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Re: (ET) L/A charging
Lead acid batteries can not be charged at thousands of amps! Major
manufacturers, Rolls, Trojan, etc. recommend charging at C/10 to C/20. For
a Trojan 105 ,C20 (their recommendation) = ~5 amps. Fast charging L/A
batteries causes plates to warp which greatly shortens battery life. L/A
batteries are rated for amp/hours, a Rolls 530S for example is rated to give
530 amps for one hour. After one hour the battery is completely exhausted.
Batteries should never be discharged to this extent. the rule is to keep the
discharge to no greater than 50% ever and even this is drastic because L/A
battery life is rated in cycles. Discharging to 50% may yield 300 to 500
cycles, while discharging to 85% may yield 1500 to 2000 cycles. Discharging
an L/A battery at 1000's of amps will very likely cause an explosion! Li-Ion
for example can be charged at higher rates so comparatively L/A is
"sluggish".
Hope this helps.
Rob
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The page on lead battery charging says " Lead acid is sluggish and cannot
be
charged as quickly as other battery systems." I'm not an electrochemist,
but I don't see how they can say that. As long as you monitor its
temperature, an AGM lead battery can be charged about as fast as it can be
discharged, as long as you're below 80% SOC. We're talking thousands of
amps. I certainly wouldn't call that "sluggish."
------------------------------
Message: 2
Date: Mon, 4 Feb 2013 18:27:15 +0000
From: Robert Troll <roberttroll hotmail com>
To: <elec-trak cosmos phy tufts edu>
Subject: Re: (ET) Battery University
Message-ID: <BLU157-W45EE6634CD05D01B1D9224BA010 phx gbl>
Content-Type: text/plain; charset="iso-8859-1"
Perhaps it should be called "Battery Community College" rather then
university.
> I came across the "Battery University" website. Some interesting
> information:
The page on lead battery charging says " Lead acid is sluggish and cannot
be
charged as quickly as other battery systems." I'm not an electrochemist,
but I don't see how they can say that. As long as you monitor its
temperature, an AGM lead battery can be charged about as fast as it can be
discharged, as long as you're below 80% SOC. We're talking thousands of
amps. I certainly wouldn't call that "sluggish."
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Message: 3
Date: Mon, 04 Feb 2013 14:26:13 -0500
From: "David Roden" <etpost drmm net>
To: <elec-trak cosmos phy tufts edu>
Subject: Re: (ET) AGM
Message-ID: <510FC505 4020 A935DAC etpost drmm net>
Content-Type: text/plain; charset=US-ASCII
On 4 Feb 2013 at 10:37, Robert wrote:
I didn't read the article but I do know about batteries. AGM have to
follow
a specific charging algorithm. If you charge them over their max rate the
one way valve can open from the heat developed to relieve the pressure and
the battery is toast.
The main concern with AGMs (and other valve regulated recombinant [VRR]
batteries such as gel) is in the final stage of charging.
The relief valve will open if the battery gasses faster than its internal
recombinant reaction can turn the hydrogen and oxygen back into water.
This
will indeed happen if you use too high a finishing voltage (and thus too
high a finishing current). You can usually hear this - it's a sort of a
ticking sound. There may be some hissing too.
However, below the gassing voltage - in the bulk charging phase - this
won't
happen. Essentially all the energy going into the battery will go into
charging it, with just a little going into heat (the amount depends on the
battery's internal resistance), and none into gassing. This is a very
efficient part of the charge.
That's why you can charge an AGM to 80% SOC at about as much current as it
can produce into a load - which can be a LOT.
Unless there's something terribly wrong with the battery, you only have to
worry about hydrogen evolution in that last ~20% of the charge (which takes
more than 20% of the time, BTW).
David Roden - Akron, Ohio, USA
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------------------------------
Message: 4
Date: Mon, 04 Feb 2013 15:24:22 -0500
From: "David Roden" <etpost drmm net>
To: <elec-trak cosmos phy tufts edu>
Subject: Re: (ET) AGM
Message-ID: <510FD2A6 27374 AC89CCF etpost drmm net>
Content-Type: text/plain; charset=US-ASCII
On 4 Feb 2013 at 10:37, Robert wrote:
If you charge them over their max rate the one way valve can open from
the heat developed to relieve the pressure and the battery is toast.
One thing more. A little too much finishing current now and then isn't
likely to ruin an AGM or gel battery, though it won't help it.
When the valves open, water from the electrolyte is being lost. Eventually
this causes the electrolyte's SG to rise. This can cause premature
positive
grid corrosion, and/or allow overdischarging of a starved-electrolyte
battery. This isn't instant death for the battery, though it might indeed
mean a shorter service life.
It's not a bad idea to weigh your battery when it's brand new and record
the
value. Later, if you think you might have had some water loss, you can
(carefully!) drill holes in the battery, add distilled water with a
syringe,
and reseal the holes. I've not tried this myself (yet), but have heard of
people getting months to years of extra service out of AGMs this way.
David Roden - Akron, Ohio, USA
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to the "etpost" address will not reach me. To send
me a private message, please use the address shown at the bottom
of this page : http://www.evdl.org/help/
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------------------------------
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End of Elec-trak Digest, Vol 11, Issue 36
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