Battery Modules Questions.

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Battery Modules Questions.

Post by francisco.shi » Thu, 31 Jan 2019, 08:22

I am considering the possibility of making standard battery modules that I could sell to people doing EV conversions.
The idea is to make a standard size battery module that can be used as an off the shelf item that can be easily installed into a car that requires minimal work.
The modules will be water cooled and have their own BMS module built in (cell level) with regenerative balancing (meaning the energy during cell balancing the energy is returned to the pack instead of being dissipated as heat.)
An extra board will be required to manage the pack(s). The BMS modules are just to manage each cell. The extra board would communicate with the module cell boards.
The extra board would be able to manage multiple modules.

From looking around the forums it seems 96V (nominal) is a very common voltage.
What I am looking is an idea of size and capacity that would be most common.
The modules can be connected in series to get a higher voltage or could be made to have more cells in series.

The benefits of this would be you would not have to do any wiring of cells or any box building.
You would just plug the comms and two big wires, cooling water feed and two brackets to bolt the module to whatever you want to attach it to.
I have considered also adding a water tight box as an option.

As a rough start I have considered two options:
1) 3P27S. Nominal voltage 97v (113v when fully charged) 189Ah (18.3kwh) weight 92kg size 340x154x1182mm arrangement 3x9
2) 3P26S. Nominal voltage 94v (109v when fully charged) 189Ah (17.7kwh) weight 89kg size 484x153x828mm arrangement 2x13

Other configurations are possible.
Each cell is (3P) is 354x36mm 3.6v 189Ah (680wh).
It would be possible to get other configurations for parallel cells (4P, 5P ...) I would need to check if the BMS modules will fit in a 2P assembly.
So if for example if we wanted to make the pack 4 long instead of 3 long (as in 1 above) the pack would end up 1536mm long
If we wanted to make the pack say 10 wide instead of 9 (as in 1 above) the pack would end up 376 wide.
At this point the height will be fixed. Only length and width can be changed.

Here are some pictures of what the modules would look like:
20190115_161922.jpg
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20190115_161958.jpg
20190115_161958.jpg (137.36 KiB) Viewed 1387 times
20190115_161933.jpg
20190115_161933.jpg (82.79 KiB) Viewed 1387 times
The pictures show extra modules on the top. What I am proposing would only have the bottom modules (not the 4 horizontal ones on the top).

When constructing the modules it is easy to add more cells length wise without having to make any special parts.
For the width I would have to have some standard sizes.

I am looking for suggestions of sizes options and price that people would be willing to pay.

Thanks in advance for the feed back.

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Re: Battery Modules Questions.

Post by jonescg » Thu, 31 Jan 2019, 10:42

I think 14s modules are the sweet spot. You would use 7 of them in a typical AC conversion, but they are also the perfect voltage for home storage (40-60 V DC)
Unfortunately, most battery management systems use LTC or TI chips which manage 12 cells each, so you'd have them spanning multiple modules.
Otherwise they are a solid bit of kit. Not the most convenient shape for conversions, but at least you don't need as many of them.
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Re: Battery Modules Questions.

Post by francisco.shi » Thu, 31 Jan 2019, 11:42

I am building the BMS and the plan is to have one board per cell. This will avoid all the wiring. The boards fit in between the cells so they do not occupy any space outside the profile of the pack.
I am not sure if using one micro for 8 cells will make wiring messy and I would still need to have individual boards for each cell because if I put all the circuitry for 8 cells on one board it would not fit between the cells.

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Re: Battery Modules Questions.

Post by Richo » Thu, 31 Jan 2019, 12:50

francisco.shi wrote:
Thu, 31 Jan 2019, 08:22
I am considering the possibility of making standard battery modules that I could sell to people doing EV conversions.
Nice in theory but the market is nowhere big enough to make this profitable.
Also I doubt one size fits all as there are too many different cars with different mounts and different user requirements.
francisco.shi wrote:
Thu, 31 Jan 2019, 08:22
From looking around the forums it seems 96V (nominal) is a very common voltage.
What I am looking is an idea of size and capacity that would be most common.
The modules can be connected in series to get a higher voltage or could be made to have more cells in series.
I would have said 144V is more common system voltage dominated by DC conversions.
144V/3 is 48V which is highly usable both in and out of the ev world.
48V modules can then also make the 96V you think is common.
francisco.shi wrote:
Thu, 31 Jan 2019, 08:22
I am looking for suggestions of sizes options and price that people would be willing to pay.
Well that is the other issue.
Aren't the cells you have for performance?!?
Other people maybe after low power / low cost.
It would be hard to compete against low power cells vs high power cells in a one size fits all module.
The other bit would be you would be up against Tesla modules which will slowly come on to the market in the next 5 or so years.

