rc solar car

[abiz]

hello, i'am new to this forum and recently joined a solar rc car race
my car is powered by 4xAA rechargable battery (4.8v),
the solar panel that was given to me can output 7.7V max,
i used an LM317T regulator to limit voltage to charge at 5.3V

the problem is that when its cloudy it gives lower then 5.3V
and i am worried that it will drain the battery rather then charge it,
is there any way that i can set it to charge only when the solar panel
can output more then 5.3V? does a capacitor help?

 

[kchriste]

does a capacitor help?

A diode would help. Post a schematic of what you have and I'll show you where to put the diode. The circuit probably needs a total redesign because a LM317T drops too much voltage and you need all you can get on a cloudy day.

 

[Hero999]

Use a low drop-out regulator, the LM317 typically needs 2.5V of headroom.

 

[audioguru]

Um,
Some people use an amplifier to increase the output of a solar panel on cloudy days.
An advertising sign in a field near my home uses a wirdmill to increase the charging current on cloudy days.

 

[Vizier87]

Some people use an amplifier to increase the output of a solar panel on cloudy days.

How does that work? Are you referring to dc-dc converters?

 

[Hero999]

I think he's being sarcastic, an amplifier won't do any good.

 

[Vizier87]

my thoughts also. that 'um's gotta be something.... anyway ON semiconductor has loads of them low-dropout regulators in their database.

 

[Nigel Goodwin]

hello, i'am new to this forum and recently joined a solar rc car race
my car is powered by 4xAA rechargable battery (4.8v),
the solar panel that was given to me can output 7.7V max,
i used an LM317T regulator to limit voltage to charge at 5.3V

the problem is that when its cloudy it gives lower then 5.3V
and i am worried that it will drain the battery rather then charge it,
is there any way that i can set it to charge only when the solar panel
can output more then 5.3V? does a capacitor help?

Just feed the solar panel through a diode directly to the battery - the panel may already have a diode anyway. You don't need the regulator IC, the batteries will regulate it anyway, and you won't be wasting any of the solar power.

 

[Vizier87]

the batteries will regulate it anyway, and you won't be wasting any of the solar power.

nigel, how does the batteries regulate the input from the solar panels? serious question.

 

[kchriste]

Since the OP is in a "solar rc car race", it is unlikely that there will be any surplus power to overcharge the batteries. Any surplus energy should be burned up by putting more power to the motor.

 

[Nigel Goodwin]

nigel, how does the batteries regulate the input from the solar panels? serious question.

The same as all other batteries do, they act as a kind of 'zener diode', and maintain the voltage within fairly close limits of their terminal voltage. As with a zener diode, if you stick too much current through it, then it will be destroyed - this isn't a concern with solar panels, as their power output is pretty feeble, and simply connecting the panel to the battery (via a diode) will provide maximum power simply and cheaply.