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Author Topic: Multi Battery Monitor, LVD, Display & Data Storage.  (Read 11234 times)
clockmanFR
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« on: November 05, 2011, 11:03:34 PM »

This relates to "REAL FACTS 48v BATTERY SYSTEMS".
 http://www.navitron.org.uk/forum/index.php/topic,14872.0.html

I now have my PCB strip board and about to start assembly.

My very sincere thanks to Ericw for his wisdom and understanding, and more importantly his knowledge in the programming of the main Arduino Mega board.

The circuit will:-
        Read the 4 battery voltages for one of the 8 banks/strings.
        Display bank number & voltages.
        Then each bank.
        Display would be static for 10 secs.
This means that every batterry is read once per minute, could read faster but this allows the reed relays to operate only 500k times per year. (relay contacts have a maximum operating life).
Every 5th time around write all voltages to file on the removable SD card. This is every 5 minutes and 288 lines per day.
      File format will be CSV so the card can be read by a PC and displayed/plot in Excel.
      Choices for arranging files, 1 per day, per week, keep data for a year etc. Use 2Gb SD cards.
      If one battery is detected at low voltage, say 12.20v – then display info on 4th line – put marker in log file.
If low for 3 minutes the circuit will operate a separate relay that shuts the inverter down properly, it closes the circuit on the Inverter off button. This way the inverter fans etc shut down properly rather that just a dirty great Relay that disconnects the battery voltage to the Inverter.
       This inverter switch operation also log time and voltage to another file.
     A start up switch that has the batteries read faster than normal just before the Inverter is switched on.
      Remove SD card and read data on a PC anytime, possible swap over SD card so not to miss any readings.

This is designed for my particular 48v 4 12v batteries in strings at present up to 8 strings so we can watch 32 individual battery's, keep an eye on each and monitor there performance weakness and charging capabilities. My particular batteries are gel type so SG/ specific Gravity readings of the battery electrolyte/acid is not possible. So using this circuit we can deeply analyze changes and rectify the offending battery before it is badly damaged, IE, I put a 80watt PV panel float charge on it.

Pic 1, Is Ericw’s minimalist schematic drawing, After the first bank of 5 wires all the other banks only have 3 wires. Each of the 32 relays has a double contact so the Arduino will ask each relay in turn to switch on at the correct time for reading each battery voltage so a relay can read battery 2 positive on one switch then become a negative read on battery 3 and so on.
To protect this arrangement and the Arduino board we have transistor arrays with there own power supply.

Pic 2. My PCB layout drawing using standard strip board.
Pic 3. Just about all the necessary parts for assembly.


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« Last Edit: November 05, 2011, 11:06:04 PM by clockmanFR » Logged

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Justme
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« Reply #1 on: November 05, 2011, 11:41:35 PM »

With the large delay in reading each voltage it could look like one battery is failing as it has a lower voltage but in reality there was a short on period high load at that time but not when the other voltages were taken.
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« Reply #2 on: November 06, 2011, 11:48:34 AM »

That's true, Justme,

But in reality the 3.7kw inverter is never fully loaded and in practice the voltage fall, as the batteries are loaded, is relatively slow, especially with the 700ah bank. And at normal working voltage of, start 53.10v down to 48.80v LVD, the time period between readings looks okay at present, but then we could allways alter this in the future. 
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clockmanFR
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« Reply #3 on: November 16, 2011, 10:20:57 AM »

Progress so far.

Reasons for the Multi LVD.

If you recall one of my main concerns was that the UPS Inverter would let the 48v battery string get down to 40v before its LVD, (low voltage disconnect) operated and shut down the inverter. But at 40v it means that the individual battery is now down to 10v, and therefore, according to the wisdom'ites on this forum, the battery will start to receive irreparable damage. This damage is also confirmed as I lost a weak second hand battery very quickly due to the battery getting to low.

So let’s get a LVD switch to shut down at 49.2v, that’s 12.3v for each battery. Again the wisdom’ites on this forum have set 12.20v to 12.30v as a reasonable low voltage that will not cause problems to the battery.

But then I find that each individual battery has a habit of going lower than the average at 49.2v, ie, 12.4v, 12.5v, 12.3v and 12.0v,  and I noticed this discrepancy got expenditially worse as the voltage dropped. But to complicated matters further it was not always the same battery in that string that went low.

