battery upgrade Question for double battery build

[Jug]

Hello to everyone, i am new in euc and i have eightball zipwheel which i will sell very soon :-P

Ok here is the question for someone who knows about battery upgrade,

I ordered two of this BMS http://www.aliexpress.com/item/16S-15A-59-2V-li-ion-unicycle-BMS-PCM-battery-protection-board-bms-pcm-with-balancing/32414515852.html

and i have a LOT batteries samsung ICR18650-30B.

So my question is can i build (connect) 32 batteries on one of that BMS so i can have 2 x 32 battery pack?

If it is possible how do i need to connect second line of batteries on one BMS and how can i make all wiring correct to have both in parallel connection 

for charging and discharging?

Thanks  

[Keith]

Jug,

i hope you mean 2x16 cells per BMS, that one is designed to manage 16 cells in series. To handle 32 cells you would have to parallel the individual cells or use more than one BMS. i.e. Each connected cell could be two parallel cells to double the capacity.

please don't forget this could be a faceplant waiting to happen, it includes feaures that will cut output power if too much current or to much/little voltage is seen and, it looks like it balances by clamping the individual cells to a max of 4.25V/cell with only 42mA clamping current. I.e it doesn't appear from the spec to hold the cells at the same voltage during charging.

[Jug]

Thank you Keith 

Is this mean that this BMS is not so good? 

I can do the shunting thing right?

Yes i know they are for 16 cells and that is why i asked can i parallel individual cell to have 32 cells per BMS?

If yes then how i need to do that if you can give me some schematics of connection ( soldering each other)? 

 

Thank you again 

[Keith]

Jug,

it is not, per se, a bad unit. You just need to ensure your demands do not exceed its limitations which, one hopes, are accurately stated on the link you gave. I've not played with shunting the protection, but if this board is the same layout as others have identified, then yes it can be done.

All the schematic you need seems to be in the picture on your link, but see below.

One of the most important, in my opinion, functions of a BMS is to keep the cells balanced I.e. Every cell at the same voltage within reasonable tolerence. THE most important is to not allow any cell to exceed 4.25V (I'd prefer that was 4.2V give a healthy margin,) it is cells exceeding that voltage under charge that may cause fire - however good quality the cells are. To do this the BMS has to connect individually to every cell as is shown in the diagram in your link and, as far as I can see that shows clearly where each cell is connected. If you wish to put 32 cells across a 16 cell BMS, then the individual cells need to be paralleled first so that (say) 3.7V 3000mAh cells become a 3.7V 6000mAh pair I.e. Positive end to positive end negative to negative on those pairs. Those pairs are then connected to the BMS as if they were individual 6000mAh cells. Make damn sure the cells are at a very similar state of charge ( I.e. Voltage less than 0.1V different - preferably a lot less) before connecting them together and remember that a built pack has a hell of a lot of energy, I've seen gold connectors touch, weld and then everything get VERY VERY hot whilst being unable to separate them.

Remember though the BMS limitations haven't changed, the unit will still handle a max of 15A continuous. Two BMS, one for each set of 16 would give you 30 amps continuous and would be the safer method.

multiple "packs" I.e. Groups of cells complete with BMS are simply connected in parallel to the power connections and, separately, in parallel to the charger connections. Again ensuring those power leads, charger, leads, etc can handle the current they will carry. A charger designed for 1 will then simply take twice as long to charge 2 packs; a single BMS according to the spec limits charging of its cells to 5 Amps.

[Jug]

Thank you very much @Keith

I am in negotiation for Gotway MCM4 with lowest 130w battery pack,

so maybe i will just add those 2x16 cells per BMS and that will be enough power for some long trips! 

 

 

[DebboR]

As mentioned in my personal EUC upgrade, I also used this BMS. Shunting is as easy as on the other BMS models (if you take the product picture as a reference, you need to shunt the 3 left-most MOSFET's). I would suggest doing it before actually soldering on the cells, as I accidentally shorted one of the gate's to a drain with my soldering iron, resulting in quite a bang and solder flying around. Fortunately, the BMS still seems to function just fine, and keeps the cells within ±0.01V.

The only downside of this BMS is the way the cells are connected to it. All the current passes through several solder joints (2 per battery) and a lot of PCB traces. This results in a higher resistance of the battery (and thus a bigger voltage drop when delivering peak currents), although it also has the huge benefit of easy pack assembly with standard U-tabs connected to the cells. I do notice some power lack when driving up some short pretty steep sections of road (guessing about 30-40% inclination), but if you take them slowly there isn't much of a problem. I'm not sure if this is due to the connection style of the pack, or just the batteries lacking power.

If you go with a dual pack, the current per pack is halved, so these effects should be much lower.

