Author Topic: Solar power battery died out not according to calculation  (Read 6045 times)

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Offline orange

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Solar power battery died out not according to calculation
« on: September 10, 2008, 06:20:30 AM »
Guys

I am pulling my hair off over this problem.  #-o  Will greatly appreciate any clue, hints, comments, no matter how small.  =D>

My remote unmanded anemometer station total load is 450mA. It is powered with a 44W solar power panel. I use a 70AH 12V battery(1). So the battery  should last 70AH/(450mA*24H)=6.5days in total darkness. I am not using a battery charging regulator, so the  44W solar panel(2) charge directly to the battery without going through a regulator.

For the past 3 weeks, it has been rainy and cloudy in Singapore but occasionally with 1-2 hours strong sunshine per day.(3)

These few days, my system went dead at 2-4am, and starts up again at 9-10am, indicating battery flat during nighttime.

I am puzzled by this, by experience of other suppliers a 5 days backup battery is normally adequate for Singapore weather even in rainy season. The yearly average peak sunshine hours of singapore is 4 hours.


I am thinking alone these angles and probabilities, what do you guys think? :


a. I did not install a battery charging regulator, thus during cloudy days, the battery cannot be charged properly and thus wear out quickly. The battery has only been in operation for only 3 months. The regulator was not supplied by system maker saying that for this small current solar system it is not needed.

or

b. The solar panel is bad in quality, and thus cannot charge the battery properly. I am not sure who and where is the manufacturer(china maybe?). But other Japanese brand is twice as expensive.

or

c. Though I placed 500g of drying agent in the panel box, but I am thinking that the high humidity caused small current leakage in the system and thus battery power dissipated more quickly.

or

d. The battery is bad in quality?

or

e. THe anemometer is outputting 4-20mA to a datalogger/modem. I used a 4-20mA signal multiplier and branched the 4-20mA signal to another datalogger. THe multiplier is eating a lot of power(about 2x,3x the original system). Since we have put in this new multiplier and a larger battery, we have been having battery flat problem. I dont have any rational clue but the multiplier "feels" very suspicious.   


Did I miss any angles? What is your experience?

Advance thanks.         





Notes:

(1) Battery specs: geocities.com/bambinorama/YC70-12.pdf

(2)Solar panel specs:
(cascade two pieces)
Nominal Max output(PM)  22Wx2 (@1kW/m2.25degC.AM1.5)
Nominal Open circuit Voltage   18V
Nominal short circuit current   1.65A
Nominal Max Output Voltage    14.4V
Nominal Max output Current   1.5Ax2
Nominal weight  3.0Kg


(3) Singapore pass twenty days weather summary:
     http://www.wunderground.com/history/station/48698/2008/8/9/MonthlyHistory.html           

http://www.wunderground.com/history/station/48698/2008/9/9/MonthlyHistory.html

    A typical cloudy day:  http://www.wunderground.com/history/station/48698/2008/9/6/DailyHistory.html   

Offline Anthony

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Re: Solar power battery died out not according to calculation
« Reply #1 on: September 10, 2008, 08:16:54 AM »
My guess is the battery is draining at night back thru the solar pannel. You need to place a diode in the circuit to keep this from happening.



Thanks,
Anthony
WB8YUE

Offline Garth Bock

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Re: Solar power battery died out not according to calculation
« Reply #2 on: September 10, 2008, 09:40:07 AM »
My guess is the battery is draining at night back thru the solar pannel. You need to place a diode in the circuit to keep this from happening.



You beat me to it. If there is no solar charge regulator or blocking diode, the batteries drain backwards through the panels in low or no sun periods. Having the panels connected directly to the batteries to the weather station as it sounds is not a good idea. The current and voltage swings could eventually damage the equipment. Also during long sunny periods the panels can overcharge the batteries ruining them ! A solar charge regulator such as a Sunforce Solar charger, regulates the battery charge, disconnects the batteries when charged, disconnects the batteries when they fall to a certain low limit, and provide regulated power to the connected devices. The main fact is to have some sort of regulator to prevent the batteries from falling below what is called depth of discharge. Go past that limit too many times and the batteries can either be damaged or be harder to recharge more and more. While a blocking diode is inexpensive, a solar regulator\charger is one step better. I know...I have one that will soon be running my wireless web cam.

Davis VPro2,VWS,WL,VVP,WD,WDL,Cumulus,WV32,VPLive

Offline SLOweather

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Re: Solar power battery died out not according to calculation
« Reply #3 on: September 10, 2008, 09:58:33 AM »

e. THe anemometer is outputting 4-20mA to a datalogger/modem. I used a 4-20mA signal multiplier and branched the 4-20mA signal to another datalogger. THe multiplier is eating a lot of power(about 2x,3x the original system). Since we have put in this new multiplier and a larger battery, we have been having battery flat problem. I dont have any rational clue but the multiplier "feels" very suspicious.   


First, I agree that a blocking diode is in order. You can check that by inserting a milliammeter in the circuit between the panels and the battery after dark. Any current flow is bad. Also, a lot of panels already include a diode, so check that too.

Second, solar systems have to be fairly well designed to match the load. If you added the second datalogger and 4-20 "multiplier" without factoring them into the system load, that could be a problem.

Third, you may or may not actually need the "multiplier" if at least one of your loggers has a floating input. Floating 4-20 ma loads can be wired in series up to the maximum load resistance. For a 24VDC powered loop, the theoretical max load resistance is 1200 ohms, but I usually limited it to 1000 ohms. Most data loggers and other 4-20 loads use 250 ohm precision resistors to convert the current to 1-5 volts, so you can stack up to 4 of them.

However, if your dataloggers have grounded inputs, you'll probably still need the multiplier.

