Building a lithium battery box out of wood.

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Building a lithium battery box out of wood.

Chris Zach
So I am working on the 20ah A123 cells and made a really nice battery
box out of 1/2 inch birch plywood. Very solid, snug, with padding inside
for the cells and compression along with a spot on the top for the
miniBMS board.

And I was thinking: "Man I could build a really long wood battery box
here or flat ones for the Prizm pack." With a separate channel for the
bms boards and temp sensor spots and nice wiring and everything!

Except: Is it a good idea to put lithium cells in wood enclosures? Or if
there is a fire is it really not going to make a difference if there's
more wood in there to burn. They're going in a 1/2 inch thick aluminum
clamshell which I guess will just melt anyway.

Thoughts? Wood seems to make a nice containment structure. I could
probably get away with 1/4 inch ply or 3/8 inch with smaller screws...

Chris

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Re: Building a lithium battery box out of wood.

Mike Golub-2
Lexan is really really nice!


Sent from my iPhone

On Jun 25, 2012, at 6:06 PM, Chris Zach <[hidden email]> wrote:

> So I am working on the 20ah A123 cells and made a really nice battery
> box out of 1/2 inch birch plywood. Very solid, snug, with padding inside
> for the cells and compression along with a spot on the top for the
> miniBMS board.
>
> And I was thinking: "Man I could build a really long wood battery box
> here or flat ones for the Prizm pack." With a separate channel for the
> bms boards and temp sensor spots and nice wiring and everything!
>
> Except: Is it a good idea to put lithium cells in wood enclosures? Or if
> there is a fire is it really not going to make a difference if there's
> more wood in there to burn. They're going in a 1/2 inch thick aluminum
> clamshell which I guess will just melt anyway.
>
> Thoughts? Wood seems to make a nice containment structure. I could
> probably get away with 1/4 inch ply or 3/8 inch with smaller screws...
>
> Chris
>
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Re: Building a lithium battery box out of wood.

Chris Zach
On 6/25/2012 10:38 PM, Mike Golub wrote:
> Lexan is really really nice!

Possible, any tips on working with it?

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Re: Building a lithium battery box out of wood.

Lee Hart
In reply to this post by Chris Zach
On 6/25/2012 9:06 PM, Chris Zach wrote:
> Is it a good idea to put lithium cells in wood enclosures?

Wood strikes me as a very poor material to use. It burns. It becomes
conductive when damp or wet. It rots. It isn't particularly strong for
heavy objects, and performs poorly when there is vibration or in crashes.

It's only real virtues are low cost, easy to get, and easy for people
with limited skills to use.

--
If you would not be forgotten
When your body's dead and rotten
Then write of great deeds worth the reading
Or do these great deeds, worth repeating.
        -- Ben Franklin, from Poor Richard's Almanac
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

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Re: Building a lithium battery box out of wood.

Rush Dougherty
In reply to this post by Chris Zach
Works just like Plexiglas, cuts on a table saw, glues with plexi glue, although you might want to
drill and tap it and also glue it.

Sintra is also another good material, PVC with air blown into it, works just like wood and you can
glue it for added strength.

Rush
www.TucsonEV.com

And how long did this one take!

----- Original Message -----
From: "Chris Zach" <[hidden email]>
To: <[hidden email]>
Sent: Monday, June 25, 2012 8:00 PM
Subject: Re: [EVDL] Building a lithium battery box out of wood.


> On 6/25/2012 10:38 PM, Mike Golub wrote:
>> Lexan is really really nice!
>
> Possible, any tips on working with it?
>
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>

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Re: Building a lithium battery box out of wood.

Mike Golub-2
In reply to this post by Chris Zach
Drill and tap holes for 4-40 screws.
Might need to get thicker stuff.
But u probably leave in an area where you can find a wholesale place.
You want lexan polycarb.
Do not get plexiglass!

