General Gel Settings

alright71

Greetings! My name is Blake and i am new to this forum. I am a missionary living in a remote part of DR Congo, Africa. I have recently purchased an inverter system for my house and i am now trying to program the Outback FM-60 charge controller.

One element that is creating issues for me is my Chinese, off-brand, gel batteries. Each post i read refers people back to a manufacturer website, which, in this instance doesn't exist.

I am running 8-100ah, 12v batteries, in a 24v configuration.

Are there some general settings for gel batteries, in a 24v configuration that someone can provide to get us up and running?

Have a great day and thank you in advance!


Blake

Cariboocoot

Re: General Gel Settings

Welcome to the forum Blake.

Okay, so too late for the advice of avoiding using gel batteries for RE use because they aren't suitable. In general they are picky about both Voltage and current and don't want a lot of either. Know in advance that these are probably going to fail sooner rather than later, and possibly in a spectacular way.

Without any specific information from the manufacturer (hurrah for bargain brands!) you have to go with the generic settings. First of all limit the Voltage to 28.2-28.4, use a remote temperature sensor (vital in this case), and never allow equalization. Second, you've got two parallel strings of four batteries in series (hopefully wired as per Smart Gauge method #3 http://www.smartgauge.co.uk/batt_con.html consider each 'one' battery in the diagram to be a series string) which means 400 Amp hours @ 24 Volts (about 4800 Watt hours worth). You need to limit the current to a maximum of 8%, possibly only 5%: 20 to 32 Amps. The FM60 can be programmed to do this and/or you would have only about 1000 Watts of array. When it is charging check the battery temperature carefully (infrared thermometer would be good) and make sure they aren't getting too hot (50C is dangerous for these - better below 40C if possible).

This system will have limitations to be sure. If you constrict the maximum current the charge controller can put out you will limit its ability to provide current for loads and charging at the same time. Thus the net charge rate will be even lower if something else is drawing current while you're trying to charge the batteries.

If I were you I'd start planning for some AGM's right now.

BB.

Re: General Gel Settings

One of the issues with GEL batteries is (for most brands) is that they cannot take very high charging currents without developing gas pockets in the gel (which are permanent and reduce battery capacity).

So, most are limit to ~C/20 or 5% of their rated AH capacity. For your bank, that would be 4 strings of 2 batteries each. And that gives you 400 AH at 24 volts. And 5% of 400 AH would be 20 amps of charging current.

The "recommended" array size would be:

• 400 AH * 28.4 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 738 watt maximum solar array

In general, GEL batteries are not recommended by our host (NAWS, a solar equipment retailer/wholesaler) because GEL batteries are so sensitive to over current during charging. And it is difficult to get a GEL battery fully charged during the relatively short time during a "sunny day" to recharge the battery bank.

For example, if you get most of your charging current from 9am to 3pm, that is 6 hours per day--At 5% rate of charge, that would be an ability to refill a battery bank ~30% per day (5% rate of charge * 6 hours of charging per day). That is a relatively slow rate of charge for solar--And would take you several days to fill the bank after a series of poor weather days (or days of heavy use).

Also--This 5% charging limit makes it difficult to manage charging and daytime loads. Very few (if any) solar charge controllers have the ability to measure current charging the battery bank while there are loads active at the same time (you want 20 amps going to the battery bank, and the charge controller+solar array also supplying XX amps to your loads during the day).

GEL batteries are pretty good for UPS systems where they are called on to supply a whole bunch of current in a short period of time (15 to 30 minutes until the computers can be safely shut down or the backup generator started--Then can take 10-20 hours of charging to get back full again). But for off grid solar, they are very difficult to use and get a good long life out of them.

Flooded Cell or AGM type batteries are usually much better for off grid power systems (sorry ).

