I have a friend who lives off the grid (solar + wind) and is concerned
with the battery charge getting low and the fluid freezing.
My view was that if it is cold enough for the electrolyte to freeze, it
will do it fully-charged or flat at about the same temp.
Can someone set me straight with some Physics here please?
Thanks in advance.
I lived in Minnesota for many years before moving to Ca and had many
experiences where I ran my battery down to what seemed to be dead
without the car starting and worried if my battery would freeze.
After studying the subject I found that the freezing point of sulphuric
acid solutions follows a snakey curve. Pure sulfuric acid freezes above
40 deg F but once water is added the freezing point drops rapidly.
If your battery is fully charged or near that point there is nothing to
worry about with the low temperatures we have in this country. The
crossover point where the increase of acid concentration causes an
increase in freezing temperature occurs at about -90 deg F.
(see charts at http://www.unionbattery.com/images/2.6.pdf ).
Furthermore , if your battery does freeze and it still contains some
acid, it won't freeze hard enough to cause serious damage.
On 1 Dec 2006 17:49:55 -0800, " firstname.lastname@example.org"
Tell a battery that. If a battery is below 1.2SG it will freeze at
-20F. At 1.16 it freezes at 0F. at 1.15 it freezes at +5F.
1.2 is 65%, 1.16 is 45%, and 1.15 is about 40% charge (SG corrected
Even crystaline ice will damage the separators and cause the spongy
lead to flake, ruining the battery.It might not quit right away, but
the damage is done.
Posted via a free Usenet account from http://www.teranews.com
No one has yet mentioned the hazard a frozen automotive battery
presents. It is VERY COMMON for the frozen battery to EXPLODE
immediately or with-in a few seconds of the application of "booster
cables" or "jumpers" from another battery in an attempt to start the
car with a "dead" battery.
If you have lots of good luck, the bottom will just sort of crack and
the contents squish/splash; but if you are at the other end of the
luck spectrum, you will get doused in acid and/or bits & pieces of
fast moving battery container and/or contents.
This can also happen under high heat in certain situations if the
battery receives a dead-short across the posts.
Not nice in either event.
A discharged battery will freeze long before a fully changed battery
will freeze. One of the ways to tell if a battery is charged is to use
a hydrometer. IIRC a fully charged battery has a specific gravity of
about 1.230, which means there is sulphuric acid mixed with the water
and making the electrolyte heavier.
Dave, popular legend is that a discharged battery freezes more quickly
than a charged one. It's too late at night here right now for me to dig
up my P. Chem book and justify this belief with fact.
I can share with you my experience that a $$$ deep cycle battey on my
boat once froze when it was discharged and burst its container. That
was in 0-degree weather. Since that singular experience I have kept my
$$$ boat batteries fully charged, and not lost any.
Dave, I can't do that wrote:
Fact, not legend.
Discharging takes ions from solution and deposits them on the plates. The
electrolyte becomes less ionic, more watery if you will. The freezing
Strictly speaking, it freezes at a higher temperature, not "more quickly".
OK I just got my Chem Phys hdbk out and here is the "straight scoop".
Pg B154 Sulfuric acid melting point 10.36 deg C BP 338 C (98.3%)
Freezing point depression:
Pg D 242 Column % by weight from 0.50 to 100.00
the column for freez point dep stops at 34% and the value is
(trumpet sound) 55.28 deg C
SO! At that conc. freezing would be, - 44.92 deg C or - 48.6 deg F
Any more questions? :-)
I love it when I see it in writing. I suspected the freezing would be
folklore. I sure hope it does NOT get down to -48 around here. It is
+22 at the moment but that's about the High for the day.
Lew Hartswick wrote:
I can tell you that the battery in my VW bug froze solid one January
night sitting in the parking lot at Pete Field outside Colorado Springs
-- the temps were well below zero that night. Went out the next day,
tried to start it (nothing, of course), and when I looked at the
battery the case was cracked with chunks of ice poking out of it and
out of the filler cap holes. Far as I know, it was charged up -- the
car had been driven the day before.
Something happened to drain the battery. You left the lights on, or
something failed and drained the battery. A fully charged battery will not
freeze in temps we will see in the states. I have seen -40F temps and my
battery made it through just fine. As I kid growing up on the farm we left
batteries in farm equipment over winter with no apparent problems. Some
equipment was used on a daily basis, some not run until spring.
As to the OP, yes a battery that is low on charge can freeze where a charged
on will not.
The thing everybody has missed is that the electrolyte gets
depleted over time. The sulphation converts the sulfuric acid
to a salt that builds up on the bottom of the battery, and the
electrolyte slowly gets turned into water. If you check the
Specific Gravity of the electrolyte in a well-used auto battery,
you will find it well below what it is supposed to be. This will
be true, even if the battery is "fully charged". Of course, the
Amp Hour capacity of the battery will be reduced by the same process.
I'm curious. Would it be worth it to change out the electrolite after ten
years on a forktruck battery? These batteries cost $1600 each and are made
light years better than a car battery. The cells are built to be repaired
but no one does it anymore - throw away society.
I couldn't justify <afford> a new battery this year and put up with
recharging it every single day.
It probably wouldn't hurt, altho I've read varying opinions on the success
of this, depending on how contaminated the acid/electrolyte is.
The key is to charge the everlovin bejeezus out of it before you do so.
I read somewhere (mebbe here?) that modern chargers use high-er voltage
pulsed DC of various wave forms for more effective charges, etc. Mechanical
tapping may dislodge crud/crystallized sulfate, etc.
Watch out, tho, in aggressive charging, as these things can be a bomb. I
know--a full sized car battery exploded while I was angle grinding something
in the same room, and, swear to god, I never found any pieces of the
battery!! What a mess.... the acid destroyed the clothes over the next few
days. Don't have much experience with grenades, but this hadda be close...
You can limit heat damage also by putting the battery itself in a water
Bosch published a book on battery charging a number of years ago, about the
size of an Airco electrode pocket guide, 6" x 4", about 100 pages. Very
interesting. I think that's where I got the pulsing and water bath from.
Mr. P.V.'d (formerly Droll Troll), Yonkers, NY
There's nothing going on that will "wear-out" the acid in normal
operation, it's not motor oil. It WILL sulphate up the plates if not
maintained correctly, you should check the specific gravity after
charging and add acid if it's too low. If it's low, chances are you've
got sulphation. If the liquid level is low, add distilled water, normal
charging will convert some of the water in the solution to gas. A deep
discharge traction battery is a lot different construction than a
modern car starting battery, it'll last a lot longer and take more
abuse. Heavier per unit of energy stored, too.
There's some cadmium-salt solutions for rejuvenating lead-acid
batteries out there, the classic stuff was VX-6, advertised for decades
in the back of the mechanics mags. It did reverse sulphating to a
certain degree in the old-style lead plate batteries with similar
construction to those traction batteries. HF carried some, don't know
if they still do. It really can't hurt to pour a slug of it into an
old battery to see if you can get more life out of it, it's cheap.
Really can't do much harm, either. Might take a bunch with large
batteries. Might work long enough to save up your pennies for another
Serious issue up in Minnesota. My job next week is to remove the batteries
from all the tractors, lawn mower, boat etc. and store inside for winter.
A new fully charged battery won't freeze even at -50. Try to start a car in
that s#$%, give up, go inside, come back out - now you got a car that still
won't start and a froze and busted battery. DAMHIKT
The greater the charge, the higher the concentration
of sulfuric acid and the lower the freezing temperature.
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