Sent from my iPhone

On Jun 25, 2012, at 7:00 PM, Chris Zach <[hidden email]> wrote:

> On 6/25/2012 10:38 PM, Mike Golub wrote:
>> Lexan is really really nice!
>
> Possible, any tips on working with it?
>
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Re: Building a lithium battery box out of wood.

Lee Hart
In reply to this post by Chris Zach
On 6/25/2012 10:00 PM, Chris Zach wrote:
> On 6/25/2012 10:38 PM, Mike Golub wrote:
>> Lexan is really really nice!
>
> Possible, any tips on working with it?

It's lovely stuff. Clear, tough, flexible, cuts easily, and can even be
bent cold like sheet metal.

But again, it is terrible stuff to make high voltage electrical boxes
out of. The main problems are that it melts easily and burns ferociously.

--
If you would not be forgotten
When your body's dead and rotten
Then write of great deeds worth the reading
Or do these great deeds, worth repeating.
        -- Ben Franklin, from Poor Richard's Almanac
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

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Re: Building a lithium battery box out of wood.

martinwinlow
In reply to this post by Chris Zach

On 26 Jun 2012, at 03:06, Chris Zach wrote:

> So I am working on the 20ah A123 cells and made a really nice battery
> box out of 1/2 inch birch plywood. Very solid, snug, with padding inside
> for the cells and compression along with a spot on the top for the
> miniBMS board.
>
> And I was thinking: "Man I could build a really long wood battery box
> here or flat ones for the Prizm pack." With a separate channel for the
> bms boards and temp sensor spots and nice wiring and everything!
>
> Except: Is it a good idea to put lithium cells in wood enclosures? Or if
> there is a fire is it really not going to make a difference if there's
> more wood in there to burn. They're going in a 1/2 inch thick aluminum
> clamshell which I guess will just melt anyway.
>
> Thoughts? Wood seems to make a nice containment structure. I could
> probably get away with 1/4 inch ply or 3/8 inch with smaller screws...
>
> Chris
>

Hi Chris,

There are plenty who will say 'don't do it' for various reasons and, yes, fire is one of them.

>From an engineering POV there are many very positive reasons why you might consider using wood - especially ply, not the least of which are ease of use and cost.  But it is also very strong, to some extent insulative and impact absorbing, certainly more so than most hard plastics and metals.  If you want no better an example of ply contruction then consider the WWII era twin-engined de Havilland Mosquito fighter/bomber, AKA "The Wooden Wonder" - http://en.wikipedia.org/wiki/De_Havilland_Mosquito

For me, if you are doing a one-off it is a no brainer and alternatively, if you are planning a production run then it gives you something that is strong enough but also easy (ie cheap) to re-jig several times to get just right before committing to steel or alu or whatever.

Just ensure that you have a sufficiently strong sub-structure which could be wood again but probably better in steel or alu.

I did one for my van - http://www.winlow.co.uk/wychwood.co.uk/EV_Conversion_-_Part_4.html

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk

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Re: Building a lithium battery box out of wood.

Chris Zach
In reply to this post by Lee Hart
On 6/26/2012 1:02 AM, Lee Hart wrote:
> But again, it is terrible stuff to make high voltage electrical boxes
> out of. The main problems are that it melts easily and burns ferociously.
>

Given that lithium batteries carry their own oxygen much like magnesium
I wonder if there's anything one can do about a fire once it gets going.
Technically in a closed pack with thick aluminum around it like the
Prizm's any fire should self-snuff out, but a fire that carries it's own
oxygen wouldn't.

A123 cells are supposed to not catch fire, but that's open for
discussion. Aside from using cast iron, what else should one use as a
battery enclosure? I need something to act as a container for the cells
and I think even CALB cells have plastic in them somewhere.

Chris

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Re: Building a lithium battery box out of wood.

