Doctorbass
100 GW
bikeraider said:
Hello Bruno, This is for someone in montreal. He is converting a mazda 3 using 100Ah thundersky.
Doc
Even Newer 4 to 24-cell Battery Management System (BMS)
- Thread starter GGoodrum
- Start date
Hello Bruno, This is for someone in montreal. He is converting a mazda 3 using 100Ah thundersky.
Doc
Doctorbass
100 GW
fechter said:
I'll post results on the thread i began for that.
It's not really different than the BMS that Steveo made for 133VDC, maybe just the charging current that is a bit more and some more optinos..
I am evaluating if i'll keep the 2.1V cut or will update for 2.7V the TC54..
Thundersky 100Ah cells seem to be ok for 2.7V lvc with high load until the end of discharge if could reach current demand of 1C or 2C.. near the 90% dod..
I think that the V sag at high load must be evaluated for every possible conditions including the IR rise at high temp that could increase the voltage sag ex: during winter at 80-90%dod diring acceleration.. to be able to keep decent power on that high power demand..
In this case maybe using the 2,1V might be the good solution.
I think that it also depend on WHO will use that electric car... ex: if it's for customer that really dont know about electronic and physics, a more conservative lvc like 2.7V might be safer for preserving the battery..
In the other hand, if it would be me, i would go for the 2.1V because i know that i would only use the lvc for protection for the battery instead of for cuting battery discharge.. I would preffer counting the Ah used instead..
Or.. choosing the 2.1V lvc for cell overdiacharge protection and to use the controller programmable main voltage LVC to decrease the throttle action.. like many controlelr have.
I guess that using 40s ( 128VDC nominal) with a controller slow doen the throttle at let say 108VDC ( 2.7V per cell)
According to the thundersky discharge curve for the 100Ah, at 0.5C, i could get 80%capacity until 2.1V
I think the driving conditions can affect alot the best LVC setting decision...
Doc
Doc
baerfoot
1 mW
fechter said:
Their site says that the charger has a "gas" cycle at 2.55/cell which would equal 91.8v. Do you think that would be high enough?
pm_dawn
100 W
Doctorbass said:
I have a 40 cells setup of this Fechter/Goorum BMS with 2,7 lvc
Cells are TS 160Ah.
At below 0degC I trip the LVC even under 1C loads. And at -14 degC I could not load more then about 0.5C before tripping the LVC.
I know the energy is there but the voltage drops really bad at low temp. I know I'll need somekind of battery heating to get the range I want.
I would love to have some 2,5v TC:s in the setup but I think a temp corrected LVC would be good to have.
BTW I'm not using the throttling function of the BMS yet, I still have some work to do regarding my charging.
I have to supervise the charging at the end stage.
But the shunting seems to work fine. I once had one shunt go crazy and shunt even though the voltage was below 3,7 and it almost costed me a cell there.
Found out dirt and moist had somehow shorted the shunt in ON state.
I'm actually doing some cables for my 5 Junsi cell monitors to be able to log the Voltage sag during normal rides. Planning on using FTP twisted pair cables. They have 4 pairs and a shield in a nice package, giving the 9 leads i need for the logger.
Regards
/Per Eklund
Middle of Sweden
Doctorbass
100 GW
Excellent info!.. Thanks for sharing!
I actually have the 2.1V LVC on my board and not the 2.7.
According to the discharge curve of the TS cells at temp of zero celsius or below, I can see that the voltage sag realy exist and why it can trip the LVC too soon. DID you noticed if it happened at the end of discharge or immediatly with a full charged battery?
I also thought it could be a nice idea about the 5 Junsi cell monitors ... cheap, efficient and... you could use the output trigger for the LVC alarm of the Junsi... instead of the BMS lvc... it is adjustable ! :wink: Using opto or relay you could connect together each of the 5 alarm output and still have them electrically isulated. to avoid shorting by the common ground of the output alaom connector.
That BMS will be used with a zivan NG1 cahrger.. I know that if it detect no battery, it cut the output.. and that may be a problem because of how the BMS PWM mosfet pulsate the current when triping the 3.7V on one cell...
I might just use a little resistor in parallel to semi. bypass the mosfet and let some little current passing from the battery to the charger to let it detect someting and not cut.
Doc
pm_dawn
100 W
Hi !
yes I have been thinking of doing a series of the Junsi logger with optos or small relays to form the LVC and HVC circuit. And you get logging all over the system as a bonus.
