For our 6-month journey north to Alaska in the Lance 1172 Truck Camper, we decided to try something new: we built a system to generate our RV’s power by charging our lithium batteries with the alternator of the vehicle!
Charging Lithium Batteries with Alternator System
We wanted to do this in order to minimize equipment (no generator or fuel) and maximize quiet operation while still remaining fully powered up. Our goal was to go a full summer with no generator, no additional fuel to carry, and no additional propane use.
We partnered with Battle Born Batteries to build out this system and try it out during our remote travels all the way to the Arctic Ocean.
The following video shares the details of the system and how it performed:
Alternator Charging System Schematic
Before starting, we laid out a schematic of what we planned to install in the truck camper. Drawing out a schematic for your build is a great way to get a good understanding of how all the components connect. It will act as your map throughout your build.
Here is the original schematic as built in the camper:
If you watched the video above you may note a few differences in the schematic. First the BIM was in the wrong place, on the camper side of the drawing, second there was an additional fuse in the truck charging circuit before the busbars. This fuse was not installed and not needed because this section of cables was protected from over-current situations by the main battery fuse, and a built in mega fuses in the inverter if it was supplying the power.
Truck Camper Electrical System Components
- Click here for list & links to all components for this build in a Kit
- (5) Battle Born Batteries 100Ah LiFePO4 12V Deep Cycle
- Victron 3000W 12/3000/120-50 Inverter
- Victron BVM712 Battery Monitor
- Blue Sea 300Amp M-series Battery Switch – Single Circuit On/Off
- 300A ANL Fuse – Spartan Power
- (2) Blue Sea Maxibus Bus Bars 250Amp
- Blue Sea 300a Battery Terminal Fuse
- 4/0 cable
- 4/0 lugs
- Lithium Battery Isolation Manager (Li BIM) – 225A
- 175A 1/0 Gauge Quick Connect Plug (for back of truck)
- ~30ft 1/0 Cables – (1) Black & (1) Red
- 1/0 lugs
- DC/DC Converter – Sterling Power (while not in our system, we recommend for better performance)
Battle Born Lithium Batteries
5 Battle Born Li-Ion Batteries make up the heart of the system, wired in parallel.
We had the unique opportunity to assemble these batteries ourselves! Watch these batteries get built in Episode 4 of our Go North series.
Why Battle Born Batteries?
Battle Born Batteries have made a name for themselves in the RV space. While we had worked on installing them in other instances (like putting in the off-grid RV electrical system in our friends’ Vintage Airstream renovation), we had never used them for ourselves – this was our first time!
These batteries have an internal BMS (battery management system) that monitors the state of the battery and will automatically shut them down if they get out of spec, i.e. too cold to charge.
Reasons for Choosing Lithium Batteries
We chose to install 5 lithium batteries for a combination of reasons:
- Weight and Space. We wanted to match weight or be less than the generator and lead acid batteries that would normally be installed.
- Power requirements. These batteries hold 1.3KWH of power each so with 5 we would have 6500 watt hours of power available. Through a few calculations we estimated that without charging we could go 5 or 6 days pretty easily on this amount of power.
For most people, this amount of power storage would last even longer, but we are pretty power-hungry. We typically run two computers, charge multiple camera batteries, and running other equipment most of the time. Five or six days would be the max amount of time that we might go without a charge.
Busbars, Inverters, and Electrical Cabling
From the batteries we land the cables on two Blue Seas MaxiBus 250amp BusBars that distribute the DC loads and charging. From these busbars we connected directly to the RV’s main DC power system. This system powers the lights in the RV, fridge, fans and any other DC appliance. This connection was easy to make as we installed the batteries in the location of where a built in generator normally is installed and we used the wires that would normally start the generator.
Also on the DC system is 200W of solar that Lance installed at the factory and will backfeed into the batteries through this system.