To me the other option is to have all this made to order as a single unit - full turn key service.
The customer tells you the max box LxWxH, the mounting holes and the V and kWh they want and you provide a finished pack that does that.
Then you also have a specific pack for a specific car on a design file.
This will then take some of the strain off the backyard converter.
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Re: Battery Modules Questions.

Post by francisco.shi » Thu, 31 Jan 2019, 16:22

Nice in theory but the market is nowhere big enough to make this profitable.
Also I doubt one size fits all as there are too many different cars with different mounts and different user requirements.
Making the battery longer is easy. No need to modify any parts except the length of the cooling tubes.
To change the width is a little more involved because I would have to make the ends longer (custom part) but chances are there are only a few sizes that are suitable
I would have said 144V is more common system voltage dominated by DC conversions.
144V/3 is 48V which is highly usable both in and out of the ev world.
48V modules can then also make the 96V you think is common.
Maybe making it 13 wide. That would be about 48v then make the. 1 long for 48v 2 long for 96 and 3 long for 144?
Well that is the other issue.
Aren't the cells you have for performance?!?
Other people maybe after low power / low cost.
It would be hard to compete against low power cells vs high power cells in a one size fits all module.
The cells are not the high power cells. The max recommended peak discharge rate is 3C however with the cooling system it is possible to run them at 3C continuously without overheating. (Temp well below 45°C) the reason for the low impedance is the connections between the cells are extremely short. The voltage drop from the output of one cell to the input of the next at 100A is 1mv.
The other bit would be you would be up against Tesla modules which will slowly come on to the market in the next 5 or so years.
This pack is far better than the Tesla packs. The Tesla packs overheat if you run them continuously at 1C even with the cooling system running.
My packs can run continuously at 3C without overheating, they have 1/3 of the internal resistance of the Tesla packs and they have the same energy density at the pack level but my pack does not need any extra structure to hold the pack whereas the Tesla pack does.
And you would be getting a second hand battery if you bought the Tesla packs.
To me the other option is to have all this made to order as a single unit - full turn key service.
The customer tells you the max box LxWxH, the mounting holes and the V and kWh they want and you provide a finished pack that does that.
Then you also have a specific pack for a specific car on a design file.
This will then take some of the strain off the backyard converter.
That was another option. I have considered this too.

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Re: Battery Modules Questions.

Post by brunohill » Fri, 01 Feb 2019, 22:30

How do you keep them below 45 'C , when the temperature is 45 "C. This is a problem for all batteries unless someone comes up with better chemistry. I need something reliable from -10 'C to + 50 'C ( but this could change with climate change). I know , I am dreaming, but this is reality.

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Re: Battery Modules Questions.

Post by francisco.shi » Sat, 02 Feb 2019, 03:25

You need to use the air conditioner to cool the water that runs thru the battery.
The issue with the Tesla cooling system is not the temperature of the water. It is the thermal resistance between the water and the cells.
My battery cooling system has a temperature difference between the water and the cells of 5°C at a discharge rate of 2C. That means that if you hold the water temperature to say 30°C and you are discharging the cells at 2C then the cell temperature will be 35°C.
The Tesla batteries have a higher temperature difference which means that to keep the cells at 35°C when being discharged at 2C you need the water temperature to be well below what you can achieve with the air conditioner. This means that the cells will get over 45°C unless you chill the water below 0°C.
jonescg » Wed, 05 Dec 2018, 15:52 wrote:viewtopic.php?f=18&t=5502&start=50#p70855
(sorry I do not know how to get the quote to come out right) measured the tesla pack temperatures and at 1.2C the temperature difference between the water and the cells was 15°C so to keep the cells at 35°C as in my pack above you would need a water temperature of 20°C instead of 30°C.
However my pack at 1.2C has a difference in temperature of only 1°C between the water and the cell. So effectively my cooling system is about 15 times more efficient than the tesla one.

