Re: [RE-wrenches] 24 volt Battery Bank comparison

[boB Gudgel]

On 5/31/2011 11:25 PM, Tom Elliot wrote:

Bob,
I totally understand the concern about multiple strings *if the 
strings are connected across the battery bank* as had always been the 
tradition in off-grid installations.  My own experience with such a 
bank in my system  showed why when I had a single cell get to near 
meltdown.  I was lucky to find it.



This might be a good reason for an installer to have one of those FLIR 
(or similar) thermal imager cameras.   They're a bit on the expensive 
side, but could
really be helpful for so many things.   Even just to know if you have 
left a nut loose (under load of course)


boB



Maintenance is another reason, such banks are far more difficult to 
maintain.  But I think those concerns are ameliorated a great deal 
with a buss bar installation and once I did that I never had another 
problem and found the battery bank much easier to maintain because the 
strings no longer had to be right next to each other.  Heck, it would 
be possible to put each series string in its own box for that matter.  
And with the inclusion of string fuses that reduces problems even 
further.
When living with an off-grid system my biggest concern was system 
reliability and redundancy and the idea of a single string failure was 
a big worry which is why I never would consider it.

Tom
*From:* boB Gudgel 
*Sent:* Tuesday, May 31, 2011 8:16 PM
*To:* RE-wrenches 
*Subject:* Re: [RE-wrenches] 24 volt Battery Bank comparison


OK, I've been hearing for years now that one battery string is best 
and maybe two but no more should be used.


What is the reason for this fear ???What is the experience with 
multiple strings in parallel ??


If it is because of current sharing of the strings, that shouldn't be 
an insurmountable problem if the wiring is done right.


If it has to do with the possibility of fire, which Darryl mentioned, 
seems that series string fuses could mitigate the possibility of that 
issue, if because of shorted cells, just like PV combiners.


Or maybe it has to do with the trouble of getting into the middle of a 
pile of batteries ?  Use battery boxes ?


The strings are in parallel and so they all get the same voltage, 
theoretically anyway if the connections are good.


I would think that the more strings, the LESS stress on individual 
batteries, not more.  The current in each battery should be less than 
it would be I would think.


So what is the real experience ??

Is a battery balancer the answer ??

Thanks,
boB







On May 31, 2011, at 8:23 PM, "Wayne Irwin" > wrote:


I think the verdict is*12* - Rolls 2-YS-31 2430 AH @ 20 HR (one 
string) and one dry spare in storage is the best case scenario!


Wayne Irwin, EE
Director of Engineering
Pure Energy Solar International Inc.
State Licensed Solar Contractor
License # CVC56695
wa...@pureenergysolar.com 
http://pureenergysolar.com
352 377-6527 Office
352 336-3299 Fax
352 316-1637 Cell



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Re: [RE-wrenches] 24 volt Battery Bank comparison

[James Surrette]

Hi boB, 

I would say maintenance is a large issue - especially when dealing with L-16's 
or the like, as the number of cells & connections gets large, i.e. 1000-1200AH 
@ 48VDC is three (3) strings, 24 batteries and 72 cells.  Will a client water 
24 cells...maybe - 72?? 

However, from Tech Support days, imbalance is the larger problem.  It seems to 
take 18 months - 3 years and then you would get SG readings where one (1) bank 
was perfect and the other(s) is significantly lower..which is hard to 
overcome without effort (either break the banks & charge independently or 
hammer the banks and allow the high string to get even higher).  

One of the key take aways that often gets overlooked is the proper initial 
activation of the strings.  It is impossible for all cells to have identical 
resting voltage.  During commissioning, each string should be charged to 
2.45-2.5VPC and held until all cells read the same voltage.  If running 
multiple strings, then connect the strings and run the entire bank at 
2.45-2.5VPC until all cells measure the same voltage.  Now the bank is well 
balanced and the chances of a major imbalance are greatly reduced.  However, 
even after this effort, if you use an amp clamp, you will notice slight 
differences in the amount of current being accepted by each bank. 

