# High voltage pack and parallel setups



## autocomman (May 22, 2020)

So im doing some research for a project. The original plan was using a tesla motor, so a high voltage pack would be needed. For range a 30-40kw pack is what were lookin for.

Here is the rub, using the chrysler LG Chem batteries, which are 60v you get 6 in series you get your 360v but only 16kw. so youd need to run them in parallel to get to 30 kw, and that well, im not so conident thats a good idea

Im watching Vintage Voltage on Motortrend, and when they say what motor they are using and how many batteries you can figure out what they are doing. Hyper 9 is a low voltage setup, so 16 LG Chem batteries, they are using the lower voltage cells, the 11v ones, which gives you about 41kw and 176 volts. But when they use a tesla motor, they are using 18 lg chem batteries....i can only assume they are using the 60v versions, and running them 6 series and 3 parallel. Or are they sourcing a different voltage pack from the manufacture and doing a proper series setup?

Paralleling batteries imo is a no no. No oem does it out side of the individual modules inside the full pack. Every battery module is in series with the next one, and the BMS inside each battery module deals with the series parallel setup inside that module. If you parallel the battery modules, you have to have a full individual BMS on every parallel string, and contactors to take that string out of the parallel loop incase of failure. And even then, it seems its just not a good idea. It could help with reliability and redundancy thats pretty obvious. You loose a cell and that one string goes down, but doesnt kill the whole pack.

I know EV west sells a board to parallel the cell taps and the board is fused, but they dont have a contactor to separate the main connections between the battery modules and take a parallel string off line incase of failure, and also the whole system I think is monitored by one BMS? I have a hard time getting on board with that.

What are the general opinions here? And if you cant stuff 16 tesla battery modules in a car, but want 30-40kw, what are the battery options? How many of these companies are sourcing new batteries from the manufacture?

Mark


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## john61ct (Feb 25, 2017)

In and of itself paralleling modules should be OK.

Same voltage before connecting.

It's the BMS interaction I'd want clarification on.


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## brian_ (Feb 7, 2017)

Your teminology is all over the place, making your post harder to follow than it needs to be:


autocomman said:


> For range a 30-40kw pack is what were lookin for.
> 
> Here is the rub, using the chrysler LG Chem batteries, which are 60v you get 6 in series you get your 360v but only 16kw. so youd need to run them in parallel to get to 30 kw..


Everywhere you put "kw" you are talking about energy, so it should be in kilowatt-hours (kWh); kilowatts (kW, not kw) is a unit of power, not energy. If you understand the difference between power and energy but are just being sloppy, please don't; if you don't understand the difference, please learn that.



autocomman said:


> Hyper 9 is a low voltage setup, so 16 LG Chem batteries, they are using the lower voltage cells, the 11v ones, which gives you about 41kw and 176 volts. But when they use a tesla motor, they are using 18 lg chem batteries....i can only assume they are using the 60v versions, and running them 6 series and 3 parallel. Or are they sourcing a different voltage pack from the manufacture and doing a proper series setup?


I don't really know what you are talking about. Any stack of cells is by definition a battery, but in electric vehicles the term "battery" is generally reserved for the vehicle's entire battery, not just part of it. A stack of cells combined as a unit and intended to be used with others to make a complete battery is called a "module"; the commonly available LG Chem modules contain 16 cells in series, for a nominal voltage close to 60 V. The cells are typical lithium-ion cells, so they each have a nominal voltage about 3.75 V; there is no cell that runs at 11 volts.

I'm not familiar with the specific project to which you are referring... but no, no small-time project or aftermarket conversion parts supplier gets modules made up to their specfications.


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## autocomman (May 22, 2020)

I will try to be better about the terminology, I do understand the terms. Please don't insult me and call it sloppy.

Take the LG Chem 60v batteries. yes, 16 cells in series in each module. Each module wires in series. No OEM wires their modules in anything other than series. Not that I've ever seen anyway. Internal to each module, yes. Bbut the actual modules are always in series.

So if someone chose that particular battery and wanted more than the 16kWh that 6 in series would provide they would have to be parallel with 2 strings of 6, you would then have 32 kWh. Can we agree on that?

But how do you safely do this. No OEM does this, if it was viable I would think that it would already have been done in the OEM world. Im trying to understand when I see someone building a project and they say they are using a tesla drivetrain and 18 LG Chem batteries, are they running these in 3 strings of 6 modules? And if so how are they doing it safely?

Also there are LG batteries that are internally 4p3s that have a lower module voltage. They arnt 60v they are 11v. Look on the zeroev website.