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Re: Battery Modules Questions.

Post by coulomb » Sat, 02 Feb 2019, 06:16

francisco.shi wrote:
Sat, 02 Feb 2019, 03:25
(sorry I do not know how to get the quote to come out right)
I don't know either, how to get the post_id etc automatically right, so that you can click on the up arrow in the quote to navigate to the original post. [ Edit: as you automatically get when you quote someone's post, as opposed to highlighting some text and using the quote toolbar icon when editing ]

However, just putting the name (and whatever else you want) after an equals sign at least names the person quoted.

For example, [quote=fred]blah blah[/quote] comes out as:
fred wrote:blah blah
In this case, you might be better off with an ordinary URL link, e.g.

Chris Jones in [url=http://forums.aeva.asn.au/viewtopic.php?f=18&t=5502&start=50#p70855]this Prelude Questions post[/url] measured ...
which comes out as
Chris Jones in this Prelude Questions post measured ...

[ Edit: Added alternative URL method. ]
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Re: Battery Modules Questions.

Post by rhills » Sat, 02 Feb 2019, 12:44

Hi @francisco.shi, @coulomb,

If you click the Quote button for a previous post as I just did for Coulomb's last entry above and then examine the quote tag it produces, that gives you the information you need to work out how to do what you want. The quote tag I got from Coulomb's post was this:

Code: Select all

[quote=francisco.shi post_id=71577 time=1549049121 user_id=5109]
The bits of info you need about the original post are the Post ID, the timestamp and the User ID. The Post ID you can find by hovering your mouse over the little "callout" icon left of the poster's username at the top left corner of the post. That will show a URL like:

Code: Select all

http://forums.aeva.asn.au/viewtopic.php?p=70855#p70855
where the "p=70855" bit tells you that the Post ID is 70855. Note, there are a number of ways of referring to a specific post, but this is the most accurate and reliable. The link Francesco used above:

Code: Select all

http://forums.aeva.asn.au/viewtopic.php?f=18&t=5502&start=50#p70855
actually translates to "show me the 50th post in Forum 18 (f=18), Topic 5502 (t=5502). Interestingly, the last part of that URL suggests this should be Post ID 70855 (#p70855) but it's not, it's actually Post 68020. From the context of Francesco's text, I believe he really meant to refer to Post 70855.

So, first tip from this post is: always use the little "callout" icon at the top left corner of a post to get a direct link to the post you want.

Anyway, back to building up our quote "manually". You can easily find the User ID by hovering your mouse over the relevant user's name and examining the URL that pops up for the "u=..." bit. For Chris Jones, the author of the post in question, this was u=1240 so his UserID is 1240. The really tricky bit is getting the timestamp number for your post. In figuring out how the average punter (as opposed to a Linux Geek :ugeek: ) might do this from his/her browser, it occurred to me that the simplest way to do all this stuff is to simply use the phpBB's own built-in quote button. How?

Assuming you're sitting there, replying to an existing post like I am now:
  • scroll up to the top of the page and right-click the "Forums Home" link.
  • In most browsers, the dropdown menu you get will include an "open in new tab" option. Pick this.
  • If your browser hasn't automatically jumped to the new tab (some do, some don't), click the new tab which should show you the Forums home page.
  • Now navigate by whatever means to the post you wish to quote.
  • Click the "Reply with quote" button for that post.
  • In the new message box below, you will have the full message quote including its BBCode tags. Highlight all this and copy it to the clipboard.
  • Go back to the browser tab containing your original reply, move your cursor to where you want to quote to appear, paste and voila! You have your quote.
  • Finish off by editing the quoted text between the tags as you would normally.
So, for Francesco's example, he might have this:

Code: Select all

In 
[quote=jonescg post_id=70855 time=1543989146 user_id=1240]
...However I found some Tesla pack data:...[/quote]

Chris Jones measured the tesla pack temperatures and at 1.2C...
Which would then come out like this:
  • In
    jonescg wrote:
    Wed, 05 Dec 2018, 13:52
    ...However I found some Tesla pack data:...
    Chris Jones measured the tesla pack temperatures and at 1.2C...
Sorry this has been a bit long and involved, but hopefully it will help some people learn a bit more about things you can do in a post with a little extra fiddling around :-)
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Re: Battery Modules Questions.

