48V dc / 110V ac inverter/charger

Due to frequent power outages I've decided to build a battery backup system.

What inverter/charger should I get? I need 2000W sustained power, 3000W surge, but most of the time the load is <150W, hence inverter idle power is somewhat important. I'd prefer a 48V dc system.

The Victron Multiplus 48/3000 look interesting, but I can't find one with 110V output (I assume the 220V models don't come with a center tap on the transformer for 110V output at half power).

I will pair this with an 8kWh+ battery I plan to build (or buy). Charging time is not critical. Recommendations? Does anyone have experience with blslifepo4battery? They have good reviews on Ali Express and Warehouses in the US for fast shipping. Look good on paper ...

How would I select? E.g. curiously battery size, capacity and weight do not always seem to be correlated.

No solar, unfortunately - I live in snow country, the panels would be ripped off the roof and often snow covered.

Welcome to the forum.

48V Multiplus II/120V is supposed to come out soon That may be your best bet if you can wait.

Since it's not a full-time application, I'd consider this:


or this:


Neither are likely great on idle draw.

Thanks for the response. Idle draw is somewhat important to me as I'd like to use this for several days without recharging, ideally. I'll get a Victron 24/2000, or the MultiPlus II if it comes out soon. I just ordered the batteries (13kWh) from Michael (via this site). Should get them in ~2 month.

My Quattro is about 30W. Multiplus is probably around 15W.

A super cheap small generator (2kW) feeding the inverter is also extremely useful.

The 24/2000 is 11W, the 12/2000 9W zero load dissipation, but the 24/3000 is 20W, per the manual. Over 3 days that's 1.44kWh, not quite negligible.

Incidentally I just checked and for the Quattro 48/3000 the manual says 25W zero power load. Did you measure the consumption of yours? Perhaps the manual is "conservative".

I do have a 1200W generator, but run it off propane and am at high altitude (2000m / 7000ft) - so I only get 600W safely. I've read conflicting information about wether the Multiplus (or Quattro) input current can be limited so it draws only 600W. I've also asked on the Victron forum and was told that the minimum current was ~8A which would be too much.

Do you know what this minimum is for yours, or, rather, if 600W can be specified as a limit for the input draw? If the Quattro 48/3000 draws only 15W idle and it's input can be limited to 600W price is it's only drawback and I may go for this solution.

A related question: Apparently these units can be programmed with Victron Connect using an MK3-USB cable (and confidential? password that I suppose I can get from someone). Can the Cerbo GX (with many more features) replace the MK3, i.e. be used to configure the Multiplus or Quattro? I saw a YouTube video that seems to do this via an external portal, but that looks a bit convoluted. Would you or someone on this board know?

These Victron devices appear very powerful and there is lots of documentation, but it's hard to answer detail questions from the manuals, it appears.

Sorry for the long message and many questions, I very much appreciate the input from this board!

Mine is a 5K. It's about 30W based on the disparity between my AC use and DC input.

For the Power Assist feature to be enabled, there is definitely a minimum current; however, I believe for AC-in and charging purposes, it can be lower, but that's not a hard known.

I do all of my programming remotely via my CCGX. I download the config file from the inverter, use VE Config to change it and then upload it via VRM.

Concerning AC-in limits:

Via DIP switches, the charge current can be set as low as 25%:



Since my 240 split phase genny only puts out 15A @ 120VAC on one leg, I have the AC current limit to 13.5A.



You would want PowerControl enabled and PowerAssist disabled.

I downloaded a spreadsheet from Victron pro site from another thread:



If you disable power assist, no lower limit.

48V Multiplus II/120V is supposed to come out soon ??????? Any more background information or preliminary spec sheets?

My 10K Generator Replacement Project:
I have a class A motorhome that I am going to replace the 10K generator with 24 100AH BattleBorn Low-Temp batteries (I purchased one of the first production runs and they are in my garage - I am very committed) and have been waiting for the 120V variant of the 48V Multiplus II/120V. What I determined is the very low leakage current draw is VERY important for my design and have been waiting.. Additionally the new form factor of the Multiplus II will fit in the front faring between the generator and the front bumper almost perfectly. I can fit 6 banks of 4 batteries running at 48V within the same footprint of the generator slide-out bay.. By simply replacing the generator with Batteries & Multiplus II and with a few wiring changes, the RV will always think it is connected to shore power all the time. This allows me NOT to have to modify the 12V subsystem in the RV at all (the coach battery side) although I did replace the four 6V batteries with the same low-temp 12V 100AH batteries.

I am hoping that there will be a 5000VA 120V unit just like for 240V units. It has been a while since I have engaged Victron directly. - Anyone have any insight???