About the TS cells .I have been seeing LVC tripping at 1- 1.5 C at these low temperatures even when fully charged. BUT it could be that i have one bad cell. That's why I need to get the Junsi's all hooked up to log the voltages during rides. That would pretty much tell me spot on if I have a bad cell. I have exchanged 1 cell that bulged due to overcharge and bad strapping. I know the one more cell did bulge a little at the same overcharge, it could be that cell that is responsible for tripping then LVC.
Anyway I think that 2,7 is to high LVC when riding in these lower temps. It would be good with a auto corrected LVC based on battery temp. Much as Dimitri has planned in the open source BMS at DIY.
Yesterday I tried to ride the pack down as far as I could with out killing any cells.
The Ah meter said 146ah drawn from the pack. It was about 0degC and I would tirp LVC at .5C at the end. Still resting voltage was 125V for the pack.
I could probably have take 10 ah more out of the pack also. But the car has a safety feature that kills the DCDC if I take the pack to low on calculated Ah and therefore my 12v circuit was getting so low that the Controller actually cut out so I had to turn of the headlights to get home.
I got about 115 km (71,5miles) on that charge, all in 0 or sub 0 temp. I think that is pretty good. I have studded M+S tires on and it is snow and ice on the roads.
My onboard computer calculated about 13.5 ah/10km.
Best Regards
/Per Eklund
Snowy Sweden
yes I have been thinking of doing a series of the Junsi logger with optos or small relays to form the LVC and HVC circuit. And you get logging all over the system as a bonus.
About the TS cells .I have been seeing LVC tripping at 1- 1.5 C at these low temperatures even when fully charged. BUT it could be that i have one bad cell. That's why I need to get the Junsi's all hooked up to log the voltages during rides. That would pretty much tell me spot on if I have a bad cell. I have exchanged 1 cell that bulged due to overcharge and bad strapping. I know the one more cell did bulge a little at the same overcharge, it could be that cell that is responsible for tripping then LVC.
Anyway I think that 2,7 is to high LVC when riding in these lower temps. It would be good with a auto corrected LVC based on battery temp. Much as Dimitri has planned in the open source BMS at DIY.
Yesterday I tried to ride the pack down as far as I could with out killing any cells.
The Ah meter said 146ah drawn from the pack. It was about 0degC and I would tirp LVC at .5C at the end. Still resting voltage was 125V for the pack.
I could probably have take 10 ah more out of the pack also. But the car has a safety feature that kills the DCDC if I take the pack to low on calculated Ah and therefore my 12v circuit was getting so low that the Controller actually cut out so I had to turn of the headlights to get home.
I got about 115 km (71,5miles) on that charge, all in 0 or sub 0 temp. I think that is pretty good. I have studded M+S tires on and it is snow and ice on the roads.
My onboard computer calculated about 13.5 ah/10km.
Best Regards
/Per Eklund
Snowy Sweden
Doctorbass
100 GW
pm_dawn said:
Thanks for these precious infos! I admit that for the fine tuning, the Junsi dataloggin is a great solution to get real world idea of each cells health and reject the low or bad one to get more km
Your EV data are very interesting since the BMS i'm working on will be used for car in Quebec province wich have cold winter too!.. sometime -30 celsius!
Do you have any website or pictures.. I would love seeing that car and installation!
Doc
pm_dawn
100 W
Hi !
I will create a post in EValbum.
Regards
/Per Eklund
I will create a post in EValbum.
Regards
/Per Eklund
AndyH
10 kW
Hi Per!
Your voltage sag may not mean damaged cells - my Thunder Sky pack sags down very near LVC with a 1.6C load in a South Texas winter - and we're only down to 45ºF/7ºC.
Thunder Sky's battery manual says that the load and LVC should be reduced from 3C/2.5V at 25ºC to 1C/1.5V at -35ºC. They don't publish numbers for temperatures between -35ºC and 25ºC so I don't know if the change in current and LVC is linear.
Stay warm!
Andy
Your voltage sag may not mean damaged cells - my Thunder Sky pack sags down very near LVC with a 1.6C load in a South Texas winter - and we're only down to 45ºF/7ºC.
Thunder Sky's battery manual says that the load and LVC should be reduced from 3C/2.5V at 25ºC to 1C/1.5V at -35ºC. They don't publish numbers for temperatures between -35ºC and 25ºC so I don't know if the change in current and LVC is linear.
Stay warm!
Andy
pm_dawn said:
Doctorbass
100 GW
A great way to conteract this voltage sag depending on the temperature would be to have a current control limited by the temperature! 
Voltage sag occur because of the internal resisance that grow on low temperature.
With high internal resistance cell are more subject to heat and have intrernal dammadge.
Since this Lithium ion cell technology is not perfect in cold temp, I think we must take account of that negative effect and preserve our cells more than sucking juice at high curent at end of SOC and reduce cycle life of these cells.