Best, 

Jamie 




>>> boB Gudgel  6/1/2011 5:00 AM >>>
On 5/31/2011 11:25 PM, Tom Elliot wrote: 


Bob, 

  

I totally understand the concern about multiple strings *if the strings are 
connected across the battery bank* as had always been the tradition in off-grid 
installations.  My own experience with such a bank in my system  showed why 
when I had a single cell get to near meltdown.  I was lucky to find it.
 


This might be a good reason for an installer to have one of those FLIR (or 
similar) thermal imager cameras.   They're a bit on the expensive side, but 
could
really be helpful for so many things.   Even just to know if you have left a 
nut loose (under load of course)

boB






Maintenance is another reason, such banks are far more difficult to maintain.  
But I think those concerns are ameliorated a great deal with a buss bar 
installation and once I did that I never had another problem and found the 
battery bank much easier to maintain because the strings no longer had to be 
right next to each other.  Heck, it would be possible to put each series string 
in its own box for that matter.  And with the inclusion of string fuses that 
reduces problems even further.  

  

When living with an off-grid system my biggest concern was system reliability 
and redundancy and the idea of a single string failure was a big worry which is 
why I never would consider it. 

  

Tom 

  

  

  

From: boB Gudgel ( mailto:b...@midnitesolar.com ) 

Sent: Tuesday, May 31, 2011 8:16 PM 

To: RE-wrenches ( mailto:re-wrenches@lists.re-wrenches.org ) 

Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison 

  



OK, I've been hearing for years now that one battery string is best and maybe 
two but no more should be used.

What is the reason for this fear ???What is the experience with multiple 
strings in parallel ??

If it is because of current sharing of the strings, that shouldn't be an 
insurmountable problem if the wiring is done right.

If it has to do with the possibility of fire, which Darryl mentioned, seems 
that series string fuses could mitigate the possibility of that issue, if 
because of shorted cells, just like PV combiners.

Or maybe it has to do with the trouble of getting into the middle of a pile of 
batteries ?  Use battery boxes ?

The strings are in parallel and so they all get the same voltage, theoretically 
anyway if the connections are good.

I would think that the more strings, the LESS stress on individual batteries, 
not more.  The current in each battery should be less than it would be I would 
think.

So what is the real experience ??

Is a battery balancer the answer ??

Thanks,
boB









On May 31, 2011, at 8:23 PM, "Wayne Irwin"  wrote:




I think the verdict is 12 - Rolls 2-YS-31 2430 AH @ 20 HR (one string) and one 
dry spare in storage is the best case scenario!

Wayne Irwin, EE
Director of Engineering
Pure Energy Solar International Inc. 
State Licensed Solar Contractor
License # CVC56695 
wa...@pureenergysolar.com
http://pureenergysolar.com
352 377-6527 Office
352 336-3299 Fax
352 316-1637 Cell 
  



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Re: [RE-wrenches] 24 volt Battery Bank comparison

[Darryl Thayer]

If one cell gets a higher internal loss than the others is hogs the charging 
current and will over charge its string partners.  It is a problem of the 
temperature of all cells in all parallel strings having the same thermal 
environment, so they all have the same voltage.  (the case of one of 4 parallel 
strings in battery house, big system, the string near the outside south wall 
caught fire)  In particular this is a problem of AGMs, a recent east cost 
problem where batteries had been in business for 2 yrs and for some reason the 
battery room erupted with one of 5 strings in thermal runaway.   this is the 
same as trying to put bipolar transistors in parallel.  

I reciently had 8 parallel strings not of my choice, advised customer of 
potential hazard,   used Midnight combiner with 30 amp breakers on each string, 
so far it is OK but this is playing with fire.  Hopfully if one string goes bad 
in thermal runaway it will trip the breaker feeding that string. .  





