Dual battery in-cabin and Solar setup

[moose545]

Dual battery Plans in the works, few questions and sorry for the long-winded post.
I plan to build a battery box enclosure that will rest behind the future Goose Gear drawers. I've still got a few questions prior to attacking the building part, such as:

2-AWG or 4-AWG run from primary battery to the AUX battery? I think 4-AWG is sufficient and a 15' kit will work
(- will run through a 40A breaker, + through a 40A to a RedArc 1225BCDC) Not sure the Redarc will take a 4AWG wire though?

3/8" or 1/2" plywood to build the box? I ended up going 3/4" for extra area to screw things together

The enclosure will house a few gauges in the upper part such as voltmeter, USBs, etc, along with the battery secured internally. Externally the entire box will be screwed to the GG base plate.
Initial plan is to run another X2Power 27F, which is roughly 100 Ah, but should you run more to run a fridge, lights, and room to grow in the future such as a water tank/pump and whatever else I haven't thought of yet that will pop up? Battery options are here, and while the monster one has less of a warranty than the 27F, it's still much cheaper than a lithium option from Victron. I think the 27F is fully sealed and ok for use in the cabin, but not 100%, of course the more expensive one states that clearly on the website linked.
Examples:
https://www.batteriesplus.com/productdetails/sli27fagmdp
https://www.batteriesplus.com/productdetails/sli8dagmdp

I plan to run 100-200W folding portable panels but haven't decided on which ones, they will go to the RedArc, and monitored with a Victron unit. Seeing how the battery isn't forever, the box design needs to be serviceable. Should/can I hook up say a 50/100A Anderson plug to the battery, through a grommet in the enclosure, and have an easy plug in/swap option there, or hardwired only? Still drawing up the diagram, neatly

I found a cool program called SmartDraw that's free for 7 days and gives you CAD-like abilities with preloaded symbols for components and circuitry that is pretty slick, posted what I've got so far below, still a few questions:

Here is what I’ve got so far, where would a switch panel go? Also keep in mind all “G” gauges will be powered to the Safety Hub. I haven’t decided on what solar panel yet. Also want to use the second battery as a starter for backup if I can, so I’m not sure how to run 4AWG into the Redarc, or if it’ll accept that gauge wire? I was trying to use a 50A Anderson plug to the rear battery but it’s not a direct run, so that’s out for now. Thoughts?

 

[Martinjmpr]

If I understand correctly you are connecting the battery to a REDARC 25A DC-DC charger? I don't think you would need anywhere near 4AWG for that. I'm going to be installing something similar with a Renogy 20A charger and I plan on using 8AWG.

I used this on-line calculator:

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

According to that, a 30A load can run up to 14.65' on 8AWG wiring which is going to be a lot easier to work with than 4 with only a 2% drop.

Also why are you putting a 40A fuse on it if the charger is only rated to 25A? Wouldn't a 30A fuse be better?

 

[moose545]

Honestly speaking I was using this as a guide, but I don't think I need the 40A breaker between the MAIN and AUX on the - side. Yes a 30A would be more logical, I'm not real familiar or projects like this so I'm not sure I can give you answer besides I saw it and it gave me a guideline I went with.

 

[rayra]

why is there a breaker on the negative / ground cables in that setup?

Having the redarc AND the victron is redundant and expensive. A simple $50 solenoid / combiner which connects both of your batteries the to high capacity charging device your vehicle already has is a much simpler and far more affordable solution. Every fancy expensive control device you add is a new potential point of failure. Besides being a reduction in the beer budget.

 

[moose545]

why is there a breaker on the negative / ground cables in that setup?

Having the redarc AND the victron is redundant and expensive. A simple $50 solenoid / combiner which connects both of your batteries the to high capacity charging device your vehicle already has is a much simpler and far more affordable solution. Every fancy expensive control device you add is a new potential point of failure. Besides being a reduction in the beer budget.

Again not sure on the breaker on the negative side, just what I saw but I think it’s unnecessary after hearing that as a general consensus a few places. I see your point on both devices; but the Redarc gives me a visual readout on the unit while the Victron will allow me to monitor via Bluetooth and log history to learn what’s happening more and understand my consumption better ideally. I’m new at this, so all the help I can get is welcomed. Explain how you would do it, what would you do differently? As for wire gauge, like hooking to solar etc to the Redarc for instance, would you just match wire gauge to the lead wire from the unit? Where/how would you hook up a switch panel running off the AUX battery?