To accomplish that a current limited controller affected by the temperature of the cell could be the solution.
In other words, we could keep the LVC away from tripping by automaticly reduce the current demand on the cell... same as reducing your foot presure on the "gas" pedal
I think that if a cell hit the LVC, whatever the temperature is, it's not good for a lithium cell. IN both case, it happen because of the internal resistance of the cell have rised.
-At end of SOC
-At low temperature
-BOTH
....
Doc
Voltage sag occur because of the internal resisance that grow on low temperature.
With high internal resistance cell are more subject to heat and have intrernal dammadge.
Since this Lithium ion cell technology is not perfect in cold temp, I think we must take account of that negative effect and preserve our cells more than sucking juice at high curent at end of SOC and reduce cycle life of these cells.
To accomplish that a current limited controller affected by the temperature of the cell could be the solution.
In other words, we could keep the LVC away from tripping by automaticly reduce the current demand on the cell... same as reducing your foot presure on the "gas" pedal
I think that if a cell hit the LVC, whatever the temperature is, it's not good for a lithium cell. IN both case, it happen because of the internal resistance of the cell have rised.
-At end of SOC
-At low temperature
-BOTH
....Doc
The first four units behave as they should do, with a voltage of 14V all four red leds lit. Possible there is a burnt trace or a bad transistor. Curios is , that applying 56V to the BMS (12s) all leds lit and the green led comes up.manfred59 said:
manfred59 said:
You might try changing the value of R3 in the control circuit from 10k to 4.7k. You can just add another 10k across the existing one to make it 5k (close enough). This will make the trigger for the auto shutoff more sensitive. We made this change in the ver. 2.6 boards and it seems to work well.
pm_dawn
100 W
Doctorbass said:
Hi !
I have created a car in my DIY garage:
http://www.diyelectriccar.com/garage/cars/222
The pictures are quite old but I will publish some more later on.
Today was -18degC. 2,7V LVC was tripping as early as 110A with 60%SOC.
Really need Heaters.
Regards
/Per Eklund
Sweden
Doctorbass
100 GW
pm_dawn said:
Thanks Per!!
That’s interesting data!
Here it is -20degC today and I just can imagine how cold it is!
So 160Ah ts cell at 60%soc will trip at 2.7V at -18 celsius.
It could be a very interesting thread to log every of these personal setup data in cold condition to establish statistic about the Ah, temp and SOC and trip voltages !
Personally i'll leave the 2.1V TC54 chip and will not replace it for the 2.7V to avoid this problem.
I think that the best cell SOC management must be by counting the Ah and to cut at let say 85-90% SOC and stop draining cells at this moment instead of draining the pack to 100% soc and let the LVC cut power for you.
The range you get is realistic since you have 40s 160Ah ( 21.1kWh).
-160km at 50km/h that's 132Wh/km at 50kmh
or
-113km at 95km/h that's 186Wh/km at 95kmh
The best i've seen for an electric car is the Tesla at 110Wh/km at 100km/h.
Doc
GGoodrum
1 MW
Okay, time for an update.
Richard and I have been working on a major new revision to the BMS, which adds several new functions and features, is more modular and expandable, can support shunt currents as high as 2A with active cooling, has an improved PWM-based current control and has an auto power on/off power detection scheme that eliminates the need for a "3rd wire" to power the control section. The new layout has multiple completely independent 3" x 4" 6s sections that are now stackable. The new control section is on one more 3" x 4" board that goes on the top of the stack. The cell circuits are laid out better and use fewer parts per channel. The number of connections between the 6s sections and the control board have been reduced to just two, by having the LVC and HVC detection functions share the same opto outputs. This makes total sense as these functions are never used at the same time. The LVC is used during discharge and the HVC during charging/balancing. This also eliminates the need for the resistor/diode network that was used to generate the ALL SHUNTS ACTIVE signal that was used in the old auto power off logic. The new control logic uses current sensing to detect when the cells are full. Finally, this new version supports both LiFePO4 and LiPo-based setups with two part changes per channel. For existing LiPo setups that already have separate LVC circuits, this new configuration can also be used as a standalone balancer but one that can be left permanently installed on the bike and left connected to the pack. Without the charger/supply connected, there is absolutely zero current drain in the control section.
