Even Newer 4 to 24-cell Battery Management System (BMS)
- Thread starter GGoodrum
- Start date
GGoodrum
1 MW
DaveAK said:
It is pretty easy to tell when cells need to be balanced, and when they are being balanced. Normally, if the cells are fairly well balanced, the amount of time between when the first LED lights up (i.e. -- which starts the timer...), and when the last one comes on, should be fairly short, like within a minute, or two. This, of course, will also be affected by the capacity difference between the lowest and the highest, but in any case, it will be fairly consistent. When the cells start getting out-of-balance, this difference in time starts to grow.
Also, as all the cells start to get full, the throttling PWM duty cycle will be low, so the LED will be mostly green. If it's not, you know you need more balance time. The timer has six selectable settings, from 30 seconds to 4 hours. If 4 hours is not enough, this can be doubled, or quadrupled, with a single resistor change.
-- Gary
The timer is just for the balancing stage though, right? I certainly hope I don't need four hours! 
As a suggestion, which is probably too late now, could this thread be split up in to the various revision levels? It would certainly help finding with finding info, and questions relating to particular models could be asked in the appropriate thread. I read the complete thing from start to finish when I first started looking at this BMS, and then dropped it for a while. Now I'm lost with all the improvements you've made. I guess I'll just have to see if I can figure out where I left off and start reading again.
Regardless, I'm looking forward to getting my hands on one of these!
As a suggestion, which is probably too late now, could this thread be split up in to the various revision levels? It would certainly help finding with finding info, and questions relating to particular models could be asked in the appropriate thread. I read the complete thing from start to finish when I first started looking at this BMS, and then dropped it for a while. Now I'm lost with all the improvements you've made.
I guess I'll just have to see if I can figure out where I left off and start reading again.Regardless, I'm looking forward to getting my hands on one of these!
DaveAK said:The timer is just for the balancing stage though, right? I certainly hope I don't need four hours!
As a suggestion, which is probably too late now, could this thread be split up in to the various revision levels? It would certainly help finding with finding info, and questions relating to particular models could be asked in the appropriate thread. I read the complete thing from start to finish when I first started looking at this BMS, and then dropped it for a while. Now I'm lost with all the improvements you've made.
Regardless, I'm looking forward to getting my hands on one of these!
Yes, we plan to start a new thread for the ver.4 stuff. You should get a prize for reading this entire thread!
I'd also like to create references for the older versions. It's on the to-do list.
GGoodrum
1 MW
DaveAK said:The timer is just for the balancing stage though, right? I certainly hope I don't need four hours!
Yes, the timer only starts when the first cell hits the CV point.
battman
1 W
GGoodrum said:So, what I have decided to do, in order to save my brain, and to not delay this any further, is to back down on the requirements, just a tad, and simplify the design a bit. I cut out the tricky current measuring logic completely. There won't be a 3rd wire required, but there will now be a very simple "start" pushbutton, to get things going. You press it once, and off it goes.
-- Gary
What advantage does the pushbutton solution have over the 3rd wire solution?
GGoodrum
1 MW
battman said:
The only real advantage is there is only a simple two-wire connection required between the charger/supply, and the board. With the old boards, a separate wire, for the control logic's ground connection, that had to be connected to the charger/supply ground, only when it was actually connected. The new board uses an SCR to control whether or not the 12V regulator section is powered. The "Start" button energizes gate of the SCR, which latches it on. The timer portion of the circuit pulls the SCR gate to ground, which cuts off the 12V.
I finished testing the changes last night, and put in the order for boards this morning. I will have them by Friday morning, which is when I will make them available. Between now and then, I will update the website, and figure out the costs. Please don't ask the price yet, as I don't know yet. The PCB-only price will be "similar" to the previous versions. If I had to guess, I'd say it will be $20-$25 per 6s section, or control board. There will be options for one control board, plus either two, three, four or five 6s sections.You will also be able to order a single control board, and or a single 6s section.
I think we now have a fairly simple fan solution, for the "boxed" version of the BMS.. Basically, each 6s section powers one fan, via a 100 ohm resistor. A FET, tied through an opto, will control whether or not the fan is on. All the opto drivers will be tied to the 12V regulator, so that when the charger/supply is connected, and the 12V supply is on, the fans will all run. This way, the fan load is distributed through all the cells, and the 12V regulator power requirement can be kept low, to logic levels. In any case, the order I submitted today includes all the various end plates required for 12s, 16/18s, 24s and 30s boxed variants. The control bards and 6s sections are identical, whether they go inside boxes, if they are used in a stacked configuration.
