Solar power regulator???

[drrogla]

My friend just got this 18V solar cell from somewhere and since I know a little abuot electronics he asked me to hook it up to a 12V car battery, which he will use for powering his portable stuff(lighting, ham station, camper...)

I know it`s not just positive to positive and neg. to neg., he needs a diode (to asure that he doesnt destroy the cell with reverse curent(or something like that) :?: ) to charge the battery and it would probably work. Except if he over charged the car battery (which could explode ).... We don`t want that to happend so he needs a regulator.

I found some schematics on the net, one seems to sense the voltage on the battery and shunt the cell with some small resistors when the battery is full.

:?: :?:
I just want to know if this can break the cell, if the shunts can draw too much curent for the cell to handle or will the cell survive?
:?: :?:

EDIT::: Deleted schematic, you can still find it on the URL provided :::EDIT

 

[zevon8]

I use 16 Volt solar panels on trialers at work, they produce about 75 Watts, full load. Honestly, we have never bothered with a regulator. We do have a diode in the line to prevent panel heating during the night, but the panels have never over charged any of the deep cycle batteries they are connected to in the trailers.

Check and see what the voltage from the panel is, full load. It will be alot less than the open circuit voltage. The ones I use are around 22-24 Volts open circuit, about 15 or 16 full load, the diode brings it down to about 14.5 Volts or so, which is fine.

Most solar panels are designed with 12 Volt battery systems in mind, so there is often just enough voltage extra to account for a series diode, or wire losses. Also for aging/partial shade, since panels produce less voltage over time as they age.

 

[Nigel Goodwin]

For a start, measure how much power the solar cell can provide - unless it's absolutely massive I doubt it can supply enough to overcharge a car battery - so it's a waste of time (and energy) implementing a scheme to prevent overcharging.

 

[drrogla]

It`s rated 18V open and 16V, 1.5A max power so thats about 25W I guess.(half square meter surface area)
I know it`s small but if it keeps charging for a couple of days without load it could be bad news for the battery...

 

[Nigel Goodwin]

It`s rated 18V open and 16V, 1.5A max power so thats about 25W I guess.(half square meter surface area)
I know it`s small but if it keeps charging for a couple of days without load it could be bad news for the battery...

No! - 1.5A is only 'trickle charging', it can be left permanently charging at that low a level without any adverse effects.

Also, 1.5A is the theoretical maximum, it's highly unlikly that you will ever reach that much charging current. Just stick an ammeter in series with the panel and try measuring the charging current - be prepared to be disappointed! :cry:

 

[zevon8]

That current rating is for nearly a short circuit, and not likely accurate.

I don't see it being able to overcharge a 12 volt battery. With a diode in series, the chargeing voltage would be about 15.2 volts.

In the setup I have with the trailers, they are out in the sun all year-round, and none of the batteries have had a problem. The current is too low to hurt the batteries. The batteries I use are deep cycle golf-cart batteries, 6 volts each, 2 in series, 4 sets like this, giving 880 AH capacity.

The simplest regulator I have seen is simply a pass transistor, say a TIP120 or similar, and a small trimmer pot on the base. Once the voltage drops to about 12 volts, the transistor is nearly off. The thing is though, in full sunlight the whole circuit is the equivalent of 2 diodes in series with the batteries ( the C- E junction drop .)

Unless you are charging really small batteries, ( in which case you don't need such a large solar panel ) there is little chance of over charging the batteries.


edit - bah! Nigel types faster than me - again

 

[Nigel Goodwin]

edit - bah! Nigel types faster than me - again

Fastest keyboard in the west! :lol:

 

[drrogla]

OK!!

Thanks for reasuring me guys!!

P.S.: Great typing action Nigel :wink: