really confused about series parallel cross tied charging and discharging

[loonogs]

I  am currently sourcing some old batteries to do conversions using info i got at this group "batteryconversions@yahoogroups.com" to make a battery bank.

now i have seen where it is suggested that if you have a large bank to parallel connect the series strings, even to cross tie them at each point in the string.

i believe that the idea is to ensure that all batteries get an equal charge.

i have seen the shunt unit here for ensuring equal charging on series parallel strings by BruceM


i do believe that if there is one bad battery it will drag down that parallel connected group causing problems.


so i am a kind of confused, should all the batteries be connected in series strings with shunts across them and then cross connected when discharging ?

this would require contactors or relays to make and break these connections as required, then there is the problem of bad contact on the contacts which will affect the system.

is solid state a better solution ?

or am i just getting blinded by thinking too much and knowing very little ?

[mobile_bob]

i think Bruce can address better perhaps what i leave out, but here is my take

those systems where you see all the jumpers in place between adjacent battery strings that are in parallel
are there to assure even loading and charging, however

they are best used on a matched set of new batteries, and not so much for a set of used batteries of unknown condition.

one bad battery in the bunch could in theory cause a rather difficult to find problem for the total bank, so i am a bit torn on
the use of such jumpers, perhaps they could be used a majority of the time, and removed periodically for testing and equalization
or topping off purposes.

personally i would either use solid jumpers or relays, and not solid state units
the voltage drops across solid state switches or relays is significant enough to cause balance problems in my opinion.

probably best to avoid too many parallel strings, in the first place
maybe use two strings, or maybe 3 so that you would either split the strings for charging and loading, or take one out of 3 to
top off and equalize from time to time and rotate through?

bob g

[mike90045]

You have to test the batteries individually before placing into a string.

But I think making a bank out of bad batteries, is a bad idea anyway, what do I know.

[Cornelius]

We haven't access to that group without joining, so why don't you explain to us exactly what you want to do, with what kind of batteries, how many, and target voltage etc.?

I have some experience with old battered batteries, both lead acid and sla; there always some Ah left, if done properly...

[rbodell]

I  am currently sourcing some old batteries to do conversions using info i got at this group "batteryconversions@yahoogroups.com" to make a battery bank.

When you are working with old batteries, your bank will only be as good as your worst battery. You will never be satisfied with what you have and in the end you will probably end up with a failed project.

Start with a bank of good batteries even if it is only one or two and run what you can off of them even if it is just a couple of lights or your computer. Build up your bank a little at a time whenever you can and then add a few more lights or a TV on the bank. Its easier to come up with a hundred bucks than a thousand dollars. In the emantime you will have a good trouble-free system.

[BruceM]

I couldn't access the article so can't comment on it.

I'm not familiar with parallel connections between series battery string elements.  I have not seen it recommended by major battery suppliers, which makes me suspicious.

[Lloyd]

I didn't access the article either. But I set up battery banks as a business in the marine industry all the time.
Series parallel of batteries is no mystery. As everyone has suggested start with new bats, or the mystery begins, it can be done with a lot of work to ferret out the bad bats.

Series parallel, begins of course with  setting your choice of bats to the voltage desired by series, then parallel by connecting the series bats...the key is to make each parallel cable exact lengths to each other. Then you tap the positive from one end of the bank, and the neg to the other end of the bank. Charge/discharge/equalize as connected no jumpers, the jumpers will cause the strongest series/bat to over work and the weakest bats to sit idle, instead of the combined amphr you will only get the rated amphr from the strong bat.

If you choose to use the old bats the first thing you have to do, is bring each seperate bat up to it's native voltage, let it set for 24 hrs, take a specific gravity reading on each bat, mark it down in a matrix.

Then you need to set up a load to draw down each bat separately at its factory rated load, compare that to the factory specs on discharge rate/time, mark it to your matrix. Recharge the bat, then run an equalize charge on the bat, let it set 24 hrs, make another specific gravity test, mark it in the matrix. I would do this through 2-3 cycles, at the end of these cycles review your matrix choose only the bats, that are equal to one another in specific gravity readings, build your bank from those, recycle the rest at an approved recycle center. Using  old bats will require that they be of the same native voltage, and amphr size.

Now the work begins, you have to monitor each bat vigorously, that means watching the whole bank and as soon as it shows signs of unexpected voltage drop, according to the rated loads being drawn. I have seen banks where one cell shorted and cascade the whole string of bats into a molten mess of cracked cases, and copious clouds of sulfuric acid.

The last boat that I saw this on, it was by the grace of god that it didn't blow. The owner called bc of what he thought was a charging issue, my first q was how old are the banks,  When he told me they were 8 years I said you most likely don't have a charging issue, you need to replace the bank...he was sure I was wrong, and would proceed to check all his charge and connections. The next Sunday morning I received a panic call. I went to the boat, before I reached the head of the dock I could smell the acid cloud, as I turned the corner I could see that all of the windows on the boat were completely saturated and dripping with fog. I disconnected the shore power cord, held my breath slid open the rear door, and told the client to go have breakfast and met me back in 2 hours. You'll never guess what I found. Can you imagine the cost to clean the acid fog off every surface in the boat.

