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Author Topic: How to make 24v bank? (Cabling wise that is)  (Read 2529 times)
Stevieboy118
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« on: August 18, 2015, 07:14:07 PM »

Just laying out some batteries to breathe life into the xantrex and I'm trying to work out the best way to make the 24v this unit needs.

Do I series a pair of 12v batteries to make one 24v battery, then parallel a few of these 24v pairs together....
OR do I parallel the 12v batteries into two "big" 12v batteries then series the two "big" batteries to make the 24v?

Thanks.
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biff
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« Reply #1 on: August 18, 2015, 07:20:37 PM »

Believe it or not Stevieboy,
                       There are 3 different ways of doing it right, good, better and the best. but I am trying to remember the link to the wiring diagram.
       Help! banghead I will get back to you.
                        Biff
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Stevieboy118
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« Reply #2 on: August 18, 2015, 07:26:55 PM »

That rings a bell actually, something about keeping link lengths the same I think...

So multiple 24v pairs going to a common point then onwards to the inverter sounds best.

I think..
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guydewdney
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« Reply #3 on: August 18, 2015, 10:17:07 PM »

Sure this was on battery university dot com?
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Justme
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« Reply #4 on: August 18, 2015, 10:46:37 PM »

Its on the Smartgauge site.
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biff
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« Reply #5 on: August 18, 2015, 11:11:22 PM »

Thank you Justme,
                  I have a memory like a hen,
     Stevieboy, It is not quite as straightforward as you might think in 24volts, The 3rd way is the best,there is quite a bit of lead swopping about but the link will keep you right.
     If in doubt, do not chance it and sit and draw it out on paper, I believe that the 24volts is the tricky one. I never had a problem with the 12 v, 48v , or the 120v  but the 24
    gave me the jitters one evening, freeze
                                                               Biff
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Scruff
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« Reply #6 on: August 19, 2015, 12:37:36 AM »

Any way that has the same wire gauge interconnects and total wire length to all cells with the main take offs balanced either equilibrium or on opposite batteries.
Best is the system that every battery has the same resistance as seen by the load/charger
Perfect is impossible.

The easiest way is make the parallel battery links all the same length and connect them to a hub or bus while connecting the series batteries with solid bar or super-short high CSA cable. Then connect all charge and distribution to the bus.

You can get arty and the same effect for a few less links but it only really works with certain bank sizes.
« Last Edit: August 19, 2015, 12:43:00 AM by Scruff » Logged
Stevieboy118
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« Reply #7 on: August 19, 2015, 09:23:45 AM »

Right, thinking two strings of 12v batteries using method 3 or 4 then series the common links before connecting to the inverter.

p.s. is it normal to giggle like an idiot the first time you boil the kettle (700w) from batteries?
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oliver90owner
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« Reply #8 on: August 26, 2015, 10:46:18 AM »

p.s. is it normal to giggle like an idiot the first time you boil the kettle (700w) from batteries?

Just passed this, for comment, to my wife.  She said ''No''.
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Scruff
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« Reply #9 on: August 29, 2015, 02:47:05 AM »

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biff
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« Reply #10 on: August 29, 2015, 09:16:04 AM »

Hi Scruff,
       I always seemed to stumble for a while on the 24v grouping,
              The cables in the top left hand Diagram are all the same length to the busbar, Difficult to draw it even though Scruff did.
             I think that this is the preferred route, I you want equal discharges and charges.
              The negatives on the left centre,run into the reds on the right in series,
        Once you go over 4 batteries, you need to go this route.
     24v grouping did trip me a couple of times,even after I had drawn it out, In the end, I used an inline fuse to test the system before finally connecting, Now you would think that such a simple bit of
     wiring would be easy peasy but when you are in the middle of it, it is a different story.
    Working on 120v x 100ah packs was so easy, Just out of one 100ah x 12v and into the next in series and the leads at either end. I initially went for this system because i thought that the Batteries would get a fair deal. That is how it should have been. But over the following months,I worked with 20 x 100ah x 12v powersafe agms and found that there was always one batter in the row that was getting picked on, I think it was the 3rd from the left bottom or 3rd from the right top. IN the beginning I suspected the batteries were not quite what they should have been, I then invested in a few pallets of Yousa 100ah x 12 v and connected them up carefully in series, 2 rows of 10 with all the cables equal lengths in the bank. Yousa is the best SLA that money can buy that I know off and
 Again I noted in the beginning that the 3rd from the ends were getting punished, but after I moved a few around, They seemed to settle down and get along better.
                                                                                 Biff
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biff
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« Reply #11 on: August 29, 2015, 09:33:19 AM »