I also need to do the BOMs, and new build/test instructions, which I will try and do in the next couple days. For the first time, I will also offer completely assembled and tested versions (boxed or stacked...), as will Andy Hecker (via his site at Rechargeable Lithium Power..., but these will be custom, and on a case-by-case basis.
As soon as I get some new pictures done, I'll start a new thread, and finally retire this one.
-- Gary
I will want mine to do a 26 cell pack. I've been told that I could use a 30 cell BMS and simply hook the 4 extra channels to four of the cells, effectively double monitoring them. I think this was based on an earlier version though that needed populated channels to be hooked up, so does this still hold true? Or to put it another way, how should we configure these for packs that don't fall in multiples of 6?
GGoodrum
1 MW
DaveAK said:
This time the sections are completely independent, with no connections between boards and the only connection to the control board is the two-wire opto "bus". That means you can populate the boards with as few, or as many channels as you like. For instance, for a "special" motorcycle application Andy and I are working on, the requirement is for 25 channels, so what we are using are five boards, each with 5 channels populated.
Kingfish
100 MW
ejonesss, do you mean this?
http://www.rechargeablelithiumpower.com/oscommerce2/catalog/bms-version-40-p-56.html
:wink:
~KF
Icewrench
10 kW
Gary sells stuff from tp packs http://www.tppacks.com/products.asp?cat=26
Re cahrgeable Is Andy and he builds up the boards
Re cahrgeable Is Andy and he builds up the boards
Kingfish
100 MW
I'd sure like to get my hands on a few of those 3p/4p JST-XH Balance Plug Adapters - but they are out of stock :?
Anyone else domestically sell something like this? I posed the question at the local hobby stores and they just look at me like I'm daft (which is true but that's beside the point)
~KF
methods
1 GW
Kingfish said:
It is fairly trivial to make those - I make them all the time.
The JST-XH-7 90 degree board connectors stack perfectly on each other.
Mate that with a cut down Hobby City extension cable and there you have it.
I don't feel bad moving in on Gary's action here because I am fairly confident I gave him the idea - I was making these over a year ago with Radio-shack perf boards.
$20 each for any size up to 6:1
Minimum purchase of 2
$5 flat rate shipping anywhere in the US
$12 flat rate world wide
PM for details
Here is a picture of one I just took out in my car. No PCB needed. Just skill with a razor.
In the spirit of NOT trying to make money off of people -> Here are the direct links to the materials used for the build.
Dont like people profiteering? Make one yourself :wink:
JST-XH-7 90 degree
JST-XH-7 Straight
JST-XH-7 Extension
I would much prefer that people help themselves to a good deal
Those who cant, are too lazy, or just have money to burn? Send your cash to me 8)
At $20 each I will be rich in no time.
To be fair - it actually takes a soft touch - get the pins too hot and they melt out of the plastic housing.
Make a cold solder joint - lose a cell
Then there is the trick of insulating the back side. Too much glue? foul the connectors.
I tape the back of mine with kapton tape - but I suppose if I were going to make 10 I could epoxy them.
It just so happens that I just ordered 40 more of those extension cables and I have over 100 board mounts connectors on hand.
Better get on it Gary
I dont want to waste my time making these - so you better!
How about Andy - he should be able to knock these out in about 1 minute each with PCB's
-methods
GGoodrum
1 MW
Get rich on building adapters?? You need to dial down the dosage on your meds.
They're a pain to make, and not worth the trouble, in my mind, but I do have some new ones I will make available with the new BMS units. One thing we've found with the new system is that with higher shunt currents, there's too much voltage drop in the standard JST-XH extension cables/pigtails, and that causes a shift in the set points for the shunts and the HVC throttling. The new adapters will have pads for a larger Molex Micro-Fit 3.0 connectors. The same connectors are on the BMS shunt boards. I then use cables with matching plugs on each end, which use 18-gauge wire.
-- Gary
They're a pain to make, and not worth the trouble, in my mind, but I do have some new ones I will make available with the new BMS units. One thing we've found with the new system is that with higher shunt currents, there's too much voltage drop in the standard JST-XH extension cables/pigtails, and that causes a shift in the set points for the shunts and the HVC throttling. The new adapters will have pads for a larger Molex Micro-Fit 3.0 connectors. The same connectors are on the BMS shunt boards. I then use cables with matching plugs on each end, which use 18-gauge wire.
