"What You Don't Know CAN Kill You"

The Solargoddess doesn't feel like a goddess today...she feels like a mere mortal very much humbled by the power of the sun. I almost ditched my project Wednesday, but I'm back. How did 5.3 amps coming out of 4 solar panels, as measured on August 30th, end up being potentially close to 70 amps coming out of the battery bank...YIKES!!! I am being very honest with my readers, the Solargoddess was scared, so scared she was on a ledge and ready to throw the project off the cliff.



I like to use all the tools I have available, especially when I'm trying something new. In this case it was the right thing to do. Using all tools available serves two major purposes:

1. Why try to recreate the wheel when you can stand on the knowledge and base of others.


2. What you don't know can sometimes kill you and in this case I do not mean that in a literal sense, it's the real deal.

Tools come in many forms but the best tools these days are information from those that have traveled the same road and information that is readily available on the internet.

Many times, since I've been licensed as amateur radio operator I've used a collective source of knowledge from my radio club, PCARC (Portsmouth Amateur Radio Club in NH). This is a pool of perhaps the most intelligent and resourceful people I've ever met, most with impressive real world experience in electronics and physics, not just degrees that hang on walls, these people actually develop projects and create. When I ran my project idea past two of them on Wednesday evening I nearly put everything for sale on EBay.

"What you have there is some lethal current". Not only one, but two people, echoed those words.

Where did I go wrong with my math?

How did a maximum of 5.3 amps go from our 4 solar panels wired in series get to an output of possibly close to 70 amps running out of the battery end that goes into the inverter?

I'll walk you through it:

Remember when we first measured the voltage on the panels with full sun back on the first day?Lets take one panel and work it through.

The highest reading on that first day was about 40 Volts and a high reading of 5.3 amps.

40V X 4 panels = 160

Now using the P = I * E formula P (or power expressed in Watts) = 5.3 X 160

P = 848 Watts

So we have these numbers now;

• 160 Volts from the Array to the Solar Controller
• 5.3 amps of current from the Array
• 848 Watts from the array

So far so good, are you still with me?

Here is where things get turned upside down. The Solar Controller runs to a 12 Volt battery bank because our Inverter runs on 12 Volts. That means the Solar Controller will need to crank down the Voltage to match that of the Inverter. Remember our formula? As you crank down voltage it will crank UP the current. Let's run the numbers;

848 (Power in Watts, we know that figure since that's what's comming from the array)

12 Volts...the voltage of the battery bank

I is what we will solve for...that will be the current we don't know that will be running from the 12 Volt battery bank we need to match.

848 = I * 12

I = 70.67

"What you have there is some lethal current".

What did I do wrong?

BIG Mistake I did not take into consideration the stepdown of Voltage to the Battery Bank.

Thank you Kriss, one of my amateur radio friends for giving me the heads up.

The Solargoddess will be back on the project but for starters I will scale it down and will work on it when the "sun don't shine"....I will use cardboard and the safety of cloud cover to stay safe. Stay tuned.