From: boB Gudgel 
To: RE-wrenches 
Sent: Wednesday, June 1, 2011 1:16 AM
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison




OK, I've been hearing for years now that one battery string is best
and maybe two but no more should be used.

What is the reason for this fear ???    What is the experience with
multiple strings in parallel ??

If it is because of current sharing of the strings, that shouldn't
be an insurmountable problem if the wiring is done right.

If it has to do with the possibility of fire, which Darryl
mentioned, seems that series string fuses could mitigate the
possibility of that issue, if because of shorted cells, just like PV
combiners.

Or maybe it has to do with the trouble of getting into the middle of
a pile of batteries ?  Use battery boxes ?

The strings are in parallel and so they all get the same voltage,
theoretically anyway if the connections are good.

I would think that the more strings, the LESS stress on individual
batteries, not more.  The current in each battery should be less
than it would be I would think.

So what is the real experience ?? 

Is a battery balancer the answer ??

Thanks,
boB







>On May 31, 2011, at 8:23 PM, "Wayne Irwin"  wrote:
>
>
>I think the verdict is12 - Rolls 2-YS-31 2430 AH @ 20 HR (one string) and one 
>dry spare in storage is the best case scenario!
>>
>>Wayne Irwin, EE
>>Director of Engineering
>>Pure Energy Solar International Inc. 
>>State Licensed Solar Contractor
>>License # CVC56695 
>>wa...@pureenergysolar.com 
>>http://pureenergysolar.com 
>>352 377-6527 Office
>>352 336-3299 Fax
>>352 316-1637 Cell

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Re: [RE-wrenches] 24 volt Battery Bank comparison

[toddcory]

Does it make any difference to do as boB recently suggested and inter-connect 
the strings? So in other words, if you have two parallel strings, what happens 
if you parallel each battery in one string with the battery in the other 
string? Has anyone tried this? It might help insure more balance between each 
series string.
 
Todd
 
 
 
On Wednesday, June 1, 2011 3:06am, "James Surrette"  said:



Hi boB,

I would say maintenance is a large issue - especially when dealing with L-16's 
or the like, as the number of cells & connections gets large, i.e. 1000-1200AH 
@ 48VDC is three (3) strings, 24 batteries and 72 cells.  Will a client water 
24 cells...maybe - 72??

However, from Tech Support days, imbalance is the larger problem.  It seems to 
take 18 months - 3 years and then you would get SG readings where one (1) bank 
was perfect and the other(s) is significantly lower..which is hard to 
overcome without effort (either break the banks & charge independently or 
hammer the banks and allow the high string to get even higher). 

One of the key take aways that often gets overlooked is the proper initial 
activation of the strings.  It is impossible for all cells to have identical 
resting voltage.  During commissioning, each string should be charged to 
2.45-2.5VPC and held until all cells read the same voltage.  If running 
multiple strings, then connect the strings and run the entire bank at 
2.45-2.5VPC until all cells measure the same voltage.  Now the bank is well 
balanced and the chances of a major imbalance are greatly reduced.  However, 
even after this effort, if you use an amp clamp, you will notice slight 
differences in the amount of current being accepted by each bank.

Best,

Jamie




 >>> boB Gudgel  6/1/2011 5:00 AM >>>
On 5/31/2011 11:25 PM, Tom Elliot wrote:



Bob,

 

I totally understand the concern about multiple strings *if the strings are 
connected across the battery bank* as had always been the tradition in off-grid 
installations.  My own experience with such a bank in my system  showed why 
when I had a single cell get to near meltdown.  I was lucky to find it.


