Additional Battery Project - Possible Extra 40 kwh

[jimbo69ny]

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-Relay-EVC-500-AAANAM-12-24-V-500A-High-Voltage-Automotive-Main-Contactor/142386677471?ssPageName=STRK%3AMEBIDX%3AIT&_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!

 

[jimbo69ny]

Questions I still have....

Is it ok that the OEM Tesla cells are 2600 mah and I add a second pack with 3400 mah cells?

Is my target of a secondary battery pack voltage of 382 to 386 correct?
Answer: I was told I could simply match the 92 series cells in the OEM pack so thats what I am going to do. Aside from making sure each new cell in the new pack is good, I am going to ignore the voltage for now. I am using the same 18650 cells in the same 92s configuration. So I should be good.

I suspect the answer is yes but by connecting the second pack either at the battery or at the battery wires Tony ran to the Jdemo, would that mean charging via j1772 or Jdemo would charge BOTH packs?
Answer: Val messaged me and said that yes, the charger would deliver power to both packs.

Thanks!!!

 

[jimbo69ny]

I have constructed my battery box. This one is wood but I plan to take it to a welder to replicate out of aluminum. It doesnt look like anything fancy now but here it is.

 

[shadowinstallz]

I'm down to build this extra pack with you but your 4 hours away. I think you would need to have it connected to the BMS somehow so the displayed range would show more, but i would think you need Tesla software to access and configure.

 

[shadowinstallz]

we should get in contact with wk057/jason hughes over at tmc. i might message him to see if he wants to take on a project like this.

 

[jimbo69ny]

I'm down to build this extra pack with you but your 4 hours away. I think you would need to have it connected to the BMS somehow so the displayed range would show more, but i would think you need Tesla software to access and configure.

Thanks for the offer! Where do you live?

I agree. It would be great to be able to collect and view data from the Tesla/Toyota computers. Unfortunately I know NOTHING about CAN or how to gather that data. I started to look into BMS options for my additional pack but a lot of them are small, like 3-12 series circuits. I am going to have 92! So I'm not really sure how to do that either.

I'm sure there are people, cough Tony, cough Val, that can do this way better than me but I have been looking for a project, I have some free time on my hands and I do have some experience. I may or may not burn my car down but I think I can figure it out. haha

 

[Philly RAV4 EV]

A good bms to use is an Orion
Orionbms.com

 

[netzerokent]

I would like to watch this as I would like to know how to do this as well. I am glad to help in any way but alas I am on the otherside of the country in the Seattle Area.

I also was thinking of creating a small camping teardrop trailer with a large battery pack to extend for long travel for camping and adding the third row into mine.

 

[jimbo69ny]

Wow thanks for the offers. I am definitely no expert so I could use advice.

This seems simple but I could use help figuring this out at the moment...
I need to find out what size power wire to run from my battery to the OEM battery.

Its been in the single digits here in NY so I haven't checked personally, but I have read that the OEM fuse at the EV battery is 325 amps. I suspect that the OEM battery cables are 1/0. Don't know for fact though.

So if I add a 92s26p battery using 3400 mah Panasonic 18650 cells, part of the current requirements would be coming from the second battery that is in parallel with the OEM battery. The problem is, how do I figure out how much current could potentially flow from the rear battery to the OEM battery? Both batteries are in parallel so current should remain the same right? I would install a 325 amp fuse at the second battery, run 1/0, and call it good if it wasn't for this....

I have Jdemo. Tony has a beautiful spacer that they call the "bathtub" at the fuse box on the main battery pack. This gives them room to connect the Jdemo wires to the battery. His wire is 2 gauge and runs from the bathtub to the Jdemo contactor box under the hood. My plan is to connect my battery to his connectors under the hood. Because of the weather, I haven't been able to get under my car to look myself but Tony said there isn't enough material to drill, tap, die, and install a larger wire gland to his bathtub. So I cant upgrade the 2 gauge wire to 1/0. I want to get under there to check it out but its too damn cold!

It would be great if I didn't need 1/0 but I suspect that I do. You guys have an answer for that?

 

[miimura]

The wire sizing really depends on how much current is passing through the wires. Have you thought about how to control that current? In my opinion, the best way to do this would be to use a DC/DC converter to pass energy from the slave pack to the main pack. That way you can control the current and you can use smaller wires. It also allows the battery characteristic and voltage to be different than the main pack. You will notice with Val's battery trial they took advantage of the different slope of the discharge curve of the slave pack so that it would be drained before the main pack.

