WK2 Dual Battery Set Up

[JamesLaugesen]

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.).

[imaz]

Spent some time on it last night.

Because the spare location is tight fit, Ive decided to use an ANL fuse holder for the circuit instead of breakers, and doing a floating install instead of mounting the fuses as spacd is an issue.



Stuck an adhiesive rubber mat on the base all the way up where battery terminals reside.


At this point I ran out of cable to run to the fridge. Will get more today and finish it off. All the hard bits done and the battery is charging. Starter battery hovers around 14.3v and Second ~13.06v.

I also installed a cig port to the rear seat onto the centre console, in between the heated seats buttons, so the kids can charge their gadgets straight from the second battery.



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[JamesLaugesen]

Looks good Fuse is better than a breaker in that scenario anyway, where it's behind other fuses/breakers for each circuit.
Can you get the fuse closer to the terminal? Just so there's less unfused cable.

I'd make make some 'wedges' to hold the battery in place using Sikaflex 227 or similarly hard mastic squirted into the voids, and mould release or wax so you can still remove the battery.

[imaz]

Originally Posted by JamesLaugesen

Looks good Fuse is better than a breaker in that scenario anyway, where it's behind other fuses/breakers for each circuit.
Can you get the fuse closer to the terminal? Just so there's less unfused cable.

I'd make make some 'wedges' to hold the battery in place using Sikaflex 227 or similarly hard mastic squirted into the voids, and mould release or wax so you can still remove the battery.

Do you mean make the fuse wire shorter that you can see on the starter battery? Infact, i made it longer after the photo was taken as the one in the picture looked like it was over stretched. How critical do you think it is? If so, I'll flip it around so its shorter to the terminal and a little more longer to the VSR.

Put the wedge where? The second battery is tight fit and cannot be moved, litterally.

Using 100Amp ANL fuses to both battery terminals, and 80Amp ANL fuse to thr anderson plug for the fridge/boot area(which will also extend to the tow bar if needed in future).

Id like a low Amp fuse instead of 80, but couldnt source any.

Im also using a normal 10Amp blade fuse for the cig lighter.

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[timsarg]

Originally Posted by imaz

Do you mean make the fuse wire shorter that you can see on the starter battery? Infact, i made it longer after the photo was taken as the one in the picture looked like it was over stretched. How critical do you think it is? If so, I'll flip it around so its shorter to the terminal and a little more longer to the VSR.

Put the wedge where? The second battery is tight fit and cannot be moved, litterally.

Using 100Amp ANL fuses to both battery terminals, and 80Amp ANL fuse to thr anderson plug for the fridge/boot area(which will also extend to the tow bar if needed in future).

Id like a low Amp fuse instead of 80, but couldnt source any.

Im also using a normal 10Amp blade fuse for the cig lighter.

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imaz you reckon there is enough room to squeeze a ctek d250s in there somewhere ?

[imaz]

Originally Posted by timsarg

imaz you reckon there is enough room to squeeze a ctek d250s in there somewhere ?

Yeh man, that is the plan. If the VSR doesnt cut it, then I'll go with the DC-DC charger - For the moment, the VSR seems to be doing its job, only time will tell though.

[timsarg]

Originally Posted by imaz

Yeh man, that is the plan. If the VSR doesnt cut it, then I'll go with the DC-DC charger - For the moment, the VSR seems to be doing its job, only time will tell though.

seeing your pics i am going to move on and go straight to the d250s . i just have to figure out where to mount it