solar panels and tow vehicle

[RPAspey]

I am in the process of installing a solar panel system in my 2000 Cherokee. As I do so, I keep realizing there are more and more things I haven't given thought to. Most of the time I am able to find the answers by researching on-line but not this time. here goes..

Do I need a blocking diode to prevent the solar panels from backfeeding to my truck?

I have a 2007 Tundra with the big V8, a Prodigee brake controller and of course my 2000 Cherokee. I'm worried that while towing, the charge controller would go into bulk mode and the higher voltage might somehow damage the brake controller or my truck electronics. I've always unplugged the camper from shore power before hooking up to my truck as a precaution. Any thoughts?

I'll post pictures of the install when completed.

[Herk7769]

I am at a loss. You plan on connecting the panels and its controller to the truck's electrical system?

Now THAT is risk taking. (May even be "chance" taking!)

If I was doing what you are trying to do, I would just have a long DC extension cord to hook up to the camper when we are in camp or use the unused "AUX" pin (the center one on most 7 pin Bargman connectors) to connect the panels to the trailer while connected but without the engine running. When the engine is running (key "ON") the alternator is connected to the camper. I think you would also need a "kill" switch to the aux power and remember to turn off the panel controller before you started the engine.

IMO, trying to fix keep the panels from feeding back through to the trucks alternator and starting battery with a blocking diode would require a fairly large capacity diode to handle say 30 amps or more the panel controller is capable of putting out.

[Rod Johnson]

You'll be fine.

There is already voltage potential on your truck's electrical system from the battery. And most likely from your converter when plugged into shore power. Its trying to charge your trailer batteries and of course your truck battery through the trailer plug.

You also do basically the same thing when you hook up jumper cables from another vehicle.

And, while you are towing and your alternator is running, the charge controller will see 14-18 volts and not try to charge anything.

I do have a question for you. Are you installing a shutoff on your panel array? I mounted my solar charge controller and started running the wires. I realized that if I had to do any work on the system, I'd have to climb up on top of the trailer and put some cardboard or blankets on the solar panels. I thought maybe a shutoff switch right there would be safer. Also, are you fusing the solar power lines near the panels?

[09grizzly1]

Hey herk.I think his concern is that with the solar system on the trailer hooked to the trailers batteries,it would would feed to the truck and cause damage to the electronics in the truck.If this was a problem,the solar panel companies would include a diode in the kit.So no,there would be no problem without a diode.

09grizzly1

[buffalohunter]

I'll be watching this thread, and looking forward to the pictures.

[Fire Instructor]

You'll be fine. It makes no difference where a 12v power supply to the batteries comes from, or even if it comes simultainiously from multiple sources. If properly wired, you can charge your batteries from the solar, from the built-in "factory" inverter, or from the 12v suply from he tow vehicle. The tow vehicle supply is the least effective, due to wire size and length of run.

[RPAspey]

Rod,

Yes I'm using finger safe fuse attachments on the fuse block. I have limited space where the controller is going. I wish I had space for the knife switches and fuse blocks. Check out the picture.

You bring up a good point about the voltage from the alternator shutting off the charge controller. Thats another problem. It would be more efficient to charge from the panels from solar while traveling instead of the 10amp limited power from the truck.

I spent the day running the #4 wire. Of course nothing could go easy, first I had to move the radio antenna, then I had to drill up thru a wall in order to get to the junction box (without damaging the wall board). I ran the cables from the junction box thru the hole where the antenna was originally located, down the inside of a wall and into the area where the charge controller is located. In the middle of all this I accidently stabbed my arm with a knife resulting in a pretty bad gash. To top it all off, one of my wife's students was helping me so I had to behave and not let any bad words slip.

Oh, this is a not a kit system. I didn't like the prices of kits nor did I like the specs on most of them. So everything is "piece meal" but not junk.

thanks for the help everyone.

[RonLynnJr]

Originally Posted by Buffalohunter

I'll be watching this thread, and looking forward to the pictures.