 

[rayra]

My setup was a takeoff from the simple '$50' setup, there's a huge topic in this subforum that describes several more simple setups. Most utilizing an inexpensive solenoid as an automatic combiner / separator in a multi-battery system which uses the vehicle's factory charging system to top things up and when the key is off the factory battery is separated from what is in essence the 'house' side of things.
My own setup is a bit more complicated, I wanted a lot of functional options for other purposes, so that affected my layout. But the upshot is I have 200A 12VDC service to both bumpers to power a carrier-mounted winch from either end of the vehicle; dual identical SLA batteries so that the 'Aux' can be substituted for the Starter battery if the latter fails on (or off) the road; the main power run to the rear also feeds a 'power module' that has several bulkhead-type sockets and inverters. 12v cig, USB, APP 15A, voltmeter(s), and a 1000W 115VAC inverter; I also added a folding solar panel in a locking roof rack which allows the panel to be readily removed and set on the ground far from the vehicle, that panel feeds a Renogy PWC in that back box which is backfeeding my Aux / everything on that side of the $35 solenoid.
THere's a bunch of other convenience electrical mods. Most of it is described in my build topic. One of these days I'll properly diagram and describe it all in once place.

My setup while slightly complex is technologically simple and has a lot of power use options. It doesn't have the sechsy monitoring tech, but it does have the benefit that it has a lot of options and redundancy and pretty much all of it was accomplished for less than the price of that Redarc. But that doesn't help you much after that more costly hardware is bought.

The biggest benefit IMAO is the larger available charge rate via the vehicle's inate alternator / regulator, via the inexpensive solenoid and that setup removes the human element. But mostly it leaves the starter battery out of the system, rather than using it as a source for a DC-DC charger. That the DC-DC charger is drawing down the starter battery is my principal problem with that 'solution'. But if you've bought the hardware it's a little late to say you shouldn't use it.

Maybe I'm not fully grasping the wonders of a DC-DC charger. To me they seem to be a low-power (20A?) charger. Compared to the 100-150A potential of a vehicle's built in charging system, it doesn't make sense to me to put it between that larger charging source and ANY battery. To me it seems like paying a premium for a device that is greatly restricting the recharge rate that's available from the vehicle and with the added negative that it is drawing down your primary battery to do its job.
Then too, if you have solar and a solar charge controller (either PWM or MPPT) ,you dont need the DC-DC charger to effectively charge the battery. This is why I spoke of redundancy.
Does the redarc have any voltage sensing to ensure it does not draw down your starter battery too far? And if it does, will that sensing circuit be confused or thrown off by having solar input on that same circuit? If so I would think there's a potential in a high camping use scenario for the DC-DC to keep trying to draw from your starter battery to feed your Aux (and your human use demands) and the DC-DC seeing high voltage due to the solar input, while continuing to draw down on the Starter well past where it should. But surely they've designed something to prevent that?

Were it me, I'd be shielding / isolating the starter battery from any 'house' draws and that sort of obviates a DC-DC solution altogether, as I understand things.
And in your wiring diagram example in particular, I'd be adding a solenoid interrupted primary charging line direct to your additional battery so that it gets charged by the alternator when the vehicle is running. And make that solenoid and line phat enough to take full advantage of the alternator's available power. 100A rated at least.

