How to make a cheap isolated dual-battery setup for $50
- Thread starter evldave
- Start date
Apologies for asking what is probably covered in this thread. As much as I searched, finding specific info in a 76 page thread isn't that easy, and I'm not great with electronics.
If I wire a dual battery system based on the diagram in post #1, what benefits does it get me? What limitations does it have over more expensive pre-made dual battery systems?
I would like the ability to:
- Self jump (I don't mind, and actually prefer using jumper cables from battery to battery)
- Have "extra juice" in the system to help run lights, radio, compressor, inverter, etc. (No plans for a 12v cooler)
- Charge both batteries while the vehicle is running
- Be as maintenance/fiddle free as possible
I'm confused on running the second battery into the fuse panel. Will it only power items run from that fuse spot or will it "back fill" the whole system?
Cons:
- What does this system lack that something else offers?
Thanks for your time.
If I wire a dual battery system based on the diagram in post #1, what benefits does it get me? What limitations does it have over more expensive pre-made dual battery systems?
I would like the ability to:
- Self jump (I don't mind, and actually prefer using jumper cables from battery to battery)
- Have "extra juice" in the system to help run lights, radio, compressor, inverter, etc. (No plans for a 12v cooler)
- Charge both batteries while the vehicle is running
- Be as maintenance/fiddle free as possible
I'm confused on running the second battery into the fuse panel. Will it only power items run from that fuse spot or will it "back fill" the whole system?
Cons:
- What does this system lack that something else offers?
Thanks for your time.
dwh
Tail-End Charlie
What it gets you, is a battery that you can use to power things while parked, without having to worry about running your engine battery down. That way, you don't have to worry about being stranded with a dead battery unable to start the truck.
Also, you can use a cranking battery for cranking the engine, and use a deep cycle battery to power your camping loads when parked. Cranking batteries don't live long when deeply drained too many times.
You don't run the second battery into the chassis' electrical system / fuse box at all. That would defeat the purpose of "isolating" the batteries.
Instead, you add another fuse box, which only runs from the second battery, and use that to power whatever you need to use while parked.
The two advantages of the more expensive systems are A) switched override and B) dual-sensing auto-connect.
A: you have a switch which can be used to keep the batteries tied if need be, or keep them isolated if need be. That's not much of an advantage, the setup in this thread keeps the batteries tied whenever the key is on, and it's trivial to rig a switch to turn the solenoid off.
B: the "brain" connects the batteries when it senses an elevated "charging voltage" on either side. Useful if you have solar going to the second battery, since the brain will make sure your engine battery gets topped off too.
Neither of these advantages is really very important though. Nice to have, but mostly never needed.
AJE
New member
I used the info in this thread to wire my system, the trigger to the solenoid comes from a keyed fuse in the fuse box. I did add a simple push button switch (and LED) off of the aux battery to power the solenoid as a self jumpstart if I kill the starting battery. Thanks for all the great info!
Sent from my SM-N910P using Tapatalk
Sent from my SM-N910P using Tapatalk
The mention of the Emergency Self Jump switch in the last few posts has prompted me to share my experience. I have pretty much built my system on the Evil Dave diagram in the first post of this thread. I had every intention of adding the self jump switch, but being a card carrying procrastinator with a hard to get thru firewall, I had put that off. But I threw a little jumper wire in the glove box to manually trigger the solenoid if the need arose before I installed the switch.
My starter battery began to stop holding a charge last week and I found myself having to self jump. But when I went digging through the glove box for my jumper wire I could not find it. (turns out it was there, just buried under gloves). Here is what I did. I knew there was still enough juice in the starter battery to trigger the solenoid because I could hear it when I turned the key on. But there was only enough juice to get maybe one slow revolution of the engine from the starter. So I turned the key on and just let the house battery feed some current into the starter battery while I continued to dig for the manual jump wire. After about 3 minutes I turned the key to engage the starter, and now there was enough juice to start the car. If it would have been zero degrees in a cold winter night I don't think it would have started the car, but on a 70 degree fahrenheit evening it started the car.
Moral of the story: If you don't have a jump switch, and you don't want to cannibalize a strip of wire from a non-mission critical accessory, try just turning the key on to see if the house battery will charge the starter battery enough to get you going. Oh and one more lesson, don't procrastinate like me.
randy
My starter battery began to stop holding a charge last week and I found myself having to self jump. But when I went digging through the glove box for my jumper wire I could not find it. (turns out it was there, just buried under gloves). Here is what I did. I knew there was still enough juice in the starter battery to trigger the solenoid because I could hear it when I turned the key on. But there was only enough juice to get maybe one slow revolution of the engine from the starter. So I turned the key on and just let the house battery feed some current into the starter battery while I continued to dig for the manual jump wire. After about 3 minutes I turned the key to engage the starter, and now there was enough juice to start the car. If it would have been zero degrees in a cold winter night I don't think it would have started the car, but on a 70 degree fahrenheit evening it started the car.
Moral of the story: If you don't have a jump switch, and you don't want to cannibalize a strip of wire from a non-mission critical accessory, try just turning the key on to see if the house battery will charge the starter battery enough to get you going. Oh and one more lesson, don't procrastinate like me.
randy
Very helpful, thank you. If I'm understanding correctly, to take advantage of this system all of my auxiliary items should be powered by the second battery, which in turn gets charged while the vehicle is on. The factory battery is only responsible for its factory designated tasks of starting and running the vehicle?
DaveInDenver
Middle Income Semi-Redneck
My rough division is things that are generally only used with the engine running can stay on the main battery, e.g. anything in the original harness.
