Well, Starr's been in the family a little over a year and I finally feel like I have a pretty good handle on his power setup...so, it's probably time to share with this community! The quick summary is: all the power components (except a battery monitor) worked from day one and I'm very happy that I went Lithium. But it took the entire year to really feel comfortable with the electrical components and tune them for best performance. I'm going to briefly cover the highlights in this post, but you can read the full details in Starr's Guide,
http://rick.samcos.com/StarrVan/StarrGuide.pdf (the Electrical section in the Appendix also has much of the detail). The Guide is a living document that I intend to continue to update as experience is gained and new equipment installed; and I'll leave it accessible on the web. It has lots of info besides electrical that folks might find useful. Now, for a synopsis of the past year re the electrical systems...
The first few months were mostly consumed with constructing a mental model of how the van's electrical components were interconnected. IMO it is a complicated overall system, not intuitively straight-forward and Sportsmobile-West didn't supply me with an electrical schematic, or even block diagram. Of course, there were manuals for all the major components, but no description of how they interconnected and interacted with each other -- all I could see were lots of trees, but little clue as to how the trees were organized into a forest. I initially attempted to document the design by tracing the van's wiring. But it is so dense and hard to access that I quickly gave up and figured that it would quickly reveal itself through usage. But it took most of the year to arrive at what I think is a complete & accurate model. Periodically I would be surprised by some electrical behavior, resulting in my having to refine my model. The result was that I didn't fully understand, and therefore trust, the electrical systems until recently. Nor was I confident that I was using them optimally. In any case, here's a block diagram documenting my system:
Oh, if only something like the above had been available to me earlier! Then I wouldn't have had to discover on my own such things as: the Master Battery Switch doesn't disconnect the battery from the alternator; the solar controller (given sun) will energize the van's 12V circuits and inverter/charger even with Master Battery Switch OFF; the Kenwood AV system's audio amplifier is only powered if the Master Battery Switch is ON (i.e., otherwise no audio, even when just driving), and so on...
In the end, I have gained confidence in Sportsmobile's electrical design and now understand the good reasons for electrical behavior that seems quirky on the surface. But I also came to the conclusion that they had little experience with Lithium batteries. That was clear soon after delivery when I discovered that the installed battery monitor was worthless for Lithium. And as I gradually dug more deeply into each component, I discovered that they all were configured for Lithium with simplistic factory defaults; no parameters were tuned for my particular battery or other component interactions. But everything did work pretty well and I learned to tune settings at my leisure. The various component settings that I ended up with are fully documented in the Starr's Guide's Appendix.
It wasn't until the past month (thanks, covid-19) that I finally dug into the last known sub-optimal electrical behavior -- slow-ish charging of the Lithium battery by the aux alternator. I wanted to minimize the length of time I need to run Starr's engine at high-idle-speed to charge the aux battery when camping. But the 280A alternator+regulator was only providing a maximum 45A charging current. I played with the regulator's programming and for some unknown reason couldn't increase the charging current. I finally determined that the ~25' cable from the alternator to the battery was slightly undersized, resulting in a significant voltage difference between the alternator and the battery cable ends during high current (1.4V difference at 90A, 0.7V at 45A). Since the alternator was measuring the battery's voltage at its end of the charging cable, it saw a false high battery voltage and wouldn't stay in Bulk/CC charging mode. It instead settled on 45A as the max that it should feed the battery. So, I ran a separate battery voltage sense wire from the regulator to the battery so that the correct battery voltage was always measured. As a result, I finally saw correct CC/CV charging behavior. But then I had the reverse problem -- I couldn't get the regulator to throttle the 280A-rated alternator's Bulk/CC charging current below 165A; i.e., down to the Relion battery's specified 100A maximum.I then worked with Nations Alternator and, with some custom modifications to my alternator (kudos to Adam at Nations!), we got the alternator's base current rating down to ~200A and the regulator was then able to further reduce the Bulk/CC charging current to 95-125A (depending on engine rpm & alternator temp). Even though it usually exceeds Relion's 100A max, I have no concerns about charging the battery at this high current. This is because I learned from Relion that the battery's BMS will only shut the battery down due to over temperature, not over current (over current can cause over temp). My alternator's Balmar regulator is monitoring the battery's temperature and has been programmed to shut down charging at a conservatively lower temperature than the battery's BMS temp limit. Note that it is critically important that all this is correctly configured -- a sudden battery shutdown will usually destroy a charging alternator.
During this process I learned that Nations apparently has a 12V 160A alternator which would have been a much better fit for Starr's Relion battery's 100A max current spec (this alternator is apparently spec'd for the Winnebago Revel Sprinter van). Thankfully I didn't have to totally replace my alternator and I'm now a happy camper with my much faster alternator charging.
I also recently installed an aux alternator disable switch for two reasons:
- To prevent the charging of the Aux Battery when the van must be driven while the battery is frozen. (Since a charging/energized alternator always requires a battery load, you cannot simply disconnect an alternator from a frozen battery. You can only remove voltage from the alternator's field circuit and thereby completely disable it.)
- To more easily drop the battery's SOC into the preferred 40-60% range before long-term van storage. For example, you can simply disable the alternator during a trip's drive home, just before the van's long-term storage.
Lastly, I've been pretty satisfied with my 230 watts of roof solar and 300 amp-hours (Ah) of Lithium battery storage. The van’s 300AH Auxiliary Battery is effectively 240Ah since discharging below 20% SOC is somewhat detrimental to long term battery health. So, given that I typically consume about 90 Ah of power a day, the van can usually be used for almost 3 days without any charging of the battery. And that time is obviously extended by any solar charging that occurs. The amount of possible solar charging varies widely depending on time of year, cloud coverage, and latitude. I calculated what the panels should produce for Bend Oregon's latitude & average weather, and those numbers are in line with my memory of this past year's van experiences:
Clearly, off-the-grid stays longer than 3-4 days are not possible during the winter without alternator charging. To help (at any time of the year), I am planning to purchase a small, foldable, external solar panel (e.g., an easily-storable Acopower LTK 120 watt panel) – a steeply inclined 120-watt portable panel will contribute the same Ah as the roof’s 230-watt flat panels during the winter!
Some additional, sundry comments regarding electrical usage:
- I saved about 33% (10Ah/day) of fridge consumption with additional insulation (described in an earlier post).
- I've never used the charger function of my Magnum inverter/charger except to test and tune its configuration; I just don't camp with hookups (but I use its inverter function heavily).
So, in summary, I have four general recommendations:
- Install a Lithium battery -- the 50% weight savings, 30% more discharge capacity, 5 times longer life, and sometimes a faster charging rate IMO easily offset the larger (but lowering) cost differential to other battery types.
- Check your battery's maximum spec'd charging current and ensure that your alternator+regulator are matched (e.g., install a Nations 160A alternator rather than the 280A model).
- Install a Lithium Battery Monitor (e.g., Relion's) so you can see your instantaneous electrical charging/consumption current & an accurate battery State of Charge (SOC); otherwise you will be flying blind and it will be extremely difficult to tune the setup and manage your use of the electrical system;
- Don't go with a charger's default Lithium parameters; rather carefully tune the charging profile parameters for the alternator's regulator, the inverter/charger; and the solar controller to match your battery's specs for recommended charging voltages, recommended/max currents, and temp limits.