Dual battery set up

[Knucklehead97]

Decided to tinker around with adding a second battery since I have a spare battery tray and an itching to add stuff to my Jeep. Also going to run AC outlets to the bed and one inside the cab with a big inverter (another main reason I'm installing a second battery). My main question is wiring. I found this diagram which seemed simple enough but I wanted to add a momentary switch just to jumpstart the Jeep without using jumper cables. Could I do that just by running a switch between a wire that goes from the aux battery to the solenoid switch terminal? Seemed to make sense to me. Also, where would/have y'all added AC outlets in your Jeep? I want to see everything! I'm also working on finding where I'm going to mount my inverter...

[Jeep Driver]

Leave it at 1+2 for normal operation. 

Switch to desired battery for engine off long play. 

Switch to opposite battery for self recovery. 

Switch back to 1+2 for engine run. 

 

And I'd use 12v plugs front and rear for jumper cables, add jumper cable end to inverter, use inverter at will. 

 

I'd not mount inverter. 

 

https://www.westmarine.com/buy/blue-sea-systems--e-series-compact-battery-switch-off-1-both-2-no-alt-field-disc--3831393?mrkgcl=481&mrkgadid=3202694843&cm_mmc=PS-_-Google-_-GSC%20-%20Product%20Type-_-3831393&product_id=3831393&adpos=1o5&creative=108421552324&device=c&matchtype=&network=g&gclid=CjwKCAjwoMPcBRAWEiwAiAqZh1qJlxP1KVELO8siLsZD-9e7U8h1XQBJa1LHfCiUdrwEtCCIQTvw8hoCNJgQAvD_BwE

[gogmorgo]

Came to post the above. 

It's common practise in marine applications to have multiple batteries with that style switch to run either, both, or neither (I.e battery disconnect). A consideration for this switch is that it doesn't really allow for multiple batteries to do separate things, it just hooks up your electrical system to either battery or both of them, one output, two inputs. You can run a separate system (like your inverter) off the second battery, but it won't charge both batteries at the same time unless you're in the 1+2 setting, and you'd have to manually switch it away from that setting to avoid draining both at once.

 

I have hardwired an inverter into a vehicle, although it was a few years ago now. We used a deep-cycle battery to run the inverter, and used a battery isolator as a more automatic form of the above switch. Effectively what the isolator did is hook up both batteries in parallel so they would both charge when it sensed alternator output, but would prevent one from draining the other with no alternator output (IIRC it did this just by reading the system voltage, so above 13v meant the alt was charging, and below meant it wasn't). I don't remember whether or not the isolator we used would allow cross-powering, but I would imagine you could get them with that functionality, although IIRC the one we had was pretty pricey, so you may be better off just going with the marine-style disconnect switch if budget is a consideration. 

 

The third option that came to mind is an older-type starter "solenoid", basically a massive relay. We've used them at work to hook up trailer battery charging systems, powering heavy-load systems like emergency lights, radios, etc, that you wouldn't want to have running when you weren't charging batteries. I've also seen them used as switched battery disconnects on vehicles as a lazy solution to a mystery battery drain. You would wire the two batteries in parallel, but one wire (generally the positive) would have the solenoid acting as a disconnect, with an ignition-on voltage source for the signal to connect the two. You could also add a toggle switch off either or both batteries to trigger the solenoid to connect them up if you've depleted one, then once you've self-boosted, switch the toggle back off, cause if you leave it on you'll deplete both batteries. The advantage to hooking up that way is that if you don't totally deplete battery 1, when you hit the ignition switch, it'll probably be enough voltage to trigger the relay, so it'll start off battery 2. The big disadvantage is that if you turn the key on to listen to the radio it'll still deplete both batteries, unless you install a toggle switch to disconnect it, and then you'd need to remember to shut the toggle switch back off (on?) to allow battery 2 to charge. 

 

As far as running inverters goes, you're getting pretty high costs for fairly low yield. A 2000W inverter will only run a 15A circuit at 120V. I'll admit you can do a lot of things on that, as it is a regular household outlet's rating, but we discovered after we'd spent over $1000 on the setup (this was a few years ago, I don't know where prices have gone) that the people who asked for it only wanted to be able to plug in the battery chargers for their cordless tools... and we could've just bought them a couple chargers that plug into a cigarette lighter and wired in a couple extra 12v sockets for ~$100, and saved all the hassle of mounting a second battery. 

 

Also, it's tough to use words to describe a circuit diagram...

[DirtyComanche]

I could be wrong, but...

 

If you want to be able to use it to boost the battery without having to do anything but flip a switch, that Blue Sea battery isolator/switch that Jeep Driver posted is probably the best bet.  However, for actual isolation (not killing both batteries by accident) you would need to manually switch it all the time, as there would be no charging on the second battery unless it was in the 2 or 1+2 position.  You could get around this using solenoids/contactors/relays, but they're heavy and clunky and don't necessarily solve the problem as you still need to remember to turn them on or off, or if they're keyed you can have other issues as gogmorgo is saying.  You can also cause some issues by having a stone dead battery and a fresh battery in the same circuit, as they will try to equalize and it can cause damage.

