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Solar charging, DC to DC chargers, Shore Power…how it all works (for us)

A few people have asked for more technical information about our vehicle and how it’s set up, so here goes. Let’s talk electrons. 

I have to tell myself it’s important to not loose sight of the ball. The whole idea here is to, a) have an actual fridge instead of a cooler. This avoids having to buy ice all the time and dig the butter out of a pool of tepid water in the bottom of a cooler and keeps the beer cold; and b) to charge the various electrical doo-dads that most of us now travel with, cameras, laptops and the rest. None of this discussion has anything to do with the regular start battery and alternator. We have left this untouched and stock to preserve reliability and serviceability.

I used to obsess quite a bit about the battery, charging, fridge status and that sort of thing. Typically this means one of my very first activities of the day is to check the battery level, to see how badly we’d depleted it through the night. Then when Jenny gets up, bleary eyed and totally uninterested, I give her a detailed battery report. She tolerates this to a point, but when I’d get too far down the rabbit hole she asks me to perhaps delay my enthusiastic report on battery chemistry or solar panel voltage until after she’s finished her tea.

Now I’ve got Jenny interested in the battery status, but not for the reasons I hoped. Sometimes she beats me to it and checks the battery level before me. I know this isn’t really her thing and told her she doesn’t have to worry about it, and she responded, “Oh I’m not worried about the battery voltage, I check it to see what kind of mood you’re going to be in.” She later elaborated that the voltage correlates to how much electrically related anxiety I’ll have on a given day.

The Cruiser electrical system has evolved since we owned it. Here is the timeline, problems and solutions so far:

In the beginning (c. 2017):

Supply side:

• Standard starting battery, sealed lead acid (SLA)
• Auxiliary battery, 102 amp hour (Ah) SLA, mounted in the engine bay. The 1HZ 79 Cruiser is sold with two starting batteries in cold weather markets. Here in Africa two batteries are not necessary, so this leaves the second battery spot available for an auxiliary battery. The problem with auxiliary batteries in the engine bay is batteries do not like heat, more on this later.
• Charging of the auxiliary battery was by the alternator via a National Luna Intelligent Solenoid.

Load side:

• A 40 liter Engel fridge that came with the vehicle when we bought it.
• A 15 liter IndelB fridge we installed between the front seats. This is a ludicrous luxury, but we like it.
• 3x two color (red and white) LED lights in the canopy.

That’s pretty much it. We have various USB rechargeable items that we charge in the cab via the 12v plug while we’re driving. The copilot is responsible for swapping through all the headlamps and flashlights and whatnot to keep us charged up. We use a cheap ($25 USD) 200w square wave inverter (this one) to charge things that require 110 or 220v charging, for us this is a laptop and camera batteries. This works totally fine for us, we’ve never found the need for a proper pure sine wave inverter

This is the setup we drove to Kenya and back 2018. It worked fine, mostly. Everything was fused with inline fuses, but we did have a short in the system when we chafed through some wiring on very corrugated roads, leading to a teeny electrical fire. 

Fortunately no serious damage was done, but I suspect this short did shorten the life of the battery, as it never held up through the night quite as well after that. 

Pros with this system: It is cheap and simple and easy to work on. If you drive most days it is adequate for almost anyone’s needs. Also at the push of a button you can parallel the batteries to allow for jump starting the car off the auxiliary battery if the start battery is dead. We have actually used this once, but this is a luxury, since really we have jumper cables and can do this manually if needed.  

Side note: the 4.2 Land Cruiser actually push starts beautifully in 2nd gear, provided you can actually get the great beast rolling. The mass of the vehicle carries enough momentum to start the engine easily. We have done this for a fellow Land Cruiser at Third Bridge campsite in Botswana. Never push start in reverse, the teeth are ramped and you can damage the gears. 

Flaws with this system: You can’t stand for more than two nights without driving, the battery gets depleted.

When we did want to stay somewhere longer there was usually at least some errand to run or game drive that topped up the battery somewhat, but for purely sitting we had no method of charging. Anytime we planned on sitting for more than one night, or if it was very hot and I knew the fridge was going to work hard, we’d turn off the 15 liter fridge for the night. This fridge is only used for drinks, so no food was at risk. 

Another flaw, perhaps not true with all vehicles, is that the auxiliary battery never gets a true full charge. This is because to fully 100% charge a lead acid battery you need to generate over 14 volts during the charging cycle. The alternator on the 70 series cruiser, as I understand it, only generates 13.7v. Add in minor voltage losses through cabling and you never quite get a 100% charge. Normally this isn’t an issue, 98% is fine, but over time the battery needs to at least on occasion get fully charged. Without shore power or being put on a standard charger every once in a while this degrades battery capacity and battery life.

Electrical Upgrade, c. 2019:

Back home, away from Africa and the Cruiser I spent too much time spent on the internet and therefore too much time pondering upgrading our electrical system. Enter, the upgrade.