[Jug]

On 12/20/2015 at 0:50 AM, Keith said:

Jug,

it is not, per se, a bad unit. You just need to ensure your demands do not exceed its limitations which, one hopes, are accurately stated on the link you gave. I've not played with shunting the protection, but if this board is the same layout as others have identified, then yes it can be done.

All the schematic you need seems to be in the picture on your link, but see below.

One of the most important, in my opinion, functions of a BMS is to keep the cells balanced I.e. Every cell at the same voltage within reasonable tolerence. THE most important is to not allow any cell to exceed 4.25V (I'd prefer that was 4.2V give a healthy margin,) it is cells exceeding that voltage under charge that may cause fire - however good quality the cells are. To do this the BMS has to connect individually to every cell as is shown in the diagram in your link and, as far as I can see that shows clearly where each cell is connected. If you wish to put 32 cells across a 16 cell BMS, then the individual cells need to be paralleled first so that (say) 3.7V 3000mAh cells become a 3.7V 6000mAh pair I.e. Positive end to positive end negative to negative on those pairs. Those pairs are then connected to the BMS as if they were individual 6000mAh cells. Make damn sure the cells are at a very similar state of charge ( I.e. Voltage less than 0.1V different - preferably a lot less) before connecting them together and remember that a built pack has a hell of a lot of energy, I've seen gold connectors touch, weld and then everything get VERY VERY hot whilst being unable to separate them.

Remember though the BMS limitations haven't changed, the unit will still handle a max of 15A continuous. Two BMS, one for each set of 16 would give you 30 amps continuous and would be the safer method.

multiple "packs" I.e. Groups of cells complete with BMS are simply connected in parallel to the power connections and, separately, in parallel to the charger connections. Again ensuring those power leads, charger, leads, etc can handle the current they will carry. A charger designed for 1 will then simply take twice as long to charge 2 packs; a single BMS according to the spec limits charging of its cells to 5 Amps.

@Keith I have some more question regarding my build of battery packs,

First, how can i equalise each cell to have same voltage like you stated  "( I.e. Voltage less than 0.1V different - preferably a lot less)"

but without some fancy electronics or such, because i do not have that, all i have is powerbank for 8 cells, see photo, i can charge or discharge

Second question is can i triple it, 3x16 per bms in parallel?

Maybe i ask and want to much 

But i think in this new gotway MCM4 there is lot of space so it can fit the triple battery pack.

So, is this possible with this bms, is there danger after or in process of making it? 

 

 

[esaj]

18 minutes ago, Jug said:

@Keith I have some more question regarding my build of battery packs,

First, how can i equalise each cell to have same voltage like you stated  "( I.e. Voltage less than 0.1V different - preferably a lot less)"

but without some fancy electronics or such, because i do not have that, all i have is powerbank for 8 cells, see photo, i can charge or discharge

Second question is can i triple it, 3x16 per bms in parallel?

Maybe i ask and want to much 

But i think in this new gotway MCM4 there is lot of space so it can fit the triple battery pack.

So, is this possible with this bms, is there danger after or in process of making it? 

 

I'm by no means expert, but the springs holding the cells in place just scare the s**t out of me... imagine hitting a bump and one of those cells moving enough for the connection to break for a split second. Usually the cells should have welded tabs between them (or welded directly to the BMS, depending on the type of the BMS).

As for the balancing, I don't know if that BMS(?) you have there has such circuitry (there doesn't seem to be any balancing cables going to the cells?), probably you should get a separate charger that can charge them one-by-one to a precise voltage before connecting them in parallel. You probably could connect 2 of those 8S-packs in series, and then connect multiple 2 * 8S -packs in parallel, AFTER making sure they're all in the same voltage. Or do you have a separate 16S BMS you meant to use?

EDIT: Doh, you state in your first post that you've ordered separate BMSs... but how are you going to spot-weld the cells together? I wouldn't trust them to hold if just soldered...

[Jug]

That is just powerbank for 18650 batteries, i just charge them thru that. 

Yes i was thinking only to solder them together in parallel and then solder it to bms in series, because i can't find anyone here to do spotwelding. 

Uh! One by one charging 64 cells will take a hell of a time.... 

[Jug]

Finally the BMS, connectors and cables arrived after one month of waiting!

Yesterday it took me all day to ensemble the batteries with bms, you can see on the pictures that it came out not bad 

Today was testing day, i first removed the original battery 130w and installed "new" one, fully recharged i measured it was 66.9v

Once i jumped on it and start riding and try to accelerate the battery indication drop down immediately and it start to beeping, so i need to slow down to 10-12kmh

i rided 14km with that battery pack but really slow with uphill and downhill and the gotway app show that i still have 50% battery when i returned to home!?

when i was riding uphill i needed to ride really really SLOW and there was beeping non stop!

