KS 14 Battery Configuration

[OliverH]

On 17.1.2016 at 5:57 PM, zlymex said:

IMO, disadvantage the KS-18A:
----bulky
----small pedals
----prone to overheat owning to the main-board is complete sealed in the top compartment while the heat-sink of a MSuper2 is exposed to the wheel.
----three battery packs connected in series(not in parallel).

Coming back to this issue. Need to know if the KS18 can be wiped from my favourite list. Are the batteries connected in series while charging (BMS) only or are they in general in series? I thought they had parallel packs. I never opened one.

I'm a heavy rider so I need power from a dual battery pack. As I rode a KS18-500 only up to now I can't do a real incline test as it's not strong enough for me to be pushed like a MSuper.

[zlymex]

4 hours ago, OliverH said:

Are the batteries connected in series while charging (BMS) only or are they in general in series? I thought they had parallel packs. I never opened one.

There are three packs in the KS-18A I opened, the charger charge the first 340Wh pack, the output goes to the charge input of the second 340Wh pack, and the output of this pack connected to the charge input of the 680Wh pack. The output of the 680Wh pack goes into the mainboard. The output of all these three packs are all 67.2V max. I opened the shrink wrap of the 680Wh pack as well, there are 64 Panasonic NCR18650PF cells in 16s4p connection.

[Cloud]

10 hours ago, NeprisFin said:

I'm glad you guys brought daylight to the kingsongs serial connected batteries issue. I'm going to buy my EUC tomorrow. My first EUC will be 18" Gotway Msuper (unless someone turns my head within these few hours before I click the "confirm" button.

My current decision is based on the overheating issue and the serial connected batteries issue. Top of that I'm worried how king song can handle the moisture and below zero temperatures.

Overheating may have been resolved.  I know its no longer a problem for my 14" and may have been resolved for 18" as well but im not sure

i rode it in slightly below zero temps and it was fine. Regarding moisture - no unicycle should be ridden in the rain, but in a very light rain my 14" was fine for almost an hour

[Mistagear]

11 hours ago, NeprisFin said:

I'm glad you guys brought daylight to the kingsongs serial connected batteries issue. I'm going to buy my EUC tomorrow. My first EUC will be 18" Gotway Msuper (unless someone turns my head within these few hours before I click the "confirm" button.

My current decision is based on the overheating issue and the serial connected batteries issue. Top of that I'm worried how king song can handle the moisture and below zero temperatures.

Are you sure some posters do not have a vested interest in degrading one brand over another ? Not everyone has experienced problems mentioned, I find that curious, why?

[Cloud]

On 18 января 2016 г. at 9:12 PM, zlymex said:

I thought too that all packs are better in parallel, simultaneously charging & discharging. I was very surprised to see the actual connections which not only gives less output current but also problematic when charging(charging happens during riding). As a matter of fact, the unit I opened for repair was damaged in the charging circuit of the third pack. Also, it won't allow fast charging like I charge my MSuper2 with a 5A charger.

I may be saying something completely stupid, but it seems to me that just because the output of one pack visibly goes to the other battery and the output of the second goes to third and third to the control board, doesnt mean the battery packs are in series.how do we know that inside the shrink wrap the first pack is not connected all the way to the output of the 2nd and 3rd and hence to the control board? 

For exampke here is the picture of the 2 battery pack connections in my 14" kingsong. It appears that the packs are in series but how do we know the output of the 1st pack is not also connected to the output of the 2nd pack? Wouldnt they be in paralel in that case? I took the voltage of each battery and it was 53 ( they were pretty drained) . When connected together the output voltage was also 53. If the packs were in series wouldnt the voltage be twice that?

anyway, i may be talking complete nonsense, forgive me for being ignorant.

 

[zlymex]

1 hour ago, Cloud said:

Wouldnt they be in paralel in that case?

Firstly, the series connection of packs is different than series connection of cells, may be I could use another term but I did not find any that time.

Parallel connection of packs meaning all the output wires of the packs tie together and the input(charge) wires tie together too. In this connection, the max. output current is the sum of all the packs allowing heavy current use and with less internal resistance(including wire resistance) and less voltage drop. Also, it allows bigger charge current to reduce charge time with(say) 5A charger.

[Cloud]

4 minutes ago, zlymex said:

Firstly, the series connection of packs is different than series connection of cells, may be I could use another term but I did not find any that time.

