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Discussion Starter #1
So I have been toying with this idea for a while. I really dove into it this week, researching specs, costs, and battery options.

Goal:
I'd like the largest battery possible but I only want to sacrifice the lower storage space in the rear cargo area.

Time frame:
Because of the cost involved, I probably wont be able to do it in the next 6 months. There are a few cheaper things I can purchase to get started but the batteries are going to be expensive so those will have to wait at least 6 months. It would be nice if I could get it done in time for NDEW this September.

Battery Options:
Battery voltage of additional pack would need to be as close to 386 volts as possible for any pack I add. I read a post from Valerun in which he said his target voltage is between 382 and 386. If you haven't seen the set up that he built you can find it here,
http://www.myrav4ev.com/forum/viewtopic.php?p=12189#p12189
I plan on using 18650 cells, the same that Tesla used, so I am simply going to match their 92 cells in series in order to match their voltage. If I was going to use a different chemistry, my voltage target would be 382 - 386.

Option 1. Tesla modules from a Model S, X or even a Rav4 EV.
Pros: Prebuilt, high quality, includes liquid cooling system
Cons: Heavy, large, expensive
I would need 16 - 24volt Tesla Model S modules in series just to get to the voltage I need. That would take up the entire lower cargo area and I would have to build up the floor to fit more, losing most of my cargo space. I dont want to do that. I can fit 5 in the lower cargo area but that wouldn't give me the voltage I need to put it in parallel with the main pack. If I am missing something here let me know.
Here are modules for sale for $1400 each.
https://www.ebay.com/itm/Tesla-Mode...881194?hash=item3d139a406a:g:q2UAAOSwPcVVv8qO

Option 2. Build my own modules using 18650 cells
Pros: Customizable to any shape and configuration I need, I can build a higher kwh pack that is smaller, cheaper than Tesla modules.
Cons: Lots of labor to build, no onboard cooling system (They would have to be air cooled).
Cost is about $1.50 per cell if it is 2600mah up to $4.50 per cell if it is 3400mah
I would build one like this. https://youtu.be/JQa5gn-7D74

There are other options but these are the two I have been looking at. I am leaning strongly towards option 2.

Battery Plans (option 2):
Option 2 seems like the best option although it would be more work. It is a huge investment so I am open to ideas if you think there is something better out there.
I can fit 9 modules in a vertical formation in the lower cargo area. I can fit up to 314 cells in each module plus more the sides of the box. I am planning on a 92s31p configuration. In order to get there I'll have 310 cells per module, 10 total cell blocks in each module plus 2 rows of 31 cells in parallel on the sides of the box. That's 2,852 total cells in this configuration.

Vertical modules allowed me to fit more compared to horizontal modules. Also, I think servicing and air flow would be better with vertical modules.

Capacity:
Assuming 92s31p =
If each cell is 2600 mah, that would be 80,600 mah or 80.6 AH (2600 x 31)
386 volts x 80.6 AH = 31,111.6 WH aka 31.11 kwh battery capacity

If each cell is 3400 mah, that would be 105,400 mah or 122.4 AH (3400 x 31)
386 volts x 105.4 AH = 40,684.4 WH aka 40.684 kwh battery capacity

Range:
Weight of car / 10 = watt hours per mile
Rav = 4500lbs
4500lbs / 10 = 450 wh per mile
31,111.6 / 450 wh per mile = 69.14 miles with 2600 mah cells
40,684.4 / 450 wh per mile = 90.41 miles with 3400 mah cells

OEM rating would be:
41,900 / 450 wh per mile = 93.111 miles with OEM 2600 mah cells
41,900 / 350 wh per mile = 119.714 miles with OEM 2600 mah cells *more realistic*

Theoretical realistic range with additional pack:
31,111.6 / 350 wh per mile = 88.89 miles with 2600 mah cells
40,684.4 / 350 wh per mile = 116.24 miles with 3400 mah cells
(not including any unusable space in the secondary pack)

Plus existing range from 41 kwh OEM pack! This could possibly be a 230 + mile car!


BATTERY UPDATE:
I have decided on a 92s31p battery pack. I have room for 9 modules in the box I created.



