# Need to balance charge LG Chem A7 packs



## frodus (Apr 12, 2008)

One thing confusing when you say 3p2s is you're talking modules, not cells. We normally discuss XsYp when talking cells, not modules. People do it a lot with Leaf cells and it's confusing. 

So it looks like you want to build two 48s packs and parallel them. Correct?

If you want to balance, you'll need either a BMS that can do it, or hand balance the cells, which is a huge PITA. I'd look into Zeva BMS a little, as they're priced well and modular. They're 12s, but you can make harnesses so you'd use 4 boards for your 48s pack. 

For charging, you want to charge just a single 16s pack temporarily? or do you want to charge the entire 48s pack? I suggest buying a charger that meets the final need, not the immediate desire.

If they're resting at a good voltage, don't worry about balancing until you're ready to install in vehicle, and charge/balance then. You don't want to fully charge them and let them sit for long periods. We recommend having maybe 50-60% SOC for storage. Charging to 100% and leaving sitting is not recommended by many battery manufacturers or OEMs.


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## EVmattyP (May 12, 2019)

Travis, thanks for the response. I think I'm just muddying the waters because I'm not 100% sure what I'm doing right now. 

My initial plan was to run the biggest/strongest 48v AC motor I could get away with and then run all of these battery modules as just a 6P configuration, so basically 60.5v @ 270Ah. I was told by a few people (who know more than I do) that these modules have issues running in parallel and I should consider going the other way with it and running it as a 320v+ @ 45Ah instead. It was mentioned that they shouldn't be run more than 2P. I'm guessing for logistical reasons. 

My initial plan was to run the HPEVS AC-35 as it would be able to provide about 100+tq which is plenty for my build but if I can't run the batteries in a xP configuration then I'd have no usable range. 

A tesla motor/gear drive will not work in my application without serious modification and I'm not interested in going that route. Currently the van has a DC motor in it (set up for 72v) but I figured a newer/better AC motor @ 60v would still be a vast improvement. 


If I'm mistaken and the harnesses I got with these units aren't used for an internal BMS then I should be ok to run them in either a 6P or 3S2P configuration, right?? At that point it seems it would just come down to which motor I'd want to use. Am i overlooking something else?


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## EVmattyP (May 12, 2019)

Sorry, one more thing I need to clarify. The A7 modules are composed of (16) cells in series. When I say "3S2P" I'm talking about how I would connect the modules together once they're in the van


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## frodus (Apr 12, 2008)

EVmattyP said:


> Sorry, one more thing I need to clarify. The A7 modules are composed of (16) cells in series. When I say "3S2P" I'm talking about how I would connect the modules together once they're in the van


Thanks for clarifying. It's difficult with so many modules out there for people to memorize what each of them are. 3s2p looks like 3 cells in series, 2 cells in parallel, as that's the industry norm. There isn't really a clear way to state module configuration, other than just saying "3 modules of 16s in series for 48s and 2 of those packs in parallel.

So if possible, I'd avoid using s and p for discussing modules.


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## frodus (Apr 12, 2008)

EVmattyP said:


> Travis, thanks for the response. I think I'm just muddying the waters because I'm not 100% sure what I'm doing right now.
> 
> My initial plan was to run the biggest/strongest 48v AC motor I could get away with and then run all of these battery modules as just a 6P configuration, so basically 60.5v @ 270Ah. I was told by a few people (who know more than I do) that these modules have issues running in parallel and I should consider going the other way with it and running it as a 320v+ @ 45Ah instead. It was mentioned that they shouldn't be run more than 2P. I'm guessing for logistical reasons.
> 
> ...


60V and lower is good for golf carts or small, slow motorcycles. Not so much for a car. I'd suggest aiming for 72-120VDC, and run either a series wound motor and controller, or an HPEVS system like AC35. They have units that can go to 144VDC, or if you want lower, use something like 96V (2 modules in series for ~96V nominal and about 130V fully charged). 

Concerning BMS, if you want to use a BMS, you will likely require a BMS for each parallel pack. 

For example, if you try to put 2 modules in parallel at their main lugs, and try to tie all the balance wires together so the cells are essentially in parallel, it will likely result in some overheating/damage of the balance wires. When you charge, or discharge, the cells will naturally share current across those balance wires. Cells have different internal resistance and share current unequally, so each cell may discharge some into a paralleled cell. Balance wires are very small compared to the high current connections and will overheat. I've seen them fry before. 