Parallel connection of packs meaning all the output wires of the packs tie together and the input(charge) wires tie together too. In this connection, the max. output current is the sum of all the packs allowing heavy current use and with less internal resistance(including wire resistance) and less voltage drop. Also, it allows bigger charge current to reduce charge time with(say) 5A charger.

So how do you know that in this case all output wires of the packs are not tied together inside the shrink wrap? And same for input wires?

arent the output and input wires ultimately going to the same 2 contacts ( plus and minus) of the battery ( pack of batteries)? Dont you charge the battery by connecting to its plus and minus, and same for discharge?

[zlymex]

48 minutes ago, Cloud said:

So how do you know that in this case all output wires of the packs are not tied together inside the shrink wrap? And same for input wires?

arent the output and input wires ultimately going to the same 2 contacts ( plus and minus) of the battery ( pack of batteries)? Dont you charge the battery by connecting to its plus and minus, and same for discharge?

Because I opened the shrink wrap. Charge wires are thin and not connected to the output wires directly.

Edit: 
True there exist packs with only one pair of wires for input and output(what is called? In Chinese it called 同口, direct translate to 'same port'), the BMS are more expensive and difficult to make for large current. Photo below is the BMS of the 64 cell pack of the KS-18A

[OliverH]

4 hours ago, Mistagear said:

Are you sure some posters do not have a vested interest in degrading one brand over another ? Not everyone has experienced problems mentioned, I find that curious, why?

I had both the MSuper and the KS18 on my list. As I'm a heavy driver I know what a good battery capacity means for me riding inclines. I've no financial interest in this companies. I like to buy the best EU for my requirements. That's all about.

[OliverH]

1 hour ago, zlymex said:

Because I opened the shrink wrap. Charge wires are thin and not connected to the output wires directly.

Edit: 
True there exist packs with only one pair of wires for input and output(what is called? In Chinese it called 同口, direct translate to 'same port'), the BMS are more expensive and difficult to make for large current. Photo below is the BMS of the 64 cell pack of the KS-18A

Only to make sure I understand all correct. If I would buy a 13xx Wh KS18. Do I've the full capacity minus the resistance drops which is how much? Only to name it. I'm not limited to 680 Wh of the first battery pack? Is there any disadvantage of BMS cut off?

The other downside is not be able to use a high Amp charger (modifying the EU anyway regardless which EU). The KS 

Charging type serial connection vs. parallel connection. There's again the resistance issue? So we've a less efficient charging? Charging of both connections types takes the same time if using the same charger to compare it 1 to 1?

[zlymex]

2 hours ago, OliverH said:

Only to make sure I understand all correct. If I would buy a 13xx Wh KS18. Do I've the full capacity minus the resistance drops which is how much? Only to name it. I'm not limited to 680 Wh of the first battery pack? Is there any disadvantage of BMS cut off?

The other downside is not be able to use a high Amp charger (modifying the EU anyway regardless which EU). The KS 

Charging type serial connection vs. parallel connection. There's again the resistance issue? So we've a less efficient charging? Charging of both connections types takes the same time if using the same charger to compare it 1 to 1?

1. I guess you will get near full capacity. When the last pack(64 cells, used directly by the mainboard) is finished, the 2nd especially the 1st pack still have something left because it takes voltage difference to be able to charge. The difference of the voltage drop may be 0.5V to 1V each depending how fast the 3rd pack is drained.

2. There is no output protection circuitry in the 680Wh pack except that there is a car fuse of unidentified color code in series with the output wire. I think this type of protection is very good and I use the fuse method for several of my battery packs before. From the thickness of the fuse wire, the closest match is 20A but the color of my 20A fuse is yellow.

3.  Because of the series connection of charge path, the max. charge current is limit to the max. charge current of each BMS(or the min. of all the max.). Further more, the limit may be even slightly lower than that because it cannot guarantee that those three consecutive charge current are all the same. It may be the case that all three BMS allow 5A charge current, this will make much worse if charge 5A for real owing to more voltage lags making both less efficient and prolong charging time. Also, when this 5A charger connect to charge the EUC at first, large part of the current will goes into the first pack, it will exceed the standard charge current per cell(1350mA in the case of Panasonic PF cells, 2.7A for 340Wh pack). While in parallel connection, the charging current is shared, voltage are the same, charge end at the same time and sooner. I know a guy who rode >200km a day, charges his modified GW18(>2000Wh) with 8A charger(two 4A in parallel).

