adding new series strings to current system How To ?

[ashenash]

Hi to everyone . I'm new to this forum, but not to pv solar

I have a working system installed, but would like to add batts

Please tell me if I can/should safely add 4 more 6 volt batteries to my system.

I now have:
4-24v panels feeding (2 panels per morningstar mppt 15 controller)
2-15 amp mppt controlers feeding
a 12v-450ah (4-6 volt series/parallel) battery bank feeding
a 12v 5k inverter feeding
various houshold loads

My goal is to keep my 12v inverter (not change to a 24v or 48v system but still add more more battery capacity.

I would like to add 4 more 6v batts series/parallel to keep a 12v bank but increase amp hours by 1/3 (2 more 6v) OR 1/2 (4 more 6v)
When I researched this question I found this...

Battery banks with multiple strings are more likely to develop cells with unequal states of charge. Weak cells will be difficult to detect because they will “steal” from the surrounding cells. The system will suffer as a whole and will cost you more in the long run. Dankoff, Windy. "Batteries: How to keep Them Alive for Years & Years...." Home Power Magazine #69. Feb. - Mar. 1999. 46-47.

I understand the concept. Too many strings cause imbalance in indidvidual batts.

It seems evident that I can add multiple strings (6v batts connected in series to create 12v string to be paralleled to the exsisting bank) since I will use 2 controllers feeding opposite ends of the battery bank.

I'm using all matched batts. GC2 6 volt golf cart. My oldest are 6 months old with maybe 50 duty cycles. never drawn below 12v

Questions

Will my 6 month old batts be extremely mismatched with new batts ?
How much of an imbalance is too much ? current range is 7v - 6.8v

I currently have no way to isolate for testing besides disconnecting cables. Would you recommend a blade type cutoff or those cable ends with a rotary cutoff built in ? Or is there something better for high amps ? I'm trying to avoid more fuses.

All serious comments are welcomed
Thanks in advance

[JimD]

mismatched battery

Generally it is not good to mis match battery's that say I have done it and what is going to happen is the bank will assume the lowest charge. If your current battery's are in good shape you will not be losing that much life. It is a judgement call if you already have the new battery's and feel it is worth losing a little life out of them go for it. good luck JimD.

[Sunking]

You need to can the 12 volt stuff and move up to either 24 or 48 volt system.

[JimD]

Battery options

You are right I run my battery's four 6v in series to make 24v then 6 sets in parallel to stay at 24 v but bring up the amps. my 12v panels I do the same bring them up to 24v .Now you can get panels in 48v or better all the better.

[Beanyboy57]

I'm using all matched batts. GC2 6 volt golf cart. My oldest are 6 months old with maybe 50 duty cycles. never drawn below 12v

Questions

Hi, I am sure you will get many interesting responses. Just wondering what you mean by 12v on you batteries? Do you mean exactly 12v or can you be more precise given the 11.96v is equal to about 60% discharged and 12.1v is 50% discharged? According to battery manufacturers if you are drawing this much from your batteries you will severely deplete their lifespan.
Also wondering why you have two CC's? What was the reasoning behind that decision?

[Sunking]

Hi to everyone . I'm new to this forum, but not to pv solar

I have a working system installed, but would like to add batts

Please tell me if I can/should safely add 4 more 6 volt batteries to my system.

I now have:
4-24v panels feeding (2 panels per morningstar mppt 15 controller)
2-15 amp mppt controlers feeding
a 12v-450ah (4-6 volt series/parallel) battery bank feeding
a 12v 5k inverter feeding
various houshold loads

I can tell right now you are in huge trouble. If you in fact have a 12 volt 450 AH battery system you had sure better have a minimum panel wattage of 500 watts, which I know you cannot possible have because that would take a minimum 40 amp MPPT charge controller.

Second problem and it is a extreme fire danger, is your inverter. a 12 volt 450 AH battery can only safely supply a 750 watt inverter. A 5000 watt inverter would require a 3300 AH battery @ 12 volts, with a copper cables the size of your wrist between the battery and inverter.

You need to can this whole 12 volt toy idea you have and move up to a 24 or 48 volt battery system. But you have nothing that works with the other.

