Help needed - 48VDC system (Skoolie)

[Tecchie]

Hello all. I'm currently in the planning stages for my Skoolie conversion. I have some power questions for you all.

I've settled on 48V (51.2V full charge OC voltage) LiFeP04 system. I've got some solar panels picked out (350W units from either Panasonic or LG)

This will be a long-ish term build for me, so I don't mind saving to buy things necessary.

A bit of background: We are a family of 6, so power requirements at certain parts of the day will be a bit high (hot water, pumps, cooking, etc)

I'm attempting to build a list of things I'll need to accomplish my goal.


What I'm looking to do;

Power nearly everything off DC (I do NOT want to use inverters unless I absolutely have to), even if DC-DC converters are needed for lower voltage things.
Be able to have multiple inputs for charging the system (shore, solar, onboard alternator and possible backup/auxiliary genset and be able to sately/automatically switch between inputs as needed)

Things that will be powered;
Refrigerator (still looking for a suitable one)
Chest Freezer (found one I think will work well, but does 24V, I think they have a 48V model)
Cooktop (may have to stick to propane for this, and would strongly prefer a griddle top as I can cook more food for the family this way)
Water heater
Clothes washer/dryer combo unit (found some, yes expensive, but wash/dry in a single unit)
Power up any computing things up to around 1KW at a time (some of this may require an inverter use, and is optional)
Lighting (all LED, so minimal power draw there)
Heating for at night when it gets cold - like winter time
Cooling (likely with a mini-split unit for efficiency, and there are some DC units out there)
Water storage tank heater for colder seasons (will b around 100 gallons/(approximately 378 liters)

My battery bank size/capacity will likely be overkill/over sized for most of you, but my plan is to be able to run everything, I've calculated (roughly) a minimum capacity of around 64kWh worth of storage, I may go with more. Yes, the whole system will be expensive, that isn't a concern as I said, this will be a long term build.

What would be needed in the way of charge controllers to tie it all together and be able to monitor power draw, charge rates, individual cell/cell group health, temperature, etc of the battery bank?

We have kids, ages from 9 to 21, so a lot of times power will be used for various things. I don't want to have to worry about draining the system flat if we are camping in an area without a lot of sunlight.

I guess I need some charge controllers that can handle a lot of amps, or balancers can can handle a lot of amps.

What about adding Super Caps in-line for things that require a sudden current draw as to not hammer the batteries - do they have a current draw of their own to maintain their charge? like what would the wattage draw (wH) be on those? I can't seem to find any information on this, as I'd leave them inline/online 24/7 but be dis-connectable for system maintenance.


I apologize for the word-vomit, I just have a lot to process and lists of things I need to start getting together, and the system to design.

Above all else, safety is required for obvious reasons. I don't do cheap stuff, as I hate replacing things that get worn out, so if there is a better quality whatever it is for the money, I get that instead. I also take care of my gear.

I appreciate the input. Efficiency is pretty important from the charge controllers

Maybe a list of devices to get the job done would work? Software suggestions? I don't mind networking the whole system. I already have several low power network switches I can use for onboard communications to BMS/Charge controllers and old decommissioned laptops I can convert to be a "hub" of sorts for the whole system

 

[John Frum]

I've settled on 48V (51.2V full charge OC voltage) LiFeP04 system.

51.2VDC is the nominal voltage.
The charging voltage can be up to 58.4VDC.
Have you done an energy audit?
See my signature for a link.

 

[snoobler]

Your "word-vomit" is premature. You haven't done enough planning.

You need to use link #5 in my signature to find available solar for your location, panel orientation and panel tilt angle.

Then you link #1 and the downloadable spreadsheet to do an energy audit.

 

[John Frum]

Power nearly everything off DC (I do NOT want to use inverters unless I absolutely have to), even if DC-DC converters are needed for lower voltage things.