So, can someone help and explain what is going on here please?

I got the mileage but there is no power for acceleration   

 

 

 

[Jug]

My shrink wrap is on the way, till then i just tape it tape isolant!

[Jug]

Update!

On my gotway app it shows 50% of battery and i measured and there is 61v, i tried to charge it but it won't, the charger stay on green light,

the other original battery pack is also on 61v and on gotway app is same 50% but when i connect charger it start to charge immediately, (i did not conected those packs together in parallel yet because of this symptoms!) 

So can someone help me with this  please? @Keith? @esaj ? ANYONE?

[esaj]

Really just guessing here, but the charge indication dropping during getting going  sounds like the battery voltage sag is quite large during high discharge. Faulty cell(s)? Can you measure the voltages of the single cells?

The charging problem could be caused by a faulty BMS or something wrong with the wiring, sounds like it could think that the battery is fully charged. But I'm not an expert on these things...

[Jug]

13 minutes ago, esaj said:

Really just guessing here, but the charge indication dropping during getting going  sounds like the battery voltage sag is quite large during high discharge. Faulty cell(s)? Can you measure the voltages of the single cells?

The charging problem could be caused by a faulty BMS or something wrong with the wiring, sounds like it could think that the battery is fully charged. But I'm not an expert on these things...

Ok, what i tried now is measure discharging cable and there is 61.0v on the charging cable is 60.6v

I will try to measure each cell but i can measure only pair of them cause they are in parallel.

[esaj]

9 minutes ago, Jug said:

Ok, what i tried now is measure discharging cable and there is 61.0v on the charging cable is 60.6v

I will try to measure each cell but i can measure only pair of them cause they are in parallel.

You can (probably) see a lower voltage even if just one of the two cells is faulty and has dropped it's voltage... do take care to check that your meter wires are in the correct holes (resistance/voltage measuring), and don't do what I did (I thought I was measuring voltage, but had the wire in the 10A current measuring -hole and shorted the pack ).

[Jug]

Yeap, that will not be good if i do shorten 

Here is what i find out, i measured each pair of batteries and there is difference, 9 pairs are 3.85v  6 pairs are 3.83v and one pair is 3.81v  

[esaj]

14 minutes ago, Jug said:

Yeap, that will not be good if i do shorten 

Here is what i find out, i measured each pair of batteries and there is difference, 9 pairs are 3.85v  6 pairs are 3.83v and one pair is 3.81v  

That doesn't sound THAT big difference, but I'm not sure how exact the balancing should be (probably less than 100mV at least?), and I think it only occurs during the final stage of the charging (although the cell-pairs in parallel should balance each other "automatically"), the spec-sheet of your BMS states 4.20 +- 0.025V balancing voltage. Since your charger works with the other pack, I would suspect that something's wrong with the charging circuitry in the BMS, but don't know for sure, maybe someone else knows better.

Btw, is it cold in Brussels right now, cold weather will also affect the batteries, causing faster voltage drop than in warmer weather?

[Jug]

25 minutes ago, esaj said:

You can (probably) see a lower voltage even if just one of the two cells is faulty and has dropped it's voltage... do take care to check that your meter wires are in the correct holes (resistance/voltage measuring), and don't do what I did (I thought I was measuring voltage, but had the wire in the 10A current measuring -hole and shorted the pack ).

Yeap, that will not be good if i do shorten 

Here is what i find out, i measured each pair of batteries and there is difference, 9 pairs are 3.85v  6 pairs are 3.83v and one pair is 3.81v  

and that last one pair with 3.81v is just near to cables, so they go like this 3.81v then 6 pairs 3.83v and 9 pairs 3.85v in order!

so is that one with lowest voltage faulty or other-end 6 to?

[Jug]

7 minutes ago, esaj said:

That doesn't sound THAT big difference, but I'm not sure how exact the balancing should be (probably less than 100mV at least?), and I think it only occurs during the final stage of the charging (although the cell-pairs in parallel should balance each other "automatically"), the spec-sheet of your BMS states 4.20 +- 0.025V balancing voltage. Since your charger works with the other pack, I would suspect that something's wrong with the charging circuitry in the BMS, but don't know for sure, maybe someone else knows better.

Btw, is it cold in Brussels right now, cold weather will also affect the batteries, causing faster voltage drop than in warmer weather?

Yes it's cold but after riding with builded pack i changed with original pack and i do not have that situation even it is smaller in watts i have power with it!

But with builded one i could not accelerate at all, if i start to accelerate the battery indicator drop down immediately and it start beeping, i could accelerate but really slowly like walking beside, and i can reach 10-12kmh maximum!

[esaj]

6 minutes ago, Jug said:

Yes it's cold but after riding with builded pack i changed with original pack and i do not have that situation even it is smaller in watts i have power with it!

