Do I need a charge controller?

[Ogou]

Hi I'm thinking about building a small solar panel to recharge a 12V, 7Ah sealed lead acid battery.

I want to reduce the cost by avoiding the charge controller.

I'm thinking about using 30 cells, 300 amp each.

This will give me about 15Volt Vcc, so the maximum power(mp) will be less than that.  Lets assume that Vmp is around 13.5 volt that means the battery voltage will never be more than 14V.  Therefore there is no possibility to overcharge the battery.

The idea is to use a panel that will never reach the overcharging volatge of the battery.

What do you think about this idea?

JRN

[WXYZCIENCE]

Your power numbers are unclear check again and try to post again. I have a simple circuit that charges a 12 volt gel to 13.67 made from 5 components. It might do the job if what you are up to is what I think. Joe

[Ogou]

OK

One cell is rated as follow :

Vcc : 0,5

Isc : 320 mAmp

Vmp : 0,45

Imp : 300 mAmp

30 cell connected in serie will give you a panel of 13.5 V at maximum power. The panel will be : 13,5V and 300 mAMp @ maximum power. So if the battery can support this voltage I think there is no need fo a charge controller

Can you tell me more about your circuit.

JRN

[nothing to lose]

Unclear.

"I'm thinking about using 30 cells, 300 amp each."

9000 amps,? for a 7 amp battery??

OK

[ghurd]

The Voc should be higher. Much higher. Like 22Voc. Below 20Voc is pretty much useless.

Have you seen the VW PVs?

With 42 cells, built in controller, cheap (for what they are), good quality, etc.

"Newer" versions have the charge controller built into the plug.

Amps actually into a 12V battery can go past 250ma.

Search this board for 'VW' for better info.

This is the opened 'plug' controller laying on a PV.

G-

[WXYZCIENCE]

It looks like your actual power is 15v at 320 ma.
Not a lot of power there. This circuit is for 2 - 100 watt solar cells. The type of 12volt relay has to be as low current as you can find for low watt cells. I have one that draws 10 ma at 12v from an old modem card. The secret to this operation is the  use of the normally closed contact of the relay.  

This circuit charges the battery till it reaches the set level EG. 13.6 then the relay is energized. The relay draws down the battery then the circuit removes the energy from  the relay presto regulation. You can add a 100mf cap across the relay, this delays turn off of the relay.

[BT Humble]

Here's an alternative design, based on a circuit published in "Home Power" magazine, which will cost about $10:

http://one.fsphost.com/smallsolar/hardware/switchreg/index.htm

(Sorry that the page is still a work-in-progress).

I usually use a rule-of-thumb that if your battery capacity in Ah is more than 5 times your solar panel output in watts you don't need a regulator.  For the project in Fiji we recommend a 10W solar panel and a 75Ah battery, which seems to work quite well for the people there.  (This is of course assuming small 12V systems).

I've also used 20W of solar and a 38Ah battery for a small system of my own, but that was using lower-voltage amorphous panels and I was running lights, etc. off it every day so the voltage never really got over about 14V.

BTH

[Hanski]

Hi Ogu,

I have two separate 4Ah batteries directly connected to two tiny panels (both 16,5V openV, 66mA) having six Panasonic cells (BP-376634 5.5V. 33mA, size:65 mm *37 mm), three in series and two parallel, without controllers.

I just poured some epoxy over the cells and there was my panel. No I did not use UV-protection in epoxy. It was kind of a test, still working third year starting.

They are in my sauna and sched where I have 15 super bright led's.

Batteries survived winter (-25C). One has now 12,5V and other 13,5V.

So it can be done at least in small scale if you don't need much power.

//Hanski

[WXYZCIENCE]

My rule of thumb is we make it idiot proof. And allow idiots to prove it does not work.
This is a good saying that I quote "Batteries don't die, they are murdered." Gel type have a very short life. I have seen a healthy set of gels get their shorts riped off in less than a year. FOLLOW MANUFACTURES RECOMMENDED CHARGING INSTRUCTIONS and you will see you batteries get old and gray.

[BT Humble]

Gel type have a very short life. I have seen a healthy set of gels get their shorts riped off in less than a year. FOLLOW MANUFACTURES RECOMMENDED CHARGING INSTRUCTIONS and you will see you batteries get old and gray.

I try to use only flooded-cell batteries, I don't much like gel cells due to their fussy nature.

(Except for those few times when the scrap metal dealer has 12V 100Ah SLAs reading 12.8V for $20 each...)

BTH

[Opera House]

Instead of letting the relay drag down the battery, add a little positive feedback.  Try a resistor like 750K from the output of the op amp to the input.  Relays won't continue to click forever.  I worked on a machine that operated for a couple months and then stopped.   I did a calculation of how many times an hour the relay clicked and how many hours the machine operated.  Sure enough, the relay had exceeded the 1.5 million operations specified in the tech sheet.  

[mjchee]

 By all means, invest in a charge controller and it will be the best thing that you will ever do! People are always upgrading their system and you'll be smart to even have one that will work for you and you can purchase a small one for a fair amount of money. A charge controller should be considered like a best friend, specially when your away. So by all means, invest in one and you'll never be sorry!