Using a spare solar panel

thenudeone

I have a small spare 70W solar panel which I was hoping to use with a cheap charge controller from ebay to charge a 12V battery while camping.

Unfortunately every controller I've looked at is designed for solar panels with a 12V or 24V output, not standard solar panels which were designed for a mains grid-tie system.

Does anyone know of a device which will accept output from a "standard" solar panel with a nominal output voltage of 50-70V and generate either 12V or mains power, without being connected to any main system (which rules out small grid-tie inverters).

The_Green_Hornet

Don't know if this company has anything that would work for you.

http://www.photonicuniverse.com/en/

rogerblack

thenudeone wrote: »

I have a small spare 70W solar panel which I was hoping to use with a cheap charge controller from ebay to charge a 12V battery while camping.

Unfortunately every controller I've looked at is designed for solar panels with a 12V or 24V output, not standard solar panels which were designed for a mains grid-tie system..

Check your panels actual voltage.
60-70V seems extremely unlikely - it would require around 100 seperate cells, rather than the more likely 17V or so @4A, which would need 28.

ermine

Is your panel 70V at the maximum power point or are you measuring the open-circuit voltage? The voltage rating you have to worry about is the input to your controller, however, you could simply control the panel manually with a series switch and 1.5A diode and monitor the battery voltage yourself under camping conditions. The panel will look like a constant current source presumably giving you about 1A under ideal conditions.

You will be discarding two thirds of the potential output but the price is right. If you want to start being more efficient you'd need something like this which has a 100V input rating it would optimise the use of your panel to give you the best charge rate.

Personally I'd wing it putting the panel across the battery but isolate when the battery voltage exceeds 14V (assuming lead-acid). You obviously want to think about the usual safety issues (70V open circuit voltage which is over the low-voltage limit, gassing of the lead acid battery so it wants to be outside, failing to monitor the open circuit voltage for some time on a sunny day which could knacker your battery and appropriate fusing of the 12V circuit close to the battery to prevent the fire hazard).

The MPPT device would be a better solution and look after all that for you but comes at a price - you'd have an awesome camping power-supply however

thenudeone

Thanks for the info..

The panel is an AxunTek CIGS module.
The plate states:
Open circuit voltage 64.5V
Max power voltage 47.6V

This seems to be suitable and not too expensive either: http://www.photonicuniverse.com/en/catalog/full/14-10A-solar-panel-charge-controller--regulator-12--24V-for-camper--caravan--boat.html

Would this work?

rogerblack

thenudeone wrote: »

Would this work?

Basically not.
Firstly 'up to 50v' - the maximum of your cells exceeds this.
What 'pwm technology' in this case means is nothing more advanced than connecting the battery to the solar panel, and disconnecting it, many times a second.
There is no voltage conversion done, and it will be spectacularly inefficient with a 50V peak power module - about 25%. (Ignoring for the moment that it may die due to overvoltage)