I actually would prefer a 10,000VA /120V single unit but would install two 5000VA120V and that easily works with the current wiring of the RV.. (The RV has two legs of 120V/50A on a single phase so either a single 10K unit or two 5K units will work)...

Thanks in advance for any responses..
g

ghhardin said:

48V Multiplus II/120V is supposed to come out soon ??????? Any more background information or preliminary spec sheets?

My 10K Generator Replacement Project:
I have a class A motorhome that I am going to replace the 10K generator with 24 100AH BattleBorn Low-Temp batteries (I purchased one of the first production runs and they are in my garage - I am very committed) and have been waiting for the 120V variant of the 48V Multiplus II/120V. What I determined is the very low leakage current draw is VERY important for my design and have been waiting.. Additionally the new form factor of the Multiplus II will fit in the front faring between the generator and the front bumper almost perfectly. I can fit 6 banks of 4 batteries running at 48V within the same footprint of the generator slide-out bay.. By simply replacing the generator with Batteries & Multiplus II and with a few wiring changes, the RV will always think it is connected to shore power all the time. This allows me NOT to have to modify the 12V subsystem in the RV at all (the coach battery side) although I did replace the four 6V batteries with the same low-temp 12V 100AH batteries.

I am hoping that there will be a 5000VA 120V unit just like for 240V units. It has been a while since I have engaged Victron directly. - Anyone have any insight???

I actually would prefer a 10,000VA /120V single unit but would install two 5000VA120V and that easily works with the current wiring of the RV.. (The RV has two legs of 120V/50A on a single phase so either a single 10K unit or two 5K units will work)...

Thanks in advance for any responses..
g

Click to expand...

Would expect it's identical to the 230V/50Hz version except, 120VAC/60Hz:


If by leakage, you mean idle power draw, the 48/5000 is 18W. Comparing the 120VAC Multi to the 230VAC multi, I didn't see an idle power draw difference, so I wouldn't expect the Multiplus II to be any different. With 2 units, you'll have 36W idle draw - 0.86kWh/day.

If the 12V is produced by an onboard 120VAC to 12VDC converter, all of your 12V power will only be about 75% efficient - possibly more influence than the idle draw if the inverters.

Assuming your rig has dual A/C units, that monster battery bank you're building can only run them for about 10 hours.

How do you plan to keep the bank charged?

Thanks for the response...
I have developed a massive spreadsheet and powerpoint presentation for all the power generation / consumption for every device for my rig to model it all out...
Parasitic consumption is a killer for when the rig.. The residential refrigerator is another killer.. And the 3 AC units are a power hungry pigs.....

I was comparing it to the Quattro 5K/10K at 48V 35W/65W respectfully to the Multiplus II 48V 5K at 18W and for two 36W so about half the parasitic draw...

On the 12V side my rig is powered by Magnum Inverter & Precision Plex Power Distribution system.. I plan on leaving that untouched except for the coach battery upgrade. By having 400 AH @ 12V for the coach 12V side it is pretty significant bank and I could add 4 more in the bay and still be weight neutral compared to the 6V batteries..

My key design goals are to make this a simple drop-in replacement model for all Class A's... So keeping the Space, Power, Cooling & Weight neutral (challenging) .

My original thinking about charging was:
1.The primary charging method will be a High-Output Alternator installed on the Cummins. Utilizing alternators with Smart Sense (only when providing current to charging the batteries will it place a significant load on the engine) and external voltage regulation
2.Solar Power will be added to compliment the Alternator charging. Solar is more like a straw versus the firehouse of an high-output alternator but admittedly solar does have the advantages that is “free”, quiet and always on (well, when the sun shines)and can be used to “maintain” base devices such as the residential refrigerator
3.Shore Power will be used when camping in RV Parks. Shore Power when attached will be used for both running the rig and charging the battery bank. It will mostly be “free” power - non metered sites

However I may change the priority and do a non-penetrating solar panel install first... my rig is 40ft long and there is quiet a bit of realestate and the sun is available more time than I drive the rig...

I am actually finding it challenging to find a shop to do the 48V second alternator work on the rig (I am an electrical engineer not a mechanical one).. Even at peak current draw the engine load is under 10 HP ..... and that load is software controllable with through an "smart" alternator controller.. I have done significant research on using an alternator as a generator source. Units can produce over 8500Watts @ 48V (my gen only produces 10K) but this work is not for the flippant - seriously bad things can happen...

Attached is my "From This to That" slide.. It may seem counter intuitive, but by doing the generator replacement - it is actually a simplier project in a lot of technical perspectives than a lot of other modifications...

