Battery pack wiring configuration

[Usman]

After reading an article in the IEE journal on importance of proper wiring of a battery-pack for a specific system, should be different from another, depending upon the no. of charging sources &  a few other parameters, I started to investigate on that.

I came across a website with the following wiring diagram. the unique thing about that is, the sub-wiring in between the packs, i.e. the low-amperage parallel wiring! (dotted lines)

More information is also there if someone is interested & have patience to go through it all.

I have 24 units of 2V batteries that I intend to tie-up in 48V configuration, to accomodate charge from a 2KW solar array and 2 units of 2KW wind turines. Also a diesel generator as back up to charge up batteries via rectifier diodes.

I am using a TS-60 as a charge controller.

I would like to know:

1. -The most effective wiring technique for the battery-pack.
   
2. -If thats a more effective way to connect the batteries (as in the figure) then what about wiring solar panels in the similar manner?
   
3. -Any suggestionson on the system schematic, as in where to connect the
   
2. x 2KW turbines,
   
20. x 130W/12v solar panels,
    
    

back-up diesel gen,

charge controller,

Dumpload,

and DC loads + AC inverter.

I till try to include a schematic on it in a later posting. Any input would be apprecited.

Thanks, Usman.

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"In order to achieve the desired 48V bus, the 20 12V batteries will be wired in series to make strings of 4 batteries (48V), and then each of the 5 strings will be wired in parallel in order to increase the amp-hour capacity. The electrical connections are shown in Figure 9. The straight lines show which terminals are connected with custom-fit, insulated copper buss bars, for the purposes of achieving the 48V bus. The curved lines show the series strings connected in parallel with welding cable in order to achieve proper energy

capacity.

The strings are paralleled in a fashion such that there are a minimal number of

junctions or terminal connections. That is, if you count the number of junctions that each string would have to go through to get to the DC bus, this arrangement has less than just connecting the strings linearly (each string paralleled with the two adjacent strings).

The dotted lines represent small cross-link wires between common voltages

(12V, 24V, 36V) whose purpose is to ensure that the batteries discharge evenly, given that there are so many in series and parallel. These lines technically should be very low current bearing. Class-T 400Amp fuses are attached at the end of each 48V string of 4 batteries, before their parallel connection, for safety and disconnect purposes.

The batteries will be arranged evenly spaced in a rack that is 4 batteries wide by

5 rows high. The 48V strings of batteries will make up each shelf of the rack, and the

cabling will be used for paralleling strands extending up the sides of the upright battery rack. The buss bars will be used for the three connections internal on each shelf level, between each two adjacent batteries".

[SparWeb]

I like the configuration.  Their objective is to maintain as much balance between individual cells as possible.

Through multiple charges and discharges, some cells in a bank will get weaker faster than others.  This is normal, and you need an equalization charge once in a while (which basically over-charges them all) to bring the weak ones back up to par.  Not all battery types can be equalized, so this extra wiring would help extend the life of, say, valve-regulated lead-acid batteries.

The heavier connections on the ends are arranged in a fashion that allows disconnection of some strings, but the fusing doesn't make sense.  There are also unequal lengths of wire, adding a miniscule extra resistance between the right-most battery string over that to the left-most string.

I am not certain that the authors of the diagram gave much thought to what happens after one of the fuses blows.  Those cross-links would leave a bunch of batteries still in the circuit, even if one fuse blew at the + of the string.  Also: since some fuses are in parallel, and others are in series with the rest, I think some faults could cause a "firecracker" kind of failure where one goes first, the rest pick up the extra balance of load, hence overloading them, and so on...  Or, the first fuse in the series will blow first, shutting it all down, so what were the other ones for?  The fuses do protect the wires, I'll grant them that.

With a bit of work, the cross-linking could be made to work as intended, but they may need fusing of their own - making this pretty complicated.

I think VolvoFarmer and others have said that it's best not to put too many strings in parallel with each other.  The author of the diagram may also be aware of this rule of thumb, too.

You said you have 24 cells of 2V that you will hook up all in series for 48V, so all this is pretty academic to you, isn't it?

It's a bit less academic for me, because I actually have 24 cells, (6 Volt VRLA's) and the cross-linking idea sounds neat.  I've been measuring quite a variance in cell voltages and this might help.  Off hand, I would connect my cross-links with 12 or 14 gauge wire, but I would put a fuse in each of only about 10 amps or so.  Or maybe better, that's an application for a "current limiter", instead.

Thanks for posting that.