But with builded one i could not accelerate at all, if i start to accelerate the battery indicator drop down immediately and it start beeping, i could accelerate but really slowly like walking beside, and i can reach 10-12kmh maximum!

The battery indicator is just a voltage meter, so it means the voltage of the pack will "sag" (drop) during high current discharge (acceleration). Things that come to mind are at least bad connections with high resistance (are the connectors soldered properly? Do they have good connection with each other?), faulty cells that drop their voltage faster during higher discharge or faulty BMS. If it's the BMS itself, I'd replace it, I wouldn't trust a "home repaired" BMS, especially when it comes to charging.

If you have a load tester with high enough ratings (voltage / amperage / wattage), you could try monitoring the voltage drop of the battery pack at different discharge rates. Be careful if you go this route though...

[Jug]

12 minutes ago, esaj said:

The battery indicator is just a voltage meter, so it means the voltage of the pack will "sag" (drop) during high current discharge (acceleration). Things that come to mind are at least bad connections with high resistance (are the connectors soldered properly?), faulty cells that drop their voltage faster during higher discharge or faulty BMS. If it's the BMS itself, I'd replace it, I wouldn't trust a "home repaired" BMS, especially when it comes to charging.

If you have a load tester with high enough ratings (voltage / amperage / wattage), you could try monitoring the voltage drop of the battery pack at different discharge rates. Be careful if you go this route though...

Huh, how can i know if it is battery or BMS, the BMS is new i just received it and i have spare same one!

I don't have load tester and fancy electronics, so i can't do that

I checked all connectors and i do not see any fault, maybe the faulty cells? But which one....  

[esaj]

3 minutes ago, Jug said:

Huh, how can i know if it is battery or BMS, the BMS is new i just received it and i have spare same one!

I don't have load tester and fancy electronics, so i can't do that

I checked all connectors and i do not see any fault, maybe the faulty cells? But which one....  

Don't know how to test the BMS itself, especially without any load. Maybe @Keith, @zlymex or someone else with more knowledge of the electronics can help there. I do know that when I ordered my custom packs, I first received only 3 packs, because the 4th BMS was broken when it arrived to the builder, so it could be faulty from the get-go... Don't know how he tested it to be faulty, but it was replaced on warranty.

[Jug]

2 minutes ago, esaj said:

Don't know how to test the BMS itself, especially without any load. Maybe @Keith, @zlymex or someone else with more knowledge of the electronics can help there. I do know that when I ordered my custom packs, I first received only 3 packs, because the 4th BMS was broken when it arrived to the builder, so it could be faulty from the get-go... Don't know how he tested it to be faulty, but it was replaced on warranty.

Thank you @esaj so far, i hope that @Keith or @zlymex can help little, i can unsolder batteries from BMS if needed.

Will see...

[Keith]

@Jug,

I have just speed read through the above, so my apologies if I have picked up the wrong end of the stick.

I think you are saying that the voltage is around 61V, the wheel suggests that is 50% charged and yet the charger goes green almost immediately?

61V is an average of 3.8125V/cell if there are 16cells which is around 40% charged. Bearing in mind most BMS  only balance once the cells hit 4.20V, then a difference of 0.04V is not excessive. 

Chargers go green when the current drops to a trickle - typically 200mA or less. I think you have a problem with the charging side of the BMS assuming the charger works OK on another pack. 

BTW the charging circuit often has a protective diode in the line, this would cause a drop of 0.6V or so compared with the output voltage.

[Jug]

30 minutes ago, Keith said:

@Jug,

I have just speed read through the above, so my apologies if I have picked up the wrong end of the stick.

I think you are saying that the voltage is around 61V, the wheel suggests that is 50% charged and yet the charger goes green almost immediately?

61V is an average of 3.8125V/cell if there are 16cells which is around 40% charged. Bearing in mind most BMS  only balance once the cells hit 4.20V, then a difference of 0.04V is not excessive. 

Chargers go green when the current drops to a trickle - typically 200mA or less. I think you have a problem with the charging side of the BMS.

No problem @Keith 

Yes, it is reading 61V on discharge cable and 60.6V on charge cable, i measured each pairs of cells and there is 9 pairs 3.85V 6 pairs 3.83V and one pairs 3.81 now it shows 3.82V

On my original pack 130w it is the same voltage on discharging and charging cable 61V and when i connect the charger it start to charge, but with my build pack it wont charge at this point, it just stay green on charger!

When it was full charged this morning i jump on it and immediately i start to ride the battery indicator drop down to the end and started beeping, but i was not even accelerate to much i was maybe 5kmh, when i slow down more battery indicator come up on normal state and i can ride really slow like walking, i could not accelerate at all like with the original battery pack!

So that is in short 

So you think is faulty BMS?