When you get a shop that says how many batteries they are using, knowing what motor they are using, you can probably do the math to figure out what configuration they are in. Tesla motor is a higher volt system, and a hyper 9 is a lower voltage system. Knowing that you can determine how the pack is set up. So for a tesla motor, which is a 400v system, and you use '18 battery modules' What configuration are they in. Knowing whats on the market and whats easily available. The LG chem at 60v in a 6s3p configuration is all I can figure.


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## OR-Carl (Oct 6, 2018)

autocomman said:


> But how do you safely do this. No OEM does this, if it was viable I would think that it would already have been done in the OEM world.


The reason that the manufacturers are not paralleling modules is that they do not have to. They design the modules from the ground up, so it makes sense that they would not do it in a way that increases complexity without any real benefit. The reason we parallel modules is to make OEM modules work at the voltages we want, and avoid the staggering cost of building something custom. 

If you parallel 2 module strings, each string will probably need its own BMS. If the 2 BMS's can communicate with each other, and several makes out there will (and have documentation on how to wire parallel strings); then you should be able to tie them together through a single contactor, but probably a separate fuse for each string. If either BMS sees a problem, the whole pack shuts off. I suppose you could also do 2 BMS's and two contactors, which would give you a certain degree of redundancy: If string A blows up, you can limp home on string B. 

I am working on a build that is going to use 2 parallel strings of Tesla modules, as I do not want full pack voltage. I am planning on running a Thunderstruck Dilithium BMS which will be monitoring both strings. I am pretty sure you can do the same thing with the Orion BMS, and possibly others.

On the topic of sloppiness: if you are serious about learning, I suggest you not let ego get in the way of being corrected by experts. It may seem trivial, but it is hard to have a technical discussion that is full of technical mistakes.


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## MattsAwesomeStuff (Aug 10, 2017)

autocomman said:


> Please don't insult me and call it sloppy.


So, you know better, and yet are choosing to use confusingly-close-sounding technical terms, deliberately backwards to the thing you intend to say?

I'm going to go out on a limb and say you're not sloppy, you're just defensive because you didn't actually know the difference and you're quick to get offended. That, or you're sloppy.

When you want help from strangers, it generally behooves you to make it as convenient as possible to them to be interested in helping you. That includes clear communication and general politeness. Just my two cents, you behave however you want and see if you like the result of it.



> But how do you safely do this. No OEM does this, if it was viable I would think that it would already have been done in the OEM world.


There is no reason for it to be done in the OEM world. OEM makes custom everything for their production, why would they create two parallel packs when they could just create a single pack with twice the capacity?


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## john61ct (Feb 25, 2017)

I have seen designs where modules are paralleled not just at their "power lead pair", but each cell-level "P group" is wired to the corresponding groups in the other modules

in effect joining the all into a single string each group

allowing the same BMS to sense / protect it.

These would then be joined in series as needed to reach higher voltage.


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## brian_ (Feb 7, 2017)

autocomman said:


> Take the LG Chem 60v batteries. yes, 16 cells in series in each module. Each module wires in series. No OEM wires their modules in anything other than series. Not that I've ever seen anyway. Internal to each module, yes. Bbut the actual modules are always in series.


I agree. OEM battery design virtually always uses modules in series (and within those modules, parallel connections between cells are only at the lowest level), for good reason as OR-Carl and Matt explained.



autocomman said:


> So if someone chose that particular battery and wanted more than the 16kWh that 6 in series would provide they would have to be parallel with 2 strings of 6, you would then have 32 kWh. Can we agree on that?.


Yes 



autocomman said:


> But how do you safely do this. No OEM does this, if it was viable I would think that it would already have been done in the OEM world. Im trying to understand when I see someone building a project and they say they are using a tesla drivetrain and 18 LG Chem batteries, are they running these in 3 strings of 6 modules? And if so how are they doing it safely?.


Doing it safely is entirely viable. It isn't done by OEMs because it is overly complex and so not cost-effective, requiring multiple sets of BMS slaves and disconnects.

Again as OR-Carl explained, DIY builders sometimes resort to this because they do not have the ability (due to their lack of purchase volume) to get modules built to their desired configuration. For instance, if the common LG Chem modules are 16s1p and they want 32 kWh, they do not have the option to buy them factory-assembled as 8s2p in order to use 12 of them in series for a 96s2p 32 kWh battery. They could just use the LG Chem modules from the Chevrolet Bolt, which are 10s and 8s, but enough of those combined in series have 60 kWh capacity: that's great, but it's more than usually needed and too large to fit in most conversions (and much less readily available than the 16s Chrysler Pacifica PHEV modules).



autocomman said:


> Also there are LG batteries that are internally 4p3s that have a lower module voltage. They arnt 60v they are 11v. Look on the zeroev website.


