Post by thread:[EE]Lithium battery charger with balancer proof of

I'm just kicking this around and would be interested in other thoughts. In the R-Pi E-14 forum someone wanted to know if there is such a thing as a series connected lithium battery charger. I suggested a module made up of a lithium charger IC, a switching mechanism that could isolate those batteries in the chain (envisaging no more than 3) once they've charged and some form of electronic load (probably a FET). It has been proposed that each battery could have its own switch controller and thinking about this a small Pic or Atmel chip could be used to provide the intelligent switching per battery with the charger/battery gauge chip providing the correct charging algorithm, the controller chip would either switch it out of the pack chain or alternatively switch in the active load to maintain that particular battery charge state. Does this seem workable in theory? Colin -- cdb, 14/05/2012 -- spam_OUTcolinTakeThisOuTbtech-online.co.uk

LiPo charging is a well developed technology. Check out: www.fmadirect.com/support_docs/item_1266.pdf This handles up to a 10S battery setup Quickly, safely, and babies the batteries. Over kill, I think, for your App but a good place to learn a bit! On 5/14/2012 6:17 AM, cdb wrote: {Quote hidden}> I'm just kicking this around and would be interested in other thoughts. > > In the R-Pi E-14 forum someone wanted to know if there is such a thing as a > series connected lithium battery charger. > > I suggested a module made up of a lithium charger IC, a switching > mechanism that could isolate those batteries in the chain (envisaging no > more than 3) once they've charged and some form of electronic load > (probably a FET). It has been proposed that each battery could have its > own switch controller and thinking about this a small Pic or Atmel chip > could be used to provide the intelligent switching per battery with the > charger/battery gauge chip providing the correct charging algorithm, the > controller chip would either switch it out of the pack chain or > alternatively switch in the active load to maintain that particular battery > charge state. > > Does this seem workable in theory? > > Colin > -- > cdb, 14/05/2012 > > -- > > > > > .....colinKILLspam@spam@btech-online.co.uk > -- John Ferrell W8CCW “During times of universal deceit, Telling the TRUTH becomes a revolutionary act” George Orwell

> In the R-Pi E-14 forum someone wanted to know if there is such a thing as a > series connected lithium battery charger. > > I suggested a module made up of a lithium charger IC, a switching > mechanism that could isolate those batteries in the chain (envisaging no > more than 3) once they've charged and some form of electronic load > (probably a FET) ... > Does this seem workable in theory? Yes. Almost anything sounds workable in theory :-) I've thought of simple ways of doing this One such follows. This can be complexicated as desired Assume all cells are roughly similar in performance and that gross mismatch does not occur. In particular. no cell should ever need to be below Vmin_usual so that it does NOT require slow trickling up beforenormal charging can start. This condition can be accomodated but is not covered below. Each cell has a simple shunt regulator placed across it. This can be as simple as eg a TL431, a transistor and a few resistors. Regulator is set to Vmax - say 4.2V. Cells are connected in series. Let's have 10 cells to make numbers easier. Provide 4.2 x N Volts current limited to desired charge rate. If charge rate is C then I is Ichg is ~= 2A for a string of 18650 cells. So Vmax = 4.2 x 10 = 42 V. I max = 2A. Assume cells are all about fully discharged with Vcell ~~= 3V Apply above supply to string of cells. Initially cells will charge at 2A. When any cell reaches 4.2V its shunt regulator will hold the cell voltage at 4.2V, the cell will take what it wants in constant voltage current tail mode and the balance will be passed by the shunt element. Dissipation per shunt = 4.2V x 2A = 8.4W = say about 10W/cell. Individual electronics modules COULD signal that they are in CV mode but some deduction and a little playing would allow the all-done state to be detected. Current tail off and terminate could be added by connecting a series element between cells and a shunt as before from top of cell to below series element. Shunt reg works as before but when shunting current rises to say 75% of max then series element is opened - disconnecting cell and shunt goes short. This removes power dissipation in charged cells. Shunted current is sent to next cells and smart smps charger backs off voltage to suit demand. When all cells are charged the needed voltage is N x short circuit shunt voltages and charger auto terminates. It would work :-). Cost of the smarter system is two MOSFETS plus simple electronics per cell. Simpler system = 1 MOSFET, TL431, few R's per cell. Russell McMahon

