Project: Building a Solar Charge Controller with a UPS Module — RenewSolar

We had the delight the other day of having the grid power problems, which was such a pain as it was off and on for some time.

The project actually was used to power our routers -  this item:
Mini UPS For modems and routers — RenewSolar

I shall be spending time on a few "tiny solar projects" in the next few weeks if I have time. Business has started its spring rush as a little bit of sun bring the solar steppers out in full force. 
Oddly I didn't see much sun, there was some a few days ago.. and of course the sun should make its self known in 5 weeks time.

The Buck Converter

A buck converter works very much like the MPPT, it will change the drop in voltage into current and it will output a stable voltage. They're about 97% efficient so pretty good, but they are not all the same and have some limits if you don't know what to look for.

You do add other things if you want to make your own fully fledged  charger, but for most two items would be required. You can use panels up to 70v for less that a ebay special PWM controller. which in my mind sound great, but it is actually very simple.

I shall Put an article on the website showing you what you need, and in the shop it will be able to buy a parts kit.

Also check out our projects page where I add projects from time to time.

I have hammered home the Not plug in or plug and socket, you can use a AC isolator but you should add protection before the unit is connected, this is because your power source is the other side of the breaker and RCD if its plugged in, so you don't get the protection. hence why I mention it is a faff to address the details of plug in solar. Its off they did do this in many of the European markets where these are "legal".

The rules were updated on April 1st 2024 they added a "special plug and socket" and the only information I read was that it was a dedicated circuit. This would make the installation  A typical installation as we would normally have with solar installations.

I should also note that these are like the Enphase systems with AC inverting at the panel. and they could be linked together to provide a bigger solar installation when installed correctly.

As you know, you can have a electrician install a dedicated circuit, this would be installed on the supply side. however if you wanted to vacate this cost, then the other alternative is to  follow the guidance:

– on the load side of all the overcurrent protective devices for a final circuit of the installation, but in this case all the following additional requirements shall be fulfilled:

(i) The conductors of the final circuit shall meet the following requirement:
Iz ≥ In + Ig

Where:
Iz is the current-carrying capacity of the final circuit conductors
In is the rated current of the protective device of the final circuit
Ig is the rated output current of the generating set

(ii) A generating set shall not be connected to a final circuit by means of a plug and socket-outlet

The first step is to remove the plug.
We can wire a different plug, like a commando. This removes the "live pin" risk.

Lets look at the math shown in the big book..

Iz,  this is usually 2.5mm T&E, they can be radial or rings and you should know the difference. the conductor is the wire.

Iz = 24 amps

In = this is the breaker, or fuse. Typically 20 amp. but on a ring main it will be 32amp.

Ig  varies and you will find this on the generator (inverter) as its current output AC.


In theory, (not in real life) the  ring main is doubled up, therefore the theory is 50 amps current capacity (Iz) but in reality it is not.

We will look at the radial. which gives us 4 amps at (Ig.) this gives us inverter power of 920W.

Therefore we need to add protection to the circuit. a 4amp MCB will provide some protection, we also want RCCB and SPD and the cost runs up.
You also need dual pole. and good luck finding a 4 amp RCBO. they don't make them. the lowest is 6 amp.

On a ring 6 amp would run you a 1360w inverter.

So the plug we removed, should be correctly wired to an enclosure unit, thought the protection and then exit. it would go to a commando or AC Isolator which is hard wired in.
smaller inverters should be protected at a lower power. You may wish to return to the distribution with a 4 amp MCB.

Remember inverters have some protection built in, but if that fails, the  "house protection" ( what I have said above) provides that fault correction as to stop wiring fires or inverter fire. I will repeat myself here, but for the costs you should be able to have a supply side installation carried out as the hardware is around £100-160..

conclusion....
Plug in solar is NOT plug in solar.