Quote:
Originally Posted by yoda42
Have you looked at lithium batteries you could use a smaller battery and still get good life for running a fridge etc and they are super light, down side is cost
|
Lithium (lifepo4 of-course.) is the definitely way to go for vehicle house batteries now. Price is pretty-much on par with AGM for useable capacity over rated life, and cheaper if managed conservatively.
1/3 weight for the same rated capacity, and better again for useable capacity.
Can work out a bit smaller, but not much once you factor cell interconnects, terminal insulation/safety and other bits-and-pieces.
Big advantage is you can play with the layout to fit your space.
Main downside is there's still a bit of misinformation and misunderstanding around, which seems to make it hit-and-miss finding a good product and installer if you can't do it yourself, and has flow-on effects like high cost for off the shelf systems.
Most lifepo4 wisdom has come from electric vehicles or large-scale storage, and some things are not as relevant for us with small low current low voltage setups.
This is 150AH in the back of my WH;
Pack is 12 x 50AH cells, so essentially 3 x 50AH batteries in parallel.
Multiple strings in parallel like this is a worst-case scenario, but lets them fit in a void in the WH when the factory boot floor is removed.
Charged via a Blue Sea CL "BatteryLink" relay (which are freekin brilliant for anything that charges off an alternator!). Basically a VSR that limits current to 60A. That's important since a discharged lithium pack will pull massive current.
DC-DC charger would also work, but nothing on the market can charge at 60A without shunting a crapload of current at low state of charge and heating up.
Undercharging lifepo4 off the alternator and using common AGM/lead low voltage cut-off (~11.8V.) makes for a pretty conservative system, much longer usable life than AGM and still more useable capacity.
No need for constant cell monitoring/balancing in a setup like this, especially when using used cells from storage banks (the majority of cell variation happens earlier in life as the chemistry settles.).