RAD4Runner

Dual-Battery System With Voltage Sensitive Relay Isolator

I'm tired of the mess and having to replenish ice when overlanding. Found a decent 20-liter compressor fridge/freezer which worked well during our Utah trip. However, I need "house" battery to keep it running when car is not.

Dual-battery versus power station / solar generator like Jackery, Goal Zero, etc?
Those are excellent and convenient. However, regardless of what I pick, I still want 6AWG wire to the back for max capacity, want to place "house" battery on top of wheel-well under roll-bar for optimum space utilization (no room in engine bay), heavy item above the axle would make ride smoother, and Jackery 500 (closest to my energy needs) is too bulky to fit there.

1) A rolling stone gathers no moss. I do not plan for car to be stationary for more than 24-hours.
2) I am guesstimating that a 55AH AGM, sealed lead acid battery would power it for approx 24-hours, and
3) would fit perfectly on wheel well below the roll bar.ELECTRICAL PLAN:




I already have the parts, and awaiting inline fuse holders for 50-amp Maxifuse, to match my existing 6AWG "B" cable, and the Anderson Powerpole supplies.

VOLTAGE-SENSITIVE RELAY (VSR):
A.k.a. voltage-sensitive isolator will sense main/crank battery voltage. It will connect the house battery to alternator ONLY after crank battery is fully charged. Meaning the alternator would not have to charge both batteries at the same time, meaning no need to upgrade my newly-installed alternator. I already got the solid-state one but may go with relay with electro-mechanical contacts if I have issues with the voltage drop inherent with solid-state ones. In comparison, continuous-duty relay isolator or simple diode charge splitter will connect both crank and house battery to alternator as soon as ignition is started. Either has the potential of straining the alternator if both have low charge.

VOLTAGE-SENSITIVE RELAY SELECTION:
Solid-state relays supposedly cause a voltage drop when contacts close to charge the house battery, meaning voltage at house battery terminal would be approximately 0.7V less than actual alt3rnator voltage at crank battery terminal. We shall see.
Another advantage of electromechanical relay is that if it fails it would more likely be open- safer and transparent to the stock circuit.



Keyline solid-state voltage-sensitive relay (VSR) isolator has lots of good reviews… (I DID NOT END UP USING THIS)


However, when I searched Amazon, I found many others that look like it with same specs. They’re all made in China so I picked the least expensive one with good reviews, this Kemimoto… (I DID NOT END UP USING THIS)


I also ordered this NVX VSR with electromechanical relay. Will compare voltage drop, if any, with the solid-state one above. I ENDED UP USING THE NVX.
THIS IS SIILAR IN FORM TO THE POPULAR REDARC RELAY



PORTABLE :
The battery will be portable, albeit heavy, so I want to be able to quickly disconnect it from the truck.

ANDERSON POWERPOLE (What the heck is that!):
The spring-loaded positive/center on the cigarette lighter connection wants to push the plug out of the socket. It also has limited current capacity. The Anderson Powerpole solves both issues. It is popular among ham radio operators, solar-power users and overlanders in Australia.

DISTRIBUTION FUSE BLOCK IN BODY PANEL BESIDE THE REAR SEAT BACKREST:
Inside body cavity just forward of the roll-bar is a convenient wiring center. Mounted a 3.5-inch wide metal plate re-purposed from some electronics chassis to the top pinch weld with 8-32 stand offs on bottom.

DRY FIT. Still need to heat-shrink the main ring terminal.

More to come.

RAD4Runner

Admins, pls delete. Duplicate post.

RAD4Runner

Does anybody have 2 D-Rings he can sell me? Ones from first-gen 4Runner are preferred to keep things standard. How much including shipping to zip 92129?

wallytoo

iTrader: (1)

let me look at my parts runner. might be able to send you the rear panels with cubby pockets, too.

OldBlueMidnight

The second battery is a worthwhile camping upgrade. After burning up two yellow-tops, I added a low voltage disconnect to my system...a few devices that are always on, mostly security related, add up to a few hundred mili amp draw. You may want one if you don't plan on disconnecting the second battery from loads between trips...it seems like even USB outlets pull a little juice when nothing is plugged into them, and these little loads can wreak havoc on a battery if left to sit for a few weeks.

swampedout

Ive only had a primitive dual battery setup but it saved my you know what before. Used my deep cycle to jump the truck battery when we were way up in the mountains.
i was doing solar at the time but if I were to do it again, Id have a tiny inverter generator and a slightly bigger fridge.

