[RE-wrenches] Surrette Battery Question

[Allan Sindelar]

Wrenches,
Thank you for the whole set of responses. 

I haven't been to the site yet, but plan to stop there this week. As the
symptoms are not easily explained, I wanted to put the problem out for ideas
here first, to reduce the chance of missing something. I will report back
with what I learn.

I will first check whether the 0.4 V discrepancy is related to battery
temperature. It seems to me that the simplest way to do this is to check the
MX60 settings during equalization. If the measured voltage is at the MX60's
temperature-compensated EQ voltage, then a warm environment is the apparent
cause of the reduced voltage.

To answer a few of your many questions and fill in some details:
1. As I noted in my original post, the MX60 is temperature compensated. The
VFX3524 is too, although the client tells me he hasn't run the generator
since we added the 1.28 kW array.
2. To the best of my knowledge, the charge controll settings have not
changed (that would be too easy!). The client hasn't changed settings, and
we take care of all of their service needs.
3. The client equalizes regularly, as he notes in his description: last EQ
(to 31.1 v) was in June.
4. The array is wired 48V, so hot modules and/or undersized wire isn't a
voltage-limitation issue. (For the curious, I had a fun time adding new to
old array; story at the bottom of this message, to avoid boring Wrenches
with better things to do than follow this post.)
5. There are 6 4V batteries, 12 cells. I had conservatively figured the
charge rate at about C/20, so the charge rate is adequate for off-grid. I
most likely have the MX60 set to two hours absorption with a 2% done amps
override to lessen gassing. After Surrette's tech bulletin about batteries
in off-grid applications (recommending higher charge voltages and longer
absorption times) came out, I started setting longer absorption times; I
will go back and increase the absorption time on these to three hours, while
keeping the 2% done amps in place. Would anyone argue with this setting
change?
6. Tri-Metric voltage readings usually vary from MX60 readings, yes, but
they don't tend to change over time. This situation is presented as a recent
change from consistent past performance.
7. The client has not checked individual cell voltages or specific
gravities. I will do that when I go there on a service call and will report
back.
8. Re the quick C/5 charge idea: I would ask Jamie Surrette for his
recommendation here. For sure, it hasn't happened; the client says the
generator (an older Honda 5500, I think) needs service before it will start.
I'll advise him not to sell it (as he plans) until we have resolved this and
gotten Jamie's advice on battery care.
9. Miscalibration of the MX60 is unlikely but possible, and I will check
this when on site.

Thank you to the many of you who responded. Jamie Surrette responded
off-list too, asking about battery temperature. I will report back after
checking all of the above.
Allan at Positive Energy

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Travis
Creswell

The temp sensor suggestion makes a lot of sense.

Also, what is the specific gravity?  I suspect they are sulphated, maybe
severely.  But that's easily remedied with an equalization charge with the
generator.

We have a 24v single string of the very same batteries in an off grid system
and if they don't get at least quarterly the max charge possible from a dual
stack of SW4024's and 12kW Kohler funny things start to happen.  That's
about 200 amps depending on a few factors.  Voltage and trimetric will
indicate a full charge but the SG is way down below 50% and of course SG
typically trump other indicators. (IE, water wasn't just added)

Travis Creswell
Ozark Energy Services