Leaf battery BMS

13088 Views 24 Replies 6 Participants Last post by jefsmk, May 9, 2020

jefsmk

Discussion Starter · Feb 22, 2020

Any recommendations on the best way to configure and wire leaf battery modules for a 144 volt system, and be able to use a BMS to monitor the batteries? I thought I could buy the 14 unit setups you see all over eBay (7 modules in series, with another 7 in parallel). That gives ~52 volts. Then I thought I could wire 3 of these in series to give me ~150 volts.

I'm told (by the helpful people at evolve electronics) that a BMS would not be pheasable with this setup tho.

Is there no way to setup the leaf modules for 150 volt 132 ah setup? Without tearing them apart, or crazy wiring all over the place?

Thanks for any advise here!!!

Jeff

1 - 20 of 25 Posts

kennybobby

· #2 · Feb 22, 2020

One of the smartest guys on this is Wolf, and he has a thread about his approach to making a parallel pack for his truck.

Do a search for threads started by wolftronix, or go look it up his website.

Tremelune

· #3 · Feb 24, 2020

Perhaps I'm misunderstanding, but what's the issue? What about an Orion or Thunderstruck BMS?

brian_

· #4 · Feb 24, 2020

jefsmk said:
I thought I could buy the 14 unit setups you see all over eBay (7 modules in series, with another 7 in parallel). That gives ~52 volts

Those "units" are presumably modules, which are each a 2S 2P combination of four cells.

I have no idea what's all over eBay - could you provide a link to an example? That combination of 7 modules is not a normal portion of a Leaf pack, so they are presumably assembling it as a replacement for a "48 volt" lead-acid battery. Is it something like this, but twice the size (two 7-module strings in parallel)?
48v Nissan Leaf Lithium ion Mini Pack Battery Golf Cart 3.5 kwh G1 w 48v Charger

jefsmk

Discussion Starter · #5 · Feb 25, 2020 (Edited)

Ok, sorry for the confusion here. This is the ebay setup I was referring to:

I was originally thinking of 3 of these in series to get ~150v. But it sounds like this won't work from a BMS standpoint. So now, I'm thinking I should take 2 single Leaf modules, and wire them in parallel like this:

Then wire 21 of those in series like this:

For the BMS, following the Orion info below:

https://www.orionbms.com/manuals/pdf/nissan_leaf_modules.pdf

It looks like it could wire up like this:

but I'm not 100% sure this is correct, and not sure how to continue on the wiring, and not sure how to exactly handle (from a BMS standpoint) when I split the pack (because of physical issues) like this:

Per my contact at EVolve Electrics, a BMS (under $10k) is not possible with these Leaf units. But I have a feeling there is some communication issue here??

Thoughts??

PS: How the hell do I embed images into a post??

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kennybobby

· #6 · Feb 25, 2020 (Edited)

if you click on your picture while in imgur, there will be a menu on the right side with various links and a copy button. Select the one down the list that says BBS and forums link, click copy, then paste into your reply on the forum. It will have a link that starts with "i." and will embed into your post when surrounded by

e.g.

What the hell is that thing on the red wires?

The problem with a parallel pack such as the 2 stacks of 7 in series, is that a bad or shorted cell in one stack could occur and drain the neighbor stack below the safe LV limit and you would never know it until the next time it was charged and caught on fire.

Please redraw your diagrams to properly show a leaf module as 2s2p; you have drawn them as 4s.

jefsmk

Discussion Starter · #7 · Feb 25, 2020

BBCode! Got it, thanks!!

kennybobby said:
if you click on your picture while in imgur, there will be a menu on the right side with various links and a copy button. Select the one down the list that says BBS and forums link, click copy, then paste into your reply on the forum. It will have a link that starts with "i." and will embed into your post when surrounded by

e.g.

brian_

· #8 · Feb 25, 2020

jefsmk said:
Ok, sorry for the confusion here. This is the ebay setup I was referring to...