Of course, you can already get ICs that will do all this for you ... IIRC Linear Technology has them, but I am sure I have also seen them mentioned by another company, possibly TI or Analog Devices. {Quote hidden}> > In the R-Pi E-14 forum someone wanted to know if there is such a > thing > > as a series connected lithium battery charger. > > > > I suggested a module made up of a lithium charger IC, a switching > > mechanism that could isolate those batteries in the chain (envisaging > > no more than 3) once they've charged and some form of electronic load > > (probably a FET) ... > > > Does this seem workable in theory? > > Yes. Almost anything sounds workable in theory :-) > > I've thought of simple ways of doing this One such follows. > This can be complexicated as desired > > Assume all cells are roughly similar in performance and that gross > mismatch does not occur. In particular. no cell should ever need to be > below Vmin_usual so that it does NOT require slow trickling up > beforenormal charging can start. This condition can be accomodated but > is not covered below. > > Each cell has a simple shunt regulator placed across it. This can be > as simple as eg a TL431, a transistor and a few resistors. Regulator is > set to Vmax - say 4.2V. > Cells are connected in series. > > Let's have 10 cells to make numbers easier. > > Provide 4.2 x N Volts current limited to desired charge rate. If charge > rate is C then I is Ichg is ~= 2A for a string of 18650 cells. > So Vmax = 4.2 x 10 = 42 V. I max = 2A. > > Assume cells are all about fully discharged with Vcell ~~= 3V Apply > above supply to string of cells. > Initially cells will charge at 2A. > When any cell reaches 4.2V its shunt regulator will hold the cell > voltage at 4.2V, the cell will take what it wants in constant voltage > current tail mode and the balance will be passed by the shunt element. > Dissipation per shunt = 4.2V x 2A = 8.4W = say about 10W/cell. > Individual electronics modules COULD signal that they are in CV mode > but some deduction and a little playing would allow the all-done state > to be detected. > > Current tail off and terminate could be added by connecting a series > element between cells and a shunt as before from top of cell to below > series element. Shunt reg works as before but when shunting current > rises to say 75% of max then series element is opened - disconnecting > cell and shunt goes short. This removes power dissipation in charged > cells. Shunted current is sent to next cells and smart smps charger > backs off voltage to suit demand. When all cells are charged the needed > voltage is N x short circuit shunt voltages and charger auto > terminates. > > It would work :-). > > Cost of the smarter system is two MOSFETS plus simple electronics per > cell. > Simpler system = 1 MOSFET, TL431, few R's per cell. > > > Russell McMahon > >

Or you could just buy a Turnigy 3S balancer and charger for $4.50, does pretty-much exactly this. Back-order at the moment though. www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html [1] > I suggested a module made up of a lithium charger IC, a switching > mechanism that could isolate those batteries in the chain (envisaging no > more than 3) once they've charged and some form of electronic load > (probably a FET). It has been proposed that each battery could have its > own switch controller and thinking about this a small Pic or Atmel chip > could be used to provide the intelligent switching per battery with the > charger/battery gauge chip providing the correct charging algorithm, the > controller chip would either switch it out of the pack chain or > alternatively switch in the active load to maintain that particular battery > charge state. > > Does this seem workable in theory? ------------------------- Msg sent via Webmail - http://hosting.myob.com/ Links: ------ [1] http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.htm

Or a Turnigy Accucel 6, charges and balances up to 6S at 5A, discharges and supports Li-xx, Ni-xx and Pb chemistries. Just around $23. Isaac Em 14/5/2012 20:04, Lee Mulvogue escreveu: {Quote hidden}> > > Or you could just buy a Turnigy 3S balancer and charger for $4.50, > does pretty-much exactly this. Back-order at the moment though. > > www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html > [1] > > I suggested a module made up of a lithium charger IC, a switching > > mechanism that could isolate those batteries in the chain > (envisaging no > > more than 3) once they've charged and some form of electronic load > > (probably a FET). It has been proposed that each battery could have > its > > own switch controller and thinking about this a small Pic or Atmel > chip > > could be used to provide the intelligent switching per battery with > the > > charger/battery gauge chip providing the correct charging > algorithm, the > > controller chip would either switch it out of the pack chain or > > alternatively switch in the active load to maintain that particular > battery > > charge state. > > > > Does this seem workable in theory? > ------------------------- > Msg sent via Webmail - http://hosting.myob.com/ > > Links: > ------ > [1] > http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html

