Dual battery questions

From my understanding, the 2nd gen Tacoma’s have voltage sensitive alternators. By adding a dual battery the second one being a deep cycle, you would need a dc to dc charger to effectively charge both batteries. Because a vsr won’t read second battery voltage and only charge starting battery for what it needs and barely charge the second battery. Here’s my question, could you run a vsr and then hook the Alternator voltage sensor wire to your secondary battery? That way it will always isolate your primary but then when you start up your taco it will send high Voltage through your primary and charge up your secondary. I believe this is possible and the only concern I have is that I might over charge my primary and this will shorten the life of it. But for a cheap and efficient system, I believe this will work. Please give me some feed back and tell me what you think.

 

Also I’m not sure if the Voltage sensor wire from the alternator is the same as the actual charging wire. And my other concern is if my secondary is full charge and my primary gets low from starting the taco and not using the secondary battery.

 

I think an in-board DC-DC charger is the best solution.

Once you parallel the batteries for charging it won't matter which battery you have the VSR wire connected to because the voltage will be the same. If you kept the batteries not paralleled but somehow charged the start battery then you would want to sense from the start battery. Then switched to charging the deep cycle battery and sensed it. You'd probably want to charge the start battery first and then the deep cycle so you'd be recovered from the start and ready to start the truck if you had multiple short trips. I'm not sure how you would automate this and switching between charging the start battery and then charging the deep cycle and switching the sense would be a pain to wire. I don't recommend you go that route.

Keep in mind the alternator, regardless of what it's sensing, is not designed to charge a deep cycle that's been deeply discharged. It's designed to top off the start battery. If you use the alternator to charge the deep cycle by paralleling them after starting the truck (using any one of the smart or manual isolators) I recommend you put the deep cycle on an AC charger once your home after doing any deep discharges. That is probably the best way to preserved the life of the deep cycle battery. A lot of things will "work" but not a lot of things are ideal for the deep cycle battery and may or may not reduce its life.

I went with an on-board DC-DC charger (C-Tek) figuring all the money I spent on the AGM would be worth preserving the AGM battery's life as long as I could.

https://www.tacomaworld.com/threads/2nd-gen-dual-battery-with-on-board-charger.636037/

 

Agree with @seafur above. DC - DC is the right answer. I have the same ctek charger and it does 5 stages to help maintain battery life and get the most out of a SLA or AGM. Pricey, but what isn't in this hobby? I have mine setup as a modular approach so I can move around from vehicle to vehicle easily.sure makes things nice and easy when I want to run my 12v fridge in the 4Runner, then move the battery to my Truck, then put it on a picnic table to charge phones.

 

@fajitas21 where do you mount your charger and battery when it's in the Taco? Seeing your approach for securing the heavy battery temporarily might help others. Pics?

 

Because it's modular I set it up to be removable. It's not mounted anywhere, it's using Anderson connects and an 8AWG wire to quick disconnect and move. The battery lives in a NOCO box in the cab or in the bed.

 

I got it, you can run just a vsr in a dual battery system and keep the voltage sensor wire connected to the starter battery. Because once the alt kicks on vsr will open back up. 2 battery connected in parallel will automatically try to balance each other out which mean your start battery will drop to the average and that will kick on the alt and charge up both batteries. Example start batt: 12.8 acc batt at 9.6v then turn on taco, alt puts out 13v (lets say) that opens vsr and links the batteries. When 2 batteries in parallel are linked they try to balance out voltage and do so within 10 minutes so now the alt is reading 11.2V and will ramp up the output and charge both batteries. I tested this on a buddy truck and seems to work great, probably not the greatest for the deep cycle but is definitely a great set up. Especially if You’re running a constant solar charge on the deep cycle with minimal draw.

 

I'm interested in this type of setup as well. Do you have any picture you could throw up?

 

same here...

 

@fajitas21 Dude, the masses want pics!

 

Here's a somewhat helpful video I made a long time ago.

https://www.youtube.com/watch?v=LDZ84tkcnaE&list=PLFmSPVJcgeY1GLNuzCzqJYdtCln7H7Tk0&index=2&t=0s

I'll be happy to discuss in more detail, I can also go take a follow up video if needed to address specific stuff.

SOrry for terrible video editing, maybe I thought I'd start an overlanding channel and make a billion dollars, I don't know what I was thinking when I made this.