-- Gary
methods
1 GW
I dont want to salt anybodies game - but you should probably raise the price on those a little because I agree - it is time consuming to put those together. I think it is better to have them "expensive but available" than not available at all. I was half joking about $20 prices but I dont think $15 would be out of line if you took your time to build them. Please do! Because I really dont want to
As far as cabling losses ->
I would suggest a 4 wire measurement. (first hit on Google for those who are not familiar)
Each 6S module would have two JST-XH-7 connectors
One connection ties to the battery for the actual balancing current
The second ties into the battery to measure the voltages right at the tap
This eliminates all losses in the cabling and will work for any balance current - 1A, 2A, 10A
To facilitate the double connection at the battery I would use a single JST-XH-7P in one of your PCB boards with a pair of pigtails extending off of it.
One pigtail goes to the balance port
One pigtail goes to the measurement port
Stepping to a larger gauge wire and heavier connector will solve the problem for 1A balance current but it wont scale if you decide to build larger scale units with higher balance currents.
-methods
As far as cabling losses ->
I would suggest a 4 wire measurement. (first hit on Google for those who are not familiar)
Each 6S module would have two JST-XH-7 connectors
One connection ties to the battery for the actual balancing current
The second ties into the battery to measure the voltages right at the tap
This eliminates all losses in the cabling and will work for any balance current - 1A, 2A, 10A
To facilitate the double connection at the battery I would use a single JST-XH-7P in one of your PCB boards with a pair of pigtails extending off of it.
One pigtail goes to the balance port
One pigtail goes to the measurement port
Stepping to a larger gauge wire and heavier connector will solve the problem for 1A balance current but it wont scale if you decide to build larger scale units with higher balance currents.
-methods
mwkeefer
1 MW
Gary - it's not the meds... it's the Meth = )_
Methods - I love the high voltage yellow wrap tape around your breakout boards... that's a nice touch (I assume needed with the voltages your running to prevent arching?).
The break out boards are convenient for newbies and for a cleaner final product (sometimes) but... I have noticed some issues (not just Gary's, even my own home built adapters) with connectivity between parallel packs. This will not likely be an issue with Gary's balance boards since you won't be connecting and disconnecting them all the time like you do with normal turnigy balance adapters (I can't remember the plug name and I'm too lazy to scroll up).
I have migrated to soldered in BMS lines (I still have plugs, but not in use) for my HVC/LVC and Balancers - This gives me the absolute most accurate measurements (tested and confirmed).
One little tidbit: I have repaired many a balance line and only recently figured out that when I repair one pack (replace the balance wires / plug) I have to repair all the packs which make up the battery or the impedance is different for the repaired pack and that throws the voltage readings out of whackon the balancer. It's not bad, 20-25mv but it's beyond tolerances... Once I fixed the remaining 2 5S packs (this was a 15S1P 5AH battery) by replacing their balance leads with the same type I used for the first pack... the full 15S battery charged to within 7mv (within tolerance of 10mv). I confirmed this with cell log 8s, my high end (and still crap) radio shack digitals and also with the local repair shops fluke meter (large benchtop model).
Regards,
Mike
PS: Gary, when can I place an order for a 18S - 20S BMS and can I use that same BMS with packs from 15S to 20S? Meaning can I use a single BMS for evaluation and planning before ordering one for each of my builds (were up to 4 now btw).
Methods - I love the high voltage yellow wrap tape around your breakout boards... that's a nice touch (I assume needed with the voltages your running to prevent arching?).
The break out boards are convenient for newbies and for a cleaner final product (sometimes) but... I have noticed some issues (not just Gary's, even my own home built adapters) with connectivity between parallel packs. This will not likely be an issue with Gary's balance boards since you won't be connecting and disconnecting them all the time like you do with normal turnigy balance adapters (I can't remember the plug name and I'm too lazy to scroll up).
I have migrated to soldered in BMS lines (I still have plugs, but not in use) for my HVC/LVC and Balancers - This gives me the absolute most accurate measurements (tested and confirmed).
