I always say to pick a C/3 rate.
Can never go wrong with that.. His is a 20ah pack, so a 5-6a charger would work well.
for those that have a 48 volt lifepo4 pack...when you take it immediately off your charger and the charger shuts down...your battery reads 58.4 volts ? But if you let your battery sit for about 5 minutes, does the voltage drop to around 55 volts afterwards..or does the battery stay at 58 + volts ?
No, it should stay close to 58v.
If it doesn't, there's something wrong with the cells.
After a few hours, yes.. After a few mins, no..
After the charger has gone green, let it sit on green for a few more hours and test again, they SHOULD stay at 3.65 per cell... If after a few hours, they drop to 3.3x after 5 mins, you have some bad cells and I would email the vendor to have them send you a new batt.
thats what I thought...but then some other people are saying its no problem...check out my other thread where I started it by saying..I think i have a battery problem.
Originally Posted by Sangesf
The way I roll
I opted for a ping battery with a 9 lead jst xh connector to run directly into any popular balance charger. These are usually meant for rc hobbiest but work wonders if you want to feel 'at one' with your battery. So my end voltage is 3.60v per cell when hot off the charger and 3.5v after sometime sat doing nothing. The standard charger did put most the cells to 3.9v but found out there is almost no gain (maybe 50ma) in capacity after using a better charger with cell read outs.
When they got charged to 3.9v they dropped down fast in minutes to lets say around 3.6 but now I charge them well to 3.6v they just sit there. So if you have a big voltage pack your going to see 0.3vx16 cells drop that equals almost 5 volts.
I have noticed none of my cells are perfectly matched in speed of charging and often go out of sync at the end of the charge. If my charger says full/end and any of my cells drop down to 3.38v I give them another quick charge (sometimes with a single feed to that cell via my jst lead adaptors) and all is well sticking at 3.50 for days. I think one cell doesnt get fully saturated every time. But I have had the odd panic where I was sure I had a faulty cell but an extra .5ah pumped in has it rebalanced for weeks.
My cellpro10s charger shows my internal resistance is pretty varied throughout my pack causing slightly random behaviour at times. I think the difference is I get to see exact voltages of each cell throughout the charge cycle and got to know the process far easier than you might do with a cheapy basic charger with no read outs other than a few led's.
As for pumping them up to 4v I see no actual capacity gain in that, just battery wear. The only reason most cheap chargers go to 3.9 (like ping) is it makes it possible to keep bouncing them up and down untill the low ones catch up. Pumping up, bleeding down etc etc didnt sound good to me so have barely used the ping charger. Plus I can charge off any 12v source or solar set ups.
If I set my charger to storage mode (lowers the voltage for long term storage) It goes from 3.6v to 3.33v per cell and reports I used around 150ma to do that. So to pump it from 3.6v to 4v is going to be about 50ma max. Not worth frying your cells.
I picked 20ah as I only need 13ah per trip and dont have to deplete the cells too far. I did once do a 55 mile round trip on a 24v 20ah ping and 500w conhis motor at 17mph average (I like to pedal allot btw). I started hitting 2.9v under load as I pulled into my road. My battery still had some pull in it and recharged with a full 20ah (measured bymy balance charger). not bad after two years getting pampered, will I ever need to replace this thing lol.
Further to this I use no bms. I have a micro voltage monitor that can be set to alarm at any voltage. So it beeps at 3.1 volts and I know Im in my last quarter of the battery and to pedal hard rather than just have it cut out on you and have to fight your motor the rest of the way home. http://www.cmfhobbies.com/details.asp?ID=1894
voltage alarm(£3 on ebay) and jst connector
Last edited by leggera16; 12-22-11 at 03:30 PM.
Reason: added info
I've recently gone to 60Ah Thunderskys and I ALWAYS charge to 3.8v.
Being that they are large format prismatic cells, the amount of capacity is the same PERCENTAGE wise..
So although I may only get 5% more battery from charging to 3.8, that ends up being another couple amp hours or 3.
Smaller cells won't get you much going past 3.65v but on large cells it's quite worth it.
P.S. Running at 20a (.3C) on the battery gets me 63.7AH from 3.8v to 2.8v.
I don't use a BMS either, I just use 3 6/12v-10a chargers and make sure at end of charge they stay balanced.
Using a month now (about 45 cycles), at end of charge they hit 3.8v within seconds of each other and are within .01-.03v after settling for an hour.
My last recorded cell voltages on each 12v pack were cells from 3.69v to 3.72v.
(VERY well matched cells!)
So do you need that extra 3ah? I mean are you running out before your homeward destination? I picked 20ah as my journey takes around 13ah and dont need to worry if some of my cells arnt at 101% charge voltage/capacity. If I had gone with 15ah I would probably be hankering after an extra half amp hour and not worry about shortening my cells life.
Id say buy as much as you can safely carry/afford and not worry about absolute maximum capacity voltages too much, giving your cells an easy longer life. Some people say you can abuse these voodoo batteries (charge to 5v, keep on charge between every ride etc) and they keep giving but I dont want to risk that with mine if I dont really need to.
Im not really up on the resistance but my charger says they are around 2.0 but when fully charged they all drift from 1.6 to 2.2 in ohm something or others. I know they say each cell is different but that sounds pretty varied in one pack but as its my first and most likely last lifepo4 purchase I guess Il never know lol
While you are using three chargers on the same ac source do you have to split the packs up? I was thinking of converting a small quad to 48v electric with 2 rc chargers but worried it might cause feed back damage if I dont split the pack before each charge/balance.
I don't NEED the extra 3Ah's BUT it's nice to know, I have them there...
And the TS prismatics are SAFELY charged up to 3.8v.
(NO loss is "cycle capacity")
Yes, sometimes I use "all" of the AHs.. (Not really, because ("all" is) I discharge only to 2.8v whereas others will routinely discharge to 2.5v to 2.7v)
The only reason why I use "3 chargers", is because I already had them, and didn't really want to spend money on a 36v 15-20a charger.
Your charging habits and mine are relative..
Look at it this way...
You use 15 out of 20ah on a daily basis and then recharge.
I use 15 out of 60ah on a daily basis and don't have to recharge. 3 days later... Yes. So I do a recharge once every 3 days, while you do it every day..
So even though I MAY get less cycles, I will have the battery last longer than yours, given the same amount of "use".
FYI, several months ago I read new specs from Thunder Sky They now recommend charging to a max of 3.8v. Da, I wonder why.....
When I first hooked these up I was not sure what would happen but everything was fused.
The info in this thread shows that above and below a certain point there is not much going on.
The Samsung cells are above the voltage of the A123 cells and the Watts up meter on the Samsung pack will go up to 5 amps when they are first connected and drops fast until they are of equal voltage.
The A123s will have up to 3.8v until I start running them but they are taking in no more current just sitting with both packs fully charged and in parallel.
The Samsung cells don't have much to give and the A123s don't have much to take and they equal out.
Last edited by biker; 02-10-12 at 11:48 AM.