4. The reason I opened the shrink wrap of the last pack(680Wh pack) is the damaged charge circuitry. I don't know exactly what happened but the best guess is too large charge current from the 2nd pack which clearly can produce much larger current than the 680Wh charge port can withstand. It simply weird enough having a thick-wire-ended-plug(from the discharge port) connect to the thin-wire-ended-plug(to the charge port)

5. The series connection of pack does exist in other cases, as people often use external battery pack connected to the charge port of the EUC to increase riding range. However, this series connection only takes place during discharge and takes place only once, the external battery pack usually small in capacity compare to internal making the issue less significant.

[OliverH]

6 hours ago, zlymex said:

Because I opened the shrink wrap. Charge wires are thin and not connected to the output wires directly.

Edit: 
True there exist packs with only one pair of wires for input and output(what is called? In Chinese it called 同口, direct translate to 'same port'), the BMS are more expensive and difficult to make for large current. Photo below is the BMS of the 64 cell pack of the KS-18A

Just realised the fuse That's autimotive stuff. It's close to the source, but a plug would be better or something like a recoverable thermostuff. Looking on the some solder points I think I'm not so bad in soldering.

[zlymex]

7 minutes ago, OliverH said:

Just realised the fuse That's autimotive stuff. It's close to the source, but a plug would be better or something like a recoverable thermostuff. Looking on the some solder points I think I'm not so bad in soldering.

I believe the fuse is a later add-on. There are no proper solder pads for it and the fuse make the pack thicker as it standout as the highest point on the shrink wrap surface. As for recoverable thermostuff, I saw them being used in external battery packs which only produce small current much lower than an EUC requires. If it does exist a 70V, 20A recoverable fuse, it must be bulky, pricey, and most of all, very slow to respond.

[dmethvin]

12 hours ago, Cloud said:

For example here is the picture of the 2 battery pack connections in my 14" kingsong. It appears that the packs are in series but how do we know the output of the 1st pack is not also connected to the output of the 2nd pack? Wouldnt they be in paralel in that case? I took the voltage of each battery and it was 53 ( they were pretty drained) . When connected together the output voltage was also 53. If the packs were in series wouldnt the voltage be twice that?

I'm very interested in this picture. If the size of the wires is any indication, it appears that these packs are wired in parallel using the charge lines of the left pack! So during charging, the right pack is connected to the external charge port and as it gains voltage it also charges the left pack via those charging lines. The two batteries are roughly at the same voltage while charging so the left-pack charge wire in the center does not have a lot of current going through it at the time, about half of whatever is being supplied by the charger.

While you're riding, the left pack is connected to the motor, the right pack supplies charge as the voltage drops on the left pack. Again, the two batteries stay at about the same voltage during discharge. I would think you could still get high current draws at times, especially during acceleration, and the charge lines aren't really designed for that. But the King Song people seem to know what they're doing so it's hard for me to argue. Maybe the BMS takes some of this into account and limits charge current.

The alternative for combining battery packs, and the one I had considered for my Firewheel, was to parallel the thick output wires. The drawback to that is if one battery pack is a bit weaker than another you are bypassing the BMS protections since the weaker battery will be force-charged through the parallel connection. I also don't know how that setup may affect the cell balancing function.

I feel like we've drifted way off the original topic, would anyone mind if I split these last few posts into a new topic named "King Song 14 battery configuration"? (EDIT: Done)

[dmethvin]

2 hours ago, zlymex said:

I believe the fuse is a later add-on. There are no proper solder pads for it and the fuse make the pack thicker as it standout as the highest point on the shrink wrap surface. As for recoverable thermostuff, I saw them being used in external battery packs which only produce small current much lower than an EUC requires. If it does exist a 70V, 20A recoverable fuse, it must be bulky, pricey, and most of all, very slow to respond.

I think it was @Jason McNeil who said they're using a 40A fuse there, it appears to be an automotive-style fuse. It's beyond the voltage rating of those fuses but probably not an issue. If it blew you'd need to solder a new one in, but if you blow a 40A fuse there was something else wrong anyway.

[Jason McNeil]

46 minutes ago, dmethvin said:

 I would think you could still get high current draws at times, especially during acceleration, and the charge lines aren't really designed for that. But the King Song people seem to know what they're doing so it's hard for me to argue. Maybe the BMS takes some of this into account and limits charge current.

This picture is of the Gen 1 design, in later builds, the higher gauge wiring is used across the battery packs.

It's a very good observation you raise in exactly how the packs are wired up: whether there's some sort of serialization going on in the BMS, or during use there exists a bypass function/wiring to the control-board for these larger currents. Having massive currents surging through the input charge side of the pack on the left would be pretty bad for cell longevity.   