Connected to the busbar is a Victron 12v/3000/120 pure sine inverter. This inverter converts the 12V DC power to AC power for the general receptacles. We did not have space in the battery compartment of the RV, so we came up with another plan. We installed this inverter in an adjacent compartment to the batteries. This also worked well because the inverter needs more air to stay cool.
Ideally, you want to keep runs to the inverter as short as possible with a 12V system like this. We kept it just on the other side of the wall about 3 feet from the busbars and ran 4/0 cable to it.
Electrical Cabling & Inverter Power
We again used wires that would normally be run to the generator to provide the inverter power. The RV also had a transfer switch installed, and we used this to make a permanent junction. This sent all the shore power through the inverter before making it into the RV.
While this requires the inverter to be on to get power to the RV even when on shore power, it can easily be switched if there was a problem with the inverter. The inverter also serves as a battery charger for when we are plugged in to shore power. It can rapidly recharge the batteries with 120A of charge or around 1600 Watts.
We used a Victron 3000VA pure sine inverter to power the RV. This is the inverter we use in our fifth wheel and it has been great.
Lastly, the main charging circuit that connects to the charging system of the truck connects to the busbars. This circuit was made from 1/0 cable and runs out from under the RV to a large 175A Quick Connect plug that connects to the truck side. On the truck side, the cables run along the frame up to the engine where they connect to the 300A Battery Terminal Fuse.
Battery Isolation Manager (BIM)
Before reaching the engine, however, the cables pass through a Lithium Battery Isolation Manager (BIM) unit. This unit disconnects the batteries when the truck is off and cycles the power 15 minutes on and 20 minutes off. This is toensure that the alternator does not overheat.
Most alternators are not designed to handle the high loads that lithium batteries put on them for extended period of time. This truck has two alternators, however, and can handle much higher loads, although we are not sure of its limits. It is rated at almost 400A of charging capacity and when on the batteries draw around 100A.
The BIM also has a manual override that we connected to a switch under the dash of the truck. This allows us to force the batteries to come on when we need. The switch helps us get a more rapid charge, leave the batteries on when they are almost topped off (as the current drops), or also help jump start the truck if we accidentally kill its batteries.
Connecting to the Truck Batteries
The truck has dual batteries so we connected one of the terminals to one battery and the other to the other battery via a 100A terminal fuse to protect the wires. We did this because the second alternator only comes on when the loads are exceed on the first and its connected to the second battery.
Connecting our batteries to the second battery drags the voltage down sooner close to the auxiliary alternator and kicks it online to help with the loads sooner.
We’re not sure why Ford does not run both alternators at the same time, although I guess to reduce parasitic losses. It is not ideal for this setup, as we still mainly tax the first alternator instead of distributing the load. But at least its there as a spare if we lost the first alternator.
Battery Monitor & Bluetooth
The last part of this system is the monitoring of the batteries and their charging with the alternator. Between the busbars and the negative battery terminal, we installed a Victron BMV712 monitoring shunt and display. This device monitors all the current into and out of they system to give us a very accurate state of charge of the batteries.
This unit has Bluetooth connectivity as well. Because of this we decided not to run the display into the RV and instead opted to just use our phones to read the battery state.
To control the inverter, we installed a Bluetooth connection to the Victron Multiplus inverter that allows us to monitor the inverter on the phone and turn it on and off remotely.
These systems have been working great and we feel no need to have a display inside the RV. We have the Victron App on 4 different devices and any of them can check the battery or turn the inverter on and off.
Alternator Charging System Performance
Since this was our first time designing a system to charge lithium batteries with an alternator, we were curious about how it would perform.
It worked…. that’s the short version.
It actually worked too well!
We ran calculations to figure out how big of wires we needed to install to maintain 80-100A charge rate when the alternators were sitting at 14-14.2V.
We didn’t expect that this truck preferred to run at 14.7 or higher voltage almost all the time.
This higher voltage helped reduce voltage drop and pushed much higher currents than we expected into the battery bank. When the bank’s voltage was low we saw upwards of 150-180A!
This is a crazy good charge and would be awesome, except for one thing: the truck couldn’t do it safely.