Right now based on the two 15 amp controllers you have I guess you have 360 watt solar panel setup. A 360 watt solar panel can only support a 12 volt 320 AH battery, and 500 watt inverter. You do not need more batteries with what you have now. You need to loose batteries, not add them.

[ashenash]

I can tell right now you are in huge trouble. If you in fact have a 12 volt 450 AH battery system you had sure better have a minimum panel wattage of 500 watts, which I know you cannot possible have because that would take a minimum 40 amp MPPT charge controller.

Second problem and it is a extreme fire danger, is your inverter. a 12 volt 450 AH battery can only safely supply a 750 watt inverter. A 5000 watt inverter would require a 3300 AH battery @ 12 volts, with a copper cables the size of your wrist between the battery and inverter.

You need to can this whole 12 volt toy idea you have and move up to a 24 or 48 volt battery system. But you have nothing that works with the other.

Right now based on the two 15 amp controllers you have I guess you have 360 watt solar panel setup. A 360 watt solar panel can only support a 12 volt 320 AH battery, and 500 watt inverter. You do not need more batteries with what you have now. You need to loose batteries, not add them.

I repectfully disagree

Nominal wattage of my panels is 512. They actually go up as high as 675
The controllers output 15 amps each. 30 amps charges my current battery bank with no problems
The wagan 5k inverter is cabled and fused per manufacturers instructions see page 11 of http://site.invertersrus.com/pdf/2012.pdf
I am not using more than 1.5kw , I merely wanted more headroom for startup of compressors and such.
There is no "extreme fire danger" the way I'm using the system. It has never blown fuses, tripped breakers run hot or out of spec
My "12 volt toy" successfully powers fridge, oil heater, basic lighting, and solar thermal pump with no problems other than battery capacity.
I need to add, not lose batteries.

I came to this forum to seek info about keeping my battery bank balanced
I do welcome reponses regarding that issue

[rreinha]

Battery balancing

I repectfully disagree

Nominal wattage of my panels is 512. They actually go up as high as 675
The controllers output 15 amps each. 30 amps charges my current battery bank with no problems
The wagan 5k inverter is cabled and fused per manufacturers instructions see page 11 of http://site.invertersrus.com/pdf/2012.pdf
I am not using more than 1.5kw , I merely wanted more headroom for startup of compressors and such.
There is no "extreme fire danger" the way I'm using the system. It has never blown fuses, tripped breakers run hot or out of spec
My "12 volt toy" successfully powers fridge, oil heater, basic lighting, and solar thermal pump with no problems other than battery capacity.
I need to add, not lose batteries.

I came to this forum to seek info about keeping my battery bank balanced
I do welcome reponses regarding that issue

It sounds like you are not using your batteries very often and adding more battery does sound like a good idea, but knowing you will not recharge them in one sun cycle if depleted.

Battery balancing is nothing new DIY-EV'ers have been doing it for for over 30 years.
There are some cheap and still available systems to buy or DIY kits ($20ea). Search the EV users groups and post the question.
Rudman regulators (Washington State) I are still available is in kit or drawing and Lee Hart in Minn, is very helpful on this matter. http://www.evdl.org/

Basically what happens is a small control board with a small resistor and some led's are installed to each battery and a master board will keep all batteries at the same voltage. it can be done at full charge SOC or DOD, most systems deal the Full charge balancing.

[ashenash]

Hi, I am sure you will get many interesting responses. Just wondering what you mean by 12v on you batteries? Do you mean exactly 12v or can you be more precise given the 11.96v is equal to about 60% discharged and 12.1v is 50% discharged? According to battery manufacturers if you are drawing this much from your batteries you will severely deplete their lifespan.
Also wondering why you have two CC's? What was the reasoning behind that decision?

I mean never below 12.00 volts. I installed an LVD set for 12 v . I usually manually shutoff the inverter when batt volts get to 12.3V to prevent depleting lifespan. With more batteries, I would have longer run time, but I'm concerned about keeping batts in balance. Thats why I posted here

2 controllers is a design strategy to allow flexibility and keep costs down. They are connected and used as advised by Morningstar's tech people.

Yes I wish I had the $20k to get a turnkey sell-all with windmill, hydro and a hamster with battery backup and a generator run on biogas from the hamster, but I decided to start small and build it myself. It has worked without a glitch in 2 power outages and numerous tests.

