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

[Mudrunner]

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Thanks for explaining the basic principles as I have heard of duel battery set up and had a good idea of why just didn't understand the "reasons" as it were.

 

[RACKMAN]

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.

Question for you...can I put a toggle switch inline on the 12GA switched ignition line? Would I then be able to leave the switch in the off position and start the vehicle only using the starting battery if the second battery is badly drained by running too many accessories on overnight camping trips. This way, you could then switch the toggle for the solenoid on and begin charging the second battery ONLY AFTER you have safely ensured the vehicle has started. The reason i ask, is because if the two batteries are immediately connected when the ignition is turned and the second battery is badly discharged, will the second battery not immediately cause a massive transfer of charge from the main batttery and possible damage both batteries and not get the vehicle started? Thanks, wiring is not my strong skill.

 

[4RunAmok]

Yes, you can do that. I would have a 3 position switch, Normal Operation, Interrupted Operation, and Manually Paired for boosting starting battery.

That said, instead of using a Constant Duty Relay, use a Blue Sea 7622 Automatic Charging Relay, which will pair the batteries after it senses voltage from the alternator. The 7622 can me manually overridden at the unit itself, or install an interior switch.

 

[Ruined Adventures]

Excellent writeup...I only have one major complaint. Why didn't you write this before February 2012, BEFORE I had someone else do an inferior setup for me???

I could've saved about $100 bucks and maybe upgraded the solenoid with the leftover cash. Maybe then I would'nt be 'stuck' in Costa Rica with a solenoid that's crapping out! Okay, I'll stop complaining, since on the good side, I'm 'stuck' in Costa Rica...drinking liters of Imperial and my starting battery is still isolated :sombrero:

Well done evldave, tip of the hat to you sir.

 

[Gravel Slinger]

Just finished reading all 10 pgs & now feel I have a good understanding of this whole set-up...I've never actually UNDERSTOOD it all before - THANKS!!!

 

[Ruined Adventures]

I have read all of the pages trying to find any mention of a separator used between the two batteries. I was under the impression this is a fairly easy way to go and essentially the same thing as an isolator I am just curious if that is true. If not what are the differences and or strengths of each? I am not at all confident working with electrical stuff but I just bought an optima yellow top for the back of my truck as the second battery. I have a fantastic vent fan for my utility shell that I plan on installing as well as an inverter and some lights for the back. I am trying to find a place to help me install it all and just wanted to make sure I bought everything in advance as well as having some idea of telling them what I want. Basically I just want a full proof way to have a dual battery setup without ever being able to kill my main battery for starting the truck. Thanks Tyler

Tyler, the setup evldave shows in the first picture is exactly what we have for our dual batteries and we are running exactly the setup you are describing for your truck. We power some LED lights, a Fantastic Vent fan, and some aux. sockets. Occasionally we even use a small inverter while driving to charge a laptop.

This system has been dummy proof and great over the past 10 months on our Pan-Am trip. It's taken a lot of abuse so far. Although I have to admit that we recently had to replace our solenoid. Due to parts availability we used a manual marine style battery selector. Very simple to install and now I have more control over the dual battery setup.

 

[ask4yah]

Very cool write up. Knowledge overload now after 10 pages. Thanks dave.

 

[Raslin]

Hi, I researched this topic extensively, and this thread is by far the best information, idea and diagrams of what you actually need. Installed my system over the last week, thanks to this thread was very confident in what I was doing.

The system is working beautifully.

Thanks for the info

Sent from my GT-P7500 using Tapatalk 2

 

[evldave]

Thanks for all the nice comments here...glad I could help out and sorry I haven't been on this thread much...

Thought I would show a picture (with explanation) of my current setup...

This is best viewed extra large so you can see the labels-click the picture, then click X3 in the top menu bar Here are comments on the picture:

• This is my 2006 H3 with 2 Diehard Platinum Group 34 batteries. One is their Automotive battery, the other is their Marine battery. Why one of each? Their ratings and size are the same, but I'm using the marine to run my 2nd circuit in the truck (in the picture, it's the battery on the left). The Marine battery has extra terminals for attaching more fun stuff
  
• All main power is 2GA - This is because the batteries are normally isolated, but I can join them (when in the ON position) via a 500A solenoid to give extra reserve power for my winch. If you tried to join the batteries via an 80A isolator, you would likely fuse the isolator 'joined' or worse yet, melt a wire and cause a fire when using the winch. I use 2GA because that is what Warn used on the winch leads when I had it refurbished. Don't go any lower than 2GA for a winch!! Ideally I should be using 0 or 1/0 wire.
  
• I do NOT have a fuse on the 2GA wiring. This is primarily because the runs are short (less chance of a short), I have everything wrapped to prevent abrasion, and if I am using it for a winch I don't want to accidently blow a fuse if the winch temporarily pulls too much current. It would also be nearly impossible for me to fuse all of the wires effectively (my 500A fuseblock is almost 2x the size of the fuseblock in the picture). It's a calculated risk and I've seriously considered fusing just the winch power cables (running off the picture in the lower left).
  
• I have a completely separate 2nd circuit running in the truck - all fed via 4GA wire to the rear. That is fused (80A) almost immediately at the battery - the closer you can fuse the wire near the battery, the better chance you have of cutting power if there is a short (in my case, the only place for the wire to short without blowing the fuse is the 6 inches between the battery and the fuseholder).
  
