Need resistor(s) for solar panel

[dflannigan]

Hello,
Its been a LONG time since my grade 10 Electronics class so please be patient.
I've made a solar panel that produces 27V and 13Amps in bright sun light. My design had a flaw in it so the amp's are much higher than expected (it should be 3.5amp) and at this point it's possible to modify the solar panel.

The problem is the charge controller I have only takes an input of 22V - 300amps.

I doesn't seem possible to purchase 1 resistor that handles the 13amp.

I have been struggling for along time trying to figure out what resistor(s) and in what configuration I need to cut the voltage by 5V.

Can someone suggest the correct series or parallel circuit configuration with the correct size of resistor(s) ?
Huge thanks
Derrick

 

[(*steve*)]

You can't do that with a resistor.

Can you post links to the specs of your panels and the charge controller?

Also useful would be wiring diagram for the panels.

What are you charging?

Are the 27V and 13A open circuit voltage and short circuit current?

 

[dflannigan]

info

Hi Thanks for the quick response

Could you explain in general terms why it cant't be done?

I've attached a diagram of my overall system, solar panels to building (it's in .jpg format, if you need it in another format just let me know). The batteries I'm using are 12V marine deep-cycle lead acid, there are 6 in total.

This is the website I got most of my info from:
http://www.freesunpower.com

Here are the links to the webpages I used to get the info to design and build the panels, I used the same basic design just added more solar cells to make a 90Watt panel.
http://www.mdpub.com/SolarPanel
http://www.diypvsolarenergy.com/installing-solar-cells-panel-frame

Also the spec sheet for the charge controller is attached.

Thanks again for any help
Derrick

 

[dflannigan]

correction

That was supposed to say it is NOT possible to modify the solar panels ... winters are pretty harsh here in Canada so I was very generous with the number of screws and volume of silicone

 

[(*steve*)]

I need the information I asked for.

Specs on the panels.

If home made, specs on the cells, how many in each panel and how they're wired. And also how the panels are wired together (Series? Parallel?)

You can't just use a resistor to do what you want to because the amount of voltage it will drop is dependant on current. This means at low loads the voltage could rise too high and at high loads the resistor will be eating a large amount of your power.

 

[dflannigan]

Panel Specs

I made the panels myself using solar cells I purchased, each cell puts out a nominal 0.5V and 3.6Amps. I soldered 6 cells together in a row, in parallel, and made 8 rows of cells for each panel for a total of 48 cells/panel all connected in parallel. There is a Schotty diode inline in the positive lead just before it exits the panel. (the diode prevents current reversing at night and low light conditions) The cells were supposed to be wired in parallel (see attached layout) so the final output would be a theoretical 24V and 3.6Amps.

I made 2 panels but haven't connected them yet, I am trying to figure out the voltage problem first. My plan is connect them in series so the voltage remains the same.

I designed them to have more voltage than the charge controller would take because the panels are 50-60 ft from the batteries and charge system. I had read that given that distance DC energy would dissipate 8-10%. When I tested the panels the open circuit voltage was 27V and there was short circuit current was 13Amps with a < 1 Volt drop over 55ft using 12G wire.

Could the extra voltage and current be a result of only testing the panels in open/short circuit and not when they're connected to the complete system?