Sure, I'll believe that *module* exists without even looking it up.



autocomman said:


> When you get a shop that says how many batteries they are using, knowing what motor they are using, you can probably do the math to figure out what configuration they are in. Tesla motor is a higher volt system, and a hyper 9 is a lower voltage system. Knowing that you can determine how the pack is set up. So for a tesla motor, which is a 400v system, and you use '18 battery modules' What configuration are they in. Knowing whats on the market and whats easily available. The LG chem at 60v in a 6s3p configuration is all I can figure.


This all makes sense, and it is what is generally understood by members of this forum, except that the nominal voltage (360 V for Tesla Model 3 and large battery Model S/X) is normally used rather than peak voltage (roughly 400 V for those Tesla models).

I agree that anyone using 18 of the 16s LG Chem modules to drive a Tesla (or any other typical modern EV) motor is likely using those modules six in series. But there are alternative ways to so that:

Typically they would have three strings of six, with no connections between the strings at intermediate points. Three complete BMS systems (3 x 96 cells groups to monitor) and three sets of disconnect relays would be advisable. This certainly works, and Mark (autocomman) described this in the first post.
There is one project in this forum currently building with two strings of six 16s LG Chem modules each - that's this scheme, but with 12 instead of 18 modules. Some builders have completed projects with two parallel strings of Chevrolet Volt modules - again, that's this scheme.​
It is also possible (but likely inadvisable) to connect sets of three modules in parallel, then connect six sets of three in series. BMS capacity to monitor 3 x 96 cell groups are still required, and ideally there would be 18 disconnects!

The other option is to connect cells in parallel at the lowest level, so each modules are wired in parallel groups of three (as in #2) and the individual BMS taps are also connected between modules. This is what Mark described as supported by boards sold by EV West, and what John mentioned. It would only require one 96-point BMS and the whole battery would be handled by one disconnect, but the amount of current potentially flowing in the BMS tap wires is a significant concern for both overloading (thus the fuses) and for cell imbalance (due to resistive voltage drop in the tap wires).Some configurations using Nissan Leaf modules have taken this route of paralleling at the cell level - this is practical only because Leaf modules have a high-capacity BMS tap terminal to which substantial wiring can be readily attached..​


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## brian_ (Feb 7, 2017)

autocomman said:


> Im watching Vintage Voltage on Motortrend, and when they say what motor they are using and how many batteries you can figure out what they are doing. Hyper 9 is a low voltage setup, so 16 LG Chem *modules*, they are using the lower voltage *modules*, the 11 *V* ones, which gives you about 41 *kWh* and 176 volts.


With corrected notation (in bold) this now makes sense. Yes, 16 modules of 4P3S (which is normally written 3S4P, if the parallel connection is at the lowest level) simply connected in series would be a 48S4P configuration, or about 176 V (nominal) and 41 kWh if they are 2.6 kWh each.

This module looks like a good choice for many DIY conversions, with a small size to help with packaging, and a capacity and voltage combination suitable for series combination to usable overall capacity and voltage levels. It does not appear to be as widely available as the 16S (presumably 16S1P) modules, which are used in the Chrysler Pacifica Hybrid; I don't know what vehicle it comes out of (note that at Zero EV they are used, so they must be salvaged from something).

These two modules are interesting to compare:

*"4P3S"*
this is presumably 3S4P​length: 358 mm
width: 151 mm
height: 110 mm
calculated volume: 5.9 L
calculated module volume per cell: 0.5 L/cell
calculated energy density by volume: 440 kWh/m3​mass: 12.8 kg
calculated energy density by mass: 0.20 kWh/kg​
*16S*
this is presumably 16S1P
specifications from EV West​length: 14.25" or 362 mm
width: 8.00" or 203 mm
height: 6.25" or 159 mm
calculated volume: 11.7 L
calculated module volume per cell: 0.73 L/cell
calculated energy density by volume: 222 kWh/m3​mass: 38 lb or 17.2 kg
calculated energy density by mass: 0.151 kWh/kg​
If we can believe these specs, the 4P3S module has smaller cells, and fewer of them, but holds more energy; it has double the volumetric energy density and one-third higher energy density by mass. I suspect that the capacity specs for the 4P3S module are either incorrect, or under different conditions from the other module.


