solar pannel, lead acid battery project

[electrikhead]

Hey everyone! I am new here but have experience repairing, building, and designing circuits. I Was curious if any body could help me with my solar construction. I have so far 116 cells that produce .55v @ .275 ma max sunlight and have 6, 7A lead acid batteries. Is there a person that may be able to help me calculate how many more cells I would need to charge my 42A of batteries in a day of full sun? And do I need anything else such as a diode or trickle circuit. I am looking to get off the grid in do time! My expertise is with small electronics like I mentioned this is all new to me. I also have a 750w power inverter and don't even have enough juice at this point to turn it on lol!

 

[Roff]

You said 0.275ma. Do you really mean 275ma? If not, your 116 cells can produce 17.5mW (actually less) in full sunlight. Not a good start.

 

[electrikhead]

Yes I meant 275ma lol sorry for the confusion and thank you very much for helping!

 

[electrikhead]

I have 29 cells @ .55v ea. in series @ 275ma per cell and paralleled 4 times. so 275 times 4 = 1.1A, and .55 times 29=15.95v

 

[Roff]

Yes I meant 275ma lol sorry for the confusion and thank you very much for helping!

Does each cell produce 275ma?
BTW, don't get your hopes up that I'm gonna answer your questions. I'm just trying to clarify what you have so that maybe someone else can help. I know we have guys here that do this stuff.

 

[electrikhead]

275ma per cell and .55v per cell I have 116 total so far and plan to keep going until I am at the right capacity. 29 in series and times 4

 

[Boncuk]

Solar charger

Let's calculate: 29 panels in series per 0.55V will give you a total output of 15.95V - far too much for the lead-acid battery. It will explode sooner or later.

25 panels in the same cofiguration will result in an output voltage of 13.75V, which is still too high. Reducing the output voltage with a forward diode (which you'll need anyway to prevent discharging of the battery in the dark) your output will be within safe limits concerning the max voltage (13.75 - 0.7).

Connecting 4 assemblies in parallel the max current will be 1.096A, which is not advisable to charge the small battery continously. Normal and good charge current is 1/10 of the capacity.

A solar panel however produces 100% of its nominal power only when directed exactly perpendicular towards the sun near the equator. For a first experiment I'd omit any extra circuitry to reduce current and voltage.

Just hook up 4 X parallel 25 panels in series and observe the charging current and the voltage increase of the battery. The diode however is mandatory. A 1N5401 willl do for that purpose. It drops the required 0.7V and can stand a continuous current up to 3A.

Use the left over of 19 panels to generate extra power for a supervisory circuit.

Boncuk

 

[Roff]

Use the left over of 19 panels to generate extra power for a supervisory circuit.

Boncuk

Or buy more batteries.

 

[electrikhead]

I figured more batteries would be a possibility. I would like to mention that the lead acids are sealed and I will use that diode by the way, and try to limit my voltage!!! thank you guys!

 

[electrikhead]

I also wanted to ask that my total battery capacity is 42A so 1.1A would be roughly 1/40th of the current wouldn't it? so I am actually under powered with my solar cells aren't I ? I highly appreciate any feedback !

 

[electrikhead]

BTW I tried charging (1) 7A Batt. w/ the 15.95v of 29 in series and paralleled 4 times and noticed the voltage increase .05v/sec until the battery reached 13.45v then over a resting period of 24hrs it had dropped to 12.52v which is where it started, and stayed as if that is the batteries capacity? Was 2hrs not long enough to charge it? They come 2/3 charged..... I figured that there would be some drop off however that seems rather dramatic to me but like I said I am new to solar charging.

 

[electrikhead]

I also used 29 to compensate for cloudy conditions, I had figured If I pointed the array away from the sun I would get indirect light to reduce output voltage and point towards the sun at the morning or at dusk with those measures taken I had figured more charging time however a lack of efficiency. I guess less time would be needed though if I point directly toward the sun and reduce to 25 in series but then I have issues on cloudy days. I should also mention my batt. also suggests that optimal continuous charging voltage be 14.4 - 15v so I am confused.

 

[Boncuk]

I also wanted to ask that my total battery capacity is 42A so 1.1A would be roughly 1/40th of the current wouldn't it? so I am actually under powered with my solar cells aren't I ? I highly appreciate any feedback !