Indeed, this is very interesting.

[Herk7769]

Originally Posted by RonLynnJr

Indeed, this is very interesting.

Ditto; on the very interesting.
While not convinced (I do have a hard, and opinionated, head), I will stand by to see how this all works out.

Without a key in the ignition there is no path from the trailer plug to the vehicles batteries due to the relay in the engine compartment fuse block.

Current is only supposed to flow from the alternator to the truck batteries and the Bargman plug when the engine is running. Current will not flow from the truck batteries to the camper or vice versa with the ignition key off.

If the camper is plugged into shore power and you connect the camper to the truck via the Bargman connector; the truck's battery should not charge. Easy to check and I will tomorrow. Since camper is in the driveway and the truck is in "Pre-Contact" position and easy to plug in. 13-14 volts or so should show up on the battery if Rod is correct.

Could I convince you to post a wiring diagram of your proposed installation? Always interested in learning something new.

[D-mo]

count me logged into this too .. cause i am really scatching my head ..
please at least give us the specs on the RV .. it could be a tent trailer for all i know..

d-mo

[Herk7769]

Originally Posted by Fire Instructor

You'll be fine. It makes no difference where a 12v power supply to the batteries comes from, or even if it comes simultaneously from multiple sources. If properly wired, you can charge your batteries from the solar, from the built-in "factory" inverter, or from the 12v supply from he tow vehicle. The tow vehicle supply is the least effective, due to wire size and length of run.

Fire Instructor,

I am making an assumption here that the batteries you are referring to are the camper's batteries and not the trucks starting batteries.

With that in mind you are correct that "It makes no difference where a 12v power supply to the batteries comes from." The highest available voltage will drive the charge. If the solar controller is providing a higher voltage than the onboard "converter"; that will be the battery charger; if the converter is outputting a higher voltage; it will. The truck's alternator also provides charging voltage and for it to be the charging source it would have to output a higher voltage than your solar controller.

I do see the logic that putting an external "plug in" charger on the truck battery does not damage the truck's alternator. I assume that is because the bridge diodes in the alternator become reversed biased and block the incoming voltage.

How that will work with the solar panels mounted on the truck is not clear to me. Without a diagram, I just can't get my head around it.

To use the onboard converter, you need shore power as you know. It "converts" 120VAC to 12 volt nominal DC. Inverters take battery 12 volt DC power and make 120VAC for use in your TV and coffee maker. If you have shore power there is no need for the truck or the solar panels to be running.

[Fire Instructor]

Originally Posted by herk7769

Current is only supposed to flow from the alternator to the truck batteries and the Bargman plug when the engine is running. Current will not flow from the truck batteries to the camper or vice versa with the ignition key off.

Herk - My Dodge isn't wired that way. In fact, look at my posting from earlier today on my solar mod, and you'll see that just having the TT plugged into the truck confused the HECK out of me earlier today.... I recall an old thread from the "other" forum, that said that Dodges could be wired, or changed, from always powered to powered when key is on with a very minor wiring change under the hood.

[Fire Instructor]

Originally Posted by herk7769

Fire Instructor,

I am making an assumption here that the batteries you are referring to are the camper's batteries and not the trucks starting batteries.

To use the onboard converter, you need shore power as you know. It "converts" 120VAC to 12 volt nominal DC. Inverters take battery 12 volt DC power and make 120VAC for use in your TV and coffee maker. If you have shore power there is no need for the truck or the solar panels to be running.

Yes, I was refering to the TT batteries, and NOT the tow vehicle batteries.

The "onboard converter" in my Rockwood is actually a 120v distribution panel, with a built-in converter. If I turn the 120v breaker that runs the converter to the off position, the 12v is fed by only the solar panels, I can then plug the 120v feed for the TT into my Xantrex, and have 120v available at all of the outlets, plus the outlets are still protected by the breakers in the distribution panel.

