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Planning on a fairly high capacity 24V or 48V system.

Tecchie

New Member
Joined
Oct 5, 2019
Messages
10
Location
Washington State
This is going to be a semi long-term planning stage for me. My requirements are firm for capacity. Everything else is open to debate.

I realize a few things, cost of batteries is nearly going to make my wallet catch on fire, which is why this is long term planning (mostly the batteries)

This system will be installed in a fairly large diesel pusher Skoolie build.
A few things out of the way already;
Got solar panels/brand nailed down
Got battery chemistry chosen (Lithium Iron Phosphate)

Planned system total capacity: 120kWh - 160kWh
Planned usable around 100kWh - 150kWh (for longevity of the cells)

System will be used for several weeks off-grid (family of 5) with most - if not all - appliances running off the batteries (hot water, cooking, heating & cooling, water pumps, etc)

Weight is not a concern, neither is the weight or wire diameter.

My questions are as follows;

The bus' on-board electrical system will be 24V

Question is, there will be a few high draw appliances like cooktop/oven/air conditioning/heating. Which would be a better system voltage? 24V or 48V? (I fully understand the high current draw from a lower voltage system, and will plan safely around this requirement like using conduit/wire chases)

Things are a lot easier to find for 24V systems (MPPT charge controllers, BMS, etc) than 48V.

Preference is leaning towards 24V system as I could also use it in an emergency situation to jump-start the bus in case the starting batteries take a crap (which will be probably a momentary draw of around 900A or more - which I know the system capacity will handle the short hard hit of that draw)

There seems to be more appliance things like refrigerators and freezers that will run off 48V (or at least capable)

I'd plan to run as many things off the DC circuit as possible, even converting some things to run only off DC (removing their onboard transformer and wire in directly fused DC power and of course with those "DC-Outlets" they will be also tied to a breaker panel)

Also, it seems to be very difficult to locate DC-DC converters for a voltage step-up or step-down (like going from 48V to 24 or even 12V for certain applications)

Basically I want to minimize the need or usage for inverters.
Speaking of inverters, RELIABILITY and efficiency are my two number one requirements. I do not care about brand.


The solar setup I have penciled out, should provide around 3-8kWh at full sun for the panels I chose.

Most likely most electrical usage would be in the evening/night time hours. The system I am planning for may be overkill for the majority of you, but I want to be sure that my family has PLENTY of power with redundancy built-in.

Also, part of the BMS/MPPT etc will also want to be able to charge the bank from multiple inputs such as (besides solar) being plugged into electrical mains (120V or 220V or hel, even one of those high voltage electric car chargers)

Desired operability is something like a central panel that will show all the stats like the Victron system is capable of (usage, charging rate, cell life cycles, temprature, etc..)

Any advice would be appreciated.

Also, this is my first post here. Also been following Will on his YouTube channel for well over a year now, and appreciate his work.


Side note; If I Can get one of those commercial grade electric 220V griddle cooktops to work on DC, that would be fantastic and make for super ease of cooking meals. Otherwise I'd use one of the Blackstone griddles and figure out proper ventilation seeing as it's propane only.


Thanks for all your time and input everyone!

-Brian


P.S.

I apologize for the massive word vomit, I have ADHD, and the thoughts come at random..

Speaking of which, how is the quaity of those MidNite controllers? They seem to be manufactured in my home state of Washington.

Thanks!
 
Sounds like quite the project! Hope you keep us updated on it.

I don't mean to pull the pin on the non-negotiable part, but 160kWh? That's more power than my house consumes in a few days and about 2.4 tons of LiFePO4. You sure about that?

Personally I like cooking with gas (absolutely nothing to do with me being too cheap to to pay the battery for it). If you go induction make sure you have a pure sine wave inverter.

Q: there will be a few high draw appliances like cooktop/oven/air conditioning/heating. Which would be a better system voltage? 24V or 48V?
A: 48V, better conversion efficiencies and large battery systems (although at 160 kWh possibly you should be at 300V).
 
Sounds like quite the project! Hope you keep us updated on it.

I don't mean to pull the pin on the non-negotiable part, but 160kWh? That's more power than my house consumes in a few days and about 2.4 tons of LiFePO4. You sure about that?

Personally I like cooking with gas (absolutely nothing to do with me being too cheap to to pay the battery for it). If you go induction make sure you have a pure sine wave inverter.

Q: there will be a few high draw appliances like cooktop/oven/air conditioning/heating. Which would be a better system voltage? 24V or 48V?
A: 48V, better conversion efficiencies and large battery systems (although at 160 kWh possibly you should be at 300V).



You're right on the weight.. Maybe I should shoot for around 60-70kWh? Because also, my bus conversion, I'm planning on around 200 gallons of fresh water storage in baffled tanks.. and maybe two or more spread out for weight distribution.

This is a long term project, meaning it will take me a few years to get everything together and built. Mostly because of high rent prices where I live..

I know propane is cheap, but without constantly checking the tank(s) or whatever, I'd hate to run out in the middle of needing it. And not to mention the excess moisture on the inside during the colder months/colder climate areas. And I don't want to have to worry about waking up dead if there is ever a leak (even with detectors).

Looking at electric heating/cooling/cooking/laundry (including a clothes dryer) Been looking at those European style washer/dryer combo units that does both in a single machine.
 
Sounds like fun for that kind of power needs I would definitely use the 48v system. You can charge more battery with less SCC's that way. if you need to start bus in an emergency you could just hook up to 24 volts or half your series of batteries, it would probably throw them out of balance but you could fix that hopefully with the bms. You can get inverter chargers from magnasine to charge off of shore power. I dont know about the tesla thing but Im sure its possible. I agree with you NO PROPANE why buy propane when you have free sunlight.
 
I dunno but I'm running 3 cotek sd3500 inverters. Set in a 240/120 configuration. Each can handle around 30amp ac. 90 amp service basically. I run propane for my generator which only kicks in when batteries get low and only charge the batteries. I run my garage including my welder and compressor off the 3rd sd3500. I run gas range (PROPANE). fridge/ freezer and the rest of the house inverters. My batteries are sla 30kw which I can get 1.5 days before the Gen kicks in. I have 8.5kw sp. 2 midnite solar classics. I have no electric at my site. I do have a pellet stove running off ac as well. I'm going to move to diy lfp. Only issue are my ac clocks which sync with the inverters. Only 5 min off every week or so. Love it. Wouldn't waste my money on dc stuff. Heavy gauge wire is a pain.
 
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