Nearly everything is not the same as everything.
If you are going to have an inverter may as well leverage the good things that come with it.
Benefits include...
Alternating current is much less prone to sustained arc by its nature, that means much less beefy switching gear can be used.
Higher voltage means loss voltage drop over distance.
Higher voltage means less amperage for the same power.
15 amps@120VAC = 1800 watts.
15 amps@51.2VDC = 768 watts.
All this and more for the price of an inverter + 15% conversion penalty.
Something to think about.

 

[snoobler]

^^ Agree

The moral imperative to use DC-only also tends to drive costs up substantially as 12/24/48V applicances/devices often cost substantially more than their AC equivalents. Many new AC-only appliances include their own "inverter" function to provide improved energy efficiency with variable power demand instead of the traditional binary ON/OFF, so the efficiency is notably improved.

The 15% hit on efficiency may be completely rectified by simply adding 1-2 additional solar panels depending on the size of your system.

The 15% hit on efficiency is also nothing compared to even the smallest waste of power by inattentive users, who will in a matter of a single moment, make a decision that shits all over your draconian efficiency efforts. Yeah, you can train them, but they'll screw you unless they're equally draconian by default. If they're not, then you're setup to the the efficiency dick.

Good luck shoving 6 people into a skoolie.

 

[SolarQueen]

Have you figured out how many solar panels you can fit on the skoolie roof? I can't imagine you can come close to generating enough solar electricity to fill a 64kWh battery bank. I'm thinking you need at least 10k-12kW of solar, a heck of a lot more if you are trying to heat with solar in the winter (assuming you are someplace cold).

 

[SolarQueen]

As for the original question of having the charge controllers coordinate and monitor, many brands will connect to each other and do a leader/follower configuration. Outback, Schneider, Midnite Solar, Victron all come to mind. Some have a separate battery monitor that can also be installed.

 

[Hedges]

Me, I like AC coupling. That can be 98% efficient transferring power from your PV panels at Vmp x Imp and delivering to appliances using the power at that time. You only pay battery inverter inefficiency and battery inefficiency for power saved to use later.

Thinking about lead-acid AGM batteries because that's what I have, 64 kWh would be about $15,000 and 2400 pounds. It might last 10 years cycled to 15% DoD or 18 months to 70% DoD. Lithium would of course be lighter and last longer, but cost per (kWh multiplied by cycles before wear-out) is similar.

If we considered it to have 45 kWh usable capacity and you planned to use 1/3 of that in a day (3 days autonomy during these smoky days?), that's 15 kWh/day, which could be produced by 3 kW of PV. That is 10 panels, about 9 x 20' of some models. Maybe you can fit 2x that on a bus. More would require fold-out or slide-out mounts.

Compared to battery capacity for multiple days, a generator for those times is cheaper and lighter. With batteries and inverter you can get by with a much smaller generator, maybe as little as 1 kW.

I like the idea of using power during the day if the sun shines, and keeping battery bank small. Battery costs more than everything else combined. So the trick it to control loads based on state of charge.

As others have said, figuring out what loads you need to run is the place to start.

 

[YellowBuddy]

I do NOT want to use inverters unless I absolutely have to

Is there a reason why? Is it just efficiency?

If so, I have a couple of thoughts but they won't be purely solar related. If efficiency is top of mind and you don't mind taking the time or spending the money to get a truly great functioning system, I think there's a couple of additional ideas.

1) You have competing thermal loads. You have multiple sources of heat generation, including constant ones from the fridge and freezer; and high temperature surges from the engine and generator - which 60-70% of fuel burned ends up as waste heat. Look into getting some heat exchangers with a dc water pump to improve the cooling efficiency for these units, but also recapture the heat to be used for your heat demand loads. You may be able to fully eliminate your whole hot water heating demand and even some "domestic" heat needs.

2) Cooktop, if you're not willing to take the 15% hit on AC/DC conversion; you shouldn't be willing to take the hit on propane cooking efficiency. An electric induction cooktop tends to be more efficient than propane. Then there's the safety factor. No carbon monoxide to worry about, faster cool down, and less waste heat to then have your AC work against.

