Using existing dual battery setup to feed new caravan - feedback needed

[Craigous Lurker Find all posts View Profile Close Craigous]

I have a 2023 VX with a duel battery setup with 90aH AGM charging off a Redarc BCDC 25ah charger (BCDCN1225). Is used just to provide power to a car fridge via 12v socket in back of car.

I have a van on order that will have an enerdrive 300ah lithium battery with a 60ah charger and 200W x2 solar panels on the roof.

For the van, the spec requires that my car have:

50 amp grey anderson plug for fridge and the lithium battery = 8mm & 10mm
50 amp red anderson plug for the ESC = 3mm

It is been suggested by someone I've spoken to that I just need to have the new wiring run from the second battery.

If the van is getting its juice via the 90ah second battery in the car, would the van battery charge if the 90ah is not fully charged?

Red flags?

I'll obviously ask an auto sparky more questions in person but I'd like to understand more before I do.

Cheers.

[Loddo Lurker Find all posts View Profile Close Loddo]

You need to run separate cables form the start battery to the Anderson plugs. That means that you should have 3 ando at the rear of you car. The dc to dc charging the 90 ah is just enough to keep it charged with the fridge connected .Is the fridge in the van a 3 way or compressor fridge ,if 3 way the 10mm sq cable would be run for the fridge and you will need a min of 16 mm sq for the charger that is connected the lithium battery.

[Craigous Lurker Find all posts View Profile Close Craigous]

Thanks.

The fridge is a compressor fridge.

[Loddo Lurker Find all posts View Profile Close Loddo]

Compressor fridge forget the Anderson for it but you need to run the larger cable for the lithium charger.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Hi Craigous,

I think your 60A van charger is actually the AC Charger and you most likely have the Enerdrive 40A DC/DC which doubles as the MPPT solar regulator to support charging while driving. If this is the case you can run the DC/DC input and fridge off a single 50A Anderson but I would still run at least 6 AWG twin core from the front of the car to the rear mounted socket via a 60A fuse and isolator like the redarc SB12 or similar so you don't have a live socket on the vehicle when the engine is off.

Definitely don't run your caravan socket from your aux battery setup as your redarc 1225 would never keep up and you would just flatten the aux battery.

[Leethal Advanced Member Find all posts View Profile Close Leethal]

As Ptommo advised run cables direct from the starter battery as your existing DCDC charger definitely has insufficient output to charge the existing 90Ah battery and the 300Ah lithium.
I run 5 gauge cable to the Enerdrive DCDC+ charger in the back of my Prado so I would run at least 5 gauge cable or preferably 4 gauge cable to connect to the van DCDC charger to ensure minimal voltage drop.

Lee

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

I agree with Lee that 4AWG would be the best solution for preventing voltage drop.

But during my DIY install I found that 6 AWG was the largest size that suited the available pins for the 50A Anderson connector and twin core 4 AWG was too awkward to run down the length of the vehicle due to size and stiffness particularly if you put conduit over it for extra protection. My van with a 3 way fridge and 30A Victron DC/DC are working OK with 6 AWG all the way from car battery to van DC/DC input with a 8 AWG pick off at that point to the fridge.

I have seen that some vans with compressor fridges and 40A DC/DC chargers run the fridge from the caravan batteries to get over the voltage drop issue as there is enough residual charge capacity from the DC/DC from the car plus solar inputs and the DC/DC is more voltage range tolerant on its input.

Have fun :-)

[OnOz Lurker Find all posts View Profile Close OnOz]

I have a 2021 Prado and have 6b&s from the car battery via a Redarc SBI12 to grey Anderson at tow hitch. Camper lithium pull 600W from car and reading about 11.7V coming in to dcdc on camper from car.
this has created at least two issues:

1) the SBI12 relay clicks in and out very often especially at engine idle when driving resulting in no charge to camper

2) my Redarc tow pro still functions but continues to flash red on/off until the batteries are nearly charged

everything works fine when batteries are nearly charged

can someone please tell me how much power the alternator can output?

I assume that if I connect the SBI12 trigger wire to ignition on then it will make no difference because I assume it still goes open cct at 11.7V

I have no room to run thicker cable, but even if I could, it would reduce voltage drop and increase current more. So I assume it will still draw 600W. Will this risk killing the primary battery by its voltage being low?

thanks all

[Leethal Advanced Member Find all posts View Profile Close Leethal]

Thicker cable will reduce voltage drop and with reduced voltage drop you should get a corresponding reduction in current draw not an increase due to the slightly higher voltage at the DCDC unit. P= V x I so if P (Power) is constant higher V (Voltage) reduces I (current)

What size lithium battery are you running that requires 50 amp charge rate, I know most can accept 50 amp charging but from what I have read you should have a minimum of 250Ah to require a 50 amp charge rate to maximize battery life.

The SBI12 cycling at idle is a result of current draw and the alternator output being low at idle, it should increase markedly above say 1200 rpm when driving, another reason I think to drive in S4.

Lee

[OnOz Lurker Find all posts View Profile Close OnOz]

Thanks Lee. The dcdc outputs to a 200AH 24V lithium with 20A output. I calculated the 12V input side should max around 50-54A.

[gunda Member Find all posts View Profile Close gunda]

2) my Redarc tow pro still functions but continues to flash red on/off until the batteries are nearly charged

https://www.redarc.com.au/tow-pro-el...ing-fault-code

[Leethal Advanced Member Find all posts View Profile Close Leethal]

OnOZ,
Okay a 24V output will effectively double the 12V input draw before any voltage drop is factored in and 20A charge rate for a 200Ah battery is moderate.
Unusual to run a 24V battery in a camper, are all your camper electrics 24V?

Lee

[OnOz Lurker Find all posts View Profile Close OnOz]

Camper is a 24v system. Much more capability. I do have dcdc for 12-24 and 24-12 though