Post the power requirements of the anemometer, loggers, and multiplier, and we'll do a quick design check and see if there is anything to improve. 

Offline orange

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Re: Solar power battery died out not according to calculation
« Reply #4 on: September 11, 2008, 06:10:39 AM »
1)The system has a blocking diode.

2)The power consumption of the system below. The actual power consumption I measured with a multimeter.

a. Anemometer: Theory 40mA, Actual 73.7mA     
b. Multiplier 1 for wind direction : Theory ?, ACtual 75.2mA
c. Multiplier 2 for wind speed: Theory ?, Actual 53.6mA
d. ilog datalogger: Theory 200mA, Actual 247mA
e. Novus datalogger: use internal battery. 0mA
Total: Actual 450mA

Solar panel 44W
Battery 12V 70AH

3)My calculation as below:

Solar panel
Singapre peak sun hours = 4H
Load in watt= (450mA)x12V =5.4W
Load in watthour= 5.4Wx24H = 129.6WH
Solar panel input=129.6WH/4H = 32.4W
+20% = 39W
(we are  using 2x22W=44W solar panel)

 
Battery
total load = 450mA x 24H = 10.8AH
5days backup= 54AH
(we are using 70AH battery)

 

4) System wiring here : http://geocities.com/bambinorama/wiring.JPG

My burning question: I am not really sure that whether both of my dataloggers, ilog and Novus, are using floating point measurement or not. None of them are connected to earth.

I am especially not sure about ilog; it has some no-no wiring configuration that might cause ground loop. I connect the 4-20mA to A+ and A-, and +12V to Vcc and -0V to Gnd. ilog ground wiring here: http://geocities.com/bambinorama/groundloop.pdf

Novus datalogger I am less concern because it is using a internal battery. http://geocities.com/bambinorama/logbox.pdf

So from the looks of it, is it possible to connect the dataloggers in series without using any multiplier? Looks to me ok.   


5) I might install a MASON SBC-7120 battery charger into the system.  \:D/




Thanks guys

Offline SLOweather

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Re: Solar power battery died out not according to calculation
« Reply #5 on: September 11, 2008, 12:06:14 PM »
OK, I'm going to redo your calcs in amp-hours, rather than watt-hours, because that's how I'm used to thinking about solar systems.

Load
.45 amps x 24 hours = 10.8 AH per day

Solar

1.5 amps x 2 panels in parallel x 4 hours per day solar insolation = 12 AH supply

There's not a lot of cushion there, 12-10.8 = 1.2 AH  or 10% on a perfect day. Combine that with batteries being about 90% efficient at recharging, and your system would seem to just keep up on a 100% sunny day. Worse, once the battery is depleted, it will take a lot of sunny days to completely recharge it. 70 / 1.2 = 58 days. Operating the battery discharged like this will damage it over time.

The battery looks large enough:
70 AH / 10.8 AH = 6.48 days with no charging. My rule of thumb is to size the battery so that worst case only drains it 50%.

Under the described circumstances and conditions, my feeling is that you need more solar panels. Twice as much capacity would be a good place to start. That would leave a best case of 13.2 AH to recharge the battery, or 5.3 days to recharge from dead.

BTW, don't parallel 2 batteries unless they are identical manufacturer and model, and brand new. Mismatched batteries will drain each other.
« Last Edit: September 11, 2008, 12:12:07 PM by SLOweather »

Offline SLOweather

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Re: Solar power battery died out not according to calculation
« Reply #6 on: September 11, 2008, 12:19:50 PM »
As far as the data loggers:


My burning question: I am not really sure that whether both of my dataloggers, ilog and Novus, are using floating point measurement or not. None of them are connected to earth.

I am especially not sure about ilog; it has some no-no wiring configuration that might cause ground loop. I connect the 4-20mA to A+ and A-, and +12V to Vcc and -0V to Gnd. ilog ground wiring here: http://geocities.com/bambinorama/groundloop.pdf

Novus datalogger I am less concern because it is using a internal battery. http://geocities.com/bambinorama/logbox.pdf

So from the looks of it, is it possible to connect the dataloggers in series without using any multiplier? Looks to me ok.   


Disconnect them from everything and use a multimeter on ohms or continuity to see if either input connection is connected to the negative power supply connection. If not, you can probably eliminate the multipliers.

Offline orange

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Re: Solar power battery died out not according to calculation
« Reply #7 on: September 17, 2008, 03:30:20 AM »
Many thanks for the helpful comments.

Code: [Select]
Disconnect them from everything and use a multimeter on ohms or continuity to see if either input connection is connected to the negative power supply connection. If not, you can probably eliminate the multipliers.
Do you mean this:
http://www.geocities.com/bambinorama/loop.JPG

Just to confirm, out of the two dataloggers, I only need one datalogger with floating point input, in order to series the data loggers on a 4-20mA signal.

Offline Jim18655

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Re: Solar power battery died out not according to calculation
« Reply #8 on: September 17, 2008, 08:06:52 PM »
In a perfect world your battery would last as you calculated it should. Don't forget that at some point the voltage will drop below the minimum required to keep the sensor operating hence the decrease in life expectancy.
See:http://www.allaboutcircuits.com/vol_1/chpt_11/3.html for a better explanation of amp-hour ratings on batteries.
Jim

Offline SLOweather

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Re: Solar power battery died out not according to calculation
« Reply #9 on: September 17, 2008, 09:25:53 PM »
Good point! You can add a low voltage disconnect to keep the load from discharging the battery too far.

Offline orange

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Re: Solar power battery died out not according to calculation
« Reply #10 on: September 26, 2008, 03:58:53 AM »
Many many thanks guys.  :grin: