Converting On-Grid Electronics To Off-Grid

Husband and wife team [Jason & Kara] hail from Canada, and in 2018, after building their own camper, sold up their remaining earthly goods and headed south. If you’re not aware of them, they documented their journey on their YouTube channel, showing many interesting skills and hacks along the way. The video we’re highlighting today shows a myriad of ways to power all the DC-consuming gadgets this they lug along with them.

LiFePO4 batteries are far superior to lead acid for mobile solar installations.

Their heavily modded F-550 truck houses 12kWh of LiFePO4 batteries and a 1.5kW retractable solar array, with a hefty inverter generating the needed AC power. They weren’t too happy with the conversion losses from piles of wall warts that all drained a little power, knowing that the inverter that fed them was also not 100% efficient. For example, a typical laptop power brick gets really hot in a short time, and that heat is waste. They decided to run as much as possible direct from the battery bank, through different DC-DC converter modules in an attempt to streamline the losses a little. Obviously, these are also not 100%

Home, sorry, truck automation system

efficient, but keeping the load off the inverter (and thus reducing dependency upon it, in the event of another failure) should help stem the losses a little. After all as [Jason] says, Watts saved are Watts earned, and all the little lossy loads add up to a considerable parasitic drain.

One illustration of this is their Starlink satellite internet system consumes about 60W when running from the inverter, but only 28W when running direct from DC. Over the course of 24 hours, that’s not far off 1kWh of savings, and if the sun isn’t shining, then that 12kWh battery isn’t going to stretch as far.

There are far too many hacks, tips, and illustrations of neat space and power-saving solutions everywhere, to write here. Those interested in self-build campers or hacking a commercial unit may pick up a trick or two.

Thanks to [Keith] for the tip!

53 thoughts on “Converting On-Grid Electronics To Off-Grid

    1. The low voltage DC microgrid idea pops up every time, and each time it goes down the same way:

      -No agreed on DC voltage standards, every device needs different voltages anyways. Higher voltages are needed for efficient transmission even for short runs inside a house to avoid losses and using excessively thick cabling; various different low voltages required by devices.

      -Electrical circuit protection and fire safety with switches and plugs: no inherent arc suppression with DC, needs heavy duty everything even at low power. Ground faults are more difficult to detect, large voltage losses in cabling is normal, so fuses and breakers don’t work well.

      -More complicated switching from house to grid power when the external long distance world is AC and your house is DC.

      -You save the inverter, except not really, just the very last DC-to-AC step. You still need a DC-DC converter to regulate your voltage, which these days is actually almost the same thing.

        1. Indeed, Much as I don’t like USB-C and PD overall it does, when done properly, solve many of those problems. Though I’d also say POE could equally be considered, lots of that about as well.

        2. In my conversion van I am wiring everything as DC and using USBC to run anything that needs to be plugged in. I get to skip the inverter which is a cool 1-3k savings. With a 24v system I can get 100watts output on a USBC plug. If I find something that needs DC power and isn’t USBC then I will make an adaptor (check out the LTT video).

      1. Yes, low voltage only works over very short distances (half the length of an RV, for example) or very low power.

        But looking at device efficiency, it’s easy these days to get very efficient step-down converters, while step-up is usually wasteful except under ideal conditions. Especially with inverters that have a big step-up and have to produce 50 or 60Hz.

        My inverter never seems to get above 80 to 85%, and that’s when I run it about 50% or 60% of its max to boil a kettle and grind coffee, or make toast.

        All the rest of the time, it’s turned off because it’s always hungry :-)

        1. The inverter gets low efficiency because the battery voltages you’re inverting from are low. Consider how much power you’d lose in the cabling if your toaster was running off of 12 Volts directly.

          500 Watts at 12 volts is 41 Amps. Losses in the cabling and in the battery itself are proportional to the square of the current. A typical lead-acid battery has an internal resistance of about 20 milli-Ohms, not even mentioning the cables and connectors in between, which means you lose 33 Watts in the battery alone, or about 7% of the total. If the inverter itself was absolutely perfect, the system still could not go above 93% efficiency when putting out 500 Watts of power – which is why getting 80-85% is actually very good.

          1. Btw. if your battery has 600 cranking amps, that means it can supply at least 7.2 Volts to a 600 Amp load when full. The voltage drops from about 13.8 Volts to 7.2, which is 6.6 volts over 600 Amps, which equals 11 milli-Ohms.

            RV and marine storage batteries, gel batteries, have higher resistance because they’re built with thicker plating to handle deep discharge. Starter batteries die more rapidly if you discharge them below 80%.

          2. Also, once you get the battery resistance down, you still have contact resistance at various points. And at lower voltages, if you happen to need a diode for something, there goes another bit of the power.

          3. > if you happen to need a diode for something, there goes another bit of the power.

            Yep, and at high currents, diode forward voltage losses are in the range of 1 Volt, which for a 12 Volt system is another 8% of your power.

      2. If we are making the battery out of 300v EV battery packs the inverter can be more efficient. The internal step-up can be skipped and just make AC.

        POE is a thing too. Could use that to trickle charge smaller batteries through the house where power is needed.

    2. I tried to reply to this with a few reasons AC is neat, but it went below. You can search for #2389843 to find the comment but basically a few of the properties of AC make it easy to do things we want to do, and choosing a single DC voltage is hard to do for a permanent home as the optimum is not clear and static.

    1. What can possibly go wrong with your 32 amp ring main, your natural gas pipe etc – the batteries are no more of a fire hazard than either, if all are treated properly. And if you really want to you can always choose much safer chemistries, shift to caps, put that petrol generator in (as petrol is oh so safe)…

      NB Not saying this particular setup is sane as I’ve not really looked at what they have done yet. Just saying done properly (which I hope this is to make it to HAD without disclaimers of danger) there is nothing wrong with batteries. I’d even go as far as to say on a moving platform they are almost certainly the safest option you would actually want to use – the battery assembled properly is a very solid hard to damage mechanically unit that will cut itself off in an over current from any damage to the wireing etc – you gas bottle or petrol systems are just as fragile if not more so and any leaking doesn’t get detected and shut down by the fuel tank…

        1. Didn’t say it was a good idea, but if you want to fill all your volume for the same energy storage you can use capacitance to store it – and those don’t always contain anything, toxic, that burns (or explodes) in its own right, just those angry pixies that can throw an arc between conductors through air… So its ‘safer’…

          1. Yes, not toxic or explosive per se, but storing energy in static electricity is analogous to storing it in a big metal leaf spring. If the insulator is compromised, it all goes off in a big BANG.

      1. Ring circuits are forbidden by our code. My and my parents house, which construction I’ve participated in myself (although I was only 16 years old then), is built of brick and has 3-phase 15kW connection to the grid. All the wiring inside is solid copper, mostly 2.5mm² for regular sockets, 1.5mm² for lights, 4mm² for cooker, washing machine, dryer and garage/workshop (lathe, welding and whatnot). Heating and hot water is provided by district heating network/grid so no need for gas or electric heater.

        I’ll take that anytime over living in a cramped old Ford filled with batteries.

    2. LiFePO4 are inherently stable. With proper treatment it should be possible to make things safer than a lot of houses, with their corroded wire nuts overheating in stud walls, cables overloaded by the owners before you, and all that. I’ve seen these things.

      It’s an engineering problem, but we already know how to solve it. We just need to decide how much risk we accept before we start.

    3. LiFePO4 is not the same as regular Li-Ion. The chemistry is much more stable. Can absorb some over/float charge. Does not burn or explode violently, etc.

      Look into it before you get mad at it. From the picture I am curious about his pack setup. 4x series is 12-14.4v on that chemistry, very nice.

        1. Meanwhile, other chemistries like NCA (Tesla batteries) undergo thermal runaway if you get it above 160 C, which is why Model 3 batteries are filled with fire-suppressing and insulating foam glue between the cells – if one goes, it’ll probably not ignite the next one in a chain reaction. Hopefully.

          1. Substances exist that are better than water at preventing flames (though not heat) from a battery short, but most departments just use tons of water because if you use enough of it you can keep the battery temperature down until it finishes discharging, and water is easier to get.

  1. What on earth do you need 12kWh for in a camper?

    Surely the amount of space and weight this adds is going to cost you more than (say) just running the engine once in a while if you have a heavy load to run.

    1. Because you need a bigger capacity. If you stay in the camper in the winter, or on dark days, you need a LOT of over capacity to run your equipment, such as a diesel heater, tv, radio, etc. It all adds up quick. It’s best to at least go double what you expect to use, to prevent bigger issues. And since batteries usually don’t like to be empty, why not? It’s not like a 550 can’t move the few extra batteries. It’s a work beast that can haul a LOT more. This way, you can avoid having to run the engine for hours on end and make it actually work off-grid. The alternative is bringing a ton of extra fuel, just for running the engine at idle for a long time, which can also leads to engine issues. Adding batteries is the way to go.