Post by jonescg » Sat, 02 Feb 2019, 14:26

The Tesla pack does indeed get hotter, but it also cools down fairly quickly. So long as the battery spends as much tome closer to 20'C then otherwise, it will live a long life. The Tesla pack heat was based on a measured DCIR of 100 mOhm, although according to Panasonic the 18650BA cell is supposed to have a 60 mOhm DCIR - it could be that these cells were form an older Tesla and thus had a higher DCIR, but I wouldn't take those results as gospel. I think the heat flux was better than it portrays.

And yes, refrigerant to chill the water going through the battery pack is how you keep it close to 25'C on a 45'C day.
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Re: Battery Modules Questions.

Post by francisco.shi » Sat, 02 Feb 2019, 18:34

Do you know what the contact resistance is in the Tesla packs?
That is the resistance between the cell output contact and the pack output contact.
That may be where the extra resistance is.

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Re: Battery Modules Questions.

Post by jonescg » Sat, 02 Feb 2019, 18:59

Not sure - as each cell is wirebonded to the nickel plated aluminium busplate. It can't be much, surely.

I guess the fairest comparison given the ambiguity around the cell's discharge performance, is to calculate peak heat removal by the cooling system. We know that quite accurately from the mass flow of the coolant, the specific heat capacity of the coolant and the temperature difference from inlet to outlet.
In the case of the Tesla pack, this peaked out at 400 W on a 5 kWh pack weighing 23 kg.
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Re: Battery Modules Questions.

Post by brunohill » Sat, 02 Feb 2019, 20:06

"And yes, refrigerant to chill the water going through the battery pack is how you keep it close to 25'C on a 45'C day."

And that is the problem. My battery would be flat before it is time to drive home. This could be the biggest nail in the coffin for electric cars, without a better solution. I do not need my ICE vehicle idling in a hot carpark for 12 hours.

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Re: Battery Modules Questions.

Post by francisco.shi » Sun, 03 Feb 2019, 04:33

The battery would be under the car and I assume would have some insulation so you will not need to run the air conditioner very hard. Also you do not need to hold it at 20°C. Probably 35 will be enough and you would only be cooling the battery not the cabin. And I have also considered putting solar panels on top which may be enough to power the air conditioner indefinitely while under the sun.
On my pajero I could get 1.25kw of panels which would be more than enough to run the compressor.

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Re: Battery Modules Questions.

Post by jonescg » Sun, 03 Feb 2019, 10:39

Yeah even Tesla doesn't do that. It has a sliding scale - if it's fully charged and the temperature is 45'C, it will run the chiller to bring it down to say, 25'C. If it's only 30% charged and it's 45'C, it might not run the chiller at all, or perhaps taking it down to 35'C.

And it will only run the chiller as needed when the vehicle is plugged in. In the case of the Prelude, it will only work when the vehicle is in use or charging. At all other times it won't run.
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Re: Battery Modules Questions.

Post by rutuja » Mon, 04 Mar 2019, 14:54

Lamentably, most battery the executive's frameworks use LTC or TI chips which oversee 12 cells each, so you'd make them range various modules.
Else they are a strong piece of pack. Not the most helpful shape for transformations, however in any event you don't require the same number of them.

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Re: Battery Modules Questions.

Post by Randall679 » Fri, 22 Mar 2019, 10:34

Francisco ... What are the overall dimensions of the big cases in your photos ...

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Re: Battery Modules Questions.

Post by francisco.shi » Fri, 22 Mar 2019, 11:34

The battery box is 1900x1025x(210/160)mm. Total capacity is about 70kwh

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Re: Battery Modules Questions.

Post by weber » Sat, 13 Apr 2019, 13:26

I've been meaning to post here ever since Francisco visited me many weeks ago. I wanted to know if I could use his battery modules to replace the ageing pack in the MX-5. And Francisco was keen to know more about the LyteFyba BMS. It was a very fruitful meeting. After having seen his samples, as well as the photos in this forum, I am convinced that his battery modules are a brilliant design, and I had a much better understanding of the possible stacking directions and orientations.