Yes I understand the advantages of 24-48v , but I won't be switching any time soon, just not practical

[ashenash]

It sounds like you are not using your batteries very often and adding more battery does sound like a good idea, but knowing you will not recharge them in one sun cycle if depleted.

Battery balancing is nothing new DIY-EV'ers have been doing it for for over 30 years.
There are some cheap and still available systems to buy or DIY kits ($20ea). Search the EV users groups and post the question.
Rudman regulators (Washington State) I are still available is in kit or drawing and Lee Hart in Minn, is very helpful on this matter. http://www.evdl.org/

Basically what happens is a small control board with a small resistor and some led's are installed to each battery and a master board will keep all batteries at the same voltage. it can be done at full charge SOC or DOD, most systems deal the Full charge balancing.

Thanks Rreinha,
That looks like a good site. I will explore.

[Sunking]

I repectfully disagree

Nominal wattage of my panels is 512.

OK you said you have 24 volt battery panels right? If that is true you got a huge Bart Simpson DOH moment coming your way trying to operate them on a 12 volt battery with a PWM controller.

A 24 volt battery panel VMP operates at roughly 36 volts. So you have two of them in parallel connected to the CC right? For a PWM controller the INPUT CURRENT = OUTPUT CURRENT. Since you said you have a total panel wattage of 512 watts and 4 panels then I can assume each 24 volt panel is 128 watts.

A 24 volt 128 volt panel will have a Vmp = 36 volts and an Imp = 3.5 amps. So with 2 panel in parallel you have an input to the controller of 36 volts @ 7 amps, or a total wattage of 256 watts. That means on the output the max is 13 volts x 7 amps = 91 watts out of 256 input. You got two controllers with 512 total input and a maximum output of 18w watts to the batteries.

DOH! You just had a Bart Simpson moment. You do not know what you are doing. You current configuration can only handle 160 AH battery.

[Naptown]

OK you said you have 24 volt battery panels right? If that is true you got a huge Bart Simpson DOH moment coming your way trying to operate them on a 12 volt battery with a PWM controller.

A 24 volt battery panel VMP operates at roughly 36 volts. So you have two of them in parallel connected to the CC right? For a PWM controller the INPUT CURRENT = OUTPUT CURRENT. Since you said you have a total panel wattage of 512 watts and 4 panels then I can assume each 24 volt panel is 128 watts.

A 24 volt 128 volt panel will have a Vmp = 36 volts and an Imp = 3.5 amps. So with 2 panel in parallel you have an input to the controller of 36 volts @ 7 amps, or a total wattage of 256 watts. That means on the output the max is 13 volts x 7 amps = 91 watts out of 256 input. You got two controllers with 512 total input and a maximum output of 18w watts to the batteries.

DOH! You just had a Bart Simpson moment. You do not know what you are doing. You current configuration can only handle 160 AH battery.

Read His OP he has 2 mppt controllers

[Sunking]

Read His OP he has 2 mppt controllers

Yes I know. On each controller he stated he has 2-24 volt panels, connected to a 12 volt battery. He has no idea what he is doing if that is correct. On a 15 amp PWM controller using 12 volt battery panels the maximum input you can run is 255 watts. However that is with a 12 volt panel operating at 17 volts Vmp and 15 amps Imp. From what I can ascertain he is running 34 to 36 volts Vmp at 7 amps Imp. Simple math.

[Naptown]

the controllers are not PWM they are MPPT.
the issue I can see is that at 256W feeding a 15A MPPT controller the output could be potentially over 20A. or he is losing about 30% from the CC clipping
It looks like an upgrade to a 45A CC is in order

[Sunking]

the controllers are not PWM they are MPPT.
the issue I can see is that at 256W feeding a 15A MPPT controller the output could be potentially over 20A. or he is losing about 30% from the CC clipping
It looks like an upgrade to a 45A CC is in order

Think that was what I said in post #6 huh? My bad. 30 amp of MPPT controller maximum input is 13 volts x 30 amps = roughly 400 watts. Back to step 1. IT is not going to work. Adding batteries is a very bad idea because he does not have enough to support what he has now.