But since you have what you have--I would suggest starting with 28.1 to 28.8 volts charging voltage and monitor the charging current. You should also have a remote battery temperature sensor to make sure that if your battery bank gets warm/hot (what is your climate like?) so that the charge controller will reduce the actually Absorb/Float voltage set points (hot batteries need reduced charging voltage, usually ~(-)5 millivolts per degree C per cell). Use 27.0 volts for float voltage.

You can find any "generic" GEL battery data sheet (such as this Trojan GEL pdf download--I just noticed the data sheet mixes "C" and "F" based temperature--I think that is a typo--and all are based on 10F rise/fall--not 10C) and use their charging requirements for your bank.

Anyway--What is the amount of sun you get in your region (some areas in Africa are extremely dry and can get >7 hours of equivalent noon-time sun per day--In the US/North America we use ~4 hours per day of sun per day as a minimum for ~9 months of the year, and recommend a genset to help for the 3 months of winter).

To read more about batteries, here are these links:

http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.batteryfaq.org/
http://batteryuniversity.com/

From the first battery FAQ:

Gelled Electrolyte

Gelled batteries, or "Gel Cells" contain acid that has been "gelled" by the addition of Silica Gel, turning the acid into a solid mass that looks like gooey Jell-O. The advantage of these batteries is that it is impossible to spill acid even if they are broken. However, there are several disadvantages. One is that they must be charged at a slower rate (C/20) to prevent excess gas from damaging the cells. They cannot be fast charged on a conventional automotive charger or they may be permanently damaged. This is not usually a problem with solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to the manufacturers specifications. Most better inverters commonly used in solar electric systems can be set to limit charging current to the batteries.

Some other disadvantages of gel cells is that they must be charged at a lower voltage (2/10th's less) than flooded or AGM batteries. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity. In hot climates, water loss can be enough over 2-4 years to cause premature battery death. It is for this and other reasons that we no longer sell any of the gelled cells except for replacement use. The newer AGM (absorbed glass mat) batteries have all the advantages (and then some) of gelled, with none of the disadvantages.

One of our posters here from Europe (stephendv) has seen GEL batteries (Tubular construction?) that appear to not have the limited input charging current... If your batteries are of "European Design", it is possible that they do not have the input charging current limit--Perhaps your battery dealer can get you, at least, the charging current requirements/limits.

I would also suggest a Battery Monitor for you installation. Makes it much easier to understand how well you are treating your battery. For off grid systems, one of the advantages of a flooded cell battery bank is that you can use a hydrometer to measure the state of charge of your battery bank directly by measuring specific gravity. With GEL/AGM/Sealed batteries, you are limited to measuring resting voltage to understand how full your battery is--A much less intuitive process.

http://www.solar-electric.com/metersmonitors.html
http://www.victronenergy.com/battery-monitors/bmv-600s%20and%20bmv-602s/
http://www.outbackpower.com/products/communications/flexnet_dc/
http://www.solar-electric.com/oupoflsymo.html (outback flexnet pricing)

You have GEL batteries at this time, and hopefully you can use them successfully within their limitations. Depending on your average loads during the day time, I believe the Outback solar charge controller can be programmed to limit charging current (say you want 20 amps into the battery and have a 10 amp water pump timed to turn on from 9am to 3pm--You could program the FM to output 30 amps maximum).

If you do not use any power during the day and only use power at night, then you could program the FM to 20 amps maximum (even if you have a larger array, the FM will safely limit charging current to the programmed maximum charging current).

That is about the limits of my knowledge... Hopefully some others here can add/correct my information.

-Bill

alright71

Re: General Gel Settings

Hey Cariboocoot,

I appreciate your advice on not purchasing the gel batteries. I am failure with the downsides of gel and that is why i am looking for some recommendations on settings. Unfortunately, in this part of the world, longevity and safety does not carry as much weight as low cost...gel is simply the only deep cycle, solar batteries available.

Thanks for the idea about pulling one leg from the other end (method 2). That is a great idea!

