We’ve had a lot of requests for updates on our lithium battery system, but the truth is that it hasn’t been getting much of a workout.
We’ve spent the past several months focusing on being near family, and we haven’t had any opportunity to tackle the solar panel project or to do any boondocking.
Instead of maximizing every electron in our battery bank, we have been hopping from pole-to-pole staying with friends and at RV parks, never really giving the batteries much chance to run down.
We have actually been making good use of the other core piece of our electrical system – our Victron MultiPlus 3000VA Inverter/Charger.
And the special features of this inverter coupled with our ample lithium battery capacity have actually given us a lot of flexibility beyond what a traditional RV setup would have been capable of, very literally improving our outlook on life.
Read on to learn how!
Converter vs Inverter vs Inverter/Charger
Every RV with a DC electrical system needs some way to power the DC system and charge the batteries when plugged into AC shore power.
The most common way this is done is via a component known as a “converter” which takes AC 120-volt input, and then converts it into DC 12-volt output.
An “inverter” does the exact opposite task of a converter – taking DC power from the batteries and transforming that into AC power suitable for running appliances like TV’s and microwaves and computers when shore power is not available.
Inverters range in size from pocket sized devices which plug into a cigarette lighter jack and which can handle just enough wattage to run a laptop, on up to big boxes that need to be hardwired with hefty cables directly to the batteries, and which can generate enough AC power to run even the heaviest loads such as air conditioners or power tools.
Many hardwired inverters are actually inverter / chargers – replacing the need for a separate converter. If you have an inverter / charger in your RV’s electrical system, it will keep your batteries charged when you are parked and plugged in, and all your appliances running when you are disconnected.
A good inverter / charger is the heart of a quality mobile electrical system.
Sine, Sine, Tell Me – Do I Need Sine?
In addition to a range of sizes ranging from 50 watts to 5000 watts (and up!), inverters are offered as either “Pure Sine” or the often substantially cheaper “Modified Sine Wave” style.
This refers to the shape of the AC power output curve coming out of the inverter – a “pure sine” inverter produces a perfectly smooth sine wave that is likely a higher quality than the hard-wired power at any RV park.
On the other hand, the curve produced by a “modified sine wave” (MSW) inverter looks like stair steps, not smooth at all.
Most small electronics can’t tell the difference – and if all you care about is powering a laptop and some lightbulbs a MSW inverter is a fine choice. But motors (like fans and power tools) and compressors (air conditioning units, refrigerators) will often eventually burn up on a modified sine input. LED lights will very faintly flicker. Some battery chargers will fail over time. And perhaps most annoyingly, some sensitive electronics and radios will pick up a buzzing noise when using a MSW inverter.
In our Oliver trailer we built the system around a 1500 watt Xantrex Freedom 458 modified sine inverter / charger – and though we were mostly happy with it, in hindsight I wish we had gone pure sine – if only because our 24″ monitor buzzed faintly if we left it plugged in, even when it was turned off!
With the bus, there was no question – we knew that we wanted to invest in the best possible inverter that we could find. And that meant not only pure sine power, but the ability to boost it.
Are More Volts Better?
24-volt components have an advantage in that they can carry twice as much power over the same size wiring as a 12-volt system, and thus 24-volt inverters tend to be available in more powerful sizes and require less massive (and expensive) battery interconnect cables.
Most RV’s however are built around a 12-volt system, but some buses (not ours) are designed around 24-volts.
Though the advantages of a 24 volt house battery bank and inverter / charger are tempting even in a 12-volt bus, we still decided against it. Since we were designing a power system from scratch, it makes sense to go with a house system that matches the chassis system so that it is easy to charge off the alternator while underway
If we had gone 24-volt, the ideal inverter / charger for us would have actually been the Victron Quattro 5000VA, but because of the size of the internal components required and lack of market demand Victron has indefinitely postponed bringing the 12-volt version of this awesome inverter/charger to production, and only the 24-volt model is available.