.

[OliverH]

The first battery close to the PCB will be drained most and act as a buffer? Is the KS battery design a real parallel design or a piggy back design?

I heard more than one time that the GW MSuper has not a real full fledged BMS. Can't remember what was the reason of this statement.

@dmethvin good idea to split the thread. But it's not only focused on KS. KS and GW is used to discuss different designs. I like this. IMHO this could be relevant in some special occasions and it would be good to know which EU has what kind if design implemented.

[dmethvin]

1 hour ago, OliverH said:

The first battery close to the PCB will be drained most and act as a buffer? Is the KS battery design a real parallel design or a piggy back design?

It's a piggyback as if the second battery was connected to the external charge port. The left battery would be drained, but constantly recharged by the right battery so that the two batteries would stay roughly in equilibrium. During regen braking the left battery only would be charged, and its voltage would go up so the right battery would stop charging until the left battery was discharged below the voltage of the right battery.

There are a bunch of engineering and design tradeoffs happening here so appreciate the dilemma. Separate packs connected piggyback mean that you can use, for example, two pre-built 340Wh packs to make a 680Wh unicycle rather than a custom 680Wh pack. If you did build a custom 680Wh pack you'd need to either find a different BMS with twice the number of balance lines, or double the number of cells put in parallel on each balance line. Either of those would be a mess to shoehorn into an EUC shell when they are on separate sides of the shell and you would need all those balance lines strung between the two lumps of cells. With the piggyback setup you just need two wires to connect the two packs together. 

The most significant downside is that during heavy power draws the behavior of a 680Wh pack is probably closer to a 340Wh pack as far as effective internal resistance is concerned, the charge port isn't designed to deliver a lot of power instantaneously. I don't know if that's a problem in practice though.

Overall it seems like a nice solution. Knowing that KS does this I am inclined to do it when I add a second 260Wh pack to my Firewheel F260 because it's probably the safest and least hassle approach.

[Keith]

1 hour ago, dmethvin said:

There are a bunch of engineering and design tradeoffs happening here so appreciate the dilemma. Separate packs connected piggyback mean that you can use, for example, two pre-built 340Wh packs to make a 680Wh unicycle rather than a custom 680Wh pack. 

But surely there is absolutely no benefit, physical or electrical, in doing it this way rather than simply having a Y-lead connection on the power side and another Y-lead connection on the charging side? Both packs would charge in parallel and discharge in parallel reducing the current demand from each pack.

It leaves me wondering if the charge and discharge connections actually terminate in the same place on the KS BMS boards so, to all intents two packs are actually parallel connected? That would be possible if the BMS is only being used to keep the individual cells in balance.

[dmethvin]

52 minutes ago, Keith said:

But surely there is absolutely no benefit, physical or electrical, in doing it this way rather than simply having a Y-lead connection on the power side and another Y-lead connection on the charging side? Both packs would charge in parallel and discharge in parallel reducing the current demand from each pack.

It leaves me wondering if the charge and discharge connections actually terminate in the same place on the KS BMS boards so, to all intents two packs are actually parallel connected? That would be possible if the BMS is only being used to keep the individual cells in balance.

I had considered doing a parallel connection with the charge and discharge lines on two packs with separate BMS, but that has potentially very bad effects and I can't see them ever shipping that way from the factory. The charge lines are usually diode protected so that current only flows one way, and they are connected to the BMS which then controls and monitors how individual cells are charged. It makes sure that no particular cell (or group of cells) is overcharged, and will try to charge them all to the same level. So paralleling charge lines wouldn't be a problem.

The result of all the 16-in-series-X-in-parallel stacked cells shows up on the discharge lines as 60-ish volts, protected by MOSFETS, fuses, or by nothing if they've been shunted with a wire. So if you have two packs with outputs in parallel the pack that has a higher charge will force voltage back into the weaker pack and some cell will have to take it. The weaker BMS can even stop trying to charge or balance altogether but it doesn't matter because the voltage will continue to sneak into the weak pack from the strong one via the output lines.

When both packs are nice and healthy that may not be a problem, but as the cells age or if one goes bad there's the potential for one of the cells to be overcharged and explode.

[Keith]

2 hours ago, dmethvin said:

So if you have two packs with outputs in parallel the pack that has a higher charge will force voltage back into the weaker pack and some cell will have to take it.

Sorry, but providing the packs are at a similar charge when first connected that cannot happen.

