Series/Parallel Batteries Connection

Serpentus · February 2017

Hello;

new to this forum.

I need advice in the best way to connect 12 12v 150AH Gel Batteries for a 48V system so it keeps the batteries balanced.

What is the best way to connect the 3 "banks" in parallel to keep them well balanced? I was looking at maybe method 3 of this page http://www.smartgauge.co.uk/batt_con.html or something like method 2?

I made the diagram in the picture like that to best resemble how my batteries are placed, easier for me to follow when connecting them, sorry if it's difficult to some to follow. By the way, I know that I have to keep Wires same lengths (short for series, shortest possible but same length for parallel and same but shortest possible length for the wires that go to Charger and Inverter). I'm using AWG 1/0.

Thank you in advanced!

*Edited, they are Gel NOT AGM.

westbranch · February 2017

here is a link to some good information: http://www.smartgauge.co.uk/batt_con.html

Serpentus · February 2017

Thank you westbranch (same link i posted, so it seems it can be trusted). Well, then I'll go with method 3, always keeping the same lengths for each type of connection (Serial connections being one type and the cables going from batteries to terminal posts being the other).

I will also periodically check the voltage of each battery to see if they are being kept balanced.

Image: https://us.v-cdn.net/6024911/uploads/editor/x8/wb554kaw3d7g.png

mvas · February 2017

Diagram in Post #1 is OK.

Diagram in Post # 3 is OK ...
Can you put each bank on a separate shelf?
Main (+) cable on the far left to each shelf, common connection via short / thick copper bus
Main (-) cable on the far right to each shelf, common connection via short / thick copper bus
Stacked layout keeps interconnect cable lengths very short.

I think this will be challenging to keep well balanced.
Leave cooling space between batteries.

BB. · February 2017

If stacked batteries--Make sure you have enough room to check electrolyte levels and add water (if flooded cell).

Also, if you parallel three or more battery banks--You should think about fusing/breakers on each + parallel connection--So that one short is not feed by the other battery strings.

These BlueSea fuse holders are hard to beat for small/easy to connect (fuse holders and fuses--Not so cheap):

https://www.bluesea.com/products/category/16/72/Fuse_Blocks/Terminal_Fuse_Blocks

5191 product image

MRBF Terminal Fuse Block - 30 to 300A

5191

Or use DC rated circuit breakers--You get both over current protection and can easily turn off one or more battery strings if/when needed.

-Bill

Estragon · February 2017

OP mentioned AGM so no checking SGs - makes it even harder to keep balanced.

Serpentus · February 2017

Thank you for the help and tips!

And I was mistaken, they are Gel, not AGM (just edited on OP).

Yes they are in separate shelf, unfortunately one bank is in a lower shelf and the terminal post are above the first shelf, so all cables are shortest possible length and same length, also they are AWG 1/0, much thicker than I actually need.

Did the method 3 (my second post). Seems all good. Will check balance once every month (have the time to do that).

I set the charger to 56.4 Volts (14.1volts per battery). The recommended voltage by battery manufacturer is between 14.1~14.4 volts.

Thank you guys, really appreciate it

PNjunction · February 2017

You are prepared for what happens if just ONE of those 72 cells in that bank shorts/dies right? At a *minimum*, a class-t fuse needs to be installed between each string, otherwise your cabling becomes the fuse. Basically a fire-trap dangerous to you and those nearby.

You did charge each one of those batteries *individually* first, prior to placing them into series/parallel right? If you don't, and especially because you can't check on the balance of each cell with a sealed gel, (or agm too), it is very very easy for one cell(s) to hide their low charge state. An INITIAL full charge is mandatory with sealed vrla prior to placing them into series/parallel service. With only 6 cells to get fully charged individually (for a 12v battery), you are more likely to have the cells get into balance.

