BMS for 52volt 14s?

E-driver_

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What BMS do I need for a 52volt battery that will have 91 18650-cells?

I want to have a pretty powerful controller. Haven't decided which controller and kit for it yet.

But to be able to pick rom high powered ones I should go higher on the BMS-side also right?

50 or 60 amps perhaps?
 
E-driver_ said:
What BMS do I need for a 52volt battery that will have 91 18650-cells?

I want to have a pretty powerful controller. Haven't decided which controller and kit for it yet.

But to be able to pick rom high powered ones I should go higher on the BMS-side also right?

50 or 60 amps perhaps?

You need to know what the complete system requirements are before you can start picking parts. "powerful controller" doesn't actually mean anything, for instance. (to me, a powerful controller would be at least several *hundred* amps, battery-side...to others with lesser needs, a 20A controller would be powerful).

What matters is whether the system has enough power to do the job you need it to do. So you first have to define what you want the bike to do for you, under the specific conditions you ride in, with your riding style, on the terrain you will ride on. Without knowing those things then anything you get may or may not be a waste of money; may or may not be capable of doing what you want.

You can use the http://ebikes.ca/tools/simulator.html to experiment and see what kind of power requirements your usage/situation/etc will need, by using the various pre-setup parts on there, or customizing it if you need more power than those can supply.


Other notes:

THe BMS is there to protect the cells. So it's current limit needs to be based on what the cells are designed to handle--you don't want a BMS that will allow more current to be drawn than the cells can safely output.

However...The BMS (and cells) must also be able to output *more* current than the controller will ever demand of them, so they are not stressed, even as they age. So generally it is safer to specify a battery pack that is capable of at least 25-50% more than you will ever need from it, both in Ah capacity and in A(mps) capability, so that even as it ages, or in adverse conditions like cold weather, it can still do the job you need it to without stressing (damaging) it.

Since many BMS may be made cheaply with FETs that dont' really do the job they say they will, a programmable BMS that is built to handle much more current than you will ever need, but can be set to only allow a small portion of that (whatever the cells can actually handle, minus a safety margin), would be better than a BMS rated for exactly the current you need. (it also means you have room for upgrading the system a little bit without replacing the BMS, just adding more parallel cells for greater current handling as needed).
 
amberwolf said:
E-driver_ said:
What BMS do I need for a 52volt battery that will have 91 18650-cells?

I want to have a pretty powerful controller. Haven't decided which controller and kit for it yet.

But to be able to pick rom high powered ones I should go higher on the BMS-side also right?

50 or 60 amps perhaps?

You need to know what the complete system requirements are before you can start picking parts. "powerful controller" doesn't actually mean anything, for instance. (to me, a powerful controller would be at least several *hundred* amps, battery-side...to others with lesser needs, a 20A controller would be powerful).

What matters is whether the system has enough power to do the job you need it to do. So you first have to define what you want the bike to do for you, under the specific conditions you ride in, with your riding style, on the terrain you will ride on. Without knowing those things then anything you get may or may not be a waste of money; may or may not be capable of doing what you want.

You can use the http://ebikes.ca/tools/simulator.html to experiment and see what kind of power requirements your usage/situation/etc will need, by using the various pre-setup parts on there, or customizing it if you need more power than those can supply.


Other notes:

THe BMS is there to protect the cells. So it's current limit needs to be based on what the cells are designed to handle--you don't want a BMS that will allow more current to be drawn than the cells can safely output.

However...The BMS (and cells) must also be able to output *more* current than the controller will ever demand of them, so they are not stressed, even as they age. So generally it is safer to specify a battery pack that is capable of at least 25-50% more than you will ever need from it, both in Ah capacity and in A(mps) capability, so that even as it ages, or in adverse conditions like cold weather, it can still do the job you need it to without stressing (damaging) it.

Since many BMS may be made cheaply with FETs that dont' really do the job they say they will, a programmable BMS that is built to handle much more current than you will ever need, but can be set to only allow a small portion of that (whatever the cells can actually handle, minus a safety margin), would be better than a BMS rated for exactly the current you need. (it also means you have room for upgrading the system a little bit without replacing the BMS, just adding more parallel cells for greater current handling as needed).

The battery cells are these HG2-cells:

https://www.aliexpress.com/item/32835679557.html?spm=a2g0o.order_list.order_list_main.169.73131802Q3NuID

It reads "Battery Current: 20A continuous discharge more than 35a."

Does that mean that the controller should not go above 35a? Or am I thinking correctly about that? A bit unsure.
 
If 91 cells in 14S means you are making a 14S6P battery, then you'd multiple the amount of current the cell can discharge by 6. If they can handle 20A continuously each, that's good enough for 120A output with each of the 14 P-groups distributing the load across 6 cells each. If your BMS was 60A discharge max using that battery, you'd still set your controller to 60A, though. Otherwise BMS would cut discharge at 60A and your ebike would stop.

