diy solar

diy solar

Help needed - 48VDC system (Skoolie)

@Tecchie said he found "Clothes washer/dryer combo unit (found some, yes expensive, but wash/dry in a single unit)" Then, who's arguing here ^^;
If its DC I'm not arguing, but I am laughing.
Even more funny if its derived from sun and/or wind.
 
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

Thumbs up on the Victron MPPT chargers, I bought a 250|100 to start out with in my solar rollout plan. I also want to focus on a DC based 48v system in the beginning, just to see how far I can go with running raw DC for essential services. I haven't installed my system yet, but have most of the components now. I am planning to add in a Sol-Ark all-in-one inverter later down the line once I get the money (for any AC requirements).

So for now, I was going to use LED lighting (I bought a bunch of automotive bracket mount LED light bars rated at 9-36v input), so I can string them in series pairs and run them on the 51.2v bus. To get me through Winter I found a marine 20k BTU 48v ceramic heater, later I plan to buy a HVAC mini-split 48v unit. And they have the 48v volt refrigerators/freezers of course.

I live on cold food mostly so I don't really need cooking stuff much, I can use the 3.5kW/h inverter on my Prius hybrid for now if I need any AC stuff like microwave oven. Or my RV has a Magnum 2.8kW inverter and a microwave, with an Onan 6.5kW generator if needed. But later will plan to get the Sol-Ark 12k for running certain other AC loads where it doesn't make sense to convert to DC. I have 28 kW/h of LiFePO4 batteries to start with.

The way I see it, if we had an EMP event and my inverter got fried, then 48v raw power seems less complicated to repair, so building a collection of devices that run on 48v DC makes sense to me. I can repair some electronic stuff, but I don't know a ton about repairing inverters when they fry.
 
Last edited:
I've been leaning towards Victron equipment for monitoring and charging likely.

I want to build the circuit to handle charging from solar, onboard power generation, & shore power.. Do controllers exist to handle more than two power sources like that?
 
Just be aware that AC appliances are wide spread and mass manufactured. So will be cheaper in the long term. Just look a the price of an AC 18 cf fridge vs the dc equivalent.

With inverters in the 94% efficient range ...

Tecchie. The Victron Quattro will handle the two AC inputs. The DC input is done by the solar controller. You're all set.
 
Just be aware that AC appliances are wide spread and mass manufactured. So will be cheaper in the long term. Just look a the price of an AC 18 cf fridge vs the dc equivalent.

With inverters in the 94% efficient range ...

Tecchie. The Victron Quattro will handle the two AC inputs. The DC input is done by the solar controller. You're all set.

What he said. The Victron Quattro is the Cadillac of inverter/chargers. If you already have an Automatic Transfer Switch (ATS) then you may be able to get by with the Victron Multiplus, which has only a single AC input instead of the two inputs on the Quattro.
 
What he said. The Victron Quattro is the Cadillac of inverter/chargers. If you already have an Automatic Transfer Switch (ATS) then you may be able to get by with the Victron Multiplus, which has only a single AC input instead of the two inputs on the Quattro.

I get inverter efficiency is up there. But my plan is to run as many things off DC as possible. For example for non-appliance things, if there is a transformer inside, I can adapt that to run strictly off DC. That’s something I’ll tackle on my own.

but it would just be probably two AC inputs (shore power & onboard backup generator if I even fit one) and two DC inputs. One from solar and the other off the vehicle charging system/generator that’s belt driven.

Will this Vistron Quattro handle all that? Looking also for a max charge current of up to 200-300A?

I think I’ve settled on a DC system voltage of 48v
 
The Quattro does not have a port for solar. Victron does not pigeon hole you into what they expect you to implement for solar. That's why they have a full line of solar charge controllers.

The 48v Quattro can handle up to 200 amps of charging. See the data sheet in the link below:


You say two DC inputs, but you really need three: battery, solar, alternator. And no, the Quattro doesn't have that. It has one DC input for the house battery bank and one DC output for the starter battery. Victron provides a full line of DC-DC chargers that would go between the alternator and the system.
 
Ah. This is more of DIY handyman adventure then. Fair enough. I should have read the earlier posts. blush.

My thoughts are more along the line of "what's most reliable" and has the best return on investment.
I'm not sure you'll have much luck with getting a decent roi on a belt driven dc generator. Same reason I mention AC appliances. Go to the store. Pick it up. Plug it in. Time is money. 700 for a great fridge. VS Dc fridge. 4500. Time to change transformers etc.

In a similar vein. 2-300 amps charging at 48v = 15,000w charging. On a mobile transport device. Seems like an enormous overhead burden.

One thing to remember. If something happens to you. Somebody else is going to have to run the system (ie. your spouse/partner). I've seen a lot of off grid systems come to an expensive tipping point due to an enthusiasm of creativity. As opposed to say, the wisdom of simplicity and reliability.

Have fun.
 
One thing to remember. If something happens to you. Somebody else is going to have to run the system (ie. your spouse/partner). I've seen a lot of off grid systems come to an expensive tipping point due to an enthusiasm of creativity. As opposed to say, the wisdom of simplicity and reliability.

Agreed. I designed my system to need minimal understanding or intervention. If I had to write instructions, my wife would object. She's there to relax, not become a technician.
 
My system was initially designed as a 48V system, but I ultimately went with a 24V configuration.

I am a power electronics engineer and my primary goal was reliability and of course reasonable efficiency. The 24v equipement options were much better for mobile systems. I quickly gave up trying to go all DC - the inverter eliminated a lot of DC-DC converters, fuses, connections, and specialized devices. The efficiency penalty was too small to worry about relative to the increased complexity and lack of options.

The 24v system also gave me more flexibility in the solar arrangement. Each panel has its own Victron MPPT which helps with partial shading on the array and provides redundancy. It also allows me to use the entire power producing range of each panel.

My original 48v battery bank was divided into to 24v banks with independent BMS, fuses, etc. This is another redundancy thing.

I have a pair of MultiPlus 3000's, so additional redundancy there.

Overall, I am happy that I went with 24v and stuck with normal AC appliances. When anything breaks - I am not dealing with a specialty device for repair or replacement. That is also a reliability improvement. At some point, something will stop working when you are on the road. I can stop anywhere and find a microwave, fridge, AC, whatever. The 48v DC stuff is skinny on the selection and generally not widely available.

At the end of the day, everything I thought I wanted/needed at the beginning ended up being different in the end. I chose to build the system is phases which allowed me to learn as I go before I was totally locked in to anything. It was nice to have the flexibility to alter course based on real world experiences.
 
I've been leaning towards Victron equipment for monitoring and charging likely.

I want to build the circuit to handle charging from solar, onboard power generation, & shore power.. Do controllers exist to handle more than two power sources like that?

You can safely combine multiple charging sources without any special controllers as long as they're all configured to the same parameters. If you're all Victron, just connect your Inverter/charger and MPPT SCC's, configure the same, and done.
 
Back
Top