# Ultimate Battery Box



## bruceme (Dec 10, 2008)

In my 4 years EV commuter experiance I have learned exactly !ONE! thing... The batteries are the car, everything else just rides along for funzies.

I am about to do a Plug-In conversion to my Gen2 Prius, and I want my batteries as happy as possible and I want to make the best battery box possible. 

- 3/4" Insulation (this is what my car has now... made a HUGE difference)
- Threading tubes between the gaps in the LiFEPo4 cells. Permanently running if the car is running or charging.
- compact-car sized fan-cooled radiator to cool/heat the fluid as needed
- micro controller sensing battery temp and outside air temp.. I could do fluid temp, but wouldn't that be either of those two depending where I put it? Maybe it will tell me if the pump is broken... but so will runaway temps.

Does anyone have a similar project? 

Thoughts?

-Bruce


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## Elithion (Oct 6, 2009)

Two things:

1) Use low resistance cells. Prismatic cells today have a bit too high a resistance. You'll need either K2, or A123 M1 cells (not the 20 Ah cells) or some of the better pouch cells. In the charge sustain mode, you need a total battery resistance of 0.1 Ohm or lower; otherwise, you'll heat up your cells too much.

2) Use the Orion BMS, no questions! It is the only BMS that also has built-in support for Prius PHEVs. DO NOT use Ron Gremban's contactor method: it will kill your cells and hurt the stock pack with the huge current inrush.

(I did the Prius and Escape Hybrid for Hybrids plus, back in 2006; and I work closely with PHEV conversion companies today. )


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## bruceme (Dec 10, 2008)

I am talking a trunk full of Lithium... 10kwh. So the draw will smoke a CALB or TS (Winston whatever)... What about headway?


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## Elithion (Oct 6, 2009)

bruceme said:


> So the draw will smoke a CALB or TS (Winston whatever)... What about headway?


Headway cells are really about the same as CALB for power applications.










> 10kwh

Well, then, you'll be fine with prismatic cells, because the resistance will be low:

resistance [Ω] = short_discharge_time  * (voltage [V])^2 / energy [Wh] / 3600 = 140 * 200^2 / 10000 / 3600 = 155 mΩ


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## Ziggythewiz (May 16, 2010)

Elithion said:


> DO NOT use Ron Gremban's contactor method: it will kill your cells and hurt the stock pack with the huge current inrush.


Do you have a link where I can read about this?


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## Caps18 (Jun 8, 2008)

How important is the active heating/cooling of LiFePO4 cells? Do they run better at warmer temps? Can you just monitor the temp and stop if the battery box gets too hot? I wasn't planning on needing to have any ventilation actually.

I plan on putting 45 cells into a Pelican case with 1" insulation around the outside. They will also be kept in a garage that will be better insulated by next winter.


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## Ziggythewiz (May 16, 2010)

Heating is important in a cold climate. Resistance goes up noticably below 60 F. Yes, warmer is better. Too hot is unlikely.


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## Elithion (Oct 6, 2009)

Caps18 said:


> How important is the active heating/cooling of LiFePO4 cells?


For what?


Heat that they generate?
Ambient temperature?
I can answer the first one, assuming 10 kWh of prismatic cells.
In a Prius the RMS current is about 50 A. So the heat generated is 
P = I^2 * R = 50 ^2 * 0.15 Ω = 375 W.
I think that's below where one would consider cooling for internal heat.
(The stock pack needs cooling because its resistance is higher: the cells are very good, but the pack is so much smaller.)




Caps18 said:


> Do they run better at warmer temps?


Yes, the hotter the better (lower internal resistance). But the resistance at 60 °C is not that much better than 25 °C. However, the cells will age faster and self discharge faster at higher temperatures. 40 °C should really be the max.


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## evmetro (Apr 9, 2012)

I see in the Orion's beta utility, there is a whole section dedicated to the prius. You can download the utility from their site and check it out, but I am not sure if the beta version that I have is downloadable yet. The beta version is the one that has a the "Prius" screen. I think the regular version has it as well, but it is not labeled "prius". I got the beta version from Orion when I was having some problems with my unit. They seem to have pretty strong support from what I can tell so far.


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## bruceme (Dec 10, 2008)

Caps18 said:


> How important is the active heating/cooling of LiFePO4 cells? Do they run better at warmer temps? Can you just monitor the temp and stop if the battery box gets too hot? I wasn't planning on needing to have any ventilation actually.
> 
> I plan on putting 45 cells into a Pelican case with 1" insulation around the outside. They will also be kept in a garage that will be better insulated by next winter.


The answer is put simply... it depends. If you know you'll only drive in San Diago, forget it. It's 75 degrees 300 days a year. But I live in Kansas. 80 days a year it's bellow 40 with lows in the single digits this time of year and there's an opposite 100 days it's over 90 with highs in the 110's last year. It can honestly be tough to keep the batteries in their operating temperature and commute every day. 

Too cold and the resistance goes way up (they act like they're smaller than they really are).. To hot and they perform wonderfully, but eat cycle life doing it. I have a closed/insulated and heated battery box. It has it's own built in thermostat and does fine in the winter. But in the summer I open it all up and run fans all night to cool it down. I want a system that takes care of itself.

-Bruce


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## bruceme (Dec 10, 2008)

I can tell you my BMW 44x100A TS (14.4kwh), pulls about 100A cruising 50mph and the batteries get warm in that insulation all on their own.


