Fun fact, the pair of lipos I own (turnigy heavy duty) cost the same as 1 turnigy graphene lipo but have a significantly higher capacity and dont get as hot since the load is split between the two I have. AFAIK the existance of the graphene lipos is for RC applications where you’re space constrained and need a lot of amp output.
I’m just saying this because im convinced that having a single lipo is very pointless and a waste. Anyone reading this in the future, do yourself a favor and get 2 lipos and a QS8 connector.
12s4p is a much better config for those cells. If your customer wants 12s then different cells are needed. 30 amps isn’t enough current and if u run the pack at 45 amps the battery ain’t gonna last long and bad shit will eventually happen. Save those cells for a bigger battery- they would be suitable in 6p or 8p config.
I’m the type of person that will weld a p-group and then check it out for flaws for the next 15 mins before going onto the next so hopefully I’ll be good.
Are you sure that Evolve motors 5065 will consume more than 30 amps continuous on 12 cell configuration?
I was thinking 12s and 40 amps rating would be a good idea. But if you guys are saying it will sag hard I have to go with 6p or different cells.
IMO, build it for future upgradability. Those motors will die sooner than later, if you have the battery maxed out to power them, you’ve left yourself no room for improvement.
The 12S4P LG pack would probably be fine if the board is urethane, but even the stock motors are going to be somewhat weak with that battery should you run pneumatics.
I have silicone 22 awg, so the wire is good for 7A, think it’s safe to to 6A through the pins? I plan to use 2A or 4A for the most part but I wanna fast charge on occasion
Getting that 22AWG silicone to fit might be a challenge.
I don’t know how hot the pins will get at 6A. It creates nine times more heat than at 2A (its rating) so it could get pretty toasty. It doesn’t have to melt to be a problem either. Just softening could cause issues.
But if @A13XR3 doesn’t have problems at 4A you might be okay at 6A. That’s only a bit more than twice the heat created at 4A. Definitely stay close and check temps the first time you do it though.
How did u wire them in parallel? Did u just shove 2 x 12 awg into the QS8? I’m thinking about replacing my graphenes soon so very interested. It’s either these or a car battery on float but I don’t build enough packs to justify that setup yet. I had 2 graphenes in parallel and was getting overcurrent errors and shit.
I glued two xt90s together and used 8awg as bus bars across the positives and negatives that went straight into the qs8. I wish I had a picture for you.
First of all, according to the test data you linked, that “4600mAh with 15 Amp discharge” is if you are discharging all the way down to the cell’s 2.5v cut off. Most esk8 battery systems use 3.0V/cell as the hard cut off, which would give you more like 3100mAh according to the test results.
It’s also going to cause a nearly un-usable amount of voltage sag, so no matter how many mAh it actually delivers, the watt-hours that it delivers will be dismal. Wh (watt-hours) are actually the important spec to look at for building an EV battery, because Wh take into account how well your pack holds up it’s voltage and therefore how much total energy it delivers.
You can use a cell with 5000mAh rated capacity, but if it only delivers 10Wh at the discharge levels you expect to use it at, then you would have been better served by a lower capacity higher current cell.
This is why nearly everyone in the DIY esk8 market is using the Molicel P42A. It simply delivers the most Wh at the discharge levels that we normally see in an esk8.
Check out these two test results sheets from Battery Mooch:
First off, the M50LT is actually only rated by the manufacturer for 7.2A discharge if it’s over room temperature (25°C). Inside of a battery pack (unless you are installing active cooling) it’s pretty safe to assume that your pack’s running temp will always be at or above 25°C.
If you disregard that rating and run the cell at 15A anyway, not only will you be degrading the cycle life of the cell faster, you will also be getting a massive amount of voltage sag and a very poor energy efficiency from these cells. According to Mooch’s test, you will get 10.0Wh delivered @15A discharge.
Compare that to 10.7Wh @20A discharge on the P42A, and you can start to see my point.
To your point of this build using small motors, if you built a 12s4p with M50LT’s and ran them according to the manufacturer’s rated 7.2A/cell, then you would have a pack which performs ok at 28.8A max discharge. That’s 14.4A per side. I doubt that would provide a thrilling ride for the user, small motors or no.
Turning up the current above that safe manufacturer’s rating may result in a slightly more fun ride… as long as the pack is fully charged. As soon as it starts getting a little lower in the discharge cycle, the voltage sag will outweigh the higher amperage you programmed, and you’ll end up right back in the same boat.
Your M50LT cells are not garbage. They are an excellent cell. Just not in the pack configuration that you are considering. You will be much better off saving these for a different pack configuration, or for an application that has a much lower current draw than esk8.
If anyone is interested in learning more about comparing cells for esk8 use, check out this great article that @Battery_Mooch and I collaborated on. It’s a little outdated (talking about 18650’s, talking about the P26A instead of the now-superior P28A, etc.) but it’s also got some custom test results, it’s got lots of nerdy cell talk, it’s got it all!
