[RE-wrenches] FLA battery setpoints with larger arrays

jay peltz jay.peltz at gmail.com
Fri May 22 17:07:05 PDT 2015


Hi Ray,

Cold isn't a problem.  It reduces capacity and yes they could freeze, but
it doesn't shorten life ( I mean besides the freezing part) in fact cooler
batteries last longer.
But hot is a problem. Those max temps are not the same thing as reduced
life from running at a hotter temperature.


As to internal temps, its really hard to do this.  IR cameras are pretty
good.  Temp sensors which stick to the outside of the case's are not as
good as ones that bolt to the post.  The post is a good thermal conductor
vs the plastic case.  The glue/stick on ones come loose as we all know and
that means less accurate metering.

My premise for bring up the temp concern is that with a larger array and
smaller battery which equals higher C rates you will have higher internal
temps, no way around it.  How high, how much/will it shorten the life
unclear but probably, how much, ?

Let me rephrase it, do you think hotter temperatures are increasing the
lifespan of the battery?

While on this subject, I've done some quick calcs and with hot areas, its
cheaper to add PV for installing daytime AC vs battery life lost due to the
heat.  We can thank the cheap world of PV for that.

And while I've thought about what Allan started this conversion with in
regards to sizing batteries.
I continue to size my batteries around best life for the battery  ( best
daily average % DOD).
There are many ways to consider the size/cost etc of batteries:  For a
larger battery (less DOD)  you could view it as buying lead futures, longer
time between problems, etc.  For smaller bank ( higher DOD)  my only reason
for doing it at this point is a bridge battery to when Li-Ion/other
technologies will overtake LA for cost/ease/MX/capabilities.

I'd be curious to hear what others think about that last part,

jay






On Fri, May 22, 2015 at 3:33 PM, Ray Walters <ray at solarray.com> wrote:

>  I thought I'd post some info on Battery Temp from a few manus:
> HUP Solar One: do not exceed 105 F
> Full River AGMs: max recommended operating temp 104F
> and from Trojan:  for every 10C increase in temperature the reaction rate
> doubles.  Thus, a month of operation at 35C is equivalent to 2 months at
> 25C.  Heat is the enemy of ALL lead acid batteries.  Even small increases
> in temperature will have a major influence on battery life.
> Their T105 RE battery has a max operating temperature of 113 F
>
> I think more batteries are hitting high temperatures than we may realize.
> This info from Trojan that a battery at 95F (35C) will only last half its
> rated life (at 25C) is very concerning.
> Once again, thanks Bob and Midnite for giving us a tool to combat over
> temperature of batteries.  We always knew cold was a problem, now I'm
> realizing heat could be just as important.
>
> R.Ray Walters
> CTO, Solarray, Inc
> Nabcep Certified PV Installer,
> Licensed Master Electrician
> Solar Design Engineer303 505-8760
>
> On 5/22/2015 3:24 PM, boB at midnitesolar.com wrote:
>
> I'm very glad to hear Midnite added the high temp disconnect to their
> system.  They may have saved a life.
>
> Bob, is battery temp logged, so we could see how often a system quits
> charging for high temp, and just what the battery temps are running?
>
>
>
> No, but that is on the list as are other things to data log.
>
> Hopefully the temperature is adjusted higher than it would ever get to
> under normal circumstances.
>
> I could see some future systems wanting to be able to regulate Absorb on
> battery temperature mixed with other
> parameters some day.   Could get REALLY complicated if you wanted to.
> We're learning more and more
> about what is good for batteries.
>
> boB
>
>
>
>
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-- 
Jay Peltz
Peltz Power
jay.peltz at gmail.com
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