For this reason, you'd want to put the batteries in series first to get your voltage required, and then have multiple parallel battery packs. Unfortunately, this would also require you to have 2x the BMS. If you have a 48s setup (2 parallel packs of 3 modules in series), you'd need 8 12s balance boards of Zeva BMS, or two Orion BMS 48s BMS. Because of the balance wire issue above (low current wires between parallel groups), you can't use just one single 48s solution. You treat the packs as if they're independent. Zeva and Elithion can do parallel packs. I don't think the Orion can.

These batteries are great, but you do need to think out the system somewhat.


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## EVmattyP (May 12, 2019)

That's very helpful insight. I'm located in the Alabama Gulf Coast and I'm really struggling to find local experts I can bounce ideas off here. I am worried I'm going to need to just ship everything to EVwest and wait several months and write them a giant check to finish this project. 

I really jumped in before knowing exactly what I was doing. I saw the batteries as a great deal and jumped on it and now I'm trying to design a system around them and it may be better to cut my losses now and start over OR temper my expectations and work with what I have. 

If you would be willing to chat on the phone sometime you could PM me your contact info and we could probably come up with a solution fairly quickly.

Thanks for your help


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## frodus (Apr 12, 2008)

I'd rather discuss here, then it's useful for the next person  You know what I mean?

What vehicle is this going into? What are your design constraints (Range, top speed, etc)?

I think they're good strong batteries that are great for an EV. I wouldn't start over at all. You just need to know some of the aforementioned design constraints before you move forward.

You really should look more at your drive train (motor/controller). IMHO, 60V is way too low. 400V is likely too high ($$$).

We know you have 6 modules to mess with? 

1) You can go 96s (6 modules in series) for about 400V fully charged, but you're in a different power level than most easily purchased controllers and motors. 

2) You can go 48s (3 modules in series, 2 packs in parallel) for ~200V fully charged, and you're pretty much the same place as above. If you use Zeva BMS, you'd need 4 modules per series pack, so 8 total.

3) You can go 32s (2 modules in series, 3 packs in parallel) for ~130V fully charged, and now you can use some of the HPEVS or Netgain equipment. For HPEVS, there's the 144V controller and the 96V controller. The 144V will work well. The 96V controller works up to 130VDC, so just undercharge slightly and you should be close to the cutoff. The Netgain 144V should work. If you use Zeva BMS, you'd need 3 modules per series pack, so 9 total.

4) You could go 16s, but you're going to have a golf cart, with underwhelming speed. 

So I'd say stick to #3 above unless you want to put some $$$ into the project. The cost goes up and choices go down for #1 and 2.


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## gwayne (Dec 9, 2017)

You can certainly run them more than 2 in series. What matters is what they are connected to. Those batteries have a peak voltage of ~65 volts (4.2 x 16). Of course, you can set your BMS to have a lower max voltage to extend your battery life. So say you charge them to a max of 60 volts, you can put 3 in series as long as your motor/controller can handle 180 volts, etc.

By any chance, do you know what the rated peak discharge of those batteries is? Thanks and have fun. gw


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## EVmattyP (May 12, 2019)

gwayne said:


> You can certainly run them more than 2 in series. What matters is what they are connected to. Those batteries have a peak voltage of ~65 volts (4.2 x 16). Of course, you can set your BMS to have a lower max voltage to extend your battery life. So say you charge them to a max of 60 volts, you can put 3 in series as long as your motor/controller can handle 180 volts, etc.
> 
> By any chance, do you know what the rated peak discharge of those batteries is? Thanks and have fun. gw


I may have misspoken earlier. I was told the LG modules could ONLY be connected in series, not parallel. I could easily run them as 360v+ but not 60v @ 270Ah.

I believe the way I'm going to try to wire this up will be (2) groups of 3 modules in series (48cells)


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## frodus (Apr 12, 2008)

You can parallel them, but I'm not sure you are understanding. 

You wrote what EVWest said here:
https://www.diyelectriccar.com/forums/showpost.php?p=1037695&postcount=16


> "Hi Matt,
> 
> Can’t dive in right this minute but I quickly scanned your email.
> 
> ...


He is right, You cannot parallel them without having a more complex design. You need a BMS per parallel string. That doubles the cost if you parallel 2 packs. It Triples if you parallel 3 packs, etc.

