Dual Battery Setups! Let's see them! Multiple Batteries Thread!

The purpose of a dc-to-dc charger makes sense to me only because I noticed that the voltage in my 2016 Tacoma is at 13.8 based on the information I read a AGM battery for proper charge needs to be 14.8 with that said I believe the new Tacomas have Smart alternators I was just seeking a second opinion for all those that have dual Battery Systems specialty members with a 2016 Tacoma. I personally is planning to put a 100 watt flexible solar panel on the top of my roof to maintain the battery and to offset the withdrawal from the refrigerator.

 

If your charging system is going down to 13.8V then you are correct Toyota may have implemented a smart alternator.

AGM is charged like a wet cell lead-acid. You notice the 3 primary stages and the voltage and current at each. he bulk-to-absorption voltage is 14.7V typically for AGM and 14.6V for flooded types, but that's not hyper critical.



This is the profile for an Odyssey AGM. I wouldn't get too wrapped around the axle on the exact voltage and current. Unless you design your own charger it's unlikely you will match them 100%. You can only do your best.



You will have to do some experimentation or research to know how it's working and what you'll have to do for dual batteries. Your charging system is still doing a higher voltage at some point to charge the starting battery. With a smart alternator it may do something higher than the traditional ~14.4V like dumb alternators. It might actually be fine to just parallel the two batteries.

You'll have to see how the charging system reacts to a DC-to-DC converter, since it will need to still be generating sufficient power for it to work. Even with a DC-to-DC your aux battery may not recharge if the current is too low. Remember that voltage and current are related by power. If the smart alternator has dropped its voltage that means it's also probably generating less current (less power overall).

If you boost the voltage the power in must remain the same as power out, so current goes down proportionally (13.8V x 10A is 138 watts and will be 14.8V x 9.3A 138 watts out). When you do this the charging system may react and go back up. You'll want this to happen because during bulk particularly the current needs to be high enough not to starve the battery.

In any case the converter will probably help smooth the charging on the aux battery so that it doesn't see the ups and downs.

 

I'm not so sure if it's just the alternator. I have an upgraded 250A High Output alternator and the highest I've seen my battery charge up to is ~14.4. I only drive my truck on trips, so it sits for long periods of time, but I also have a solar panel hooked up to my aux battery, but the Blue Sea ML-ACR senses the charge and connects the two batteries so they both are charging.

 

That's working correctly. A dumb alternator always runs at ~14.4V.

 

I think that's the ideal setup. Alt+Solar and a dual sensing ACR!

 

Question for those of you using the Blue Sea setup. Drove the truck for about 8 hours last Sat. The Ml-ACR latched and unlatched the way it's supposed to do. However when I got hone Sat evening, it stayed latched, and it's still latched. This is unusual for me. Normally unlatches overnight, or by noon next day. Starting battery maybe a little weak. Both batteries reading about 12.3 V.
Any ideas?
Could the ML-ACR unit be bad?

 

I've had mine stay latched overnight and up to a day but the battery voltage is still high and usually it snaps when I unlock the doors or something like that, just enough to dip the main battery.

If the batteries are reading 12.3V then something's not right. I've had mine get confused and not close. In my installation I just grounded the ACR, don't have the switch hooked up yet. So I don't have the overrides. The box doesn't actually need the switch, just needs to be grounded for the logic to work.

It seemed to not like that I manually latched the batteries using the big button. Pulling the ground wire seemed to reset it and return to normal operation.

Long way of saying you might try switching if you have the switch or just pulling the ground before you assume it's failed.

 

I'll try turning off the unit and the switch. Normally I'll turn on my light bar or headlights and it will unlatch. Something's not right.

 

If you checked both batteries with the ACR latched then both batteries will read the same voltage. You must unlatch the ACR to read the battery voltage seperate.

 

Right, I'll check them with it unlatched. I just went out and turned off the red switch, and the ML-ACR unlatched. I'm going to leave it off until the weekend when I get more time. Thanks.

 

Mine is not a DD but I do drive it on the weekends. Typically mine stays latched for several days before the voltage difference between the 2 batteries is large enough for the ML-ACR to sense it and unlatch them.

I do agree tho, 12.3 volts is a bit low for a healthy battery.

 

Any ideas as to a cause of the problem? I got nothing.

 

No, but separating them manually is where I would start to see if one battery was draining the other one. I suppose this could be an ML-ACR issue but it would surprise me if it were. It is such a simple device.

What type of batteries are you running, AGM or 'wet' lead/acid? Are they the same age and brand and size?

 

Optima Yellowtops Type 27 starting batt 5 months older​

 

Are you doing a maintenance charge on them? I think that is helping to keep my AGM types healthy and to hold a charge better.

We had a good discussion of that a few pages back. This post started the discussion:

https://www.tacomaworld.com/threads...-batterys-thread.295653/page-71#post-13840209

 

Below is pic of my air duct re-route. Hose is a Sprectre #9751 and a bit pricey at $33. But it is good quality that should last the rest of the truck's life. I'm using a group 34 battery and did not have to re-route any other components. Only possible issue is going to be when I smog the truck next year. I saved the OEM hose just in case.

 

thanks, looks good!

 

@Taco_life tons and tons of information in here.

 

What does your engine bay look like? (I can't keep up with the diff years and models and what's in each engine bay)

I only ask because my "mount" was just something I did homemade and it was prob less than $15 total - and that includes the tie down from vatozone

 

With a little modding with mending plates, you should be able to fit a Wirthco tray in there somewhere. The 21085 ($14) for groups 24/34, or 21087 ($20) for groups 27/31 batteries.