Looking forward to what you come up with. Keep in mind that once you get everything wired up, youre going to start thinking of other gadgets you can add.

RAD4Runner

Absolutely. Shopping for USB outlets with "hard" switches, and the SB50 Anderson connector will make it easy to disconnect. The whole system would be practically transparent to stock battery system.
Yeah, I know LOL! However, I try to resist that especially because I only have a 55AH one that barely fits the space. Too much gadgetry takes away from the outdoors experience.

muddpigg

iTrader: (1)

I haven’t pulled trigger on dual batteries yet. But do intend to use VSR from Bluesea. Check out 4crawler he mounted dual AGM under body but above frame. I also DD my rig, I learned the hard way the short trips will cut a battery’s life significantly. Might be worthwhile to look into a smart charger to bring both batteries back up to full charge periodically. What I don’t know is if the VSR and smart charger will allow me to connect to primary battery with charger and open after fully charged to charge house battery. Solar seems a hot ticket but not really best option for what I do.

swampedout

You really have to be stationary for a couple days for solar to make sense. Thats why I think the small inverter generator makes sense. You can stop for a couple hours, crank it up and keep your batteries topped off.

RAD4Runner

My considerations now are:
1) How to run 6AWG "B" wire for house battery into cabin:2) Battery Tray / Frame. I wonder if I could simply capture all bottom perimeter of battery with angle bracket, or if I have to provide a floor for entire bottom of battery.
3) Enclosure: Batt3ry is spill-proof, but to be safe, I'll wrap like a christmas present it with PVC Shower Pan Liner like this . Durable, inexpensive and low-bulk. I can also re-use my tailgate cover that I need to replace with wider one. #ZeroWaste! Top will be left open to make sure gas, if any escapes. Terminals will be protected, of course.
Yes, I saw 4Crawler's system. I decided on above the wheel-well so it can be more portable; easier to remove than in engine compartment (already tight, to begin with). Anderson Powerpole SB50 connector will facilitate disconnection.

Yes, VSR will leave house batt3ry disconnected from alt3rnator until it senses that crank batt3ry is fully-charged. Only then will it connect to charge the house batt3ry. When crank battery level goes down, it will disconnect house batt3ry again.It prioritizes the more critical cranking batt. I'll try to make a video of voltmeters monitoring crank and house batts when these happen.

I don't really understand the need for inverter if alt3rnator will charge batteries while driving. When not driving, I'd rather not strain the cranking batt in order to charge the less critical house batt3ry. However, on modern vehicles, computer makes alt3rnator voltage output (for fuel efficiency and emissions reasons) and cause issues with VSR isolator. Hence, an inverter or DC to DC charger is needed to charge the batt3ries.

Yeah, solar only makes sense if I plan to stay stationary for long - which I do not, except on backpacks when I leave the truck parked at trailhead.

muddpigg

iTrader: (1)

found it interesting about converter for charging even for single battery on an lithium system. But I wasn’t talking a converter. Sometimes my thought don’t translate to writing very well.

after a battery issue that killed an awesome battery prematurely. I nerded out on the topic. So batteries don’t have a memory what happens is that the chemical process that causes electricity is reversed during charging process. But if batteries are not fully recharged then the chemical process can not be reversed. Something about slag hardening. This slag even before it hardens and becomes permanent it can increase the internal resistance of battery which in fool’s alternator that battery is fully charged. So using a charger periodically can increase life of battery as it will reverse chemical reaction thus improve potential of battery. You can do it with any charger but you could easily overcharge battery easily. So an answer is a smart charger that will not overcharge battery. An example would be that if you purchase an optima smart charger at time of purchase of battery they extend your battery warranty significantly, well atleast years ago when I got this battery. Don’t get me started on optima this comment is way too long already. It was a national replacement warranty for battery that got me down this rabbit hole.

RAD4Runner

@muddpigg ,
I see. Yes, I think same reason for using a battery tender, especially when leaving truck in-op for sometime.

muddpigg

iTrader: (1)

many of the “smart chargers,” I have a NOCO genius. Have some sort of repair mode. Suppose to pulse current mixing high and low amp to better reverse slag. But seems articles on topic go both ways. My charger charges and tends. So set it and forget it. I still have an old school “dumb charger” because especially AGM batteries can discharge to such a low state that “smart charger” won’t even initiate a charge.