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## GeoMetric (Aug 13, 2010)

K2 Energy Modules are my choice . Here is a link with detailed info:

http://electricmotorsports.proboards.com/index.cgi?board=6576567&action=display&thread=14


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## Jesse67 (May 12, 2009)

Well with the older CALB and all TS and sinopoly cells the air channels can be used. My TS cells are in 4 columns of 6 cells each. I have two layers of 1/2" insulation in the bottom of my box, the top layer has 5 - 1/2" wide channels cut through it running across the columns lining up with the cell air channels. These 5 channels meet up in a manifold of sorts built into the side insulation and some modified hair dryer guts provide heat and airflow. A thermostat in the box controls temperature. Since the box is enclosed the air flows through the channels and out on top of the pack, past the thermostat and is circulated back through the heater and around again. The system delivers ~40deg C air right out of the heater but the air flowing out the top of the channels is barely above the pack temp indicating that just blowing air through the channels is very effective for heat transfer to the cells. The idea was to get more even heating of the pack than just a battery blanket around the edge or on the bottom. The heater draws about 350W and heats the pack up about 10deg C per hour.

I have a digital timer which can turn the heater on whenever I program it and a relay controlled by the BMS prevents the heater from coming on if the pack is still charging ( so it doesn't blow the 110V breaker). If it's cold the idea is to plug it in to charge as soon as I get home so the pack is warm from the drive. It charges right away and then ~2hours before I need to leave the heater comes on (if the thermostat calls for it) and it's warm and ready to go. In reality I just drive it and live with more voltage sag and less performance unless it's below about -10 deg C when I do need to heat the pack for it to be drivable. I could use the same channels to blow ambient air through the pack to cool it in summer quite effectively but I haven't needed to yet. I can attest that the cell performance is best above ~25 C and it sucks below about 5 deg C.

I will probably do something similar for my next conversion when it comes but I'd like to use the new CALB cells and they don't seem to have much for air channels that I can see. Can anyone confirm, is there much room for air circulation when the cells are packed tight together?


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## planetaire (Aug 2, 2010)

bruceme said:


> In my 4 years EV commuter experiance I have learned exactly !ONE! thing... The batteries are the car, everything else just rides along for funzies.
> 
> I am about to do a Plug-In conversion to my Gen2 Prius, and I want my batteries as happy as possible and I want to make the best battery box possible.
> 
> ...


Hi, Bruce

Then, why not have a look here ?

I have begin with 70 A123 20Ah cells and now use 140 of them, so 9kWh.

If you read french (or use a online translater) this link is better.

Here, just boxes:









And with cells, bms wires...









I use a peter perkins bms and bms+ (from hybridinterfaces.ca)


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## bruceme (Dec 10, 2008)

planetaire said:


> If you read french (or use a online translater) this link is better.


Merci beaucoup,
Je veux un système plus forte avec 10kwh. Mais, tu est faire bien.


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## Siwastaja (Aug 1, 2012)

planetaire said:


> I use a peter perkins bms and bms+ (from hybridinterfaces.ca)


Did I see right -- are the IC's in IC sockets!? The images are a bit small but it sure looks like that.

If so, ditch the BMS immediately and ask for money back and get another BMS instead. Try to get something people have experience on. Using IC sockets _at all_ is a sign of a total beginner design, and using them in an automotive environment and critical safety system is absolutely and totally unacceptable. Even if they wouldn't have contact problems (which they _will_ eventually have), it's a sign that the designer is totally out of this world and cannot design BMS's.

An IC socket is a special product that serves two purposes
(1) In some rare cases, allows old-style ROM chips to be changed. This is clearly not the case here.
(2) they are sold to beginner hobbyists alongside with a (totally false) claim that IC's are easily destroyed when soldered. Instead, contact problems with IC sockets are a real problem.

I hope my eyes are wrong and those are not IC sockets. If this is the case, forget what I said about the system.


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## kennybobby (Aug 10, 2012)

Hey Planetaire,

i love it, it looks like a first class job you did there--as good or better than "store-bought"...That is the true essence of DIY and you got it done.


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## CroDriver (Jan 8, 2009)

planetaire said:


> Hi, Bruce
> 
> Then, why not have a look here ?
> 
> ...


This looks quite dangerous. You should isolate the cells, i.e. put something non-conductive between them.


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## planetaire (Aug 2, 2010)

bruceme said:


> Merci beaucoup,
> Je veux un système plus forte avec 10kwh. Mais, tu est faire bien.


Merci.
Thank you bruceme. And thank you too kennybobby.

I don't know how many *kwh usable* you need.
In my P2 plug-in 8.3 kwh are usable.
The 140 A123 cells are added to the factory nimh (1.3 kwh, may be 0.5 usable)

In summer I can drive 80km in 100% ev mode, maximum I drive was 100km (average speed 44 km/h) without any gazoline.
In winter 60km if temp is close to 0°C always in 100% ev mode. I suppose less km under 0°C but don't have this winter.If trip is longer I use hybrid mode.
I use my prius phev since one year 1/2. This is a two car in one. Electric for short trips and hybrid for longer. With lithium cells in hybrid mode regen is better, internal resistance is really reduced: 0.045 ohms in summer (0,35 without lithium).

The boxes are made with 2 sheets. Frontal 10mm and the body in one piece (2mm thickness polycarbonate.
Total weigth is only 80 kg.


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## ishiwgao (May 5, 2011)

CroDriver said:


> This looks quite dangerous. You should isolate the cells, i.e. put something non-conductive between them.


take advice from the man who made it all happen! (on a side note: congrats on first delivery )


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