 This might be a good reason for an installer to have one of those FLIR (or 
similar) thermal imager cameras.   They're a bit on the expensive side, but 
could
really be helpful for so many things.   Even just to know if you have left a 
nut loose (under load of course)

boB







Maintenance is another reason, such banks are far more difficult to maintain.  
But I think those concerns are ameliorated a great deal with a buss bar 
installation and once I did that I never had another problem and found the 
battery bank much easier to maintain because the strings no longer had to be 
right next to each other.  Heck, it would be possible to put each series string 
in its own box for that matter.  And with the inclusion of string fuses that 
reduces problems even further.

 

When living with an off-grid system my biggest concern was system reliability 
and redundancy and the idea of a single string failure was a big worry which is 
why I never would consider it.

 

Tom

 

 



 


From: [mailto:b...@midnitesolar.com] boB Gudgel

Sent: Tuesday, May 31, 2011 8:16 PM

To: [mailto:re-wrenches@lists.re-wrenches.org] RE-wrenches

Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison

 



 OK, I've been hearing for years now that one battery string is best and maybe 
two but no more should be used.

What is the reason for this fear ???What is the experience with multiple 
strings in parallel ??

If it is because of current sharing of the strings, that shouldn't be an 
insurmountable problem if the wiring is done right.

If it has to do with the possibility of fire, which Darryl mentioned, seems 
that series string fuses could mitigate the possibility of that issue, if 
because of shorted cells, just like PV combiners.

Or maybe it has to do with the trouble of getting into the middle of a pile of 
batteries ?  Use battery boxes ?

The strings are in parallel and so they all get the same voltage, theoretically 
anyway if the connections are good.

I would think that the more strings, the LESS stress on individual batteries, 
not more.  The current in each battery should be less than it would be I would 
think.

So what is the real experience ??

Is a battery balancer the answer ??

Thanks,
boB








 On May 31, 2011, at 8:23 PM, "Wayne Irwin" <[mailto:wa...@pureenergysolar.com] 
wa...@pureenergysolar.com> wrote:



I think the verdict is 12 - Rolls 2-YS-31 2430 AH @ 20 HR (one string) and one 
dry spare in storage is the best case scenario!

Wayne Irwin, EEDirector of EngineeringPure Energy Solar International Inc. 
State Licensed Solar ContractorLicense # CVC56695 
[mailto:wa...@pureenergysolar.com] wa...@pureenergysolar.com
[http://pureenergysolar.com] http://pureenergysolar.com
352 377-6527 Office352 336-3299 Fax352 316-1637 Cell
 

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[RE-wrenches] 24 volt Battery Bank comparison, Why a single string?

[Larry Crutcher, Starlight Solar Power Systems]

Hi boB,

We know that current will flow through the lowest resistive path. In a perfect 
world, the resistance from end to end of a battery string will be identical. 
Real world conditions show that one or more cells have a slightly higher 
internal resistance. Add to that the imperfect terminal crimp, improper torque 
at battery terminal, and perhaps terminal corrosion and we now have paths of 
differing resistance. The parallel strings have an unequal distribution of 
current and ergo undercharged cells. These cells retain a small amount of 
amorphous lead sulphate that, without correction, will begin to crystalize. We 
all know what will happen over time. 

Granted, this can be prevented by the proper knowledge and attention but I see 
far too many failures from neglect and/or lack of understanding. My experience 
comes from 10 years of working with hundreds of small 12 volt systems with 2 to 
6 parallel strings of batteries. In our shop we often see 2 to 3 year old 
battery banks that are damaged and I believe this is a contributing factor. It 
is often too late by the time the problem is discovered. So, my opinion is to 
reduce this possibility by decreasing the parallel paths whenever possible.

More strings of a given size battery means less stress per string. But, if you 
decrease strings you are normally increasing cell size to maintain the capacity 
so this should not be an issue.

Battery balancing is a great idea. I would like to see an active system for 
shunting current on a string to keep an equal current across all strings. I 
know this is done in the EV business.