They are NOT saying you can't parallel, they're saying there are caveats. They are saying you can create multiple "battery packs" and parallel them, as long as each parallel string has its own BMS and control. 

Cells like from the Leaf, have high current connections for each cell, that you can parallel each cell group easily. The LG cells do not, and you CANNOT use the BMS wires to parallel the packs for balance purposes, as they'll use those connections to share current. It will likely cause the balance wires to overheat and you risk fire.


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## EVmattyP (May 12, 2019)

That's great info. Just for clarification, it wasn't EV west who told me they couldn't be run parallel, only that's how they recommend it. That email is from another installer/builder. 

I think I understand what you're saying now. I'm perfectly fine with buying a second BMS if it means I'm able to ensure the cells will stay in top shape and I can use all 17kwh I've purchased. 

If each module contains 16cells and I'd have (3) modules connected in series I would need a BMS capable of charging 48cells at a time. Is that correct? Then I'd need two of those and I'd need a charger that could power both BMS' at the same time (ideally). 

Can you suggest the appropriate BMS and Charger I would need to pull this off? My goal is to have a system I can just plug in like my regular Cmax and have it charge the batteries fully, appropriately and quickly. I'm trying to avoid charging one bank and then going out and charging up the second bank after the first is finished.


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## frodus (Apr 12, 2008)

Please draw out your proposed system. Label everything, include your proposed connections.

It's likely the builder you reference doesn't want to mess with it or have to painstakingly support it, due to the extra wiring and work.

Slight correction: BMS doesn't charge the cells, it manages and balances them. The charger does the charging. You would only need a single charger to charge all packs that are wired in parallel. I'd highly recommend going to a BMS manufacturer website and reading some manuals to get familiar. We aren't going to want to explain in detail how a BMS works and functions.

One that I know does parallel packs is Zeva BMS. Since the BMS comes in 12s modules, and you have 48s, you'd need 4 of those per 48s string of cells. If you have 2 strings in parallel, then you'd need 8 12s modules and a master BMS controller and LCD. 3 parallel strings would be 12 12s modules. 

Elcon charger is one that people like to use, but anything that does 48s is going to be fine.

Remember 48s, and 4.2V a cell (max) is ~200VDC, so ensure your motor/controller will handle that. If you choose 32s, you'd need 3 12s modules (you'd leave 4 unpopulated), and you'd need a charger and controller that handles ~135VDC.


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## gwayne (Dec 9, 2017)

Let's back up a step. You have six batteries and are asking which way they should be configured - cart before the horse. 

Normally you (overly simplified):
i) pick the car you wish to convert conscious of its weight, drag, etc.
ii) pick the motor(s) and controller(s) you wish to use to provide the desired performance using one of the available performance models;
iii) choose a series of modules and cells necessary to produce the input voltage required to drive the controller
iv) choose the number of modules or cells necessary to produce the driving range (kWh) and/or the performance (peak current) you want.

gw


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## EVmattyP (May 12, 2019)

Thanks again for the prompt replies. Admittedly I'm in a bit over my head so I appreciate the constructive feedback. I will work on a simple drawing tonight that lays out what I'm attempting to do and how I have it planned in my head. 

To comment on your last topic about the controller needing to handle 200V+ : https://www.evwest.com/catalog/product_info.php?products_id=482&osCsid=0td1go2hqvsm45hr94ue5t33c0 This is what I was planning to purchase. I may be mistaken but I was under the impression the controller could see more volts than it's rated for but not use them all. This way I could feed 200v+ to the controller but it would only output the 180v the motor can use. 

I was also told by the owner of HPEVS that motors don't "see" voltage, only amperage and that's regulated by the controller...so the controller feeds amps to the motor and the motor is then being "run at a specific voltage".

Is this accurate?


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## EVmattyP (May 12, 2019)

gwayne said:


> Let's back up a step. You have six batteries and are asking which way they should be configured - cart before the horse.
> 
> Normally you (overly simplified):
> i) pick the car you wish to convert conscious of its weight, drag, etc.
> ...


1. I already have the vehicle.

2. It was already an electric vehicle with a 72v DC motor. My plan was to replace the 72v DC motor with a stronger, "48v AC motor" (HPEVS AC-35)

3. The 60v LG batteries I purchased were just going to be run all in parallel for a 60v 270Ah pack which would've been far more powerful, provided double the range and increased the top speed.