One little tidbit: I have repaired many a balance line and only recently figured out that when I repair one pack (replace the balance wires / plug) I have to repair all the packs which make up the battery or the impedance is different for the repaired pack and that throws the voltage readings out of whackon the balancer. It's not bad, 20-25mv but it's beyond tolerances... Once I fixed the remaining 2 5S packs (this was a 15S1P 5AH battery) by replacing their balance leads with the same type I used for the first pack... the full 15S battery charged to within 7mv (within tolerance of 10mv). I confirmed this with cell log 8s, my high end (and still crap) radio shack digitals and also with the local repair shops fluke meter (large benchtop model).
Regards,
Mike
PS: Gary, when can I place an order for a 18S - 20S BMS and can I use that same BMS with packs from 15S to 20S? Meaning can I use a single BMS for evaluation and planning before ordering one for each of my builds (were up to 4 now btw).
GGoodrum
1 MW
Okay, we're getting close. The boards are here, but I haven't don BOMs or instructions yet. Andy, Richard and I still have some divider and cap value changes we're sorting out today, trying to optimize both for LiFePO4 and for LiPo setups.
The new layout has separate traces on the shunt boards for the LM431 dividers, and I've tested the latest solution with 1.5A shunts and 45 cm long 18-gauge wires, and there's no issue.
Another reason for the switch to a larger, more robust connector, is the JSTs don't like being plugged, and unplugged, all the time. These have a positive connection, with a retaining clip.
I'm getting some cables made, so I don't have to spend every waking moment with a $500 crimper.
-- Gary
The new layout has separate traces on the shunt boards for the LM431 dividers, and I've tested the latest solution with 1.5A shunts and 45 cm long 18-gauge wires, and there's no issue.
Another reason for the switch to a larger, more robust connector, is the JSTs don't like being plugged, and unplugged, all the time. These have a positive connection, with a retaining clip.
I'm getting some cables made, so I don't have to spend every waking moment with a $500 crimper.
-- Gary
methods
1 GW
GGoodrum said:
I agree on that account. What JST is missing is a board mount version of the socket end. Then we could build little sacrificial extension connectors.
(female on one side, male on the other for the sole purpose of preserving the "important" connectors on the battery. They take the brunt)
I will be interested to see how it goes with farming out the cables. I dont imagine these are very delicate or complex so it should go real smooth.
I have had some real nightmares with outside cable vendors but they usually revolved around cables with 200 x 30gauge conductors with no strain relief.
-methods
AndyH
10 kW
GGoodrum said:I'm getting some cables made, so I don't have to spend every waking moment with a $500 crimper.
-- Gary
AMEN! I was finally getting comfortable with my crimper and the Molex Mini-fit/Val-U-Lok pins - but my magnifier and current crimpers aren't yet up to the Molex micro-fit pins.
Andy
dammit. Used to read in the dark. Now I need a ceiling full of fluorescents to see these blasted pins. :wink:
GGoodrum
1 MW
UPDATE...
Unfortunately, the news is not good. the new boards I just got are not usable. Well, it is the 6s shunt board sections that aren't going to be usable. In the latest round of changes, we had switched around how the LED gets lit, so that it will also light when the LVC trips. Part of the problem is that this won't work with LiFePO4 setups, using the 2.1V versions of the TC54 detectors. The bigger issue, however, is that with this scheme, it screws up the opto operation with the HVC/throttling logic, by not reacting "crisply" enough for the PWM-based throttling circuit. I didn't discover this until I tried the new layout with actual cells connected. The net effect is that it reduces the current a lot more than it has to in order to keep the cell voltage at the set point.
Anyway, I need to go back one generation, to what works well, and forget the idea about lighting the LEDs for LVC trips. I will have to turn in another run of boards on Monday, which means I won't have them ready to go before Thursday/Friday.
The new control sections work great, however, so all is not lost. I will also be able to use these shunt boards, populated with just the shunt circuits themselves, in the standalone external balancers I'm working on, in a parallel effort, for use with the CellLog-based setup, shown below:
The CellLog units connect into a PCB that has an opto-coupled buffer for the alarm outputs of each CellLog unit. This keeps each of the alarm outputs isolated, which they need to be as each is referenced to the cell 1 ground connection for its pack.The opto outputs are all ganged together, like they are in the BMS, and sent to the control board, which is identical to the latest ones used with the full BMS. The CellLogs have been programmed to have the "HVC" alarm point at 4.15V. The control board uses this signal to make sure no cell can go over this point, using the same PWM-based "throttling" circuit. The shunt circuits are completely separate, in their own box, and only get plugged in when the balancing is actually required. The box shown, when completed, will hold four 6s shunt boards, which are also set to be fully on at 4.15V. The box has four fans, two at each end.