Larry Crutcher
Starlight Solar Power Systems
11871 S Fortuna Road, #210
Yuma, AZ 85367

la...@starlightsolar.com
(928) 342-9103



On May 31, 2011, at 11:16 PM, boB Gudgel wrote:

> 
> 
> OK, I've been hearing for years now that one battery string is best and maybe 
> two but no more should be used.
> 
> What is the reason for this fear ???What is the experience with multiple 
> strings in parallel ??
> 
> If it is because of current sharing of the strings, that shouldn't be an 
> insurmountable problem if the wiring is done right.
> 
> If it has to do with the possibility of fire, which Darryl mentioned, seems 
> that series string fuses could mitigate the possibility of that issue, if 
> because of shorted cells, just like PV combiners.
> 
> Or maybe it has to do with the trouble of getting into the middle of a pile 
> of batteries ?  Use battery boxes ?
> 
> The strings are in parallel and so they all get the same voltage, 
> theoretically anyway if the connections are good.
> 
> I would think that the more strings, the LESS stress on individual batteries, 
> not more.  The current in each battery should be less than it would be I 
> would think.
> 
> So what is the real experience ?? 
> 
> Is a battery balancer the answer ??
> 
> Thanks,
> boB
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Re: [RE-wrenches] 24 volt Battery Bank comparison

[Michael Welch]

Every now and then I see reference on this list to the need for thermal 
detection. Here is an interesting, inexpensive piece of equipment that could be 
used for finding hot (loose or corroded) connections, hot batteries, hot PV 
cells in modules, and even poorly insulated spots, its original intended 
purpose:

http://www.blackanddecker.com/power-tools/TLD100.aspx

I have one and used it for finding uninsulated spaces, but cannot attest to its 
durability or suitability for the other uses mentioned above.


boB Gudgel wrote at 01:00 AM 6/1/2011:
 
>This might be a good reason for an installer to have one of those FLIR (or 
>similar) thermal imager cameras.   They're a bit on the expensive side, but 
>could
>really be helpful for so many things.   Even just to know if you have left a 
>nut loose (under load of course)
>
>boB


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Re: [RE-wrenches] 24 volt Battery Bank comparison

[Bill Loesch]

Hi Michael,

With all due respect, do the reference "idiot lights" do that much for you?
I have always thought a thermal camera/viewer/FLIR/etc. would be great but
so would a used car. My digital IR thermometer at several orders of
magnitude difference in price has served me well, if tediously, to do some
of the uses described.

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094



- Original Message - 
From: "Michael Welch" 
To: "RE-wrenches" 
Sent: Wednesday, June 01, 2011 12:43 PM
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison


Every now and then I see reference on this list to the need for thermal
detection. Here is an interesting, inexpensive piece of equipment that could
be used for finding hot (loose or corroded) connections, hot batteries, hot
PV cells in modules, and even poorly insulated spots, its original intended
purpose:

http://www.blackanddecker.com/power-tools/TLD100.aspx

I have one and used it for finding uninsulated spaces, but cannot attest to
its durability or suitability for the other uses mentioned above.


boB Gudgel wrote at 01:00 AM 6/1/2011:

>This might be a good reason for an installer to have one of those FLIR (or
similar) thermal imager cameras.   They're a bit on the expensive side,
but could
>really be helpful for so many things.   Even just to know if you have
left a nut loose (under load of course)
>
>boB


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Re: [RE-wrenches] 24 volt Battery Bank comparison, Why a single string?

[boB Gudgel]

On 6/1/2011 8:41 AM, Larry Crutcher, Starlight Solar Power Systems wrote:

Hi boB,

We know that current will flow through the lowest resistive path. In a 
perfect world, the resistance from end to end of a battery string will 
be identical. Real world conditions show that one or more cells have a 
slightly higher internal resistance. Add to that the imperfect 
terminal crimp, improper torque at battery terminal, and perhaps 
terminal corrosion and we now have paths of differing resistance. The 
parallel strings have an unequal distribution of current and ergo 
undercharged cells. These cells retain a small amount of amorphous 
lead sulphate that, without correction, will begin to crystalize. We 
all know what will happen over time.