For several years now I use the old voltage meter to check how the batteries are behaving, and if I feel one needs rejuvenating, I clip a trickle charge of 100w PV power for a few days to assist that particular battery. I have 2 x 100w panels that are for spring/rainwater pumping but I can switch the power to where it is needed.

The New Circuit Concept.

I do not have vast wads of cash just to buy something similar of the shelf, so I am trying to keep the cost of this project down to about £100.

A knight in shining armour arrived, EricW, and suggested a new approach to this LVD problem.
Lets “get a Arduino Mega Board, like, http://www.ebay.co.uk/itm/Mega-1280-ATMEGA1280-54-I-O-Pin-USB-Cable-Arduino-Compatible-00916-/270826714991?pt=LH_DefaultDomain_3&hash=item3f0e87b76f
  Which is a mini computer that can be programmed to do tasks”. For us it is going to pulse a relay that closes its contacts, and sends the resultant voltage to be read, it does this quite quickly on every relay 32 off on my PCB board, (I only have 24 batteries, 6 strings of batteries at present but will add more soon), and these voltages are stored by the mini computer on to a removable 2Gb SD data card, like this ,, http://www.nuelectronics.com/estore/index.php?main_page=product_info&cPath=7&products_id=20&zenid=2bad6d8f5e9276b82f0cd6cb297c4a2b
  And this unit plugs directly on top of the mini computer Arduino Mega Board.
We are also adding a LCD display that will show what’s going on in real time, like this,,,http://www.ebay.co.uk/itm/20x4-LCD-display-module-HD44780-Green-LED-Backlight-UK-/250772597780?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3a63362c14
   And which particular battery shut down the LVD, and show the voltages of the rest. It was also shows readings at start up of the Inverter, and also show readings just after LVD as the batteries recover.

Now the 2Gb SD data card can be put into your PC in the comfort of your home and all the readings can be looked at, and then you can see which particular battery needs some loving attention, as well as all the other possibilities, of caring for the power supply, but the most important is that you can use the batteries to there FULL POTENTIAL, knowing that the mini computer will monitor and take action, LVD.

The Circuit.
We have used ULN2003 16 pin transistor arrays to trigger the relays, small reed types, I can not specify these at present until Maplin Electronics get some more in, if they do, then I can use the pin layout on a proper fabricated PCB. (Anyone interested).

I have used strip board for the trial, and this can be easily modified where appropriate.
Once you have the main + and – 48v small cables coming in then each bank only requires 3 cables, so on my 6 bank that’s just 1off  5 core ribbon cable for the first String/Bank and then 5off 3 core ribbon cable for the other 5 Strings of batteries. I have spade males fastened at each battery link, and I will keep these cables all at the same length.

Pic 1, The latest modified PCB strip board actual layout. I also have a mirror copy of this so when I turn the PCB over I can see on the mirror drawing the track side.
Pic 2, The PCB.
Pic 3, The track side.


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« Last Edit: November 16, 2011, 10:39:42 AM by clockmanFR » Logged

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Justme
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« Reply #4 on: November 16, 2011, 11:56:59 AM »

LVD's are a problem. If set to save the battery from damage then when under full load they will cut off to soon, if set for full load voltage then at low loads they will allow damage. What is really needed is a method that measures the load & alters the LVD to match.

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« Reply #5 on: November 16, 2011, 07:07:06 PM »

Justme, I noticed that when my inverter is loaded at 3.5kw, then watch those batteries voltage go down. But at say 2kw they steady out at 51.0v and have a slow voltage drop/decline that is reasonably proportional, and predictable, but which individual battery triggers the LVD at say 12.20v or 48.8v.?

As i have allready mentioned the data storage will log all the voltages on a time log as well, so we included a switch that is pressed when the Inverter is switched on for logging the voltage. So if i give some known datum loadings, then by using this system it will give you a graph etc, that tells you proportionality of voltage drop at what loadings, and therefore give you a management system that will optimise your batteries use for different loadings.
 This particular information is important, as it then can be offset against what power is also coming in, in this instance my wind turbines, and therefore with extrapolation you can get an accurate calculation for what goes into the batteries by what is being taken out.