That is getting close to a solar power plant. If you get enough participants for the idea of making own electric power you might order a bunch of solar panels in China. The latest version is 200W (short circuit current 6.5A). They are extremely cheap but this is the bitter pill: The MOQ is a lot of 360 pieces.

 

[k7elp60]

BTW I tried charging (1) 7A Batt. w/ the 15.95v of 29 in series and paralleled 4 times and noticed the voltage increase .05v/sec until the battery reached 13.45v then over a resting period of 24hrs it had dropped to 12.52v which is where it started, and stayed as if that is the batteries capacity? Was 2hrs not long enough to charge it? They come 2/3 charged..... I figured that there would be some drop off however that seems rather dramatic to me but like I said I am new to solar charging.

12V Sealed lead acid batteries require between 13.5 and 13.8 volts to fully charge in the standby mode. Or from 14.4 to 14.7volts in the cyclic mode at 77 degrees F. In either case with the charger removed they will return to approximately 12.7 volts in 24 hours. The exact contact potential depends upon the remaining capacity of the batteries. When charging in the cyclic mode the charging current must be monitored and when the charging current reduces down to C/100 the charger must be removed or the charge voltage stepped back to the standby voltage of 13.5-13.8Volts.

 

[electrikhead]

Thats exactly what the batt. says except instead of 14.7 it says 15 for the high end. I like where this thread is going, thanks Roff,Boncuk, And K7elp60!

 

[electrikhead]

sealed lead acid

I was also curious if there is a difference in proper charging between sealed and unsealed lead acid batts. And is a trickle/stand by charge necessary? or can I use a constant charge like that of a car battery?:

 

[electrikhead]

I was also curious if there is a difference between charging techniques of sealed and unsealed/wet lead acid batts like that of a car batt. Is a trickle/stand by charge necessary or can I use just a constant current flow?

 

[Boncuk]

I was also curious if there is a difference between charging techniques of sealed and unsealed/wet lead acid batts like that of a car batt. Is a trickle/stand by charge necessary or can I use just a constant current flow?

Hi electrikhead,

a lead-acid battery doesn't use constant current other than NiCad batteries. Lead-acid batteries use constant voltage for charging. The higher the charge the lower gets the charging current with increasing voltage in the battery.

Overcharging either a dry or wet battery has the same effect. They start gasing (oxygen and hydrogen = mixed highly explosive). Charging lead-acid batteries should be done in a well ventilated room for that reason.

Since a dry battery has no openings for the gas to escape it is a simple method to build a timed bomb!

Good dry batteries have a safety valve for the risk of explosion. It opens and reliefs the pressure. After openening the valve the battery is ready to be recycled.

Boncuk

 

[k7elp60]

I was also curious if there is a difference between charging techniques of sealed and unsealed/wet lead acid batts like that of a car batt. Is a trickle/stand by charge necessary or can I use just a constant current flow?

On thing to remember is that car batteries are used for one reason, that is to start the engine, once the engine is running the electrical load is on the alternator.
I don't think there is a difference in charging techniques between the sealed lead-acid and the flooded type. Both can be charged with a constant current charger.
I have solar PV panels and some flooded lead-acid that are charged with the solar panels. I use a charge controller that is set to the standyby charge method or in my case 13.8V. The charge controller adjusts for ambient temperature. The capacity of the batteries is 12V at 450AH. I have 3ea 75 watt panels connected in parallel with isolation diodes.
The best technical hand book on sealed lead acid batterys that I have found is by Powersonic. I'll try to upload it.
Something else to keep in mind only parallel batteries that have the same date code/and or the same AH and charge status. No doing so will cause some batteries to discharge into the other batteries.

 

[electrikhead]

I guess I better get going on my diodes! cathode to battery neg right? I calculate I only have around 20w so far but making my own panel is a great and rewardingthing! I will just keep paralleling to decrease my charge time. this site is the best thing since the advent of the light bulb! I will be in need of some charging/control schematics. my myspace url is deffdrumindave or davidmlady@hotmail.com. My email is davidmlady1@yahoo.com! I appreciate all this info soooo much! if you guys think of anything else let me know PLEASE! thanks!