He said I just don't understand...I have a smart charger this shouldn't happen...an owner installed system, with no temp sensor on the bank, a smart charger is designed to push the voltage in at the rated amps, it requires a temp sensor to stop it. With a 12 volt bank, and one shorted cell, the charger is going to due it's best to bring what is now an 11 volt bat upto 14 volts.

Lloyd

[BruceM]

"Charge/discharge/equalize as connected no jumpers, the jumpers will cause the strongest series/bat to over work and the weakest bats to sit idle, instead of the combined amphr you will only get the rated amphr from the strong bat."

This doesn't make any technical sense as written, perhaps a re-write would help?

[Lloyd]

Bruce,

I'll try to simplify.

bat 1, 6v series w/bat 2, 6v = Group 1, =12v
bat 3, 6v series w/bat 4, 6v = Group 2, =12v
bat 5, 6v series w/bat 6, 6v = Group 3, =12v

Parallel group 1 w/group 2  w/group3 =12 v, then tap the positive load group 1, and the negative load group 3.

Charge/discharge(=load)/equalize without adding any jumpers or dismantling the string.

I've seen setups where peps then parallel bat 1 to bat 3 to bat 5 with jumpers =6v
then jumper bat 2 to bat 4 to bat 6 with jumpers =6v...this is a complete mess and waste of good cable, and serves no purpose other than to work the strongest series/bat/group, and the weakest sit idle.

The only time you would need to break the string, is a once a year rotation of the bats, move the ends to the middles. Or if the string was showing signs of abnormal voltage drop against the rated load. You can't get an accurate specific gravity read of the individual cells when the bats are connected any way....series or parallel. Each bat has to be isolated, fully charged with no charge/load for 24 hrs, to make a specific gravity reading that will be accurate.

Hope that helps. My bank is 6 t240 trojans built as above, I installed the bank in 2003, I equalize once in the fall and once in the spring. I run a test load against factory specs once a year, it currently maintains close to 89 % of it's original capacity. The best investment I made in the bank were water saver caps, I have added a little over one gal of water to the bank since it was installed. I try to run a charge cycle before the bank hits 12.4 v, it's only been discharged below 12.2v twice in its life, that was the original condition cycle. Most important all charge cycles are temp managed, I set the temp calibration ratings at the beginning of the really cold season, and again in the late spring.

When I put new bats into service I run a condition cycle, which consists of the factory rated load drawn down to 11.7 volts over the factory spec time, then charged to full, then a second condition cycle is run, and the bats recharged to full again, topped with an equalization cycle. The lead plates in a new battery are very smooth and shiny, this condition cycle erodes the shiny surface increasing the working area by about 3 times the shiny surface area. If a condition cycle isn't run then new banks tend to develop a surface charge/discharge pattern until they have been used  and deep cycled a few times, if you follow the rule and don't discharge the bank below 50% you will never get the full amphr rating out of the bank.

Lloyd

[loonogs]

Hello all, sorry for the delay in getting back to you,

Mobile Bob, i take your point, 3 strings sound like a good idea.

Cornelius, more info wolud be helpful.
i would source some lead acid batteries typically 65ah rating 12v, i am living off grid using a lister 8/1 som with the 4.5 kva alternator,  iwant to build a battery bank to run small critical loads all the time, this is a low budget system and am using a 3kva ups  with a 96volt bus.
the battery conversion forum convert the batteries which appear to be at their end by using alum electrolyte and bring them back, reports have it that they have better characteristics than when they functioned initially as lead acid batteries.

I have contacted 2 members of the group to get their permission to post 2 of both their messages here to give members some detail of the process, i think it might interest lots here.

Bruce M here is the connection method
http://www.youtube.com/watch?v=sn4zzV0wqlk

Lloyd, thanks for the detail

[mobile_bob]

loonogs:

not to rain on your parade, but rather to make you aware of the very serious nature of what you have in mind

96volt battery string is not what i would call a safe voltage at all, and it is really unsafe using old and questionable batteries

the reason being is all you need is one shorted plate in one cell and you have ~94 volts potential across that short, violent explosions are
not unheard of.

when i read about reconstituting a battery with alum or some other salts, acid, aspirin or monkey blood, it seems innocent enough
when one is trying to recover a bad battery for a low voltage system, experimentation and hobby , all good.

but when i then hear of one trying such a thing with a high voltage string, i start to cringe and my nether regions start to pucker.

just be very careful, make sure the batteries are well contained, especially during charging, wear eye protection, full face mask
and have lots of water around as well.

ear protection is also a good idea, because if a battery blows up it will damn near deafen you, don't ask how i know this.

i have a large ups system that had a 240vdc front end buss, one of the batteries shorted internally and it blew a hole the size
of a quarter through the battery tray (about .100" thick) the size of a quarter, out the side of the carrier (another .100" plate) about
the size of a dime, and finally out the front panel (about .065" steel) that was about the size of a #2 pencil.

the batteries were 34amp/hr units, not very large at all.