The Transformational Magic of Boosting
There are two commonly sized plugs used to connect an RV to shore power.
Most larger RV’s use a hefty 50-amp cord that when connected to a four-wire split-phase (240V) source actually provides 100 amps (two 50-amp legs) of 120 volt power – up to 12,000 watts! This is enough power to run multiple roof air-conditioning units, charge the batteries, run the microwave, and more – all without risking blowing a fuse.
Smaller RV’s (especially those with just a single roof AC unit) usually have a 3-wire 30-amp shore power cord that can deliver a maximum of 3,600 watts. This is plenty for most needs, but turning on the AC, a microwave, and a hairdryer all at once still risks blowing the fuse on your incoming line. And with a powerful enough charger, even charging a depleted battery and running the AC at the same time risks overloading a 30A shore power circuit.
Most RV parks offer 30A and 50A sites (and commonly charge more for 50A), but very few people (we love those who do!!!) have 30A RV plugs in their side yards.
If you are setting up camp in a friend’s yard, a typical home power plug and heavy duty extension cord can only deliver a maximum of 15 amps, and if you use an adaptor to plug in your 30A or 50A cord and then draw more than 1800 watts you will be blowing the fuse of the circuit you are plugged into.
It isn’t hard to do this – particularly since outside outlets are often sharing a 15 amp circuit with other home loads, such as exterior lights or the electric garage door opener.
A depleted battery and a powerful battery charger might actually be enough to blow a 15A shore power circuit even if no other RV loads are turned on.
Blowing fuses constantly is not a good way to get yourself invited back to camp in a friend’s side yard…
Fortunately, many higher end inverter / chargers have the ability to set a maximum shore power draw via a control panel or a dial. This way – as long as you remember to tell the inverter that you are on a 30A or 15A circuit, it will scale back and charge the battery slower – keeping you from using too much power and blowing a fuse.
But… What if even after the battery charger is dialed back to zero, you need 20 amps of power, and you are on a 15 amp circuit? Or 35 amps, and you are on a 30 amp circuit? What if you only need that surge of extra power for a minute or two, like the initial heavy surge current draw of an air-conditioning cycling on?
Depending on the inverter you have and how it is configured – in this case you are back to blowing a fuse on the shore power circuit, having your inverter shut down and black-out RV loads, or having the inverter switch over to power all the AC loads only by the battery – draining it exceedingly rapidly and leaving you with a dead battery even though you may think you are plugged in and charging.
The few, the proud, the boosters…
An exceedingly few inverters support the ability to “boost” the incoming shore (or generator) power with battery power – for example, taking 15 amps of shore power and adding 5 amps of inverted power generated from the batteries to provide 20 amps overall.
This lets you use electricity as needed within your RV, without worrying about overwhelming a limited shore power connection or undersized generator. As long as your average usage remains below what your shore power input can provide, your batteries will not end up depleted.
This seems like an absolutely invaluable feature – but for some reason none of the primary US inverter manufacturers support boosting at all. The only alternative from the traditional RV inverter manufacturers is the long-discontinued and now legendary Xantrex / Trace SW4024 and SW2012. Those in the know hop on these when used models come up for sale on eBay.
Our needs were substantial – since our bus has no dash air, we needed an inverter powerful enough to handle at least one of our roof air conditioning units off of battery or alternator power while underway without needing to constantly run a generator.
After a lot of research – we settled on the Victron MultiPlus 3000VA model, one of the most powerful and capable boosting 12-volt inverter / chargers we could find. The MasterVolt Mass Combi 12/4000-200 was a close second choice, and also has a stellar reputation.
Update: Magnum released the MSH3012M Hybrid Inverter, which has now been out for a couple of years – and has become a common similar booster to our Victron in the RV space.
Boosting Inverter = Smaller Generator
RV generators have traditionally been sized so that they can handle the absolute peak load that they might ever need to power – in particular, the surge current of multiple roof air conditioners turning on at once.