The OEM radio is something I would move if rewiring my truck wasn't a pain, so it stays because I also like clean wiring and especially when it matches the wiring diagram the factory provides. Further, I feel this is acceptable because in my case Toyota provides a time-out or ignition-only feature for the dome light, headlights, radio so that the risk of running the battery down is low.
Things that I add go to the aux battery, two-way radios, accessory lighting, fridge.
The only exception is the winch, which I feel defaults to the starting battery because it normally is only used with the engine running and is more of a large current, short duration discharge that isn't good for a deep cycle battery. If your aux battery is dual purpose then running the winch from it is possible as long as the wiring from the main battery and/or alternator is sufficient to do that safely.
The OEM radio is something I would move if rewiring my truck wasn't a pain, so it stays because I also like clean wiring and especially when it matches the wiring diagram the factory provides. Further, I feel this is acceptable because in my case Toyota provides a time-out or ignition-only feature for the dome light, headlights, radio so that the risk of running the battery down is low.
Things that I add go to the aux battery, two-way radios, accessory lighting, fridge.
The only exception is the winch, which I feel defaults to the starting battery because it normally is only used with the engine running and is more of a large current, short duration discharge that isn't good for a deep cycle battery. If your aux battery is dual purpose then running the winch from it is possible as long as the wiring from the main battery and/or alternator is sufficient to do that safely.
Thank you. One last post and I think I've answered all my questions (for now).
My confusion above in my first post about the fuse panel- if I'm understanding correctly now, the wire from the fuse box (that's only powered with the key on) just allows the solenoid to open, allowing power from the alternator to charge both batteries. Then with the key off, the batteries are separated and any aux items I have running is just draining the battery power. Correct?
Reposting the original diagram for ease of reference:
DaveInDenver
Middle Income Semi-Redneck
With the 'on' controlling, the solenoid will connect the batteries during cranking or winching (with the engine running). That may or may not be what you want. Generally deep cycle batteries won't like being asked to supplying cranking current, although in the circuit it may not be a problem since the starting battery will probably do most of the work either way. The Yellow Top in your diagram wouldn't care, although wire and fuse sizing may be insufficient. Most commercial combiner/isolators have a delay built-in or a way to start-defeat the solenoid that prevents this.
dwh
Tail-End Charlie
Right idea, but you got the terminology backward.
In electrical, open means disconnected, closed means connected.When you turn the key on (ign hot), that energises an electromagnet (the coil) which then pulls down a heavy contact bar which bridges the two large battery terminals on the solenoid.
When the batteries are connected, we say that the circuit is closed. When the power is removed from the solenoid, the batteries are no longer connected, and we say the circuit is open.
Yes. Factory items will be drawing from the engine battery, extra stuff you added from whichever battery you connected the extra stuff to.
Right idea, but you got the terminology backward.
When you turn the key on (ign hot), that energises an electromagnet (the coil) which then pulls down a heavy contact bar which bridges the two large battery terminals on the solenoid.
When the batteries are connected, we say that the circuit is closed. When the power is removed from the solenoid, the batteries are no longer connected, and we say the circuit is open.
Yes. Factory items will be drawing from the engine battery, extra stuff you added from whichever battery you connected the extra stuff to.
Thanks, I guess I knew that but I work in emergency medicine where IV lines and others are open=things flow and close/clamped=no flow. I understand how it is different for those magic little fairies that flow through wires to make light and turn motors.
200amp weather proof connector
I've read/skimmed through all 77 pages of this thread. Thank you, its been educational. Im about ready to start my build but have one last question.
I plan on mounting my battery in a box that can be removed from my bed while I am daily driving my truck. I plan on using 2AWG wire and want to have a quick connection inside the bed. This way I can plug and unplug the battery box.
Is there a connector that is weatherproof and able to handle the emergency jump if needed? I could remove the box or run jumper cables but if the existing system could handle the load then I wouldn't have to.
Thanks
I've read/skimmed through all 77 pages of this thread. Thank you, its been educational. Im about ready to start my build but have one last question.
I plan on mounting my battery in a box that can be removed from my bed while I am daily driving my truck. I plan on using 2AWG wire and want to have a quick connection inside the bed. This way I can plug and unplug the battery box.
Is there a connector that is weatherproof and able to handle the emergency jump if needed? I could remove the box or run jumper cables but if the existing system could handle the load then I wouldn't have to.
Thanks
Hillbilly Heaven
Explorer
Anderson SB350 connectors with boots and covers will work great for what you want.
patoz
Expedition Leader
I would use Anderson SB175® Connectors, which are rated up to 280 Amps. These are not waterproof, but their design make that almost irrelevant. Rubber Dust Caps are available for them, so you could cap the one left in the bed when you remove the battery and just make sure it's pointing up to keep out the majority of the water. People use these for mounting removable winches, jumper cable attachment points, and other types of equipment, and I've never heard about any problems cause by rain.
https://www.amazon.com/Anderson-SB175-Quick-Connect-175/dp/B00DK88XU8
http://evwest.com/support/Anderson-175.pdf
https://www.amazon.com/Anderson-SB175-Quick-Connect-175/dp/B00DK88XU8
patoz
Expedition Leader
The OP said 200 Amps which is why I suggested the SB175 connector, but I would go larger myself also, just to be on the safe side.
Thanks for the heads up on the boots. I haven't seen those before, so I looked them up.
https://www.amazon.com/Heavy-Duty-P...=8-1&keywords=Anderson+SB+ENVIRONMENTAL+BOOTS