DrInnovation
100 W
My thunderpower-based Lipo pack is starting to show its age after a year on my bike (bought them in 2008 and used them for UAV... so >500 cycles now). My commute is short but steep so I max out my 500w 24v motor, so use 30A for 2-3 min of the trip that is 6-8% grades, whole trip is only 6min). The high load is probably why my old Lipos are loosing balance quickly Getting harder to keep them in balance and I lost one 3P group and had to replace it with a backup from another pack (which already lost other groups). Now I'm out of spare parts ;-(
Will see how long that lasts but Wanted to start on figuring out my replacement before the lipo pack is totally dead.
Though about replacement lipo, maybe some zippy or tunegy but then felt maybe lifepo4 might be a better choice so I don't have to mess with them as much
So started looking at other choices and found these on ebay:
http://www.ebay.com/itm/A123-16-Cell-8S2P-26-4V4-6AH-motorbike-battery-starter-/201209153745?pt=LH_DefaultDomain_0&hash=item2ed90008d1
The price built is about the same price as buying the raw cells (in low quantity) from a123
https://www.buya123products.com/goodsdetail.php?i=11
And various posts have been positive on sz_ohmygod's builds, they will even add the JST-XH Balancing connector for me so hard to beat the price.
So looking for feedback on my proposed build. If I'm drawing 550w (assuming maxing out 500W motor plus 10% losses in the system) at 24v nominal will be 22A, which for the 2.2Ah minimum rating is a draw of 10C per cell, and in a 2P configuration should mean 10A/5C, well below the A123 70A continuous rating From the specs (https://www.buya123products.com/uploads/vipcase/844c1bd8bdd1190ebb364d572bc1e6e7.pdf) it says at 10A draw, they would say above 3v until almost 2ah per cell is used. 4Ah should be more than I need for my commute. I know many will say go big.. but that is more $$ and weight.
I also want to add a BMS for added protection. Many good posts here about Signalab used in Ping
(which from what I've seen is the same as this
http://www.ebay.com/itm/BMS-for-24V-25-6V-8S-LiFePO4-Battery-Pack-50A-10A-limit-With-Balance-/161637237107?pt=LH_DefaultDomain_0&hash=item25a2548173
or maybe the
https://bmsbattery.com/bmspcm/330-smart-bms-513-cells-in-series-bms-pcm.html#/discharge_current-20_40a
(which I might be able to reprogram if I go back to lipo)
Anyone have experience with this model?
http://www.ebay.com/itm/PCB-BMS-for-24v-8s-LiFePO4-Battery-Pack-60A-Limited-Equilibrium-Tem-Switch-/171820665804?pt=LH_DefaultDomain_0&hash=item28014f4bcc
(which physically is a better fit for my battery box, and has included temp sensors. With the A123 smaller size I think I can get the signalab to fit)
Any comments? Am I underestimating my needs in estimating that A123 8s2p 4.6Ah should be enough for short but hard rides on 500W bike?
Any recommended design changes/tweeks? which BMS's that I should consider?
Background: My setup is 24v and I've tested it working up to 29.6 but like to play it safe and run at well below max voltage.
currently I'm running effectively 7s 6p (really 2p/3p) lipo cells). I generally charge to 4.005v per cell, normal discharge is only down to 3.8v. I've been doing mean-well bulk charging @2a for the pack (<.3a per cell) with monitoring (cell8s). I rebalance the 3s components when any pack is more than .1 off. Balance used to be need less than once a month last summer, increase to almost every week this spring, and last week twice -- wich is why I swapped out a weak group of 3P which I also noted was getting warm to the touch when charging).
Will see how long that lasts but Wanted to start on figuring out my replacement before the lipo pack is totally dead.
Though about replacement lipo, maybe some zippy or tunegy but then felt maybe lifepo4 might be a better choice so I don't have to mess with them as much
So started looking at other choices and found these on ebay:
http://www.ebay.com/itm/A123-16-Cell-8S2P-26-4V4-6AH-motorbike-battery-starter-/201209153745?pt=LH_DefaultDomain_0&hash=item2ed90008d1
The price built is about the same price as buying the raw cells (in low quantity) from a123
https://www.buya123products.com/goodsdetail.php?i=11
And various posts have been positive on sz_ohmygod's builds, they will even add the JST-XH Balancing connector for me so hard to beat the price.
So looking for feedback on my proposed build. If I'm drawing 550w (assuming maxing out 500W motor plus 10% losses in the system) at 24v nominal will be 22A, which for the 2.2Ah minimum rating is a draw of 10C per cell, and in a 2P configuration should mean 10A/5C, well below the A123 70A continuous rating From the specs (https://www.buya123products.com/uploads/vipcase/844c1bd8bdd1190ebb364d572bc1e6e7.pdf) it says at 10A draw, they would say above 3v until almost 2ah per cell is used. 4Ah should be more than I need for my commute. I know many will say go big.. but that is more $$ and weight.
I also want to add a BMS for added protection. Many good posts here about Signalab used in Ping
(which from what I've seen is the same as this
http://www.ebay.com/itm/BMS-for-24V-25-6V-8S-LiFePO4-Battery-Pack-50A-10A-limit-With-Balance-/161637237107?pt=LH_DefaultDomain_0&hash=item25a2548173
or maybe the
https://bmsbattery.com/bmspcm/330-smart-bms-513-cells-in-series-bms-pcm.html#/discharge_current-20_40a
(which I might be able to reprogram if I go back to lipo)
Anyone have experience with this model?
http://www.ebay.com/itm/PCB-BMS-for-24v-8s-LiFePO4-Battery-Pack-60A-Limited-Equilibrium-Tem-Switch-/171820665804?pt=LH_DefaultDomain_0&hash=item28014f4bcc
(which physically is a better fit for my battery box, and has included temp sensors. With the A123 smaller size I think I can get the signalab to fit)
Any comments? Am I underestimating my needs in estimating that A123 8s2p 4.6Ah should be enough for short but hard rides on 500W bike?
Any recommended design changes/tweeks? which BMS's that I should consider?
Background: My setup is 24v and I've tested it working up to 29.6 but like to play it safe and run at well below max voltage.
currently I'm running effectively 7s 6p (really 2p/3p) lipo cells). I generally charge to 4.005v per cell, normal discharge is only down to 3.8v. I've been doing mean-well bulk charging @2a for the pack (<.3a per cell) with monitoring (cell8s). I rebalance the 3s components when any pack is more than .1 off. Balance used to be need less than once a month last summer, increase to almost every week this spring, and last week twice -- wich is why I swapped out a weak group of 3P which I also noted was getting warm to the touch when charging).