Connecting solar panels and batteries.
A few weeks ago I talked about all the things you need to add solar power and batteries to a campervan. It’s now finally time to connect it all up. I’d say most people could do it themselves, as long as they know which is the important end of a screwdriver. 48v Solar Panel
There are a few decisions you should make ahead of time, however, that can have some impact on your system. One of those is whether to hook everything up in series, or in parallel. You won’t need an electrical engineering degree to figure out which to choose. There are some easy-to-understand pros and cons.
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Here’s a simplified breakdown of how my system is wired:
Each stage of the above has a fuse in-line, for safety.
I left out the fuse bar part from the above video because it’s a mess. One of my projects in the coming weeks is to re-do the wiring so it looks less like the end of Superman III. More about this below.
I highly recommend a good crimping tool if you’re doing this yourself. Save yourself annoyance, time, and your hands.
The wires to connect the panels together, and then down to the charge controller.
One of the more confusing aspects of connecting everything is the difference between series and parallel. There are pros and cons for each, though there’s no “wrong” answer for most builds. If you’re using an MPPT controller, you can choose either method.
To start, it’s important to keep in mind that watts equals amps times volts (A*V=W). So, for example, 100 watts can be 12V and 8.3A (12x8.3=100), or 24V and 4.15A (24x4.14=100). Both are 100 watts, but are handled differently. If you connect two 100 watt solar panels together, you’ll have 200 watts of power, but volts and amps change depending how you connect them.
If you connect them in series, you double the voltage. So you’ll get 37.8V at 5.29A (37.8*5.29=200). The benefit of this is you can use thinner wires since 5.29A doesn’t require thick cables. If you have a 24V system, you’d also need to use this method, but for smaller campervans you likely don’t need a 24V system, 12V is fine. The downside is shading, which I’ll discuss below.
If you connect these same panels in parallel, the voltage stays the same but the amps double. So with the same panels mentioned in the previous example, that means 18.9V and 10.58A. For van builds, the cables aren’t typically very long, so this amount of amps doesn’t require super thick cables. An MPPT controller doesn’t care which of these you do, it will send your batteries what they need to charge.
For extra safety (and in some cases, just basic safety), put a fuse in line with each device.
The main difference between the two methods for most campervan builds is what happens if you have partial shade. Let’s say you have to park under a tree, and for part of the day one half of one of your panels is in the shade. In a parallel system, that panel will produce 50W, but the other will still produce 100 watts (in reality, neither will max out like that, but let’s keep it as simple as possible). If they were instead connected in series, both panels would drop to 50 watts, even if only one of them is in partial shade. They adjust as a pair, not independently.
I intended on connecting them in parallel, but when my mechanic mounted the panels he wired them in series and I haven’t changed it back. For my build, I have so much capacity and I’m generating so much more power than I need, it hasn’t ended up mattering. I’ll be cleaning up my build and interior in a future project, and if I readjust the panels I might switch them to parallel.
This photo implies this is my garage. If "my garage" means "being friendly with your local mechanic ... [+] so you can use his stuff occasionally" then yes, totally "my garage."
As I’ve mentioned above, I’ve added a fuse for everything. For the safety of your gear, and your van, this is a good idea. How you do this can certainly vary. I built out a car-style fuse box, powered from the battery, that connected out to the charge ports. It’s a veritable rats nest and a borderline embarrassment, but it works. One of my upcoming van projects is to make this more manageable and aesthetically pleasing.
You should figure out how you want to secure everything. The batteries are especially heavy, and you don’t want them sliding around. I built a frame to some leftover OSB and they’re reasonably secure. I’m considering adding some rails to the system so I can pull it out the back to working on it.
The Renogy gear I bought has an available Bluetooth transmitter, and I recommend it. I can check the power levels and what the system is doing from anywhere near the van.
There's nothing more permanent than a temporary solution. This is a rough brace I built for the gear ... [+] so it wouldn't slide around. I intend to make something less horrible looking in the near future.
The DC-to-DC charger is installed and it works. It’s a good backup, letting me charge the batteries from the van’s engine. However, I had a kill-switch installed, currently set to off. The panels keep the batteries well charged, and even though the charger is self-regulating, only turning on when the batteries need it, that ended up being more often than I felt necessary, especially when driving at night. This is the only piece of equipment other than the panels I farmed out to my mechanic, not trusting my skills with anything that interacted with the operation of the van. My van also has an auxiliary fuse box in the back, which made things simpler in some ways, and more difficult in others.
Up next, building a bed and a desk. Stay tuned!
Solar Panels For Tiny House In the mean time, get caught up from the beginning: