Dual battery option?

[GORM]

I'm going to build a dual battery system using the 120A blue sea "add a battery kit". It seems good way to go, simple. I have a question about the wiring however. The entire HOUSE side of the project is straight forward. However, I am wondering if I need to do the STARTER battery in that way which leads me to my question.

So rather than remove the red positive battery terminal side and strip off the connectors to meet the diagram, can't I simple run the 2 sides of the switch terminals back to the positive lead? It would see that the starter battery WILL NEVER BE ISOLATED from the engine when I do this. I cannot think of why it matters if the starter battery gets isolated. While my switch has 3 choices (I think) in doing as I propose, I will simply have 2 choices as the starter will always be linked to the engine, the house will be isolated unless I combine them (like if my starter is dead) and in that case it does not matter. The only thing I will not be able to do is use my house battery to start the vehicle on its own ... Who cares, when will I need that exact setup?

Please damage control my logic here. Land rovers are already finicky and I figure no reason not to undo what is already hooked up and simply add in the ability to add an isolated second battery which will be a deep cycle battery anyway.

Thanks in advance ....

 

[DiploStrat]

An Opinion

The "Add a Battery" product is really designed for outboard motor boats. The advantages of combining a manual switch AND and ACR escape me.

For a camper, you really don't need the big manual switch. Simply buy the Blue Sea ACR of your choice, either the 120A rated model or the 500A rated model which has the advantage of a really useful remote switch. I prefer this one: https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A If your alternator is less than 120A you could save money and use this one, but you would lose the remote switch. https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

To your question, the cable to your house/camper battery simply attaches to the positive terminal of your starter battery. I like the Blue Sea terminal fuse block (https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A) because it is so easy to install and gets your fuse as close as you can get to the power source.

 

[GORM]

First off, thanks for quick repsonse. I think we are in same page. I want the automatic part of the system to charge the HOUSE battery after staring (and voltage on STARTER meets certain level) and leaves that batteries isolated. In reality, the starter will always be hooked to the alternator. I should never need to touch the switch unless my starter battery has an issue. If that occurs, I open the hood the flip the switch, then start-up using the power from both batteries. Then, I can flip switch and re-isolate and then what should happen is that the alternator will charge the STARTER battery until is is fully charged, then automatically hit the HOUSE one.

My point being I never need to isolate the STARTER battery from the system so I can a void untiring what is there already. On a boat, one might want to work out both batteries, but on land this level of redundancy is just not needed in most applications especially when you have a backup battery that can be used to start the vehicle.

Thanks

 

[DiploStrat]

As a practical matter, you can do that with the remote switch that comes with the 500A model.

Unless Verkstad can come up with a really good reason for that switch, go with a dash switch - so much easier to wire and more useful.

N.B. With most modern trucks, isolating the starter battery would probably give the computer fits and it might well refuse to run.

 

[GORM]

Let me try a different approach ...

I had started with a review of this system:
https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A (same one DiploStrat noted).
I thought to add the switch so I had a emergency backup by combining them to start the vehicle but maybe that is not required.

So if I just get the ACR, how do I jump the main battery if there is a battery problem with the starter.

Maybe that will help ...

 

[DiploStrat]

Not "Cheap" - Just Saving Money!

Some points to consider:

-- A good dual battery system, with an intelligent relay and charge sources (solar/shore) on the camper battery actually keeps the starter battery in better health than a system that simply isolates them when the engine is not running. (Assuming grossly similar, lead acid batteries.) Thus the need to jump the truck from the camper battery is reduced. This eliminates the need for products like the AMP-L-START. (http://www.lslproducts.net/ALS_Overview_Page.html)

-- Should you ever need to do it, and you don't have an override switch, the two terminals are, as noted, only inches apart. You can easily use a jumper cable, or, assuming a service loop in the wiring, you can unbolt one wire and contact it directly to the other side. All of this argues against the need for the cost/effort of a manual override switch on a typical overland camper. (I don't have one, nor have I ever had need of one in two years of heavy use.

 

[GORM]

2 items, I think I'm good and see no reason to get anything other than ACR.

1) this is in a vehicle, no camper. Batteries will be 3 ft apart
2) if there is no danger using jumper cables between batteries in the same vehicle elvtrical system then that was a key piece of learning I did not have - I thought something special had to be due to protect the system.

