[Old Goat]

I am teaching a college level course in Alternative Fuels and the EV. This semester, we're planning a motorcycle conversion. Last semester, the team purchased 144 small (5.5 AH) flat Lithium Polymer cells that are only 7"X1.5"X0.28". They are marked with a label that suggests their web site is fatbatteries dot com but I cannot find such a web address other than some sort of MP3 music download site.
Our plan is to put four of these cells in parallel and then 36 of these quad (22AH) mini-packs in series to achieve a pack voltage of about 145V (the top end of the motor and controller capability). But each of these cells has a rather small (and seemingly flimsy) pair of tabs that comprise the positive and negative terminals. Can anyone share a photo or video of other experimenters connecting these tabs to something more substantial that can, in turn accept bolt type terminals for interconnection? Since the bldc hub motor in this motorcycle is rated at 10KW, we will be drawing potentially a fair amount of current out of this pack but not for long. The batteries are marked 25C! The vender tells me they have been tested to 60C and thus, the title of my post -- super duper. BTW, the voltage at full charge is said to be 4.15V and empty, I'm told, they should be down to 3.00V. I'm slightly concerned about fire hazard here, too. Any ideas out there?

 

[dragonsgate]

The vender tells me they have been tested to 60C and thus, the title of my post -- super duper. BTW, the voltage at full charge is said to be 4.15V and empty, I'm told, they should be down to 3.00V. I'm slightly concerned about fire hazard here, too. Any ideas out there?

Keep a super duper fire extinguisher handy... Or how bout sandwiching a fire retardant material between the batteries so if one cell went the others would be protected.

 

[onegreenev]

Or just undercharge and underdischarge. Keep the fire extinguisher handy anyway.

You might do some testing of the cells first. With small cells like that you can do some pretty heafty discharge rates just using a PowerLab 8 and be able to log all the results. Put in some temp sensors and manually log the temps too. Should be easy to do.

 

[onegreenev]

Want to send a couple for testing. I have a PowerLab 8 just waiting to do some testing.

 

[dougingraham]

I am teaching a college level course in Alternative Fuels and the EV. This semester, we're planning a motorcycle conversion. Last semester, the team purchased 144 small (5.5 AH) flat Lithium Polymer cells that are only 7"X1.5"X0.28". They are marked with a label that suggests their web site is fatbatteries dot com but I cannot find such a web address other than some sort of MP3 music download site.
Our plan is to put four of these cells in parallel and then 36 of these quad (22AH) mini-packs in series to achieve a pack voltage of about 145V (the top end of the motor and controller capability). But each of these cells has a rather small (and seemingly flimsy) pair of tabs that comprise the positive and negative terminals. Can anyone share a photo or video of other experimenters connecting these tabs to something more substantial that can, in turn accept bolt type terminals for interconnection? Since the bldc hub motor in this motorcycle is rated at 10KW, we will be drawing potentially a fair amount of current out of this pack but not for long. The batteries are marked 25C! The vender tells me they have been tested to 60C and thus, the title of my post -- super duper. BTW, the voltage at full charge is said to be 4.15V and empty, I'm told, they should be down to 3.00V. I'm slightly concerned about fire hazard here, too. Any ideas out there?

The nominal voltage of these cells is closer to 3.6 or 3.7 so you could think of this 36S4P pack as being 2.93kwh. If the 25C figure is accurate you should expect to be able to pull 550 amps without them sagging too much. I don't trust the C ratings given for the pouch cells. They are more or less advertising ratings. it would be a good idea to discharge a cell at the rate you expect to use them and watch the temperature. If there is a rapid rise then you are overloading the cell and probably shortening the life. At 550 amps and 133 volts (nominal) the pack would be expected to be able to produce 73kw which is over 7 times that of the rating of the motor.

What seems most common is to bend the tabs together and clamp them between a block of aluminum and an aluminum plate. The aluminum block can be tapped and you can attach your bus bar or cable to the block.

Because these types of cells are more susceptible to thermal runaway it is a good idea to have a battery monitoring device that can watch the voltage and temperature of each paralleled cell block. This will tell you if a cell block goes over voltage during charge or drops too much during discharge. Overvoltage (more than about 4.35 volts) will cause the electrolyte to out gas and the pouches will puff. Overcharge will eventually lead to a thermal event which years ago I read was referred to as "Venting with flame" by the industry. Likewise over discharge will cause the pouches to puff up. If they puff they may still look like they are working but it wont be very well and you should retire that cell.

You will get long life (several hundred cycles) out of them if you keep them to 15C or below. If you try to run them at 60C you may only get 20-30 cycles with each cycle showing poorer performance than the one before it.

Good luck on your conversion.

 

[Karter2]

It sound like you only expect 5-10C (50amps) from these cells , so you should be ok.
BUT..dont believe any thing you are told about the cells,...you should definitely test them yourself for capacity and voltage sag before spending the time and money to build them into a pack. As doug said , test them at the load you expect them to perform at.
The last time someone came on this board with a "super new high C rate racing cell" ... (Hayin)... and built them into a large , expensive, pack ,.. he discovered that at anything more than a fraction of their claimed rating, the sag was 50% of the pack voltage.
Much time and money wasted for no result. !
Also..Check our the "Bike" section of this forum for Ripperton;s and Jones's more successful pack building reports.