dc-dc or ac charger off of inverter

[Adjake]

Trying not to spend too much more on this system. I currently have a small system I use for camping. 100 ah renogy lithium victron mppt victron 17amp ac charger, viltron 800 watt inverter victron shunt and a victron battery protect. This powers a 12v dometic refrigerator, laptop charger iPad and phone charger top off camera equipment batteries and an electric blanket in the winter
Usually I can get away with topping off the system before I leave for a weekend, one night camping. I have a 160 watt solar panel, but it is mostly useless camping in the woods. If I do more than one night the battery alone will sometimes last as long as I can find enough sun when I park somewhere to explore.

I'm thinking about adding a dc-dc to charge in-between destinations as I rarely stay in one place on a multiday trip.
My other thought was to disconnect the inverter from the lithium system, plug it into the car (I already have large power wire where I would need it from an amp) and use the 17amp ac charger to top off the lithium.
I'm leaning toward method 2 as it would cost just a few Anderson connectors and some wire which I already have, and it wouldn't cost me more space. Downside to this is I would have to remember to turn it off when I park so I don't drain the jeep battery.

any and all suggestions welcome
Advantages and disadvantages either way?

 

[sunshine_eggo]

Human battery management systems have a near 100% failure rate.

Lots to be said for automatic systems.

Something in the middle would be:

https://www.amazon.com/Automatic-Converter-10A-Waterproof-Transformer/dp/B07WFMG11F

13.8V is enough to get the LFP battery to very nearly full after a couple hours AT 13.8V. Once the battery is held at 13.8V and near full, it draw very little from the chassis battery, thus you could "forget" to disconnect from the 12V for some time. Fuse both ends of course. There are also options higher than 10A.

 

[justinm001]

Get a DC to DC charger and plug into a relay so it only charges when the engine is on by plugging the relay into some key switched 12v outlet. Going from 12v to 120v to 12v seems like such a waste, also much more work and risk of being stuck.

Theres also things like this but i dont like them as they can overload your alternator since it's basically just connecting the batteries together then disconnecting then connecting again.

LiFePO4 Battery Isolation Manager (BIM)

LiFePO4 Battery Isolation Manager (also known as the BIM) monitors voltage and connects and disconnects batteries when needed. Click here to read more!

battlebornbatteries.com

 

[Rocketman]

I am using Victron’s Dc-Dc charger 30a. It works well.
It has an automatic engine detection. So if the voltage is high enough that the alternator is running - it will charge the lithium battery. Once it drops below that value, it shuts off.

I love automatic things rather than having to remember myself to do something…

 

[justinm001]

I am using Victron’s Dc-Dc charger 30a. It works well.
It has an automatic engine detection. So if the voltage is high enough that the alternator is running - it will charge the lithium battery. Once it drops below that value, it shuts off.

I love automatic things rather than having to remember myself to do something…

I'm with you. I'm automating everything I can with my coach so it's effortless when we use it. Luckily my new coach has a dedicated alternator for my coach lithium batteries so I just installed a wakespeed ws500 regulator and can program it to charge however works best. It's only 12v 300a but the new one will be 24v 450amp so tons of charging

 

[Adjake]

10-4. It’s what I figured. I’m sure I would forget to turn it off and get stranded somewhere.. oh well more money

thanks

 

[Rocketman]

If you don’t want to buy the dc-dc charger - you could run the wire to the fridge off a relay that only works when the engine is running.

That way you would never be stranded… but your food might be warm in the morning. ?