# What size BMS ?



## maestro7879 (Sep 25, 2018)

I'm working with a Miles ZX40s. 

The configuration will be - 
10 Nissan Leaf modules (car is a 72v system)
Curtis 1209B controller. 

The car will be stock other than the batteries. 
What size BMS would I need for this system ? 
I'm thinking 450 at least because that's what the controller can pull.

Thanks

Looking at this again. Based on the motor XQ-6.3-6H http://czhsdj.com/english/upload/product/201711915302930.pdf this would be max 105amps ? 
Am I reading that right ? What's the max size BMS I would need (in the neighborhood of 150amps) ?


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## jbman (Oct 26, 2017)

You can get a BMS that does not go in line with the batteries, and it manages the charger, balancing, and the main contactor. Zeva and Orion are examples. Why not use one of those?

Sent from my SM-N960U using Tapatalk


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## cricketo (Oct 4, 2018)

Yeah, at such currents you definitely need a BMS that supports external contactors for switching load/charger. Orion, Zeva, Batrium can do that. Batrium definitely can scale up to 20 cells. With Zeva you could use multiple cell monitors, like three 8-cell ones, or two 12-cell ones. Orion also supports wiring multiple units in series for larger strings.

If you're feeling adventurous, you could try Chargery BMS24T. There are very serious concerns over quality of their products though.


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## frodus (Apr 12, 2008)

I've used the Elithion and Orion in the past and they're great BMS with tons of features.

Currently I work a lot with the Zeva, and it's a great budget BMS.


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## maestro7879 (Sep 25, 2018)

Is it possible to estimate the discharge amps without running the vehicle first ?

I think I answered my own question - The primary fuse in the car is 300amps, I can't exceed that.


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## cricketo (Oct 4, 2018)

maestro7879 said:


> Is it possible to estimate the discharge amps without running the vehicle first ?
> 
> I think I answered my own question - The primary fuse in the car is 300amps, I can't exceed that.


I believe Leaf modules are only rated for 240A continuous, though they certainly can peak more. Make sure your controller limits the current to the motor correctly, and ideally it should also be configured for maximum draw from the battery pack. I don't know if this Curtis can be setup like that though.


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## Duncan (Dec 8, 2008)

maestro7879 said:


> Is it possible to estimate the discharge amps without running the vehicle first ?
> 
> I think I answered my own question - The primary fuse in the car is 300amps, I can't exceed that.


I'm using Volt modules and a Volt main fuse - I believe it is about 330 amps

However my controller is set to 1200 amps and my battery current reaches that value as I accelerate

So far I have nor blown the "Main Fuse"

Tesla use a pyrotechnic main fuse that can blow immediately you exceed that current but the wire type main fuses will take quite a while (seconds) to blow even with a 400% overload


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## maestro7879 (Sep 25, 2018)

Duncan said:


> maestro7879 said:
> 
> 
> > Is it possible to estimate the discharge amps without running the vehicle first ?
> ...



Are you using a bms on the discharge side ?


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## maestro7879 (Sep 25, 2018)

Would this bms work and support the discharge side ? https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/192702426670


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## Duncan (Dec 8, 2008)

maestro7879 said:


> Are you using a bms on the discharge side ?


No
No BMS at all

I use a Batt Bridge and charge using a BRUSA charger - no BMS


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## cricketo (Oct 4, 2018)

maestro7879 said:


> Would this bms work and support the discharge side ? https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/192702426670


It may work... Noname Chinese vendors are known to overstate the specs, and often they don't use correct parts (such as MOSFETs). If you happen to order that board, double check if those MOSFETs are indeed rated for 300A (which I actually doubt, more likely that's peak).

Here is a good thread about various BMSes :

https://endless-sphere.com/forums/viewtopic.php?f=14&t=88676


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## Duncan (Dec 8, 2008)

I suspect that we are all talking at cross purposes

I would NOT expect any BMS to actually try and control discharge current - you have got a controller and some contactors to do that

A BMS will monitor some cells and MAY do some cell/cell balancing

But it will NOT shut off the charger - it will instead instruct the charger to shut off

At the discharge side most do nothing - but IF it does do anything it will instruct the controller to cut back or off

The BMS needs to handle the balancing current - a piddly small amount


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## cricketo (Oct 4, 2018)

Duncan said:


> I suspect that we are all talking at cross purposes
> 
> I would NOT expect any BMS to actually try and control discharge current - you have got a controller and some contactors to do that
> 
> ...



You are mistaken. Many BMSes intended for use in high current applications have specific port(s) for connecting charge/discharge contactors. Here is a wiring diagram for Zeva BMS16, with two separate contactors clearly visible :

http://www.zeva.com.au/Products/images_lge/BMS16v2_Example.jpg


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## jbman (Oct 26, 2017)

cricketo said:


> You are mistaken. Many BMSes intended for use in high current applications have specific port(s) for connecting charge/discharge contactors. Here is a wiring diagram for Zeva BMS16, with two separate contactors clearly visible :
> 
> http://www.zeva.com.au/Products/images_lge/BMS16v2_Example.jpg


I don't think that diagram proves what you think it proves...

The discharge current is not under the control of the BMS normally. The controller throttles that and keeps it within limits. This diagram shows the BMS controlling the main contactor (to open it if a cell is low) and a charge contactor (to prevent overcharging). Neither of those are concerned with discharge amperage. The only reason it has a shunt is for state of charge calculation, probably. That's all my Zeva does with the current sensor.

