All electrical experts - need to connect Second Battery to ACC

[lone]

I'm not sure if it is possible but I would like to use a second (auxiliary battery) battery to power the ACC for inside the vehicle lighting along with using the alternator to charge the second battery and the starter battery by the alternator. I believe I'd need to use a dc-dc charger and possibly a battery selector switch.

If my direction is not a good way to accomplish my goal then suggestions would be great. I've included graphics that may explain better what I'm trying to do.
Thank you,
Lone

 

[tx2sturgis]

Trying to automatically route another battery thru the ACC side of the ignition switch is adding a LOT of complexity: interfacing with the vehicle wiring and ignition harness, probably using relays, diodes, ECM cutoffs, etc. 

You COULD use a manual switch to do this, but the possibility of forgetting to change it over every time you want the ACC function means you will likely end up either with a dead starting battery or trying to start the engine with your house batteries.

Why do you need that particular feature? I'm guessing that you don't....but I'm willing to hear a good argument for it. 

Just run the house loads on the house batteries...and keep the starting battery for starting. A DC-DC charger will keep the house battery in good state of charge while driving.

 

[Scorpion Regent]

Tx2sturgis is right running a secondary power supply with aftermarket wiring through your ignition switch is problematic, at best.  What seems simple in concept is complicated in reality.  It can be done, but it is far more trouble than it's worth.  For powering items from a secondary battery it's better to rig up a parallel system run through it's own master power switch and circuit protection and switches for individual items.  
As to charging your secondary battery you don't need a DC to DC charger you can use the alternator charge the secondary battery.  A battery isolator will do this automatically or you you can have manual control buy wiring your alternator to the secondary battery, in parallel, and controlling it with a constant demand solenoid.  This is switched on to allows the alternator to charge the secondary battery and switched off when it doesn't require charging.   I am only describing how these things can be done in broad strokes.  I need to know more about what you have in mind to go further.
As to which battery to use I'm sure someone else has better answer than I do.  It's kind of like deciding what is the best guitar for you, too many complicated choices.

 

[lone]

Right now if I were to go out and start up the van I would be able to use all interior lighting, stereo, TV, DVD player, Wi-Fi, as provided through Onstar, air conditioner, USB ports, DC to AC plugs for laptops or other 120v devices.

If I were to shut off the van and place the key into ACC I can still use all the exact same devices except of course the air conditioner would not blow out cold. As we know if I were to continue to use all those devices without the motor running, the battery would run down completely.

I have no other additional devices that need to be power outside of what I've described that are built into the van and what the starter battery currently powers.

If it is not possible the way I have described then if I were to use a second battery to power all that stuff, I would need to wire all those built in items, all interior lighting, stereo, TV, DVD player, Wi-Fi, as provided through Onstar, USB ports, DC to AC plugs for laptops or other 120v devices individually to that second battery, correct?

Or is there some other way to wire all those items to the second battery through a fuse box or something? Oh I also came across under a seat a Magnum Dimensions 400W 12VDC Modified Sine Inverter that must be handling the 120 stuff.

Thank you for the input,
lone

 

[ahh_me2]

"lone Wrote: 
Right now if I were to go out and start up the van I would be able to use all interior lighting, stereo, TV, DVD player, Wi-Fi, as provided through Onstar, air conditioner, USB ports, DC to AC plugs for laptops or other 120v devices.

If I were to shut off the van and place the key into ACC I can still use all the exact same devices except of course the air conditioner would not blow out cold. As we know if I were to continue to use all those devices without the motor running, the battery would run down completely."

Based on the info you just posted, I would add a secondary battery in parallel with the starter battery but with a battery switch in between the 2. If you run down the starting battery to where you can't start the vehicle, you switch your auxiliary battery on and use it to basically boost the starter battery.You should probably have the batteries fairly close together if possible because you would want large cables, and it would be a good idea to have a battery isolator between them. I like to use ACR's (automatic charge relay) as opposed to diode based isolaters.

 

[Scorpion Regent]

lone -  I think it best you have a professional auto electrician do your work for you.  From what I have read I gather this is not something you should DIY.

 

[lone]

Yes Scorpion, I have and do consider it and may do so if possible. A big problem for me is finding someone in my area capable of taking care of it but I'm still looking. Until then I'm trying to learn and understand as much as possible on how this stuff works. Thanks for the input.

 

[Scorpion Regent]

Don't get me wrong, you have a good idea, you just have such a limited grasp of how it works.  The fact that you didn't understand that anything you wire up needs to be circuit protected gives me a great deal of pause.  It's super basic rule: any electrical circuit can go bad and circuit breakers and fuses are the only insurance you have against total failure when something shorts.  
The circuits you want to install are pretty complicated.  You really need to know how it works, not just that it does.  This is the sort of thing that if you don't understand what you are doing, things can get damaged that you can't afford to repair or replace.  I don't want to be a buzz kill, just keeping you from getting in over your head.     