Thanks

There's nothing special about the way these modules are combined - you can make whatever length of stack you want, and as you have realized the modules can be linked by bars. Later modules are bonded together in pairs with alternating polarity orientations, making parallel combinations more difficult, but there have been some clever bus bar designs to address that.

jefsmk said:
I was originally thinking of 3 of these in series to get ~150v. But it sounds like this won't work from a BMS standpoint. So now, I'm thinking I should take 2 single Leaf modules, and wire them in parallel like this:
...
Then wire 21 of those in series like this:
...
For the BMS, following the Orion info below:
...
It looks like it could wire up like this:
...
but I'm not 100% sure this is correct, and not sure how to continue on the wiring, and not sure how to exactly handle (from a BMS standpoint) when I split the pack (because of physical issues) like this:
...

That looks good (other than that the actual internal arrangement of the cells doesn't look like that, as kennybobby mentioned), and the physical separation of parts of the stack shouldn't matter to the BMS, unless I have misunderstood something about the BMS.

kennybobby said:
What the hell is that thing on the red wires?

That looks like a common inline fuse holder, of the style often used by extreme auto sound system builders.

jefsmk

Discussion Starter · #9 · Feb 25, 2020

kennybobby said:
Please redraw your diagrams to properly show a leaf module as 2s2p; you have drawn them as 4s.

You're referring to how a single Leaf module is configured internally, correct? There are 3 taps on the module, so I was not sure how to show 2s2p schematically, and didn't think it was important because I'm not interacting with the internals? This was my generic method below. Or am I missing something here?

Can you share a correct example?

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jefsmk

Discussion Starter · #10 · Feb 25, 2020

brian_ said:
Thanks
There's nothing special about the way these modules are combined - you can make whatever length of stack you want, and as you have realized the modules can be linked by bars. Later modules are bonded together in pairs with alternating polarity orientations, making parallel combinations more difficult, but there have been some clever bus bar designs to address that.

Thanks for the info about the bonded pairs. I'm trying to get as much of the design done before buying a lot of suff, and this would of thrown a wrench in my plans had I not known. Anybody sell those offset & bent bus bars made to handle that situation?

brian_

· #11 · Feb 25, 2020

jefsmk said:
You're referring to how a single Leaf module is configured internally, correct?

Yes, that's the concern; although I didn't even notice it until kennybobby commented on it, the drawing is misleading if taken literally.

jefsmk said:
There are 3 taps on the module, so I was not sure how to show 2s2p schematically, and didn't think it was important because I'm not interacting with the internals? This was my generic method below...

The long and short bars in the common schematic symbol for a cell are intended to represent the electrodes, so the version with a couple of them stacked looks like two cells in series (the symbol for a multi-cell battery). In your drawings, it then appears that the module is four (or more) cells in series with only one tap (for BMS) in the middle.

My suggestion would be to use the symbol with only one pair (short and long) of bars, indicating a single cell. The paralleling of two cells to effectively make one big cell is irrelevant to the design, so could be ignored.

brian_

· #12 · Feb 25, 2020

jefsmk said:
Thanks for the info about the bonded pairs. I'm trying to get as much of the design done before buying a lot of suff, and this would of thrown a wrench in my plans had I not known. Anybody sell those offset & bent bus bars made to handle that situation?

I don't think anyone sells them. I also couldn't find the forum thread(s) discussing this setup in a quick search; perhaps someone else remembers who did this, which would make the discussion easier to find.

jefsmk

Discussion Starter · #13 · Feb 25, 2020

Thanks for all the help. Sure looks pretty simple to do half of my batteries in series, and the other half in series parallel to that. I think it would be called 21S2P. I think the guy at the BMS supplier confused me on this whole thing. Also, the Thunderstruck BMS manual explained it all pretty well too.

Thanks fellas!

kennybobby

· #14 · Feb 26, 2020 (Edited)

jefsmk said:
You're referring to how a single Leaf module is configured internally...
Can you share a correct example?

Sure, here's one way to illustrate it. (Using KiCad Schematic tool)

Do not use Figure 5 of the Dunderhead Dilithium Design Manual for your guide, unless you follow Wolf's approach: Each series string must be monitored and isolated from other series strings using contactors. You would need 84 BMS channels in two separate 42-channel BMS packs, plus a Master BMU to manage the relays and commands to the 2 BMS units. They did not show the contactors in their diagram and this would be a fatal mistake in the event of a bad cell.

