How to make a cheap isolated dual-battery setup for $50

evldave

Expedition Trophy Winner
#1
So there are a lot of kits you can buy to have truly isolated dual-battery setups. Those are VERY NICE kits. They are also very expensive. I try and replicate those kits without spending as much money, while still having a similar level of quality and/or reliability. There are constantly posts on this forums about 'How to do dual-battery setups' and most are from people who don't want to spend the $$ on the kits. I didn't want to spend the money either, so came up with a simple list people need to buy to get a reliable and safe dual-battery setup.

Step #1 - Get a beer, this will take awhile

Step #2 - Look at the diagram - study it in detail as this is an incredibly complicated setup that will take years to learn properly. Plus, there will be a test at the end.



Step #3 - Have another beer, that was a rough diagram and you deserve a reward

Step #4 - Source your parts!

Get your own batteries - I won't go into batteries, which are best, etc. I have 2 DieHard Platinum batteries in my truck and a cheap Wal-mart battery in my trailer. Some like Odyssey, some like Optima, some like Trojans :)

Get your cables ($14)...for a simple setup you can go w/8 or 6 gauge, but I've found that 4 gauge battery cables with the ends cut off work well, because they are cheap and carry a decent amount of current.

http://www.handhelditems.com/20$$-guage-booster-cable-p-47794.html

You'll also need some 12 gauge wire. If you don't have 12 gauge wire laying around, you probably shouldn't be wiring your own dual-battery setup. Or borrow some from a friend. If you don't have any friends, turn off your computer and get a life! :sombrero:

Get your connectors ($7)...you know, to connect your cables to your batteries and stuff

http://www.amazon.com/IMPERIAL-71861-STUD-BATTERY-LUG/dp/B001E5A3UC/ref=pd_cp_hi_3

Get your fuses!!!! ($13) ... you need one fuse for each battery, trust me on this one :)

Go here are order part number ANB740N0N02, they are 80A ANL fuses + the fuse blocks

https://www.vtewarehouse.com/content/electromech/fuse/html/anl/anlfuse.php

Note: If you are wondering why 2 fuses, it's because each battery has power and could blow up your truck, so it's best to fuse both batteries. Put the fuses as close to the battery as is practical.

Get your solenoid ($16) ... this is what keeps one battery from draining the other battery, or something similar to that (mostly it keeps them 'isolated' from each other so you can still start your truck to make a beer run)

Cheap -->http://www.amazon.com/Continuous-Duty-Solenoid-80AMP-12V/dp/B0050I94XG/ref=pd_sim_sbs_auto_1
Good -->http://www.amazon.com/Cole-Hersee-24106-Continuous-Solenoid/dp/B001FQL43U
Way good -->http://www.amazon.com/gp/product/B001YIPXR2/ref=oh_details_o00_s00_i00

Step #5 - While you're online, order some good beer from the great Pacific Northwest (they ship everywhere!)

http://www.northwestliquidgold.com/

Step #6 - Wiring everything up

Follow the picture above :)


  • Find somewhere to put everything in your engine compartment (or truck bed, or wherever your 2nd battery might end up...unless it's one of those fancy sealed-up battery things, don't put it inside your rig or it might leak hydrogen gas and Hindenburg your *****, so just don't do that, okay? :)).
  • Make a short 4GA wire from your main starting battery POS (short for positive, not for piece of $hit)to your fuse block.
  • Make another 4GA wire from your fuse block to the isolator
  • Make another 4GA wire from the other side of your isolator to the other fuse block
  • Make a short 4GA wire from the other fuse block to your other battery POS
  • Make a single 4GA wire from the NEG on your starting battery to the NEG on your other battery
  • Connect a 12GA wire from pin on the isolator to a fuse in your fuse box that is only 'hot' when the key is in the 'ON' position (aka the truck is running)

Note: You can use fancy heat shrink on your wire connections, and that will work very well. Or you can take a roll of electrical tape (UL Listed, please) and wrap each connector-wire connection in electrical tape. It's about 80% as effective at about 10% of the cost or effort.

