Before I plug this in...

[donb108]

I've had a couple of funny things happen while building my sheds solar system.

-While installing the second string of panels, I got a couple of minor shocks (just tingles).
-After everything was installed, I added a buck converter to the battery for Solar Assistant. A few weeks later, it burned up.
-I tried to replace the buck converter with a better one. When I connected it, there was a spark, and then it didn't work.
-I disconnected the panel ground wire from the system ground block, and got a shock (more than a tingle).

I've taken some readings that I don't understand.

-The PV strings ground wire (in free air) to system ground measured 135 Vac. Where does that come from?
-After removing the string (+) and (-) wires from the inverter, the inverters PV +/- terminals measured 20 Vac. Is that normal?

Is all this normal, (and before I replace the buck converter again), should I be looking a little closer?

 

[timselectric]

This is why a grounding system is important.
And yes, the readings are more than likely normal.
Most of today's high frequency AIO's do not have complete isolation between the different parts of the system. It's not a problem for a properly grounded system.
And as with anything electrical, make sure that you have turned everything off, before working on the system.

 

[donb108]

And as with anything electrical, make sure that you have turned everything off, before working on the system.

Right, I worked most of my career with controls, where everything was class-2; usually 24Vac. Most of our equipment was embedded computers, so we rarely turned anything off, it took too long to boot up. I'm forming new habits now.

 

[donb108]

I went back and took more readings. I turned off the battery and PV breakers, which makes the inverter power-down.

-The PV strings ground wire (in free air) to system ground measured .6 Vdc / .007Vac.

, then removed the PV string (+) and (-) wires from the inverter and turned on the PV breaker.

-The PV strings ground wire (in free air) to system ground still measured .6 Vdc / .007Vac.

I was concerned that one of the panels might have a short. I guess only a megger can tell for sure, but this may be good enough.

 

[timselectric]

I went back and took more readings. I turned off the battery and PV breakers, which makes the inverter power-down.

-The PV strings ground wire (in free air) to system ground measured .6 Vdc / .007Vac.

, then removed the PV string (+) and (-) wires from the inverter and turned on the PV breaker.

-The PV strings ground wire (in free air) to system ground still measured .6 Vdc / .007Vac.

I was concerned that one of the panels might have a short. I guess only a megger can tell for sure, but this may be good enough.

Sounds like everything is normal.

 

[Mkgough]

I've had a couple of funny things happen while building my sheds solar system.

-While installing the second string of panels, I got a couple of minor shocks (just tingles).
-After everything was installed, I added a buck converter to the battery for Solar Assistant. A few weeks later, it burned up.
-I tried to replace the buck converter with a better one. When I connected it, there was a spark, and then it didn't work.
-I disconnected the panel ground wire from the system ground block, and got a shock (more than a tingle).

I've taken some readings that I don't understand.

-The PV strings ground wire (in free air) to system ground measured 135 Vac. Where does that come from?
-After removing the string (+) and (-) wires from the inverter, the inverters PV +/- terminals measured 20 Vac. Is that normal?

Is all this normal, (and before I replace the buck converter again), should I be looking a little closer?

Is your shed properly grounded? The shed have a ground line to the building itself?

 

[donb108]

The shed have a ground line to the building itself?

Yes, there are two ground rods directly behind the structure, but nothing is connected to the house electrical system.

 

[timselectric]

Yes, there are two ground rods directly behind the structure, but nothing is connected to the house electrical system.

You're not using the power from the inverter, in the house?

 

[donb108]

You're not using the power from the inverter, in the house?

No, it's a stand-alone system. It's my first solar install and I wanted to go through the learning curve on something simple. And, the cable runs from my electrical panels to the shed would have been fairly difficult and expensive to run. Or, at least, that's my excuse.

I'm planning to install a small system (EG4 6000x and 3 batteries) in the house this winter, but that will be a separate from the shed. Is there a reason to make it a single system.

 

[timselectric]

I'm planning to install a small system (EG4 6000x and 3 batteries) in the house this winter, but that will be a separate from the shed. Is there a reason to make it a single system.

No, as long as they are separate in all ways.

 

[donb108]

I searched Amazon for the right buck converter without much luck. I found lots of units, but they had the wrong voltage, or wrong current, or was the same as the last one that failed, etc. I ended up buying one from the Solar Assistant site; they've already done the searching and have one that works (and it includes a fuse).

It's installed and working.

SolarAssistant

solar-assistant.io

 

[timselectric]

That's the ones that I use.

 

[Johno1066]

What is a buck converter?

 

[Johno1066]

Ok I see that they are DC to DC power supplies obviously to power instruments. How are you using them on your solar panels.
There is much stuff available that I never knew existed, 30 to 40 years ago they would have been priced so high no one would be able to afford them.

 

[robbob2112]

A buck converter is used to step down voltage - always from a few volts - 2~5 higher than your target voltage. A boost converter is used to step up voltage to a higher one. A Buck/Boost converter does whatever it takes to output the correct voltage.

Step down and more current is available, step up less current is available. And there is always a slight cost for conversion.

Most MPPT work as a buck converter

 

[Johno1066]

Thanks for your explanation, just amazed at the cost of these boards on Amazon, some of them 6 or 8 for $10 or so.

 

[robbob2112]

I use a DROK buck convertert to step down 12vdc to 9.5vdc for the Don Joy Ice machine I use after surgery.

I did some tests when I got it and found the included PSU would only put out 1.5amps or so, but the twin motor/pumps in the unit each draw about an amp at full capacity. So using the 5 amp DROK dialed to the correct voltage and unlimited current I got the unit to function better.

 

[donb108]

What is a buck converter?

Here's an explaination of why we're using it.

D

Post in thread 'Solar Assistant setup question'

Aug 25, 2024

Get the pi zero2 W kit from Canakit and plug it into a 110 outlet. Why make it so hard?

It's currently plugged into a wall-wart in the shed, which is powered by the inverter, which is powered by the battery. As I recall, the inverters default battery-state-of-charge thresholds are 20% and 95%.

If the battery goes below 20%, the inverter stops supplying power, and the wall-wart looses power. The solar panels will recharge the battery, but the inverter won't start supplying power to the wall-wart until the battery gets over 95%. Solar Assistant is out-of-service until the...

• donb108

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