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## autocomman (May 22, 2020)

Ok so then my thinking on what I've been seeing on these TV shows makes sense. 

So setup I've seen offered is with the LG Chem 16s modules. 360v pack 32kw using 16 battery modules, and 2 battery boxes, 200v each box. This means 6 battery modules in each, 3s2p. This doesn't seem safe to me. 

Let's take a hypothetical situation. The scenario would be if you have the vehicle off, not charging, say just parked in your garage. You've got battery modules in parallel, connected with this parallel board between the cell taps with fuses. These boxes are as I described above, 2 boxes with 6 battery modules. Each box is wired 3s2p. Then the 2 battery boxes are wired in series. If a cell in a module went south and blew the fuse between it's shared parallel cell, what would happen? The main connections at each battery module are still connected. If a cell tanks in a battery module, because the cells in the battery module are in series (16s). Is there potential for a catastrophic failure? Would you be able to add fuses to take that battery out of the series loop to prevent it from going all wrong? 

I would think it would make more sense to do 2 boxes at 360v each box being 6 battery modules in series, then the 2 boxes paralleled with contactors for each box. 2 separate BMS systems, one for each battery box. This way the boxes are not paralleled when the vehicle is off, and when the vehicle is on or charging the batteries are all monitored properly and can be shut down via the main contactors incase of a failure. But you end up with 2 high voltage boxes and I know with some design you wanna try to avoid that.

Sorry if I seemed like my ego was hurt, it just seemed aggressive is all. I'm here to learn, and we all learn new stuff even with tons of experience. I've got my first kid on the way due in 6 weeks, I have been unemployed for a few months and I'm trying to get a business off the ground right now. This particular project I knew was coming down the pipeline, but I didn't realize the potential battery setup which has cause quite a conundrum. Im just working through it. So if I came off defensive I apologize. Lots of smart guys here and I hope to be able to contribute as much as anyone else here soon enough. I've been part of a few EV builds already, I worked for Icon 4x4 for a number of years. The 66 Fiat 500EV and the 49 Mercury they build I had my hands in pretty deep. I'm only now really immersing myself with the design and planning of a full EV setup.

Mark


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## dtbaker (Jan 5, 2008)

If you are using a DC motor like Warp9, it makes a lot of sense to stick below 160v. Lots of connectors, chargers, dc-dc converters, wire, etc are all more available. I'm old school... and believe a DC setup, with large format cells (100ah-200ah) in series, is the way to go for a DIY conversion if you want to keep it simple.

no need to pull apart OEM high voltage packs designed to run AC motors at high voltage, no need to reconfigure hundreds of cells to proper s-p config, no need to re-program OEM BMS.

... but this approach doesn't seem to be too popular currently.


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## brian_ (Feb 7, 2017)

autocomman said:


> I would think it would make more sense to do 2 boxes at 360v each box being 6 battery modules in series, then the 2 boxes paralleled with contactors for each box. 2 separate BMS systems, one for each battery box. This way the boxes are not paralleled when the vehicle is off, and when the vehicle is on or charging the batteries are all monitored properly and can be shut down via the main contactors incase of a failure.


I agree - contactors in each parallel string seem appropriate.


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## brian_ (Feb 7, 2017)

dtbaker said:


> I'm old school... and believe a DC setup, with large format cells (100ah-200ah) in series, is the way to go for a DIY conversion if you want to keep it simple.
> 
> no need to pull apart OEM high voltage packs designed to run AC motors at high voltage, no need to reconfigure hundreds of cells to proper s-p config...


This logic make sense to me, to the extent that it avoids the complexity of parallel connections. But at about 120 volts nominal, for example, 38 LiFePO4 cells would be required - that means 37 high-current interconnections and BMS wiring for 38 cells. Very few builders actually reconfigure cells within modules, so realistically the alternative for most people (as in this discussion) is a much smaller number of connections between modules, and a slightly lower number of BMS connections (due to the higher cell voltage of anything other than LiFePO4).

The trick to avoiding parallel connections is to start with a module with sufficient amp-hour capacity. Any pack at the typical 360 V of 36 kWh to 72 kWh will have 100 Ah to 200 Ah capacity. This is one reason that the 3S4P modules found at Zero EV and discussed earlier would be appealing: only 11 would be required for 120 volts, and they are 240 Ah (the specs say 60 Ah but that's per cell and they have 4 cells in parallel interally) so no parallel connections would be required.


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