Different watts, differe nt amps...

[mlail]

I have read some of the threads but what I've done is slightly different.
I have 1 - 80 Watt 6-7 AMP panel tied in parallel with 1 - 15 watt panel at 1 amp. From what I've read I will only get about 80 Watts combined and only about 6-7 amps.

So basically the 15 watt panel is wasted. correct?

Just for my understanding I also have tied two seperate charge contollers to the panel combiner. One 7Ah charge controller goes to some UPS batteries while the other goes to a Xantra 35 Ah charge controller for a 104Ah battery. Is there any downside to running two controllers?

Thanks

[Mike90250]

Well, maybe not. it will likely add something , but you need to know the voltage of the panels too, Vmax power & V max open ckt

[mlail]

These are both 12 V panels and I only could get the specs on the 80 watt sharp panel. The other 15 watt (play) panel is found at Northern Tools and they do not offer details beyond watts, amps, and basic voltage. So I'm guessing that half information is not going to get us anywhere!

Other than taking long classes in electronics, is there somewhere I can learn about why Vmax power & V max open ckt are important?

The Sharp 80 W panel has the following specs:
Cell Poly-crystalline silicon
No. of Cells and Connections - 36 in series
Open Circuit Voltage (Voc) - 21.6V
Maximum Power Voltage (Vpm) - 17.3V
Short Circuit Current (Isc) - 5.16A
Maximum Power Current (Ipm) - 4.63A
Maximum Power (Pmax)* 80W (+10% / -5%)
Module Efficiency (hm) - 12.40%
Maximum System Voltage - 600VDC
Series Fuse Rating - 10A
Type of Output - Terminal Junction Box

[Mike90250]

Other than taking long classes in electronics, is there somewhere I can learn about why Vmax power & V max open ckt are important?

Panels have a "power curve", like a car engine has a power curve. Torque and Horsepower. Not the same as Watts-volts-amps, but there is a specific curve relating to silicon solar cells. All brands are pretty much the same, just tiny variations.

V max open ckt becomes important when selecting a charge controller, you don't want to burn it out with too much voltage, which is what Vmax is before the controller "wakes up". for a standard "12v battery" is often around 20-25V

Vmax power is THE specific voltage, where the pane is producing it peak power. If you let it rise above that, toward Vmax, you waste power, if you drag it down by connecting directly to a 12v battery, you waste power. If you use a PWM controller (that's everything that does not call itself a MPPT controller) it regulates the voltage to about 14 or 15V wasting about 4 volts of possible power. Sort of like a car with gear # 1 & 3, gear #2 is missing, and you cant run as best as you can.

If you us a MPPT controller, it's like a 20 gear transmission in a truck - no matter what the conditions, there is a gear for it, and no power wasted. MPPT matches the PV max power voltage, and "transforms it" to the best charging voltage for the batteries. Closest thing to magic you can buy.

Charge controller info:

http://www.windsun.com/ChargeControls/ChargeCont.htm

http://www.windsun.com/ChargeControls/MPPT.htm

[mlail]

Finally, someone that can break the misery into every day language!

Well I have learned somethings here and as expected, even when I buy from a quality manufacturer I end up with less than expected. Murphy and I are on first name basis

My Xantra C35 charge controller is a PWM with 3 gears. The sales sheet sold it as a high end change controller and after reading many peoples equipment list, it read like a good unit. Still its better than the Northern Tool controller and it probably is OK with my low end panels. When I look into a whole house project I will head your advice and if you don't mind I will probably have more questions as I go.

So my change controllers Max PV open is 55 Vdc and 80 Watt 12 Vdc panel has a Voc of 21.6V and a Max Power Voltage Vpm of 17.3. My one battery is a SunExtendor (Concord) 104Ah battery for the Xantra charge controller. I guess I can still add another battery but the time to full charge will take longer with only one panel.

So from the sounds of things, it would not be in my best interest to buy a 130W 12V panel to add with my 80 Watt. My original thinking was that I could add what ever size panels and the wattage and amperage would be additive. Lesson learned. So maybe I can still replace the 15 W panel with another 80 Watt. That way the panels are matched and I will have increased charge capacity. I have already read in this forum to not mismatch batteries so I now need to remove some UPS batteries from that battery array on the cheaper charge Controller. I was trying to use some batteries that I have laying around from several UPS's. My ignorance or in light humor Murphy's suggestion!

Now if I can only find really cheap 80W 12 v panel and another 104 Ah battery!

Thanks for answering this new bee's questions!

[Mike90250]

C35 is a good, solid charge controller.

You could add panels in parallel, as long as the new panels Vmax power is around your existing 17.3V (17-20V would work fine). More panels = less charge time.