Charging an 12v AUX battery from a cig lighter

[joshik]

So I've been reading up and searching around google about this topic. I have a 18ah SLA 12v DIY battery box (aka solar "generator"). Like this one: https://www.youtube.com/watch?v=2NIzIR_Lbkw

ATM, i don't have use for a full blown dual battery setup with a 100ah AGM. I just use my battery box to charge phones, cameras and runs some LED lights when camping. I don't have a fridge and as of now don't really see myself getting one.

I charge it using a small 18v/18w solar panel through a cheap 20a pwm charge controller (was looking at changing to a renogy mppt controller). Slow, I know, but it get's the job done.

So I was thinking of charging the battery box through the cig lighter in the cargo area while driving... even possibly leaving it there semi-perm so it charges while driving at all times. I did a bunch of reading and its hard to parse through all the different conversations. I am trying to avoid having to buy an expensive DC-to-DC charger.

Of course, I want to be safe and not destroy anything and I think what I am understanding so far is that the issue with charging from the cig lighter is:

* The battery box, even through the pwm charge controller, won't regulate how much power it will draw through the cig lighter. If the battery is super low, it could draw more than what the cig lighter is rated for and blow the fuse or melt stuff...

* This is different when compared to the small solar panel because the solar panel is whatever it is rated at... 18v/18w/1amp, no more than that (less on cloudy days). So no issues of blowing up fuses or melting wires really.


Does that sound about right? If so, is there a way to limit how much the battery box could draw from the cig lighter.

or

Is that too complicated and not worth it? Just get a dc-to-dc charger?

 

[4r-4ever]

go for a dc-dc charger. you can't parallel charge your battery and your auxiliary battery. the other one will not reach a full charge in that situation. in my case, i built a battery box with the dc-dc charger and wired a #8 guage wire from the battery to the back of my 4runner. here's my video of it. All in one box. https://www.youtube.com/watch?v=ZbVtZvK-f9s

https://www.youtube.com/watch?v=ZbVtZvK-f9s

i use it to store stuff too and i could take it out easily when not used or use it on my other 4runner.

 

[joshik]

go for a dc-dc charger. you can't parallel charge your battery and your auxiliary battery. the other one will not reach a full charge in that situation. in my case, i built a battery box with the dc-dc charger and wired a #8 guage wire from the battery to the back of my 4runner. here's my video of it. All in one box. https://www.youtube.com/watch?v=ZbVtZvK-f9s

https://www.youtube.com/watch?v=ZbVtZvK-f9s

i use it to store stuff too and i could take it out easily when not used or use it on my other 4runner.

yeh you are probably right. Buy once, cry once. I could always upgrade the battery to something nicer/bigger and still use the dc-to-dc.

It just seemed like a fun project to figure out how to do it on a "budget" or with other DIY parts/tech. The pwm solar charge controller wouldnt really care what was supplying the power as long as it was within it's capacity.