> Or you could just buy a Turnigy 3S balancer and charger for $4.50, > does pretty-much exactly this. Back-order at the moment though. > http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html looks good. Appears to use special magic. It says it is a balancer.How do you balance 3S LiIon with no centre taps? That's not to say you can't do it - just that the lead acid method would be unwise. With some battery chemistries you can bring up a low cell by charging the overall battery at a higher than usual voltage so that fully charge cells are driven into the steep upper tail of the charge curve while the low cell ramps up to meet them. LiIon frowns extremely severely on such practices. Normally, when a cell reaches its upper voltage limit the cell is put in a constant voltage mode and accepts whatever current it wishes and the current "tails off". The tail current is controlled by the most charged cells. There is no way to apply a higher current that this without pushing the cell out of CV mode and back into voltage increasing mode - magic smoke may follow. What MAY be done is to rely on the fact that charging is less efficient as the end of CC mode is approached and then also as CV is initiated. ie for a given number of amp-seconds of charge a cell will accept a greater percentage of charge if it is more discharged. By charging the good cells up into the edge of CV and then discharging and repeating the lowest charged cells are operated in a higher charge efficiency region and so their stat of charge asymptotes towards that of the more charge cells. Maybe. Russell {Quote hidden}> [1] > > I suggested a module made up of a lithium charger IC, a switching > > mechanism that could isolate those batteries in the chain > (envisaging no > > more than 3) once they've charged and some form of electronic load > > (probably a FET). It has been proposed that each battery could have > its > > own switch controller and thinking about this a small Pic or Atmel > chip > > could be used to provide the intelligent switching per battery with > the > > charger/battery gauge chip providing the correct charging > algorithm, the > > controller chip would either switch it out of the pack chain or > > alternatively switch in the active load to maintain that particular > battery > > charge state. > > > > Does this seem workable in theory? > ------------------------- > Msg sent via Webmail - http://hosting.myob.com/ > > Links: > ------ > [1] > www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html >

These chargers DO use taps for each cell. Nowadays all R/C hobby Li-xx packs have a balancing connector ( usually a JST-XH connector ),besides the heavy duty main wires. Low power chargers charge the cells only through the balancing connectors, while discharge is done via the main wires. High power chargers push current via the main wires and use the balancing connector just to monitor and balance the charging current. Some electronic speed controllers for brushless motors (Turnigy Sentry) connect also to the balancing connector to monitor individual cell voltages during discharge. Isaac Em 15/5/2012 10:20, RussellMc escreveu: {Quote hidden}>> Or you could just buy a Turnigy 3S balancer and charger for $4.50, >> does pretty-much exactly this. Back-order at the moment though. >> http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html > > looks good. > Appears to use special magic. > It says it is a balancer.How do you balance 3S LiIon with no centre > taps? That's not to say you can't do it - just that the lead acid > method would be unwise. > With some battery chemistries you can bring up a low cell by charging > the overall battery at a higher than usual voltage so that fully > charge cells are driven into the steep upper tail of the charge curve > while the low cell ramps up to meet them. > LiIon frowns extremely severely on such practices. Normally, when a > cell reaches its upper voltage limit the cell is put in a constant > voltage mode and accepts whatever current it wishes and the current > "tails off". The tail current is controlled by the most charged cells. > There is no way to apply a higher current that this without pushing > the cell out of CV mode and back into voltage increasing mode - magic > smoke may follow. > > What MAY be done is to rely on the fact that charging is less > efficient as the end of CC mode is approached and then also as CV is > initiated. ie for a given number of amp-seconds of charge a cell will > accept a greater percentage of charge if it is more discharged. By > charging the good cells up into the edge of CV and then discharging > and repeating the lowest charged cells are operated in a higher charge > efficiency region and so their stat of charge asymptotes towards that > of the more charge cells. Maybe. > > > > Russell > > > > > > >> [1] >> > I suggested a module made up of a lithium charger IC, a switching >> > mechanism that could isolate those batteries in the chain >> (envisaging no >> > more than 3) once they've charged and some form of electronic load >> > (probably a FET). It has been proposed that each battery could have >> its >> > own switch controller and thinking about this a small Pic or Atmel >> chip >> > could be used to provide the intelligent switching per battery with >> the >> > charger/battery gauge chip providing the correct charging >> algorithm, the >> > controller chip would either switch it out of the pack chain or >> > alternatively switch in the active load to maintain that particular >> battery >> > charge state. >> > >> > Does this seem workable in theory? >> ------------------------- >> Msg sent via Webmail - http://hosting.myob.com/ >> >> Links: >> ------ >> [1] >> www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html >> -