Battery Box:
I'll hire a welder to build me an aluminum battery box that fits inside of the rear lower cargo area. I have built a wood version of the box for the welder to copy. I am going to look into some kind of fire extinguisher system too. Not sure if its possible but I want to protect my family.



Weight:
Batteries:
92s31p = 2,852 cells
2,852 x 45 grams = 128,340 grams aka 282.94 lbs
Box:
100 lbs ish?
Wiring and other components:
200 lbs ish?
628 lbs total?

Cost:
92s31p = 2,852cells
2600 mah $2 x 2,852= $5,704
3400 mah $4.50 x 2,852= $12,834
That's just for the cells :(

Parts Purchased To Date:
Contactors $61
https://www.ebay.com/itm/Tyco-TE-Re...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Inertia Switch off ebay $13
20 Dead 18650 cells off ebay $13
400v 300 amp fuse off ebay $15
(2) Panaflow high speed fan NMB120mm FBA12G12H $20
https://www.ebay.com/itm/NMB120mm-F...396a6f96c:g:s~sAAOSwjyhaTFZI&autorefresh=true
Temperature fan control module $2
https://www.ebay.com/itm/W1209-12V-...var=413176014560&_trksid=p2057872.m2749.l2649
Gigavac Hbd41AA $49
http://www.gigavac.com/shop?title_op==&title=hbd41aa1
M22x 1.5 cable glands 5 pack for $8.85
https://www.amazon.com/gp/product/B071VT8NLM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Price per kwh:
Only for the cells. No box or system parts.
2600 mah - $5,704 / 31.11 kwh = $183.34 per kwh
3400 mah - $12,834 / 40.684 kwh = $315.46 per kwh

Connections:
I've read that connecting right at the battery is best. Val connected his pack directly to the inverter. However I have Jdemo and Tony has 2 gauge wires going from the battery to a conactor box under the hood. There isn't room to connect additional cable directly to the battery. So I am going to make my connection at the Jdemo Contactor box under the hood. I am going to run high amperage, 2 gauge, shielded EV cable. Its capable of up to 255 amps. Here is a link to the wire specs. http://evwest.com/support/Shielded_Battery-Irradiated_XLE.pdf The existing pack has a 325 amp fuse. But based on my math, and talking to Val, 2 gauge should be fine.

BMS/System monitoring:
I haven't explored this yet so I dont know what options are out there. I would like a unit with a display that shows voltage, temp, amp hours, etc of the batteries. Possibly a Batrium unit, https://www.batrium.com/

Links/Info:
Inside a Tesla Model S battery pack
https://teslamotorsclub.com/tmc/threads/pics-info-inside-the-battery-pack.34934/
Tesla Battery Specs
http://evwest.com/support/Tesla Model S Batt.PDF
Photos and info on Rav4 EV battery pack
http://www.myrav4ev.com/forum/viewtopic.php?f=8&t=765
http://www.myrav4ev.com/forum/viewtopic.php?f=7&t=2061
http://99mpg.com/blog/somanybatteriessolittletime/
Cut away of Rav4 EV
https://www.youtube.com/watch?v=4XstWdvDWsc
Tear down of Rav4 EV battery
https://www.youtube.com/watch?v=7ZLst_4N4Sw

My Photos:
http://s59.photobucket.com/user/jimbo69ny/library/Rav4 EV Additional Battery

If any of my math, stats or theories are wrong please dont hesitate to correct me. I'd rather know NOW than AFTER I spend $10,000!
 

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Discussion Starter #2
If anyone has any input or suggestions I’m all ears.

Right now I am researching the effect of having two different capacity batteries. Seems as though the new one will have lower resistance and be the primary battery for the cars needs. Then when voltage drops the OEM pack will transfer voltage to the new pack. Is there anything wrong with that if that is actually the case? Do I need a battery isolator? I haven’t looked at them at all. Are there isolators available that can handle 325 amps and 386 volts?
 

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Battery Options:
...
I plan on using 18650 cells, the same that Tesla used, so I am simply going to match their 92 cells in series in order to match their voltage.
...