So, if i understand what you are saying, in my settings, i have 3 options: limit absorb and float. I should set the limit somewhere between 10-16 amps. Absorb should be set a 28.2-28.4 volts. Where should float be set? Right now it is 27.2.

Is that the only modifications i should make?

I appreciate your advice!

Cariboocoot

Re: General Gel Settings

alright71 wrote: »

Hey Cariboocoot,
So, if i understand what you are saying, in my settings, i have 3 options: limit absorb and float. I should set the limit somewhere between 10-16 amps. Absorb should be set a 28.2-28.4 volts. Where should float be set? Right now it is 27.2.

Not options so much as necessities. The Voltage for Absorb and Float need to be kept low and the current needs to be restricted. I believe the correct Float Voltage is slightly more flexible, but should probably be 26.8

Is that the only modifications i should make?

I appreciate your advice!

It's about all you can do without any actual manufacturer's data.
Sorry I misread your original post regarding the # of batteries so the calcs were off by 2X. I've edited my first post to correct this and hopefully did not introduce any new errors.

alright71

Re: General Gel Settings

After further inspection of the batteries, i did find this information:
cycle use: 14.5-14.9v (25 deg c)
(Initial current less than 20A)
Standby use 13.6-13.8

Does that have any affect on what has just been shared?

BB-
We live almost right on the equator and we have a solid 5 to 5.5 hours each day. I do have the battery temp sensor and i am using it.

Do you have a recommendation on a battery monitor? I have been looking at 3 different monitors: Outback flexnet, Mindnite MNBCM, and the TriMetric 2025.

Thanks!

Cariboocoot

Re: General Gel Settings

alright71 wrote: »

After further inspection of the batteries, i did find this information:
cycle use: 14.5-14.9v (25 deg c)
(Initial current less than 20A)
Standby use 13.6-13.8

Does that have any affect on what has just been shared?

This is good news. If we can trust that info it means these batteries actually were designed to operate at "normal" Voltage levels for RE. I would stick with the lower end just the same: 14.4 Absorb (typical for an AGM) and 13.6 for Float. Note there is still a need to limit current - although 20 Amps on a 100 Amp hour battery of any type is substantial. Makes me wonder just what these batteries really are inside, or if they've just slapped labels on them. That is always a difficult thing when dealing with non-specific makes/models.

Do you have a recommendation on a battery monitor? I have been looking at 3 different monitors: Outback flexnet, Mindnite MNBCM, and the TriMetric 2025.

Thanks!

The MidNite is more of an intelligent Volt meter than an actual battery monitor. The Outback Flexnet is very complex and somewhat expensive. The Trimetric is practically the standard. You might also look into the availability of the Victron monitor as several forum members use them happily. I would also warn that any monitor is only as good as its programming, and you may find you're missing info for those batteries like their efficiency rating. As such you may be able to keep track of Amps in and out but not necessarily have an accurate SOC reading.

SandyP

Re: General Gel Settings

BB. wrote: »

One of our posters here from Europe (stephendv) has seen GEL batteries (Tubular construction?) that appear to not have the limited input charging current... If your batteries are of "European Design", it is possible that they do not have the input charging current limit--Perhaps your battery dealer can get you, at least, the charging current requirements/limits.

-Bill

One must be carefull to not confuse the Gel batteries made specifically for RE systems with those of UPS or general sealed 12V purposes. As Bill states the 'European Design" RE Gel batteries (generally in 2V cell configuration) can accept 20% charge rates with no problems and charge Absorb voltages of 2.4V / cell (28.8V in 24V config).

Cariboocoot

Re: General Gel Settings

After getting the Voltage info off the batteries it rather looks like these are meant to be RE gels rather than the common type. Hence the change in recommended charging parameters.

SandyP

Re: General Gel Settings

Cariboocoot wrote: »

......14.4 Absorb (typical for an AGM) and 13.6 for Float. Note there is still a need to limit current - although 20 Amps on a 100 Amp hour battery of any type is substantial......

