[EVDL] aluminum vs steel battery racks

harry henderson wrote:

> first i was surprised by the strength of aluminum vs steel, then i =

> was further surprised by the price, if i'm reading this information =

> correctly there are several aluminum size options for battery racks =

> that are cheaper and stronger than steel!?!
>
> so my question: is yield strength what i should be looking at for =

> running lengths of racks while the tensile strength should be used =

> for measuring the "hanging" part of the battery racks?
>
> ASTM A36 Mild (low-carbon) steel: Ultimate Tensile Strength, =

> psi---58,000 - 79,800---Yield Strength, psi---36,300
>
> 6061-T6 Aluminum: Ultimate Tensile Strength, psi---45,000------Yield =

> Strength, psi---40,000
>
> onlinemetals.com 25-oct------------------
>
> 6' section ----------al---------------thickness------------fe-------
> -----------------0.125"---0.1875--0.25-***--0.125---0.1875---0.25
> size----------------------------------------------------------------
> 1=94--------------$6.09-----9.19---10.7---***--7.75---10.79---12.69
> 1.25=94------------8.16----13.81---15.31--***-9.66----13.76---17.35
> 1.5=94-------------10.55---14.59---19.33--***--9.83---14.85---20.84
> 2=94---------------14.58-----20----27.16--***-11.67---21.09---27.72
>


I'm a big fan of aluminum. I use it extensively in my business.

As far as yield and tensile strength is concerned, Neither on is =

truly relevant. What your probably most concerned with is flexural =

modulus. You don't want springy, saggy battery racks, so you'll =

probably want at least 3/16" thick angles. You need a spool MIG gun =

or a TIG for aluminum.




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EV Convert wrote:

>
> When Al is welded, the weld and the area near the weld has its
> tensile
> strength reduced to the near fully annealed state. In the example of
> 6061
> alloy this is less than 20.000 PSI. Welded mild steel (low carbon,
> typical
> structural steel) retains a much higher percentage of its original
> tensile
> strength. Al backpack and bicycle (and motorcycle) frames are
> typically heat
> treated after welding to restore the original tensile strength-not
> something
> easily done by DIYers.

I have heard this argument before, and don't doubt its true, however,
20,000 PSI is still way beyond the stresses you would encounter in a
battery rack. Failure in aluminum structures is almost always due to
fatigue. There should be no fatigue in a properly mounted rack.

>
> You can design a structure where the welds are away from the most
> highly
> stressed areas. Better yet,use bolts or rivets to tie the structure
> together-this is the option aircraft builders use.

Sure, just make sure the bolts or rivets are stainless steel.

>
> Also Al is much more susceptible to damage from battery electrolytes
> and as
> mentioned, has only 1/3 the stiffness of steel alloys


Absolutely false. If your talking about sulfuric acid, aluminum will
way outlast steel. It is even slightly superior to stainless steel.
I have over 20 years experience using aluminum in acidic environments
without a single failure due to corrosion. I can't say the same about
stainless steel.

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Roger Heuckeroth wrote:
> If you're talking about sulfuric acid, aluminum will
> way outlast steel. It is even slightly superior to stainless steel.

The problem comes if that aluminum ever touches steel. Then you get a
corrosion couple, and the aluminum is the loser.

As an example, my ComutaVan had aluminum battery boxes and flooded
batteries. The boxes were fine *except* where they were bolted to the
frame with steel bolts. The steel bolts were protected by the aluminum
completely corroding away around them!

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Lee Hart <[email protected]> wrote:

> Roger Heuckeroth wrote:
>> If you're talking about sulfuric acid, aluminum will
>> way outlast steel. It is even slightly superior to stainless steel.
>
> The problem comes if that aluminum ever touches steel. Then you get a
> corrosion couple, and the aluminum is the loser.
>
> As an example, my ComutaVan had aluminum battery boxes and flooded
> batteries. The boxes were fine *except* where they were bolted to the
> frame with steel bolts. The steel bolts were protected by the aluminum
> completely corroding away around them!
>

You can use plastic washers or gasket material.

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George Tyler wrote:

> What Ali can't stand is an alkali electrolyte, I would hesitate to
> use it
> with cells that use one, like Li, NiCD, or NiMih.
>


Yes, aluminum and alkali don't play well together. I wouldn't use it
for a flooded type alkali battery, but AFAIK Lithium batteries are
sealed, and do not off-gas. I would not hesitate to use Al for
LiFePO4 bats.



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George Tyler wrote:
>
>> What Ali can't stand is an alkali electrolyte, I would hesitate to
>> use it
>> with cells that use one, like Li, NiCD, or NiMih.
>>
>
>
> Yes, aluminum and alkali don't play well together. I wouldn't use it
> for a flooded type alkali battery, but AFAIK Lithium batteries are
> sealed, and do not off-gas. I would not hesitate to use Al for
> LiFePO4 bats.
>
>
>
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-- =

David D. Nelson
http://evalbum.com/1328

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Lee Hart <[email protected]> wrote:
> On 10/31/2010 10:52 PM, David Nelson wrote:
>> The pitting in the Al battery box in each of my Gizmos is significant.
>> Over half of the thickness had been eaten away by the acid from the Pb
>> batteries. This is with ~6 years and ~12k miles in one and the other
>> one with ~5 years and 12-24k (it was used as a pizza delivery car in
>> Minneapolis MN) miles on it. I put LiFePO4 bats in one and the other
>> got a bedliner spray put in it.
>
> The Gizmos have a steel frame, and the aluminum is right against it.
> Also, there is a lot of road salt in Minnesota. Even if the batteries
> don't leak, the road salt provides an "electrolyte" for the
> steel-aluminum corrosion couple. The aluminum loses.
>
> --
> Lee A. Hart | Ring the bells that still can ring
> 814 8th Ave N | Forget the perfect offering
> Sartell MN 56377 | There is a crack in everything
> leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
>
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-- =

David D. Nelson
http://evalbum.com/1328

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Lee Hart <[email protected]> wrote:
> Yet another is to have a DC leakage current flow from the metal to a
> battery. When wetted with electrolyte, this forms an electroplating
> 'cell', which removes metal from one electrode and deposits it on the
> other one.
>
> If you can see the outline of the batteries in the corrosion, I'll bet
> the latter was the cause. There was probably a film of electrolyte going
> from the cell terminals down the side to the battery box, and then back
> up to another cell terminal.

That is probably it because I would regularly see a voltage between
the battery box and the battery terminals. In fact, I burned out a
PakTrakr remote because one of the leads bumped the battery box while
I was installing it. That was my introduction to how sensitive things
really are.

--
David D. Nelson
http://evalbum.com/1328

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