Dual Battery Isolator

rogue909

New member
So I am installing a deep cycle battery in my 2005 suburban and I'm trying to figure out how to separate it from the starting battery to prevent them from depleting themselves when the vehicle is off (also, I want to use the deep cycle to run things when the truck is off.)

From my understanding, diode based isolators will prevent the batteries from depleting each other but have a voltage drop. This voltage drop stops the batteries from getting a full charge and is a no-no.

They have solenoid based isolators, these combine the batteries in parallel when the vehicle is on but separate them when it is off; they can also be designed as voltage regulated isolators that isolate when starting battery is below a threshold. When operating a deep cycle battery with the vehicle off it can decrease the voltage across the battery (duh) but when the solenoid turns on a surge of power will run from the starting battery to the deep cycle. This can short the batteries and fry electronics (this is also a no-no).

I have seen some solidstate isolators but the ones I have seen have been in excess of $400, this seems like quite a lot considering what I am getting out of it.

What have you guys done for battery isolation and where did you get them? o_O
 

rogue909

New member
I've read that post, unfortunately that solution involves a solenoid that simply connects the batteries in parallel while the vehicle is on. If the aux battery is depleted and the batteries become linked it can cause a drop in voltage which can damage the vehicle's electronics. So I want to avoid going that route. I may read through the thread again, someone is bound to have noticed that problem.
 

UK4X4

Expedition Leader
"If the aux battery is depleted and the batteries become linked it can cause a drop in voltage which can damage the vehicle's electronics"

not sure where you get that from....the physical voltage diference is small....and would not damage anything.

Just like a car with a single flat battery, it does not damage anything , it just does not have to the amps to start the car

solenoid or simple switch works both relatively cheap and suitable for the job
 

unseenone

Explorer
There are two units that I would consider. The Traxide http://www.traxide.com.au/ being in the 400 range, and another one, that is more reasonably priced is the Sidewinder http://www.sidewinder.com.au/page79.html I've been running the traxide for quite a while now with absolutely no issues. I'm planning on installing the sidewinder for the purpose of testing it, but it was highly recommended from a friend who has used them for years.

I installed a National Luna for a friend who had one, it is a solenoid based system. Honestly it was a piece of junk in my opinion, with no craftsmanship involved at all. That's contrary to what I would have expected with their top of the line fridges.
 

rogue909

New member
Voltage drop happens as follows...
This is assuming a solenoid isolator (isolated when vehicle off, when the vehicle is on combines the batteries in parallel.
From my understanding, if you run your aux battery down (fridge, lights, w/e) then start the car, you end up with a surge of current going from the starting battery to the aux battery. This results in the starter losing its charge & ultimately a drop in voltage.
They have voltage sensitive solenoids that will only kick on when the starting battery is at a set voltage (typically 12.9 ish) but then you have a case of the battery charging to 12.9 -> connecting to the aux and discharging -> charging to 12.9 -> connecting to aux... etc. This is bad for the battery - constant discharging and charging (this is what diode styled are supposed to prevent), its also bad for the electronics (dirty power).
 

rogue909

New member
I read through the link that modernbeat had posted and kept flipping through the pages... ultimately on page 28 someone brings up the concern I had.
Basically the voltage drop amounts to nothing because the voltage of a dead battery is still relatively high.
http://www.smartgauge.co.uk/nosurge2.html offers good reading material on this.
 

BigSwede

The Credible Hulk
I would think with the alternator feeding current to both batteries the transfer between batteries would be relatively insignificant.
 

rogue909

New member
I would think with the alternator feeding current to both batteries the transfer between batteries would be relatively insignificant.

Electrician version (what I was worried about)...
If you had a battery at 0v and another battery at 12v hooked up in parallel with an alternator charging them. The voltage across the batteries would immediately drop to right around 6v. Since you're car operates on a 12v system this is no bueno. Also, the wires (unless they were a ridiculous 4/0) would probably become quite hot. With the alternator feeding them, the current from the alternator would be minor and unable to keep up with the draw, you'd be lucky to get 7v.

The readers digest version of the posted article is....
What it comes down to is a definition of a "dead" battery (this is where I made my error).

Real Life automotive version...
Batteries are useless at 11.8v and at that point are considered "dead". Batteries are also charged to 12.7v~ before they are considered "good". Hook up a 12.7v to an 11.8v in parallel with an alternator charging them. Then the voltage drops to 12.4v, which will still work for an automotive system. As for the current flow between the batteries, the current is acceptable and our "stock" wires can handle it. This also doesn't account for the alternator charging the setup or what the writer of the linked article calls the "dead band" for the dead battery.
 

dstock

Explorer
I installed a National Luna for a friend who had one, it is a solenoid based system. Honestly it was a piece of junk in my opinion, with no craftsmanship involved at all. That's contrary to what I would have expected with their top of the line fridges.

Interesting you feel that way, been running the NL system for a couple years with no issues. Not sure about the "craftsmanship" issue but it just plain works.
 

unseenone

Explorer
Well, it just had a lot of mismatched bits, connectors, wrong sized bits, and I was spoiled by a simpler setup. I'm sure it's fine and not trying to beat up on it, or anyone who uses one, it's just not for me. Granted, it was a couple of years old, new in the box, and improvements may have been made by now.
 

Dennx

Adventurer
When I'm ready to do my dual battery setup I plan on getting a Blue Sea ACR 7622 magnetic latching solenoid with automatic charging. It also includes an in cabin switch.

http://www.bluesea.com/products/762...rging_Relay_with_Manual_Control_-_12V_DC_500A

7622.jpg
 

Scott B.

SE Expedition Society
I also run the Blue Sea ACR.

One thing - when I shut the truck off, I manually disconnect the batteries (via the in-cab switch.) When not running (charging) I want the batteries to be isolated. If not, a drain on one will drain the other - all the way to dead.
 

unseenone

Explorer
You can, but it's a bit of a pain. I like the looks of the Blue Sea system, I use Traxide and am in the process of testing another system which seems very nice the sidewinder system from Australia (actually the last 2 systems are from Australia). The primary difference between the last two are about 300 dollars and the sidewinder only connects when the engine is running, but can be overridden.
 
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