Just checking terminal voltages on a sealed setup, especially this large, won't be absolutely trustworthy. The mantra for sealed setups is to keep your cell count down as low as you can get it - which means using the largest capacity batteries you can to cut down on a series/parallel nightmare from a forest of cells you can't touch.

If this was a professionally designed UPS system, (albeit wrong battery cycle type) that would be one thing. But if you are just slapping together batteries that are old/used, mismatched in manufacturing dates and the like, you have just put on the wedding ring for constant maintenance, not only from a performance standpoint, but from a major safety standpoint as well.

Like right now - if you haven't done so already, tear the system apart, and charge each battery individually at the very least before putting it back together. If you don't, you are just setting yourself up for a balance nightmare pretty quickly on as individual cells in the bank cannot be measured for balance being a sealed vrla type setup.

Again - get some class-t fuses pronto!

And oh yeah, do NOT exceed 14.1v (2.35v per cell) for your gel, since it IS such a huge sealed parallel / series nightmare. You can bet that over time, a few cells will try to go much higher than that, as an RE application for gel that isn't perfect, is a good candidate for premature sulfation and or individual cell over-voltage / gel voids from related balance problems.

mvas · February 2017

Who is Mfr and what is Model # of those Gel Cells ?
Are they all brand new?
Why did you choose Gel vs AGM ?

A Direct Connect Marine Fuse ...
http://www.pbase.com/mainecruising/battery_fusing

BB. · February 2017

In the US, GELs have been known for failing if charged much over 5% rate of charge (i.e., 100 AH battery, >5 amps of charging current). They can (will?) form permanent gas pockets in the GEL which quickly reduces capacity of the battery.

They are great for low self discharge, high efficiency, and can supply very high current for short periods of time--All very nice for UPS type installations. But they can only be charged (relatively) slowly--Not great for a solar power system where 10% or more rate of charge usually works out best for full time off grid systems.

Apparently, European versions of (some/all?) GEL batteries do not have this problem/limitation.

-Bill

Serpentus · February 2017

Hi, yes they are all brand new, same date of manufacturing and, if to be trusted, even same inspector checked them.

Why did I chose them? To be honest I didn't (don't ask

), they even sold them as AGM <.< .... That's why I said AGM in the first place, now that i went to manufacture's website, I see they are actually Hybrid Gel.

They are Wolong, the Model is 6-GFM-150J 12v 150Ah/10Hr Hybrid Gel (http://www.wolong-battery.com/production/GFM-XJ_Series.pdf) sold in my country as Deep Cycle batteries...hmmm..... Sent an e-mail to manufacturer asking them about some things (mainly the intended use of the batteries and max. charge volts, maybe in the store they got it wrong, I already lowered charger to 13.95 volts just in case).

And my previous batteries died after 7 years, but they were extremely badly treated and had less capacity than this new bank, I mean they turned on motors (water pumps) even when not fully charged or when it was very cloudy, and they were 4 banks in parallel, not 3... And they were connected like in the first post (unbalanced for 4 banks). This ones won't be treated like that, I hope.

Thanks PNjunction and mvas.

mcgivor · February 2017

Been searching for batteries in Asia for a while and have seen many VRLA similar to the ones you have, Nano Silica Gel, some have glass matt separators, AGM, others do not make that claim. The ones with AGM state renewable energy in the useage description, the Web site for Wolong is not very informative but it would appear that they are better suited to standby use, UPS &Telecom etc, as no mention of deep cycle or renewable energy is mentioned.

Serpentus · February 2017

Hi mcgivor and BB, thanks for helping out.

Yes, I came to the same conclusion when I saw the battery description, seems they are not fit for the intended use. Still waiting for the manufacturer response.

It all indicates, as of now, that I'll have to discuss this with my supplier and see if I can get the money back, they insist that they are deep cycle batteries and AGM-Gel Hybrid even though it just says Hybrid and nowhere to be found that they are deep cycle... The nearest is that they say it has a good recovery from deep discharge, but don't think it's the same, and nowhere it states that they can be frequently discharged.

