Hi all,

 

We just got our new solar panels installed (9x330W), including a (Mecer-branded) Axpert 5KVA and a 48V Pylontech battery.

 

To monitor the system and be able to switch battery/grid based on real SoC of the battery, I installed ICC on a raspberry Pi and connected it to the Pylontech and the inverter. It all seems to be working reasonably well.

 

My question is - what is the best way to power the Pi? It seems silly to have to plug in a USB charger into a power outlet somewhere and connect it when the Pi is literally next to a battery and an inverter. Has anybody found a way to power it from the inverter or from the battery directly?

I've browsed the internet for a DC 48V to 5V (USB) converter, but it doesn't seem to be something that's readily available, at least not in SA.

 

Thanks!

Frans

2 hours ago, SolarFrans said:

I've browsed the internet for a DC 48V to 5V (USB) converter, but it doesn't seem to be something that's readily available, at least not in SA.

The simplest way is to use a buck converter of sorts, but you are right: Finding one that can handle above 60V input (that is essential) is not easy. Typically I'd just use one of these, it's a garden variety LM2596-based thing, add a 1A fuse for safety, and bob's your uncle... except that thing potters out at 35V. So no good unless you're on a 24V system. There are higher-end models, such as the LM2596HV (max 60V), but you really want at least 75V to be safe. And those things are a little hard to find, because they aren't that popular through the usual hobbyist channels.

But that's where you should be looking.

6 hours ago, plonkster said:

Typically I'd just use one of these, it's a garden variety LM2596-based thing

But then it's not isolated from the 48 V battery. If everything else is isolated, that might work.

I use a Meanwell SKM30C-12 in my system; it's an isolated 36-75 V to 12 V 30 W DC-DC; it runs up to 7 contactors, a BeagleBone Black (via a 5V regulator), and the battery management system. A smaller 5V version would work for you.

7 hours ago, Coulomb said:

But then it's not isolated from the 48 V battery. If everything else is isolated, that might work.

Right. Now usually the way we handle this in blue land is we make the other things isolated, so your VE.Direct, VE.Bus (aka RS485) and canbus connections are all isolated. It's also only really a problem if you have some sort of mismatched reference, eg the ground side of the serial connection to that inverter isn't at the same potential as battery negative. I seem to recall though that I saw some optos on that board... so doesn't it already have isolation?

I did a quick and dirty one here.

Used one of those 10000mA (printed on the box, not that I believe it) powerbanks to power the Pi. 

The Powerbank is Powered/Charge via a normal USB charger from a plug from the Inverter out power rail.

HOWEVER......

Not all Powerbanks support simultanious power "pass through", and most will cut the output power, the moment you insert the charger cable. I was lucky the second different type I bought worked 100%. Much cheaper than even one of those Pi UPS HAT's.

Thanks for the tips, guys. I'm more of a software than a hardware guys, so not sure what isolating means in this context, but I'll Google around a bit for that

 

@Sidewinder, how are you connecting the charger to the inverter?

1 hour ago, SolarFrans said:

Thanks for the tips, guys. I'm more of a software than a hardware guys, so not sure what isolating means in this context, but I'll Google around a bit for that

The full term is "Galvanic isolation". A simple example of that is a transformer (no direct electrical path, it is magnetically linked across). In electronics it is common to use "opto isolators", which uses a light signal to send data across so that electricity need not pass between the systems.

The reason you might need to do this, us because the "ground" signal on a data cable might not be at the same potential as the negative cable of the battery, and when you start interconnecting things that are powered from the same battery... you have the potential to blow things up. Isolating them means simply that you never have to worry about that.

I use the following DC-DC buck converter with great success: http://www.mantech.co.za/ProductInfo.aspx?Item=372M0042

It can take an input of 36V-72V and works fine off the Pylontech batteries as well as lead acid / AGM batteries. Just put a fuse in-line, on both sides

@SolarFrans,

On my incoming, as well as outgoing grid, (as seen from the inverter), I have install a separate small DB, with Isolator, RCD & CB. From each side, I have a set of double plugs.

So in my Inverter room, I have "Grid" plugs and "UPS" plugs. The extra fans (to cool the inverter and extractor fan to "de-gas" the room) and Powerbank charger are plugged into the "UPS" plugs.

In future I will power a small Aircon as well, as the small room does get a bit too hot in summer for my liking. Am busy planning installing temperature probes as follows:

1) Inverter 1 

2) Inverter 2

3) Inv. Room

4) Battery Bank

5) Outside

6) Under PV panel 

The first 2 are required, as the Infini/ICC combo looses it ability to report this, when inverters are paralleled, so I have no idea. Better to know, you know!

17 hours ago, SilverNodashi said:

I use the following DC-DC buck converter with great success: http://www.mantech.co.za/ProductInfo.aspx?Item=372M0042

It can take an input of 36V-72V and works fine off the Pylontech batteries as well as lead acid / AGM batteries. Just put a fuse in-line, on both sides

Sweet! So on the 5V side I'd put in a 3A fuse? And on the 48V side? 15VA means I'd only need a 15/48 = 325mA fuse?

 

18 hours ago, plonkster said:

The full term is "Galvanic isolation". A simple example of that is a transformer (no direct electrical path, it is magnetically linked across). In electronics it is common to use "opto isolators", which uses a light signal to send data across so that electricity need not pass between the systems.

The reason you might need to do this, us because the "ground" signal on a data cable might not be at the same potential as the negative cable of the battery, and when you start interconnecting things that are powered from the same battery... you have the potential to blow things up. Isolating them means simply that you never have to worry about that.

Thanks for explaining, that makes sense.

 

But a buck converter is basically a transformer, so isn't the isolation then taken care of?

3 minutes ago, SolarFrans said:

But a buck converter is basically a transformer, so isn't the isolation then taken care of?

Depends on the topology. The simplest (and therefore cheapest) type of buck converter (switch, flyback diode, inductor) is more like an auto-transformer, so there is no isolation. Once you add a transformer to a buck converter it is called a "forward converter", and then there are all sorts of caveats that you can google if you really want to... suffice it to say, that unless explicitly stated, you cannot count on a DC/DC converter being isolated.

13 hours ago, SolarFrans said:

Sweet! So on the 5V side I'd put in a 3A fuse? And on the 48V side? 15VA means I'd only need a 15/48 = 325mA fuse?

 

I put a 1A fuse on the 48V side, purely cause that's what I had.