In any case, my suggestion is not that useful because I don't know where to get a 10-20kW 300-400VDC DC/DC converter.

 

[jimbo69ny]

The wire sizing really depends on how much current is passing through the wires. Have you thought about how to control that current? In my opinion, the best way to do this would be to use a DC/DC converter to pass energy from the slave pack to the main pack. That way you can control the current and you can use smaller wires. It also allows the battery characteristic and voltage to be different than the main pack. You will notice with Val's battery trial they took advantage of the different slope of the discharge curve of the slave pack so that it would be drained before the main pack.

In any case, my suggestion is not that useful because I don't know where to get a 10-20kW 300-400VDC DC/DC converter.

I know the wire size depends on how much current is passing through the wires..... It will be in parallel with the main pack so if the fuse on the main pack is indeed 325 amps (too cold outside to verify) then 325 amps could flow through the wires and that would mean that I need 1/0 gauge wire.

I have no plans to use a DC/DC converter.

 

[jimbo69ny]

I made some progress on the box and module tonight. Box is almost done. Then, using dead 18650 cells, I was able to mock up the first module. I can fit 9 modules total and each module can hold a maximum of 362 cells. There is even room on the sides for quite a few more if need be (and if money permits).

I fabricated the box out of 1/2" plywood but soon it will be made out of 1/4" aluminum. I am also going to add blower fans on the side of the box. One blowing, one sucking.

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

 

[dstjohn99]

You want the current flow to be based on the new battery pack capabilities (charge and discharge). Remember also that the pack is not temperature controlled, only air cooled. You will need to size the fuse and wire for the additional pack based on these requirements. However, fuses will not limit current only blow if the rated current is exceeded.

 

[jimbo69ny]

My Dayton blower fan arrived today. It is a big fan! Over 500 cfm! A little louder than I hoped but not annoyingly loud. Here is a video about it. https://www.youtube.com/watch?v=ZpX2VcjZqkU

In order to fit it in I need to cut the oem plastic a bit. A little nervous about it. Wires can be removed but cut plastic cant be repaired....

 

[Philly RAV4 EV]

Your fan is way over kill for that size box. You can go a lot smaller! FYI

 

[jimbo69ny]

Your fan is way over kill for that size box. You can go a lot smaller! FYI

You think? There is going to be a lot of battery in this box and the cells are pretty close together. I thought it would take a fan with some brute force to get air through. You could be right though.

There is this option. Fan is smaller but its also HALF the CFM. https://www.grainger.com/product/DAYTON-Rectangular-DC-OEM-Specialty-3HMH7

I dont even know how hot these cells are going to get. Im just guessing here.

 

[Philly RAV4 EV]

All you need to do is circulate the air in and out of the box. With that fan you’ll blow them out of the box! check this item out on eBay, 2 of them will work fine #122827850456

 

[jimbo69ny]

All you need to do is circulate the air in and out of the box. With that fan you’ll blow them out of the box! check this item out on eBay, 2 of them will work fine #122827850456

Thanks for the suggestion. I just thought bigger was better. But that was a bit too big and a bit louder than my wife would tolerate. I have reached out to the seller to return it. I found this one and thought it would be good. But if you think those little cooling fans are good enough you might think that this one is overkill too. https://www.ebay.com/itm/Dayton-Rectangular-OEM-Blower-With-Flange-Voltage-12VDC-1875-RPM-Wheel-Dia/142484064733?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

Until I have it all together and see how hot the cells get I wont know exactly how big of a fan Ill need. I am doing it now because I need to plan the fan as part of the box building.

 

[Philly RAV4 EV]

That fan is still over kill. You only need the small ones I showed you. Put them at one end of the box and install vent holes at the opposite end of the box.

 

[jimbo69ny]

That fan is still over kill. You only need the small ones I showed you. Put them at one end of the box and install vent holes at the opposite end of the box.

Ok. They would probably be cheaper and use less energy. How are you so sure? Ive heard that it is better to have them suck air out than push it in. You think that is true? I wanted to have them blow in so I could put a heater in front of them at some point.

Update:
I just looked at the specs for the fan you sent. Really good! 103.8 cfm and only 4.44 watts! Not very loud either! When I first looked at them I thought they were basic computer cooling fans that dont move much air. These look great!