The two packs must remain at the same voltage, and therefore same state of charge because they are connected in parallel. If a cell gets weak, it doesn't "leak" voltage, it's voltage simply drops at a higher rate as its capacity has reduced. As soon as one pack starts to loss voltage faster than the other, then it delivers less current and more is drawn from the other pack, I.e. both packs' voltages will remain the same at all times, current draw will not necessarily be equal if one pack is weaker than the other. The opposite will happen during charging, a weaker pack's voltage will try to rise faster, but cannot, instead more charge current will flow to the higher capacity pack. Current will never significantly flow between packs if they are permanently connected in parallel except when first connected if not at the same voltage.

Like a lot of model flyers I regularly fly a 12 LiPo cell helicopter. I do not own a charger capable of more than 6 cells So I use two, 6 cell 5000mAh, in series to fly and I charge them in parallel at 10 Amps, even when the packs are getting older and some cells have lost capacity, there are no issues doing this. Our chargers monitor and display individual cell states, current and voltage in real time. Just in passing that is a flight pack of 222Wh and flights last 7 minutes. So these packs take a real beating compared with EUC packs!

[OliverH]

What I understand up to now.

Disadvantage:
OK Main battery (the buffer) will be drained under load and it will immediately charged by the piggypack battery pack 2,3,...,n? So the cells of the main battery would have more stress (heat)/ C.
you don't have the full capacity of all packs (e.g. 1360 Wh) only the main battery (680 Wh) for acceleration. The piggybacks only prevent the voltage drop of the main battery.

Advantage:
Scalability to add 1-n battery packs.

Can a heavy rider have a disadvantage (to much drain) on acceleration/ inclines? Is the overheat tiltback also a limitation of this battery setup. Is this "problem" theoretical or real (small/ medium limitation)? I ask from a buyers point of decision.

[dmethvin]

5 minutes ago, Keith said:

Sorry, but providing the packs are at a similar charge when first connected that cannot happen.

The two packs must remain at the same voltage, and therefore same state of charge because they are connected in parallel.

Maybe I'm understanding it wrong, but if charging a series set of Li-Ions could be done only through the discharge lines we wouldn't need a BMS. Basically I have been learning what I can by watching videos like this one (for an example see the 7 minute mark). Specific cells in a series pack may end up at different voltages. That's why the BMS tries to balance them by selectively charging cells that have lower voltages. Normally the BMS would never overcharge any specific cell to get the entire pack up to voltage. Once you start charging via the output there's no control over that--as you say, the two packs must be at the same potential, even if that ends up overcharging a cell in the process.

16 minutes ago, OliverH said:

Can a heavy rider have a disadvantage (to much drain) on acceleration/ inclines? Is the overheat tiltback also a limitation of this battery setup. Is this "problem" theoretical or real (small/ medium limitation)? I ask from a buyers point of decision.

A bigger battery with true parallel cells is going to be able to deliver higher instantaneous currents than a piggyback config. I don't know if anyone does that, @esaj do you know how the bigger Firewheels are set up? As for the overheat issue on KS, wasn't that determined to be overheating of the control board MOSFETs since they're in an enclosed space and not able to dissipate heat well? That would mean it's not battery related.

[OliverH]

3 minutes ago, dmethvin said:

Maybe I'm understanding it wrong, but if charging a series set of Li-Ions could be done only through the discharge lines we wouldn't need a BMS. Basically I have been learning what I can by watching videos like this one (for an example see the 7 minute mark). Specific cells in a series pack may end up at different voltages. That's why the BMS tries to balance them by selectively charging cells that have lower voltages. Normally the BMS would never overcharge any specific cell to get the entire pack up to voltage. Once you start charging via the output there's no control over that--as you say, the two packs must be at the same potential, even if that ends up overcharging a cell in the process.

A bigger battery with true parallel cells is going to be able to deliver higher instantaneous currents than a piggyback config. I don't know if anyone does that, @esaj do you know how the bigger Firewheels are set up? As for the overheat issue on KS, wasn't that determined to be overheating of the control board MOSFETs since they're in an enclosed space and not able to dissipate heat well? That would mean it's not battery related.

The Firewheel setup is strange. I think a F779 has two in series and in parallel with the other two packs if I remember right. To compare we've to look on a GW MSuper

[dmethvin]

Found the post @esaj made about the F779 pack, and it sounds like he's saying it has parallel packs with separate BMS like @Keith suggested? I'm not sure how the separate BMS manage to balance the cells for that case. Balancing doesn't kick in until the very end of the charge cycle and by then it's possible some cells could be over voltage.