You really want to learn?  Let's start with this.  Go do your homework.  
Learn all you can about batteries and alternators.  Learn what deep cycling is.  Learn the difference between starting batteries and deep cycle batteries.  Study circuit protection.  Look on the internet, in libraries, bookstores, & community colleges.   
Understand that this is just barely scraping the surface.  Let me know when you are ready for more.

 

[tx2sturgis]

As to charging your secondary battery you don't need a DC to DC charger you can use the alternator charge the secondary battery.  A battery isolator will do this automatically or you you can have manual control buy wiring your alternator to the secondary battery, in parallel, and controlling it with a constant demand solenoid.  

Actually this will only work well when the house battery is another lead acid battery. Since the OP wants (and shows) a LiFePo4 battery, he does need a Lithium-capable DC-DC charger, one that is rated for the higher charge voltage and cut-off that a LiFePo4 needs. 

Despite the marketing hype about LiFePo4 batteries being 'drop-in' replacements, in practice, this is not exactly correct.

 

[tx2sturgis]

Right now if I were to go out and start up the van I would be able to use all interior lighting, stereo, TV, DVD player, Wi-Fi, as provided through Onstar, air conditioner, USB ports, DC to AC plugs for laptops or other 120v devices.

{snip}

 As we know if I were to continue to use all those devices without the motor running, the battery would run down completely.

{snip}

Or is there some other way to wire all those items to the second battery through a fuse box or something? 

Based on all of this, here is what *I* would do, if it was MY vehicle...and this is what I DID install in my van, back in 2016:

I would add a second lead acid starting battery under the hood. Similar to diesel pickups, adding a second battery, wired parallel with the existing starting battery, will give you extra piece of mind. 

If there is not enough room for a second battery under the hood, you can buy or build an auxiliary frame-mount battery tray. I fabricated my own, but you can buy them online. I did this on my van when I needed extra capacity.





This would effectively double the time you can operate your desired loads on the ACC selection. 

For even more piece of mind, you can use a parallel switch OR you can carry a lithium jump pack OR a simple set of jumper cables to connect your fully charged house battery to your stating batteries in the case of a depleted starting battery pair. OR any combination of these backup plans.

But seriously, if you have managed to run down TWO starting batteries playing with the TV, stereo, Onstar and wifi and such, you probably need to re-assess your power use patterns...and look into another, and more robust, internet solution and entertainment options, which are independent of the ACC selection. 

Sooner or later, you WILL run down your starting battery and that will happen when you least expect it and really really really need the vehicle to start.

I recommend you do not tamper with the vehicle under-dash wiring harness, but adding a second battery is not difficult, with battery brackets and remote battery wiring kits available online.

 

[Weight]

It is common in the marine world to use a house battery bank to power everything except the starter and ignition (the engine management system). Then the alternator can recharge the starter battery. Using the proper DC2DC charger from the starter battery that can handle the LiFePo bank could do it. You can't rely on the alternator to charge the house bank but should have as much solar as you can mount.

 

[Spaceman Spiff]

My 2¢:

 - Get a jump box.  You need an alternate way to start your vehicle if the starter battery can't.
 - Don't modify your vehicle's electrical system unless you know what you are doing; mistakes can get expensive.
 - Determine how many amp-hours you use in a day and how many days between charging your battery(s).

Once you figure out how many amp-hours you will be using we can advise you on how to provide them.
Until you know that you (and we) are just guessing.

 

[lone]

"lone Wrote: 
Right now if I were to go out and start up the van I would be able to use all interior lighting, stereo, TV, DVD player, Wi-Fi, as provided through Onstar, air conditioner, USB ports, DC to AC plugs for laptops or other 120v devices.

If I were to shut off the van and place the key into ACC I can still use all the exact same devices except of course the air conditioner would not blow out cold. As we know if I were to continue to use all those devices without the motor running, the battery would run down completely."

Based on the info you just posted, I would add a secondary battery in parallel with the starter battery but with a battery switch in between the 2. If you run down the starting battery to where you can't start the vehicle, you switch your auxiliary battery on and use it to basically boost the starter battery.You should probably have the batteries fairly close together if possible because you would want large cables, and it would be a good idea to have a battery isolator between them. I like to use ACR's (automatic charge relay) as opposed to diode based isolaters.

Based on all of this, here is what *I* would do, if it was MY vehicle...and this is what I DID install in my van, back in 2016:

I would add a second lead acid starting battery under the hood. Similar to diesel pickups, adding a second battery, wired parallel with the existing starting battery, will give you extra piece of mind. 

If there is not enough room for a second battery under the hood, you can buy or build an auxiliary frame-mount battery tray. I fabricated my own, but you can buy them online. I did this on my van when I needed extra capacity.





This would effectively double the time you can operate your desired loads on the ACC selection. 

