Beginner's problem

RuenRuen Registered Users Posts: 7
I built two 12 V, 7.2 A, 125 W solar panels from eBay Everbright Solar cells, planing to produse 18 V, 14.4 A, 250 W and to store in 5 X 12 V 200 AH batteries.Each 12 V battery is made from 6 X 4 OPzS 200 AH .When I put the first panel on the roof, the open circuit was 19.5 V and when I connected the first battery, the current was 3.75 A .The temperature was 30 C (86 F) fully sunny day and the panel was on 30 degrees S SW.
The connecting wire is 8 AWG 10 m (30')
I decided that the battery was weak and I left it for 2 days to charge. Finally the current fell down to 1.2 A.Then I swiched to the next battery and the current rised to 2.6 A.
I continued to change the bateries untill yesterday when I connected the 5 batteries in parallel 12 V 1000 AH.Then I checked the voltage It was 12.66 V. I left the panel to charge - the voltage was 13.5 V and the current 1.3 A .
I desided to leave the batteries for 3-4 days to charge and then to check the density of the electrolite with a density meter. I put a 20 A fuse for security.
At the moment I havn't got a charge controller (my son is working on an 12 V 20 A controller).
I made some mistakes during the building - First the measures of the panels are too big - 1.75 m X 0.75 m (5.7' X2.5') Second, I put the cells on a glass and cover with Lexan.Finally when the Lexan expanded from the heat and broke the glass bottom and now I'm planing to change the second panel's Lexan with normal glass.
This is the begining, as I'm planing to double the panels till the end of the summer.
I will use the batteries for lighting during the weekends and mainly for a refrigerator for the hot summer.
I will not use the batteries untill they are not fully charged.
Here are the stupid questions :blush:
Is the current drop normal for this moment and this wire connection?
What can I do to rise the current of the panel to his optimum current of 7.2 A?

Comments

  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Beginner's problem

    For the battery bank--the typical rule of thumb is around 5-13% of Bank AH rating as charging current... So for a 1,000 AH battery bank, you would like to see:
    • 5% * 1,000 AH = 50 Amps (on the low side)
    • 13% * 1,000 AH = 130 Amps (on the high side)
    So, if you are planning on powering part of your home form the battery bank using a solar array--You have some aim points for how much current will be required for a useful installation.

    Next, see if you can get a copy of the charging instructions for the batteries you are using... And with an accurate DMM (digital multi-meter), and measure your battery charging voltage... And make sure you are reaching those values (to fully charge the batteries).

    For your panels, set your DMM to 10 amps and measure the Isc (short circuit current) of each panel (don't exceed 10 amps max on meter or it will be damaged--or whatever yours is rated for). If your panels do not get near Isc/Imp on a very sunny day around noon time--then you may have some wiring problems in the panels or in your array harness.

    Charge controllers have several modes they operate in:
    • Bulk--As much current as the solar array can output
    • Absorb--As much current needed to maintain charging voltage at battery (say 14.4 volts). Charge current will taper down over time as batteries reach full capacity).
    • Float--One batteries are charged, a lower votlage (like 13.6 volts) which will keep the batteries charged but now "boil" away water (electrolysis) and "over charge" the battery bank. Typically important for batteries which may set days/weeks or longer without use.
    Without knowing the battery voltage while charging (and the charge controller settings)--I don't know what the cause of the low charging current is (or-it even may be normal if the batteries are 100% charged).

    You can take a look at the Battery FAQ's to get a better idea of how to manage your battery banks so they have a long life:

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    Just a warning about DYI solar panels--the problems you have experienced are common with DYI solar panels. It is difficult to make panels at home with typical materials that will last for decades under wind/rain/sun/snow.

    Also, I would recommend that you install the panels over non-flammable surfaces like a gravel base (and not on roof of your home). On occasion, the failure of solder joints/tabs/wiring have caused arcing and started fires.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Beginner's problem

    current drops are normal for batteries when they are near fully charged. i can't say for sure if your batteries are fully charged or not, but if they aren't it's due to your homemade pv not being right somehow. how many cells did you place in series as 12v pvs normally have 36 of them. are you sure none of the cells got accidentally bypassed while soldering?
    did you measure the open circuit voltage while optimally aimed at the sun around solar noon? how about the short circuit current? what type of battery are these, fla, gel, or agm? if anything other than the fla type you can damage the batteries with no regulation on them.
    and finally you better invest in a quality utility battery charger as you should have at least a 5% charge rate on the batteries and that equates to 50a. now you might squeak by with 30a, but it will take considerably longer to charge and no way should you think you can charge it well below that.
    i might add that i don't recommend you placing this on your home's roof and a controller should be obtained as well as more pvs if you intend to lien solar as the primary charge source. pvs are lower priced these days and there is no way you can build a pv that would equal a commercially made panel and keep it at or lower than the cost of the commercial pv.

    btw bb, what does dyi stand for as i thought it to be diy for do it yourself?
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Beginner's problem
    niel wrote: »
    btw bb, what does dyi stand for as i thought it to be diy for do it yourself?

