[winzeracer]

. Hi all,

I am building a small lipo pack for my E-kart (build log here http://www.diyelectriccar.com/forums...ead-75205.html )

I am using Turnigy Nanotech's 6s 5ah 35-70C. My goal is 20 min runtime and 20 min charge time. For this I think I will run 30s5p for 111v and 25ah for 2.7kwh.

EDIT: I will run 30s6p for 111v and 30ah for 3.3kwh.

For charging I would like to charge at 80 amps ( 3.2C) with the 10kw EMW charger.

As for pack construction, I am leaning toward a thin outer steel box with a layer of Anti-Vibration Flame resistant material that I found. Possible with an inner steel box and have the "bricks" individually wrapped in fiberglass (welding blanket) material. This way if one cell gets overcharged, or over discharged by mistake it will not send the entire pack up in smoke. This may be overkill but it will be safe and I hope effective at keeping the driver and bystanders safe. I bought some copper bar .75" X 1" to build buss bars out of, I want to leave the factory bullet connectors on the batts so that I can balance charge with the PL8 ( I ordered it it they are out of stock) when at home. I will have short pigtails off the bullet connectors to the buss bars. I will probably go with some high quality terminal end ring connectors and bolt them to the buss bar. Will I end up with too much Resistance through the ring connectors? The ones I am looking at are copper however they are still crimp connectors. So I have some reservations about them. Any suggestions on better connectors? I though about trying to mate bullet connectors to the bussbars like Jozztek's but it looks labor intensive, and buying all my bussbars from Jozz would cost around $500, I bought my copper for $80.

[DIYguy]

Originally Posted by winzeracer

. Hi all,

I am building a small lipo pack for my E-kart (build log here http://www.diyelectriccar.com/forums...ead-75205.html )

I am using Turnigy Nanotech's 6s 5ah 35-70C. My goal is 20 min runtime and 20 min charge time. For this I think I will run 30s5p for 111v and 25ah for 2.7kwh.

For charging I would like to charge at 80 amps ( 3.2C) with the 10kw EMW charger.

As for pack construction, I am leaning toward a thin outer steel box with a layer of Anti-Vibration Flame resistant material that I found. Possible with an inner steel box and have the "bricks" individually wrapped in fiberglass (welding blanket) material. This way if one cell gets overcharged, or over discharged by mistake it will not send the entire pack up in smoke. This may be overkill but it will be safe and I hope effective at keeping the driver and bystanders safe. I bought some copper bar .75" X 1" to build buss bars out of, I want to leave the factory bullet connectors on the batts so that I can balance charge with the PL8 ( I ordered it it they are out of stock) when at home. I will have short pigtails off the bullet connectors to the buss bars. I will probably go with some high quality terminal end ring connectors and bolt them to the buss bar. Will I end up with too much Resistance through the ring connectors? The ones I am looking at are copper however they are still crimp connectors. So I have some reservations about them. Any suggestions on better connectors? I though about trying to mate bullet connectors to the bussbars like Jozztek's but it looks labor intensive, and buying all my bussbars from Jozz would cost around $500, I bought my copper for $80.

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.

[winzeracer]

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.

[winzeracer]

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.

[winzeracer]

The beginings of some kickass bussbars

[lithiumlogic]

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.

[Ziggythewiz]

Save the car, flame the driver!

[winzeracer]

Originally Posted by Ziggythewiz

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/

[sunworksco]

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.

[winzeracer]

Originally Posted by sunworksco

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...ck-p-5118.html