4. I didn't do this. I only looked at the voltage of each module and the overall capacity to determine range. Although I should say I was GOING to purchase Smart fortwo modules from EVwest but they had a much lower rated continuous output. Michael from EVW told me that these LG modules would be capable of 800Ah where-as the Smart modules were only good for 100Ah (200Ah peak). At this point I decided that the LG modules were the ones I wanted to use. Admittedly I may not have had all of the information or wiring knowledge prior to buying them. 


This vehicle I'm building is just a play thing. I'd like to take it to shows, do some burnouts and maybe tool around to the shops in it with my son. I'd really like to be able to make a profit on it when I decide to sell it on but that's not paramount. I'd just like to have some fun and turn some heads. 

I'm confident that no matter what motor/controller I end up being forced to use I'm going to make a ton more power and range than I would if I just restored it to stock. If I'm able to run a 168tq Hyper9 or a 110tq AC-35, it's going to be a lot more fun than the standard 12hp DC motor I'm taking out. 

also, this vehicle has a manual transmission and a Dana 44 rear end so I'm able to add limited slip and any rear end size I want to adjust for either top speed or acceleration.


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## gwayne (Dec 9, 2017)

If you use the standard voltage Hyper 9, you can put 2 LG Chem modules in series. The High Voltage version won't do you much good since 2 modules in series gives you about 130 volts which is too low for the HV version. 3 modules in series gives you over 180 volts which is too high for the HV version. Good luck with your project. gw


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## EVmattyP (May 12, 2019)

gwayne said:


> If you use the standard voltage Hyper 9, you can put 2 LG Chem modules in series. The High Voltage version won't do you much good since 2 modules in series gives you about 130 volts which is too low for the HV version. 3 modules in series gives you over 180 volts which is too high for the HV version. Good luck with your project. gw



You're suggesting I order the 120v Hyper9 kit and just run (3) sets of 2S modules? It would require me to buy 3 BMS' and the power is slightly less but if this reduces complexity in the system then I'm all for it. 

I have a feeling,. from what we've been discussing here, that I'm going to have to take apart the LG modules and have the BMS' wired directly to each cell. One of the most attractive things about these modules was how tidy the packs were and easy to package. I hope the addition of the BMS' doesn't impact this too much. 


Also, of the 6 modules I have (4) are at 60v+ and (2) are at 55v+. I was hoping to somehow condition them (bottom/top balancing) prior to using them. I've heard others mention they need to be used in the vehicle first and THEN balanced. Any opinions on this or what I would need to accomplish it?


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## gwayne (Dec 9, 2017)

The standard Hyper 9 motor is good quality and produces much more power for the money then the HP-50. The reason EV West carries them is they provide very good power/$. I use 2 of them for a cobra kit car I've made and we are using 2 of the HV type for a conversion of a 1950 Chevy Pickup. Given the batteries you have, I'd run them 2S3P. That will fully power the motor and give you 75 miles of range or more depending upon how light your car is.

DO NOT open up the batteries. The plastic cases are factory welded shut. Those batteries have a voltage tap for each cell. Those batteries have a socket for 16 voltage taps and 4 thermister taps. The pin-outs are listed on the EV West site. If you need to get the matching plug, Thunderstruck should be able to provide you with the plugs and crimps, especially if you use their BMS. I would ask John at Thunderstruck for the best topology to wire their BMS to you 2 modules in series, 3 in parallel. 

gw


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## x.l.r.8 (Oct 20, 2018)

The Pacifica modules are certainly not welded shut, I have one apart on the bench


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## frodus (Apr 12, 2008)

EVmattyP said:


> Thanks again for the prompt replies. Admittedly I'm in a bit over my head so I appreciate the constructive feedback. I will work on a simple drawing tonight that lays out what I'm attempting to do and how I have it planned in my head.
> 
> To comment on your last topic about the controller needing to handle 200V+ : https://www.evwest.com/catalog/product_info.php?products_id=482&osCsid=0td1go2hqvsm45hr94ue5t33c0 This is what I was planning to purchase. I may be mistaken but I was under the impression the controller could see more volts than it's rated for but not use them all. This way I could feed 200v+ to the controller but it would only output the 180v the motor can use.
> 
> ...


That's if the controller can handle over 200VDC, which it will not. Absolute max for the 144V X1 controller they use on the Netgain is about 180VDC. 

See if the place you got the batteries will take them back, unused. It sounds like you may still be far off from needing batteries and it may not be a great design voltage for 2 of those modules in series, 3 strings.

