DIY milk crate build

[timsim]

Hello! I'm very new to DIY solar power and battery stuff but I'm interested in building my own milk crate "solar generator", similar to the build Will did in his milk crate 2.0 video. My primary goal is to have serviceable, reliable, and portable backup power for power outages and camping. I'm envisioning building a few over time, and I have a few questions about what I have in mind for my first build. I've attached a bad diagram. But the tl;dr plan is:

• Put the battery, inverter, smart shunt, fuse box, and maybe a 12v connection panel in the milk crate
  with a single anderson connector coming out of the fuse box for charging.
• A 30A MPPT charger with a matching anderson connector in a separate enclosure to attach to my solar panels and connect to the milk crate.
• A 30A AC charger with 3 outputs (all hooked up to the same anderson connectors) in a separate enclosure that I could use to charge 1 to 3 of these kinds of setups simultaneously.
• The main reason for the decoupled chargers is I'm thinking about how convenient it'd be to be able to not buy more of them as I make more crates and to be able to move them around and charge flexibly. I'm not sure if that's a dumb thing to do or not but it seems fun to me.

Questions

1. Is a 1200W inverter good to connect to a 12v battery with max continuous 100a discharge without a fuse? Presumably the battery and the inverter both have overcurrent protection via the BMS and fuses, respectively.

2. Is a 1200w inverter the largest I could reasonably expect to power with a 12v battery with 100a discharge? 12v * 100a = 1200w continuously, is that how the math works?

3. Is my plan to decouple the MPPT charger and AC charger a wild thing to do? Is there something inherently unsafe about what I'm proposing there? Both of them charge at 30a, so I'm assuming I can use the same connector and swap them out, is that valid?

4. If I have the anderson connector coming out of the milk create hooked up to a 35a fuse in the fuse box, do I need any other fuses/circuit breakers between that and the MPPT charger/AC chargers?

5. If I get one of these 12v rocker switch panel things, how can I ensure the 12v outlet is going to run something like a 12v fridge? Is it regulated somehow? Is there something I should be buying instead if I'm interested in running something like that? Or should I just use my inverter?

6. Is anything I've wired here dumb or dangerous?

Parts (I've purchased nothing):
Battery - 12v 100ah Battleborn, SOK, or Amperetime or some such
Inverter - 1200w Giandel https://www.amazon.com/Inverter-1200Watt-Control-Outlets-Emergency/dp/B07G36Z2TH
Smart Shunt - Victron https://www.amazon.com/Victron-SmartShunt-500AMP-Bluetooth-Battery/dp/B0856PHNLX
AC Charger - (12v/30a/3 outputs) https://www.victronenergy.com/chargers/blue-smart-ip22-charger
MPPT Charger - (100/30) https://www.victronenergy.com/solar-charge-controllers/smartsolar-100-30-100-50

Thank you so much, genuinely, to anyone that takes the time to read this. I really appreciate it, thanks for the cool forum, I've learned a lot by lurking!

 

[svetz]

Welcome to the Forums!

Questions

1. Is a 1200W inverter good to connect to a 12v battery with max continuous 100a discharge without a fuse? Presumably the battery and the inverter both have overcurrent protection via the BMS and fuses, respectively.

If the battery has overcurrent protection built in, hard to get better than that. But, if that's a fuse, you might consider adding a lower amp fuse outside that is easier to access/replace, oftentimes the "built-in" are hard to get to or sometimes not repairable.

2. Is a 1200w inverter the largest I could reasonably expect to power with a 12v battery with 100a discharge? 12v * 100a = 1200w continuously, is that how the math works?

The math right is correct, but the question struck me as odd until I recalled your battery has overcurrent protection (most don't).

3. Is my plan to decouple the MPPT charger and AC charger a wild thing to do? Is there something inherently unsafe about what I'm proposing there? Both of them charge at 30a, so I'm assuming I can use the same connector and swap them out, is that valid?

Both devices will change from CC to CV so it probably depends on how they get the battery's SoC. I'd write and ask the manufacturers to see what they say.

4. If I have the anderson connector coming out of the milk create hooked up to a 35a fuse in the fuse box, do I need any other fuses/circuit breakers between that and the MPPT charger/AC chargers?

Fuses protect the wires and should be as close as possible to the source. Think about it from the perspective of the wire, if a wire rubs against something (before the fuse) and shorts, what will happen? The wire might be cheap to replace, but what it sets fire to might not be.

5. If I get one of these 12v rocker switch panel things, how can I ensure the 12v outlet is going to run something like a 12v fridge? Is it regulated somehow? Is there something I should be buying instead if I'm interested in running something like that? Or should I just use my inverter?

Rocker switches are just switches. The voltage is set by the battery based on the current draw. As the battery SoC goes down so does voltage and it may adversely affect things. You can get 12V regulated power supplies that will run on DC, but you need to know that max number of watts the fridge draws to properly size it (they may also consume watts in stand-by). I'd start by asking the fridge manufacturer what their cut-out voltage is (or experimenting) and then check that against the batteries SoC to see if you need to take action.

6. Is anything I've wired here dumb or dangerous?

Electricity is always dangerous and even the best plans won't prevent silly mistakes. You'd be hard-pressed to find someone that works with power a lot that hasn't, though some moment of inattention, done something amazingly stupid (I sure have, and I don't even work with power that much). Be sure to wear safety glasses, 12V might not shock you, but if can sure shoot bits of metal good distances. Test all connections for resistance/voltage before applying any power or turning anything on.

 

[timsim]

Thank you so much for answering my questions!

If the battery has overcurrent protection built in, hard to get better than that. But, if that's a fuse, you might consider adding a lower amp fuse outside that is easier to access/replace, oftentimes the "built-in" are hard to get to or sometimes not repairable.

The math right is correct, but the question struck me as odd until I recalled your battery has overcurrent protection (most don't).

Yeah I've never messed with any sort of lead acid battery and it seems like they don't have the same things (like this) that seem to be more or less standard on the LiFePO4 batteries I'm looking at.

Both devices will change from CC to CV so it probably depends on how they get the battery's SoC. I'd write and ask the manufacturers to see what they say.

It looks like they both read voltage from the battery, presumably that'll be possible through a fuse and a couple of connectors without much of an issue.

Fuses protect the wires and should be as close as possible to the source. Think about it from the perspective of the wire, if a wire rubs against something (before the fuse) and shorts, what will happen? The wire might be cheap to replace, but what it sets fire to might not be.

This makes a lot of sense to me, the idea of "fuses protecting wires" rather than devices hadn't really sunk in for me until now. Thank you.

Rocker switches are just switches. The voltage is set by the battery based on the current draw. As the battery SoC goes down so does voltage and it may adversely affect things. You can get 12V regulated power supplies that will run on DC, but you need to know that max number of watts the fridge draws to properly size it (they may also consume watts in stand-by). I'd start by asking the fridge manufacturer what their cut-out voltage is (or experimenting) and then check that against the batteries SoC to see if you need to take action.

Yeah it looks like I'd need a DC-DC converter of some sort and set it to the voltage I want if I wanted to be sure it'll work well. Good info, thank you.

Test all connections for resistance/voltage before applying any power or turning anything on.

Great advice, thank you again, so much I really appreciate it!