<WOW! I had to re-read that twice to make sure that it made sense.... I sure hope it makes sense to SOMEONE!>

[Herk7769]

Just spent over an hour with Volume 3 of the GMC service manual.
That is the one that covers the wiring and electronics.

It is just too darn complicated to predict what the outcome will be to the computers and electronics. So, I give up and put this one in the "too hard to do" pile.

Good luck and good night.
I need a

[Rod Johnson]

Originally Posted by herk7769

Without a key in the ignition there is no path from the trailer plug to the vehicles batteries due to the relay in the engine compartment fuse block.

Originally Posted by Fire Instructor

Herk - My Dodge isn't wired that way.

Yeah, neither is my Chevy. I'm sure it varies from year to year and model to model.

I wasn't sure, and verified two ways.

With my truck running, the battery monitor in my trailer indicates the batteries are charging. Probably because the 14.4V output from the alternator.

With my trailer on shore power and the converter charging, and with my truck off, I'm seeing 14+ Volts at my truck battery with a multimeter.

Short of ohming out the wiring from the bargmann connector to the battery with the ignition switch off, I'm pretty sure they are hardwired to each other.

I might also add that I've had my truck well apart several times. The first week I had it, I put in a substantial car stereo. That included some mods to the battery, alternator charge wire, and underhood fuse box. It was at this time I found that Chevrolet left 2 wires disconnected from the factory for the trailer brakes. Not knowing what they were for, and assuming The General put my truck together right, and assuming I must have forgotten that I disconnected them... I just plugged the blue wires together, and slipped the red wire with the ring terminal over the bit +BAT terminal right there.

Later that month I installed a pretty crazy remote starting alarm... Never again... And of course the offroad lights and junkyard factory foglights... Did I mention that alarm? And stereo?? Yeah, I've taken that truck WAAAAAY apart and cut my knuckles on sharp spots even the UAW doesn't even know about.

[Herk7769]

Hmm. Might be 2500 specific. I have a trailer plug light that I use in the Bargman socket in my truck bed. It only works if I have the ignition on.

Like I said, the truck is set up for the test tomorrow.
I will let you all know what I find.

[Rod Johnson]

Originally Posted by herk7769

Hmm. Might be 2500 specific. I have a trailer plug light that I use in the Bargman socket in my truck bed. It only works if I have the ignition on.

Like I said, the truck is set up for the test tomorrow.
I will let you all know what I find.

I was just thinking about that...

Hell, maybe I put that ring on the wrong terminal? And its not fuse protected like its supposed to be.

[Herk7769]

This is the correct connection.
You are correct.
It is hot all the time. If the camper is powered it should provide charging current to the truck battery.

I still have concerns about hooking up the solar controller at a random location in the truck.
Lou

[Rod Johnson]

Originally Posted by herk7769

This is the correct connection.
You are correct.
It is hot all the time. If the camper is powered it should provide charging current to the truck battery.

I still have concerns about hooking up the solar controller at a random location in the truck.
Lou

Look at that. This post proves you're a standup guy. And trust me, that goes a long ways.

I would add that for the most part, my tow vehicle sits unused between trips. 2004 model, and it has 30k miles on it. I go through batteries like oil filters, like windshield wipers, like car washes?... Seems like everytime I'd go out to use it, the battery would be dead. And of course, then the battery would never be quite right again. I leave the trailer on shore power because it keeps the truck charged up. I mentioned that ridiculous remote starting alarm right? It sucks all sorts of power.

Can't wait to finish up this solar project. I'm learning so much, I hope to run my workshop off grid. Then I can keep all my project cars nice and freshly charged.

[Herk7769]

Originally Posted by Rod Johnson

Look at that. This post proves you're a standup guy. And trust me, that goes a long ways.

I could claim it was an April Fool's Joke; but that would just be silly.

I am still going to check out the truck Bargman light issue. It will only work with the ignition on. It may draw its power from the parking light circuit.
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