diy solar

diy solar

Questions for the confused ....

I am concerned about the risk and complexity of introducing an external relay. I haven't spent enough time researching them to understand how they handle failure, fail closed as an example.
I use contactors that can only fail open. If you use the normally closed contacts of a relay, then if the coil failed then you would have a failed closed situation. That, however in my mind would be a design failure.
 
Excellent context, thank you.

I have a travel trailer with 50 amp service. Picked it up in the fall so the system is your traditional OEM to get it off the lot, no inverter and a single deep cycle marine battery. If you're managing with 440ah of lead acid I feel anecdotally I'll be fine. My current plan is Multiplus 12/3000, 150/60, 800 watts of solar with room to move to 1200 watts and batteries ... well that's why we're here :).

I've been looking into the larger BMS's, the brand you mention pops up often. It's pricey but that isn't the reason for my hesitation, I am concerned about the risk and complexity of introducing an external relay. I haven't spent enough time researching them to understand how they handle failure, fail closed as an example. Curious, you're designing for a single bms to manage two batteries? Didn't know that was possible.
Food for thought on an external relay. A quality built contactor will at 28 volts DC and loaded to 500 Amps have an estimated cycle life of 100,000. How many times do you plan on it triggering it? A well built system will "very rarely" trigger.
 
So to summarize, I was correct in my assessment that a.) this is a very deep and dark rabbit hole and b.) I have a lot to learn :)

That's this weekend's objective, to learn what I can about this specific BMS. I've thrown together this quick and overly simplified spreadsheet to help me understand my needs. The actual consumption numbers are best guess based on quick Internet research and the usage is a stab. I'm unclear on panel efficiency and how that should be baked into the equation so I've tried to be conservative at 30% loss using the lowest average sun hours for my area that I could find. With my current plan and this rudimentary sheet I should be in the positive in terms of daily usage vs. recovery.

Thoughts (go easy!)
 

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So to summarize, I was correct in my assessment that a.) this is a very deep and dark rabbit hole and b.) I have a lot to learn :)

That's this weekend's objective, to learn what I can about this specific BMS. I've thrown together this quick and overly simplified spreadsheet to help me understand my needs. The actual consumption numbers are best guess based on quick Internet research and the usage is a stab. I'm unclear on panel efficiency and how that should be baked into the equation so I've tried to be conservative at 30% loss using the lowest average sun hours for my area that I could find. With my current plan and this rudimentary sheet I should be in the positive in terms of daily usage vs. recovery.

Thoughts (go easy!)
Solar is easy.... Install "all" the panels you can fit. It is "vary" rare to here : Oops I installed to much solar on my RV..........
 
I think 800 watts of solar is a good place to start. Place them so if you decide on more you can add more easily.

I found in Alaska last year my 800 watts was plenty as long as my spot was in the sun. But there were many places I was in the trees and needed the generator for an hour a day (or so).

Those sunny places I would turn the fridge to 120v electric at noon to about 5. use free sun - save propane.

After I get the lithium’s- I will use AC-2 and hook it up to my electric water heater - then program the Multiplus so if state of charge is 70% or higher turn AC2 on. Free power to heat hot water! I may even move the fridge to that circuit too. Just an idea to keep in mind.
 
For a fridge there are great 12V DC models - AC power for fridges in a camper van doesn't make sense I don't think.
Anyway AC voltage with a good inverter is a decent alternative for charging batteries while driving, even idling, or to run that microwave for cooking.
The problem is that most cars have pretty weeny alternators, many offer at idle RPMs under 1000W. But you can install a beefy aftermarket replacement alternator with 225 - 240A of power, which gives you about half that rated power at idle, like 120A. 120A x 13.5V dc = 1,620 Watts. Basically what you could run off an outlet in your house.
They run about $400 to $475 at various websites like powerbastards dot com, guys that have massive stereo systems with subs that shake the neighborhood need them or they simply haven't got the watts.
This should probably be higher on folks lists than a gas generator. Maybe even than solar panels.

- Varimu
 
Okay, so I’m moving forward with 8 270’ish ah. Configuration and BMS still undecided but I have a couple of months to figure that out.

Bit of a digression here but is there any consensus on the CATL cells yet? Seems to be the most readily available at the moment.
 
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