The Voltages quoted above are similar to those recommended for my VRLA OPzV solar.power batteries, with a maximum charge current of 20A/100Ah of battery capacity. With these parameters and sensible DoDs (20 - 30%) it is claimed the number of cycles will range from 5,500 - 8,500.

alright71

Re: General Gel Settings

I really appreciate everyone's input, it has been very helpful. So it's a really long story, but the short version is that initially i was starting with 1 pair of batteries, and now the additional 3 pairs (total of 8 batteries) have arrived. Our small town is served by small aircraft with major weight restrictions. So now i have all of the batteries and i am really looking closely at the smart gauge #3 method. Can someone point me in the direction of an appropriately rated, insulated bus connection or terminal block suitable for joining all of these batteries in a 24v configuration? If i understand Cariboocoot's post correctly, i should create 4 series pairs of batteries and then parallel them together using the #3 method. This means that i need a way to join 5-3/0 cables (1 for each 24v battery and 1 for the inverter) and 1 #6 cable (from the PV CC). Any thoughts?

Second, i have located in Kinshasa (the capital city) some 12v light tubes. as my batteries are 24v, how would you recommend stepping down to that 12v voltage? I have seen equalizers and also DC to DC converters.

Have a great day and thanks again!

westbranch

Re: General Gel Settings

Do you have access to flat copper bar (for buss bars) and some NON-conducting material ( plastic , poly , Plywood ? that you can use to insulate the bars from any conductive material (pipe etc) that may be in the vicinity?
you can also use the non-conductive materiel to separate the 2 buss bars.
you drill several holes in the bar and use Stainless steel bolts to connect the cables to the bar.

see photo in post #10 here http://forum.solar-electric.com/showthread.php?16748-battery-switch&highlight=buss

BB.

Re: General Gel Settings

I prefer Brass/Bronze bolts over stainless...

If you use stainless steel (or probably steel), you want to use an "anti-seize" compound/grease. Most types of stainless will "cold weld" when spinning a nut onto a bolt (sometimes, finger pressure is almost enough).

You can usually get an anti-seize grease from a local auto/truck parts store (many small engines use aluminum cylinder heads/block and you need to grease the spark plug threads (and bolts during rebuilding) to keep the aluminum threads from locking/being torn out.

Some people have talked on past threads about using aluminum bus bars (cheap, light weight). Aluminum has an issue were it generates a hard/insulating corrosion layer when "raw" aluminum is exposed to air/oxygen (in minutes). There are anti-corrosion greases available for use with aluminum (and use star lock washers that "cut into" the base metal)--But it is, for me, a distant second place recommended metal.

-Bill

YehoshuaAgapao

Re: General Gel Settings

Cariboocoot wrote: »

Welcome to the forum Blake.

Okay, so too late for the advice of avoiding using gel batteries for RE use because they aren't suitable. In general they are picky about both Voltage and current and don't want a lot of either. Know in advance that these are probably going to fail sooner rather than later, and possibly in a spectacular way.

Jeremy at Affordable solar initially tried to push Deka Gel batteries on me. I knew they won't handle high current so I said no way I was going to buy the batteries from NAWS (they only offered Deka and Surrette at the time, both are expensive). Thats when he he offered me the sweet deal on the surrettes ($288 each, free shipping if I got the 2nd string but the vendor turned sour and they had to drop-ship from surrette instead but still got big shipping discount from it). I noticed that Affordable solar dropped surrette and they only offer Deka now. Deka is very overpriced and at that quality level, Trojan and Crown are better deals, and Deka pushes all kids of GEL batteries, though Trojan has some GELs too. Are GEL batteries good for anything?

BB.

Re: General Gel Settings

I believe, in general GEL are good for UPS/Standby/Float setups and very high current draw (like AGM).