Thanks again.

mvas · February 2017

Serpentus said:

Hi, yes they are all brand new, same date of manufacturing and, if to be trusted, even same inspector checked them.

Why did I chose them? To be honest I didn't (don't ask ), they even sold them as AGM <.< .... That's why I said AGM in the first place, now that i went to manufacture's website, I see they are actually Hybrid Gel.

They are Wolong, the Model is 6-GFM-150J 12v 150Ah/10Hr Hybrid Gel (http://www.wolong-battery.com/production/GFM-XJ_Series.pdf) sold in my country as Deep Cycle batteries...hmmm..... Sent an e-mail to manufacturer asking them about some things (mainly the intended use of the batteries and max. charge volts, maybe in the store they got it wrong, I already lowered charger to 13.95 volts just in case).

And my previous batteries died after 7 years, but they were extremely badly treated and had less capacity than this new bank, I mean they turned on motors (water pumps) even when not fully charged or when it was very cloudy, and they were 4 banks in parallel, not 3... And they were connected like in the first post (unbalanced for 4 banks). This ones won't be treated like that, I hope.

Thanks PNjunction and mvas.

My interpretation of their Charging Graph ...

Bulk at 10% of CA until 14.1 Volts @ ?° C << They do not state what "CA" is: C10, C3 or C1? What is the temp?
Absorb at 14.1 Volts = ( 2.35 V x 6 ) until below X amps @ ?° C << They do not state what X amps is. What is the temp?
Float at 13.5 Volts = ( 2.25 V x 6 ) @ 25° C << The transition to Float Mode is not shown on their Charging Graph.

1) They do not specify the Bulk Amps charging rate for your battery. Is it 10% of C10, C3 or C1?
2) They do not specify the amps target to switch from Absorb Voltage down to Float Voltage. Is it 1% of CA?

Ask for detailed settings for Bulk, Absorb, Float ( volts, amps and max time )

The charging graph indicates ...
a) Time spent in Bulk mode = 4 Hours to 8 Hours
1) Is 4 hours for 50% DOD ?
2) Is 8 hours for 80% DOD ?
b) Time spent in Absorb mode = 8 Hours (minimum)

The total recharge time is minimum of 8 Hours and maximum of 16 hours ?

Float Life is 15 years ( wow ! ) <edited>.
But maximum number of deep cycles is not given. Why?
Maybe it is a stand-by, infrequent use, Telecom Backup type of battery

Serpentus · February 2017

Hi mvas, yes, the floating voltage is between 13.5 ~ 13.8 volts, Equalizing voltage is 14.1~14.4 volts. Good thing I never set them over 13.65 volts (54.6 volts). What I said before, was never done (13.95 volts, all that was said during the night before I applied a charging voltage, so it always was at 13.65 volts). Float life is 15 years. Edit: Charging Current C10 is 0.25 Max. Temperature compensation: -0.018V/°C

Deep cycles is not given because it seems they are not designed for that. At least in that pdf it doesn't say they are for deep cycle, it only says "Good deep discharge recovery performance", If you ask me, I would say that is not the same as Deep Cycle, or is it? As I understand it, they are meant to be for emergency, reserve power or UPS systems. No where they say that they are to be used for off-grid/renewable systems. I sent them an e-mail (some time ago) asking this, just got a reply, they ask if they are Wolong.... Let's see what they tell me.

However, I read a paper about Hybrid Gel/AGM batteries. They state that they handle repetitive discharges very good (Link to said paper if you guys are interested, seems to be a quite new technology: http://www.docdatabase.net/more-hybrid-advanced-gel-vrla-batteries-1057001.html )

Still have my doubts about the batteries, and I don't think the store they were bought from will return the money or exchange them. Will call them tomorrow.

