2nd Battery Install-Isolation

[trailrider]

My Chevy Silverado had place to mount a second battery up front. I bought a group 24 deep cycle from Walmart which fit the tray perfectly. I bought the factory hold down clamp. I was fortunate to find very heavy battery cable with lugs already attached. Napa, Autozone and Oreilly have premade cables. I did have one cable custom made at a battery shop. I wanted heavy gauge for fast charging.

For isolation I went old school like my previous motorhome. I used a high amp solenoid to isolate the deep cycle batter from the starting battery-charging system. A solenoid is an electrically operated switch. It operates via a coil. All coils create an inductive load when they are de-energized. Do not connect this directly to a switch or your trucks electrical system. It needs to be driven by a separate relay. Even a relay can create and inductive load which is bad for modern computer vehicles. You need to get a relay with a built in flyback diode that prevents this from happening. I found the solenoid at etrailer and Napa has relays with flyback diiodes. All cables and connections to the batteries need to be fused. My truck already used a large 175 amp fuse at the cable. I bought some and fused both sides of my cable at the battery connections. If the solenoid is off both cables need to be protected.

Aux battery installed in spare battery tray.



Fused connections


Cables Installed


Solenoid and relay

 

[trailrider]

I could not find a key switched power source that only worked in the run position. I chose to install a manual switch on the dash. I control when I want to charge my auxiliary battery to charge. There is a light on the switch that reminds me when the auxiliary battery is connected. If my starting starting battery fails I can flip the switch and use the auxiliary battery to start the truck.



Switch with indicator light (from RadioShack)

 

[ntsqd]

Just a note of caution; if the starting battery just needs a little boost the solenoid should be fine. If it's flat then attempting to jump thru the solenoid will likely damage it. I've never seen a parts house source-able Constant Duty Solenoid rated for more than 200A and starting loads can easily be double that or more.

I usually wire a marine type battery bank switch in parallel with the charging solenoid. That way I can select which battery to start from, or both if desired or needed. I didn't do this on our CTD, because I don't think that the 6 ga.that I used is good enough considering the run length.

 

[trailrider]

Very good point. Thanks for the reply. I could probably use a jumper cable to utilize my auxiliary batter for starting.