really confused about series parallel cross tied charging and discharging

[Lloyd]

Jens,

You better go read about circular mils in sizing wire, how it relates awg, sae and the various societies.

Lloyd

refer to rule #2 Semantics is for sitting around the fire drinking stumpblaster, as long as noone is belligerent.

[mobile_bob]

in any case the video illustrates how the current must travel on the outer part of the jumpers, because they
are made of copper tubing!



not much current going to flow down the middle of those conductors!

bob g

[TimSR2]

For a couple years I worked for a Club Car golf car dealer as a mechanic. One day I was in an underground car barn trying to revive a neglected fleet, to test and replace whatever abused batteries and get the cars ready for the season. This one cart was dead, really dead, I think about 8v showing for the 36v bank. CC used automatic chargers that were new at that time (1992) They required about 12v to detect the connection and start their cycle.

So this cart would not initiate it's charge so I could charge the bank and take my readings. No problem, I thought....I'll just use some automotive jumper cables and parallell it to the cart next to it to get the charger to initiate. My father had always warned me of the dangers of letting the jumper ends clash against each other on the ground, so I was taught  the habit of clamping one clamp on the handle of the other. That's how Grandpa did it, that's how Dad did it. Bad Habit!

The jumper cable had developed a crack in the insulation on the handle, so I inadvertently hooked up a dead short, with #0 cable  to 6 fully charged Trojan T105's, with my face 2 feet away from the top of the bank.

The bank exploded instantly. 4 of the 6 batteries blew the tops clear off in a great flaming geyser of sulphuric acid spray and burning hydrogen and chunks of plastic shrapnel. I was working alone, was blinded by the explosion and disoriented. It was pretty scary. I very nearly lost my eyesight. I lost my eyelashes, half my hair and eyebrows, and all the clothes I was wearing.

Be careful with those batteries guys. Know what you are doing before you hook them up.

TimSR2

[Lloyd]

Tim,

Thank someone(god) whom ever, you are here to recant that story......my point exactly about being complacent with those things we are all to familiar with.

I don't know whats more dangerous...complacency....or ignorance...from my life experience (many years ago on the volunteer fd).

It's good to have true life stories that tell the true danger...thanks.

Lloyd

[Ronmar]

And that is another serious hazard with series/parallel banks.  Each series string MUST be fused ahead of where it is tied in parallel with another string.  This fuse must be no larger than the peak operation current for that string(determined by the size of the load).  If one of the series batteries shorts(or a conductor falls across a battery's terminal), it then becomes a load for the other series strings to instantly attempt to dump all their stored potential into.  A fuse on each series string just adequate to provide for normal ops should help keep this type situation from becoming a  complete meltdown.  I can quite comfortably weld 1/4" plate together with 2 car batteries in series.  Fully charged they are good for half an hour of welding.  Batteries are nothing to be taken lightly...

DC current capacity of wire is mainly based on it's cross sectional area.  1/2" copper pipe has about the same cross sectional area as #6 AWG wire.  Good for about 80 amps?

[Cornelius]

Loonogs:
First, i'll second the others here; 96VDC are not something to fool around with. With only one series string @ 65Ah, you'll have over 6kW, maybe ten times that when short circuited... That's a lot of power if something goes wrong.

Now, to your batteries (to be).
Try to get equal batteries, preferrably some that has been in a bank together before. That way, the chances that the batteries are in similar conditions are good.

Now, charge up the batteries and at the end of the charge, check and top up the electrolyte level with distilled water. Let the batteries sit with a maintenance charge (13.6-13.8V for a 12V battery) for some hours after that.
If you want to do this a bit more 'scientific', measure the Specific Gravity for each cell and note it down in a table. Actually, it's a good idea to measure the SG anyway, because that's the best way to really get an idea of the batteries health. Measure the SG no shorter than 4 hours after finishing the charge, to get an accurate reading.

With the batteries charged, apply a C/20 load (1/20 of the rated capacity) to each 12V battery, and start the clock. Stop the clock for each battery when you measure 12.0V with the load connected! Measuring 12.0V with a load connected should equal around 50% discharged, so if it took 10 hours to get down to 12.0V with a C/20 load on your 65Ah batteries, it would mean that the capacity of the battery are at 100% of the rated capacity.

Now, charge the discharged batteries at within a few hours. Take a SG reading after an hour after disconnecting the load before charging if you want.
Repeat this procedure at least 2 more times.

After 3 rounds with charge/discharge this way, you should have revived the batteries as much one can hope for.

If the SG of the cells are very different, you should do an equalizing; charge at around 15.0V for a couple of hours. Keep an eye on the electrolyte level, because heavy gassing will occur. (good ventilation and no sparks are a must. )

One thing to remember: most 'normal' batteries' Ah rating are at C/20 (your 65Ah batteries will provide you with 20 hours of 12V with a load of 3,25A), and the discharge curve/time are not linear. Discharging your batteries at C/5 would not give you 5 hours with a load of 13A; probably more like 2-3 hours.
Keep that in mind when drawing 3kW out of your ups.