The LG modules have cell voltage taps and temp sensor taps you can use, you don't need to take them apart to attach a BMS. It seems like you may not fully understand what a BMS is, and how it works and how it is connected. Take a look at Zeva BMS manuals or Orion BMS manuals to see how they do it. 

You needed to do way more research before you started purchasing items. You're not in over your head, you just haven't gotten your "design" to a point you were ready to purchase. It needs refinement.


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## swo (May 17, 2019)

some motors you can over volt but may not last as long
also have to check your controller voltage/amperage


if no batteries in there now could just charge these to 65v and put in now use your old controller and motor just to see how it works...


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## LDT3 (Jun 19, 2019)

x.l.r.8 said:


> The Pacifica modules are certainly not welded shut, I have one apart on the bench



Can the LG units be easily re-wired? 

Problem is that for my application 2 modules in series (120V) would be too low, and 3 in series (180V) would be too high. 37 cells in series would be ideal giving me 140.6V, additionally I'd wire 3 cells in parallel and would only have to get a single BMS which can handle 37s.


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## x.l.r.8 (Oct 20, 2018)

3p becomes problematic, 2P means each module is 8S 
So 2P 32s fits in 4 modules.


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## LDT3 (Jun 19, 2019)

x.l.r.8 said:


> 3p becomes problematic, 2P means each module is 8S
> So 2P 32s fits in 4 modules.



I see your point - but I was thinking of re-packaging:
Could you remove 1 cell from each module and then re-wire so that each module now becomes 3p5s? Effectively 19V per module?


Later you could take the spare cells, parallel cluster them in 3's and string them along. It's makes sense to me on paper but without seeing the inside of the module I don't know if it's feasible or not. If it can be done, it would be an ideal and inexpensive solution to my design.


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## x.l.r.8 (Oct 20, 2018)

Not really, the tabs are at their limitations on 2P unless you make a link to connect the P groups across 3 modules.. They need to be substantial but They only keep the P groups balanced. You could join 3 modules together in 3p and series then to another 3 modules joins at cell level. You can take a number of cells easily from the modules you have plates to keep the pouches together . 
As you can see from the first picture, 2P makes the module tight for joining the tabs. Unless you ultrasonically weld them your stuck with solder as spotwelders do not work. Making it a 3P will simply not work. I removed the redundant copper tabs from the faceplate and widened the openings to fit the tabs through. The redundant tabs make ideal clips to hold the pouch tabs to solder them. 

Picture 2 shows linking 2 modules to make a 2P 16S module, they are side to side as I plan on mounting them to give maximum exposure to the cooling plates. But you could stack differently. As long as the pack is balanced it will pull evenly through the series connectors so the P group plink needs to be good enough to allow group balance if there is an uneven load on the S connectors. The danger being is if you have a S connection the load will increase across this link. You have the option of making it a) fusible or b) big enough to carry a fair amount of power. It would be worth measuring the internal resistance of each 37S before doing this as if one is considerably higher you need to rectify that before making the P connections. 3rd picture shows each leaf of the module after the tabs have been separated. Each hold 2 pouches either side of an aluminium heatsink. So when together 2 pouches are in contact with each other on one side and against the heatsink on the other. When you remove the pouches you are left with just the trays picture 4. 
If you revert back to picture one, a 2P has 4 tab connections and uses the heat sinks as they were intended. Making them 3P would require extending the tabs.


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## LDT3 (Jun 19, 2019)

Thanks! - These internal pictures really help, based on what I'm seeing I may just leave the cells as they are and follow your suggestion in photo#2, setting up three modules' cells in parallel this way, hence having to get only a 32s BMS for 6 modules arranged in 3p2s.
My interest in breaking apart the cells and going to 37s cells was to use the higher voltage Hyper9 motor - it might be more trouble than it's worth. Looks like these modules can easily handle the higher amperage of the lower voltage Hyper9 anyways.


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## LDT3 (Jun 19, 2019)

x.l.r.8 said:


> Picture 2 shows linking 2 modules to make a 2P 16S module, they are side to side as I plan on mounting them to give maximum exposure to the cooling plates. But you could stack differently. As long as the pack is balanced it will pull evenly through the series connectors so the P group plink needs to be good enough to allow group balance if there is an uneven load on the S connectors. The danger being is if you have a S connection the load will increase across this link. You have the option of making it a) fusible or b) big enough to carry a fair amount of power.