Right now, like I said, this is a parallel, lower priority effort, but one that will be great for those already using, or contemplating using, the nifty little CellLog units. I'm not sure how these will be packaged, but I may end up combining the control board onto the interface/opto board the CellLog units are attached to, so that only one board is required. Also, since these units can do 8s, I'm going to do the connections in a way that two CellLog units can be used with 12s or 16s, and three can be used with either 18s or 24s, using jumper blocks. I need the latter for my own setups, which are either 18s or 24s.
-- Gary
Unfortunately, the news is not good. the new boards I just got are not usable. Well, it is the 6s shunt board sections that aren't going to be usable. In the latest round of changes, we had switched around how the LED gets lit, so that it will also light when the LVC trips. Part of the problem is that this won't work with LiFePO4 setups, using the 2.1V versions of the TC54 detectors. The bigger issue, however, is that with this scheme, it screws up the opto operation with the HVC/throttling logic, by not reacting "crisply" enough for the PWM-based throttling circuit. I didn't discover this until I tried the new layout with actual cells connected. The net effect is that it reduces the current a lot more than it has to in order to keep the cell voltage at the set point.
Anyway, I need to go back one generation, to what works well, and forget the idea about lighting the LEDs for LVC trips. I will have to turn in another run of boards on Monday, which means I won't have them ready to go before Thursday/Friday.
The new control sections work great, however, so all is not lost.
I will also be able to use these shunt boards, populated with just the shunt circuits themselves, in the standalone external balancers I'm working on, in a parallel effort, for use with the CellLog-based setup, shown below:The CellLog units connect into a PCB that has an opto-coupled buffer for the alarm outputs of each CellLog unit. This keeps each of the alarm outputs isolated, which they need to be as each is referenced to the cell 1 ground connection for its pack.The opto outputs are all ganged together, like they are in the BMS, and sent to the control board, which is identical to the latest ones used with the full BMS. The CellLogs have been programmed to have the "HVC" alarm point at 4.15V. The control board uses this signal to make sure no cell can go over this point, using the same PWM-based "throttling" circuit. The shunt circuits are completely separate, in their own box, and only get plugged in when the balancing is actually required. The box shown, when completed, will hold four 6s shunt boards, which are also set to be fully on at 4.15V. The box has four fans, two at each end.
Right now, like I said, this is a parallel, lower priority effort, but one that will be great for those already using, or contemplating using, the nifty little CellLog units. I'm not sure how these will be packaged, but I may end up combining the control board onto the interface/opto board the CellLog units are attached to, so that only one board is required. Also, since these units can do 8s, I'm going to do the connections in a way that two CellLog units can be used with 12s or 16s, and three can be used with either 18s or 24s, using jumper blocks. I need the latter for my own setups, which are either 18s or 24s.
-- Gary
i think it is better off to not light the leds on lvc since.
1. you would not see them on the ride.
2. even if the panel was up where you could see them it would do no good anyways since the lvc trips on and off so fast you probably wouldnt see them.
leds are better for balancing and charge indicator.
leds on discharge may be ok in a case if you could have a second tc54 set up to trip before the discharge curve goes down hill so you may be able to know before the lvc trips.
1. you would not see them on the ride.
2. even if the panel was up where you could see them it would do no good anyways since the lvc trips on and off so fast you probably wouldnt see them.
leds are better for balancing and charge indicator.
leds on discharge may be ok in a case if you could have a second tc54 set up to trip before the discharge curve goes down hill so you may be able to know before the lvc trips.
GGoodrum said:
The idea is by having the LED light up for LVC is you can identify a weak or bad cell without having to measure each cell's voltage. For those that don't want to tie the LVC into the throttle, it would be quite easy to wire up a 12v piezo alarm that could be mounted remotely (where you can hear it).
This whole project has me pulling my hair out. Individually, the sections of the circuit behave, but when tied together, all kinds of unexpected things happen. We are zeroing in on the remaining issues, however, and I am confident that everything can be sorted out eventually. It's just taking a lot longer than anyone wants.
This whole project has me pulling my hair out. Individually, the sections of the circuit behave, but when tied together, all kinds of unexpected things happen. We are zeroing in on the remaining issues, however, and I am confident that everything can be sorted out eventually. It's just taking a lot longer than anyone wants.
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