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

evldave

Expedition Trophy Winner
Time for another update!!!

Thanks to dwh, we now have fully grounded switches in our cab! Please note that you can't run the switch power off a Duracell battery - that is for illustrational porpoises only!
I caught an error myself - remember to use the same gauge wire for ground that you use for power! I had the diagram with 4GA ground in the 'high-current' circuit...not a great idea! It's been upgraded to 2GA

Making the system modular on the cheap

So, you want to make it so you can quickly disconnect your solar panel? Easy! Use a weatherpack connector!

Get them from our friendly Amazon tribe HERE - you only need a 2-pin connector. Just wire it in between the charge controller and the battery. Then, when you want to disconnect your solar circuit, just unplug the connector! (note: to prevent risk of fire or explosion, disconnect the sun from your circuit before unplugging the weatherpack connector).
Addendum: If you want to leave the charge controller plugged into your battery and just disconnect the panel, you can do this by moving the weatherpack connector between the panel and the controller. See how easy, cheap and flexible this is????​

So you went right out and wired up your trailer based on the first diagram and now you are wondering how to disconnect your trailer? Yes, I forgot trailer disconnects!

Easily fixed! Go HERE and buy part number SB50. Then just wire this into your 4GA wire where it shows in the new diagram (the connector is for 6GA, but you can shove the wire into the connector and using the smaller connector is important for...). While you are at it, order a few extra connectors of the same size (we'll need them later on in this thread, trust me:))

Here's the new diagram!

Changes:


  • Added ground for switch and illustrated power source in dash
  • Updated ground wire in high-current circuit to 2GA
  • Added connectors to both solar and trailer circuits
  • Changed main power lines to red to make it easier to see

 

dwh

Tail-End Charlie
Boy oh boy. That's like Viagra for electricians. Makes me wanna stick my tongue on a 9v battery!
 

dwh

Tail-End Charlie
And if all else fails, you can always call in a U.S. Navy electrician:

[video]http://www.videodetective.com/movies/down-periscope/6290[/video]
 

LaOutbackTrail

Adventure Photographer
Thanks for the info. I'm a visual learner.... words just blur together. I only look at picture books and magazines.... for the pictures. :drool:Never said I was smart or 'nuthin.
 

pods8

Explorer
Anyone bought those 4ga 20' cables in the first post? If so they okay looking or cheap wire? How fine are the strands and how flexible is the wire?
 

dwh

Tail-End Charlie
I don't have that exact set, but I do have a cheapo set of #4 jumper cables. The wire is VERY flexible, though I haven't bothered to even look at the strand count. The insulation is...eh...fairly tough, though not real tough.

They are a helluva lot lighter and easier to work with than my jumpers made of welding cable.
 

pods8

Explorer
I don't have that exact set, but I do have a cheapo set of #4 jumper cables. The wire is VERY flexible, though I haven't bothered to even look at the strand count. The insulation is...eh...fairly tough, though not real tough.

They are a helluva lot lighter and easier to work with than my jumpers made of welding cable.
I'd be running stuff in a loom anyways its got potential.
 

evldave

Expedition Trophy Winner
Anyone bought those 4ga 20' cables in the first post? If so they okay looking or cheap wire? How fine are the strands and how flexible is the wire?
I have basically the same set, been running them from the engine bay to rear of my rig for quite a few years. They run exposed along the frame rail and I haven't seen any abrasion that's anything close wearing through (except where I ran them too close to the exhause :)).
 

evldave

Expedition Trophy Winner
What program do you use for these awesome diagrams?
Thanks
I use Microsoft Visio...and a bunch of google image searches. Could do a whole schematic diagram if I wanted (plenty of stencils of electrical circuits) but I like the pictures, makes it really easy to visualize.
 

Smith

New member
Many thanks for the diagrams, they're fantastic and REALLY help. I'm just about to install my second battery and found this thread...now i'm making provisions to add a solar array the cap...i'm noticing an inverse relationship between amperage flow and cash flow....

Few questions:
- Does the setup assume that the solenoid is not engaged while cranking the engine? Meaning the 'on' source from the Truck's Fuse Block is not actually 'on' until the engine has started? I'm guessing the vast majority of automakers disengage all electronics during ignition except for the starter?
- What would the difference be if I used a 'battery isolator' instead of a 'solenoid'? I see WARN makes one...
- What would be the best quick-disconnect for the 8GA solar power? I see the weatherpack typically only accomodate up to 10GA...
- Is there a problem with running accessory lights, radio, etc from the solar to battery connection or should I run a separate wire from the battery out to these devices?
 

evldave

Expedition Trophy Winner
Many thanks for the diagrams, they're fantastic and REALLY help. I'm just about to install my second battery and found this thread...now i'm making provisions to add a solar array the cap...i'm noticing an inverse relationship between amperage flow and cash flow....

Few questions:
- Does the setup assume that the solenoid is not engaged while cranking the engine? Meaning the 'on' source from the Truck's Fuse Block is not actually 'on' until the engine has started? I'm guessing the vast majority of automakers disengage all electronics during ignition except for the starter?
- What would the difference be if I used a 'battery isolator' instead of a 'solenoid'? I see WARN makes one...
- What would be the best quick-disconnect for the 8GA solar power? I see the weatherpack typically only accomodate up to 10GA...
- Is there a problem with running accessory lights, radio, etc from the solar to battery connection or should I run a separate wire from the battery out to these devices?
#1 - I'm not sure. I've never checked mine to see if it disengages while actually starting the truck. If it doesn't disengage, you could hypothetically be 'mini jump starting' your battery if you just turn it on and don't start the truck right away.
#2 - Depending on the type of isolator, they are essentially two diodes that prevent current from running back between batteries. For your typical cheapo isolator, they will use regular diodes, which will result in a 0.7V drop across the diode - not great for charging batteries! More advanced isolators don't have the voltage drop so they work great too (but are generally more expensive than a cheapo solenoid)
#3 - hmmm, not sure on waterproof 8ga quick connects...you could downgrade to 10ga wire and use the weatherpack...10ga should handle 120W solar no problem (that's only 10A or so, which means you could even get away with 12 or 14ga, but remember, bigger wire = less voltage drop over distance :))
#4 - as long as the accessories are connected to the battery and not the charge controller, you should be ok. Technically you could connect them to the charge controller, but it's better to have them ties to the battery (as use fuses!). Don't connect accessories directly to the panel - the output of the panel changes with sunlight and you could under or overvoltage your accessories. That would be bad.

I'm sure someone else will chime in if I'm wrong here :)
 

dwh

Tail-End Charlie
All diode type isolators have a voltage drop across the diodes. Good ones just have less voltage drop.

The voltage drop doesn't really matter until the battery approaches a full charge. Then, with the diode isolator, the battery will always be, in evldave's example, .7v below full charge. That's a significant amount.

The voltage drop though a wire is a little different. It varies depending on load, so as the battery approaches full charge, the amp flow gets less, and so does the voltage drop. So even if there is a voltage drop though a wire at high load, eventually, the battery will reach full charge voltage as the amp flow reduces and the voltage drop goes away.
 
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