If the battery has two A numbers one is usually what it can sustain continuously over a long time and the other is what is OK to pull maximum, briefly, during something like acceleration.
 
lnanek said:
If your BMS was 60A discharge max using that battery, you'd still set your controller to 60A, though. Otherwise BMS would cut discharge at 60A and your ebike would stop.

Do you mean that if the BMS is 60A and the controller is 35A(max) would that present a problem for me? Or would a problem just arise if the controller has higher A than the BMS?
This is something I need to learn. A bit confused about that part.

Regarding the order inside the battery it looks a bit strange so I am not sure if it is 6 in parallell across the board. It looks like the pic below.
 

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Controller set to use 35A max and BMS set to 60A max discharge would be fine. You can think of the BMS as a cheap digital circuit breaker or fuse that uses transistors instead of actually cutting the connection. If certain conditions are met then it disables discharge. Those conditions are usually a certain max current being reached, detected by a shunt, or one of the individual p-groups in the battery reaching low voltage cut off, LVC, detected by the balance wires going to each p-group of the battery.

Controller on the other hand, actively decides how much current to draw based on the throttle or pedal assist sensor input. Half throttle might draw 15A, full throttle might draw 30A. If it decides to use more than the BMS allows, however, the BMS cuts off discharge. So setting controller to 35A max would make sure it never attempts to draw more than a 60A BMS allows.
 
lnanek said:
Controller set to use 35A max and BMS set to 60A max discharge would be fine. You can think of the BMS as a cheap digital circuit breaker or fuse that uses transistors instead of actually cutting the connection. If certain conditions are met then it disables discharge. Those conditions are usually a certain max current being reached, detected by a shunt, or one of the individual p-groups in the battery reaching low voltage cut off, LVC, detected by the balance wires going to each p-group of the battery.

Controller on the other hand, actively decides how much current to draw based on the throttle or pedal assist sensor input. Half throttle might draw 15A, full throttle might draw 30A. If it decides to use more than the BMS allows, however, the BMS cuts off discharge. So setting controller to 35A max would make sure it never attempts to draw more than a 60A BMS allows.

Ok good explanation. What about if I have a controller with max-current of 55 a when the bms is 60? That is also okay right?

The BMS would only cut discharge at above 60 and not 55 right?
 
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Do you mean that if the BMS is 60A and the controller is 35A(max) would that present a problem for me? Or would a problem just arise if the controller has higher A than the BMS?
This is something I need to learn. A bit confused about that part.

Regarding the order inside the battery it looks a bit strange so I am not sure if it is 6 in parallell across the board. It looks like the pic below.
Could someone maybe explain the reasoning behind this pack's nickelstrip and cell-slots? It is a pack that came with 91 cell-slots. For a 14s-system with 52 volts.

But when building a 14s system I thought everything had to be in rows? So for example rows of 6 making it 6*14=84.

But this package had more slots for the 14s-system. It has 91 cell-slots. Also the nickelstrip that came along with it is not in rows but rather seems to be wiring diagonally and not making the parallells in 90degrees angle from the series-cells.

Also, there are missing nickelstrip for seven of the slots. So do you think they mean for the builder to wire these last slots by themselves somehow? And if so, how can I do that in a smart way? Wold be nice to use all the cell-slots of the 14s-system to make the AH as high as possible.

Can you see from this link and picture how they are supposed to be wired?

Product is Polly DP9 with nickelstrip in the link: https://www.aliexpress.com/item/400...der_detail.order_detail_item.3.53c7f19ceaUmiW

I also provide a picture to try to show what I am talking about.
 

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Looks like 14s6p = 84 cells. 14s7p would have been 98 cells, so doesn't fit in that case.

The reason you have two rows of 6 next to each other most of those plates is because you are suppose to put six cells' positive ends down on one half of the plate, then 6 cells negative ends down on the other half - creating the series connection between two p-groups. You'll notice the end of the battery has a plate with only 6 instead of 12 spots. That's because that's for the last p-group which only needs one serial connection, which is done by the 12 spots plate on the other half of the battery. So that half of the battery only needs a 6-spot plate facing the 12 spot one.
 
Looks like 14s6p = 84 cells. 14s7p would have been 98 cells, so doesn't fit in that case.

The reason you have two rows of 6 next to each other most of those plates is because you are suppose to put six cells' positive ends down on one half of the plate, then 6 cells negative ends down on the other half - creating the series connection between two p-groups. You'll notice the end of the battery has a plate with only 6 instead of 12 spots. That's because that's for the last p-group which only needs one serial connection, which is done by the 12 spots plate on the other half of the battery. So that half of the battery only needs a 6-spot plate facing the 12 spot one.
Hmm I understand most of what you are saying(I think). That means I should only use 84 spots correct? It would not be possible to use all 91 right?

