was happy with. I may raise LVC to 3.5v and retest to see how much capacity vs. voltage spread that yields. I also had some Batt boxes build but they were to heavy, I am now looking into building a Kevlar sidepod/battery box which would be very nice both form and function wise. In the way of function, if there was ever a crash no metal could penetrate cells and cause a fire, and it would not be that heavy. This would also give a nice professional finish look to the Kart as a whole.


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## sunworksco (Sep 8, 2008)

Try to get your hands on some Alulight aluminum sandwich panel.


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## winzeracer (Apr 3, 2012)

So I did another higher discharge test at 8C with LVC set to 3.5v, 4.5ah cap out so that went to 90% DOD and still had a 100mv spread in the cells. Cell number 2 had a lower IR of 1.4mOhm where the rest were between 1.6-1.8mOhm

More testing coming soon.


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## winzeracer (Apr 3, 2012)

So after quite a bit of battery testing I have decided on a method that I am going to test all batteries with Charge to 4.190v at 15amps(3C) Discharge to 3.55v at 40amps( sometimes limited by supply voltage ) this generally discharges 
4.5ah with about 50-70mv spead between cells. I will post all data when complete.


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## DIYguy (Sep 18, 2008)

It seems that they guys who have had the most trouble with the RC cells are the ones that pushed them too close to their max Crate without some pack "overbuild". These ones tend to cause greater imbalances and can even cause thermal runaway. (a fire you can't put out). 
Sorry if I didn't read all your specs. . . but if you test current level are anything close to your racing current levels, that seem like a very comfortable margin. Maybe even more than you need. I would ask Steve about this also. John Metric has had some good success with keeping the Crate lower. I know Olley just burned Black Current 111 to the ground with Flight power cells. This sounded like thermal runaway, not the balance wires issue he had last year.


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## winzeracer (Apr 3, 2012)

DIYguy said:


> It seems that they guys who have had the most trouble with the RC cells are the ones that pushed them too close to their max Crate without some pack "overbuild". These ones tend to cause greater imbalances and can even cause thermal runaway. (a fire you can't put out).
> Sorry if I didn't read all your specs. . . but if you test current level are anything close to your racing current levels, that seem like a very comfortable margin. Maybe even more than you need. I would ask Steve about this also. John Metric has had some good success with keeping the Crate lower. I know Olley just burned Black Current 111 to the ground with Flight power cells. This sounded like thermal runaway, not the balance wires issue he had last year.


My racing current levels will be a bit more extreme, but there is still quite a bit of head room. The current the motor will see is 400amps thus the batteries will see a bit less, lets say that they saw the full 400amps then they would be at 13.33C a level that I am quite comfortable with. I have emailed with Steve, and he was comfortable with these levels. The "bricks" are rated to 35C constant under RC conditions and I am well under half their rating at my max current.

As for BMS as you had previously brought up, I looked into different types and almost bought one but after talking with Steve he just runs Methods HVC/LVC on pretty much all his lipo, with the controller cutting voltage at 3.5v which is what I plan on doing. I will have plenty of hardware with me at the track for checking and balancing cells if it needed.

I appreciate you looking in on the build, and encouraging me to seek the expertise of others.

Thanks!


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## DIYguy (Sep 18, 2008)

winzeracer said:


> My racing current levels will be a bit more extreme, but there is still quite a bit of head room. The current the motor will see is 400amps thus the batteries will see a bit less, lets say that they saw the full 400amps then they would be at 13.33C a level that I am quite comfortable with. I have emailed with Steve, and he was comfortable with these levels. The "bricks" are rated to 35C constant under RC conditions and I am well under half their rating at my max current.
> 
> As for BMS as you had previously brought up, I looked into different types and almost bought one but after talking with Steve he just runs Methods HVC/LVC on pretty much all his lipo, with the controller cutting voltage at 3.5v which is what I plan on doing. I will have plenty of hardware with me at the track for checking and balancing cells if it needed.
> 
> ...


Oh. .  my pleasure. Sounds like you are doing it right. For relative short durations, like racing, I think that is a good way to go for Poly. Im not the biggest fan of li-poly for a daily driver, but for racing it makes the most sense. Pretty much what all the RC guys do also (balance charging after a run). I think u r going to make out just fine

Lowell Simons just burn up his battery pack in Black Perl and sounds like BMS may have been part of it.. I think he was pushing it pretty hard also.


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