Budget Dual Battery System

[AustinCruiser]

I've been wanting to get a dual battery system going for quite a while now and I have been slowly acquiring parts over the last few months. Well, I'm finally done.

My criteria for a dual battery system was:
1) Low cost
2) Simple operation
3) Simple installation
4) Safe isolation of house loads from recreational loads (winch, fridge, lights, etc.)
5) Ability to self-jump (with cables for now)

I shopped around quite a bit and considered National Luna and Hellroaring, but I opted for a 120 Amp Automatic Charging Relay Blue Sea (PN 7610). It is sealed and it does not require any user input or switching once installed and most importantly, it was way cheaper than the alternatives (about $78 on flea bay).

I also needed a second battery tray (got it from 'Mud), a battery (also from 'Mud), battery hold downs (from local Toyota place), 10' of 1 gauge wire, 1' of 6 gauge wire, conduit, crimp-on cable ends, stainless self tappers, zip ties and electrical tape.

The installation was very straight forward. Once I decided where to put the Charging Relay everything else was quite easy. I put the relay high on the firewall above the brake booster in order to keep it as dry as possible during water crossings.

The wire routing was also very simple. I used 1 gauge from the main battery to the "A" side of the relay. I ran another length of 1 gauge wire from the "B" side of the relay to the positive terminal of marine battery. I grounded the marine battery with a 1' length of 6 gauge wire. The relay itself was grounded to the firewall with a small ground. All of the connections were protected with heat shrink and conduit where possible.

The total cost breakdown for my budget 2nd battery system was:
$78 for the relay
$15 for the battery
$45 for the battery tray
$30ish for the hold down hardware from Toyota (next time it will be tractor supply!!!)
$12 for the wire
$3 for the conduit
$.80 for the tape

Grand Total:
$183.80

Here are some pics ...

 

[AustinCruiser]

And a few more pics ...

I'd say this is about a or job. Once everything is hooked up properly, you get a satisfying little green light. (see last pic)

Ed

 

[slow91fj90]

Im kind of slow when it comes to all the different types of dual battery setups. Does the relay just keep the 2 battery's charged and separate from each other? Would you be able to add a marine switch and combine both or each battery separate with this setup?

 

[Wheelingnoob]

Looks great!! I really like how simple it is, no switches or any extra wiring at all.

I take it that is a load sensing isolator that separates the batteries when one is dropping from use when not running?

Looking froward to see how this works out for you.

 

[CycloSteve]

Ed, nice writeup...I too have been collecting parts and will dive into this in the Springtime. Simple fits the bill.



Steve

 

[AustinCruiser]

More info ...

The nice thing about this isolator is that it "combines both batteries during charging and that it isolates them when discharging and when starting the engine." (per the user guide)

You could add a marine switch to combine the batteries per the instructions but I don't plan on doing this. The schematic is for boats, so I don't know how to combine the batteries in the Land Cruiser.

I plan to add a switch downstream of battery 2 once I get a winch installed, but this is to prevent accidental use of the winch (I have curious kids).

Im kind of slow when it comes to all the different types of dual battery setups. Does the relay just keep the 2 battery's charged and separate from each other? Would you be able to add a marine switch and combine both or each battery separate with this setup?

Looks great!! I really like how simple it is, no switches or any extra wiring at all.

I take it that is a load sensing isolator that separates the batteries when one is dropping from use when not running?

Looking froward to see how this works out for you.

 

[BirfMark]

If it isolates the batteries "when starting the engine", how do you self-jump with this system? Or is that not possible?

 

[AustinCruiser]

If it isolates the batteries "when starting the engine", how do you self-jump with this system? Or is that not possible?

You can combine the batteries with a marine switch but haven't done that.

To hard wire a self jump ability, all you have to do, is wire a marine switch from the hot of battery "B" to the hot of battery "A." This would allow you to do self rescue when battery "A" dies.

I plan to just use my jumper cables if my main battery goes dead since I want to keep the batteries isolated from one another. Keeping them isolated reduces the risk of inadvertently running your starting battery down.

