[EVDL List]

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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Lexan is really really nice!


Sent from my iPhone

[quote] Chris Zach <xxx@xxx.xxx> 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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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

[quote] Chris Zach <xxx@xxx.xxx> 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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[quote] 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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[quote] Christopher Zach <xxx@xxx.xxx> 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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From: Mike Golub <gol.xxx@xxx.xxx>
>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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From: Christopher Zach <xxx@xxx.xxx>
> 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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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

[quote] Lee Hart <xxx@xxx.xxx> wrote:
> From: Christopher Zach <xxx@xxx.xxx>
>> Given that lithium batteries carry their own oxygen...
>
> You're thinking of the Lithium-Cobalt cells. These are the ones that prov=
ide 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 i=
t 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 it=
s 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
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
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-- =

http://www.evalbum.com/2149

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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)
*xxx@xxx.xxx*
*+++++++++++++++++++++++++++++++++++++++++++++++*
*Offering a 12 day class July 9 to 21, 2012 in Central Florida. more info
on Web; WWW.ElectricVehicleTechnicalinstitute.COM<http://www.electricvehicletechnicalinstitute.com/>
*
++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++

[quote] Lee Hart <xxx@xxx.xxx> wrote:

> From: Christopher Zach <xxx@xxx.xxx>
> > 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
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere. Thanks.
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[quote] 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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