RAD4Runner

(Added details on Voltage-Sensitive Relay isolator to original post above.)

Running Wire Into Cabin:
Aft of the starter relay, near wiper motor is a good place for the isolator. The existing opening near the fuse block to the wheel-well is already crowded, and would add approx 4 feet to wire run. There is an existing small hole below the start3r r3lay, so I just enlarged it to accommodate a grommet. Wire runs through that to wheel-well, and through hole vacated by radio antenna. I think it is less invasive than messing with existing firewall grommets.




Before adding wire loom wrap/cover.

Wire then runs along the door threshold...


Up and inside the body panel near the fuel tank inlet tube, alongside fuel door release cable and right side taillight wires...


Inside body panel...

(I put random foam pieces I happen to have around over the Peel & Seal vibration dampening material for added sound insulation)

This cubby aft of the rear seat and forward of the roll bar is a perfect place for the wiring center.


I want the "B2" wire to be one continuous piece all the way to battery connector so distribution fuse block simply taps off it; no need for additional wire terminals nor crimps.


6AWG "B2" Wire will terminate in an Anderson Powerpole SB20 (50-amp, 6AWG) connector and reach the battery on the wheel-well. The 15-foot 6AWG battery wire I bought from Amazon is just perfect!

coopster

Hey Mr Rad.
Nice work. I always appreciate your insight on things Electron.

Where did you get the Anderson connectors, fuseholders and your other parts from? Been trying to avoid purchasing any parts direct from mainland chyna. Altho guess most stuff originates there. But I did get rocker switches made in Taiwan.

I am also in process of thinking about adding a second battery (tbh getting the thing running should be a bit higher priority!). So I wonder in your sketch why you put the acc'y connector tied off the 6 ga between? My thought was a single cable, fused both ends of course, but my acc'y panel if you will ties direct to the second battery terminal (and would be fused as well). This is of course theory, as not much really exists yet.

RJR

I've run the equivalent of dual battery systems for years, charging my camping trailer battery from the vehicle while driving, and having it isolated when stopped. My feeling is that you are over-thinking and over-designing this. All I have ever done is the following:
- Run a 12 AWG wire back to the trailer plug (more on why not a 6 AWG in a minute)
- Put a 30 amp relay in series with the wire powered from "Ignition ON" to isolate the trailer battery when the engine is stopped. (BTW, any 4th gen and up 4runner comes with this relay and wiring from the factory if it has the towing package)
- Put a 20 amp resettable circuit breaker in series with the 12 AWG wire, on the source end.

This works well. No issues with overloading the alternator, and the trailer battery stays charged as long as the load while driving is not more than 5-10 amps or so.

Some theory
- First, you don't really need the voltage sensing relay to protect the alternator. The main battery normally is in a state of full charge - even starting the vehicle takes less than 0.5 amp hours of energy if the engine is in good shape and starts readily. The alternator will bring the voltage up to about 13.7 volts immediately upon engine start, so your voltage sensing relay will always be on anyway. A plain mechanical relay is simpler, cheaper, and has less voltage drop.
- So why not 6 AWG. Number #1, it's expensive, stiff, and hard to route. But more importantly, some resistance in that circuit is good. When you start the engine, the voltage of the main battery will drop as it sees a load of a few hundred amps. The relay to the aux battery will be closed because ignition is ON. The aux battery will dutifully try to "help" by sending a hundred amps or so back to the starting circuit. You don't really want or need that. The 15 feet of 12AWG (1.8 milliohms/foot) provides enough resistance to limit the current, and the 20 amp resettable circuit breaker is there as a backup in case of excessive current flow. As long as your continuous DC loads on the aux battery are less than 5 amps (a compressor fridge is about 2-3), 12 AWG will provide plenty of current capability without excessive drop that would limit fully charging the aux battery.
- It's also worth noting that batteries are very non-linear regarding charging current vs. discharging current. A fully charged battery can easily put out 200 amps while only dropping about 1 volt from its normal rest voltage. However, you cannot get 200 amps of charging current back into the battery with only 1 volt of differential above the rest voltage. "Fast chargers" that put 100's of amps into a battery typically run up around 17-18 volts or more to do that. Your alternator will never put out that kind of voltage. Consequently, even if the main battery is 50% discharged (a rare event unless you leave your lights on or the battery is deficient), the alternator will likely only be charging it at 15-20 amps max - not a huge stress on the alternator.