Supply side:

• We ditched the solenoid charging and got a National Luna 25A DC-DC charger. Utilizing Ohm’s law, DC to DC chargers drop the charging amperage to increase the charging voltage, thus enabling the battery to get a true full charge. The trade off is it takes longer to achieve the full charge, as it only charges at 25A instead of whatever the surplus from the alternator was. We drive long distances often, so this usually isn’t a problem. Note: National Luna has a few excellent blog posts on this topic here. Given that we have a 102Ah battery, and hopefully we are not depleting it more than 50% (to preserve longevity), we should only ever have to replace roughly 50 Ah. You’d think that a 25A charger would manage this in 2 hours, but that is not the case, because of the charging profile. Batteries don’t accept charge in a linear fashion, so the charger must top off the final stages of capacity more slowly. Regardless we’ve never had an issue achieving a full charge.
• The DC to DC charger has a solar MPPT charge controller built in. This means in one box we can charge from the alternator when driving and from solar when parked. 
• Added a 120v flex solar panel from 4x4direct in Cape Town. This is also the same time we got the Alu-Cab roof top tent. The hard shell tent provided an easy location to mount a 120w flex solar panel. We were assured by the fitment center that they install these all the time and how great this whole setup works (except when it doesn’t).
• Added “shore power”. Now we can plug in to 220v power if we’re in a place that offers power at campsites. This is pretty common in Southern Africa, but very unusual in East Africa. The shore power is simply a 15A Victron battery charger hardwired to the auxiliary battery. We have a ~10m power cord, plug in, and presto, the aux battery is always getting charged and all 12v things can run as normal. Cold beer with no battery stress!

Load side:

• The new tent has a LED light built in, as well as two USB ports and a 12v socket in the tent. This is convenient to charge things via USB when we’re parked. This load is minimal.
• We hardwired our GPS, leaving the 12v socket in the cab always free. I highly recommend this small modification, we did it ourselves for free and it appreciated every day we drive (i.e. a lot of days). This is very luxurious and now involves less juggling of cables for the copilot. Also the GPS power cord no longer dangles around in the cab, very nice to have this cleaned up. Actual load increase is also minimal, since this load is only realized when driving.

Pros with this system:

• Now we can plug into shore power, super. Very nice when you stop for a few days and want to torture the fridge to clean it out or load a lot of new warm things and you don’t have to worry about your grocery trip depleting the battery.
• Solar! In good sunlight we generated 6 A, but usually less. This is not really enough to power us indefinitely, but is enough to keep us going for a few days with careful fridge use and little to no driving. 
• The DC to DC charger is charging the battery fully, which should promote battery longevity. 

Flaws with this system:

• The National Luna DC-DC 25A charger does not have the ability to charge both the aux and main batteries via solar. Some DC-DC/MPPT chargers do have this feature.
• The shore power also does not charge both aux and main batteries. This is an issue because we leave the vehicle parked for long periods of time. Batteries do not like to sit, and self discharge over time. We’d love to tell the storage place that they can just plug us in and top us off, but because the shore power doesn’t do both batteries it’s not that simple.
• Solar. The MPPT charger seems to kick on when the panel reaches around 18v. This doesn’t happen as early in the day as I’d like, and kicks off earlier in the afternoon than I’d prefer too. This is when the angle of incidence of the sun is too low.  
  • The panel is fixed on the tent. This is a trade off. Many elect for portable panels that you store in the vehicle, pull out, unfold, plug in, and then move around through the day. This enables parking in the shade and ideal panel placement, avoiding the issues I just described above. The downside of that is you need a place to pack the panels, it’s another thing to fuss with in camp, and they don’t work when you’re parked at, say a water hole or grocery store or whatever. If you are the type of camper that often spends four or five days in one spot often then I think portable panels are the way to go. For those that move a lot, like us, I think fixed on the roof is more practical. Pick your poison.
• Heat. This is a big one. The National Luna DC-DC charger has an optional temperature sensor on the aux battery. Once the battery reaches 60°C it stops charging to protect the battery. This is all well and good in theory, except when you travel in Southern Africa in November or December, where ambient temperatures run into the 40°s before you’ve even turned on the vehicle. Once we drive for a few hours at any sort of speed the engine bay is over 60°C, and then the DCDC charger will not allow charging. Since we might drive like this all day, that means our battery never gets charged. Kind of a big problem. My solution, I took off the temperature sensor. Hey, look, now it charges all the time, ta-da! Is this good for battery life? No. And for a higher amperage charger or a different type of battery it is also not safe. We just accept that we’ll have shorter battery life. 
• Heat, again. Because we keep the aux battery in the engine bay we are essentially excluded from going to a lithium battery or even AGM. No battery likes this much heat, but those batteries are expensive and would fail much sooner. Note there are a few very interesting Youtube videos of some Australians testing lithium batteries in the engine bay, but this requires some very specific batteries and very specific charging systems. The whole idea here is to go camping with cold beer and good food, not spend all day every day obsessing over electrons while going broke, so we skipped that option.