I only have one turbine, so my system schematic won't deal with your specific question, but it is posted with the rest of my files.  It may be of use to you.  Your web browser may re-size the image because it is quite large.

System Schematic (as of January 08)

[Flux]

Fuses in battery strings look sensible to those who have never used a battery. The idea is presumably that a faulty cell in one string will take the fuse. In real life the remaining cells in that string will over charge to compensate. The fuse will not blow.

You would not blow the fuse unless a complete group of cells failed ( that would have other effects that you would notice). I seriously doubt that the fuses will contribute anything other than a volt drop and extra cost.

There is good reason to keep all the connecting leads the same length and bring them to common points, but if they are short and you keep things symmetrical there is no need to take this to extremes.

I assume you meant 12v not 2v cells as a series string of 24  2v cells presents no problem.

Flux

[veewee77]

Here is how I would do this. . .

Leave the batteries sitting as they are there and take out the crosslinks.

Strings numbered 1-4 across the top. . .

On the plus side, connect the plus side of the bus to 1-a, 2-a, 3-a, 4-a in that order.

Then on the minus side, do it just back wards. . .

On the neg side, connect the minus side of the bus to 4-d, 3-d, 2-d, 1-d.

This will balance the resistance between all strings and charge them equally.

Keep all interconnects as close in length as possible.

Doug

[Usman]

Thank you all for contributing.

I agree with Flux on unnecessarily using too many Fuses.

Here I have a further comment; I have also noticed in quite a few diagrams emphasizing on getting the +ve lead on the opposite side of that of -ve lead, I hope you got my point. In simple words, the +ve cable should be pointing towards the East and the -ve from the last battery towards the West. Is that important or effective to any extend?

Thanks, Usman.

[SparWeb]

"I have also noticed in quite a few diagrams emphasizing on getting the +ve lead on the opposite side of that of -ve lead, I hope you got my point."

That's what I do.  The + terminals are connected together in a row; so are the - terminals.  The charging leads are on, say, the + Northwest and - Southeast corners, while the inverter leads are on the + Northeast and - southwest corners.  It's still not a perfect balance because I can charge at 20 Amps and the inverter can pull over 100 amps.  If you look carefully, you can see that on my schematic, but I admit I wasn't trying to draw that clearly, so it isn't obvious.

[Usman]

Thanks Steven,

Before you sign off, I thought you could as well look into the second part of my posting.

Its very basics, but I am investigating connecting the 20 pieces of 130 watt Solar Modules for a 48V configuration in the most efficient way.

I asked the board if a similar connection to that of the battery-pack, as per the given diagram, would be any better i.e. low gauge wire sub-connections.

Secondly, do similar 'East/West out' rule for the +ve/-ve cables also apply to the solar modules, as in case of the batteries.

Thanks, Usman.  

[kitestrings]

Hi Usman,

I have a few comments:

First, many batteries do not have the posts or flag terminals in line dead center down the top of the battery as in your drawing.  Maybe yours do.  If they are staggered (+NE, -SW), I've found that turning every other battery (180 degrees) within each series string allows for shorter connections.

I would dump the fuses for the reasons stated.  They also are expensive and not mechanically well-suited to bolting to a terminal/flag as some folks suggest.  The alternative is a fuse-holder and then still more connections.  My opinion is the less (soldered) connections you have the better.

On the parallel connections you'd have varied lengths on the cables as Stephen mentioned, but you also will have to connect four very large cables and ring terminals to a single post/terminal.  Personally, I'd work to avoid this.  The cross-corner strategy makes sense to me.  

Lastly, don't overlook venting.  If you vent them properly you'll have a lot less corrosion.  The cross links seem logical.  I'd have to weigh the added connections and complexity against say, periodic rotation for roughly the same result.

Good luck,

-kitestrings

[SparWeb]

Hi Usman,

Sorry I couldn't get back to this posting sooner.  Weekends are my time to "play" and I don't spend much time with the computer.

These parallel and series connections all relate back to Ohm's law, so there isn't much to say about parallelling your solar panels that you should not already have from other sources.  If you can't ask the manufacturer or distributor where you bought them, then it's up to you to work out the connections that match the battery system's voltage.  I don't know what kind of panels you have.

This south-east / north-west idea is just one way to make the cable lengths roughly equal from any given circuit to another.  It works for me, and bear in mind that I don't have any solar panels, yet.  If there are any nuances to these installations, there are better guys to answer that than me.

Checking with the manufacturer is the best way to do it right, without blowing the warranty.