I'm definitely going this route (#2), now that I've opened the modules I see that it will be pretty simple to do (although somewhat tedious).
I'll be soldering the balancing P wires to the small copper tips on the top of the cell tabs. What would be the right gauge wire for this? Would 16awg silicon wire suffice?
Mind you, I will still have a 1/0 cable connecting the terminals of my 3p sets of modules together.

Originally I figured that I would simply parallel the modules together, however I've been advised that parallel strings of cells can cause problems.

Thanks again.


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## LDT3 (Jun 19, 2019)

x.l.r.8 said:


> Picture 2 shows linking 2 modules to make a 2P 16S module, they are side to side as I plan on mounting them to give maximum exposure to the cooling plates. But you could stack differently. As long as the pack is balanced it will pull evenly through the series connectors so the P group plink needs to be good enough to allow group balance if there is an uneven load on the S connectors. The danger being is if you have a S connection the load will increase across this link. You have the option of making it a) fusible or b) big enough to carry a fair amount of power.


I'm definitely going this route (#2), now that I've opened the modules I see that it will be pretty simple to do (although somewhat tedious).
I'll be soldering the balancing P wires to the small copper tips on the top of the cell tabs. What would be the right gauge wire for this? Would 16awg silicon wire suffice?
Mind you, I will still have a 1/0 cable connecting the terminals of my 3p sets of modules together.

Originally I figured that I would simply parallel the modules together, however I've been advised that parallel strings of cells can cause problems.

Thanks again.


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## e7c (Aug 1, 2019)

x.l.r.8 said:


> As you can see from the first picture, 2P makes the module tight for joining the tabs.


Do you have any photos of the 2P packs complete? How has this worked out for you?

Thank you very much for the photos you provided they provide much more insight into these packs than most out there.

I am in the similar boat as this thread's OP. I wanted to run the pacifica packs as a "parallel series", as even evwest now recommends on their site until I encountered this very strong counter recommendation in orion's BMS wiring manual. This doc talks about it in depth: https://www.orionbms.com/manuals/pdf/parallel_strings.pdf









So that leaves me trying to figure out a good way to do 96s2p to avoid those issues. I considered your "option 2". But it ends up being a lot of work to fab up bridges for these (192 of them). It seems better to do it your way and avoid bridging.


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## e7c (Aug 1, 2019)

LDT3 said:


> I'll be soldering the balancing P wires to the small copper tips on the top of the cell tabs. What would be the right gauge wire for this? Would 16awg silicon wire suffice?


Did you ever end up doing this? Do you have any photos? I think the parallel wires should be able to handle the max pack current but I am not sure. This is what really turned me away from this approach, as that means like 4/0 wire which is expensive and hard to work with.


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## EVmattyP (May 12, 2019)

Big thanks to all those who have contributed to the discussion. I'm learning a lot just from listening to you guys banter back and forth. 

I want to shift the initial topic slightly to see if this resolves my problem. 


Each A7 module has 16cells in series, correct? We've been discussing how to balance charge the cells within each module as I understand it. What if I only wish to treat each module (I have 6) as a singular battery and want to configure my final "pack" a 1S6P (modules not cells) so I should have a 60.5V @ 270Ah or approx. 16kwh pack. 

Could I somehow buy a BMS that would only monitor those 6 modules? Would that cause problems based on how I want to connect the modules? Would there be a restriction in how many amps a charger could throw at a "pack" in this configuration? Is that based on the BMS used? 

On a different topic, EVWest rates each module as being able to discharge 200-400A continuous with a peak rate of 800A for 10s. If I connect all 6 of my modules in a parallel configuration how does that affect the output rating, in terms of amps? Does it stay the same or does it multiply/stack like the Ah rating does? so 6 modules in parallel would be capable of outputting 4800A for 10s?? That seems highly unlikely but I wanted to make sure in case I needed special wiring to handle an increased load. 

Thanks again


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## john61ct (Feb 25, 2017)

EVmattyP said:


> Each A7 module has 16cells in series, correct? We've been discussing how to balance charge the cells within each module as I understand it.


However you end up doing it, you definitely should be at least regularly checking at that level, and be able to restore balance as it goes out, even if manually not "live" while in use.

> What if I only wish to treat each module (I have 6) as a singular battery and want to configure my final "pack" a 1S6P (modules not cells) so I should have a 60.5V @ 270Ah or approx. 16kwh pack. 