    DYI = "Do Yourself In" an unfortunate but frequent by-product of DIY. :p
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Beginner's problem
    DYI = "Do Yourself In" an unfortunate but frequent by-product of DIY. :p

    DYI == Do it yourself for "distracted while typing" dyslexics. :blush:

    -Blli
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RuenRuen Registered Users Posts: 7
    Re: Beginner's problem
    did you measure the open circuit voltage while optimally aimed at the sun around solar noon? how about the short circuit current? what type of battery are these, fla, gel, or agm? if anything other than the fla type you can damage the batteries with no regulation on them.
    1.I have measure the OC voltage while optimally aimed and it is 19.5 V as I have written below.
    2.I haven't measure Isc. Can I damage the cells while I do it?
    3.The batteries are lead-acid. http://e.energia.dn.ua/catalog/accumulators/opzs.html

    As I'm a east european what is "fla, gel, or agm"?
    edited by niel in replacing the text lingo you used as mine did not con-notate anything derogatory whereas yours did.

    Edit: As I have mentioned before - the generated electricity will be used only during the weekends with a very small consumption.This is a mountin cottage!
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Beginner's problem
    Ruen wrote: »
    As I'm a east european wtf is "fla, gel, or agm"?

    FLA = Flooded Lead Acid, like the OPzS range
    Gel = Batteries with a gelled instead of liquid electrolyte, like OPzV batteries
    AGM = Absorbed Glass Mat, another type without a liquid electrolyte
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Beginner's problem
    Ruen wrote: »
    As I'm a east european wtf is "fla, gel, or agm"?

    FLA - Flooded Lead Acid (the type you have)
    GEL - Gel cell (acid in a gelatinous suspension)
    AGM - Absorbed Glass Matt (also sometimes called "starved electrolyte")

    Glossary of terms used here: http://forum.solar-electric.com/showthread.php?t=6136

    Reading your post I see 250 Watts of panel and 1000 Amp/hrs of battery? That isn't going to work.
    I suggest you check your batteries' State Of Charge with a hydrometer rather than a Voltmeter. Specific Gravity readings are the best way to tell if they are indeed charged. Generally as the battery Voltage comes up, the current will go down.

    There should be no trouble measuring a single panel's current output if your meter is capable of handling the expected Amperage.
  • RuenRuen Registered Users Posts: 7
    Re: Beginner's problem

    Thanks for the definitions :D
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Beginner's problem
    Ruen wrote: »
    1.I have measure the OC voltage while optimally aimed and it is 19.5 V as I have written below.
    That sounds a bit low for Voc (voltage open circuit) for a panel used to charge a 12 volt battery...

    For a Vmp=17.7 volts (Voltage Maximum Power), Voc should typically be around 22.1 volts.

    If Vmp of a single panel is too low, then it will be difficult to charge a 12 volt battery bank (14.4 volts battery charging + 1-2 volts controller+wiring drop = 15.4-16.4 rough minimum Vmp with charge controller).
    2.I haven't measure Isc. Can I damage the cells while I do it?

    Solar panels are "current mode sources"--so they are naturally current limited (basically, current is proportional to the amount of sunlight hitting the panel). Isc will be roughly 5% greater than Imp (not a big difference).

    If your panel is damaged by simply placing a DMM set to 10 amp scale on the output of one solar panel--then the panel was not constructed correctly.

    In general, a panel should be able to handle roughly 1.25-1.56x Isc by design (this is what the US National Electric Code assumes).
    3.The batteries are lead-acid. http://e.energia.dn.ua/catalog/accumulators/opzs.html

    As I'm a east european wtf is "fla, gel, or agm"?
    [/QUOTE]
    • FLA=Flooded cell Lead Acid (typical "car type battery"--open a cap to add water/electrolyte until the plates are covered)
    • GEL=The electrolyte has been turned into a gelly/jelly like substance. Like a FLA, but you cannot spill it if the battery is turned up side down for example).
    • AGM=Absorbed Glass Mats. The space between the plates has a fiber glass mat which holds the electrolyte like a sponge.
    GEL and AGM batteries are "Sealed" batteries. As such, you cannot add distilled water to the cells if they start to dry out, unlike a flooded cell battery.

    If a GEL or AGM (or other sealed battery) is overcharged, the safety vent can open and let out hydrogen and electrolyte. While AGM's are about "perfect" lead acid battery types.

    All sealed batteries are very sensitive to over charging as the electrolyte/water/gel cannot be refilled. Sealed batteries have a catylist (like palladium, platinum, or something) that recombines the hydrogen+oxygen back into water to keep the cells from "drying out". The catalyst does eventually wear out or fail--and the batteries can fail soon after (there are replacement catalyst caps available for some batteries).

    The Battery FAQ's have lots of more detailed discussions:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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