I find that, on long trips with my rPod trailer, the combination of vehicle charging while driving and a 100 watt solar panel while parked keeps my trailer battery charged indefinitely, particularly in the desert where there is lots of sun. Of course, since I have a propane fridge, my electrical needs while parked are less than yours. However, the fridge does take 10 amps at 12VDC while driving, and the battery still charges.

For overlanding trips without the rPod, I use a 40AH AGM wheel chair battery (sealed, spill-proof, indoor rated) to power my thermoelectric cooler. The battery is connected to the vehicle charging system as described above. An Arduino processor on the cooler manages internal temperature and battery voltage to prevent excessive discharge. A compressor fridge would be better than the thermoelectric, and use about half the power. I should add that I've been running this system on two vehicles for 4 years with zero battery issues.

Just my thoughts. I like to keep things simple, although it is fun to design the ultimate system!:-)

muddpigg

iTrader: (1)

interesting and cool to see different sides of this topic. once again, all of my experience is purely research as I have not pulled trigger on dual batteries and it is lower on to-do list than homebrew hydro-assist steering. VSRs don't cause the voltage drop of old school isolators, depending on voltage rating, prices aren't too bad but still more expensive than a heavy switch but with no possibility of forgetting to disconnect battery and draining both batteries overnight.

I do intend to build my system with heavier gauge wire solely of ability to combine batteries for self jumping and prolonged winch operation. But this is where my research fails. It is safe to say the winch pulls heavy electric loads depending on workload and this can be upward of 380amps. I am assuming that second battery would need to be wired to support this amperage and wire resistance to for appropriate distance of wire. or could it be smaller gauge wire as winch is directly wired to starting battery?

Next has anyone on this post used a shunt to measure alternator output? of course this would need to be under max electrical load. I tend to get overly concerned about details; alternator is rated at 160amp. The cutoff for most VSR is 140amp then next is 500amp, I like Bluesea products. Loads of items are rated above actual output for marketing.

RAD4Runner

I bought Anderson Powerpole parts from Powerwerx. U.S.-based so no hassle, quick shipping, reasonable pricing and guaranteed authentic parts. There are many imitations out there online.
Thank you! I am also anti #CommunistBully. I try not to send money that way.

Absolutely. You should have learned from members here to do things methodically, and not throw parts at it.

Electrically, it would be the same thing, whether tapping off the 6AWG or directly from the auxiliary battery terminal. However, tapping off closer to where I need my outlets require less wiring for me, and keep battery terminals uncrowded. Furthermore, I can easily/quickly disconnect the aux battery by simply unplugging the Anderson plug. The fuse and half of Anderson connector is mounted on battery, the other half on pigtail to stay on truck. When aux battery is unplugged, auxiliary circuits will still be powered by stock battery when isolator closes its contacts

Fuse and Half of Anderson SB50 Connector is Mounted on Top of Battery.

RAD4Runner

Same here and you nailed it! LOL!

Great point on continuous-duty relay. I saw that upon completing the install; Isolator would close as soon as truck was started, and remained closed after engine/alternator shutdown because the crank battery still had more than 12.7V. It is not until I turned blower and high-beams on that it opened.
I was concerned about straining the alternator i the rare case when cranking battery is severely depleted. My new alternator got too hot to touch trying to charge the stock battery that was down to around around 10.5 V without load after running truck on battery power only while waiting for replacement alt. Charging voltage stayed below 12.7V for some time. That condition went away fast.

That is one part I did not have to think hard at all, where Form-Fit-Function all just worked out.
I guesstimate my aux load to be around 50-amps, I wanted to use the Anderson SB50 battery disconnect to differentiate it from my 15/30/45-amp Anderson outlets, its 50-amp pin is made for 6AWG, the 50-amp Maxi Fuse holders have 6AWG pigtails and would go directly between battery post and SB50 pin.

I'm estimating about similar conditions, altho I got a compressor fridge @45Watts max.

Yes, I did not see any voltage drop between crank and aux battery posts on either of the VSR's above I tested.
I would not feel safe jump-starting or running a winch through the VSR. If you have the aux battery in the engine compartment it would not be much trouble to hardwire the batteries together for such occasion.

RAD4Runner

Ran the Anderson Powerpole connector for the fridge to the body panel cavity between B-pillar and the fuel tank fill downtube. Need to come up with a cubby to protect connection and be a place to stash cord and AC adapter when not in use.