-Bill

YehoshuaAgapao

Re: General Gel Settings

Found a comparison. GEL is good for high depth of discharge and low current draw. AGM is good for high current draw. GEL and AGM are worse than flooded in withstanding high temperatures.

http://www.trojanbatteryre.com/PDF/RE_CompareFLAvsVRLA_0212FL.pdf

inetdog

Re: General Gel Settings

YehoshuaAgapao wrote: »

Found a comparison. GEL is good for high depth of discharge and low current draw. AGM is good for high current draw. GEL and AGM are worse than flooded in withstanding high temperatures.

http://www.trojanbatteryre.com/PDF/RE_CompareFLAvsVRLA_0212FL.pdf

From what I have seen, the biggest limitation of GEL is that they will not tolerate high charging current since gassing will cause bubbles in the gel itself which cannot easily be gotten rid of. As long as no electrolysis takes place or the gas creation rate is so low that it diffuses through the gel instead of forming bubbles, they are OK.

SandyP

Re: General Gel Settings

YehoshuaAgapao wrote: »

Found a comparison. GEL is good for high depth of discharge and low current draw. AGM is good for high current draw. GEL and AGM are worse than flooded in withstanding high temperatures.

Some info on Temperature for OpzV GEL batteries see images below :

Attachment not found.Attachment not found.Attachment not found.

alright71

Re: General Gel Settings

Westbranch, thanks for the great idea! My wife is in the US right now and is able to bring back whatever is needed to get this thing rocking! Is everyone making their own bus bars? This seems to be a great area to make some real $$ by producing a large bus bar just for this purpose!

So there has been a development in the battery saga! With the arrival of the new batteries, i found, in several of the boxes, a small paper with some relevant info!

First, the paper is labeled "valve regulated lead-acid battery"! Well that sure clears some stuff up!

Second, it says "floating charge 12v battery 13.6v-13.7". "cycle use 12v battery 14.6-15". It then goes on to say "max charging current is .1c-.25c where c is the AH of the battery". I understand all of this in regards to 12v batteries, my question is; do i simply double thoes numbers for a 24v configuration? For example, is my float voltage 27.2v-27.4? for my max charge current would i calculate as 200ah (2-100ah batteries)?

Third, in the discharge section it says "relationship between discharge current and final discharge voltage". I assume this is talking about the DOD of the battery? It proceeds to give a small chart:
.2c or below 1.75v/cell
.2c to .5c 1.7v/cell
.5c to .1c 1.55v/cell
above .1c 1.3v/cell

BB.

Re: General Gel Settings

alright71 wrote: »

Second, it says "floating charge 12v battery 13.6v-13.7". "cycle use 12v battery 14.6-15". It then goes on to say "max charging current is .1c-.25c where c is the AH of the battery". I understand all of this in regards to 12v batteries, my question is; do i simply double thoes numbers for a 24v configuration? For example, is my float voltage 27.2v-27.4? for my max charge current would i calculate as 200ah (2-100ah batteries)?

For 24 volts, simply double the 12 volt numbers (or 12x the cell voltages).

For current, nothing changes.

Remember, adding batteries in series, you add voltages (2x 12 volt batteries in series, is 24 volts).

Adding two 12 volt @ 100 AH batteries in parallel, you add the AH ratings (200 AH).

For batteries in series parallel, you get 24 volts @ 200 AH.

Third, in the discharge section it says "relationship between discharge current and final discharge voltage". I assume this is talking about the DOD of the battery? It proceeds to give a small chart:
.2c or below 1.75v/cell
.2c to .5c 1.7v/cell
.5c to .1c 1.55v/cell
above .1c 1.3v/cell

I am not sure I understand the chart... There may be some typos?

.2c or below 1.75v/cell
.2c to .5c 1.7v/cell
.5c to 1.0c 1.55v/cell
above 1.0c 1.3v/cell

Those would appear to be the Volts per Cell for a discharged battery at those loads... I.e., a battery being discharged at 0.2c * 100 AH capacity = 20 amp discharge rate at 6 cells * 1.75 = 10.5 volts.

