Do i need a charge controller for this?

[DongBeetle]

Hi all
I'm building a small solar panel that is gonna deliver about 13.5V (2 x 27 cells) and about 13,5W max, I'm gonna use it to charge a small sealed lead acid battery (maybe 7Ah)
My question is.. Do I need a charge controller for this? since the PV panel can only get as high as 13,5V and 1Amp which is within the level that the battery can handle without overcharging!?

Regards.

 

[BeerBelly]

I wouldn't bother with one for a 13.5 volt maximum. Some panels will create a drain at night though.

 

[MikeMl]

Hi all
Do I need a charge controller for this? since the PV panel can only get as high as 13,5V and 1Amp which is within the level that the battery can handle without overcharging!?

If the open-circuit voltage of your panel can get over 13.8V, 1A during bright sun will cook a small SLA in short order. A dirt-simple shunt regulator made from a TL431 and a power transistor will protect the SLA/

 

[DongBeetle]

Well I haven't put it together yet, but 27 cells @ 0,5V each, shouldn't be able to get any higher than 13,5V total, and even if the cells can get a tiny bit above 0,500V I'm not to worried about that, since I live pretty far North (denmark) and the days we have with blazing sun for hours on end is few and far between
But Mike, if you wouldn't mind, can you draw me a simple Circuit of that TL431 & power transistor combo you are talking about?
Also I'm gonna build a darkdetector that turns on some LED light when it gets dark, maybe that could be made into a combo of, turning on the light and cutting the panel of!? any ideas and schematics are welcome

Regards.

 

[alec_t]

The panel will 'cut off' by itself in the dark! But you will need something to prevent reverse current flow from the battery into the panel. Maybe the panel already has that?

 

[MikeMl]

Everything I know about solar cells says that a single cell puts out more than 0.5V open-circuit in direct sun. Look at this reference, for example. Note that the open circuit voltage is very temperature sensitive.

I think you need to connect your 27 cells, then measure the open circuit voltage in bright sun (note the temperature). I would also measure the short-circuit current, too.

Once you have those numbers, I have a couple of regulator circuits for you...