Thanks, again, to all of you. You guys have helped a lot. Hope this thread helps more people.
Serpentus

mvas · February 2017

Serpentus said:

At least in that pdf it doesn't say they are for deep cycle, it only says "Good deep discharge recovery performance", If you ask me, I would say that is not the same as Deep Cycle, or is it? As I understand it, they are meant to be for emergency, reserve power or UPS systems.

Yes, I would equate their statement of "Good deep discharge recover performance" to be the same as "a Deep Cycle".
But the question remains, "How many deep cycles?"

Per Trojan, they claim their Deep Cycle GEL VRLA ( not a Hybrid Gel ) = 1,000 Cycles at 50% DOD.
But I assume these 1,000 Deep Cycles occurred at a cool temperature of 68° F because of this footnote:
"... Gel batteries may be utilized at higher temperatures with the understanding that battery life will be reduced by 50% for every 18° F increase in operating temperature over 68°F ..."

So, keep them cool, discharge them to 50% DOD every day and they should last for 3 years.
But, will you actually need a 50% DOD, every day, for three years?

Interestingly, Trojan then states: "For Renewable Energy, Hybrid Systems & Backup Power Applications"

LivEN (Living Energy) states, "The proven silica gel technology improves [hybrid gel] battery cycle life and performance at cold ambient temperatures. The number of deep discharge cycles is increased much, compared with the normal AGM batteries."

Serpentus · February 2017

mvas;

Interesting what other companies say. Maybe Wolong focus on another market and don't care about renewable energy market and don't state it, I'm thinking this because when they replied to my enquiry (a few hours ago) they asked me if they were Wolong, found that odd... Anyways, lets see what they reply, will post it here as soon as I get an answer.

At least in summer, they will probably never get discharged under 10% (some nights probably 5%).... During the day there is enough power from the solar panels to run everything needed and keep them in the floating voltage and charged.

Winter though, it's another animal, we sometimes get 2 weeks straight without seeing the sun (funny thing is, cloudy at day, clear sky at night hahaha). However when it's sunny, the same applies as summer, enough power to run everything and keep them in the floating voltage. We use a generator (for a few hours) in the night and sometimes at day when cloudy days strike.

For what I can tell, it seems Wolong made tests with a T° of 25°C (77°F), gives more working T° than 68°F (20°C). I will see if I can add some low power fans near the batteries, they are separated a bit more than 1.5" from everything. However, doing this means I have to balance the air flow to keep all batteries near same T°.... Maybe I'll figure out a better way.

Thanks for your research and help mvas.
Serpentus

Serpentus · February 2017

Hi again.

Well, It seems we got bad batteries from the dealer here. Still don't want to jump to a 100% conclusion...

From factory they told me this:

The full charge voltage should be 12.8V, cut off voltage 11.1 V

For battery storage, if in 25 degree need to charge battery per 6 months. if in 35 degree need to charge battery per 3 months, if in 45 degree need to charge battery per 1.5 months. If not charged in time, the battery life will be shorter.

The batteries they sold us were 7 months old.... I highly doubt they maintain them at 20°C, the temperatures have been pretty high the past months (25~35°C), So I'm pretty sure they have damage.--- Edit: Just talked to dealer.... they say there storage room is below 25°C (they have it thermally isolated, hope is true).

After Using about 500W, the batteries read 50,8V. IF my calculation are correct that voltage corresponds to a 6% DoD (1296 Watts). They should be reading about 51V (2~3% 432~648 watts DoD) .

I attached the spreadsheet with calculations, if anyone is kind enough to check them please.--- Edit: Of course, theoretical calculations and in real measurements aren't 100% certain.

Edit: By the way, I disconnected them for 7 hours before the sunset to let the voltage settle down, After that time they read 51,3 Volts. This is good, so maybe there is another problem, the cables are same lengths, so don't think that's the problem, maybe inverter is very inefficient?

What's your take on this?

(They still haven't told me how many Cycles they can withstand I hope they answer that tomorrow).

Thank you again!
Serpentus

Series/Parallel Batteries Connection

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