Ed

 

[lt1fire]

how do you have your accessories wired in to the second battery??

 

[AustinCruiser]

I haven't started moving stuff yet. I plan to get a Blue Sea fuse block (I can't remember the exact name) and Blue Sea bus bar for all of the grounds. I am using the Blue Sea stuff because it is easy to work with and readily available at Academy and West Marine. It seems to be pretty well made too since it is designed for marine use.

 

[clandr1]

What sort of voltage drop do you have, if any, across that device? Do you run an additional cable from your main battery to the device, then another cable to the 2nd battery? What is the small wire coming from the bottom of the box? Is that something vehicle related, or a sensing wire run to your ignition switch to enable the connection of the two batteries?

 

[Landcruiser97]

Groundwire>>>>>>>>>>>>>>>>

 

[veeLC]

Mahalo for sharing this project with the rest of us "dreamers". Very nice, very clean, simple install. Yet another task to add to my "to do" list.

 

[adalnay]

Did you use a kit to move the washer bottle to the back? Might be a dumb question. Sorry in advance.

 

[AustinCruiser]

What sort of voltage drop do you have, if any, across that device? Do you run an additional cable from your main battery to the device, then another cable to the 2nd battery? What is the small wire coming from the bottom of the box? Is that something vehicle related, or a sensing wire run to your ignition switch to enable the connection of the two batteries?

The little green wire is just a ground for the internal workings of the relay.

There is a large hot wire running from my main battery, to the relay, then to the 2nd battery. It is a 1 gauge wire (very big).

I just measured the voltage at high idle and it is 14.7 volts from the alternator and battery 1 to the relay. The other side of the relay shows 14.7 volts as well (with the relay [STRIKE]open[/STRIKE] CLOSED). The voltage at the positive terminal of battery 2 is 14.6 volts.

When the relay is [STRIKE]closed[/STRIKE] OPEN, the voltage on side A of the relay will show 14.7 volts and side B will show the actual voltage in battery B.

Oh yeah, I used a Slee washer bottle relocation kit to make room for the new battery.

I hope this makes sense.

 

[TrickyT]

...When the relay is closed, the voltage on side A of the relay will show 14.7 volts and side B will show the actual voltage in battery B...

You mean the other way around, when the relay is OPEN the A side will read the alternator charging voltage (14.7) and the B side will be the aux battery voltage. When the relay contacts are closed, both relay terminals will be at the same voltage since the contacts electrically connect the two terminals together.

 

[AustinCruiser]

You mean the other way around, when the relay is OPEN the A side will read the alternator charging voltage (14.7) and the B side will be the aux battery voltage. When the relay contacts are closed, both relay terminals will be at the same voltage since the contacts electrically connect the two terminals together.

You're right. I am electrically challenged and mixed up the terminology. I've corrected the post.

 

[chrisc16]

Ed, I looked at the installation diagram from BlueSea, they recommend fusing both sides of the relay. Did you consider this?

Thanks,
Chris

 

[clandr1]

The little green wire is just a ground for the internal workings of the relay.

There is a large hot wire running from my main battery, to the relay, then to the 2nd battery. It is a 1 gauge wire (very big).

I just measured the voltage at high idle and it is 14.7 volts from the alternator and battery 1 to the relay. The other side of the relay shows 14.7 volts as well (with the relay [STRIKE]open[/STRIKE] CLOSED). The voltage at the positive terminal of battery 2 is 14.6 volts.

When the relay is [STRIKE]closed[/STRIKE] OPEN, the voltage on side A of the relay will show 14.7 volts and side B will show the actual voltage in battery B.

Oh yeah, I used a Slee washer bottle relocation kit to make room for the new battery.

I hope this makes sense.

Thank you! I have an isolator in my truck now, but the voltage drop is about .75 volts from input to output. I will be looking at this as a solution. Thanks!

 

[AustinCruiser]

Ed, I looked at the installation diagram from BlueSea, they recommend fusing both sides of the relay. Did you consider this?

Thanks,
Chris

Yes, but I didn't do it. I will probably add fusible links to the installation between the cable ends and the battery, but I haven't done it yet.