battery temp compensation

[fiddlerkelly]

I don't have currently a battery temp compensator in my system. How would I do this on paper and how would I measure the temperature directly into the battery or from temp of air around my battery banks. My reading currently are about 1.28 to 1.30 and that is with air temp around batteries at 0 degree C or 32 degrees F .

Batteries are U.S batteries golf cart ones 232 amp hours in each 6 volt battery with total of 18    6 volt batteries  made as 12 volt batteries. set up as 12 volt system               

[Resthome]

I don't have currently a battery temp compensator in my system. How would I do this on paper and how would I measure the temperature directly into the battery or from temp of air around my battery banks. My reading currently are about 1.28 to 1.30 and that is with air temp around batteries at 0 degree C or 32 degrees F .

Batteries are U.S batteries golf cart ones 232 amp hours in each 6 volt battery with total of 18    6 volt batteries  made as 12 volt batteries. set up as 12 volt system               

One way is to get a hydrometer with a built in thermometer. It will have a scale on it based on the temperature  that you need to add or subtract from your readings.

[tecnodave]

Fiddlerkelly,


Correct temp comp for the batteries is    -5mv /deg C / cell.   (Temp above 25C)
                                                          +5mv / deg C / cell.   (Temp below 25C)

So at 0C with nom at 25C  and 6 cells     Is     +5 mv. X 25 (degree diff). X 6 cell   = +.75


U.S. battery recommendation:  Bulk = 14.4.  Adsorb = 15.5.   Float = 13.2. Equalize = 15.6

                              Charge rate = C/10 or 23.2 amps each set or 211.5 amps for 9 sets in parallel

Those are the published recommendations

Now my comments:   9 strings in parallel=====Asking for trouble!!!!

Why are you doing 12 volts========Asking for Trouble!!!!!!

You should be at a higher voltage for that kind of a.h. capability

What kind of charger are you using?  Recommended charge rate this setup 211.5 amps hard to do an 12 volts!

Maximum number of strings in parallel recommended by pro's and installers = 2

Read a lot on this subject before going further down this alley!

Read the temp of the electrolyte solution, not the air around the batteries, charging warms them up and t comp will vary with temp.

Just my opinion.....been doin lectrix for 46 years!

td

Edited typo on total t comp number

[Resthome]

For Rolls Batteries the S/G correction is

SG of acid is temperature dependent. If the temperature is very cold or very hot this can lead to incorrect readings. To correct for temperature use the following equations the equations or below 70ºF subtract points (0.03 per 10ºF) and above 70ºF add points.

•Correction factor = (0.331 x T/ºF - 23) / 100 or 0.03 pts per 10 ºF
•Correction factor = (0.595 x T/ºF - 12.5) / 100 or 0.03 pts per 5 ºC

[fiddlerkelly]

IF i am reading your post right i am now concerned about my batteries. I have a 12 volt system  as i cheaped out on a power invertor from canadian tire . 1000 watt pure sine wave  which had only the option of 12 volt with 250 watts of solar panels. I am in the middle of upgrading to 1100 watts of panels and plan on running them at 48 volts and alos upgrading my invertor to a magnum 120/240   4000 watss pure sine wave . I correct me if I am wrong am going top take apart my battery bank and equalize  the system two 6 volt batteries at a time hoping to reverse any possible sulfation that has occured in my system . I need to measure the S.G. when  I go up this week to see where it is now that it has warmed up in my part of the country.

[tecnodave]

Fiddlerkelly,

That is exactly what I would do.  12 volts is a dead end.  Separate all batteries. Charge as pairs until you get a specific gravity of 1.250-1.275 across all the cells. Pick your closest matched sets and use them.

Magnum at 48 volts is a real system, now what kind of charger are you proposing?  Get one that is totally programmable at the least. Many lower cost units will not properly maintain battery sets. You have a few bucks in those batteries, now is the time to get a good charger for them.

Might I suggest a Classic 150 with the current measuring device "Whizbang jr." This charge controller will protect and maintain your investment better than the others.

The Classic comes with the Whizbang jr. and a battery temp. Sensor " MNBTS" but you will need a current shunt for the Whizbang jr.  The correct one is a "Deltec 500 amp/50 mv."

Batteries in parallel is one of the major fail points in solar, the 48 volt route is the best path for a whole house system, at least 24 volt for a small house and system.

td

[fiddlerkelly]

Actually I am planning for Midnight solar 200 as this was advised to me as to my VOC when all my panels are put to get her will be approximately 160 volts.

[vtmaps]

I am in the middle of upgrading to 1100 watts of panels and plan on running them at 48 volts and also upgrading my inverter to a magnum 120/240

Actually I am planning for Midnight solar 200 as this was advised to me as to my VOC when all my panels are put to get her will be approximately 160 volts.

Hold on, there might be a better solution... For the upgrade, how many panels, what are their Voc and Vmp, and how far between the combiner and the classic?  Are you planning to keep your existing panels?  How many of them and what's their specs?

I'd like to find out if you can configure the system to use a Classic 150, but as you realize, you cannot put all the panels in series on a Classic 150 when the Voc is 160.

I'm guessing that your 1100 watt upgrade is 4 panels, each with a Voc = 40.  In which case all 4 in series is the only way to configure on a 48 volt system.  But if your old panels can be used, there might be a way to make 2 strings at a lower Voc.   