In "real life", I would suggest you not discharge the batteries down to those levels. You will probably damage the batteries. It appears to be a rating that would be used for a UPS or a telephone switch room where the batteries are discharged until dead in an emergency (for battery/equipment rating calculations). In those types of situations, a company would mostl likely replace the bank after the emergency was over.

-Bill

NorthGuy

Re: General Gel Settings

BB. wrote: »

.2c or below 1.75v/cell
.2c to .5c 1.7v/cell
.5c to 1.0c 1.55v/cell
above 1.0c 1.3v/cell

Interesting chart. Looks like they think that 1.0c discharges are Ok for their batteries.

The inverter will need some minimum voltage (somewhere around 1.85V/cell), so if discharged with 1.0c currents or alike, the battery will become unuseable long before it discharges to 1.3V/cell level.

alright71

Re: General Gel Settings

BB. wrote: »

I am not sure I understand the chart... There may be some typos?

Bill, you are correct, i added a . there. It's 1 not .1. Thank you for catching that!

Blake

alright71

Re: General Gel Settings

I have been really studying the situation I have with these batteries. As we have discussed before, I have 4-24v batteries (2-12v batteries in series). The space I have for the batteries, allows for 2 pairs on the bottom shelf and 2 pairs on the shelf directly above.
If I understand everyone very well, and if I understand Smart Gauge method #3 well, instead of wiring the 4-24v batteries in a parallel chain, I need to take each 24v battery terminal to a lug of a common bus (one bus for + and one separate bus for -) and each cable from battery terminal to the bus bar needs to be of equal length, correct? If I do this, I will have 8 battery cables and 2 inverter cables, totaling over 40ft in length. This does not include the series cables.
Are the gains of the #3 method so great that it is worth the cost and voltage losses of over 40ft in battery cable and the time and expense of a bus bar? I’m not trying to be argumentative; I’m just trying to justify this cost. If I were to do a parallel chain, it would take 28ft of cable, including the inverter run and I can easily do SG method #2. The other savings here would be the time and money of building a bus bar.
I do appreciate everyone’s input…you wouldn’t believe how difficult it is to do this on the other side of the world hundreds of miles from your nearest supply of anything!
Thank you!
Blake

BB.

Re: General Gel Settings

Method three (battery strings in series, then the +/- ends to a common bus) is better in terms you can now add a fuse/breaker per string. With three or more parallel strings, you should do this as large paralleled strings of lead acid batteries can supply huge amounts of current into dead shorts.

The second method, if you are not adding fuse/breaker per series battery string, is otherwise fine.

If you where to use method two and add a fuse per series string, this guy from Blue Sea is pretty nifty:

Attachment not found.
Attach one end to your battery terminal, and run your bus wiring from the fuse terminal. The fuse should be size for the maximum current/wire capacity (i.e., 1.25x the maximum sustained current you expect).

But--Frankly in Africa in the middle of nowhere--You would be hard pressed to justify the time/expense to get the holders (and fuses, ordered separately) into your place.

So--The next part of the plan is to build the battery bank enclosure in such a way that if there is a cable fire (or worse) that 1) it does not hurt/kill anybody and 2) limits the extent of damage to the battery bank/enclosure and does not take out anything more (i.e., a concrete block or mud brick shed next to your home/structure). I would also suggest a fire ax or set of cable cutters nearby (with face shield to protect your eyes/face) and easy to access--There is nothing like looking a glowing red wires on a battery bank and no way to stop the current flow.

-Bill

alright71

Re: General Gel Settings

BB,

I really appreciate your willingness to think outside of the box.

I will use method 2 and pull my + from one end of the string and my - from the other. I will also keep all the cables the same length so as to not create imbalances.