 

I'd propose instead that you could use a 13V zener diode to trigger a solenoid that would provide charging, in conjunction with the Blue Sea switch.  You could leave the switch in the 1 position unless you wanted to start off battery 2, in which case you could switch it to 2 just to start it and then switch it back to 1 once running, however charging would be automatic on battery 2 assuming the alternator output voltage was over 13V as it would then trigger the solenoid to charge it.  You might get some nasty solenoid chatter using this in real life, but you shouldn't assuming your alternator has enough jam and you don't throw a massive charge wire onto battery 2.  Or it just won't work for some reason I don't know, but that's how it goes sometimes.

[Jeep Driver]

The Aussies have figured this out, overland, check out some of their off-road sites. 

There are likely 6 different ways to do this and do it right for a multitude of purposes. 

 

You can use an oil pressure switch to activate a solenoid, engine running- A and B are connected, engine off- B is isolated. Switch on dash completes the same ground circuit to activate B for self-recovery. 

 

I intend to build an overland teardrop trailer for my truck, batteries, charger, inverter, and small generator............all makes dual batteries in the truck pointless. 

 

Switch- if you are doing something to consume power intentionally anyway such as running a wench or other.......turning a switch is not a big deal. 

 

 

Doing it and doing it right is not a 'tinkerers' project. It's going to be expensive. Two decent deep cycle batteries, inverter, cable, solenoid, lugs, switch......ect.......$1500++

 

 

 

Suggestion- get a good high performance alt and high-end deep cycle battery, see XS Power. That alone will set you back a $grand. Get a good marine deep cycle to throw in the back of the truck with inverter and run your $#!& for the day and be done with it.

 

If you want to talk serious recovery power- bank of SuperCaps..........that's another discussion. 

 

 

[Knucklehead97]

I looked into the Marine switch but couldn't find a good place in the cab to mount it because in all honesty Its an eye sore to me and I would hate to have it easily seen in the cab  my main reason for wanting to use a solenoid/isolator was so it was automatic with the possibility of a pushbutton jump start. From what ya'll are saying, though, I think I know how my wiring is going to go. Basically the above diagram with the push button wired how I said. And I'm going to try adding a switch into the solenoids IGN power wire so I can choose to just charge the positive battery to save from the batteries leveling out and possibly causing issues. Probably will add a voltage meter for each battery so I can see the levels in the cab. As far as going to the extreme with this... I don't plan to. I have chosen to run the inverter off of jumper cables when needed, because realistically I won't need it often. I also don't have a winch or anything to require a massive load. When I do use an inverter, it'll only be for a camp stove and other small things so I guess it won't technically be a "big" inverter.

[Jeep Driver]

25 minutes ago, Jeep Driver said:

. 

 

You can use an oil pressure switch to activate a solenoid, engine running- A and B are connected, engine off- B is isolated. Switch on dash completes the same ground circuit to activate B for self-recovery. 

 

 

 

13 minutes ago, Knucklehead97 said:

I looked into the Marine switch but couldn't find a good place in the cab to mount it because in all honesty Its an eye sore to me and I would hate to have it easily seen in the cab  my main reason for wanting to use a solenoid/isolator was so it was automatic with the possibility of a pushbutton jump start. From what ya'll are saying, though, I think I know how my wiring is going to go. Basically the above diagram with the push button wired how I said. And I'm going to try adding a switch into the solenoids IGN power wire so I can choose to just charge the positive battery to save from the batteries leveling out and possibly causing issues. Probably will add a voltage meter for each battery so I can see the levels in the cab. As far as going to the extreme with this... I don't plan to. I have chosen to run the inverter off of jumper cables when needed, because realistically I won't need it often. I also don't have a winch or anything to require a massive load. When I do use an inverter, it'll only be for a camp stove and other small things so I guess it won't technically be a "big" inverter.

Then is is your cheapest route........and most mindless too, IOWs, you won't have to think about it, it will just function. 

 

Just make sure that whatever you want to use with engine off is tied only to battery B. 

[johnj92131]

Think I would be inclined to buy a small inverter generator, instead of a second battery set up

Had a 1 kw Honda for years for camping. Even used it when my main breaker at home failed for several days.

 

Many choices today for 2 kw generators

 

[yxmj]

Nobody asked this yet so.....you got another battery tray.....were where you thinking of putting it?

[Knucklehead97]

1 hour ago, yxmj said:

Nobody asked this yet so.....you got another battery tray.....were where you thinking of putting it?

I'm putting it where the airbox was. I have a cowl intake, forgot to add that into my first post. As far as the oil pressure switch goes, what's the pro's compared to just using an IGN wire connection?