Ah so the reason because it is 12 is because one row is down and one row is up? Making it only six in parallell, correct?
 
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Yep, a 52V battery needs 14 p-groups in series since 52V / 3.7 V per cell = 14 cells needed in series.

91 cells fit in the case / 14 p-groups = 6.5 cells per p-group . Since your p-groups need the same number of cells, that means 14s6p is that most that will fit.
 
55amp is ok for the cells. He pack can run cooler with better parallel connections. And a BT BMS for checking and customizing the BMS function. The slots are for easier welding with a spot welder. What spot welder do you have ?
Mid-drive or rear hub ? What frame ?
 
55amp is ok for the cells. He pack can run cooler with better parallel connections. And a BT BMS for checking and customizing the BMS function. The slots are for easier welding with a spot welder. What spot welder do you have ?
Mid-drive or rear hub ? What frame ?
I haven't decided where to use the battery yet. But the idea is to be able to use it on a few different bikes. Most of my batteries are 48volts so I think it will be fun to build one of my own and make it a bit more powerful at 14s 52 volts.

The bms I am going to use is this one for 14s 60a:

Battery pack is this big Polly 9, 91 slots 52 volt:
 

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Yep, a 52V battery needs 14 p-groups in series since 52V / 3.7 V per cell = 14 cells needed in series.

91 cells fit in the case / 14 p-groups = 6.5 cells per p-group . Since your p-groups need the same number of cells, that means 14s6p is that most that will fit.
Ah a bit weird that they make it 91 spots then? Any idea why they do that?

Pack is this one, dp9 52v:
 
Just reusing the case of a 13s battery, I suppose. 91 / 13 = 7. Perfect fit.
 
Maybe room for the BMS. That BMS that you're looking at will it fit in your battery case or will it be external. They make three or four different size packs for 36 48 and 52 volt the combination of cells you put in there is you do the math. But I even noticed on professionally made and resold battery packs on battery hookup there's some hollow spots in the center.
 
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Maybe room for the BMS. That BMS that you're looking at will it fit in your battery case or will it be external. They make three or four different size packs for 36 48 and 52 volt the combination of cells you put in there is you do the math. But I even noticed on professionally made and resold battery packs on battery hookup there's some hollow spots in the center.
Ah ok so that is normal that some are sometimes left out.

The BMS is supposed to be inside the battery case. Now any advice, ideas or safety measures when building this thing are much welcomed. Since it is the first pack I am building.
 
Did you buy the kit that showed the case and the nickel strips with cell holders ? I would get those little brown donut shape insulators for the positive side
 
Did you buy the kit that showed the case and the nickel strips with cell holders ? I would get those little brown donut shape insulators for the positive side
Hmm which ones do you mean? Those sticker ones?

I have to get some nickel strips of the cells first also I think. The cells are HG2 from Ali. These:


I wrote in another thread that I had not thought about the fact that these already came with nickel strips. So I am thinking about perhaps getting some of those of with pliers or something. What do you think?

Since the wiring will already be taking care of through the metal wire thing that came with the battery box, right.
 
1681425346977.pngThis one the one you posted. I think this is a kit ? Anyway you're the one who posted it and that's when I'm asking about the kit that's in the picture.
 
Yes it doesn't make mathematical sense.
91÷14=6.5
So how are the nickel strips setup. It must be 14s 6p so are the three empties. I think I see him at the top.
So the outside is of a generic size. For many different combos and voltages.
Well it looks like you don't have room or a place for the BMS to fit in the case in the old days ping used to have his BMS outside the battery pack.
 
Yes it doesn't make mathematical sense.
91÷14=6.5
So how are the nickel strips setup. It must be 14s 6p so are the three empties. I think I see him at the top.
So the outside is of a generic size. For many different combos and voltages.
Well it looks like you don't have room or a place for the BMS to fit in the case in the old days ping used to have his BMS outside the battery pack.
Hmm I will receive the BMS soon. I hope to fit it inside the case. I haven't really measured yet. But yeah maybe it does not fit. A bummer in that but I have to work around it somehow if that is the case.
 
The stuff I've got looks like this like in the pictures below. Perhaps I could fit the BMS either on the ceiling or on the floor over or under the cells(?) somehow when they have been wired together and wrapped in blue inside the battery. What do you think?
 

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Maybe room for the BMS. That BMS that you're looking at will it fit in your battery case or will it be external. They make three or four different size packs for 36 48 and 52 volt the combination of cells you put in there is you do the math. But I even noticed on professionally made and resold battery packs on battery hookup there's some hollow spots in the center.
I think I will have to cut off the three plastic ones that will be empty to fit the bms inside the case. The ones that are circled.

In that way I could fit my bms, which is rather big beneath the cells, inside the case, I think.

Now they become a bit too high because of the bms beneath as you can see from the three last images.
 

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