TOTAL COST - $50 (cheap) $59 (good)


  • Cables - $14
  • Connectors - $7
  • Fuses - $13
  • Solenoid - $16/$25


Note: Cole-Hersee solenoid will be much more reliable, so spend $9 less on beer and upgrade to the nice solenoid :)
Note #2: Don't try and jump-start your truck using your other battery using just this setup (ie through the solenoid). Instead, pull out your jumper cables (you DO have jumper cables, right? you didn't just cut up the pair you keep IN THE EVENT OF EMERGENCIES, right? right?) and jump from your backup to your starting battery using the jumper cables
Note #3: The big difference between this and the fancy setups (other than the cool battery gauge things) is those will usually use a voltage-sensing time-delayed-opening solenoid-type dohickey that allows your starting battery to charge first, before charging up your other battery. If that means anything to you, it might be worth spending the $200 more to get one of those sets. If you have no idea what that means, get in line, I don't really understand it either, but apparently it's worth $200 :)

Final Step - Have a beer, enjoy how cool you are, and now go build a cheap $100 awning with the money you just saved.
 
#3
This is a great writeup - if I wanted to add solar to the "house battery" what would I need other then a controller and a panel - can the solar panel be charging the house battery at the same time the alternator is?

thanks

J
 

evldave

Expedition Trophy Winner
#4
How to add 60W Solar for Under $125

Adding solar is fun and easy...first step, make sure you live somewhere other than THESE PLACES

Step #7 - Get a solar panel ($80)

I prefer to just use some tin foil and spare speaker wire, but if you want a real solar panel, you can't go wrong with Solarblvd

60W on sale

Step #8 - Get a beer

Did I mention you can order beer off the internet? No, really...you don't even have to leave your chair! (except when the UPS guy comes)

Step #9 - Order a 'Charge Controller' ($44)

wtf is this, you ask? It's a complicated thingymajig that makes sure your solar panel (or tin foil) doesn't overcharge your battery, leaving you stranded somewhere warm and sunny but with a dead battery (which means no power for your cheap Edgestar fridge, and NO COLD BEER!)...luckily people way smarter than either you or I figured out how to make it also work with your normal alternator, so you don't have to keep unplugging it every time you start your truck.

Apparently, tribes in the Amazon have a website that allow you to order this magical device delivered from the man in brown. Hopefully it survives the trip down the river and through the rainforest.

Note: Hooking up a solar panel is really easy, check out the schematic for the above controller...a few squiggly lines and some funny arrow-things can't be that hard to do IRL, right?
Note 2: Since like the crackhead you were in your youth, you'll jump right on any bandwagon driving by, make sure you get a larger charge controller now, so you can hook up more tin foil later, otherwise you'll have to re-buy another controller and then it won't fall under the 'cheap solar' category anymore, kapish?

Step #10 - Hook it up like this picture




Total cost - $124

  • Solar panel - $80
  • Controller - $44


I'm sure there's more to it than this, right? right? I can't believe, if you have two batteries already, and you have $200, you aren't fully equipped for a solar-charged, isolated, dual-battery setup yet, right? I spent $200 in beer in MARCH! Get out your credit card and contribute to our economic recovery!!
 
#5
Perhaps I'm not understanding your diagram correctly but I don't see how this is a true isolated dual battery system. You have one battery isolated but when you want to use it, it's run in parallel through the other. A true isolated dual battery setup would allow you to run solely on battery 1, solely on battery 2, both or neither.
 

evldave

Expedition Trophy Winner
#6
Perhaps I'm not understanding your diagram correctly but I don't see how this is a true isolated dual battery system. You have one battery isolated but when you want to use it, it's run in parallel through the other. A true isolated dual battery setup would allow you to run solely on battery 1, solely on battery 2, both or neither.
Good point. Technically it is still 'isolated' from the starting battery, and so isn't affecting your starting ability, but it doesn't have the flexibility that many kits (that cost more) have - being able to switch around as you indicated. Adding those abilities would add significant cost and/or complexity, and let's be honest, for 80% of the people who want an isolated dual battery setup, this will work for them (plus jumper cables if they end up draining their starting battery).
 