My system is 'overkill' for glamping purposes, as I was chasing the desire to support the heavier draw of a large capacity winch. So I chose 200A as a baseline. Upgraded to a high output alternator, replaced its charge lead with a 1/0 cable, ran the power lead from that charging junction as a 1/0, to the 200A-rated solenoid and on to my Aux battery. And again 1/0 to my rear cargo area and finally just this past month to completion with bumper and front grill Anderson SB175 plugs. Got two different rotary cutoff switches in the circuit for those plugs, one rated 275A-continuous, the other 300A-continuous. So with the key on, engine running I've got 200A continuous for as long as any winch can stand it. With both batteries to draw on and without hardly running them down at all when I'm done with the pull(s).
The byproduct - which was the primary product for the first couple years - and STILL as I still don't have the winch itself - is that I've got an electrical system that can support just about any camping need in peak draw. But is a little shy in depth of storage capacity. But I've added and will be expanding rooftop solar capacity. That too is another 'option' I've been pursuing and expanding, for its own purpose, but it serves to supplement my Aux / House capacity in a camping situation. I get about 5A that way and hope to double that by adding a second fixed panel to my roof mount.
And I've still got room in my rear power box to add an additional ~40Ah of battery storage, which would also be charged by the alternator but would have to be isolated from any deep discharge experienced by the other pair of matched batteries. I would likely segregate those additional batts to be the power source for all the rear power box outlets / connections, sans the 1000W inverter. Have a solenoid or diode preventing their discharge back down the main cable / charging input. And re-arranging the module power sourcing to likewise isolate that fuse panel from the main power and feed if from the ~40Ah setup in the box. Leave the big inverter on the main feed.
I could even likewise use a diode on the PWM output and have it feed both the Aux battery and the ~40Ah setup, without being a cross-connection between the two.

I guess what it comes down to is that the solenoid solution sort of spawns from the high output competition car sound system sector and stuff like the DC-DC, MPPT etc spawn from the off-grid solar sector. And that they are different schools of thought.
Then there's the third school, RVs and boating, which seem to have a better overall grasp of separation and integration when it comes to 'vehicle' v 'house' power setups. And better protection of battery assets on both sides.

And I'm having trouble seeing how DC-DC charging suits any of it. It seems to be working at cross-purposes. Or so solely focused on one aspect that it violates other precepts. But I readily confess to not knowing enough about such devices. Just noticed that suddenly they seem very popular / 'go to' and I'm left wondering why, because they seem to be totally reducing the available recharging capacity for an Aux battery, in the way the devices are implemented..

 

[rayra]

case in point, another gent that just started a DC-DC topic and again his diagram shows it between the Starter battery and the additional battery, 25A, which means all that greater available power of the vehicle charger system is blocked from the additional battery -

DC-DC charger setup question

Currently working on installing a second battery and DC-DC charger in my Discovery 2. My requirements are that I do not lose offroad capability, and that I have a 1000W inverter mounted in the boot. I also do not want to loose any boot space, so the new battery will go instead of the compressor...

www.expeditionportal.com

IMAO a terrible setup on a vehicle system when a much higher rate of charge is built right into the vehicle already. People are paying a premium for a DC-DC charger to reduce the rate of charge available to their 'house' system.

 

[rustypayne]

How much are you powering in your vehicle that you need 100 amps of charge into the house battery while running down the road? My CTEK DC-DC is smart, it only works when the start battery is fully charged and the vehicle is running, when I park in one spot it's charging off solar. That's been more than enough the past two years here in cloudy Michigan. Even at 20 amps if I draw my 100ah AGM down 50% it should only take 2 1/2 hours of charging to be near 100% right? **I AM NOT an electrical expert so I could be all wet, but I'm a die hard DIY'r and try to educate myself on anything that might kill me or set something on fire!

 

[rustypayne]

the quick answer is no. It will take considerably longer.
Lead/acid batteries accept less and less current as their state of charge increases. To get from 50% to 100% can take several hours.
Nevermind how much current is available at proper voltage, the battery just wont accept all of it.

So pushing 100 amps rather than 20A it is only going to be marginally quicker to go from 50% to 100% for the same reason?

 

[Hopeless Diamond]

Don't forget there will be loads in addition to charging that would have to be satisfied with the 20 amps thereby reducing the available charging current

Sent from my SM-G975U using Tapatalk

 

[rustypayne]

Don't forget there will be loads in addition to charging that would have to be satisfied with the 20 amps thereby reducing the available charging current

Sent from my SM-G975U using Tapatalk

Well I've personally travelled 42 days straight without shore power and my 12v fridge was running the whole time so real-world experience tells me that the DC-DC setup works just fine.

 

[john61ct]

So pushing 100 amps rather than 20A it is only going to be marginally quicker to go from 50% to 100% for the same reason?

Takes at least 6hours to get lead to truly Full, even if at 80% in the first 2-3, no matter how many amps made available.