> Could I somehow buy a BMS that would only monitor those 6 modules? 

Yes in theory anyway no problem.

You choose what goes through the BMS protection, and to that extent yes BMS must be able to handle the max amps +X% safety factor.


> EVWest rates each module as being able to discharge 200-400A continuous with a peak rate of 800A for 10s. If I connect all 6 of my modules in a parallel configuration how does that affect the output rating, in terms of amps?

6x 200A = 1200A

Series boosts voltage leaves amps as is.

Your motor controller settings let you set a maximum Amps cap.


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## EVmattyP (May 12, 2019)

john61ct said:


> > EVWest rates each module as being able to discharge 200-400A continuous with a peak rate of 800A for 10s. If I connect all 6 of my modules in a parallel configuration how does that affect the output rating, in terms of amps?
> 
> 6x 200A = 1200A
> 
> ...


So if each module is connected + to + and - to - that would be parallel so my voltage would stay the same and total Ah capacity goes up to 270Ah, correct? 

Are you saying that I can configure the controller for (hypothetically) 800A of draw from the battery pack and that would be approx. 133A from each pack? 

I'm fairly confused about motor voltage as I was under the impression that the controller just passes through the input voltage as it sees it from the battery pack. Now that I think about it more it seems like the controller is determining the output voltage based on how many amps it can pull from the pack. As the amps drop so would the voltage, am I on the right track?


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## brian_ (Feb 7, 2017)

EVmattyP said:


> I'm fairly confused about motor voltage as I was under the impression that the controller just passes through the input voltage as it sees it from the battery pack.


No. For a first approximation, assume that the power from the battery into the controller is the same as the power from the controller into the motor. Power (for DC, in watts) is just amps multiplied by volts. For an AC motor the calculation is more complex, but the principle of power in (approximately) equals power out is still true.

This is why in the low-speed range where the motor current is limited (to protect the motor or by the current capacity of the controller), as the vehicle speeds up and the motor voltage and so power rise, the battery current and so power rise (with a constant battery voltage).

The controller typically is unable to boost voltage, so the battery pack voltage is the limit for the voltage which can be provided to the motor.


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## john61ct (Feb 25, 2017)

Lower speeds starting out need lots of power, torque. Also climbing hills.

Voltage is needed as speed rises, not torque any more.

Power / amps usage varies a lot minute to minute, voltage scales more gradually with speed.

Is all that correct?


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## brian_ (Feb 7, 2017)

john61ct said:


> Lower speeds starting out need lots of power, torque. Also climbing hills.
> 
> Voltage is needed as speed rises, not torque any more.
> 
> ...


I would say that's close...

Torque to the wheels is just another way of expressing driving force (multiplied by the tire radius); you need force to overcome drag (more aero drag at higher speed), and lots of force to accelerate or to climb (regardless of the speed).

Voltage is mostly proportional to motor speed, due to back EMF. There is also a smaller component of voltage needed to drive current through the resistance of the windings, and that voltage is proportional to current. The need for more voltage with higher speed is not instead of current or torque.

The result is conveniently straightforward:

motor torque is roughly proportional to motor current
motor voltage is roughly proportional to motor speed
electrical power is current multiplied by voltage
mechanical power is torque multiplied by speed (motor torque by motor speed, or wheel torque by wheel speed... same thing)
In motor design, in gearing, and in battery configuration there is always a trade-off with no right answer: whether it is speed and torque, or current and voltage, you can't get around the need for power.


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## john61ct (Feb 25, 2017)

That all hangs together well, very satisfying, thanks


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## john61ct (Feb 25, 2017)

EVmattyP said:


> So if each module is connected + to + and - to - that would be parallel so my voltage would stay the same and total Ah capacity goes up


Yes, and serial multiplies voltage keeping Ah the same.

Watt hours stay the same whatever the layout.


> Are you saying that I can configure the controller for (hypothetically) 800A of draw from the battery pack and that would be approx. 133A from each pack? 


Yes not sure if all controllers let you set a limit, maybe in watts power rather than amps current?


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## brian_ (Feb 7, 2017)

john61ct said:


> ... not sure if all controllers let you set a limit, maybe in watts power rather than amps current?


I don't know about aftermarket controllers, but OEM EV controllers definitely include power limits. For instance, from about 2700 rpm to 10,000 rpm, a pre-2018 Leaf is limited to 80kW by the controller programming, not battery voltage or motor performance.


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