Because of the issue we mentioned above, the truck would rarely use its second alternator and thus we could overload the first one. (We actually didn’t overload it, but it was not designed to sustain the load for extended periods of time and would get way to hot.)
Why the Second Alternator?
As a rule of thumb, alternators can sustain 100 percent duty cycle at about half their peak rated load. The main alternator was a 225A unit and had a base load of around 50-80A on it, more when running glow plugs, heated seats, or the trucks rapid heat system ( a 1500W cabin heater).
I think that this cabin heat thing is the main reason for the second alternator, as it was connected directly to it. My belief is the truck was probably programmed to turn the second alternators voltage up when it kicked on.
Why the Second Alternator Didn’t Work
Let me explain this second alternator not-kicking-in thing.
Alternators are actually AC power generators then have diode packs on the back to convert it to DC. They can regulate their voltage by varying the excitation field of the windings and thus create smart charge profiles.
The field windings are commonly controlled by the vehicles computer system and this truck would keep the main alternator at a very high voltage for a long time, and the secondary alternator at a much lower voltage. This, in turn, basically disabled it until the main alternator dropped its voltage and they then matched.
My guess is that under certain conditions like the trucks rapid heat (only used well below freezing) would the trucks computer “turn on” the second alternator. It would be best if they were synchronized all the time. I assume a little rewiring could probably make that happen.
Well, we didn’t charge the lithium batteries with the alternator much in the first week on the road as were plugged in, but realized the issue while we were already on our way north… thus we lived with it.
I happened to have a IR thermometer with me and took the alternator temps regularly to figure out when they were getting too hot. I assumed anything above 220F was too hot.
We determined that they would get too hot after about 7-10 minutes of engine running depending on the outside temp. So, we set alarms on our phones and would manually cycle the alternator every time it went off to charge the RV’s lithium batteries as we drove. If this sounds ridiculous….it was!
Saved by the Voltage Drop
Now, the good part is we did’t have to do this forever, because the truck would eventually drop the alternator voltage and we could just leave the system on to charge more slowly. But, that meant monitoring the voltage of the truck each day, too.
Once it dropped, which happened anytime from 1 hour run time to never, we would just switch the system on and let it go. This usually charged around 50-80A depending on the Battle Born Batteries state of charge.
Is there a fix?
I would have liked to implement a fix for it but we were traveling the north having a grand old time. Trying to line up a package delivery and do the work was tough with a tight schedule and being in the middle of nowhere. So we just lived with it.
Ideally, I would have put a DC-DC converter in between the truck and camper.
The image below is a DC-DC charger unit that would have solved all of these problems. These do as the name suggests: they charge. They take one input source and modulate it so that it matches the required output charging characteristics. Usually, they are fully programmable for your requirements.
This is one DC-DC option. Sterling Power has a whole line of DC-DC converters for different options. Battle Born Batteries carries them for sale.
A DC-DC unit would not only have helped during our truck’s absurd bulk charge sky-high voltage, but also when the voltage dropped. It can keep the output voltage constant regardless of what the alternators are doing, and you can set limits so you don’t overload your vehicle. The result: a nice even charge of the lithium batteries from the alternator.
This would add cost to the system but would take away lots of headaches and make it just work.
This is a redesigned schematic that I would recommend. A DC-DC converter would allow you to run smaller wire and you would not need the LI BIM disconnect switch as it takes care of that.
So, would you do alternator charging of lithium batteries again?
Totally. We loved not having a generator, not messing with fuel, etc. Between the Battle Born Lithium Batteries power storage capacity and the ease of charging them off the alternators as we drove, the system worked as we hoped!
Even with our hiccup, the system did what it was supposed to do and helped us create Go North. For future projects, I would happily build the same system but with the DC-DC converter. I’d also use smaller charge wires from the truck.
I might also modify a truck with dual alternators to run both of them all the time so I could get a better charge.
Overall, we were very happy with system and love having quiet power whenever we needed it!
*Note: This article contains affiliate links.
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