I'd continue looking at those design choices, especially so if you're sticking with DC. You're going to be dealing with some extremely high voltages or more likely really high amps. That's not exactly a safe nor easy thing to do. So the better you can get your skoolie operating as an ecosystem, the easier that task will be. Especially on thermal retention, heat in the winter is no easy task on a battery bank. If you can get it all working in harmony your power requirements would be significantly less and much easier to obtain.

 

[JiPe]

Hi We are a family of 6 doing a bus build as well (we are in a vintage Greyhound bus - 35ft long)

We have had our power system up and running for about 2 years and we have similar goals in mind.

The specs on our system are 3480 Watts of solar, Victron 48|5000 Inverter/charger, 24 kWh of Nissan Leaf Battery.
(see the show and tell sub-forum for pics)

We have had to "prematurely" start using our system as we had to move our project to some land with no power or water.
It has been a great learning experience and I believe it is testing our system far better than we could have otherwise - here is why:
1) We are in Arizona during the hottest summer ever recorded in the history of the state. We are using 3 or 4 air conditioners (depending on what we are doing)
2) We are building the bus so we are running big power tools off the bus system constantly - saws, welders, compressors ...
3) We are constantly going in and out - forcing the air conditioners to work even harder.
4) During the beginning of the summer, we were not even fully insulated.

Here are some of the learnings and assumptions we had made and some of the rationale behind them.

Energy Audit
When we first started we did a run-down of everything we might use and how much power that would use. We also took a stab at about how much power we thought might be our "baseline" power. The number we kept coming up with (assuming decent weather) was about 6-8 kWh per day. I still think this is probably a pretty good guess for us (we will see once we actually start traveling)

Refrigerator
Very early on we decided we did not want a propane refrigerator.
They are terrible at cooling and they are pretty dangerous (2nd leading cause of RV fires).
They are also EXTREMELY inefficient on 110V AC power. We ran tests with our Dometic RV refrigerator and it needed just over 10 kWh of power PER DAY. (we made a video specifically about this)
To give you some idea of the difference - we got the $300 magic chef 10.1 cf refrigerator from Home Depot - it uses about 0.8 kWh per day to power it.

BMS
The number 1 reason is simply safety and peace of mind.
We knew to get the power density we needed we had to use Lithium batteries.
Once that decision was made a BMS was a MUST and we are super glad we have.
Our BMS prevents under and overcharging as well as temperature (cannot charge at 3 degrees or less), ours also controls our Victron equipment
with charge curves etc to optimize battery life and balances our cells.

Heating
Heating was a weird area for us (please keep in mind we are from AZ). We were really tempted to do electric heating but we just couldn't get the numbers to work well for a few reasons. 1) Heating is needed during the winter when there is significantly less sunshine available (because the days are shorter and there seems to be more rain/clouds). 2) we don't have a way to tilt out panels so again we will have reduced solar input. 3) heating takes A LOT of energy. For heating the air we decided on Diesel heaters (two 5 kW units - our mini-split will also do heating but it draws about 1000W to do so). For heating water, we decided to go with an instant propane water heater because of the energy involved and because we have 6 people on the bus)

What to put on 12V
We went really small with our 12V loads. Lights, Fans, Chargers, Diesel Heaters. We also made this system redundant with our chassis battery.
Small loads on the DC side was a big driver in us adopting 48V. We have big stuff like air conditioners, induction cooktops, washer/dryer etc all on the AC side.

Tracking Energy usage and seeing trends
Being able to track your energy usage is super helpful. Victron VRM has been a dream come true. We can see if something is working harder than it used to. Or if our battery pack is acting strange. Or if our solar panels need to be cleaned.

