This is an update to our DIY How To series on How to Build a Large Solar Generator. In this follow up post, I will show you how we can use the quick connects designed into our solar generator to expand both the solar charging capacity, as well as the battery bank for increased run times.
A lot of the feedback was asking how to expand the solar generator to an even bigger capacity system. When I designed the base unit, I wanted it to be very easily expandable using quick connects. There are two areas where we can easily do that with our system:
Increasing Solar Panel Array
First is solar charge capacity, which will increase the rate at which the unit can recharge our batteries. We used a 30 amp charge controller in our build, as well as a single 100 watt solar panel.
When this panel is in peak conditions, we can expect slightly over 5 amps. The panel is rated with a 5.25 amp Optimum Operating Current, which is the current we would get out of the panel in 100% perfect conditions with the panel operating at peak efficiency.
There is a second rating, the Short Circuit Current, which for this panel is 5.75 amps. Unless there is a problem with the wiring from the panel, we should never see this full current, but its good to understand what it means and take it into account when sizing wire. This value is the maximum possible current the solar panel could create when it is in full direct sunlight, and the output wires are shorted together.
Knowing these specs, along with the manufactures recommendations for our charge controller not to exceed 80% of its max current rating, we can add up to four of these 100 watt solar panels in parallel.
By connecting these panels in parallel, the current from each panel will add together, giving a max short circuit current of 23 amps. But the output voltage will balance between them, not add together. It is possible to connect panels in series as well, but it doesn’t make as much sense for our usage scenario to wire them that way. I will explain the differences in a later post, so make sure you subscribe if your interested in that.
We can easily wire our four panels in parallel using some 4 to 1 MC4 cable adapters. We will use on adapter to connect all 4 positive (+) wires from the panels into the positive wire leading to the solar generator. Likewise, we will use the other 4 to 1 adapter to do the same with the negative (-) connections.
Expanding The Battery Bank Capacity
We included a high current connection to our large solar generator, so that we could easily expand the battery bank. Adding 1 or more additional batteries will give your inverter an increased run time at higher loads, or when solar conditions are poor.
As a bonus, the battery bank expansion unit we build here can also be used independently with our quick connects, which give you an easy way to get a large 12v power source for jump starting vehicles, powering a 12v winch on a trailer for example, running a 12v tire inflator, and with an inexpensive option, you can even have an extremely large capacity USB power bank.
We use two high current quick connectors on the battery expansion unit, that way we can daisy chain as many additional batteries as we want. It also allows us to still use our other high current accessories with the solar generator, such as jumper cables, or a 12v winch without needing to disconnect the additional batteries.
The batteries are wired so that when they are connected together, they form a parallel battery bank. This means the total voltage will stay the same, but the battery capacity will increase. Our main solar generator unit has a Optima Blue Top battery, which has a 55 amp hour rating. We will use a VMAX SLR-125, which is rated at 125 amp hours in the battery expansion unit. So the total capacity will increase to 180 amp hours when they are connected together.
The battery is quite heavy though, weighing in at 75 lbs. It is also a Group 31 battery, so it is fairly big. I purchased this battery case, which is compatible with group 31 batteries, as well as several of the other larger battery sizes. We will be using it as an inexpensive housing for our battery expansion unit.
Components Used in this Tutorial
To see the components used in the main solar generator unit, see the post for Part 1 in this series.
Solar Panel Expansion
Battery Bank Expander Unit