Sent from my SM-N960U using Tapatalk


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## cricketo (Oct 4, 2018)

jbman said:


> I don't think that diagram proves what you think it proves...
> 
> The discharge current is not under the control of the BMS normally. The controller throttles that and keeps it within limits. This diagram shows the BMS controlling the main contactor (to open it if a cell is low) and a charge contactor (to prevent overcharging). Neither of those are concerned with discharge amperage. The only reason it has a shunt is for state of charge calculation, probably. That's all my Zeva does with the current sensor.
> 
> Sent from my SM-N960U using Tapatalk


You are technically correct here, you just misunderstood what I was saying. The question of current is only relevant to the way BMS may be switching load/charger on/off. Many low current BMSes do that by means of on-board MOSFETs. Since it is impractical to use solid state devices as switches in high current applications, BMSes meant for high current applications rely on contactors, while providing control interfaces for those contactors.

I still insist you were mistaken in your previous comment regarding shutting off charger by means of communication. Some BMS/Charger combos indeed do that, such as Chargery BMS. Zeva, as I've referenced above, has no means of instructing the charger or controller to switch themselves off should any of the cells be pushed beyond their operational parameters. Instead Zeva will kill the load/charger via contactor should it detect any cell has approached a charge/discharge threshold.


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## Duncan (Dec 8, 2008)

cricketo said:


> You are mistaken. Many BMSes intended for use in high current applications have specific port(s) for connecting charge/discharge contactors. Here is a wiring diagram for Zeva BMS16, with two separate contactors clearly visible :
> 
> http://www.zeva.com.au/Products/images_lge/BMS16v2_Example.jpg


That is EXACTLY what I said
The BMS does NOT control the current in either situation but it does effectively tell the charger or the controller to STOP


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## cricketo (Oct 4, 2018)

Duncan said:


> That is EXACTLY what I said
> The BMS does NOT control the current in either situation but it does effectively tell the charger or the controller to STOP


Except you said 



> But it will NOT shut off the charger - it will instead instruct the charger to shut off


Which I explained it often can't do, as there there may be no integration between the BMS and the charger.


I also responded to jbman thinking that was your comment. Sorry jbman


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## jbman (Oct 26, 2017)

cricketo said:


> Except you said
> 
> 
> 
> ...


It's all good. 

ZEVA can communicate with several chargers via canbus or by triggering an enable relay. I even used a TC charger and ZEVA was able to set the charge parameters over canbus. 

The type of BMS that the OP is referring to actually pushes all power through the BMS, hence his question of how large he should go. I don t see any reason to use a BMS like that in this application, even if they have one that is robust enough for it.

Sent from my SM-N960U using Tapatalk


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## maestro7879 (Sep 25, 2018)

jbman said:


> It's all good.
> 
> ZEVA can communicate with several chargers via canbus or by triggering an enable relay. I even used a TC charger and ZEVA was able to set the charge parameters over canbus.
> 
> ...


I'm partially interested in having a speedo and odemeter. I don't have one currently and the law requires it.
I'm also interested in having something that shows the amps. 
This all in one solution is nice and I can mount it in the dash.

If I were to bypass the discharging portion of this BMS I'm guessing I would lose the amps function.


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## daltonguitar (Apr 18, 2018)

maestro7879 said:


> Would this bms work and support the discharge side ? https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/192702426670


I don't think that BMS will work with your system. I am also making a build with Nissan Leaf batteries; each Nissan module is rated at around 8 volts. That BMS has a battery voltage detection range of 1-5V so its a little too low to detect a leaf module. Maybe it could work if you set it up to each cell in the module but i think your best bet is to find something similar to this but with a little higher voltage detection. If you find something please let me know though I'm also in the market for a BMS for Leaf batteries! Ill msg here if I find anything as well.


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## SeanOrk (Jul 7, 2016)

daltonguitar said:


> I don't think that BMS will work with your system. I am also making a build with Nissan Leaf batteries; each Nissan module is rated at around 8 volts. That BMS has a battery voltage detection range of 1-5V so its a little too low to detect a leaf module. Maybe it could work if you set it up to each cell in the module but i think your best bet is to find something similar to this but with a little higher voltage detection. If you find something please let me know though I'm also in the market for a BMS for Leaf batteries! Ill msg here if I find anything as well.


Leaf packs have a central "tap" terminal which enables BMS connection to each internal cell (actually a pair of cells in parallel) - so a BMS with a working range of only 5v will be suitable for use with Leaf packs.


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## frodus (Apr 12, 2008)

daltonguitar said:


> I don't think that BMS will work with your system. I am also making a build with Nissan Leaf batteries; each Nissan module is rated at around 8 volts. That BMS has a battery voltage detection range of 1-5V so its a little too low to detect a leaf module. Maybe it could work if you set it up to each cell in the module but i think your best bet is to find something similar to this but with a little higher voltage detection. If you find something please let me know though I'm also in the market for a BMS for Leaf batteries! Ill msg here if I find anything as well.


All of the BMS that I know of on the market are made to be attached to each cell, not each Leaf Module. 

There are 3 taps on a Leaf cell. B-, B+ and a center tap that goes to the connection inside between the two cell groups. This allows you to tap off each cell and use a standard BMS. 

I'd never suggest someone monitor at the module-level. Always monitor at the cell-level.

Background on me, since you're new to the forum: I've been selling BMS for years so I know a lot of the vendors of BMS, and how they work and are configured. Elithion, Orion, Zeva and have built multiple designs of a BMS.


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## daltonguitar (Apr 18, 2018)

Ahh okay I understand how this works now. Thank you for the clarification on the use of the center tap. I've been doing research on how all of this works from home so I appreciate the knowledge. Its gonna be put to good use!


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