Baseline Loads
For us baseline loads (Refrigerator, Inverter, security cameras, cell booster, internet router, 12V converters, main computer) all use about 10% of our battery per night. Of course, this is in AZ where the weather is very hot so the refrigerator and inverter are working pretty hard to stay cool. We are hoping this number gets a little better as things cool off - and because we have a great way to track energy usage - we will be able to tell. An example: We recently added a battery charger for the 12V chassis batteries to ensure that they are always topped off and healthy - this cost us an additional 1% of battery life (we decided it was worth it).

Energy per day
On a really good day with 3480 Watts of power on the roof (flat non-tilted), we can make almost 25 kWh of power. Clouds or even (more recently) smoke can easily cut that number in half.

That's all I got for now

 

[Tecchie]

Your "word-vomit" is premature. You haven't done enough planning.

You need to use link #5 in my signature to find available solar for your location, panel orientation and panel tilt angle.

Then you link #1 and the downloadable spreadsheet to do an energy audit.

The system capacity is going to be fairly large, and be installed on a Skoolie conversion. The panels I picked would fit in the roof without issues (350W units or higher when the time comes to purchase)

I'm strictly in the planning stages at the moment, but I need solid info, because I prefer to DIY. I realize the full system voltage will be higher than 48V target, and I can use some voltage regs as needed for things that are more sensitive to higher voltages.

In addition, I do like to leave several things running 24/7 for my needs, radios, server gear, etc, and likely a mobile broadband link.. Total draw would be around 800W under heavy loads, idle wattage would be less than half of that, but running things off an inverter wouldn't be very efficient under those lighter loads. I can handle converting some of what I need to DC only.

The solar array will be enough to cover my energy needs during the day at least. The plan for me is to have the large capacity energy storage for days where there isn't a lot of solar energy available or grid tie and if I'm trying to conserve fuel (from the bus/generator) for instance.

Cost of DC appliances doesn't matter to me. I care about how reliable they are, less bells and whistles. Like those RV Washer/dryer units that do the complete cycle in one machine, I've already found a company that makes chest freezers that can do 48V, so that part would be perfect.

I do have a gas GRIDDLE, but I'm unsure of the safety if I integrate it into the countertop (versus propane burners anyways,) a topic for another time.

The Skoolie will be as insulated as I can get it, so likely a DC powered heat pump that can also do cooling during 100 degree days, or keep us warm if temperatures drop below freezing

Interior lighting will be low volt and using buck converters to power those as needed.

The biggest energy consumers overall for our family of 6 would be the washer/dryer probably 3-6 loads a week, hot water heater (and water pump)

I mean I could probably get by on a 30kWh bank, but I'd rather have the extra capacity just in case.

I considered a 24V system with the additional functionality of if the onboard starting batteries went dead on a trip, I could at least use the bank to get the bus started (self jump-start) but logistically that would require a bit more planning. higher voltage bank for efficiency and smaller diameter wires reducing weight overall

Battery chemistry I'm going with is going to be LiFeP04 (Lithium Iron Phosphate) for many reasons, including the safety aspect.

Larger battery bank so I Can cycle it less thus extending its overall life cycle, more consistent voltage output, lighter weight, maintenance free (no adding distilled water or electrolyte), and I don't like replacing things if I don't have to.

Bottom line, I prefer to "Buy Once, Cry Once".

Safety devices will be installed on all circuits; breakers/resettable fuses, properly rated for the intended loads, cut-off switches to isolate the batteries & solar panels.


The system would be able to take input from three sources which is why I'm unsure of what type of MPPT I should be looking at;
Shore power (120V/240V as available), Solar, and onboard generator (maybe like an ONAN Diesel). But a minimum of two sources of input (shore & solar)

Sorry for the late reply everyone, I appreciate the input.. I've been very busy with taking kiddos to doctors appointments, working on one vehicle and the other in the shop for things I don't have tooling/space for and a bunch of other stuff.

I really value Wills reviews, testing and teardowns he does on all these batteries and helps in my purchase decision.