Thanks

 

[DiploStrat]

Jumping two batteries under the hood is easy. (Don't ask about WHY I had to do this. Let us just say I have learned a thing or three about dual battery systems over the years.)

A general rule for modern vehicles is that you never want to get between the alternator/regulator and the starter battery. Connecting to the starter battery - making it "look" like simply a larger battery to the vehicle is generally fine. As with everything, there MAY be exceptions to this. (I don't do this for a living.)

One big rule is that the camper battery must have a charge profile that is grossly similar to that of your starter battery, voltage being the biggest issue. If not, then you may be in the market for something like the CTEK SmartPass/D250S combo. (More money, more space, and less amperage than an intelligent relay, but does include an MPPT solar controller in the price.)

 

[GORM]

So I've got supplies inbound for my dual battery/ blue sea acr and I must install the optional SI circuit to ensure batteries are isolated during starting. Here's the instructions given:

Connect a wire from the quick connect terminal marked SI (starting isolation) to the terminal or wire running from the start key switch to the starter solenoid. Make this connection through an in-line fuse of 1 to 10 Amps. This connection can be made at the start key switch or at the starter solenoid, but must be to the line that is positive only when cranking. Connection to a line that is positive while the engine is normally running will prevent the charging relay from working properly.

So:
1) can I use a fuse tap on the starting fuse or tie directly to starter or another circuit?
2) what are the downsides to not isolating the batteries a startup?

What seemed at first to be simple is getting more complex as I approach project time.

Thanks in advance for the help.

 

[GORM]

So I thought I'd share what I learned talking to the tech at Blue Sea Systems. The tech suggested that there are very few situations in which NOT HAVING START ISOLATION would even be a factor and basically indicated he'd not think twice about setting it up without it. If the STARTING battery has not fallen off the peak charge where the combine function is off (13.6v for 30 sec or 2 min at 13.0V) then there could be situations in which BOTH batteries could be used to start the vehicle. He stated that given the alternator will call from the starting battery because it is first line and follow the path of least resistance so not likely a factor. Both batteries are protected with 100A fuses and the peak rating of the ACR is 210A so it is possible that the ACR (which is warrantied lifetime) blows if is exceed it's rating.

The only thing he could come up with was a peak starting battery getting combined with a weakened AUX battery and the resulting impact on the electrical system not knowing what to do with that possible voltage drop from the second in line battery. Again, starting battery would be getting amp call anyway.

Thanks for the help ... LR3's have touchy computers so I want to be wary of doing anything that can affect that!

 

[Ducky's Dad]

A toggled solenoid isolator is a much simpler and probably more reliable solution. You are in full control, no ACR to rely upon.

 

[dstock]

A toggled solenoid isolator is a much simpler and probably more reliable solution. You are in full control, no ACR to rely upon.

The ACR has a remote switch as well, you can control it manually if you like. I don't know how much simpler it needs to be, AUTO, Combined, Separated.

 

[Ducky's Dad]

Quote Originally Posted by Ducky's Dad View Post
A toggled solenoid isolator is a much simpler and probably more reliable solution. You are in full control, no ACR to rely upon.
The ACR has a remote switch as well, you can control it manually if you like. I don't know how much simpler it needs to be, AUTO, Combined, Separated.

There are no electronics in a toggled solenoid. It's all electro-mechanical so less to fail, and it's a lot cheaper than an ACR. A Blue Sea rotary switch is even simpler and more reliable, but requires some pretty fat cables in my setup. I don't really need or want anything that's automatic on my truck, but that's just me.

 

[dstock]

There are no electronics in a toggled solenoid. It's all electro-mechanical so less to fail, and it's a lot cheaper than an ACR. A Blue Sea rotary switch is even simpler and more reliable, but requires some pretty fat cables in my setup. I don't really need or want anything that's automatic on my truck, but that's just me.

I agree, that is just you :sombrero:

The Blue Sea ACR 7622 has a mechanical switch under the hood in case there is any "electronics" issue. I would also argue that automatic takes out the ever present "human error" factor out. While expensive doesn't guarantee reliability, neither does being cheap.

 

[dstock]

Some versions of BlueSea ACR dont have a manual combine function. If thats important to somebody, they need to know.

Good point, thanks.