For even more piece of mind, you can use a parallel switch OR you can carry a lithium jump pack OR a simple set of jumper cables to connect your fully charged house battery to your stating batteries in the case of a depleted starting battery pair. OR any combination of these backup plans.

But seriously, if you have managed to run down TWO starting batteries playing with the TV, stereo, Onstar and wifi and such, you probably need to re-assess your power use patterns...and look into another, and more robust, internet solution and entertainment options, which are independent of the ACC selection. 

Sooner or later, you WILL run down your starting battery and that will happen when you least expect it and really really really need the vehicle to start.

I recommend you do not tamper with the vehicle under-dash wiring harness, but adding a second battery is not difficult, with battery brackets and remote battery wiring kits available online.


tx2sturgis,
I really like all the info you added tx2sturgis but I need to clarify some things to make sure I am understanding correctly. You say "I would add a second lead acid starting battery", so I take that as meaning to NOT GO with a LiFePO4 Battery, correct?

So I would use a lead acid battery for the second battery and place in parallel with the starter battery. There would be no devices between the 2 batteries so both would simultaneously power what is on the ACC selection but giving me double the amount (or so) of time that the ACC could be used, right?

As for "a parallel switch" could you give me an example/link as to what one is and this is the only thing that would be placed between the starter and second battery?

Also there is not enough room under the hood so I would need some type of "auxiliary frame-mount battery tray" as you indicate, or is it possible to locate the second battery inside the van and build some type of case to mount it in?

"I recommend you do not tamper with the vehicle under-dash wiring harness" no worries on that one cause I sure don't have the kind of knowledge that would allow me to risk screwing something up in there.

Thank you for the help,
lone

 

[lone]

ahh_me2,

You indicate "I would add a secondary battery in parallel with the starter battery but with a battery switch in between the 2", I got it.

On this statement "it would be a good idea to have a battery isolator between them. I like to use ACR's (automatic charge relay)". I'm not exactly sure what a ACR is or looks like but will look it up. Would the ACR be in between the 2 batteries just like the switch? And would the ACR need to be between switch and starter or switch and second battery?

Thanks much for the help,
lone

 

[lone]

It is common in the marine world to use a house battery bank to power everything except the starter and ignition (the engine management system). Then the alternator can recharge the starter battery. Using the proper DC2DC charger from the starter battery that can handle the LiFePo bank could do it.  You can't rely on the alternator to charge the house bank but should have as much solar as you can mount.

Thank you for your input,
lone

 

[lone]

My 2¢:

 - Get a jump box.  You need an alternate way to start your vehicle if the starter battery can't.
 - Don't modify your vehicle's electrical system unless you know what you are doing; mistakes can get expensive.
 - Determine how many amp-hours you use in a day and how many days between charging your battery(s).

Once you figure out how many amp-hours you will be using we can advise you on how to provide them.
Until you know that you (and we) are just guessing.

I'll need to determine how to figure out the amount of amp-hours I'll be using since I'm not sure how to do that. I only know by what I've read that a Lithium 100ah LiFePo appeared to work beyond what I had in mind.

Thank you Spiff,
lone

 

[ahh_me2]

ahh_me2,

You indicate "I would add a secondary battery in parallel with the starter battery but with a battery switch in between the 2", I got it.

On this statement "it would be a good idea to have a battery isolator between them. I like to use ACR's (automatic charge relay)". I'm not exactly sure what a ACR is or looks like but will look it up. Would the ACR be in between the 2 batteries just like the switch? And would the ACR need to be between switch and starter or switch and second battery?

Thanks much for the help,
lone

An ACR is an "automatic charge relay", it is more of a "smart" isolator. There are typically 2 kinds, the standard one and the other one that can combine the batteries for starting.
If you used the standard one, and you ran your starting battery down to where you can't start the vehicle, you would need a battery switch between the 2 batteries to be able to boost your start battery from your Aux battery.
The ACR and Battery switch would be wired in parallel between the 2 batteries.

With the combinable ACR, it can automatically provide a connection from Aux battery to starter battery when needed.
In this case, there is no switch and you have the ACR between the 2 batteries.
Here's a link if you want to read up on it

 

[grandpa pete]

Where are you ? I'm in the ST. PETE FL. area if you need help with Van Wires

 

[lone]

Where are you ? I'm in the ST. PETE FL. area if you need help with Van Wires 

Thanks for the offer but I'm a far piece away out in Texas.

 

[lone]

An ACR is an "automatic charge relay", it is more of a "smart" isolator. There are typically 2 kinds, the standard one and the other one that can combine the batteries for starting.
If you used the standard one, and you ran your starting battery down to where you can't start the vehicle, you would need a battery switch between the 2 batteries to be able to boost your start battery from your Aux battery.
The ACR and Battery switch would be wired in parallel between the 2 batteries.

With the combinable ACR, it can automatically provide a connection from Aux battery to starter battery when needed.
In this case, there is no switch and you have the ACR between the 2 batteries.
Here's a link if you want to read up on it

Thank you very much for the help.