• All wires are secured tightly - which means no movement and little risk of abrasion/shorting. Where there may be a possibility of that, I have put wire loom. Technically I could loom all the wires, but there is little risk given they are secured. I can't emphasize enough here - it's worth the $3 to buy a bag of 6" zipties and ziptie the heck out of everything! With all the offroading we do, there is a measurable risk of having a wire vibrate and get a small short (enough to cause issues, not enough to blow a fuse) that can be a real pain to track down. Trust me I know
  
• Ground wires are the same size as power wires. Think of the circuits as a loop - energy goes from your battery through the power wire to your whatevermajig then back to the battery through the ground wire (or through the body of your vehicle). Make sure all the wires are the same size. This is extra important for sensitive electronics like CB/Ham/Radios and lights.
  
• All wires are either marine grade or welding wire. I like welding wire and it can be bought relatively inexpensively at that place in the Amazon
  
• Notice that none of the wires have a sharp bend. If you try and bend them too sharp, the outer insulation won't show, but there's a risk you can break off some of the internal wires. Welding wire is great for this because it uses lots of really thin wires to make a big wire and so it's less likely to have this happen. All those expensive Monster Cable wires and stuff you buy at Best Buy? Not as good as welding wire A generally good rule of thumb for bending wire safely is 5x - never bend the wire less than 5 times it's diameter. In my truck, the smallest loop on these wires (which are about 1/2") would be a 2-1/2" bend, about what I have in the upper right wire - I could have run it straight from the terminal to the fuse block, but then I would have had a 'tight' bend right at the fuseblock. It may look like the wire coming off the fuseblock is bent tight, but for that I actually pre-bent the eyeloop connector before attaching the cable so the bend is actually in the metal, not the wire.

Want to know another great trick with this setup? You can jump-start your car by yourself! Remember, the 2nd battery is isolated, so when you turn the switch ON, they are automatically joined and you can use your 2nd battery to jumpstart your car!

But wait, Dave...what if you've worn down your starting battery so much there isn't enough power to energize the solenoid?

Easy, buy some of these and then you just have to jumper from your 2nd battery to the little post on the solenoid (it's labelled in the picture "Connected to ON). It will spark, but no big deal, you are basically energizing the solenoid with your backup battery instead of your main battery.

 

[Fallon 40]

I'm getting ready to start crimping the lugs to my battery cables and was wandering if there is some thing I should coat the wire with before crimping it to help protect it from corrosion?
Thanks

Ken

 

[Southwest Chuck]

I'm getting ready to start crimping the lugs to my battery cables and was wandering if there is some thing I should coat the wire with before crimping it to help protect it from corrosion?
Thanks

Ken

I'll tell you what I do, since I don't have a professional crimping tool. I cut back the wire insulation about an inch past the lug. Before crimping, I dip the end of the wire in soldering flux, then install and crimp the (copper) lug. Then I take my propane torch and heat the lug and wire and fill it with solder. The flux boils off as it fills and bonds it to the wire. To clean it and make it look nice, simply put some soldering paste on an old rag and immediately wipe off the lug (while its still hot). It comes out looking sweet. By doing this, it also keep any residual battery acid from creeping into the lug that could corrode the wire over time. By cutting back the insulation, you won't burn off too much of the insulation when you solder.

Also, cut two 3" pieces of 3/4 or 5/8" electrical shrink wrap (red or black as the case may be) and slide it over the bare wire before crimping the lugs. Keep them far enough up-line so they won't get hot while you're soldering or they will start to shrink. Let the lugs cool. then slide (one at a time) the shrink wrap into position, slightly overlapping the lug, and heat with your torch or lighter. Two layers of this makes a very tough insulator.

As for corrosion protection, my grand-pa always used a bit of plain old grease on his "clean" battery connections. Always worked for him! (and me too, just don't go overboard!)

Good luck!
SC

 

[Fallon 40]

Thanks for the reply,
I wanted to stay away from soldering since I have never done it and I read you could make the wires brittle if you did not know what your doing. I thought there might be something like flux to put on the end of the cable before putting it into the lug that would protect the wires.

 

[wRadar]

As many have said, this is some great information! Thanks to all who have contributed.

If I were to use the originally-diagrammed set-up, how could I connect an AC-powered (shore-powered) charger - something like a Battery Tender, or similar - that would charge both batteries? I believe I've read that it should be of adequate voltage and amperage that will keep the solenoid closed during charging. Would this then require that both batteries be of the same size/type?

Does having the solar set-up (second diagram in this thread) change the ability to use an AC-powered charger at all?

Thanks!
-Radar

 

[elee]

I always over think electrical projects so I have a few questions
Both batterys are being charged with the one alternator?
Many people with silverados do what they call a "Big 3 Upgrade" with 1/0 gauge wire, would it hurt if I used 1/0 to replace all the 4 ga.?
Here is a link to the Big 3.. it may work http://www.gmfullsize.com/forum/showthread.php?t=106041&page=6

 

[dwh]

As many have said, this is some great information! Thanks to all who have contributed.

If I were to use the originally-diagrammed set-up, how could I connect an AC-powered (shore-powered) charger - something like a Battery Tender, or similar - that would charge both batteries? I believe I've read that it should be of adequate voltage and amperage that will keep the solenoid closed during charging. Would this then require that both batteries be of the same size/type?

Does having the solar set-up (second diagram in this thread) change the ability to use an AC-powered charger at all?

Thanks!
-Radar

You could connect a charger to either battery - but it won't activate the solenoid and charge them both. That's one advantage of a more expensive system. They (well...some of them) have a brain that will activate the solenoid and tie the batteries when it detects the voltage rising (charging is going on) on either side of the solenoid.

You could also rig a manual switch to activate the solenoid manually. Just remember to turn it off when you don't need it on. The solenoid draws around 1a (or less) so just about any charger will put out enough to keep it energized.