Thanks again, I do enjoy the feedback,
g

Concerning 12V, I don't have any familiarity with the magnum or the power center, but I can tell you that inverting your DC battery to AC and then powering an AC-DC converter is only about 75% efficient. I assume the Magnum is an inverter/charger, so it's likely no different. When you're consuming 12V power off-grid, you're consuming 33% more from the 48V battery.

The residential fridge is probably about 2kWh/day - that's great compared to a LP/electric absorption fridge.

With charging method 1, it sounds like you traded a small efficient generator for a very large inefficient one at great expense. Surely a 10kW generator (about 13 hp) is substantially more efficient in kWh/gal than spinning a huge diesel and charging with alternators. If done while driving, it's probably comparable since it's a secondary load, but if you're going to idle it to charge your batteries, that's got to be way less efficient.

Given the BB purchase, this is looking like something on the order of $40K or more. Given that those monster rigs rarely cost less than 10X that, it's probably something the market might consider, but from an engineering/efficiency standpoint, I don't see any point unless you have the roof dripping with PV and have deployable panels - something like 4-5kW total, If #1 is just an option, but #2 is the primary, then yes. I see a lot of value for folks with that kind of money.

Thanks for the feedback... Your math is spot on and you are not far off the costs...

I think my real argument is.... if you were buying a new rig... would you pay a $20K-$30K upgrade to go all LiFePO4..

Battery technology and density is rapidly changing and will easily outpace generating technology. The price is also rapidly declining. There is a coming inflection point..

The 10KW generator costs about $1/KW so about $10K .... Offsetting a significant cost of the batteries... And if I were to not be retrofitting the rig I could have a single instance of battery (with different tap points) and avoid unnecessary/redundant voltage conversions... and I could easily shed another 200+ lbs of static weight and that is a lot of diesel power over time/full to push... I am tracking my weight carefully.

A computer controlled 48V alternator is way more efficient than you are giving it credit.... It only loads (effectively) the engine when generating current, else it mostly free-spinning (746 watts = 1 horsepower). The amount of load, timing of loading and duration of loading is all computer controlled. It is a lot lighter than the 750 lbs of the generator..

Another perspective that I learned by being a Telsa EV owner is - Minding the Gap - meaning what brings me back to grid.. I am never impacted to charge my car my daily life - I drive it... park it at home at night and plug it in.. Only when do long trips do I have to charge and am impacted...
In my RV, what brings me back to grid first?
Electricity
Diesel
Propane
Food
Grey/Black water
Fresh Water....
-->Fresh Water always brings me back to grid first... So even if I am boondocking off grid.. water water everywhere and not a drop to drink - I will have to get water .
We are long weekenders - 3-4 day trips often... off grid only a few days.. so the gap almost non-issue/pretty small if I am traveling or staying at RV Parks - actually unless they have metered service - I will get free charging

At a 50% loading of the alternator I the battery bank will charge in about 5 hours of driving/running the engine... So if i move every few days to new camp sites .. Batteries will be charged while driving...

Even at idle - the 48V alternators can charge at 90% of their capacity charge the bank of batteries in hours in about 5 hours - pretty fast considering..

I agree that converting to power is inefficient - hence the dual banks.. 12V for 12V coach systems... 48V for coach 120V systems..

With solar augmentation, I may not need the alternator source if the gap is small enough and the sun is shining. Hopefully when the sun is shining the heat creation is helping the solar power generation to help offset the three ACs running...

I do think is weird to be driving down the highway with all that Diesel HP & Torque mostly idle at cruse speed and I have to run a generator to cool down the rig..


Thanks so much for your insight...

g

Have you run the numbers on the 10kW generator's kWh/gallon vs. the diesel engine idling producing the same?

I'm not debating the efficiency of the alternator. I'm guessing you have at least a 6.7L diesel engine. The 10kW Onan is 1.5L. They each have different energy needs just to rotate/actuate that much mass. A 6.7L diesel producing 10kW is going to burn more fuel at idle than a constant speed 10kW generator optimized for 10kWh output.

Roughly speaking, I would think you need dual alternators rated for 200-300A EA but only delivering 100A EA due to the extended charge times.

Your description of typical use makes a lot more sense. You get enough charging to and from to top off the batteries, so you never need the "generator" unless you have heavy A/C use. Sufficient solar on the roof might make the "generator" unnecessary even for mild to moderate A/C use.

Honestly, Given that 4kW of solar on the roof is maybe $3000 on the package price, I can't imagine not just including it outright.

My pockets are way too shallow, but that system as an option on a new beast might be very viable. 4kW solar would probably allow 2 A/C units during the day and possibly one at night for a 2-3 days w/o having to go to the "generator." 4kW might be too much for the available surface, but I would expect you could get more than 3kW up there.