The issue of maintenance is a not brainer of course...  i.e. the need to 
add water...


Imperfect crimps would be a problem with a single string of batteries 
too.  If the resistance
is higher in that cell in the one string, then yes, that one string will 
not be working nearly as
hard as the other strings.  Bad workmanship is not an excuse for not 
using multiple strings

as far as I know.


If one string is discharged more than another parallel string, then its 
finishing (ending) Amps
will will certainly happen later than a string that wasn't discharged as 
deep, but if using a
timed Absorb cycle, why does this matter ??   They're all receiving the 
same voltage and
should be treated the same in that case.  Right ??At least for timed 
charging cycles.


As Darryl pointed out, AGMs like to get hot when unbalanced and this is 
definitely what I
have seen.   But that again can happen for a single string rather than 
multiple strings.


One thing that hasn't been mentioned, unless I missed it, is the 
possibility that a shorted
cell in one string can drag down the other strings it is in parallel 
with.   The more strings
in parallel, statistically, there would be more of a chance for that to 
happen.


That would be more of a self discharge issue I would think which isn't good.
boB




Granted, this can be prevented by the proper knowledge and attention 
but I see far too many failures from neglect and/or lack of 
understanding. My experience comes from 10 years of working with 
hundreds of small 12 volt systems with 2 to 6 parallel strings of 
batteries. In our shop we often see 2 to 3 year old battery banks that 
are damaged and I believe this is a contributing factor. It is often 
too late by the time the problem is discovered. So, my opinion is to 
reduce this possibility by decreasing the parallel paths whenever 
possible.


More strings of a given size battery means less stress per string. 
But, if you decrease strings you are normally increasing cell size to 
maintain the capacity so this should not be an issue.


Battery balancing is a great idea. I would like to see an active 
system for shunting current on a string to keep an equal current 
across all strings. I know this is done in the EV business.


Larry Crutcher
Starlight Solar Power Systems
11871 S Fortuna Road, #210
Yuma, AZ 85367

la...@starlightsolar.com 
(928) 342-9103



On May 31, 2011, at 11:16 PM, boB Gudgel wrote:




OK, I've been hearing for years now that one battery string is best 
and maybe two but no more should be used.


What is the reason for this fear ???What is the experience with 
multiple strings in parallel ??


If it is because of current sharing of the strings, that shouldn't be 
an insurmountable problem if the wiring is done right.


If it has to do with the possibility of fire, which Darryl mentioned, 
seems that series string fuses could mitigate the possibility of that 
issue, if because of shorted cells, just like PV combiners.


Or maybe it has to do with the trouble of getting into the middle of 
a pile of batteries ?  Use battery boxes ?


The strings are in parallel and so they all get the same voltage, 
theoretically anyway if the connections are good.


I would think that the more strings, the LESS stress on individual 
batteries, not more.  The current in each battery should be less than 
it would be I would think.


So what is the real experience ??

Is a battery balancer the answer ??

Thanks,
boB



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Re: [RE-wrenches] 24 volt Battery Bank comparison

[boB Gudgel]

On 6/1/2011 10:43 AM, Michael Welch wrote:

Every now and then I see reference on this list to the need for thermal 
detection. Here is an interesting, inexpensive piece of equipment that could be 
used for finding hot (loose or corroded) connections, hot batteries, hot PV 
cells in modules, and even poorly insulated spots, its original intended 
purpose:

http://www.blackanddecker.com/power-tools/TLD100.aspx

I have one and used it for finding uninsulated spaces, but cannot attest to its 
durability or suitability for the other uses mentioned above.


Yep.  These are very handy indeed !  AND they're cheap !