Although the new PCB has one control board and three 6s sections, organized in the familiar "tearoff" configuration, you will be able to order the control section and however many 6s sections that are required. The 2-wire opto lines are left connected, which allows flexibility in how the overall BMS is physically laid out. They can all be in one stack, or all laid side-by-side, as with the current BMS PCB, or a combination of both. When stacked, the opto lines are connected between boards with two board-to-board headers. The spacing between boards is 15mm. Here's what the new control and 6s sections look like:
View attachment 18s LiPO BMS-v3.9d-01.png
View attachment 18s LiPO BMS-v3.9d-02.png
As you can see, the connections all exit one end of the boards and the LEDs are all at the other end of the board. The LEDs can be installedat a 90-degree angle so that they are at the edge of the board, facing out. There has been a lot more attention paid to thermal considerations this time, with onboard pads/heatsinks with thermal vias between layers. The traces for the shunt transistors and the shunt resistors have been beefed up to support higher shunt currents. Also, in addition to having a flat mounting for the "standard" BD136 TO-226 packages, mounts are also provided to use a larger TO-220 - based TIP105 darlington power transistor in place of the BD136. Also, to make assembly a bit less tedious, the parts are all oriented in the same direction, wherever possible. The parts used are pretty much the same as before, just fewer of them. There is one difference. This version needs to use the non-complementary open drain version of the TC54, which has the designation TC54VN-xxx, vs. TC54VC-xxx. This saves having to add a diode to isolate the HVC and LVC functions.
The new control section is most of the changes have been made, and new features have been added. The first is a replacement for the old "throttling" logic. The new circuit now uses the HVC signal to control the duty cycle for a PWM circuit, much like a controller does. This sounds like a subtle difference, but what it does is allows the charge current to be higher, for a longer period, before the "throttling" of the current starts, as the cells get close to being full. The two-color red-green LED remains (the one on lower right...), which starts out red during the CC phase, and starts to transition to green as the PWM duty cycle is reduced. It will gradually turn from red to orange, then yellowish, light green and finally fully green, when the cells are full.
There are now provisions for two FETs to be used to control the charge current. This is primarily to be able to support higher voltage EV setups. Normally, the FET just sees the difference between the pack voltage and the charge voltage, so a single 100V IRFB4110 works for most setups. A higher voltage FET, like the 150V IRFB4115 can be used, but these have a higher on resistance, so provisions for adding a second one in parallel are provided. This should support much larger configurations with pack voltages up to 400V, or so.
There is now also a spot for another FET, which is used to control a fan, or multiple fans in series. The fan(s) are connected to the main pack/charger positive connection so that we can keep the current down in the 12V control section to logic levels. Otherwise, we would need to beef up the 12V regulator.
To eliminate the need to have a "3rd wire", to keep the control logic off until the charger is connected, Richard has come up with a clever SCR-based scheme to not turn on the 12V regulator until suddenly there/s at least a volt difference between the charger voltage and the pack voltage. Once on, the SCR keeps it latched on. There are two conditions that will cut off the power to the control section. The first is if the current suddenly drops down close to zero, which would happen if the charger/supply was disconnected. The second condition is via the new end-of-charge detection logic. A current sensing circuit is used to monitor the charge current. When the current gets down to the level that the shunts can bypass, that means at least one cell is full. There is now a switch-selectable option that will either stop the charging process at this point, or will continue on to balance the cells but for a selectable period of time. This balance time can be for 15 minutes, 1 hour, 2 hours or 4 hours, selectable via a jumper block. This range of balance time elections can be adjusted up or down by changing the value of one resistor. At the end of the time period, the charge current is cutoff. There is another LED (on the bottom left...) that will initially be red, during the basic charge phase, and then "blink" changing between red and orange while the balancing mode is on and the timer is operating. So, during the initial CC charge mode both of the LEDs on the control board will be red, and the cell circuit LEDs will be off. Once the shunts start operating, the LEDs for those channels will come on (orange...). As the cells get fuller, and the PWM logic kicks in, the control board LED on the right will start transitioning towards green, while the one on the left remains red. Finally, if the balancing mode is enabled, the LED on the left will start blinking orange. When complete, the whole system shuts down, and all the LEDs go off. Power to everything remains off, until the charger/supply power is recycled.
