50W solar panel to charge 2 x Calcium car batteries

Jared88

Hi, I have two 12V calcium car batteries, I would like to charge them both with a 50W solar panel to run a few items in my shed, 50W solar panel is all I need. Would anyone please recommend a charger and a 12V to 240V inverter and how to connect it all together please.

Thanks.

Jared.

doodling

Hi,

Without knowing what "few items" you want to power and for how long it is impossible to answer this question.

If your only source of energy is a 50W panel then hopefully you only want to power a few lights for an hour or two, in which case an inverter is overkill.

QrizB

Jared88 said:

Hi, I have two 12V calcium car batteries, I would like to charge them both with a 50W solar panel to run a few items in my shed, 50W solar panel is all I need. Would anyone please recommend a charger and a 12V to 240V inverter and how to connect it all together please.

A 50W panel with give you around 100-150Wh a day, on average. Much less in the winter. You need more panel if you're going to do anything much that needs 240V.

One of these will work but will lose you roughly 30% of the potential power (so 70-105Wh/day, rather than 100-150Wh):
https://www.ebay.co.uk/itm/373954140851

If you want to make the most of your panel you'll need one of these - although, from a cost perspective, you'd be better off buying a bigger panel and sticking with the cheap controller:

https://www.ebay.co.uk/itm/304331480485

I've got a controller like the first one in a portable power bank I built last year, mostly for fun. This video isn't my build but it's similar:
https://www.youtube.com/watch?v=g2cLMk3nD3Y

My Dad's got a controller like the second one (but with a higher power rating) in his off-grid shed but that's got 750W of solar, not 50W. His kit was something like this (but with more panel):

https://www.bimblesolar.com/offgrid/complete-packages/shed-kits/305W-kit-mppt-mounting

chris1973

I bought a Battery Control PCB Module from Aliexpress, and hooked it up to a 30W Solar Panel. The circuit board, contains a dedicated I.C controller which monitors battery, type, voltage and condition and controls the charging current accordingly. I originally bought it to keep the car battery in good condition whilst it was off the road for 12 months during lockdown, but now use it to constantly trickle charge a couple of AGM batteries as back up for power failures. The 30w panel was about £25, and the Ready Built PCB Module was about £3 - I just mounted it into a cheap ABS box from CPC. Back then this DIY approach was far cheaper than anything available commercially as a kit and worked flawlessly in both my applications.

markin

Use all 12v led lighting to avoid inverter losses when that isn't needed.

wrf12345

With such a small solar panel you could just connect it directly to the battery or via a voltage regulator if max panel voltage is high compared to the battery (two  batteries can be wired to take 24V) and then just run everything on 12V DC, checking it with a voltage meter and disconnecting when necessary or leaving the lights on to balance things out.

QrizB

wrf12345 said:

With such a small solar panel you could just connect it directly to the battery

This is terrible advice and will kill your batteries within a year.

wrf12345 said:

... or via a voltage regulator

In other words, a solar panel controller which is what the OP is referring to and for which I've provided two recommendations.

Also beware of solar panels from eBay, AliExpress, BangGood etc. A lot of seemingly cheap ones claim output powers that are never going to be achieved. Many of the ones sold as 20, 30 or 50 watt panels are closer to 10 watt in practice.

Take this one for example:

https://www.ebay.co.uk/itm/194879515238

A good quality modern solar panel will produce around 200 watts per square metre of active surface. The panel in that listing is 43cm X 20cm, only 0.086 square metres and so the maximum possible output will be 16-18 watts. Not 50 watts.

In practice a good part of the surface area of that panel is made up from the border around the cells, and is inactive. Actual output is likely to be closer to 10 watts.

Astria

Exactly why are you doing this? I did think about this a year ago, but it turned out cheaper and more future-proof to have electric installed where I wanted it and run everything off the mains.

In the shed I do have a similar arrangement as you, but there's no inverter, probably a smaller solar panel, and the charger is a basic unit I acquired from ebay. It just runs a LED strip at night. It would easily run a week without the solar panel.