Well, that's the Plan?

However, i see your point, and one could modify the program that for particular timed voltage drop then a different LVD voltage could be activated. In theory i suppose, but i am not the programmer, and we have to get this lot working first!.
 

 
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ericw
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« Reply #6 on: November 16, 2011, 07:49:09 PM »

In principle the load current could be monitored by a Hall effect based current transformer and the cutoff voltage adjusted.
As the whole circuit is tied to the battery being measured it has to be done in an isolated manner.
There are still a few unused I/O pins on the Mega board.
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clockmanFR
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« Reply #7 on: November 19, 2011, 07:55:00 PM »

I do wonder sometimes if any one out there is interested in this?

Would any one be interested in a simplified kit form, and ready to go software. ? That's when we get it going and tested okay. 
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Andy the Inverter Man
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« Reply #8 on: December 31, 2011, 10:39:21 AM »

Progress so far.

Reasons for the Multi LVD.

If you recall one of my main concerns was that the UPS Inverter would let the 48v battery string get down to 40v before its LVD, (low voltage disconnect) operated and shut down the inverter. But at 40v it means that the individual battery is now down to 10v, and therefore, according to the wisdom'ites on this forum, the battery will start to receive irreparable damage. This damage is also confirmed as I lost a weak second hand battery very quickly due to the battery getting to low.

So let’s get a LVD switch to shut down at 49.2v, that’s 12.3v for each battery. Again the wisdom’ites on this forum have set 12.20v to 12.30v as a reasonable low voltage that will not cause problems to the battery.

But then I find that each individual battery has a habit of going lower than the average at 49.2v, ie, 12.4v, 12.5v, 12.3v and 12.0v,  and I noticed this discrepancy got expenditially worse as the voltage dropped. But to complicated matters further it was not always the same battery in that string that went low.

For several years now I use the old voltage meter to check how the batteries are behaving, and if I feel one needs rejuvenating, I clip a trickle charge of 100w PV power for a few days to assist that particular battery. I have 2 x 100w panels that are for spring/rainwater pumping but I can switch the power to where it is needed.


I'm quite taken aback by the statement "the battery will start to receive irreparable damage... if it goes down to 10Vdc".
It's simply not the case.
As some of you know I have run my own UPS business for the last 10 years.
And over that time I have tested 1000's of batteries.  Both in UPSs and tested batts individually.
Running a battery that is in good condition, down to 10Vdc does no irreparable damage.
If that was the case then every UPS would only be able to handle 1 power cut before the batts needed replacing.
Also battery manufacturers quote the capacity of a battery down to around 10Vdc.  They wouldn't quote a voltage to run down to, if it was going to damage the battery.

When a batt is run down under load, the batt will suffer some 'wear & tear'.
I.E. the are only so many times a battery can be cycled (discharged & charged).
The depth of the discharge effects the number of cycles.  Maybe this is what was meant by the 'wisdom-ites'?
From a Yuasa NP24-12 datasheet ....
LIFE EXPECTANCY:
STANDBY USE 3 to 5 years
CYCLE USE (approx.)
100% depth of discharge 250 cycles
50% depth of discharge 550 cycles
30% depth of discharge 1200 cycles

It is true the battery will have a shorter life if 100% discharged compared to say a 30% discharge.
But then you need a much bigger battery bank if only going to 30% discharge.
And don't forget batts suffer wear & tear all the time they are being trickle charged.
If you want to increase the life time of your batts then stop charging when they are fully charged.

12.3Vdc as a low voltage cut off point is very high indeed.
I often test batts from UPSs individually.
E.G. a 12v 7Ah batt with a 100 watt load.
Once it is under load, the starting voltage is about 12.3Vdc so would have no run time if I used a cut off of 12.3Vdc.
I personally run down to 10.5Vdc.

I guess my post will generate some questions.  Please ask on here and I will try and answer.

Regards
Andy the UPS, Inverter & Battery Man
PS: I have loads of UPSs & Inverters for sale.
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Justme
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« Reply #9 on: December 31, 2011, 03:01:30 PM »

There is a huge difference between UPS & off grid battery use.
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Andy the Inverter Man
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« Reply #10 on: December 31, 2011, 03:42:28 PM »

There is a huge difference between UPS & off grid battery use.