But good news is, longevity only requires 3-4 times a week ("most cycles")

or even once a week won't kill it too fast

just budget to replace the bank a bit more frequently

 

[rayra]

How much are you powering in your vehicle that you need 100 amps of charge into the house battery while running down the road? My CTEK DC-DC is smart, it only works when the start battery is fully charged and the vehicle is running, when I park in one spot it's charging off solar. That's been more than enough the past two years here in cloudy Michigan. Even at 20 amps if I draw my 100ah AGM down 50% it should only take 2 1/2 hours of charging to be near 100% right? **I AM NOT an electrical expert so I could be all wet, but I'm a die hard DIY'r and try to educate myself on anything that might kill me or set something on fire!

Well for myself, I often run some handheld power tools off the 1000W inverter in the back, off the Aux battery. I also have plans to connect a towed camper trailer to this power setup. And I have future plans converting a toy hauler camper trailer into a mobile woodworking / carpentry shop, so this setup is a proof of concept for me. As well as the 12k winch setup I've long hand in mind. So I figured 'go big' and be able to power anything I care to try. Except those $1000 ARB fridges, I doubt I'll ever go for that extravagance.

 

[rayra]

Don't forget there will be loads in addition to charging that would have to be satisfied with the 20 amps thereby reducing the available charging current

Sent from my SM-G975U using Tapatalk

iPads, iPhones, camera battery charger, playing a DVD in the dash unit or on a fold down ceiling TV, LED rope lights, fans, blender etc etc etc. A DC-DC as the only charging source isn't going to keep up. And again, it's drawing from the Starter battery or you have to run the vehicle for a long time. AND keep in mind that a standard alternator at idle isn't putting out anywhere near its max rating.

I very much advocate that any other batteries be connected to the full output of the vehicle charging system while driving down the road. Without the chokepoint of a DC-DC charger. Rig the DC-DC in parallel

 

[moose545]

My setup was a takeoff from the simple '$50' setup, there's a huge topic in this subforum that describes several more simple setups. Most utilizing an inexpensive solenoid as an automatic combiner / separator in a multi-battery system which uses the vehicle's factory charging system to top things up and when the key is off the factory battery is separated from what is in essence the 'house' side of things.
My own setup is a bit more complicated, I wanted a lot of functional options for other purposes, so that affected my layout. But the upshot is I have 200A 12VDC service to both bumpers to power a carrier-mounted winch from either end of the vehicle; dual identical SLA batteries so that the 'Aux' can be substituted for the Starter battery if the latter fails on (or off) the road; the main power run to the rear also feeds a 'power module' that has several bulkhead-type sockets and inverters. 12v cig, USB, APP 15A, voltmeter(s), and a 1000W 115VAC inverter; I also added a folding solar panel in a locking roof rack which allows the panel to be readily removed and set on the ground far from the vehicle, that panel feeds a Renogy PWC in that back box which is backfeeding my Aux / everything on that side of the $35 solenoid.
THere's a bunch of other convenience electrical mods. Most of it is described in my build topic. One of these days I'll properly diagram and describe it all in once place.

My setup while slightly complex is technologically simple and has a lot of power use options. It doesn't have the sechsy monitoring tech, but it does have the benefit that it has a lot of options and redundancy and pretty much all of it was accomplished for less than the price of that Redarc. But that doesn't help you much after that more costly hardware is bought.

The biggest benefit IMAO is the larger available charge rate via the vehicle's inate alternator / regulator, via the inexpensive solenoid and that setup removes the human element. But mostly it leaves the starter battery out of the system, rather than using it as a source for a DC-DC charger. That the DC-DC charger is drawing down the starter battery is my principal problem with that 'solution'. But if you've bought the hardware it's a little late to say you shouldn't use it.

Maybe I'm not fully grasping the wonders of a DC-DC charger. To me they seem to be a low-power (20A?) charger. Compared to the 100-150A potential of a vehicle's built in charging system, it doesn't make sense to me to put it between that larger charging source and ANY battery. To me it seems like paying a premium for a device that is greatly restricting the recharge rate that's available from the vehicle and with the added negative that it is drawing down your primary battery to do its job.
Then too, if you have solar and a solar charge controller (either PWM or MPPT) ,you dont need the DC-DC charger to effectively charge the battery. This is why I spoke of redundancy.
Does the redarc have any voltage sensing to ensure it does not draw down your starter battery too far? And if it does, will that sensing circuit be confused or thrown off by having solar input on that same circuit? If so I would think there's a potential in a high camping use scenario for the DC-DC to keep trying to draw from your starter battery to feed your Aux (and your human use demands) and the DC-DC seeing high voltage due to the solar input, while continuing to draw down on the Starter well past where it should. But surely they've designed something to prevent that?