Electrical Update, c. 2021

We made two trips on the 2019 iteration of the electrical system. It worked great, barring the heat issue. Then we returned in 2021, assuming that after over a year of sitting that we’d have to replace both batteries and we’d be pretty much good to go. After we got the vehicle out of storage we noticed right away that the solar panel was not working. After some basic troubleshooting we confirmed, yes, broken.

I fired off emails to National Luna and 4x4direct, both well known to offer excellent support. National Luna offered some troubleshooting advice that confirmed what we already suspected, it was the panel and not the charger. 4x4direct said that if the panel was confirmed to have failed to bring it in and they would replace it. Since they were over 1000km away that wasn’t all that convenient, but a generous offer.

A fitment center in Windhoek said they quit carrying the flex panels due to high rates of failure.

Also apparently a frequent cause of panel failure is a diode on the panel. These can be replaced for a few dollars, but on the flex panels the box that holds the diode is a sealed unit and cannot be repaired. 

The fitment center offered to replace our 120w panel with glass panels, but the only ones they had in stock were 90w. We pulled the trigger on two 90w glass panels, 180w total, mounted on the tent. 

Note that since fixed panels have an air gap under them, which keeps them a little cooler. Cooler panels are more efficient, delivering more electrons to the battery. 

To summarize where we are now:

Supply Side: 

Load Side:

• 40 liter Engel fridge
• 15 liter IndelB fridge between the seats in the cab
• 3x red/white LED lights in the canopy
• GPS hardwired to the 12v socket in the cab. Only powered when driving
• 200w square wave inverter, only used via 12v socket in the cab when driving
• We now use a fancy 12v socket USB outlet to charge our laptops via USB-C, capable of 3.0A 45W charging of a laptop with various circuit protections built in. It’s this one: https://www.amazon.com/dp/B08CVR9FYC?ref=ppx_pop_mob_ap_share. Now the only thing we use the inverter for is my camera batteries. Why convert DC power from the vehicle to AC in the inverter and back to DC in the laptop power supply? Now we can direct USB charge a laptop with less cables.
• 12v Caframo SEEKR fan. The tent has a 12v socket and this fan is a lifesaver on those sweltering nights. Only draws 0.18A on low speed. This thing is worth it’s weight in gold.

Pros with this system:

It works! The beers are cold, we have cool water to drink on hot days, cheese and other luxuries can be kept for long periods of time. We have achieved camping electrical nirvana, or near enough anyway.

Several times we’ve managed stays of five days without shore power in partially shaded camps or with some rain. This is long enough that I would consider it “indefinite”, as after five days we usually need to go provision, get more water or something. The only caveat is sometimes I close the tent during the day so the solar panels are flat, to optimize sun exposure. 

Over the three months we’ve now been on this trip I spend less and less time thinking about the battery. What more evidence need there be that this system works well? 

Flaws with this system:

As I said, we do need to close the tent in some camps to maximize sun exposure on the panels. Because of the more efficient panels we see them kick on sooner in the morning and stay on longer into the afternoon. Midday we our record output is 13A. In shade or heavy cloud cover, maybe just 2A. A lot of time it is somewhere in the middle. 

Battery capacity is an issue. I think to run two fridges or bigger fridges you really need to have more amp hours. We can just get by with careful management and turning off the little fridge sometimes. If we went lithium this would get us there, but that is expensive, and would require moving the battery to the back somewhere. Where? We’ve just decided not to go down this rabbit hole. Maybe someday.

The little fridge, the Indel B, is not a very good fridge. I have a clamp on amp meter, so we’ve seen it draws the same amps as the back fridge when it’s running, but due to the lower quality insulation and smaller thermal mass of the contents this fridge runs more often than the back, and therefore uses more power. Both fridges use 2.4A when running, but how often they kick on is the difference.

Right now all of the loads are wired directly to the battery. This is an embarrassing setup, where we have a three studs leading off the auxiliary battery with wires stacked up on the studs. Each load has an inline fuse somewhere along the line. This is stupid. Soon we plan to run a single wire from the aux. battery to a fuse block, and then all loads from the fuse block. This will be much tidier, easier to troubleshoot, be less susceptible to chafe, etc. 

Also the DC-DC charger is mounted in the engine bay. I don’t really recommend this setup. If we had a better packing system in the back I’d be inclined to put this near the perspective fuse block.

I also plan to install a Victron battery monitor with a shunt for real time load senseing [edit: This is now done! It’s much better. I will update the post soon[, to get a better idea of what exactly is using power, when and how much. This will inform any future changes to our battery, either chemistry or capacity.