brianjonesphoto wrote: ↑
Jun 14, 2018 6:58 pm
Hello I’m new to the board, but it’s been a great resource for my Lipo project. This is for my son’s OSET 36v electric motorcycle I’m replacing the aging 3 series connected 12v10ah SLA batteries with lipo.
I have 4 turnigy 5s 5000mAH packs that I’ve configured in a 10s2p set up. I’m trying to decide if I should use the Battery support 60A BMS I ordered or if I’d be better off with a quad channel hobby charger. After reading about storage voltage and also noticing the low voltage cutoff of the BMS I’m a little concerned that the BMS will make life more difficult than simpler.
I am using a Kelly KDS36100E programmable speed controller and have the voltage cut off set at 32v so I hopefully the ESC will cut out before the 2.85v of the BMS. The fact that the cut off of the BMS is below the danger level (3.0-3.2v) of a lipo worries me. I have the max current set to 30A contentious/50 burst for now as he get more skilled I will likely increase the limits. The controller is rated for 60/100 amps. There is also a relay and 45amp fuse protecting the everything from the battery. So there are already some protections from a short on the bike side, but the battery it self would not be fused which is pretty normal in the RC world.
Since this is something that will only be used at most a few times a week I’m always going to need to be achieving at storage voltage somehow. I’m pretty sure the BMS will not balance below a 39V charge not to mention I haven’t been able to find an adjustable power supply that costs less than a quad channel balancing charger.
So I’m at a crossroads. Do I call the BMS a loss (maybe try to sell it to someone here if I’m lucky) and run the batteries with low voltage alarms and the ESC cutt off as safety measures while investing in a decent hobby charger? Or use the BMS and 42v5a power brick I’ve already sourced for this project? Maybe a 3rd option would be the 0-60V 5A lab power supplies available on Ebay and return the brick.
Like all project as I learn more the more I realize I don’t know. I want to do this safely and right now I’m thinking that not using the BMS might be the safest route which goes against everything I knew at the beginning of this project.
Thanks in advance for your time and knowledge.
First off, forget the BMS w/ LiPoly.
I don't get your math. 32 V(LVC) / 10(cells) = 3.2 Volts
I ran 2S/1P of Turnigy 6S/ 5000 mAh (20C) on a genaric controller w/ a LVC of 31 Volts for a while and what happens is this;
Below approx. 3.65V/cell, one or two of the cells start to stray downward, setting off the LVC around 3.2 or 3.3 V avg./per cell w/ some variances. I didn't much like the cells getting out of wack, so I went w/ 9S resulting in a LVC avg. of 3.5 or 3.6V w/ little cell variance, acceptable.
Your test is to run your Pack down to LVC, and check the cells. If the variance spread is less than, say, .5 Volts, they should come back together during charging and you are good.
My 9S system was for a "boardwalk bike", where my speeds were very low. When I moved back to "street" riding, I went back to 12S, a much preferable system because most controller's set LVC is 42 Volts and the resultant actual LVC is 3.65V/cell, or right before they start to stray.
At the other end of the cycle, charging, I bulk charge using a Mean Well HLG 320 series power supply and ck/balance(rarely) w/ Battery Medics. This is preferable because I don't have to "break the string" to charge. I have detailed my set-up many times and if you are interested, search my posts w/ key words like "bulk", "Mean Well", "Battery Medics", etc.
Although most of my LiPoly is the Multistar, I used Turnigy bricks for years and still have a couple. Great stuff, excellent value! The main reason I went w/ the Multistar was it used to go sale a lot and it's avail. in big capacity bricks like 10 Ah, 16 Ah, etc. Big bricks is the easy way to add capacity while retaining a 2P string. Going to a 3P string complicates bulk charging.
I should point out that using a Voltage alarm as an audio alarm is difficult. The stray cells taking a nose-dive when accelerating set the alarm off prematurely. I have used them as a visual tool and as such, they work well.