What is your end charge condition? upper voltage limit?
I fucking love batteries.
We charge them to about 4.2V per cell, and we discharge with 24 cells in series, so around 100V is the upper limit. The lowest we’ve discharged to so far is about 3.7V per cell, we have a lower limit alarm at 3.5V, though we could easily go lower than that.
The calibration on the chargers we have isn’t perfect, so I charge through a long section of thin wire to ‘trick’ the charger into thinking the batteries are nearing EOC more rapidly and taper the current off. Out of the box, the chargers just force 200W into the batteries until it hits the 4.20 cutoff, which is a bit harsh on the cells for extended life. The chargers start off with CCCV and once the ‘assumed’ 4.20V/cell is reached it kicks over to a crude Delta V logic. I charge in ‘fast charge’ mode which simply hits EOC more rapidly and wont sit there with a minor float for 30 minutes. Final cell voltage is right at 4.15 volts, no real balancing has been required thus far. I have originally balanced the cells after a few cycles manually. The voltage cutoff on the chargers is not configureable, but its much safer to just doing bulk charging with power supplies in series. We discharge in 24S2P, and charge in two strings of 6S4P, with dual 200W ECO 6-10 chargers. Balance taps are in parallel during charge to help balance cell voltages and provide monitoring of all cells.
Of course, charging can be done much more rapidly with just a string a power supplies in series, set to 100.2V. The batteries are rated for 2C charge, so charging at 1500W wouldn’t be an issue. Safety would be fairly low with this setup unless well monitored, configured, and understood.
The controllers have a programable LVC, which shouldn’t allow for a well balanced pack to be over discharged. I currently have it set to around 80V, which is about 3.4V per cell. This is assuming sag under load at this very low tSOC condition, and should be about where it needs to be to protect the pack without cutting out prematurely. I have yet to take my pack below 3.7V/cell, but I will assume it would be easy enough to find the appropriate LVC to ensure the pack can be fully discharged safely.
Heres a discharge curve for a new 3S pack of the Turnigy 5000mAh pack. The steep dropoff beyond 3.6V is why we don’t discharge much below that. There is simply no real capacity to be gained and you can almost guarantee the cells will go out of balance at low voltages. 3.5 -> 4.15 is very safe, and we should expect to get 500-1000 cycles before the degraded capacity will have any major impact. Even then, they should provide thousands more cycles, just with slowly diminishing capacity. There is a great thread on endless-sphere forums which has data about the cycles you can get out of an average LiPo pack given different EOC cutoffs. Anything beyond 4.2V/c increases capacity quite notably, but halves life for ever .05-0.1 volt.
Cool project. Looks like fun. Even though this is not every ones cup of tea. I dont see the reason to be an ass to him on somthing that took alot of time and some thinking to build.
I’m not trying to be a hater. I really just don’t get it even a little bit.
But I ALWAYS like when people are really into something that requires skill and knowledge, so from that standpoint, rock on.
Glad to see you guys are on top of the battery situation (especially since your balls are literally on top of the batteries).
Not that I really give a damn…but it’s a slow day at work so here is my rationale.
It’s nice to be in bicycle mode on the streets, then go off the road and hit the old railroads or trails for some nice back ways. I built mine because I wanted to stop driving my car to and from work 4 times a day and there is an old railroad line going from my OLD house going right to my store. I used to ride as much as I could when going to work taking less time than my car did, all while being more fun. 30MPH off road with no suspension is a little sketchy but awesome.
Now that I own a house further away, I rarely ride it anymore. Mainly because I feel like a major douche while riding up the street with that fucking thing blasting away and passing old ladies. Camping, and off road is the shit especially since mine has a clutch and I can go as slow as necessary.
Here is my old route to work.
LOL. Good image.
You’re cumming kinda near my house.
hahaha I did not see that the first time I looked
Do you have regenerative braking? Very cool
I was almost done making it before I realized the phallic qualities of the image that were later embellished.
The controllers have regen capabilities, but I’m currently the only one using it. Its really almost necessary for high speed stops. Stopping hard from 40+ can cook most brakes in a dozen stops or so. Only issue is that it tends to destroy the dropouts on the bike due to the massive moment the 26" wheel has on the tiny axle holding back the force. Instead of the axle only resisting the force from acceleration, it now is being rocked back and forth under braking and acceleration. I’m running nord-lock washers to prevent the axle nuts from loosening, and really need to beef up the dropouts with some thick steel soon.
Funny nobody mentioned battery bunkers, figured you guys would have been all over that.
They’re made of uhm… something, ceramic I think.
It’s kinda like a cookie jar that you put the battery in to, even has a little spot for the cord… then you place the cover on and give it a half turn, then it’s good to go.
Only way I charge Li-Pos for RC planes. I recall seeing videos of Lipos blowing up in them, and not causing a single ding on the inside of the bunker.
I always laugh my ass off when I see guys using a field charger for their Lipos connected to their 12v battery on their car… With the battery/charger tucked away under the hood with it closed. That would make a nice little video I’d say.
edit;
Here ya go
http://batterybunker.com/
Usually Li-Po’s balloon or puff before they succumb to thermal runaway, then smoke, then catch fire. It is very rare one “Blows up” without being used in an unsafe manner. We fly large 12s bricks in our 700 sized heli’s and 95% of the time you see one come down smoking…it is the ESC and not the pack.
The newer generation LiPo batteries are fairly safe when properly used. Thermal runaway should never be a remote issue, as we are only discharging at a PEAK of 6-7C, when the batteries are rated for 20/30 cont. / peak. High discharge/charge rates promote uneven cooling of the cells, which can lead to uneven wear, which over time can lead to notably increased degraded capacity. Without proper monitoring, such as a typical application in RC cars or even low end notebooks and portable devices with more than one cell in series, this can cause issues. The inner cells that operate at higher temps are forced to be run at exponentially lower tSOC’s as capacity degrades, exponentially degrading the capacity further, relative to the other cells. This can lead to issues with a cell going into reversal under high load. If its a inner cell, its most likely to not have room to expand notably, and will vent, likely burning the entire pack. This kind of thing is really only an issue in something like a high power RC car or heli that can fully discharge a pack in just a few minutes.
The majority of videos on the internet regarding LiPo fires are with older generation cells with high cycles and bad cells. Any of the notebook fires tend to be with older cylindrical cells without shutdown separators, and are exposed to uneven high cell temps. The foil pouch prismatic cells tend to be very safe within normal operating ranges. One cell having an issue might just lead to the cell expanding, reducing its power significantly, whereas a cylindrical cell has nowhere to expand.
That said, the average user of these batteries has no clue how to treat them and is discharging at very high rates without adequate monitoring. This of course inevitably leads to fires.