Help with setting up multi 12v battery to car and solar with one way cutoff

[gold64bond]

I have 1 X 12V 100w Renogy solar panels on top of my Truck with EpEver 20A MPPT Charge Controller
I have 1 Main Battery that starts my car 12V
I have 350 amp 12V Alternator
I have 4 X 12V 80 AH Batteries in Parallel in the Back of my GMC Envoy
That Run - Power a lot of stuff Laptop Computer, LED Off road lights, 6 x 12V Dash/360 cameras 24/7 recording CB, Ham, and some other stuff (( NO --->> Everything don't run at the same time ))
How do I make it so the Alternator Charges and Solar Panel Charges them 80 ah Batteries one way with out draining / touching my main Truck Battery

Main thing that stays on 24/7 is my security Camera system / Dash Cam - 360 Camera syatem 6 cameras total recording on 3 X 256 Micro SD Cards
At times I run these below in the evening
I get on my laptop at night using free public wifi
I chat on the CB/ Ham radios -

I often drain my Batteries getting caught up on the internet video watching youtube flixto.to CB/Ham chatting
Only to find I drained my Main Battery as well
NO -->> My 4 x 80ah batteries are not hooked to my main battery I only have 1 x 8 gauge wire going from Alternator to them and Grounded to the Frame
YES it is connected to the same wire that connects to my main battery. After 8+ hours internet - talking over the airway I go to start my truck My main battery is DEAD -- If I charge the Batteries - Disconnect the wire from alternator to my 4 x 80ah batteries 8+ hr later I go to start the truck it STARTS RIGHT UP and only my Backup 4 batteries are Drained
I often have to use the solar panel to charge up my main battery to get me started then I disconnect it and let the alternator charge all the batteries

I want to know how - to charge my 4 x 80ah Batteries ONE WAY and stops draining my main battery
I heard you can put splice the positive wire to alternator put something in between that only allows current to flow one way
and will not drain juice from the main battery the person I talked to said it could be done but did not know how it is done
he seen many in the Campervan community hooking up their batteries some how that way


What do I need to Buy
Where can I get it
Any diagrams how to hook it up I can download (( PDF )) file
Please and Thank you Jeff

 

[gold64bond]

I want to Charge the 4 x 80ah batteries with the Alternator as I drive back home
Then flip the circuit breaker to the solar charge controller and charge the Batteries during the day time while
I am sleeping then 5-6pm head back out to
Mount Marcy in NY and Talk all over the world by CB and Ham Radio and I tether my laptop to my phone Hotspot to access the internet
I don't know what it's called I have tried googling - youtube several different ways like How do I charge 12V battery one way so it can't discharge etc... But I don't know how to word it - what it's called etc...
Thanks for any and all help Jeff

 

[400bird]

You've got two basic options:

Fancy relay that will disconnect the second battery when the engine is not running. This isn't ideal because when the relay closes, the 4 dead batteries would be smacked with hundreds of amps. Something like this:

https://www.amazon.com/Universal-Sensitive-Off-Roader-Protection-Controller/dp/B08NT7QX32/ref=mp_s_a_1_3

The better option is a DCDC battery charger, but the you're limited on current.

https://www.amazon.com/Orion-Tr-12-30A-Isolated-Charger-Booster/dp/B07ZKG396Y/ref=mp_s_a_1_3

 

[kbeefy]

Did you upgrade your alternator? I think they are 150A stock.

You can install a ignition triggered solonoid, an isolator, a combiner, or a DC-DC charger to accomplish your goals.

It will likely take alot longer than you think to recharge those batteries. Have you tested them or checked the resting voltage?

 

[mikefitz]

Consider the Victron Cyrix combiner, diagrams shown on download pdf, ( 230A unit)

Cyrix Battery Combiners - Victron Energy

Automatically connect batteries in parallel when one of them has reached a pre-set voltage using the Cyrix Battery Combiners. Find a dealer near you.

www.victronenergy.com

Mike

 

[fratermus]

How do I make it so the Alternator Charges and Solar Panel Charges them 80 ah Batteries one way with out draining / touching my main Truck Battery

A combiner (VSR triggered by voltage, solenoid/relay triggered by D+), isolator (diode- or FET-based splitter), DC-DC charger

an overview of the concepts, problems, solutions

I have 1 X 12V 100w Renogy solar panels on top of my Truck with EpEver 20A MPPT Charge Controller

Can you add more panel? The 20A mppt would be happy with 300w and this would help the rig go into sundown with highest SoC possible.

when the relay closes, the 4 dead batteries would be smacked with hundreds of amps. Something like this:

I'll push back on this. 320Ah of consumer-grade lead is very unlikely to pull hundreds of amps. At 50% DoD AGM acceptance would max ~0.33C (~107A) and falling, and FLA would be ~0.2C (~65A) and falling. IMO a 350A alternator + $50 VSR is a reasonable solution for bulk charging 320Ah of lead.