Option 1. Tesla modules from a Model S, X or even a Rav4 EV.
..
I would need 16 - 24volt Tesla Model S modules in series just to get to the voltage I need.
...
I can fit 5 in the lower cargo area but that wouldn't give me the voltage I need to put it in parallel with the main pack. If I am missing something here let me know.
There's also one generation of the Smart ED, but the Smart modules seem like a really awkward size to put anywhere else... and they are 15s. Six of them would be needed to get close (90s), and no number would match 92 (or 96).

My understanding is that all Model S/X modules are 6s, with varying numbers of cells in parallel to suit capacity. Either 14 modules (e.g. 60 kWh variants) or 16 modules (e.g. 85+ kWh variants) are used in series, again to suit capacity (the extra two are in that taller lump at the front). The recent ones all seem to be 16... but that's 16x6 = 96 cells in series, not 92.

It seems popular to fixate on voltages being multiples of 12. The nominal voltage of 6 of these lithium cells in series is not 24 volts (4 volts per cell), but a bit lower. Perhaps your "target voltage" is the maximum reached during charging, rather than the nominal voltage?

Some people have reconfigured these Tesla modules with some cutting and adding of jumpers to make them 12s; with that approach only eight would be needed for 96s... but it looks like that's still too many.
 

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Discussion Starter #4
Thank you for the input but any currently available OEM pack would take up more space than I am willing to give up. A custom made 18650 pack in the lower cargo area is the ticket.

I use my car for work and I cant lose any space inside the car.
 

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A 92s31p battery (2852 cells) in 9 modules is an interesting configuration challenge. It would be really nice if all nine modules were identical and connected in series - it would be easier to plan, and easier to wire without errors. Unfortunately 92 isn't evenly divisible by 9.

The layout has a notation of "362 cells", but that would be for the full 24 x 14 rectangle; as shown it has 314 cells. Nine of those modules would be 2826 cells... not quite enough for the 92s31p total.
 

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Discussion Starter #6
Yeah the series parallel configuration is going to take a close look. I am working on figuring that out now. I think I have it but here is my thread about that.

https://endless-sphere.com/forums/viewtopic.php?f=14&t=92814&p=1357720#p1357720

It’s really not very clear but I think option 3 is the way to go. That option includes the most connections.

I am going to have 9 modules with 10 series blocks in each plus 2 more blocks on the right side of the box.
 

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I am going to look into some kind of fire extinguisher system too. Not sure if its possible but I want to protect my family.
You should plan for a fire and understand that a fire extinguisher will not work. What I'd suggest is that you copy the Tesla battery system and include both the pressure valves and fire management ducting to buy your family as much time as possible.

Chris Hazell has produced 3D models of the pressure valves (here) :cool:
 

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Discussion Starter #9
Where are you located?
Interesting project.
I see you linked a few of my things.
Hey Green Tec! Yeah I loved your Rav 4 battery dissection video. Is it possible to let me know if you receive another Rav 4 battery? If its working I might be interested in buying it.
 

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Discussion Starter #10
You should plan for a fire and understand that a fire extinguisher will not work. What I'd suggest is that you copy the Tesla battery system and include both the pressure valves and fire management ducting to buy your family as much time as possible.

Chris Hazell has produced 3D models of the pressure valves (here) :cool:
Nothing is ever perfect, not even tesla. Of course safety is of the utmost importance. My plans currently are as follows.
1. I have a strengthened and fireproof aluminum box to protect the pack in an accident.
2. I have a trailer hitch that wraps around the lower cargo area for reinforcement. (Where the battery is)
3. Possibly adding a rear heavy duty bumper bar.
4. I want to incorporate some kind of fire suppression system. A fire extinguishing system that senses fire and sprays an ABC fire extinguisher right into the box.
5. I will have a temp/fire sensor that turns off the cooling fans if a fire breaks out.
6. Also, the sensor will switch an actuator that will move a piece of metal that covers the entrance and exit for air circulation. Goal is to suffocate the fire.
7. The same sensor will disengage the contactors.
8. A smoke detector inside of the box. Hearing the beeping will be my first clue to pull over and get the family out.
 

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1. I have a strengthened and fireproof aluminum box to protect the pack in an accident.
It's worth reviewing Tesla's approach for separating the battery cells from the cars occupants;

1mm mica sheet

2mm (iirc) steel sheet (top of battery box)

10mm fire blanket

4mm (iirc) aluminium sheet (floor of car)

4mm (iirc) fire resistant carpeting

They also put a lot of effort into managing the gases produced in a fire and exhausting them away from the cars occupants.


