Questions with my DIY setup and charging via Car

[leesamuelm]

Hey everyone.

I have a DIY "solar generator" that I built (roughly 300-500wh of 12v lifepo4) and a PWM charge controller.

If I wanted to charge it with my car through the 12v power socket, how does that work?

What limits the amount of current demand my batteries will draw from the car?

What I know: 14+v alternator voltage from the car. 15amp fuse for the 12v socket.

Charge controller is a PWM "30 amp" (which i am suspicious about)

What I don't understand: If I make a cig power plug and plug it into the 12v socket and the other side goes to the PWM solar in, will it POP smoke/blow the fuse because nothing is limiting the amount of amps/current demand?

I'm still an electrical newb, so I wanted to ask before doing something stupid.

Thank you all

 

[time2roll]

Yes there is a good chance of opening the fuse. Depends on how low the battery is and the resistance in the connection. The lower the battery is the more it will draw. The longer and thinner the connection the more voltage drop. They could balance each other out. Or you might need a replacement fuse. The cigar connector is really a poor solution except for the smallest of batteries.

Far better to install a dedicated circuit with more available power. Still need a fuse.

 

[No Idea]

Those 12v cigarette sockets are wired with thin wire so aside from a low amp fuse to protect the wire, even if you change fuse you will risk fire and also see a big voltage drop when trying to pull a large current.

However, 500wh is small so you dont need a large amp charger. I also think a 30A SCC sounds high.

500 wh is 40Ah cells in a 4s configuration. Depends on C ratingof those cells for charging so you need to check. My 50Ah cells are rated 0.5C charge but yours may be 1C charge.

For 15A cigarette socket fuse you would not want to pull that max fuse rating continuously so if fused 15A you could charge at 10A with a DC DC charger (which uses a little extra amps on top for inefficiency).

As previous poster says better with dedicated wires of correct gauge and fuse for your planned charge current if more than 10A.

If you cani lve with a 10A charger then cheapest solution is a 10A AC to DC charger and a 12v modified sine wave inverter to plug into your cigarette socket.

DC DC chargers for LiFePO4 tend to be more pricey.

Although this one is 200w (i dont plan on using it in a car) so long as you only plug a 10A AC to DC charger into it then it would be ok but open to other forum members if they think DC > AC > DC would push the total amps too close to the 15A fuse limit.