The "normal", non-balancing mode can be used by those concerned with "top-balancing" issues that have been discussed in detail, here on E-S and elsewhere. I do not want to discuss this issue in this thread, so please don't. Use the other threads. What I will say here is that Richard and I believe that if balancing is not to be done, the way we have it here is a better solution than simply letting the high cell get to a much higher HVC point, and then simply cutting power. In some of the schemes I've seen the HVC set point is at something like 3.85V, while the charge voltage is set lower, to like 3.60V per cell. The theory is that the lowest capacity cell is allowed to go higher than the normal CV point, until it hits 3.85V and then the charge process is stopped. I have a couple of problems with this approach. Forst of all, what I've found is that the higher the charge current is, the greater the reverse voltage sag there is going to be between the cells resting voltage, and the voltage the detection logic will see. What this means is that the higher the charge current the sooner the cell is going to be pushed up to 3.85V, so if you stop at that point, the cells are going to end up not getting as full a charge. Another concern I have is that although the LiFePO4 cell manufacturers, like Thunder Sky, might tell you it is okay to repeatedly let cells hit 3.85V per cell, the jury is still out, IMO, on what this will eventually do to the longevity of the cells. To make matters worse, the only cells that will be allowed to overvolt will be the weaker, less capacity cells, so my gut tells me this technique will further hasten their eventual demise. Also, for LiPo-based setups, with the more volitole Litium-Cobalt-based chemistries, this sort of planned overcharging of cells, weaker, or otherwise, is simply not an option. Your overvolt these cells and you are going to end up with an early 4th of July.
What our design does differently is to not ever let any one cell go over a safe point, which is set just above the per cell CV set point, byt using PWM control on the charge current. The shunt turn-on is set just below this HVC set point. When the charge current drops to the amount the shunts can bypass, like 1A for instance, at least the low capacity cell will be completely charged to whatever the desired level is set to, so in the above example 3.60V. If you don't want to balance the rest of the cells, that's fine, the "normal" mode setting will stop the charge process, but at least the first/lowest cell has been safely charged full. If balancing is allowed to continue, the full cells don't get "cooked" by trying to stuff more current into them, as it has been suggested (
). It doesn't work that way. Full cells simply can't absorb any more current at all, unless the voltage is allowed to keep climbing. Once full, that's it, the shunt circuit absorbs all the current. Eventually, all the cells are at the point they can't accept any more current and the shunts are bypassing it all.
One other point. You can't just assume that the first cell that hits the cutoff every time is the lowest capacity cell. Ths doesn't take in the possibility that cells still have the same capacities, but just happen to be out-of-balance, or at different states of charge. Whether at the "top", or the "bottom", at some point the cells need to be balanced. Richard and I both feel strongly that so-called bottom balancing is dangerous, and just not all that practical. Balancing at the top, but without letting cells overvolt, is a much better solution, in our opinion.
Okay, soapbox mode off... :wink:
Although the cell circuits and the new PWM logic have been tested, and the new auto power detection circuit has been breadboarded, we still need to test the whole system together, using the new boards. There's still a few resistor and capacitor values that need tweaking, but that shouldn't take long. I'm hoping we can get that effort down by Christmas, or the end of next week. I will the make at least the PCBs and BOMs available shortly after that. As before, Andy Hecker will also provide fully assembled and tested units, for those that are soldering skill-challenged. This version should be a lot easier to assemble though, and over all, uses fewer parts. Because of a larger order for customer doing a new electric motorcycle, we are finally going to be able to do a surface mount version that can be automatically assembled. These we will make available sometime in the 1st quarter of 2010.
Finally, there will also be an option to order the control section alone, for those who want to upgrade their exiting v2.x BMS units, with the new control features. All it will take is a two wire connection to the existing BMS boards.
When we get some more info, and I have something more to report, we will retire this thread, like we did after the last major revision/update, and start a new thread for this one, which will have the initial version designation of v4.0a.
-- Gary
Richard and I have been working on a major new revision to the BMS, which adds several new functions and features, is more modular and expandable, can support shunt currents as high as 2A with active cooling, has an improved PWM-based current control and has an auto power on/off power detection scheme that eliminates the need for a "3rd wire" to power the control section. The new layout has multiple completely independent 3" x 4" 6s sections that are now stackable. The new control section is on one more 3" x 4" board that goes on the top of the stack. The cell circuits are laid out better and use fewer parts per channel. The number of connections between the 6s sections and the control board have been reduced to just two, by having the LVC and HVC detection functions share the same opto outputs. This makes total sense as these functions are never used at the same time. The LVC is used during discharge and the HVC during charging/balancing. This also eliminates the need for the resistor/diode network that was used to generate the ALL SHUNTS ACTIVE signal that was used in the old auto power off logic. The new control logic uses current sensing to detect when the cells are full. Finally, this new version supports both LiFePO4 and LiPo-based setups with two part changes per channel. For existing LiPo setups that already have separate LVC circuits, this new configuration can also be used as a standalone balancer but one that can be left permanently installed on the bike and left connected to the pack. Without the charger/supply connected, there is absolutely zero current drain in the control section.