Your drawings above would be the correct way to wire up the cells and the BMS. You would have a pack with 42s4p cells. You would need 42 BMS channels, each channel would monitor 4 parallel cells.

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jefsmk

Discussion Starter · #15 · Feb 26, 2020 (Edited)

kennybobby said:
Sure, here's one way to illustrate it. (Using KiCad Schematic tool)

Do not use Figure 5 of the Dunderhead Dilithium Design Manual for your guide, unless you follow Wolf's approach: Each series string must be monitored and isolated from other series strings using contactors. You would need 84 BMS channels in two separate 42-channel BMS packs, plus a Master BMU to manage the relays and commands to the 2 BMS units. They did not show the contactors in their diagram and this would be a fatal mistake in the event of a bad cell.

Your drawings above would be the correct way to wire up the cells and the BMS. You would have a pack with 42s4p cells. You would need 42 BMS channels, each channel would monitor 4 parallel cells.

I'm confused on how it would wire for 42 channels. Would the BMS wiring not look like this? Don't see how it could be done with more than 21 channels.

And would this not also be possible? I assume the downside is there if there is a problem I won't know exactly what cell is causing it. Is this true? Or are there safety concerns with this "reduced resolution" version?

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onegreenev

· #16 · Feb 27, 2020

To get a 144 volt system you may need a custom BMS that you can fully configure and that has 38s or more for configuring the cells. You just won't be using them all. The cheap BMS systems you see that are 14s are for a 7pack of modules for a 48 volt system and those are being used mainly for battery backup systems for homes. So each module takes two leads not one because the module is 2s/2s. My plan is to build a 7s pack with 12p for a high capacity 48 volt pack for my home and use one of the 14s BMS systems to monitor the voltage of each 12p stack. Once built I can easily deal with high currents if needed but won't really need to but only want one BMS. I'll control the discharge voltage using my SSR to turn off my inverter when the first 12p stack reaches the desired voltage. It will be a redundant system as my inverter also has a nice low voltage cutoff. I could even use a 6s 13p setup and use the Tesla Algorithm and get the same usable range of power. My inverter will handle the slightly lower voltage without issue.

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onegreenev

· #17 · Feb 27, 2020

If you want a 144 volt system you would need 19 modules in series for a nominal 144.4 volt system. Fully charged it would be 155.8 if you charge the modules to only 8.2 volts each. Only to get a BMS system that will let you connect up to 38 leads to monitor each side of the module. Each side is monitored because the BMS systems are designed to disconnect when one cell reaches a specific voltage of 4.15 or what ever the BMS is set for. A good BMS will allow you to tweak your charge and discharge needs. As long as you can use your BMS to trigger a relay to either stop a charge or stop a discharge you will be fine.

onegreenev

· #18 · Feb 28, 2020

My BMS is a 14s and parameters can be set via the Bluetooth phone app. Sweetness.

jefsmk

Discussion Starter · #19 · Feb 28, 2020

onegreenev said:
If you want a 144 volt system you would need 19 modules in series for a nominal 144.4 volt system. Fully charged it would be 155.8 if you charge the modules to only 8.2 volts each. Only to get a BMS system that will let you connect up to 38 leads to monitor each side of the module. Each side is monitored because the BMS systems are designed to disconnect when one cell reaches a specific voltage of 4.15 or what ever the BMS is set for. A good BMS will allow you to tweak your charge and discharge needs. As long as you can use your BMS to trigger a relay to either stop a charge or stop a discharge you will be fine.

This makes sense, but the other catch is I'm looking at another set of 19 in parallel to double the AH. What brand BMS you using?

kennybobby

· #20 · Feb 28, 2020

i don't know how serious you are since you have incorrect and inaccurate diagrams and haven't bothered to fix them and probably didn't go read any suggested threads by Wolf, but there is another thread about this right now that might help you understand the issues:

https://www.diyelectriccar.com/forums/showthread.php?t=202393

Good Luck to you.

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