Are there any systems that can handle monitoring of individual cells/cell groups? I like the idea of Battleborn batteries, but two things keeps me from keeping them high on the list, and they are there is no way to monitor their own charge controllers, not the condition of each cell group... it's like you feed them and let them be.. And systems I can tie into an old laptop or touch screen (likely just software + interface) controls that can show live energy audits?


My brain just jumps all around when thinking of all this stuff..

thank you all for your help, I appreciate it!

 

[Tecchie]

Refrigerator
Very early on we decided we did not want a propane refrigerator.
They are terrible at cooling and they are pretty dangerous (2nd leading cause of RV fires).
They are also EXTREMELY inefficient on 110V AC power. We ran tests with our Dometic RV refrigerator and it needed just over 10 kWh of power PER DAY. (we made a video specifically about this)
To give you some idea of the difference - we got the $300 magic chef 10.1 cf refrigerator from Home Depot - it uses about 0.8 kWh per day to power it.

BMS
The number 1 reason is simply safety and peace of mind.
We knew to get the power density we needed we had to use Lithium batteries.
Once that decision was made a BMS was a MUST and we are super glad we have.
Our BMS prevents under and overcharging as well as temperature (cannot charge at 3 degrees or less), ours also controls our Victron equipment
with charge curves etc to optimize battery life and balances our cells.

Heating
Heating was a weird area for us (please keep in mind we are from AZ). We were really tempted to do electric heating but we just couldn't get the numbers to work well for a few reasons. 1) Heating is needed during the winter when there is significantly less sunshine available (because the days are shorter and there seems to be more rain/clouds). 2) we don't have a way to tilt out panels so again we will have reduced solar input. 3) heating takes A LOT of energy. For heating the air we decided on Diesel heaters (two 5 kW units - our mini-split will also do heating but it draws about 1000W to do so). For heating water, we decided to go with an instant propane water heater because of the energy involved and because we have 6 people on the bus)

Glad to know that you have been successful so far. I was considering some of the Victron products, but unsure how I can integrate everything into a central control panel to get the type of monitoring and real time display I'm after or if all the gear would work together. I was considering MidNite MPPT controllers as they're made here in my state of Washington not far from where I live.

For heat, I was considering a Heat Pump as there is at least 1 company that makes DC powered units. but the alternative "backup" would be a small but effective "Rocket Stove" with some thermal mass built-in so it would burn the minimal of combustible material while outputting the most about of heat. I was also considering those diesel heaters, but if I went that route, I'd have to plumb in it's own tank as to not accidentally use too much from the main tank(s) to ensure I can drive out of wherever we decide to "camp out" of..LOL

SunDanzer has a nice 48V freezer for food storage, there are a few other manufacturers that offer fridges that'll do 48V also.

What can be done for individual cells like BattleBorn batteries that have onboard BMSs but don't communicate outside the large cell itself? What is a good high current capable BMS & MPPT controllers?

A Rough calculation of an energy audit tells me I'd be using roughly 2-6kWh/day for some base things including the server, which if needed, can be shut down on occasion.

 

[snoobler]

Glad to know that you have been successful so far. I was considering some of the Victron products, but unsure how I can integrate everything into a central control panel to get the type of monitoring and real time display I'm after or if all the gear would work together. I was considering MidNite MPPT controllers as they're made here in my state of Washington not far from where I live.

Oh yes. Color Control GX or other Venus GX device.

Here's mine:

VRM Portal - Victron Energy

vrm.victronenergy.com

 

[Maast]

I'd also like to chime in on the "no inverter" bit: If you get a high efficiency inverter with a minimal idle loss (think Victron, et al NOT one of those awful MPP and clones) you actually lose less power than a DC/DC converter, furthermore you lose less power moving it's 120V power around. 48V (nominal) DC is highly lossy for anything involving large currents or more than a few feet away unless you use HUGE expensive cables.

DC lighting makes sense, DC appliances do not; they're quite a bit more expensive and furthermore the selection is quite limited. If you design your system correctly you can keep the inverter in 'search mode' and only using a watt or two and then kick on when you turn on an appliance.
I would recommend you get a normal high efficiey fridge and have its own small inverter for it, the Victron small inverters are great for this. It'll keep your main inverter on 'low power' idle.