Were it me, I'd be shielding / isolating the starter battery from any 'house' draws and that sort of obviates a DC-DC solution altogether, as I understand things.
And in your wiring diagram example in particular, I'd be adding a solenoid interrupted primary charging line direct to your additional battery so that it gets charged by the alternator when the vehicle is running. And make that solenoid and line phat enough to take full advantage of the alternator's available power. 100A rated at least.

My system is 'overkill' for glamping purposes, as I was chasing the desire to support the heavier draw of a large capacity winch. So I chose 200A as a baseline. Upgraded to a high output alternator, replaced its charge lead with a 1/0 cable, ran the power lead from that charging junction as a 1/0, to the 200A-rated solenoid and on to my Aux battery. And again 1/0 to my rear cargo area and finally just this past month to completion with bumper and front grill Anderson SB175 plugs. Got two different rotary cutoff switches in the circuit for those plugs, one rated 275A-continuous, the other 300A-continuous. So with the key on, engine running I've got 200A continuous for as long as any winch can stand it. With both batteries to draw on and without hardly running them down at all when I'm done with the pull(s).
The byproduct - which was the primary product for the first couple years - and STILL as I still don't have the winch itself - is that I've got an electrical system that can support just about any camping need in peak draw. But is a little shy in depth of storage capacity. But I've added and will be expanding rooftop solar capacity. That too is another 'option' I've been pursuing and expanding, for its own purpose, but it serves to supplement my Aux / House capacity in a camping situation. I get about 5A that way and hope to double that by adding a second fixed panel to my roof mount.
And I've still got room in my rear power box to add an additional ~40Ah of battery storage, which would also be charged by the alternator but would have to be isolated from any deep discharge experienced by the other pair of matched batteries. I would likely segregate those additional batts to be the power source for all the rear power box outlets / connections, sans the 1000W inverter. Have a solenoid or diode preventing their discharge back down the main cable / charging input. And re-arranging the module power sourcing to likewise isolate that fuse panel from the main power and feed if from the ~40Ah setup in the box. Leave the big inverter on the main feed.
I could even likewise use a diode on the PWM output and have it feed both the Aux battery and the ~40Ah setup, without being a cross-connection between the two.

I guess what it comes down to is that the solenoid solution sort of spawns from the high output competition car sound system sector and stuff like the DC-DC, MPPT etc spawn from the off-grid solar sector. And that they are different schools of thought.
Then there's the third school, RVs and boating, which seem to have a better overall grasp of separation and integration when it comes to 'vehicle' v 'house' power setups. And better protection of battery assets on both sides.

And I'm having trouble seeing how DC-DC charging suits any of it. It seems to be working at cross-purposes. Or so solely focused on one aspect that it violates other precepts. But I readily confess to not knowing enough about such devices. Just noticed that suddenly they seem very popular / 'go to' and I'm left wondering why, because they seem to be totally reducing the available recharging capacity for an Aux battery, in the way the devices are implemented..

Thank you for the reply and your setup is much more advanced than my plans are. My guess/assumption is yes, the Redarc has the "smart" technology to know when the primary has enough and then switch to the AUX to charge it. As much as I want to be parked in a spot for days and using whatever accessories I have chosen to, the fact is that I'll probably be moving from spot to spot at that time, in which case the alternator will have it's time to shine again charging things up while the engine is running and I'm off to find the next spot to camp. The Redarc is smart and does shutoff the connection to the primary while the truck is shut off, so I don't believe there is a possibility to drain the primary while the truck is off and parked. I might be over-engineering my idea, or having redundant devices, but I have to learn somehow. The battery I plan to use for the AUX is the same as my primary now, X2 Power 27F; 92 Ah and 930CCA. I will also drop my breakers to 30A since that seems more logical for the load, still not quite sure how/why though, and that's why I'm inclined to use what I see working for others, because I don't 100% understand how to fully do the math for the entire system.