         "Is it normal to giggle like an idiot the first time you boil the kettle "700watt) from the battery"
    Someone like me Rab,
                                   Will still dance with delight and laugh out loud when I score a goal, That is what I do sometimes still when a little miracle occurs. Renewable energy achievements are little miracles and big miracles to some one like me who has been reared with very little knowledge of electrickry,
  Yes,!  I can well understand someone being so happy boiling a kettle that proves that his system works,, To me, it would be perfectly normal.
 Yet I perfectly understand that there are people who know that all these things are as normal as rain.
  Sometimes, I come in and Bend her ear about something that I am trying to do, She will put the kettle on the hob and share my excitement,
 Of course then I went and crashed the turbine and dropped to the back of the class.
         All is good.
                          Biff
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Scruff
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« Reply #12 on: August 29, 2015, 11:34:46 AM »

They're all the same Biff for intents and purposes.
The only difference is the contact resistance and the length of cables or bar which is in the order of mΩ.
Bar is slightly better by ~ 4mΩ per link because you don't have the resistance between the cable and the lug.
For instance the leftmost two spec-ed with 35mm≤ conductor swings in favour of the lower one by 0.7W with a 100A load, after calculating that I didn't bother with the rest because I doubt most people would care.

All you need to do is equalise the series resistance of each string to the main bus.
I dunno about 700W but I'm pretty happy with my power station producing 40W to post this.  bike
« Last Edit: August 29, 2015, 11:41:51 AM by Scruff » Logged
biff
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« Reply #13 on: August 29, 2015, 12:51:58 PM »

In my first installations,
                       I used a round insulated copper gas or oil pipe,10mm I think,
          When i got to where the connection on the battery pole was, I removed enough insulation,flattened the pipe,drilled the hole and bolted it on.
      It was just pure chance that I used this method because I had plenty of spare oil pipe. I did think at the time that I would have had a better job with solid cables but then I discovered that the
     round copper pipe actually carried the current better than the solid wire one. The current travels around the pipe or wire, not through it, so the shiny round copper surface was the best job of all.
    That what I was told at the time.
     Our first big joy was our 800watt microwave oven, Then we bought a dyson vacuum cleaner that was happy with 600watt but it fell apart(even with TLC) after 3 years. Then we got a cheapie B,N,Q     vacuum cleaner for £64.00,with soft start and it outperforms the Dyson everyway. Last but not least was our 2050watt washing machine which our chinese inverter can handle around noon,
  These were little battles that were won over as period of time. Of course, before all that, there was always the generator in the background but now we seldom ever use it apart from pulling it out to check it and make sure it is ok. Living off grid and not using fossil fuel is all about balance and making do with what is necessary without skimping. Easier said than done. It takes time. Every off-gridder like me, will tell you thast our biggest breakthrough came with the drop in PV prices and it is very true. PV makes harvesting energy easy, all you have to do is find a way to store it. In out case, 2 ton of forklift cells (60) and 500ltrs of hot water between two tanks.
   Learning all about batteries, is a good place to start, Grin
                                                  Biff
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Scruff
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« Reply #14 on: August 29, 2015, 01:17:28 PM »

Hi Biff,
I believe you are referring to the skin effect which is a phenomenon exclusive to Alternating Current.
https://en.wikipedia.org/wiki/Skin_effect
This is the reason domestic installations ought to be stranded cable not solid core 'cept tis more expensive so tisn't.

DC uses the whole conductor so bar or solid core is better if flexibility isn't an issue. Copper work hardens so solid core is not reliable the same way stranded is.

What you need to look to is conductor cross sectional area (CSA) for it's true rating. Just a guestimate here but say 10mm pipe flattens down to 15mm with 3mm walls = 15mm X 6mm =  90mm≤ CSA which is aboot 450A according to my leky bits catalogue.
« Last Edit: August 29, 2015, 01:31:21 PM by Scruff » Logged
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