 

[JiPe]

Glad to know that you have been successful so far. I was considering some of the Victron products, but unsure how I can integrate everything into a central control panel to get the type of monitoring and real time display I'm after or if all the gear would work together. I was considering MidNite MPPT controllers as they're made here in my state of Washington not far from where I live.

For heat, I was considering a Heat Pump as there is at least 1 company that makes DC powered units. but the alternative "backup" would be a small but effective "Rocket Stove" with some thermal mass built-in so it would burn the minimal of combustible material while outputting the most about of heat. I was also considering those diesel heaters, but if I went that route, I'd have to plumb in it's own tank as to not accidentally use too much from the main tank(s) to ensure I can drive out of wherever we decide to "camp out" of..LOL

SunDanzer has a nice 48V freezer for food storage, there are a few other manufacturers that offer fridges that'll do 48V also.

What can be done for individual cells like BattleBorn batteries that have onboard BMSs but don't communicate outside the large cell itself? What is a good high current capable BMS & MPPT controllers?

A Rough calculation of an energy audit tells me I'd be using roughly 2-6kWh/day for some base things including the server, which if needed, can be shut down on occasion.

Oh man if data-gathering is your thing there is nothing that even comes close to the Victron stuff. It's nothing short of amazing.
With the Victron Color Control GX, Victron Venus GX, or the new Victron Cerbo GX you can see all your data both historically and in real-time anywhere in the world. You can see things like Solar output by hour, week, month as well as consumption both DC and AC. What kind of loads the system was experiencing, battery temperature, individual cell voltages its a crazy amount of data.
Our BMS communicates natively with our Victron eco-system to tell the system what to do and when to do it.

Here is what our system is doing on our bus about 5 miles from my house in real-real time as well as how our solar and energy usage did today.

 

[snoobler]

Rocinante... sweet.

 

[JoeHam]

Schneider does the same data porn thing via the ComBox. Just getting my toes wet now with it.

And the Victron data looks great for sure.

@snoobler what’s up with the celsius temp? Thats just unAmerican ?

 

[snoobler]

JoeHam I'll have you know HBR is reporting °F. I believe your beef is with @JiPe

 

[berksrunner]

Nearly everything is not the same as everything.
If you are going to have an inverter may as well leverage the good things that come with it.
Benefits include...
Alternating current is much less prone to sustained arc by its nature, that means much less beefy switching gear can be used.
Higher voltage means loss voltage drop over distance.
Higher voltage means less amperage for the same power.
15 amps@120VAC = 1800 watts.
15 amps@51.2VDC = 768 watts.
All this and more for the price of an inverter + 15% conversion penalty.
Something to think about.

The “conversion penalty” at 48v will be quite a bit lower than 15%. For a Victron unit, I can tell you it will be 8% or less.

 

[berksrunner]

I'd also like to chime in on the "no inverter" bit: If you get a high efficiency inverter with a minimal idle loss (think Victron, et al NOT one of those awful MPP and clones) you actually lose less power than a DC/DC converter, furthermore you lose less power moving it's 120V power around. 48V (nominal) DC is highly lossy for anything involving large currents or more than a few feet away unless you use HUGE expensive cables.

DC lighting makes sense, DC appliances do not; they're quite a bit more expensive and furthermore the selection is quite limited. If you design your system correctly you can keep the inverter in 'search mode' and only using a watt or two and then kick on when you turn on an appliance.
I would recommend you get a normal high efficiey fridge and have its own small inverter for it, the Victron small inverters are great for this. It'll keep your main inverter on 'low power' idle.

^^^^^^^this all the way. Even with our 24v system, using a victron MP, we don’t notice the losses — AC fridge, AC cooktop, AC water heater, and of course, TV. Those together represent thousands of savings over their arguably lesser-performing overpriced DC counterparts.