Caveat: to be sure, there are premium lead batts (odyssey, rolls, etc) that will accept more but people aren't shy about mentioning when they own them. OP didn't, and the 80Ah size suggests even more strongly that they commodity batts.

 

[fratermus]

I want to Charge the 4 x 80ah batteries with the Alternator as I drive back home
Then flip the circuit breaker to the solar charge controller and charge the Batteries during the day time while

It's more common to just let each charging source work when it can, with no human intervention.

I have tried googling - youtube several different ways like How do I charge 12V battery one way so it can't discharge etc... But I don't know how to word it -

some youtube results

 

[400bird]

I'll push back on this. 320Ah of consumer-grade lead is very unlikely to pull hundreds of amps.

Fair point, I'll agree if the "house" or 4 aux batteries are lead. I made an assumption of lithium and I don't see where the OP specified battery chemistry.

 

[fratermus]

I made an assumption of lithium and I don't see where the OP specified battery chemistry.

You're right - I mis-read OP's post as AGM for some reason. Hopefully @gold64bond will reveal the battery chemistry.

Related but maybe off-topic for this thread: I've been collecting data on installs where people direct-charge LiFePO4 from alternator. The max C-rate (average among all reports) accepted from the alternator was 0.31C. The max C-rate for typical vehicle installs (100-300Ah) was slightly higher, averaging 0.33C.

There is one 320Ah LFP bank in the dataset, mounted in a Ford Transit. It pulled 120A (0.38C) when the bank was at 10% SoC, and 70A (0.22C) at higher SoC. That's pretty close, C-wise, to what mine does (100Ah in a Promaster w/180A alt).

 

[J.P.]

Related but maybe off-topic for this thread: I've been collecting data on installs where people direct-charge LiFePO4 from alternator. The max C-rate (average among all reports) accepted from the alternator was 0.31C. The max C-rate for typical vehicle installs (100-300Ah) was slightly higher, averaging 0.33C.

There is one 320Ah LFP bank in the dataset, mounted in a Ford Transit. It pulled 120A (0.38C) when the bank was at 10% SoC, and 70A (0.22C) at higher SoC. That's pretty close, C-wise, to what mine does (100Ah in a Promaster w/180A alt).

I grown to HATE Lead-Acid batteryies over the past few years and I am experimenting with building 12V auto (lawnmower, ATV, generator, gate opener, etc.) batteries with my own 3D printed battery boxes. For the lawnmower and ATV batteries I am using well matched (top balanced) cells with cheap BMS's and for the auto batteries I am using JBD 4S 150A Smart BMS Common Port with Balance and Heat for Car Starting (DP04S007L4S150A) and 38120HP Headway Cells.

I have been testing my first Auto prototype (4P4S) in my 2015 Mazda 6 for a few months now and according to the BMS, the most amps the starter has drawn is 317.97A and the most the battery has drawn from the alternator is 97.26A. I have never allowed the battery to get to a low SOC because I am concerned that it will burn out the alternator. Because of overheating issues (battery in the engine compartment) I am about to relocate the battery to the trunk and swap it out for a smaller (2P4S) Battery (to limit the alternator stress if the battery ever does get to a low SOC). I carry a NOCO Battery Booster with me and am not worried about the battery getting to low to start the car.

I guess we could start a different thread if anyone is interested in more details of this.

 

[GooseF16]

I think the Renogy 50 DC to DC might be a good candidate for you since you have a 100 watt panel.. get rid of the MPPT, and this will charge your house battery at 25 amps if solar is present, and 50 if you turn off the solar. your alternator can handle it.. but it also trickle charges in reverse your starter batt if the house batt is full.. I have something similar on my MC.. it charges off my primary alternator/starter batt.. and I have a second alternator dedicated for the Lithium.. the outputs are ganged at the battery and I get good power on each leg.. its a simple system, and you can get a blue tooth dongle and see it in action.. fwiw.. the transit has a 60 amp customer attach port by the seat. that will do it for the DC to DC charger.. the victron will do the same thing without the solar.. also good.. both those units are silent