I understand the added 12V bank, but it's not clear to me. Are you going to disable 12V charging and only run 12V off the 12V bank? If you have it connected to the on-board "off-grid shore power," it's going to ultimately pull from the 48V bank. Will it operate on a "recharge" threshold, i.e., use batteries until 12.4V, then charge to 14.4V from the Magnum inverter/charger?

For added awesome, you should have an automated "storage" mechanism. LFP batteries deteriorate with stored fully charged. If the owner is putting it in storage for the winter, or knows they're not going to use it for a couple months, hit the button, and the charging will stop at 50%, or it will automatically run something until it's down to 50% - fridge?

I appreciate your optimism on battery technology, but I don't share it. The evidence doesn't support it. Battery technology is improving asymptotically towards a minimum (see Moore's Law for computer transistors for an analogy). Existing technology and it's current state of the art improvements will take another 10 years before it potentially gets to 1/2 the cost of where it is now vs. the previous halving in less than 4 years. Increased demand and decreased supply may further slow that improvement as the globe demands more battery storage for more applications.

Cost for NiMH batteries used in Toyota hybrids for the last 20 years haven't decreased significantly in that time. Nor has it improved in any meaningful way. Eventually a technology matures and stops progressing. Lithium prices only beat NiMH prices about 5-6 years ago.

Sure, there will probably be another breakthrough or new technology, but even it will take many years to mature and improve once it's established as viable on a production scale - thus net progress is very incremental.

Sincerely and respectfully, I do appreciate you feedback and I am enjoying the conversation.. So many times threads do not maintain decorum. I learn a lot through these exchanges and the thoughtful discourse improves my thinking and design. In my day job, I am a Technical Fellow and one of my key roles is to teach and encourage junior engineers how to think and problem solve and to accept challenges without being defensive.

My Onan 10K consumes about 3 gallons per hour and will NOT operate below a ¼ tank (33 gallons) – this can be a bummer and have to plan to be full before stopping for any period of time. Many times in my rig I am “sprinting” 600+ miles/day to the East Coast from Denver and often stop at “no services” pull-offs. As long as I fill up before stopping, running the generator all night is not an issue (mostly because I am sandwiched between a bunch of semis that run their diesels all night). But when I boondock or state camp – I do get a LOT of other camper scowling and coming over to remind me of the gen rules (I strictly comply and keep the rules at hand – many time they do not pay as much attention to them as I do myself – this happened 3 times last year) My rig is almost all electric, except for forced air heat and hot water so it is significantly dependent and AC power. So, I do have to run the gen a significant amount of time when in living in the rig – induction cooktop, TVs, AC/Heat pumps, washer/dryer – there is no lite impact camping (I have two kids 2 and under – LOL) and two dogs so the AC has to be set to run during the day when we don’t take them on the day trips..
There is a price to pay for servicing and maintaining another diesel powerplant on the rig but in contrast with the battery approach that should be pretty maintenance free – just managed.
So, what I am trying to say, the diesel gen does need to be managed and it is not “free”.

My Cummings 380 is provides plenty of power/torque to make through the CO passes at a respectfully 50 mph+ fully loaded with water(100g) fuel (100g) for about total of 1500lbs and flat towing a Jeep. While I would enjoy a bigger engine, I do not want a bigger rig, 40 feet is perfect me. On the average, I get about 7.5 gal per hour at 2200 RPM. I have not carefully monitored the consumption at idle (don’t remember idle rpm). But when driving the rig, I start it the morning and leaving it running all day till I stop, never turning it off.. BTW – this keeps the 12V battery bank fully charged of off the stock alternator.

I plan to be able to control how the 12V subsystem gets charged by adding the necessary software control relays to avoid what I call ping-pong charging between the 12V subsystem and the 48V subsystem. You are correct that this is very wasteful and should be avoided.
https://www.americanpowerinc.com/high-output-alternators/
At 48-56V they can run steady state producing 160 Amp or around 8600 Watts of power
This is what you don’t want to do……
So you need something like this:
http://wakespeed.com/products.html
You are very correct in your statement about including solar natively, I have come to that same conclusion. Looking at my old math, of I baseline just trying to run the three ACs at 1725 Watts each on solar, I need a minimum of 5K watts of solar.. This is my homework now, to design the solar subsystem..