    2. Because 12 kWh is just about equivalent to a liter of diesel fuel or a kilogram of propane. You can’t really do much with it, especially if you want heat in some form.

      1. Consider for example, an RV shower head gives about 3 liters a minute. In the winter you need to heat your water by about 30 C to make it warm for the shower, so you need about 6 kW of power to wash yourself.

        1. At one point, when talking to someone trying to do similar things, it turned out it made more sense for him to slowly heat an insulated tank of water primarily with surplus power and (if necessary) then fuel. And if you want to do that, a bunch of cheap peltier devices could give you a bit more heat than you’d otherwise be able to get, especially if your input voltage gets low due to clouds or such.

          1. If you’re in a house, it makes more sense to have a big storage boiler. If you’re in an RV, you kinda have to do with what energy you have available in the past 24 hours.

            Peltier devices have the problem that they’re not one-way streets. They leak heat quite terribly, so when you turn the power off they turn into heat sinks rather than heat sources. Most of the power they consume when turned on is simply to fight against heat leaking back the wrong way.

          2. I would still consider heating just enough water for your shower over the course of only a day to be slow, compared to instant heating at 6kW.
            As for the peltier heating, of course you’d want to prevent the heat from leaking back out – but you could use a few dollars on a slow pump rather than apply them directly to the insulated tank, assuming thermosiphoning is not practical. You’d also then be able to circulate the water through other heat sources.

    1. I think it’s saying a lot of waste is in the inverter. Going DC to AC to DC is usually bad news for efficiency, and running the inverter way below its rated output tends to make that worse.

  2. off grid here as well, been doing this for a few years…making my own adapters.\

    For most 110/220v appliances you can find some with external *usually 12v adapters. TV screens, projectors and lights have them.

    The ones they supply are anyways usually not very efficient so you save right there…

    Another thing I do is convert the devices by building in the DC converter so I can plug them into a car adapter splitter. A soundbar with sub was a huge success since it could run on 24v and very easy to transport and use outside.

    For heavier audio I have a car stereo also 12v.

    Then stuff like laptop chargers and power tool battery chargers are standard car appliances. From kettles to fans.. vaccuum cleaners a lot of things are available.

    A lot of devices have their own built in batteries nowadays so you can usually also charge these with a dc converter. From mixers to cleaners with 3 funtions with vaccuum and water.

    Off grid can be very efficient and it’s a hobby I guess.

  3. AC is useful in a lot of ways – transformers, some motors, and thyristors are parts that are used for good reasons despite requiring AC, and AC lets you do things with inductance and capacitance. For things that run at variable power levels, like lights or fans, with DC you need to use PWM (or an adjustable dc converter if you need to create a smooth voltage) unless it’s low enough power to use a resistor divider. Otherwise, I guess certain things could run straight from the generation voltage as it goes up and down within a certain range, but you’ll probably want MPPT (which is a dc-dc stage) and to set a floor and ceiling value.

    With AC, you can use reactance instead of resistance in order to avoid waste heat while doing the same essential thing as a resistive voltage divider. Some kinds of electric motor are naturally synced to the AC signal, making them run at a speed determined purely by the grid frequency and their construction without any electronics involved. And the grid can be regulated well enough that a synced motor in a clock will keep correct time on average, as was commonly done in the past. Not sure how many things make use of that fact now. Variacs are great, but rarely used now.

    The nice thing when you think about generators and consumers of power, is that it’s a lot easier in a home to have multiple sources of DC power in parallel because you don’t have to sync them. And you can buffer power with just a capacitor or even a battery if the voltage stays in range. The equivalent thing for AC is more like the rotating mass of the turbine at the power plant, and people don’t have flywheels at home buffering their power. An inverter that doesn’t happen to support operating in parallel is just not going to do it, although a couple of generators can be manually synced if you have control over the parameters so you can match phase and voltage and frequency before throwing the switch.

    1. >With AC, you can use reactance instead of resistance in order to avoid waste heat

      Not entirely. You will shift the power factor, which means you won’t consume as much at the target, but you need more current for the same effective power, which means you increase transmission losses.

      1. Oh, absolutely. You only avoid most of the waste heat, not all of it. And sources can care; inverters in UPS’s are why the UPS’s are labeled with their volt-amp rating, and grid scale AC producers and consumers put a lot of effort into managing reactive power. But it’s better than a variable resistance in terms of waste heat, and at home you’ll definitely use it when appropriate.

    1. He designed and built the boards himself. It’s all shown in his video titled “Designing and Building Custom P-Channel Driver PCB’s in Mexican Lockdown”.
      And the phrase refers to his electronics mentor Todd.

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