4. I want to incorporate some kind of fire suppression system. A fire extinguishing system that senses fire and sprays an ABC fire extinguisher right into the box.
That will not help in a lithium-ion battery fire. If you're in any doubt watch this and read the first responders instructions...



Nothing is ever perfect, not even tesla. Of course safety is of the utmost importance.
I agree that nothing is ever perfect but I think we can all learn a lot from the monies Tesla have spent bringing EV's to market using 18650 cells.

Two further comments;

afaik you have no battery cooling system in your design :confused:

afaik you have no way of exhausting the gases that are produced when you have a fire. By definition isn't this a bomb?
 

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Discussion Starter #12
I have already purchased two high CFM fans. They are on their way.
https://www.ebay.com/itm/NMB120mm-F...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

I also tried this but it was too loud for my wife's liking.
https://youtu.be/tHBNalKaFwA
https://youtu.be/ZpX2VcjZqkU

If there is a fire I said I want to have actuators that close the intake and exhaust. That should help suffocate the fire and give us enough time to get out.

I appreciate the input. You can pick apart my design and ideas all you want. The whole project is a risk, driving a car is a risk, leaving your house is a risk. I think I am doing a pretty good job taking all things into consideration. The fireproof carpet and mat are a good idea. Ill include that too.
 

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If there is a fire I said I want to have actuators that close the intake and exhaust. That should help suffocate the fire and give us enough time to get out.
Lithium battery fires do not require fuel or oxidiser from an external source and sealing the battery box will simply turn the battery into an explosive device, that's why Tesla includes pressure release valves.

The whole project is a risk, driving a car is a risk, leaving your house is a risk.
I'm trying to help you understand so that the risks you take are known as far as possible.

Here's a good example of what happens when a battery 'expert' gets thing wrong (like we all do);

 

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Discussion Starter #15
Lithium battery fires do not require fuel or oxidiser from an external source and sealing the battery box will simply turn the battery into an explosive device, that's why Tesla includes pressure release valves.

I'm trying to help you understand so that the risks you take are known as far as possible.

Here's a good example of what happens when a battery 'expert' gets thing wrong (like we all do);


What is your goal here? To scare me? If you are concerned about my well being give me solutions and not scare tactics. Fear doesnt drive me.
 

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Ok will it seemed like your posts were aimed more at scaring me away from doing it rather than helping me.

Ill accept the fact that you say your just trying to help and move on.
 

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Ok will it seemed like your posts were aimed more at scaring me away from doing it rather than helping me.
My approach is simple, I imagine that one of my children is stuck inside my electric conversion when a battery fire starts. I don't do this to scare myself rather to ensure I produce the safest design possible based on the available data.

I recommend you read the Tesla battery patents and watch the various disassembly videos that are online. It's clear that Tesla went to a great deal of trouble and expense to use 18650's in cars.

One final thought, if you have access to a Tesla Roadster put your hand over the radiator vents after a 'moderate' drive... I've always found it astonishing how much heat the battery is producing :eek:
 

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Discussion Starter #20
My approach is simple, I imagine that one of my children is stuck inside my electric conversion when a battery fire starts. I don't do this to scare myself rather to ensure I produce the safest design possible based on the available data.

I recommend you read the Tesla battery patents and watch the various disassembly videos that are online. It's clear that Tesla went to a great deal of trouble and expense to use 18650's in cars.

One final thought, if you have access to a Tesla Roadster put your hand over the radiator vents after a 'moderate' drive... I've always found it astonishing how much heat the battery is producing :eek:
Yup, this is why I dont think I will need a battery heater. I have a timer to charge my car in the morning. Charging warms them up, then of course driving does too.

I have 2 - 104 CFM fans and time will tell if that is enough to cool the pack. I can always add another one if I need to.

I definitely want to be safe and I appreciate comments that help that goal. I just felt like you were trying to tell me not to do it. I am so sick of people being negative on my posts. Every day people tell me not to do it, I CANT do it, its stupid and its dangerous. It can be done, it can be done safely and it will work.
 
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