#8
Perhaps I'm not understanding your diagram correctly but I don't see how this is a true isolated dual battery system. You have one battery isolated but when you want to use it, it's run in parallel through the other. A true isolated dual battery setup would allow you to run solely on battery 1, solely on battery 2, both or neither.
I'm no expert and still on step 1 of drinking beer ... but the solenoid only isolates the batteries... if you want more "features" like which one to use, etc.. cut off switches bells and whistles , etc... you would have to pay for it. A $ 60. solution to to the dual battery problem is pretty good :)
 
#9
I want to make sure I understand that you can jump the starting battery off the house
battery .... just hook up the cables ....

Best regards,

Mike
 

evldave

Expedition Trophy Winner
#10
I want to make sure I understand that you can jump the starting battery off the house
battery .... just hook up the cables ....

Best regards,

Mike

Yes...and really you only have to hook up the POS since NEG is already hooked up. When you turn over the key, it will engage the solenoid creating a circuit through the solenoid, but it can't handle the current draw of a starter (measured in hundreds of amps for a few seconds). By hooking up your set of jumper cables between the batteries directly, it creates a nice way for the current to flow and you can jump-start yourself. Just be aware don't do this too often, especially if (1) you use a deep cycle battery for your 'house' battery as they don't like these 'fast' current draws and it will wear out your house battery sooner than normal, and (2) you don't want to go blind.
 
#11
There's a "oops" scenario here. Say you shut off the truck and leave your lights on. Come back later and red battery is dead, but with enough juice to engage the solenoid when the key is turned on. Even though the red battery is still dead and incapable of starting the truck, the yellow battery provides voltage to all circuits (except starter) before you hit 'start' so you don't know red battery is dead. But when you engage start, starting current will blow yellow fuse. It's not such dangerous failure mode as long as the fuse blows.

The way around this is having a smarter solenoid that only engages at over 12v. That way the yellow battery begins charging only when alternator is charging so you can't try to start with it.
 

evldave

Expedition Trophy Winner
#12
The way around this is having a smarter solenoid that only engages at over 12v. That way the yellow battery begins charging only when alternator is charging so you can't try to start with it.
Yes, you are totally correct. I think a lot of the full kits have that built into them. I use the 'don't leave your lights on' capacitive cranial neuroreactor to make sure that doesn't happen to me :)
 

RHINO

Expedition Leader
#13
i have pretty much the same set-up, even solar, but i control mine with a manual switch in cab rather than keyed. i recently swapped the ford solenoid for a continuous duty one.

one of your links is bogus, and a real let down, i cant even cuss you out properly cause i have to go lie down for a bit.
 
Last edited:
#14
Great design evldave, thanks a lot for sharing it and the links to the pieces to build it :D

The way around this is having a smarter solenoid that only engages at over 12v. That way the yellow battery begins charging only when alternator is charging so you can't try to start with it.
Easier/cheaper than getting a "smarter solenoid" might be simply having an "on delay" relay controlling the solenoid's switched power supply.
If it were set to switch on power to the solenoid 5 minutes after receiving power (5 min after ignition key turned) then the driver would have discovered if the starting battery will start the vehicle or not. So 5 minutes after ignition key is turned (and typically engine started), the house battery starts getting charged.

Something like this one : http://www.aliexpress.com/product-f...time-relay-0-6-minutes-AH3-3-wholesalers.html
(although the environmental/electrical specs aren't quite perfect for this application, it's basically what I'm talking about.)