But these types are quite different from what I was talking about when I 
mentioned the very pricey thermal imagers like FLIRs.
For the single point thermometers like the B&D device, you must run it 
over EVERY single spot that you want to check
for heat.  Batteries, Connections, Cables and each one individually.  
With something like the FLIR you can just hold it
and stand in one place and it will show you where any hot spots (or cold 
spots) are AND give you the temperature.
That is, if the emissivity is close enough, but you can still see if 
something is really hot with the imager.


I just wish they were cheaper !

boB






boB Gudgel wrote at 01:00 AM 6/1/2011:


This might be a good reason for an installer to have one of those FLIR (or 
similar) thermal imager cameras.   They're a bit on the expensive side, but 
could
really be helpful for so many things.   Even just to know if you have left a 
nut loose (under load of course)

boB


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Re: [RE-wrenches] 24 volt Battery Bank comparison

[Christopher Warfel]

I recently purchased one and it has been useful. It can also be used to 
find poorly insulated buildings, air leaks etc. I have been told that in 
some states, fire departments will make their thermal imaging cameras 
available to qualified people for conducting these types of surveys.

Chris

On 6/1/2011 1:43 PM, Michael Welch wrote:

Every now and then I see reference on this list to the need for thermal 
detection. Here is an interesting, inexpensive piece of equipment that could be 
used for finding hot (loose or corroded) connections, hot batteries, hot PV 
cells in modules, and even poorly insulated spots, its original intended 
purpose:

http://www.blackanddecker.com/power-tools/TLD100.aspx

I have one and used it for finding uninsulated spaces, but cannot attest to its 
durability or suitability for the other uses mentioned above.


boB Gudgel wrote at 01:00 AM 6/1/2011:

   

This might be a good reason for an installer to have one of those FLIR (or 
similar) thermal imager cameras.   They're a bit on the expensive side, but 
could
really be helpful for so many things.   Even just to know if you have left a 
nut loose (under load of course)

boB
 


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Re: [RE-wrenches] 24 volt Battery Bank comparison

[dan]

Good thread. Thanks. In my experience, it all boils down to the customer. I've seen one temp. set up with like 12 strings (for a concert). but they were recharged and sold individually within a few weeks.. I've also seen a single string (Teledyne aircraft batteries) fail in less than a year.. they were in a brand new airplane tug that was never charged -- ever. (the guy said "I dunno, it just stopped working"). I have one customer who (last I knew) was running 6 strings of mixed aged L-16s going on 8 years. Thing is, he's a retired phone company dude (Who's missing half of his right hand from using one of those pocket pal screwdriver thingys on a key chain in a hot DC rack.. like he'd done hundreds of times before.. but that's another tale). But I do like his set up.. he has each string set up with it's own fused Disco and Trimetric.. Gives him random control over each string. And yes, he keeps a very detailed log, and you can bet that when he takes a battery out of service, it's done. Me? for an average bullet proof off grid system, I shoot for a max of two strings for 24V systems (for the redundancy), and manually reconfigure them every few years. for 48V systems, I shoot for one string of two Volt cells.. thinking that if I loose a cell I can still operate a 46V system until I get a replacement. And Yes, as we all know, there are folks out there that really shouldn't be allowed to operate a popsicle stick. dbDan BrownFoxfire Energy Corp.Renewable Energy Systems(802)-483-2564www.Foxfire-Energy.comNABCEP #092907-44


 Original Message 
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison
From: Michael Welch 
Date: Wed, June 01, 2011 1:43 pm
To: RE-wrenches 

Every now and then I see reference on this list to the need for thermal detection. Here is an interesting, inexpensive piece of equipment that could be used for finding hot (loose or corroded) connections, hot batteries, hot PV cells in modules, and even poorly insulated spots, its original intended purpose:

http://www.blackanddecker.com/power-tools/TLD100.aspx

I have one and used it for finding uninsulated spaces, but cannot attest to its durability or suitability for the other uses mentioned above.


boB Gudgel wrote at 01:00 AM 6/1/2011:
 
>This might be a good reason for an installer to have one of those FLIR (or similar) thermal imager cameras.   They're a bit on the expensive side, but could
>really be helpful for so many things.   Even just to know if you have left a nut loose (under load of course)
>
>boB


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Re: [RE-wrenches] 24 volt Battery Bank comparison

[Allan Sindelar]

  
  
I had done this a few times in the distant past, and also had done
it in recent years on my own previous battery bank (four strings of
S-530s - yes, I know; it was in anticipation of future plans to
upgrade to 48V, and two strings wouldn't have been enough).

