I think we had a record low production day for the solar today... 9.1kwh. my high score is 163kwh, my average sunny day is 100-120kwh....

Was this before or after finding the burnt cable in the MPPT?

The only acceptable response when dealing with a nagging wife 🪵🪓🌄🏕

Safety on solar panels.

Most solar panels make between 30Vdc-50Vdc just sitting in the sunshine. There's a positive and negative wire that are NOT connected to the aluminum frame. That frame should be grounded and I'll tell you why. Glad you asked!


When we connect solar panels to a MPPT charger or an inverter, we usually connect 3,4 or a dozen in a row. This makes the voltage add higher and higher. So 10 panels that individually make 50v end up making 500v. they add up like 50, 100,150....450v, 500v.


Now let's say something happens to panel number 9. The glass cracks and next time it rains, water gets inside. Well kids, that water shorts out the wires to the frame of the panel. That 9th panel should have between 400 and 450v on it's positive and negative wires because of it's position in the array... but now the aluminum frame has got 450v on it because of that water inside. Now you walk up to the panel and touch it and you're gunna get shocked.


How do we solve this? We ground the panels together. We ground the metal beams that connect the panels. We connect every piece of exposed metal to the earth that you are standing on.


When your inverter wakes up each morning, if it's a well designed proper inverter, it will check to see if the positive wire is connected to ground and if the negative wire is connected to ground. If it finds that the pos or neg is not "floating" relative to earth ground it will give a ground fault error or refuse to operate.


Now you know why we ground solar panels. It's not needed day to day, but it is needed when something goes wrong.


One of my favorite sayings is "it's not that it works, it is how it works when something is wrong".

How to load a tire after 30.

Had to put my thinking cap on last night.

Did a software upgrade on one of my MPPT chargers that directly charges the 48v batteries. Presently, I have one of them programmed to shut off at the moment we connect to the grid because that's usually at the peak of solar produciton and I can't squeeze all the power I make thru the utility transformer in front of the house. So the easy solution was just to shut 3kw off for the rest of the day. Recently I found that new firmware in the MPPT could allow it to have it's charging rate remotely controlled. but it requires me to format numbers in IEEE 754-2008 "Floating point 16" format. So I spent yesterday evening writing code to decipher that format. Since most floating point numbers are expressed in 32bit or 64bit, the 16 bit is uncommon and there are no libraries for it.

In a nutshell, you get a 16 bit integer and break it down into 10 bits on the right. These 10 bits give you a range of numbers from 0-1023. if you calculate a ratio of n/1024 and add 1 to it, you have the mantissa. For example, 512 here would be 1+(512/1024) or 1.5

From the left the first bit being a 1 means the entire number is negative, and the remaining 5 bits give us an exponent that can range from 0-31. Subtract 15 from the exponent and you get an exponent that can range from -15 to 16. If the exponent is 18, we subtract 15 from it to get a value of 3.

Now we're ready to do the actual conversion..... 2^3 x 1.5 or.... 8 x 1.5 = 12. So exponent of 18 combined with mantissa of 512 is the number 12. Fun stuff...

So tonight I'll write code to look at how much power I'm exporting and control the MPPT chargers in 1amp increments. That's approximately 50watt increments.

Side comment: I took computer programming in college. They NEVER taught us this. I took algebra in high school and calculus in college and they NEVER taught us that one of the uses for the quadratic equation was curve straightening... and I used it in industry to calibrate nuclear weight sensors. College is NOT teaching your kids a damn thing that has a practical use. Kids spend $100k on a college education for knowledge that can be had for $1.50 in late fees at the public library.

Here are some real world numbers for you. Remember, everything can be explained with a car analogy.

MPPT is a like a transmission in a car. It uses a "gear ratio" to change the volts and amps from the solar panels to the volts of the battery and more amps.

Here we have 4.1amps coming from the panels run thru the "MPPT gear ratio" and converted to 28.2amps. It's about a 7:1 "gear ratio".... but look at the voltage... the panels are at 346v and the battery is at 52.25v. That also is about a 1:7 ratio.

If this was the older style PWM controller the amps could never go up. I would be getting 4.1amps into the battery. All PWM can do is "slip the clutch", it cannot change "gear ratio".

PWM would make 200watts.... but MPPT makes 2412w.

The keystone meat in a can is actually good.

https://a.co/d/gbMq71V 2300w inverter generator. $300.