Morgan LaMoore
On Tue, Jun 26, 2012 at 7:48 AM, Christopher Zach <[hidden email]> wrote:
> ...
> Given that lithium batteries carry their own oxygen much like magnesium
> I wonder if there's anything one can do about a fire once it gets going.
> Technically in a closed pack with thick aluminum around it like the
> Prizm's any fire should self-snuff out, but a fire that carries it's own
> oxygen wouldn't.
> ...

I believe that the big safety advantage of LiFePO4 is that the
Phosphate (PO4) has a much stronger bond to the oxygen than the Cobalt
Dioxide (CoO2) or other oxides used in other Lithium chemistries, so
that oxygen is *not* available to a fire (or not nearly as available).

The electrolyte is still flammable (as it's a solvent), but it has to
get its oxygen from the surrounding air instead of the batteries
themselves.

-Morgan LaMoore

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Re: Building a lithium battery box out of wood.

Chris Zach
On 6/26/2012 10:54 AM, Morgan LaMoore wrote:
> I believe that the big safety advantage of LiFePO4 is that the
> Phosphate (PO4) has a much stronger bond to the oxygen than the Cobalt
> Dioxide (CoO2) or other oxides used in other Lithium chemistries, so
> that oxygen is *not* available to a fire (or not nearly as available).
>
> The electrolyte is still flammable (as it's a solvent), but it has to
> get its oxygen from the surrounding air instead of the batteries
> themselves.

Oh, then that makes a big difference in life; if the thing can't self
oxidize, then it is not going to get much oxygen from within a prizm pack.

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Re: Building a lithium battery box out of wood.

Lee Hart
In reply to this post by Chris Zach
From: Mike Golub <[hidden email]>
>Drill and tap holes for 4-40 screws.
>Might need to get thicker stuff.
>But u probably leave in an area where you can find a wholesale place.
>You want lexan polycarb.

Tapping polycarbonate is tough; it doesn't hold threads very well. When I make polycarbonate boxes, I use screws and nuts, or pop rivets.

>Do not get plexiglass!

Good advice. Plexiglass (acrylic) is glass-like, as the name implies. Crystal clear and brittle, it cracks and breaks very easily. And burns ferociously!

If you must use plastics for battery boxes, use polypropylene (which is what battery cases are normally made of). Very strong, and readily available in fire retardent sheets. Some electrical boxes are polypropylene.

Or polyethylene. It's not as strong, but has the best chemical resistance and is very easy to hot-air weld into boxes.

--
Those who say it cannot be done should not interrupt the one who is
doing it.    --    Chinese proverb
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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Re: Building a lithium battery box out of wood.

Lee Hart
In reply to this post by Chris Zach
From: Christopher Zach <[hidden email]>
> Given that lithium batteries carry their own oxygen...

You're thinking of the Lithium-Cobalt cells. These are the ones that provide their own oxygen. They would probably keep burning underwater!

> I wonder if there's anything one can do about a fire once it gets going.

A metal or other noncombustible box's job is to slow the fire, and keep it from spreading.

> Technically in a closed pack with thick aluminum around it like the
> Prizm's any fire should self-snuff out

Aluminum has a fairly low melting point, so a fire may be able to melt its way out.

> A123 cells are supposed to not catch fire, but that's open for
> discussion.

Lithium-Iron based cells are less combustible, but they still burn nicely. One cell in open air is pretty safe; but pack a bunch of them tightly in a box and they are still a fire hazard. I like to say LiCo cells are like a box of matches; while LiFe cells are like a box of kindling wood.

> I need something to act as a container for the cells
> and I think even CALB cells have plastic in them somewhere.

Why not a plain old steel box?


--
Those who say it cannot be done should not interrupt the one who is
doing it.    --    Chinese proverb
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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Re: Building a lithium battery box out of wood.

Bill Dube
         The LiFePO4 type cells need oxygen (air) to burn. They burn
a bit like a Duraflame log when overheated and then exposed to air.
An aluminum box is a big help to exclude oxygen and help suppress a
fire. A wooden box would probably just add to the available fuel.