Although the new PCB has one control board and three 6s sections, organized in the familiar "tearoff" configuration, you will be able to order the control section and however many 6s sections that are required. The 2-wire opto lines are left connected, which allows flexibility in how the overall BMS is physically laid out. They can all be in one stack, or all laid side-by-side, as with the current BMS PCB, or a combination of both. When stacked, the opto lines are connected between boards with two board-to-board headers. The spacing between boards is 15mm. Here's what the new control and 6s sections look like:
View attachment 18s LiPO BMS-v3.9d-01.png
View attachment 18s LiPO BMS-v3.9d-02.png
As you can see, the connections all exit one end of the boards and the LEDs are all at the other end of the board. The LEDs can be installedat a 90-degree angle so that they are at the edge of the board, facing out. There has been a lot more attention paid to thermal considerations this time, with onboard pads/heatsinks with thermal vias between layers. The traces for the shunt transistors and the shunt resistors have been beefed up to support higher shunt currents. Also, in addition to having a flat mounting for the "standard" BD136 TO-226 packages, mounts are also provided to use a larger TO-220 - based TIP105 darlington power transistor in place of the BD136. Also, to make assembly a bit less tedious, the parts are all oriented in the same direction, wherever possible. The parts used are pretty much the same as before, just fewer of them. There is one difference. This version needs to use the non-complementary open drain version of the TC54, which has the designation TC54VN-xxx, vs. TC54VC-xxx. This saves having to add a diode to isolate the HVC and LVC functions.
The new control section is most of the changes have been made, and new features have been added. The first is a replacement for the old "throttling" logic. The new circuit now uses the HVC signal to control the duty cycle for a PWM circuit, much like a controller does. This sounds like a subtle difference, but what it does is allows the charge current to be higher, for a longer period, before the "throttling" of the current starts, as the cells get close to being full. The two-color red-green LED remains (the one on lower right...), which starts out red during the CC phase, and starts to transition to green as the PWM duty cycle is reduced. It will gradually turn from red to orange, then yellowish, light green and finally fully green, when the cells are full.
There are now provisions for two FETs to be used to control the charge current. This is primarily to be able to support higher voltage EV setups. Normally, the FET just sees the difference between the pack voltage and the charge voltage, so a single 100V IRFB4110 works for most setups. A higher voltage FET, like the 150V IRFB4115 can be used, but these have a higher on resistance, so provisions for adding a second one in parallel are provided. This should support much larger configurations with pack voltages up to 400V, or so.
There is now also a spot for another FET, which is used to control a fan, or multiple fans in series. The fan(s) are connected to the main pack/charger positive connection so that we can keep the current down in the 12V control section to logic levels. Otherwise, we would need to beef up the 12V regulator.
To eliminate the need to have a "3rd wire", to keep the control logic off until the charger is connected, Richard has come up with a clever SCR-based scheme to not turn on the 12V regulator until suddenly there/s at least a volt difference between the charger voltage and the pack voltage. Once on, the SCR keeps it latched on. There are two conditions that will cut off the power to the control section. The first is if the current suddenly drops down close to zero, which would happen if the charger/supply was disconnected. The second condition is via the new end-of-charge detection logic. A current sensing circuit is used to monitor the charge current. When the current gets down to the level that the shunts can bypass, that means at least one cell is full. There is now a switch-selectable option that will either stop the charging process at this point, or will continue on to balance the cells but for a selectable period of time. This balance time can be for 15 minutes, 1 hour, 2 hours or 4 hours, selectable via a jumper block. This range of balance time elections can be adjusted up or down by changing the value of one resistor. At the end of the time period, the charge current is cutoff. There is another LED (on the bottom left...) that will initially be red, during the basic charge phase, and then "blink" changing between red and orange while the balancing mode is on and the timer is operating. So, during the initial CC charge mode both of the LEDs on the control board will be red, and the cell circuit LEDs will be off. Once the shunts start operating, the LEDs for those channels will come on (orange...). As the cells get fuller, and the PWM logic kicks in, the control board LED on the right will start transitioning towards green, while the one on the left remains red. Finally, if the balancing mode is enabled, the LED on the left will start blinking orange. When complete, the whole system shuts down, and all the LEDs go off. Power to everything remains off, until the charger/supply power is recycled.