[Lloyd]

Here is a Peukert equation for a 65amphr bat

Peukert               Total Amp Discharge               Corrected       Hours Rate        Time         Amps          Available 0.1         500.00           0.13           65.00 1.3        50.00      1.30           65.00 2.6        25.00      2.60           65.00 3.9        16.67      3.90           65.00 5.2        12.50      5.20           65.00 6.5         10.00      6.50           65.00 13.0         5.00            13.00           65.00 19.5         3.33            19.50           65.00 26.0         2.50            26.00           65.00 32.5         2.00             32.50           65.00 39.0        1.67            39.00           65.00 45.5        1.43            45.50           65.00 52.0        1.25            52.00           65.00 58.5        1.11            58.50           65.00 65.0        1.00            65.00           65.00 Typical Factory Load   Spec                3.25        20.00      3.25           65.00

[Cornelius]

That chart cannot be right, unless you use a peukert's exponent of 1.0, which are never right for lead acid.

[Lloyd]

Cornelius,

That chart is an excel spreadsheet, with a Peukert factor of 1.3. It is not temp corrected, it assumes a temp of 80 degrees F. All corrections for temp should be made, as they will affect the bank, if anything over ten degrees or more either side.

Many bat manufactures don't ascribe, and do the 20 hr rate.

Lloyd

[Cornelius]

Getting a bit off-topic, but...

Regardless of temp correction, i'd say that your spreadsheet would be useless in real life.
According to the chart above, the battery are  providing 65Ah no matter what the draw is.

Let's take a load of 13A; i calculated that we could draw 13A for 3.3 hours, giving us 42,9Ah out of a battery rated 65Ah @ 20 hours with a Peukert exponent of 1.3.

Here are probably an answer for why: http://www.smartgauge.co.uk/peukert2.html

Take a closer look at the math here: http://www.smartgauge.co.uk/peukert_depth.html

[Lloyd]

Cornelius,

I don't mean to seam short but, it appears you didn't understand the chart. According to Peukert(see the chart) with your load of 13 amps, the bat would last to about 5 hrs...of course un-corrected for temp. I think you failed to see that the right-hand column was the total amphr bank, and not the hrs remaining according to Peukert.

Lloyd

As asked before I'm happy to post the excel spreadsheet if someone can point me how?

Believe me I wanted, in the beginning to hang my hat on the guy at smart gauge...but atlas I didn't
remember the dog aint linear, it's exponential.






* 4* When I was a kid me older brother, told me to shite in one hand, and wish in the other, see which one gets fuller faster?

[mobile_bob]

if you can save your spreadsheet file as a pdf, txt, jpeg
you can then attach it to a post directly just like you do a picture

otherwise i am not sure how to get it posted and retain it as an excel spreadsheet

bob g

[Lloyd]

Cornelius

I'll be civil

Evidently I didn't refresh the spreadsheet    Cornelius , I hope you'll accept my apology, this is the updated spreadsheet.

                           Peukert          Total Amp
Discharge               Corrected       Hours
Rate        Time        Amps             Available
0.1       1313.26      0.05      170.72
1.3      65.82      0.99      85.56
2.6      26.73      2.43      69.50
3.9      15.78      4.12      61.54
5.2      10.86      5.99      56.45
6.5       8.12      8.00      52.80
13.0       3.30      19.70      42.88
19.5       1.95      33.38      37.97
26.0       1.34      48.52      34.83
32.5       1.00       64.85      32.58
39.0      0.79      82.19      30.84
45.5      0.65      100.43   29.45
52.0      0.54      119.46   28.29
58.5      0.47      139.23   27.31
65.0      0.41      159.67   26.46
                  
13      3.30      19.70      42.88


Lloyd,

It's not the stumpblaster it's the ****Cognac

[Lloyd]

Bob,

I'm up late you're up early.

I still don't know how to attach, I can link, but not attach.

As a matter of fact I can't even figger how you guys, attach the little thumbnails that click and get bigger...It seems I can link a big pic, not just attach??

Lloyd

[Cornelius]

You have the '+Additional Options' link on the left bottom of where you write; there you can attach the .xls file if .xls filetypes are allowed, that is...

What i'd be most interested in, would be to see the formula used in the spreadsheet...

And i'm NOT reading your chart wrong. I mean no disrespect, but take a closer look yourself and you'll see that it cannot be right. According to your chart, drawing 13A would give you 5 hours of 13A, which equals 65Ah, but that wouldn't happen in real life with a battery rated at 65Ah at C/20.

Try the spreadsheet available from those guys at smartgauge: http://www.smartgauge.co.uk/calcs/peukert.xls and you'll se that you'd get numbers that looks nothing like your chart, but will be close to correct in real life.

As those guys at smartgauge states: the basic Peukert formula: T=C/Iⁿ are only correct when drawing 1 Ampere. (Where: I = the discharge current in amps, T = the time in hours, C = the capacity of the battery in amp hours, and n = Peukert's exponent for that particular battery type.) It cannot be used un-altered for other draws...

Again, i mean no disrespect.

Ahhh.
I'll be fair to you; i prepared an answer, and saw your last reply, so i've just striked out my reply to you; my apologies for being hardheaded. (but i was right, wasn't i? )

Now, mixing Cognac into a spreadsheet does seldom compute...

I'm glad we got it sorted.