It worked fine - and that turned out to be a problem. I had noticed
reduced capacity, but assumed foolishly that it was simply to age
and cycle life (going on six years and three teenagers). Found out I
had two failed cells in two different strings. The parallel
connections probably - I'm not sure here - allowed the bank to
perform more robustly and less obviously weakened. It might have
even allowed the bank to perform as if both failed cells had been in
the same string. But it also allowed me to not pay enough attention
to a potentially serious problem by disguising it.

I blame myself more than the parallel connectors (just some #2
interconnects I had lying around). I'm just not sure I would use it
on a customer's system.
 

  
  
  Allan Sindelar
  al...@positiveenergysolar.com
NABCEP Certified Photovoltaic
  Installer
  NABCEP Certified Technical Sales Professional
  New Mexico EE98J Journeyman Electrician
  Positive Energy, Inc.
  3201 Calle Marie
  Santa Fe, New Mexico 87507
  505 424-1112
  www.positiveenergysolar.com
  
  
  
   

On 6/1/2011 9:20 AM, toddc...@finestplanet.com wrote:

Does it make any difference to do as boB recently suggested
  and inter-connect the strings? So in other words, if you have
  two parallel strings, what happens if you parallel each
  battery in one string with the battery in the other string?
  Has anyone tried this? It might help insure more balance
  between each series string.
 
Todd
 
 
 
On Wednesday, June 1, 2011 3:06am, "James Surrette"
   said:
  


  Hi boB,
  
  I would say
  maintenance is a large issue - especially when dealing
  with L-16's or the like, as the number of cells &
  connections gets large, i.e. 1000-1200AH @ 48VDC is three
  (3) strings, 24 batteries and 72 cells.  Will a client
  water 24 cells...maybe - 72??
  
  However, from
  Tech Support days, imbalance is the larger problem.  It
  seems to take 18 months - 3 years and then you would get
  SG readings where one (1) bank was perfect and the
  other(s) is significantly lower..which is hard to
  overcome without effort (either break the banks &
  charge independently or hammer the banks and allow the
  high string to get even higher). 
  
  One of the
  key take aways that often gets overlooked is the proper
  initial activation of the strings.  It is impossible for
  all cells to have identical resting voltage.  During
  commissioning, each string should be charged to
  2.45-2.5VPC and held until all cells read the same
  voltage.  If running multiple strings, then connect the
  strings and run the entire bank at 2.45-2.5VPC until all
  cells measure the same voltage.  Now the bank is well
  balanced and the chances of a major imbalance are greatly
  reduced.  However, even after this effort, if you use an
  amp clamp, you will notice slight differences in the
  amount of current being accepted by each bank.
  
  Best,
  
  Jamie
  
  
  
  
>>> boB Gudgel 
6/1/2011 5:00 AM >>>
On 5/31/2011 11:25 PM, Tom Elliot wrote:
  

  

  Bob,


   


  I
totally understand the concern about multiple
strings *if the strings are connected across the
battery bank* as had always been the tradition in
off-grid installations.  My own experience with such
a bank in my system  showed why when I had a single
cell get to near meltdown.  I was lucky to find it.

  

  
  

This might be a good reason for an installer to have one of
those FLIR (or similar) thermal imager cameras.   They're a
bit on the expensive side, but could
really be helpful for so many things.   Even just to know if