Err, there isn't that much difference (relating to the batts) assuming you're using SLA AGM batts.
What "huge differences" do you think there are?

Off grid batt use is more cyclic, but I've already covered the depth of cyclic discharge.
Regards
Andy the UPS, Inverter & Battery Man
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clockmanFR
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« Reply #11 on: January 01, 2012, 02:31:27 PM »

Hi Andy,
Its true i am afraid, there is a difference between Inverter UPS battery systems than Off Grid battery banks.

As i originally said somewhere in my posts, when i allowed the UPS LVD to function and auto shutdown at about 42v for a couple of months, i very quickly lost 2 of my 12v 110ah battery's, with 2 others damaged, (would not hold voltage). To me caring for the expensive batteries is a must as i need them to last as long as possible and at the same time give their best.

Listening to the wise old sages on this forum who are actually using batteries Off Grid day in day out, made me understand real operating usages with batteries. And it was seemed that 12.2v to 12.3v LVD was a good way to care for operational batteries without causing them excessive deterioration.

Again, i will report back on how this 12.2v LVD works with my particular system, but with my observations to date, the last 18 months my 20 12v 110ah batteries have behaved. But the new circuit should give me more accurate data.

Also recharge times are not consistant like a UPS when it reverts back to mains supply, some times my batts get a quick charge if its sunny and its blowing a good wind, sometimes becalmed it can take days just trickle charging from overcast solar PV.  Again, the new circuit data will give me info on the most efficient charging rates. 

Sustainability matters to me so the care and quality of my equipment and its longevity is very very important.

 Unfortunately as i get older and wiser, i realise that a lot of data sheets issued by manufacturers is not allways telling realistic tales.. Roll Eyes
 
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clockmanFR
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« Reply #12 on: January 01, 2012, 02:41:52 PM »

Now that Crimbo is over and the new building is usable, (orders by her indoors to get it finished by 21.00hrs New years eve),  i can at last get back to this circuit and start messing with the programming bit.     signofcross
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biff
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« Reply #13 on: January 01, 2012, 03:22:56 PM »

lo clockman,
           i hope you have had a good christmas, your new circuit is truly impressive and a credit to your know-how. as you know we all have our little problems and work to improve our lot.its funny,but i worried for ages that our turbine would overspeed because out controller was in danger of frying and losing the grip on things but there i was with a few boxs of the said controller and all i had to do was just connect another controller to the bank bring my resistors up to 4kw which would have been more than enough to weather any force 8 unattended,
     we live and we learn,our weather has been truly horrible,wet ,slushy,windy and dark so nothing has been done to our turbine,instead we came through christmas using our generator for so many hours each day and the new pv works very well but of course needs a bit of sun.
                                                                                                                                         biff
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clockmanFR
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« Reply #14 on: January 02, 2012, 06:43:01 PM »

what oh biff,

Good news that you had a good Christmas, sad to here you have no Sun, been lovely today but squally showers, i get 5 minutes warning as i can see the rain coming.

Its true, your spot on as usual, things that you worry about can be rectified with a little thought. but i was so sorry to here how your babe 'bit the dust'. My No1 is squeaking each time it turns into the wind, (needs Grease) No2 needs balancing, No 3 is down and is under reconstruction (properly).

Regards PV and trackers, how's your swing system coming on?
Mine, the Mrs spent 2k on bits for the gite to get it operational for New Years eve night, 4 staying, but it bust me getting it operational, the skirting boards and mouldings still had wet Caulking on the primered timber surfaces, as the folk settled in.
Today, just fitting the stairs bottom door and mouldings and caulked up.
 
Mrs has let me off for the rest of this week as i have the new faster and lighter Pedal car to build, success on that front as i have got another Engineer, Pascal he's French, to start manufacturing bits and has joined the team. We are putting 2 cars on the Normandy circuit, 6 races this season, but hopefully others will take over the load? (they all want to get on the French TV)  Roll Eyes

My PV Trackers are going ahead but i might have to scrape around the barrel ab-it to find 3k as the Mrs spent 2k.  Sad spentrpe   

Happy New Year biff, and to Mrs biff,  and the hounds etc.
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