[SOLVED] Basic questions about connecting devices to solar panel (volts? watts? what?)

[SimonSays12]

Hi

Sorry for asking such a basic question, but i'm a total electronics noob...

I want to connect 2 devices to a solar panel. Everything operates at 12V and I assume the solar panel produces DC. I want to connect the devices directly to the panel without using an inverter or a regulator. So i guess I have to pay attention that the devices use DC as well. Now, how do the watts have to be? Does the panel need to produce the same amount of watts as the 2 devices together consume? What happens if this is not the case? What happens if, for example, the panel produces 25W, but the devices only consume 10W together (one at 4W and the other at 6W)? Will they blow up or something?

Thanks
Simon

 

[betwixt]

Solar panels can be difficult to predict unless you have the manufacturers graphs of output under different lighting conditions and loads.

In general, the voltage they specify is what you expect to get at a particular load current. There is an upper limit of voltage 'open circuit' where nothing is connected across it and it drops as you draw more current.

The panels do produce DC so be careful of the polarity of connections but the 12V panels may produce more voltage if you under-load them your devices. The only sure way to know is experimentally, rather than sacrifice your devices, use a power resistor, chosen to draw the same current and connect it across the panel. The resistor value should be the voltage squared then divided by the Watts so for 12V and 10W you should use 14.4 Ohms (15 Ohms is a 'near enough' standard value).
If the voltage with the resistor connected is about 12V you should be OK, if it's more than about 14V you should consider using a voltage regulator to keep the output constant at 12V.

Brian.

 

[Audioguru]

My "12V" solar panel produces 18V with no load or low load current when pointing directly at the sun at noon on a sunny day.
It produces 14V when loaded with its rated load when pointing directly at the sun at noon on a sunny day. But much less voltage when not pointing directly at the sun, or in the morning or afternoon, or on a cloudy day.

Electricity is not "forced' on something. The battery in a car can deliver 400A (12V x 400A= 4800W) to its starter motor when the temperature is below freezing but the clock in the car is connected to the same battery and draws only 0.002A (12V x 0.002A= 0.024W) so it does not blow up.

 

[SimonSays12]

Thanks to both of you. You took my fears a little bit, so i guess i'm just gonna test it out.