Powering with Lithium

As built, the 2019 Crossfit comes with 200Ah of lead acid batteries and 200 watts of solar. The lead-acid’s are under the chassis behind the rear wheels. Coachmen installed a 12.2V automatic battery disconnect, so the under ideal conditions the coach batteries get disconnected when about 60% full. In cold weather the disconnect occurs when the batteries are significantly less discharged.

The major power consumer is the compressor refrigerator, which draws over 5A when running. A quick bit of math and a few nights of camping and I realized that I’d get at best one night on batteries, and only if they were fully charged in the evening.

In any less than ideal conditions the solar will not have the batteries charged at dusk, and the batteries will not last through the night. There isn’t really room on the roof for more solar. Portable panels are an option though. The coach has a generator – noisy enough to discourage it’s use- and a battery isolation relay that allows the alternator to charge the coach batteries. Lead-acid’s don’t accept a charge at a high rate, so long idle time or long generator runs are required for topping off the batteries.

I decided to attack this problem in two ways. First by increasing battery capacity, second by reducing power consumption by improving the efficiency of the refrigerator and attacking parasitic draws.

Battery Capacity – Adding Lithium to the mix. My first stab at this is to add a single Battleborn 100AH LiFePo4 battery, isolated from the lead-acid via a Redarc 40A battery-to-battery charger. The B2B keeps the lithium battery charged using whatever power is available from the alternator, generator and/or solar. The coach loads are connected to an A/B switch the permits me to manually switch coach loads to draw from either the lithium or lead-acid batteries. I’m using a Thornwave Bluetooth battery monitor to track the state of the Lithium battery.

The lithium battery should offer at least twice the usable capacity of the existing 200Ah lead-acids, and more importantly will permit faster charge rates, so generator and idle times should be greatly reduced. Initial testing supports this conclusion. I can charge the lithium battery at close to 40Ah from either shore, generator or alternator, and the lithium offers at least twice the usable capacity

Here’s a couple views of my final implementation:

High level diagram

In this design, the lead-acid batteries are always connected to the solar, converter and alternator charge sources. The load is switchable between the lithium and lead-acid batteries. The B2B can be disconnected – primarily so that I can limit current when both lead-acid’s and lithium’s are discharged.

Campervan Electrical – as built, 08/2020

For the installation I stole a bit of space under the passenger side jump seat. The battery, switches and Redarc B2B fit with a bit of room to spare. The space is next to the Truma furnace/water heater, so it’ll stay a bit warmer in winter. If it gets too cold where it’s parked over winter I’ll probably have to pull the battery out and store it inside the house.

I’ve since added a cosmetic grey felt covered panel to hide the battery.

The Transit has a heavy duty alternator, so if I were to add more lithium capacity I believe that I could safely double or triple the alternator charge rate. To do that I’d have to run heavier wire from the van batteries to the coach 12V supply.

After monitoring voltage drops (.3V ground side and .5V hot side) , I’m sure I’ll have to increase the wire gauge between the lead-acid supply and the B2B charger, and perhaps between the van batteries and the 12V supply side. I’ll also have to re-run the ground on the lead-acid side.

[2020-02-12 – I wrapped the battery with Battle Born’s extremely expensive OEM battery heater & thermostat, and fitted some insulation. The battery should stay a bit warmer so I think I can leave it in over winter as long as I have the campervan plugged in and charging.]

[2020-04-05 – The ‘as built’ campervan electrical is described in detail on the Campervan Electrical page.]

[2020-08-01 – Redesigned Solar, added battery combiner. The ‘as built’ campervan electrical is described in detail on the Campervan Electrical page.]

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