[Dzimm]

To add a "jumper" switch, run a wire from the secondary battery to a switch, then from the switch to the solenoid signal.  

 

Basically do just like the digram but there would be a second signal wire coming from the secondary battery that is switched. 

[yxmj]

11 hours ago, Knucklehead97 said:

I looked into the Marine switch but couldn't find a good place in the cab to mount it because in all honesty Its an eye sore to me and I would hate to have it easily seen in the cab  my main reason for wanting to use a solenoid/isolator was so it was automatic with the possibility of a pushbutton jump start. From what ya'll are saying, though, I think I know how my wiring is going to go. Basically the above diagram with the push button wired how I said. And I'm going to try adding a switch into the solenoids IGN power wire so I can choose to just charge the positive battery to save from the batteries leveling out and possibly causing issues. Probably will add a voltage meter for each battery so I can see the levels in the cab. As far as going to the extreme with this... I don't plan to. I have chosen to run the inverter off of jumper cables when needed, because realistically I won't need it often. I also don't have a winch or anything to require a massive load. When I do use an inverter, it'll only be for a camp stove and other small things so I guess it won't technically be a "big" inverter.

Just re-read this.....so your doing this to run a electric camp stove......?

[bad_idea]

12 hours ago, Knucklehead97 said:

As far as the oil pressure switch goes, what's the pro's compared to just using an IGN wire connection?

 

Let me preface my statement by saying I have ZERO experience with overlanding or multiple battery setups.  BUT, I have an abundance of experience with custom automotive wiring.  So, the oil pressure switch will only energize the circuit when the engine is RUNNING.  The ignition wire will energize the circuit when the key is in the RUN position.  If you were to leave the key in the RUN position to use some accessory that is wired to the ignition circuit, then you could drain both batteries.  Basic example comes to mind - wife cleaning the car and has the radio playing with the key in the run position.  Kills the batteries (both of them), and you are as stuck as you would be if you only had one battery.

[Jeep Driver]

Not to go off in a different direction............

 

I mentioned SuperCaps, there are tons of vids on this, guys are running their cars on these. What interests me is- I wonder if a 12v bank would neutralize or destress an electrical system?

 

 

[yxmj]

To try and  answer to the original question ....This is what i have had in a YJ ......works and will not break you.....

 

...In my crude drawing the "X" box is a simple 3 terminal heavy duty ignition solenoid....basically a switch.....it turns on and compleats the circuit between the two large terminals when a positive voltage is introduced to the small terminal (the unit is bolted to a metal chassis component for ground)

 

Your set up would be this.....stock battery is in its original spot and has  1 additional battery cable installed to the positive terminal and connected to one of the large terminals on the x box ......

 

Your second battery is mounted as you say in the air box space....ALL the extra outputs you want get attached to this battery....you have one battery cable sized lead that is run from the positive terminal to the second large terminal on the x box. Your second battery will need to be ground well. I would suggest running an individual ground to each output no mater were you mount it.

 

The third terminal on the x box is the activation switch......this switch will require 12 volts but minimal current.....

 

So as my poor drawing shows now you are free to have these any cheap and easy options to activate the x box and connect the batteries

you could run it the ignition

you could run it from a toggle

you could run it from a push button momentary.

Or any other.

 

I run mine with a illuminated toggle......so i can visually see when it is connected no mater what state the motor is in.

 

I 

 

 

[Knucklehead97]

On 9/8/2018 at 1:40 PM, yxmj said:

To try and  answer to the original question ....This is what i have had in a YJ ......works and will not break you.....

 

...In my crude drawing the "X" box is a simple 3 terminal heavy duty ignition solenoid....basically a switch.....it turns on and compleats the circuit between the two large terminals when a positive voltage is introduced to the small terminal (the unit is bolted to a metal chassis component for ground)

 

Your set up would be this.....stock battery is in its original spot and has  1 additional battery cable installed to the positive terminal and connected to one of the large terminals on the x box ......

 

Your second battery is mounted as you say in the air box space....ALL the extra outputs you want get attached to this battery....you have one battery cable sized lead that is run from the positive terminal to the second large terminal on the x box. Your second battery will need to be ground well. I would suggest running an individual ground to each output no mater were you mount it.

 

The third terminal on the x box is the activation switch......this switch will require 12 volts but minimal current.....

 

So as my poor drawing shows now you are free to have these any cheap and easy options to activate the x box and connect the batteries

you could run it the ignition

you could run it from a toggle

you could run it from a push button momentary.

Or any other.

 

I run mine with a illuminated toggle......so i can visually see when it is connected no mater what state the motor is in.

 

I 

 

 

Perfect, thanks! That's basically how I thought everything would work, just wanted to make sure before I started wiring. And camp stove was more so an example of what type of current I'm going to need. Doing this isn't going to cost me much because I have an extra brand new battery already, and an extra battery tray. So I realistically see me being able to do this for about 120$ and I figure why not do it if it's gonna be inexpensive.