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!
We built out this system in Go North Episode 4: The Journey Begins
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:
Note: 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 back feed 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 into 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 the first and it’s 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 it’s 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 the 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 voltage of the second alternator 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 vehicle’s 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 truck’s rapid heat (only used well below freezing) would the truck’s 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 an 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 didn’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 and 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 the 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!
Learn more about Battle Born Batteries here!
*Note: This article contains affiliate links.
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Tuesday 18th of May 2021
RE: Victron Multiplus Inverter Charger 3000 W 12 V I wanted to draw attention to one of the specs I spotted on the datasheet. The quiescent current (or Zero Load Power in Watts) for the Inverter is specified to be 20 Watts. Since the nominal input voltage is 12.0 VDC that computes to 20W/12V = 1.7 Amps. This is the current consumed from the batteries even if no load is on the 120VAC. The maximum efficiency is specified to be 93% which at first seems quite good but keep in mind that is measured at a full load of 3000 W (which equates to 3000W/120V = 25 Amps of load current). This means that at a load of 3000W the wattage from the battery will be no less than 3000/.93 = 3226W. Let's take an example of connecting my laptop power supply which is rated to consume 1.7A @ 120VAC. This would correspond to ~204 watts of load on 120VAC or 17 Amps of load on the 12V battery line if the inverter were 100% efficient. But we know that the Inverter has a quiescent draw of 1.7A so the battery draw is actually 18.7 Amps (some assumptions are implicit in this estimate but it should be close). Notice the input power will be 18.7A x 12V = 224 W but the output power is only 204 W which means the efficiency has dropped to 91%. The efficiency will be much less at even lighter loads like charging a cellphone.
The lesson to be learned is that any inverter has optimal efficiency at the maximum rated power and the efficiency degrades with light loads. If you are only going to charge a cellphone or some camera batteries you should either do so when the Inverter is already powering other loads or find a smaller dedicated charger which is more efficient with light loads.
Tom, how did you minimize the quiescent current drain of the Inverter?
Tuesday 18th of May 2021
RE: Why the Second Alternator Didn’t Work Tom, it hit me last night I may have tumbled upon a possible explanation as to the behavior of the second alternator and why it did not seem that the second alternator was 'online' and sharing the load. Please start by reading my previous post, especially the part about Ford introducing 2-wire communication to the alternators in ~2012.
The only explanation I can think of to explain why you measured voltages over 14 Volts on the battery was that Ford has an algorithm that attempts to get a better charge on the batteries by changing the voltage during the different charge phases: (Simplistically) Bulk, Absorption and Float. Smart chargers use this.
One must ask whether the Ford engineers anticipated the use which you had and intended the results which you witnessed. Assuming that this was not by intentional design, then I would like to suggest that perhaps Ford either has a software error in the PCM firmware -OR- that your particular truck exhibited a hardware failure. If the PCM is not changing the voltage of the secondary alternator 'on the fly' then the voltage of the two alternators will not be the same and 'load sharing' will not occur. I have previously read of users on the different forums who had used clamp-on ammeters and measured typical load sharing of 40/60% between the two alternators. The second alternative is that of a hardware failure. for whatever cause If one of the two wires which control the serial communication with the alternator has failed then the secondary alternator will not be able to be reprogrammed.
Just an aside, I use the free OBDII program FORSCAN on my laptop which has benefitted me in troubleshooting engine failures on my 7.3L. It has both monitoring and diagnostics for Ford vehicles. During an extended trip in 2019 the weather had turned cold by the time I got to Wyoming and the truck became very difficult to start unless I plugged in the block heater each night. With the help of FORScan I discovered that the digital serial communication with the California Glow Plug Control Module had failed. In my case it was not a failure of a connector or wire but rather the module itself. Once I replaced the module the truck started easily and FORScan confirmed reliable communication. Also note that the CEL (Check Engine Light) never came ON. The CEL only alerts the driver and technicians to safety and emission failures.
What do you think?
I apologize for being long winded. Jim
Sunday 7th of March 2021
Tom, Great writeup. I'm building up similar sytem for my Ford F450 dual Alternators, Artic Fox AF1140 camper, 40A dc-dc charger. I started following you a few years back with your Tesla battery build and DIY BMS. Whay are your thoughts on 270AH prismatic cells and Overkill solar BMS for a DIY LiFePo4 battery build? I'm a retired EE. Ed
Friday 22nd of January 2021
I have heard of other alternator charging setups that functioned more like a trickle charger and taking hours of driving to charge to batteries part way. Do your modifications and the BIM over-ride allow for a more rapid charge?
Wednesday 6th of May 2020
Do you like Battle Born better than Tesla batteries?
Friday 8th of May 2020
Apples and Oranges really. BB is great for ease of installation and guaranteed safety. Not great for cost and weight. Teslas or other re-used systems are cheap and typically lightweight. Great for packing tons of power in small spaces but more complicated to install and safety is up to you as if they get out of spec they will catch fire. Gotta be confident you know what you are doing with them!