Mike (@coulomb) then used this information, along with the dimensions in this thread, and the dimensions of the 6 largest battery boxes (of the 10 in the MX-5), to determine how many cells we could fit, using Franciso's modules. Unfortunately, no matter what orientations he tried, it always seemed to work out that we could fit 1.9 or 2.9 cells in length, which of course had to be rounded down to 1 or 2. Because of this, we could not get anywhere near the capacity we presently have, despite the fact that Francisco's cells have much higher energy density. And we could not get anywhere near the voltage we need for full power. This is disappointing, but can't be helped.
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Re: Battery Modules Questions.

Post by jonescg » Sat, 13 Apr 2019, 16:13

I wonder if the high energy modules I'm putting in the Prelude could work for you then Dave. They are 195 mm x 340 mm and 180 mm tall, 44.4 V nominal and 70 Ah (3.1 kWh).
They aren't anywhere near as cheap as the LG pouches though.
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Re: Battery Modules Questions.

Post by weber » Sat, 13 Apr 2019, 18:23

Your modules look good too Chris, but I'm afraid the price is OOTQ.

In case Francisco can figure a way, here are the MX-5 dimensions:

All the battery spaces in the MX-5 are 215 mm high. The existing cells are a total of 218 of 40 Ah LFP (nom 3.2 V), all in series. The 6 largest spaces can be seen here:
http://forums.aeva.asn.au/viewtopic.php ... 608#p41608
and are:
678 x 500 (with a 92 x 124 rectangle missing from one corner) (54 cells).
1092 x 253 (presently 36 cells, but space for 46)
678 x 253 (28 cells)
678 x 253 (with 46 x 124 rectangles missing from two corners) (26 cells)
908 x 130 (19 cells)
632 x 130 (13 cells)
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Re: Battery Modules Questions.

Post by francisco.shi » Sat, 13 Apr 2019, 19:16

Thank you for the good report.
Can you tell me the size you have available?
If it is so close I may be able to modify something to make the batteries fit.

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Re: Battery Modules Questions.

Post by francisco.shi » Sat, 13 Apr 2019, 19:59

Correct me if I am wrong but you have 218 cells at 3.2v. This equates to 700v.
The ncms are 3.6v so you would need 194 cells.
The current battery capacity is 40Ah at 700v so total of 28kwh.
I can get 85cells in the 678x500x215 and 102 in the 1092x253x215 (Will need to make it slightly bigger but only a few mm)
These two alone will make 187 cells. Just need to find enough space for another 7 cells.
We may be able to redesign the manifold to make it fit.

Also if I add all the number of cells in the spaces you have listed I only get 186 cells.

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Re: Battery Modules Questions.

Post by brendon_m » Sat, 13 Apr 2019, 20:32

francisco.shi wrote:
Sat, 13 Apr 2019, 19:59
Also if I add all the number of cells in the spaces you have listed I only get 186 cells.
There are more cells in the picture /link.
That list appears to only have the larger spaces

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Re: Battery Modules Questions.

Post by weber » Sat, 13 Apr 2019, 21:28

That's right. Thanks Brendon. The sizes of the other battery boxes can be calculated in one dimension as as 123.5 mm per row plus 6 mm overhead, and in the other dimension as 46 mm per cell plus 34 mm overhead.

I'd prefer not to use the 908 x 130 space behind the rollbar as it gets too hot there, from the sun.

Yes, Francisco, 28 kWh is right, and 194 NCMs is about right for the voltage. 190 would be acceptable. But if it must be a multiple of 3, then it must be 192 cells. I also need to be able to divide them electrically into two equal (or nearly-equal) half packs, for charging.

Your modules appear to be 153 or 154 high, and to require n x 36 + 16 in one dimension, and m x 354 + 120 in the other dimension, where n and m are integers, and the number of cells is 3 x n x m.

Don't forget the 678 x 500 has a piece missing, as you can see in the diagram
http://forums.aeva.asn.au/viewtopic.php ... 608#p41608
so it really only offers rectangles of either 678 x 376 or 586 x 500.

Coulomb calculated that we could only get 45 of your cells in the under-bonnet box (using the 586 x 500 rectangle), n = 15, m = 1. 46 cells if we ignore the multiple-of-3 requirement, and 48 cells if we lay them flat and stack them 16 high.

The 1092 x 253 could possibly be extended a few millimetres in the 253 direction, but there is no chance of even one more millimetre in the 1092 direction.
Last edited by weber on Sun, 14 Apr 2019, 09:13, edited 1 time in total.
Reason: Corrected two ocurrences of 568 to 586
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