The "normal", non-balancing mode can be used by those concerned with "top-balancing" issues that have been discussed in detail, here on E-S and elsewhere. I do not want to discuss this issue in this thread, so please don't. Use the other threads. What I will say here is that Richard and I believe that if balancing is not to be done, the way we have it here is a better solution than simply letting the high cell get to a much higher HVC point, and then simply cutting power. In some of the schemes I've seen the HVC set point is at something like 3.85V, while the charge voltage is set lower, to like 3.60V per cell. The theory is that the lowest capacity cell is allowed to go higher than the normal CV point, until it hits 3.85V and then the charge process is stopped. I have a couple of problems with this approach. Forst of all, what I've found is that the higher the charge current is, the greater the reverse voltage sag there is going to be between the cells resting voltage, and the voltage the detection logic will see. What this means is that the higher the charge current the sooner the cell is going to be pushed up to 3.85V, so if you stop at that point, the cells are going to end up not getting as full a charge. Another concern I have is that although the LiFePO4 cell manufacturers, like Thunder Sky, might tell you it is okay to repeatedly let cells hit 3.85V per cell, the jury is still out, IMO, on what this will eventually do to the longevity of the cells. To make matters worse, the only cells that will be allowed to overvolt will be the weaker, less capacity cells, so my gut tells me this technique will further hasten their eventual demise. Also, for LiPo-based setups, with the more volitole Litium-Cobalt-based chemistries, this sort of planned overcharging of cells, weaker, or otherwise, is simply not an option. Your overvolt these cells and you are going to end up with an early 4th of July.
What our design does differently is to not ever let any one cell go over a safe point, which is set just above the per cell CV set point, byt using PWM control on the charge current. The shunt turn-on is set just below this HVC set point. When the charge current drops to the amount the shunts can bypass, like 1A for instance, at least the low capacity cell will be completely charged to whatever the desired level is set to, so in the above example 3.60V. If you don't want to balance the rest of the cells, that's fine, the "normal" mode setting will stop the charge process, but at least the first/lowest cell has been safely charged full. If balancing is allowed to continue, the full cells don't get "cooked" by trying to stuff more current into them, as it has been suggested (
). It doesn't work that way. Full cells simply can't absorb any more current at all, unless the voltage is allowed to keep climbing. Once full, that's it, the shunt circuit absorbs all the current. Eventually, all the cells are at the point they can't accept any more current and the shunts are bypassing it all.One other point. You can't just assume that the first cell that hits the cutoff every time is the lowest capacity cell. Ths doesn't take in the possibility that cells still have the same capacities, but just happen to be out-of-balance, or at different states of charge. Whether at the "top", or the "bottom", at some point the cells need to be balanced. Richard and I both feel strongly that so-called bottom balancing is dangerous, and just not all that practical. Balancing at the top, but without letting cells overvolt, is a much better solution, in our opinion.
Okay, soapbox mode off... :wink:
Although the cell circuits and the new PWM logic have been tested, and the new auto power detection circuit has been breadboarded, we still need to test the whole system together, using the new boards. There's still a few resistor and capacitor values that need tweaking, but that shouldn't take long. I'm hoping we can get that effort down by Christmas, or the end of next week. I will the make at least the PCBs and BOMs available shortly after that. As before, Andy Hecker will also provide fully assembled and tested units, for those that are soldering skill-challenged.
This version should be a lot easier to assemble though, and over all, uses fewer parts. Because of a larger order for customer doing a new electric motorcycle, we are finally going to be able to do a surface mount version that can be automatically assembled. These we will make available sometime in the 1st quarter of 2010.Finally, there will also be an option to order the control section alone, for those who want to upgrade their exiting v2.x BMS units, with the new control features. All it will take is a two wire connection to the existing BMS boards.
When we get some more info, and I have something more to report, we will retire this thread, like we did after the last major revision/update, and start a new thread for this one, which will have the initial version designation of v4.0a.
-- Gary
pm_dawn
100 W
Doctorbass said:
Hi !
No you have to read again.
When pulling 110A @ 60%SOC @18degC i trip the LVC.
That would be about .7C draw before trippping LVC @ -18degC
Otherwise correct.
I have to read about the new BMS.
The new BMS should actually been a new thread I would say.
This thread is getting far to full.
Regards
/Per Eklund
Malcolm
10 kW
Great work Gary and Richard! You've obviously put a lot of thought into this redesign and it really looks like you've covered every angle. There are very few simple, reliable (analogue) and affordable BMS offerings around, especially for DIY car conversions, so I'll be passing the word around.GGoodrum said:
liveforphysics
100 TW
This is fantastic!
This will be the first BMS I've ever used
Great job on bringing an awesome and affordable BMS to the grassroots EV building world
This will be the first BMS I've ever used
Great job on bringing an awesome and affordable BMS to the grassroots EV building world
AndyH
10 kW
GGoodrum said:Okay, time for an update.
<lots-o-snips>
-- Gary
Beautiful job Gary! I can't wait to get one to play with. And yes - once I figure out how to build it I'll be happy to make them for others.
Merry Christmas All,
Andy
AndyH
10 kW
richmpdx
100 W
Long time lurker. I seldom post because I unfortunately don't usually have much to add. But entirely appropriate to express gratitude for the efforts of Gary and Richard to continue the development of their BMS. Their contribution to EV development just really cannot be overstated. This community is so fortunate that they continue to work on BMS improvement as well as provide their expertise in so many ways .
