Hey fellas, I guess this isn’t really a 7.3 question but maybe you can help me anyway?

What is this solenoid used for? Can I run a heavy ga. wire from it to my two deep cycle batteries (in the bed of the truck) to charge them while driving but isolate them from the starting batteries when the truck is off? Or is it not that simple?

I have a fridge and cpap unit I use for camping that I run off of the deep cycle batteries but they only last a few days in this heat (fridge runs a lot). Would like to charge them while driving if that makes sense. Don’t want to be left with dead starting batteries while out in the boonies.

 

My camping setup is primitive but man that fridge is worth its weight in gold. Cpap keeps me breathing so that’s cool too lol!

 

That looks like the starter relay on the fender of an up to 2001 MY. If it is, you can hook off of there with no problem but I can't tell you how well that will charge your batteries. And yes, it would be a good idea to have it disconnected when not running.

 

Your best bet is to buy a battery isolator. They have several uses and are for exactly what your looking for. They can be found at any good auto parts store, RV store and online and a very affordable. I have included a link to a cheap one on Amazon.

 

I'm assuming you have tow package on your truck. What I did with mine is upgrade the charging circuit for the 7-pin plug because the factory wiring wasn't worth it's weight in copper any more. Only about 13.1 volts arrived at the trailer battery with most of the voltage drop being in the truck's wiring. You can take this plan and use it for your own needs. I found a 250 amp relay online somewhere and built an 8 guage circuit, throttled it down to 30 amps with a circuit breaker and used the exciter leads for the existing trailer charge relay to activate this one. I think it doesn't switch on until the alternator is charging, but don't quote me on this. This setup would be perfect for charging your aux batteries while the engine is running, then when you cut the ignition the relay shuts off and the two systems are separated.
Basically tie into the two smaller wires on the trailer charge relay that you see is unplugged in the picture for illustration and use those two to the two small spade terminals on the big relay to turn the relay on and off as the truck is operated.
Make new wiring from the battery to the relay and then from the relay to the aux batteries in however fashion that you decide.

 

I need to add to this that the picture of the relay shows one post covered up with a piece of heat shrink to the left and behind all the other connections. Reason for that is it's a "switching" type relay. When the ignition is off, the post I insulated has power. The other post would be turned off. When the relay is activated, it switches which output post has power and the other post goes dead. Handy feature for someone who wants to have that type of circuit, but since I didn't, I covered up the one that goes hot when the key is off.

 

Thanks everyone for the help! I’m taking notes might try and tackle this one sooner than later.

 

Watch out that the "Battery Isolator" doesn't have Voltage Drop across them.

some of the cheaper ones just use a heavy Silicon diode, and that will cause 0.7 volt drop across it.

I prefer to use a Starter Relay/Solenoid, like I put on my water wagon to run the water pump so we can water our new trees. Trigger it from the Ignition switch somehow... Running Lights, etc...






This is a RV Water Pump, puts out 50 psi and 5 gallons per minute.




I put a Spigot on the 55 gallon water barrel, because the pump will dribble water out thru the hose and eventually empty the barrel.

The oil bottle is for the Chainsaw, you can't see it.

 

Thanks John, I googled it a bit as well and I’ve been over complicating it—I have a habit of doing that lol.

So key switched power to the solenoid…. Just use a fuse tap or something different? I don’t really want to splice into factory wiring all that bad.

Thanks again fellas.

 

Yes, finding switched power and using that will work just as well to run the relay of your choice. One thing you need to watch out for is making sure that the relay you do purchase is rated for "continous duty" Starter relays are not, repeat NOT "continous duty". Make sure whatever you get has that rating or it will burn out the coil and quit working. Ask me how I know....

 

I would like to echo the thoughts from Kwikkordead about "continuous duty". This is very important in an effort to not create an electrical fire or a critical system short.

Also, the Victron isolator that truckeemtnfords linked is likely not plagued by the voltage drop condition John mentioned. Victron is a top class supplier of electrical components in the solar and 12v - 48v capacities. Their components are often considered a benchmark within the category.

That is not to say that there are not many other electrical component suppliers that could meet your requirements, but I would and have recommended Victron to a friend.

Choose wisely sir, electrical is easy to get right, but it is easy to get wrong as well.

 

In My Defense about Isolators,
I am an old electronics geek from 1958 who has seen his fair share of "junk" sold to the innocent.

I did not "research the above mentioned device"

 

Just about every one of those blue finned isolators are a guarenteed voltage drop. I quit using them decades ago and have just used relays with 100% success rate on recharging auxiliary batteries from discharged state. I just want to emphasize that the charge circuit needs to be throttled with a self resetting circuit breaker or the alternator will soldier up and go max charge. I don't want to see anyone burning up their alternator and/or the wiring system.
Here is a 30 amp circuit breaker like I used on my truck. $4.29 is very inexpensive insurance.
https://www.napaonline.com/en/p/BK_7...pressionRank=1

 

Sorry to sound dumb but where does the circuit breaker go in the circuit? Is it the same as using an in-line fuse?

Thanks again I really appreciate the help!

Edit: I know the difference between a fuse and a breaker just wondering if they both offer the same protection for the alternator? Don’t want that ol’ girl to burn up!

 

Voltage Drops.

when I hooked up my Tilt Bed motorcycle trailer to the Excursion last June, the lights were so pathetic as to be useless.

the "ground wire" in the 7 pin connectors is a Joke....

I put a big Ring Terminal on a piece of 12 ga Automotive Primary wire, and screwed it to the trailer frame.

I then "in a hurry" just clamped the other end of my "new ground wire" to the truck's bumper with a pair of Vice Grips, which I squirmed back and forth so they bit deep into steel, not paint....

Now, the trailer lights are Twice as Bright as the Excursion's tail lights, the effect on traffic behind me is enormous, they don't crowd me anymore when I am stopping.

that was a hurry up fix, when I discovered the trailer lights were for chit....
I needed to go "NOW", not tomorrow.

I later fixed a good short "Ground Wire" with a plug on it on the truck's bumper near the hitch..... all of those Receiver Hitches are for crap, when it comes to good grounds.