Another auxiliary battery thread!

[Walty87]

Whoooo!

Sorry to be a pain and start a new thread about this topic, but hey it’s keeps things fresh!

Finally going to upgrade my auxiliary battery system.

Im getting a 200ah LiFePO4 battery (still not not 100% on which brand im still doing some final research) and i want to charge it off my alternator like my current setup does. If anyone’s seen my old thread, it’s been suggested that I don’t use my vans current setup to charge a fancy new battery. My current setup is originally a country homes conversion and had an auxiliary battery setup in it when I got the van. It looks really similar to what the Basic Gowesty aux battery kit used to be with a solenoid to charge both aux and the starter battery off the alternator. This old system wouldn’t charge a nice new LiFepO4 battery safely? Like it could damage it because the charge rates would be inconsistent. I’d be better off going with a dc to dc charger?

Anyways, I just want to confirm I’d be buying the right parts and wiring everything correctly.

I also plan to buy a dc to dc charger: https://a.co/d/h83hB0X

My understanding is that I would run a positive wire from the alternator -> dc dc charger then a positive wire from dc to charger to aux battery. Then a negative from dc dc charger to aux battery?

I couldn’t find a good simple diagram of this charging off an alternator.

Or could I simply just remove that solenoid device and replace it with the dc to dc charger? Take the wires off there and swap them to the dc to dc charger? Like positives to postives and negative to negative? But then how would the batteries (aux and starter) be separated? I believe The solenoid separates them? I don’t want to accidentally drain my starter battery


Thanks in advance! Hope y’all have a nice day

[fxr]

Negatives should all go direct via the shortest path to chassis.

Positives: Alternator > DC-DC charger > LiFePo4 battery.

Just discard the solenoid. The DC-DC charger will not discharge your starter battery, as it won't start to take current until the voltage is over 13V - usual threshold is 13.6V. So the engine has to be running, and the starter battery happily charged before the LFP battery takes current.

Now you have to ensure your alternator is up to the task - this depends on what the Dc-Dc charger will try to use from the alternator. That 60A charger you referenced needs at least a 130A alternator. Better perhaps to consider a much smaller current device, unless you want to shell out for a new alternator as well.

Here's a reasonably cheap one that offers solar as well should you want to add it later:

https://www.amazon.com/ECO-WORTHY-Batteries-Multi-Stage-Charging-Alternator/dp/B0BZCXNHDV
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[PDXWesty]

Depending on where you're placing your second battery, a direct lead from the alternator is not absolutely required. If your battery is under the rear seat, then by all means that would be the way to go. My second battery is up front so I just took my power to it from the starting battery. There's already a very large conductor from the alternator to the starter battery, so it can also be used.

Good luck with the project!
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89 Westy 2.1 Auto

[Walty87]

[Walty87]

[Howesight]

I agree with FXR above, although I will be a bit more blunt - - a 60 amp DC-DC charger is WAY too much.

Your LiFePo4 battery will last longer being charged at a lower rate. The battery manufacturer's promotional literature will say it can safely be charged at a high rate, but, unless you are using a Battleborn or equal quality battery, you will get far longer battery life at a lower rate of charge.

I use a Redarc 40 amp DC-DC charger on my home-made 280 A/h LiFePo4 battery and even 40 amps (almost 600 watts) is, often, too much. In the summertime, I run my airconditioning system while driving, which requires the rad fan to run (a 400 watt draw when at maximum fan speed) plus the evaporator fan whose power draw I do not know. I have to shut off the battery's connection to the DC-DC charger (using my i-phone) if I am driving at low engine speeds, as in stop-and-go traffic or else I can hear the Subaru alternator complaining. (At highway speeds, the alternator is spinning fast enough that the strain on my alternator is far less).

If I had to do it all over again, then to avoid this, I would either upgrade my alternator, or go with a 30 amp DC-DC charger. Or . . . I could sweat without using my air conditioning. (Like that's going to happen!)

In terms of how to wire your DC-DC charger, you will likely find that the manufacturer's recommendations are the best approach. The Redarc uses the wiring connections (there are several ways to connect them) to indicate to its logic what type of battery is being used. Some DC-DC units use dip switches for that task. Hopefully, whatever unit you choose will have clear instructions.
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'86 Syncro Westy SVX

[fxr]

[OlisGarage]

Fxr,
Do you have the Renogy 50a dual charger thing?

If so, how dark does it have to be outside so that the device allows the alternator to give the full 50A?

Also, how is your alternator holding up? Is it able to give 50A at idle? I have a 120A alternator on my tdi.

If this is too much of a thread highjack, I’m sorry. I’m more than happy to start a new thread. Feedback on all fronts welcome
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1981 VW Vangagon TDI (in progress)
1984 VW Rabbit Convertible (daily)
2003 VW Jetta Wagon TDI (recovering from a hit and run)

[fxr]

[Chilepines]

I have a 300Ah LiFePO4 battery and 30A DC-DC charger, no solar. I barely used 30Ah per day running a 12 V fridge and everything else (lights, radio, etc.). So I can recharge a days battery use in 1 hr of driving, and can go many days without charging if needed.
My charger under the driver seat is connected to the starter battery. The battery is in the rear closet and my breaker and fuse panel is in the hidden space next to the water tank.
IMHO this is a great setup!
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White 89 Westy with 2004 Subaru EJ25 - Betty