Rich
Rich
mwkeefer
1 MW
Gary,
When will the BMS / Balancer boards be available on your site again? I've been checking for a while and they show out of stock still.
I need enough units to manage up to a 20S pack (though initially I will test with 15S)... the config at 15S is 4P and will be 3P at 20S.
Does the balancer work with LiPo (instructions for voltage calibration?)?
Does the BMS board do LVC protection?
Has fecter integrated throttling of input current?
-Mike
When will the BMS / Balancer boards be available on your site again? I've been checking for a while and they show out of stock still.
I need enough units to manage up to a 20S pack (though initially I will test with 15S)... the config at 15S is 4P and will be 3P at 20S.
Does the balancer work with LiPo (instructions for voltage calibration?)?
Does the BMS board do LVC protection?
Has fecter integrated throttling of input current?
-Mike
GGoodrum
1 MW
mwkeefer said:
We are retiring the current v2.x series of BMS boards, as the new version will replace these. They will hopefully be available right after Christmas. I get the first boards on Monday, but I ordered a limited number in case our final testing uncovers any changes that might be required. I'm hoping we will haave everything tested/sorted by the end of the week, but that's Christmas and since both our domains are controlled by females, especially this time of year, we might have some unplanned shortening of available test time.
Like the existing BMS design, the new one does include the LVC function. The opto signal is now shared with the HVC function, but we isolate it with a Schottkey diode. One of the big improvements in this version is for the "throttling" of the input current. The existing throttling logic simply cut the charge current off, whenever any cell was over the HVC point. It stayed off until all the cells were below the cutoff, and then it came back on. The net result of this was that the charge current stayed off a lot longer than it needs to, which increases the amount of time it takes to balance a pack. The new scheme use the HVC signal to modify the duty cycle of a fixed frequency PWM circuit, which ends up being a lot better way to control the current. My preliminary tests of this show a significant improvement, but I can't quantify it with real numbers until I get the first board built.
I've decided that instead of having a whole separate series of balancer-only boards, the new ones can be used as balancers simply by not populating the LVC parts. Since my current packs all have LVC boards inside the packs already, I'm going to do this initially, for my own use, but what I'm going to do is permanently mount the "balancers" to the bike, on a piece of aluminum screwed into the bottle holders. The new circuit allows everything to be connected to the packs at all times, and just a single two-wire plug brought out for the charger. I'm even thinking of putting my "stack" of 4 Meanwells in a bag which will stay on the rear rack. That way I can simply plug in an extension cord and charge the 15Ah packs at a 1C rate.
-- Gary
mwkeefer
1 MW
Gary,
This is awesome news... with regards to the meanwells... if they are the 350w models... they have slightly boxier 600w units available and they will fit on a rear rack side by side (not too long) also they fit in the bottom of pannier bags... then you just leave them alone on there.
When you have it sorted, let us know.
Personally I'll stick with a single S-350-48 for mobil charging (opportunity charging) at 6-10A (depending on settings) into a 15S pack... for on the road use, it's adequate. At home I have the "bulk" charger which is actually 2 S-350-24 units modified to each deliver 31.5v maximum (set at 31.125 right now for max v of 62.25 or 4.15v per cell) and at that cutout they are pushing 15A out for a 1C charge of my 15AH packs (3P)... I may double them up ( I have more of the 24v units than anything else) in parallel for 4 units in the office / showroom when it's done (2C charge) but,
that's all I need - (Can't believe Im saying I am satisfied with my charging setup, but I am at long last happy with my charging systems).
-Mike
This is awesome news... with regards to the meanwells... if they are the 350w models... they have slightly boxier 600w units available and they will fit on a rear rack side by side (not too long) also they fit in the bottom of pannier bags... then you just leave them alone on there.
When you have it sorted, let us know.
Personally I'll stick with a single S-350-48 for mobil charging (opportunity charging) at 6-10A (depending on settings) into a 15S pack... for on the road use, it's adequate. At home I have the "bulk" charger which is actually 2 S-350-24 units modified to each deliver 31.5v maximum (set at 31.125 right now for max v of 62.25 or 4.15v per cell) and at that cutout they are pushing 15A out for a 1C charge of my 15AH packs (3P)... I may double them up ( I have more of the 24v units than anything else) in parallel for 4 units in the office / showroom when it's done (2C charge) but,
that's all I need - (Can't believe Im saying I am satisfied with my charging setup, but I am at long last happy with my charging systems).
-Mike
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