that blast must have been horribly load in an enclosed space.

just be careful, we like having you around, with both eyeballs, and working ears.

bob g

[mobile_bob]

Jens:

i would expect that normally in a flooded cell that has plenty of electrolyte a shorted cell shouldn't be much of an event,
and to be fair the one i alluded to was a gell cell or agm i can't remember, with a short in one of those, the starved electolyte
would boil away quickly forming a bunch of hydrogen and oxygen in a confined space, then comes the arc/spark followed in
a millisecond later a huge boom.

evidently what happens next is a spray of hot liquified lead, or maybe even vaporized lead which would make a nice plasma
to carry massive amounts of kwatts to the case ground which probably explains the incredible damage done to the steel plates
in this case.

also i have seen numerous flooded cells explode, one caused by me and an errant spark from an arc welder, luckily my welding helmet
was down when it went off, the aftermath was ugly and my ears rang for days.

another happened to a fellow mechanic who happened to have his face right over the top of the cells checking water when one let go,
had it not been for the fast action of two other mechanics he likely would have been blinded. they flushed his eyes for about half hour with
a garden hose till the paramedics showed up.

it has been my experience that with dc and batteries as the voltage goes up, so does the possibilities of some really bad things happening
that is why i am not a big fan of working with unknown batteries using experimental methods in an effort to recover them.

my eyes are worth more than any set of batteries, and for that matter the eyes of my worst enemy are worth more than any stack of batteries.

just my opinion of course, ymmv

just felt like i would be seriously remiss if i just set back and said nothing, and then later found out a fellow board member or a guest got seriously injured, especially if me opening my big mouth might have averted the issue.

if that makes sense?

if one considers a 6/1 produces approx 4.5 kwatts of mechanical power, and no one i know will risk trying to arm wrestle its flywheel
a battery bank of even a small size can deliver 4.5 kwatts of instantaneous power as well, so just because it has no massive flywheel
to wrap you up, it has the ability to kill you just as dead under the right circumstances.

i have a healthy respect for batteries or for that matter any form of energy storage device.

bob g

[mobile_bob]

also there is probably a very good reason why the NEC limits us to 48volts nominal, and why those ups systems that use
over 48volts nominal usually are encased in several layers of steel with all sorts of interlocks and generally no user serviceable parts.

if for no other reason electrocution hazards go up with increased voltage, and DC seems to hang on tighter than AC in my experience
maybe it is because AC goes to zero 100-120 times per second ?? (depending on where you are in the world)

bob g

[Lloyd]

Professor, what you said as usual...hehe

A shorted cell in a lead acid battery while in discharge(drawing a load) is probably going to cause more damage to any motors that are running because of the lower voltage(heat generation). Although there will be some additional heat at the battery, which could then create a plum of hydrogen gas from the sulfuric acid remaining, that hasn't transcended to the plates.

The biggest issue comes, when the charge cycle starts... a shorted cell drops the bat voltage by 1.2 volts, but the charger is hell bent on charging the bat to it's nominal voltage, which it can never achieve. The heat generated boils all of the sulfuric acid into a large  plum of hydrogen gas... the smallest of sparks then ignites the dreaded h-bomb.

It's funny we talk about building stills and refineries on other threads and everyone puts their guard up... but everyday most humans interact with gasoline, batteries, driving down the highway, ...each with the ability to send us to our maker, and at the very least maim us for life. Casual relations with one of the above is a very dangerous thing...accidents come because we disrespect the danger, that we have become so accustomed to.

Experimenting is good...and can be very dangerous.....especially when we don't respect, or understand. So if you want to be an Einstein educate first then experiment.

12 volts when dead shorted will give you enough amps to make black scorch marks, and nick metals....24 volts is almost enough to weld with, and will make little explosions without gas, not to mention that it borders on impossible to remove the devise causing the short. 48 volts you can weld with, will cause a big explosion without gas, and is impossible to remove the devise causing the short because of welding its self. Now add a battery nearby, square the danger if it's in a charge cycle...call the paramedics.

Lloyd

[Lloyd]

WARNING>>>WARNING>>>>WARNING

DANGER MR. WILL

I just watched the video...now there is a boneheaded example of how not to set up a bat bank.

First rule of safety...don't disrespect that which you are so accustomed to.

Bat voltage discharges from the negative plates to the positive plates, and charges, from the positive plates to the negative plates..this has nothing to do with the danger...but in his explanation of how lopsided the charge/discharge cycle is, and this system as proposed makes it better, is unsupported.

As bat voltage(amperage edit for Jens) flows along the surface, as opposed to through the conductor, be sure the conductor  is in line with the voltage drop. In the diagram they show a nice and tight bat bank...but when you look at the video of the bank distributed across many shelves, I don't the see the copper pipe being very efficient. Second can you imagine all of those live conductors(copper pipe pieces) uninsulated, and dropping  an accidental conductor(think wrench...ie anything metal) and it landing on the bank, the video shows a 24 volt sys, so we are are talking near welding amps/voltage....who is going reach their hand in there to grab the wrench causing the short before it blows up the bank???

Lloyd