How to make a cheap isolated dual-battery setup for $50
- Thread starter evldave
- Start date
I'm still on good old sealed lead-acid batteries. Have obviously replaced the original Diehard batteries I had when I started this thread, but I kept them in the garage and they still hold a charge (they are 13 years old!)
Pappa Weasel
New member
I think I found this answer somewhere before, but I will ask here. I want to activate my solenoid from two SPST switches. The red battery is my starter battery with IGN on to the first switch. The yellow battery is my house battery. The second switch is normally off unless I need to self Jump. By placing the diode in this way I will not get back flow between batteries.
I therefore have a manual setup to activate the combining of batteries as I wish. Am I correct in my diagram?
Thank you in advance!
I therefore have a manual setup to activate the combining of batteries as I wish. Am I correct in my diagram?
Thank you in advance!
helenandtoby
New member
Yes, but not for lithium!
I used the simple setup for years, with both flooded and AGM batteries. Worked great.
But it won't work with lithium.
Two problems:
First, you must have some way to limit the charging amps. Otherwise the lithium battery will draw the full amperage of the alternator, and overload it.
Second, your alternator is temperature compensated, and reduces the charging voltage as the temperature rises. The lithium doesn't want this. So, in warmer weather, the lithium battery will never get the voltage it needs for a full charge.
So, if you want to go with lithium, get a dc-dc converter.
I used the simple setup for years, with both flooded and AGM batteries. Worked great.
But it won't work with lithium.
Two problems:
First, you must have some way to limit the charging amps. Otherwise the lithium battery will draw the full amperage of the alternator, and overload it.
Second, your alternator is temperature compensated, and reduces the charging voltage as the temperature rises. The lithium doesn't want this. So, in warmer weather, the lithium battery will never get the voltage it needs for a full charge.
So, if you want to go with lithium, get a dc-dc converter.
Pappa Weasel
New member
Thank you! That's what I thought, but occasionally I question my failing memory. I am running two AGM's in a Tacoma.
Baller
New member
This is a heck of a thread that's spanned years. I've started looking into this again and stumbled on the below linked kit. Looks, effectively, like the original system in the first post of this thread. Would love to hear people's opinion of it. Thanks.
fratermus
FT boondocker
It is a VSR, which the original post mentioned: "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". Prices have come down since 2012.
There are gotchas to be aware of with any relay setup, but all types work fine.
I have used a VSR with both a 220Ah FLA banks and now a 150Ah LiFePO4 bank, despite claims that the latter cannot be done. Fortunately, my bank follows the physics (I=V/R) rather than the opinions of people on the internet.
hmmm, I still have the H3, and pulled the dual-battery setup a few years back. Dusting things off for a complete overhaul this winter, maybe it's time to make a new thread with some great updated technology....
I very much appreciated your original post and have been running your setup on flooded batteries for many years. Since we rarely stay put for more than 2 nights in a row, it’s kept our battery charged enough to easily cover our needs without investing in solar. Thanks a million evidave!
thebmrust
Active member
Keep it low cost if you can. Or a low mid and top end price options.
How did you know I was planning on doing this? Now I can find this thread when I'm ready to do this after a beer run. Solar stuff and all, thanks!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
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 -->Good -->Way good -->
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 those more knowledgeable than me:
Does anyone see any issue with installing a 2nd battery in parallel without any additional hardware such as an isolator or DC-DC charger?
This is to start out. I'm sure I will get to a point of needing a true isolated dual battery setup, but I want to jump in right now with minimal cost and running wires to new 12v plugs in the cab. Simply installing a second battery and wiring in parallel is very straight forward.
- I drive a 2021 diesel colorado with the battery rated at 90ah.
- The 12v plugs in the truck can be switched to always hot by putting the fuse in the adjacent slot. So no aux wiring required.
- The truck has a smart alternator that reduces voltage once it senses full charge
- I plan to get a Dometic CFX 55IM which uses about 37-40ah per day in normal temps
- I'm not looking to run the fridge off the main battery for prolonged periods. 24hrs at the very most, followed by lots of driving time.
Does anyone see any issue with installing a 2nd battery in parallel without any additional hardware such as an isolator or DC-DC charger?
This is to start out. I'm sure I will get to a point of needing a true isolated dual battery setup, but I want to jump in right now with minimal cost and running wires to new 12v plugs in the cab. Simply installing a second battery and wiring in parallel is very straight forward.