         Lexan is better than wood, but it melts and then allows air
into an over-heated pack. Lexan is better than wood in that it does
not absorb water and become conductive, and it also has very good
impact resistance, while wood does not.

          LiPo cells do _not_ need oxygen to burn and they will, in
fact, burn quite well underwater once they are touched off. It helps
to submerge or flood the pack with water, however, to keep the
burning cells from heating the others to the combustion point.

Bill D.

At 10:29 AM 6/26/2012, you wrote:

>From: Christopher Zach <[hidden email]>
> > Given that lithium batteries carry their own oxygen...
>
>You're thinking of the Lithium-Cobalt cells. These are the ones that
>provide their own oxygen. They would probably keep burning underwater!
>
> > I wonder if there's anything one can do about a fire once it gets going.
>
>A metal or other noncombustible box's job is to slow the fire, and
>keep it from spreading.
>
> > Technically in a closed pack with thick aluminum around it like the
> > Prizm's any fire should self-snuff out
>
>Aluminum has a fairly low melting point, so a fire may be able to
>melt its way out.
>
> > A123 cells are supposed to not catch fire, but that's open for
> > discussion.
>
>Lithium-Iron based cells are less combustible, but they still burn
>nicely. One cell in open air is pretty safe; but pack a bunch of
>them tightly in a box and they are still a fire hazard. I like to
>say LiCo cells are like a box of matches; while LiFe cells are like
>a box of kindling wood.
>
> > I need something to act as a container for the cells
> > and I think even CALB cells have plastic in them somewhere.
>
>Why not a plain old steel box?
>
>
>--
>Those who say it cannot be done should not interrupt the one who is
>doing it.    --    Chinese proverb
>--
>Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net
>
>_______________________________________________
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Re: Building a lithium battery box out of wood.

dave cover-2
In reply to this post by Lee Hart
I have had good luck with wooden boxes, just not plain wood. I built
the boxes using 5 layer quarter inch plywood and some oak pieces glued
and screwed together. I then painted them with a coating of fiberglass
resin. When that set I applied a couple of layers of fiberglass to the
outside. This strengthened the structure and protected the wood. There
was no exposed wood. I provided drain holes in the bottom for rinsing
and airflow. I also use a rubberized paint on the inside to provide a
little more protection from my NiCads electrolyte. These boxes have
been in my car for at least 5 years with absolutely no sign of
degradation. They are protected from sunlight but the bottoms are
exposed to the weather.

DAC

On Tue, Jun 26, 2012 at 12:29 PM, Lee Hart <[hidden email]> wrote:

> From: Christopher Zach <[hidden email]>
>> Given that lithium batteries carry their own oxygen...
>
> You're thinking of the Lithium-Cobalt cells. These are the ones that provide their own oxygen. They would probably keep burning underwater!
>
>> I wonder if there's anything one can do about a fire once it gets going.
>
> A metal or other noncombustible box's job is to slow the fire, and keep it from spreading.
>
>> Technically in a closed pack with thick aluminum around it like the
>> Prizm's any fire should self-snuff out
>
> Aluminum has a fairly low melting point, so a fire may be able to melt its way out.
>
>> A123 cells are supposed to not catch fire, but that's open for
>> discussion.
>
> Lithium-Iron based cells are less combustible, but they still burn nicely. One cell in open air is pretty safe; but pack a bunch of them tightly in a box and they are still a fire hazard. I like to say LiCo cells are like a box of matches; while LiFe cells are like a box of kindling wood.
>
>> I need something to act as a container for the cells
>> and I think even CALB cells have plastic in them somewhere.
>
> Why not a plain old steel box?
>
>
> --
> Those who say it cannot be done should not interrupt the one who is
> doing it.    --    Chinese proverb
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net
>
> _______________________________________________
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--
http://www.evalbum.com/2149

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Re: Building a lithium battery box out of wood.

