diy solar

diy solar

Newb here, already searched forum.. weak spots on my plan for a backup gen?

blasetheodore

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Joined
May 4, 2022
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Hi all. I'm dipping my toes into all of this, and could use a kind soul willing to offer feedback. Thanks in advance to anyone willing to read...

I'm adding a backup generator to my solar rig, and I'm nervous to mess it up by not knowing something. (see full setup details in my sig.)

I plan to feed a 900w Inverter Genny > AC120v > Victron IP65 charger (12v/15A) > 100ah LiFePOS4 battery.
From my layman's understanding, that should get the job done. However I'm unsure about:

1. Charger's Amp rating:
Victron claims 95% efficiency for the charger, so lets say 12A. I read somewhere that you should be supplying at 20-30% of the battery capacity, which I'm well under at 12%. The person who said it seemed smart, but didn't explain, so I don't understand. If true, I don't know if its a problem (gear damage), or just inefficiency (wasted power), or just annoyance (time loss.)

2. Generator load:
I am super unconfident on core skills here. If the charger is pulling 15A, that means the generator is at about 180w, or roughly 20% load? Do I have that right? I read somewhere that generators seem to optimize fuel efficiency around 70% load. Anything reasonable to be done here?

3. Back flow concerns:
I'm not quite clear on how I'd wire this in correctly. Just feed it straight to the battery? Do I need diodes or anything to prevent back flow?
The current setup has a 1kw DC>AC inverter thats also connected straight to the battery. Does that need a diode or anything?

4. Load while charging:
It would be nice to allow for load on the battery while it charges, but thats not a constraint. Mostly I just need to know the rules I have to obey. Any mistakes here that would cause damage?


Thanks to anyone who made it this far for your patience.

All the best,
Blase
 
It is time efferent to have a charger close to the charging capacity of the battery. Smaller charger just takes much longer, that is more generator fuel.
Generator is pushing 120 volts. The charger converts that to 12 volts. 12 amperes at 12 volts needs 1.2 amperes at 120 volts. Plus extra for losses.
Number three needs some clarification as I don't understand the question. I answer based on the OP parts list. The charger should have diodes as part of it's circuitry.
Yes, my battery bank feeds loads while it is charging. Must be careful that the device maximum voltage needs do not fall under the charger voltage maximum output. I put that very convoluted, but I am sober so have an excuse.
The rule is Fuses Protect Wires. Have appropriate fuse located at the battery positive.
 
Thanks for that Zil. I appreciate the detailed response.

I returned the Victron 12v15A and bought a PowerMax 12V 55A charger instead. (The "Lithium Plus" model.)
I hear they're not as power efficient, but hopefully that 15A vs 55A difference should still be more fuel efficient. No?

 
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