Larry and Tom,
Thanks for the information. I will boost the
voltage and the charge hours for the array. The inverter is good as is.
The batteries charge quickly since they are not
generally cycled deeply. The cabin is only used
for three or four days a week, giving the
batteries plenty of time to be maintained.
Interestingly, Tom's email never reached me
directly. I read it through Jay's reply.
Drake
At 03:02 PM 7/22/2013, you wrote:
Drake,
When you said, "The batteries usually reach
absorb voltage shortly after the sun hits the
array", I wondered if you had more of a problem
with that system. Glad to hear it's not that way.
Absorb time is an issue I have with the design
of most charge controllers: They do not measure
current to the battery and use that as the
source info to determine if a battery is
completely full and when to transition into
float mode. Blue Sky Energy does this which, in
my book, makes it a great charge controller. If
you know how much current any battery draws
(they are all different and change with age)
when it is completely full, then the charge
controller can be programmed to stay in absorb
until that parameter is met. It could be 1/2
hour one day and 4 hours the next. Many things
affect how batteries charge and this is the only
true method I know of to accurately determine when it is full each day.
For your situation, I would go with Trojans
recommendation of 2 hours absorb at 29.6. If you
see that this is not fully charging each day,
you can try increasing the time or choosing a
higher voltage. If you have the sun hours
available, I would choose longer charge time.
There are many areas in the States that simply
do not have enough sun hours to completely
charge the battery from PV solar alone. In this
case, using higher absorb voltage may be a solution.
Larry
On Jul 22, 2013, at 10:04 AM, Drake
<drake.chamber...@redwoodalliance.org> wrote:
Hi Larry,
I will bump up the absorb voltage to 29.6 V. How
long do you think the bank should stay in absorb
at that rate? The bank now seems healthy, with
the bad battery replaced. It does accept
charge, without going high prematurely. The max
charge rate from the array is around C/10. The
system can also be fast charged from a Honda
6500 inverter generator through the Outback 3524 VFX.
We have a Trimetric meter on the system. The
discrepancy between the percent charge and the
voltage is what demonstrated that we had a problem.
Thanks,
Drake
At 09:30 PM 7/19/2013, you wrote:
> Hi Drake,
>
> It always concerns me when I hear that a
battery bank reaches absorb setting very
quickly. It typically means one of two things:
very few AH were removed from the bank; the
battery bank has sulfated cells due to chronic
undercharging. Far too often I find the latter to be true.
>
> Healthy batteries will accept current and
hold the charge voltage down with a fairly
linear, slow climb to absorption voltage.
Sulfated batteries do not accept current well
which allows voltage to climb rapidly as the
battery presents little load on the charging
system. I'm not sure how this plays into your
original post about a bad cell but it seemed worth mentioning.
>
> My opinion is to aggressively charge, by
using higher voltage, large flooded batteries.
This is especially true when the PV system is
moderate or undersized. 29.6 volts is what
Trojan recommends. You can go as high as 32
volts on the L-16's but make sure the
temperature compensation is installed properly
and working. You will use more water.
>
> One last comment, I highly recommend that ALL
off grid systems have a battery capacity
monitor installed. It's kind of like flying an
airplane without a fuel gaugeĀ
it might not end in disaster.
>
> Larry Crutcher
> Starlight Solar Power Systems
>
>
>
> On Jul 18, 2013, at 1:11 PM, Drake
<drake.chamber...@redwoodalliance.org> wrote:
>
> Tom,
>
> The batteries usually reach absorb voltage
shortly after the sun hits the array. The
reason the bank wasn't working correctly is
that one cell was dead in one of the batteries.
>
> I could increase the absorb time to 4.6 hours
and the voltage to 29.6, especially since the
bank has a new battery. That is longer and
higher than I'd previously heard recommended.
What would be the effect on water
consumption? How did you calculate the absorb time?
>
> Thanks,
>
>
> Drake
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