Dennis Miles
In reply to this post by Lee Hart
The steel box updated with perhaps aluminum angle as an exo-skeleton and
panels of galvalume sheet metal which is like galvanized but with aluminum
plating instead of zinc over the steel. a coating of truck bed spray
coating over a good primer will protect it
Regards,
*Dennis Lee Miles*   (863)944-9913 (call noon to midnight Eastern time)
*[hidden email]*
*+++++++++++++++++++++++++++++++++++++++++++++++*
*Offering a 12 day class July 9 to 21, 2012 in Central Florida. more info
on Web; WWW.ElectricVehicleTechnicalinstitute.COM<http://www.electricvehicletechnicalinstitute.com/>
*
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

On Tue, Jun 26, 2012 at 12:29 PM, Lee Hart <[hidden email]> wrote:

> From: Christopher Zach <[hidden email]>
> > Given that lithium batteries carry their own oxygen...
>
> You're thinking of the Lithium-Cobalt cells. These are the ones that
> provide their own oxygen. They would probably keep burning underwater!
>
> > I wonder if there's anything one can do about a fire once it gets going.
>
> A metal or other noncombustible box's job is to slow the fire, and keep it
> from spreading.
>
> > Technically in a closed pack with thick aluminum around it like the
> > Prizm's any fire should self-snuff out
>
> Aluminum has a fairly low melting point, so a fire may be able to melt its
> way out.
>
> > A123 cells are supposed to not catch fire, but that's open for
> > discussion.
>
> Lithium-Iron based cells are less combustible, but they still burn nicely.
> One cell in open air is pretty safe; but pack a bunch of them tightly in a
> box and they are still a fire hazard. I like to say LiCo cells are like a
> box of matches; while LiFe cells are like a box of kindling wood.
>
> > I need something to act as a container for the cells
> > and I think even CALB cells have plastic in them somewhere.
>
> Why not a plain old steel box?
>
>
> --
> Those who say it cannot be done should not interrupt the one who is
> doing it.    --    Chinese proverb
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net
>
> _______________________________________________
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Re: Building a lithium battery box out of wood.

martinwinlow
In reply to this post by Chris Zach

On 26 Jun 2012, at 13:48, Christopher Zach wrote:

> On 6/26/2012 1:02 AM, Lee Hart wrote:
>> But again, it is terrible stuff to make high voltage electrical boxes
>> out of. The main problems are that it melts easily and burns ferociously.
>>
>
> Given that lithium batteries carry their own oxygen much like magnesium
> I wonder if there's anything one can do about a fire once it gets going.
> Technically in a closed pack with thick aluminum around it like the
> Prizm's any fire should self-snuff out, but a fire that carries it's own
> oxygen wouldn't.
>
> A123 cells are supposed to not catch fire, but that's open for
> discussion. Aside from using cast iron, what else should one use as a
> battery enclosure? I need something to act as a container for the cells
> and I think even CALB cells have plastic in them somewhere.
>
> Chris
>

Hi Chris,

If you are concerned about fire - and you should be - the most obvious design requirements are:-

 a/ Use a system not prone to catch fire in the first place ie fail-safe BMMS', minimal balancing currents, properly rated wiring correctly installed (no chaffing etc), correct fusing etc etc, all the things that get discussed regularly and often on the EVDL
b/  Provide effective monitoring and alarm systems to warn of high temps during normal use and smoke/fire when 'off-line', ie charging etc, and
c/  Some means of fire suppression or extinction to give one time to evacuate safely if on the move and/or buy some time before the cavalry (FD) arrive.  

Unfortunately, as you say, if the cells provide their own oxygen then the order of priority of the above measures should be as I have stated them.  If things get to the point of ignition it seems the end result is pretty much decided.  So, best we do whatever we (reasonably) can do to prevent a fire in the first place.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk

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