You thus end up with 7,000W – 15,000W generators typically running at a fraction of their capacity, only rarely ever even approaching full power.
If you instead use a boosting inverter to handle spikes in demand, you can get by with a much smaller, cheaper, and more fuel efficient generator. It is a win all around, and the money you save by going with a smaller generator will likely more than cover the cost of a more capable inverter.
Cummins Onan has even embraced this design philosophy in their new flagship hybrid generators, bundling a matched inverter / charger right with the generator itself.
Victron MultiPlus Thoughts & Observations
Overall we have been really pleased with our MultiPlus inverter – but there have been a few disappointments and issues.
- The Victron manual and spec sheet claim to support a shore current limit as low as 11 amps, and the control panel UI allows this. But only after noticing it not limiting as expected and contacting Victron did they confirm that the low limit had been raised to 15 amps. This makes it harder to share a shore power circuit that may also have other loads on it like exterior lights or a garage door.
- The Victron inverter has a built in ground relay that automatically connects the Neutral output to the chassis if no external AC supply is available. Inverters that lack this feature will trip any GFCI outlet that they are plugged into. Since most exterior home 15A outlets are required by modern electrical code to have a GFCI, an inverter lacking this could end up severely limited when side-yard surfing. The classic SW2012 lacked this feature – I do not know about the new version.
The Victron is fabulously programmable via the “Blue Power Panel” remote control, and we can precisely set the charging profile to match our lithium batteries. But certain settings I wish were more configurable to better match our lithium battery setup. For example – the “DC Low Shutdown” can be set to any voltage, but the “DC Low Restart” must be at least 1.00 volts higher than the shutdown, and the Victron often needlessly flashes “low battery” any time the voltage is in this range. This is great for lead acid batteries, but lithiums drop so slightly over their range of use that I would prefer the ability to better customize this.
- Victron’s newest (2012) models have added explicit support for talking directly with Victron’s own lithium batteries and battery management systems. I do not know if there is any way to integrate this in with a third-party lithium EMS, like the one we are using from Elite Power Systems. Our older inverter model is also not upgradeable.
- I discovered a very weird bug with how the Victron Inverter and Blue Power Panel work together while installing the system, and actually thought that our inverter had died completely. In a nutshell – it is possible while connecting / disconnecting the battery power for the inverter to “crash” and get locked in a state that it will not wake up from – even toggling the hardwired power switch on the case does nothing. But – if you fully disconnect and reconnect the remote control panel (after leaving it disconnected for a full minute), everything resets and is fine again.
Using an Inverter to Improve Your Outlook on Life
The reason that so few companies have offered boosting is because so few people have really understood the benefits of it. So let me give a few examples from our past few months in Florida where being able to boost literally improved our views.
#1 – We spent the month of January staying on a friend’s absolutely beautiful patch of land in Kissimmee, with the only available source of power being a single outdoor outlet 50 yards away. By dialing our shore current limit down to 15 amps we were able to keep from blowing fuses, and thanks to boosting we were even able to run our electric heater on the coldest nights. In the morning the batteries would get charged, making up for the drain in the evening. Without our boosting inverter, we would have had to go without heat, or stay in a drab commercial RV park.
We love staying with friends whenever possible, and having a boosting inverter makes this vastly easier than it would be otherwise.
#2 – Just this week we have been staying at a commercial RV park on the water in Cedar Key, FL. Though we have a 30-amp outlet available, to reach it with our shore power cord we have to park the bus rear-end towards the water. But since we can get by with 15 amps thanks to boosting (and can even run the AC during the heat of the day!), we have been able to use a common heavy duty extension cord to allow us to plug in and park the bus nose in. (Sure we could carry around a huge and expensive 30A extension cord, but the bulk wouldn’t be worth the rare times that we’d actually be able to use it…)
Facing the other way, we would spend the day looking at a parking lot full of generic 5th wheels.
Tell me, which view would you rather have out your front window???