One more question:  You mentioned a Magnum inverter, but you did not indicate (clearly) whether it would be 24 or 48 volts... which is it?  Especially if it's 24 volts, you should really try to use the Classic 150.  With an 1100 watt array, a 24 volt system voltage might be practical, although if your design goal is to use as many of your existing batteries as possible, 48 volts would mean fewer parallel batteries. 

--vtMaps

[tecnodave]

Fiddlerkelly,

What vtmaps is saying is very valid,  gather info on all panels and post the specs. There is an optimum voltage to run the panels and controllers. This will depend on distance from panels to charge controller. Generally speaking use  p.v. Voltage 1.5 to 2.5 times battery voltage. The controller will work harder converting 160 volts down to 48 than if you use some lower voltage on your panel strings.
When the panels are more than 100-125 feet then the Classic 200 with 4 in series maybe more efficient but at shorter distances the Classic 150 with 2 panels in each string will probably more efficient.

The trade off is more power lost in wiring at the lower voltage vs. more power lost in the controller due to the lower effiency at the higher voltage.


If you have a very long run from solar array > 150 feet then higher voltage works out better.

Give us more info about placement , panel details etc. And the group of users will advise you as to the best configuration.

td

[fiddlerkelly]

I will attempt to attach photos with info on them. I am going to be mounting my panels on the roof of my cottage so maximum distance from panels to charge controller is 40 feet. I have a #10 multistrand wire to wire panels to combiner box then to charge controller. I chose 48 volt as to keep wire size down.

Specs for 150 watt panels are to very right and the 50 watts towards the left. I already have 5 -  50 watts and would like to use them in my upgrade , 4 of them at least to make 2   -100 watt panels.

Thanks for all of the assistance.

[fiddlerkelly]

Here is the magnum I was looking at. It is the 120/240 volt   48 volt.  I initally chose that one as I planned on connecting my batteries into two lines each totaling 48 volts. To do this I would have to remove two batteries from the system but would I still be able to keep this 2 and have 3 lines of 36 volts. 6  6 volt batteries in series then 3 of those lines in parallel.

Make sense?

[vtmaps]

6  6 volt batteries in series then 3 of those lines in parallel.

Make sense?

No, it does not make sense.  You would need 8 in series to make 48 volts.  Two strings of those would use 16 batteries.

What I think you should do is calculate your loads and then design the ideal system on paper.  Then you can try to figure out what to do, what compromises to make, to utilize as much of your current system as makes sense.

Your batteries are ephemeral... your panels and inverter will long outlast your batteries.  I wouldn't necessarily base a lot of decisions on trying to use those batteries.  If, for example, you would be better off with a 24 volt system, then do it that way.  You would have four strings of batteries (not ideal) but only for a few years.

--vtMaps

[tecnodave]

Fiddlerkelly,

All of the panels that you have are 36 cell panels with a v@pmax (volts at max power) is 17.2 
Most of the 250-300 watt panels are 60 cell about 30 volts......not a good match.....keep looking for your upgrade panels......some builders are making 72 cell panels........now then if you use two 72 cell panels in one string and 4 36 cell panels in another string everything will balance as the 72 cell panels are about 34 volts. This is what I am doing as I have many legacy Siemens 36 cell panels working well with SunTech and EPolly panels.
I use 2 72 cell panels or 4 36 cell panels in each string for a total cell count of 144 and volts about 68.8

Rule of thumb when mixing panel types:

Panels in a series string must have the same current at max power within a few percent
Strings or panels in parallel must have a total string voltage within a few percent.

Manufacturers that do have 72 cell panels include : SunTech , poly cell only, Canaidan Sun , ePolly

The largest bulk of panels are 60 cell but 72 cell can still be found, it is probably a easier way to go.

You really have several options here,  use a mix of panels having same voltages
Or use separate charge controllers for 36 cell banks and 60 cell banks.

Best deal I found for non standard grid tie panels are the 72 cell EPolly panels at northern Arizona wind sun.

I have been eyeballing those Magnum units for a while, they just brought out a new model, though not 120/240 it has some compelling features for me.....load sharing with a generator or utility
The MSH 4024 RE for 24 volts, they have not released this one in 48 volts yet...stay tuned

td

[tecnodave]

Fiddlerkelly,

Vt posted while I was writing but he did catch the 36 volt bit.  36 volt is used but is very rare, 24 volt and 48 volt are the common off grid voltages used. If your needs are small a 24 volt system will have advantages but if you plan a 4 bedroom house with all that you are used to when living on grid then a 48 volt system is called for.

Personally I am using 24 volt as I live in a small space and have a small workshop, it's a good trade off for me. I could have done a 12 volt system but the losses in the lower voltage inverters and wiring made that not feasible and I converted my motorhome to 24 volt right from the start, I separated the original 12 vehicle system and left it as is and added 24 volt system for all the house systems , inverters etc.

It helps that you post all info about what your needs are so everyone does not second guess as to what your desired system is to do.

td

[fiddlerkelly]

Yes where I currently have 18   6 volt batteries to wire for 48 volts I would have to drop two to 16 with 2 lines of 8  6 volt batteries but if I wanted to utilize all then I was thinking 3 lines of 6 batteries. 

Panels are already bought and en route.  The guy I am buying off suggested putting two groups on roof comprised of 3 150 watt panels and a 100 watt panel made of two of the 50 watts that  I already have. Then running the two groups down to a combiner box and then to controller.