In my day job, I am very much a student of Moore’s Law and Ahmdel’s Law.. Not at all arguing the asymptotically nature of the curves. However, over the last year or so I have seen a 20-30% increase in power density of Li batteries (both Tesla and Battleborn). I would have to guess they are running on a 30-50% costs of goods and think competition and advancements in manufacturing will erode some of their margin and reduce the consumer price. And there are disruptive new technologies that might mature, like Lithium Titanate Cells and Batteries – lighter and faster to charge_

One of the biggest logistic camping problems that I have is that I have to store my RV off of my property without power. Unloading and loading the refrigerator is the biggest pain in our RVing. Of course, with this system I can easily maintain the temp refrigerator between trips.
I run a Peplink (4G & WiFi router) device in the RV and can access it remotely and since the over-all solution will be software controlled (mostly by Victron) I should be able to dial in all the charging, storage and consumption almost anywhere..
Regarding the price of my science project – Shhh don’t tell the wife ;D
Happy Sunday…

So doing quick dirty math... Say at 75MPH the engine burns burn 7.5 or about 10 Gal per hour at 2200 RPM under load... At idle guessing the rpm is around 600 (I googled it) .. Interpolating (10X600)/2200= 2.7 gallons/per hour at idle.... I am guessing since the 2200 number is under load and at alternator load is about 8 HP for 8600 Watts@48V it would not be appreciably affect the idle consumption.


Correcting myself, the Onan 10K burns about 0.88 Gal /Hour (I stated 3 g/hr) at full load..



Interpolating to 86% (8600Watts)
the Gen consumes 0.62 gal/hr at 86% load

So as a percentage
0.62/2.7 Gal to generate the same power - The 380 engine is only 23% as efficient as the generator ... Or stated differently, the engine consumes 4 times the amount of diesel for the same power generation... but then again the diesel is also generating the 12V power and a LOT of everything..

Does my math track?

For sure a very dirty way of modeling but the numbers seem intuitively to make sense.....

The difference between a generator and an engine is the generator works at constant rpm and has a proportional relationship between POWER and consumption with them typically being most efficient at peak output.

An engine does not operate at constant rpm. Engines have an "island" where a combination of mass air flow/rpm and power output produce optimal specific fuel consumption.

From https://x-engineer.org/automotive-e...ormance/brake-specific-fuel-consumption-bsfc/:



Power on the y-axis, engine rpm on the horizontal.

As you can see, lower power output has substantially higher specific fuel consumption, so there is no correlation between engine rpm and fuel burn as you computed without considering the power produced.

Your linear assumption of fuel burn as a percentage of rpm is not valid as it doesn't include the affect of power on fuel burn, but it happens to produce an answer that is within the realm of reason. 4X isn't so bad if you're only running it 1/4th as much, AND the influence of charging while driving will have efficiency comparable to the generator... with full access to all 120VAC equipment.

There are clearly advantages to your proposed system on the scale of your rig and your usage patterns. It's clear you've designed a solution that solves your problem. I can imagine there's a market for it as well for similar usage patterns.

I just can't place enough emphasis on solar. Don't even think about offering it without solar... SO much bang for the buck!

Yeah, like I stated earlier... so not the mechanical engineer and my dirty linear math was, well very badly applied to an admittedly non-linear environment... My tesla is pretty easy to model in comparison - lol.. Thanks for being nice about it -lol...

Yes, solar yes... I will pull out my roof maps... This biggest questions I have around the constructs of the solar system is how many to run in series and how many to put in parallel to optimize the power into the 48V battery subsystem.. Thoughts?

That will be based on the voltage limit of your MPPT SCC.

Common limits are 100, 150, 250, 450 and 600 volts with increasing cost as the operating voltage increases.

Due to roof protrusions and partial shading, you'll want to shoot for a balance of series and parallel. You'll want a string Vmp of no less than 66V or so for a 48V system. If you find that several panels are more prone to partial shading, you should have as many of those on one string as possible with other strings comprised of those that avoid shading or partial shading in most cases.

Since this is also a big-ticket/luxury item, panel optimizers might also be warranted - about $50-60/panel additional. These work in concert with all panels in a string and maximize power even during partial shading.

I will install as many panels as I can make fit on the roof... Partial shading is a dynamic problem for sure. The RV will move pretty constantly... I do desire to have a non-penetrating design and plan on running the cables to the back of the rig to run the the rear faring instead of through the roof. I will put the solar charging controllers in the current coach battery bay or the current Shore Power Connection..

This mounting system is very interesting to me as it very lightweight and non-penetrating...

And this guy has a 5th wheel implementation that has solar close to what I want.... (I will have more than double the amount of battery storage)

thoughts?

Shading during movement isn't the primary concern. It's once you're stationary and parked for your 3-4 days.

Absolutely do not consider flexible panels. They've improved in recent years, but I would not trust them to last like hard panels.