I have just ordered an inline type T fuse to sit between my batteries and my inverter.

Thank you!

Blake

Ohmslaw

Re: General Gel Settings

Hi,
I have to install 48 8g8d Gel batteries. They will be connected to 6 inverters. Could someone tell me the preferred method to connect the three 48 volt banks.
900 AH for each bank. I plan on 2/0 interconnections and 4/0 to the inverters with 200 amp fuses at each inverter feed.
I also would like to know the best method for fusing the system.

Ohm

BB.

Re: General Gel Settings

Welcome to the forum Ohmslaw,

Is this system for Off Grid or emergency backup to grid power?

Do you have the charging requirements for the GEL batteries? In the US, most of the GEL batteries have a charge rate of C/20 hour charge rate (i.e., a 100 AH @ 20 hour rate battery would have a maximum charging current of 5 amps).

For solar, that is a very difficult road to haul. With solar, you have around 3-6 hours a day of "good sun" to recharge that battery bank and we usually recommend a charging rate of ~C/10 or C/8 rate of charge (to quickly recharge the battery bank from the available sun). If you charge at higher than C/20 charge rates for most GELs, it causes gas pockets to form and permanently reduce battery capacity.

-Bill

Ohmslaw

Re: General Gel Settings

The batteries are Deka 8g8d. They will be in three banks of 16 batteries each. The 20hr rate is 225ah. per battery. The 4 strings equal 900 ah. The spec calls for 30% of C/20. 1.75 vpc. the system will eventually have 24kw of solar. The generator will be 80kW. Does this make sense? Current solar is 4400watts. I really appreciate the guidance here. I want to be sure to get the wiring correct to keep the batteries balanced. The system is off grid.
Tim

Cariboocoot

Re: General Gel Settings

Ohmslaw wrote: »

The batteries are Deka 8g8d. They will be in three banks of 16 batteries each. The 20hr rate is 225ah. per battery. The 4 strings equal 900 ah. The spec calls for 30% of C/20. 1.75 vpc. the system will eventually have 24kw of solar. The generator will be 80kW. Does this make sense? Current solar is 4400watts. I really appreciate the guidance here. I want to be sure to get the wiring correct to keep the batteries balanced.
Tim

These are 12 Volt batteries. You would have four in a string for 48 Volts. Four strings in parallel is one 900 Amp hour battery bank, not three. There is no way to divide them equally into three separate banks. The fact you may be power six individual inverters from this one bank does not alter the bank specifications.

Ideally there should be a terminal post fuse on each strings, and all strings connected to positive and negative bus bars. From there every charge source and load will run, and each of those circuits would have its own over-current protection.

I'm reading a Voltage limit of 2.43 per cell under all charging stages. That would be 58.32 for a 48 Volt system, and must not go higher. Minimum charge Voltage would be 55.2. At least they give you a range. It also recommends Float Voltage lower at 53.52-54.24. I am amazed at the 30% charge rating and don't see that on the spec sheet. More likely 12 Amps per string, or 48 Amps total. Check with the manufacturer directly on this and make sure you explain the application as solar controllers do not have the same functionality as standard battery chargers.

4400 Watts of solar could output 70 Amps of current, which is about 7% rate - possibly a tad high.

Without knowing the size of the inverters it is impossible to tell how much current they may draw and what size wire/fuse is needed.

Ohmslaw

Re: General Gel Settings

I am sorry I was not clear. There will be three banks of 16 batteries each. A total of 2700 ah at 20hour . I will bring the three strings to the buss bars and then connect the buss to the 6 outback 3600 watt inverters. Fuse sizing recommendations? 2/0 battery interconnect and 2/0 to the buss? 4/0 to the inverters?
negative on one end and positive from the other?

Attachment not found.

Ohmslaw

Re: General Gel Settings

http://www.mkbattery.com/documents/6427Renewable%20Energy%20Charging%20Parameters%20Rev%204.pdf