So I did a mode to my truck for a third source of charging. I know the guys will say its inefficient and ill blow up my alternator etc etc..The camper package battery has a fuse behind the batt. Impossible to get to without removing battery..This battery powers the 7 pin and has an isolator. I can leave the truck plugged in all night to parallel with my other two batts on trailer.\So I removed the 40 amp fuse and replaces with 100 amp breakerSo with dead batts on the camper I can push 16 amps or so through the 7 pin. But hardly nothing pulling while dry camping. It seems it pulls 95% from the camper batts first, especially at high draw.So I made this mod with 6 gauge direct off aux batteryUpon a few tests with 6 gauge wire and a andreson plug tied to the 40 amp mega fuse, the fuse would blow.I had an extra 100 amp breaker so I removed the mega fuse and replaced it with this set up. I can now parrellel my RV batts with the truck with this 100 amp 6 gauge set up.Running a 70 amp load off inverter and with truck running, the truck supplied the whole 70 amps. This is fine. Im happy with this set up but,,,,,I know ohms law comes to play here. When im plugged into the TT and all 3 batts are parrellel the truck batt still seems to not pull the amps as the two camper batts. ( with truck off)Example if im pulling 20 amps from TT batts I may only be drawing 2-3 amps from truck batts.Is there anyway to correct this? I can push fine but cant pull very well.I have a similar connection on the TT batts side. I connect this when dry camping. ( as seen in short vid)Its about 11 ft of 6 gauge winch cable.Just a side note possibly the isolator is faulty? I wouldn't think so if it pushes amps properly. It would work both ways I assume. Also it is a GRP 78 - 70 AH batt. Ratted at the 20AH rating per exideShort video.Charging off alternatorPics

lawrosa wrote:Upon a few tests with 6 gauge wire and a andreson plug tied to the 40 amp mega fuse, the fuse would blow.I did the same mod several years ago so I could load support my single G27 trailer battery with my Avalanche but since it didn't have an aux battery I pulled directly from the truck battery with it running. I used 10' of 4 gauge booster cable for minimal voltage drop and that worked well ... what didn't were those same Anderson SB-50 connectors it looks like you've used, which burned & melted. I recently bought a new 4 gauge booster cable and this year will be load supporting my new G31 AGM trailer battery with my Silverado but this time I won't be using those d***** Anderson connectors but instead will clamp directly from the truck battery and truck chassis ground. I still have those Andersons and can take pics if you need proof ... JMO but I'd get rid of them before yours too melt.

SoundGuy wrote:lawrosa wrote:Upon a few tests with 6 gauge wire and a andreson plug tied to the 40 amp mega fuse, the fuse would blow.I did the same mod several years ago so I could load support my single G27 trailer battery with my Avalanche but since it didn't have an aux battery I pulled directly from the truck battery with it running.I did the same with my old truck and why I did it to this one. I used it on the old truck for charging. This one I want to use for both charging and adding the third batt with heavy gauge wire instead of 7 pin. I used 10' of 4 gauge booster cable for minimal voltage drop and that worked well ... what didn't were those same Andersen SB-50 connectors you've used which burned & melted. Really? They good for 120amps I believe. I bought these KFI products connectors. Ill keep an eye on them. I ran 60 amps on my other truck through them with no issues.Yeah post a pic? Did you make the ends yourself? I always crimp and solder when I can.https://www.kfiproducts.com/quick-connect-ends.htmlI recently bought a new 4 gauge booster cable and this year will be load supporting my new G31 AGM trailer battery with my Silverado but this time I won't be using those d***** Andersen connectors but instead will clamp directly from the truck battery and truck chassis ground. I still have those Andersens and can take pics if you need proof ... JMO but I'd get rid of them before yours too melt.[COLOR=]Just a note the silverados are BCU controlled. Meaning the volts are controlled by the computer.I charge as high as 15.5 volts. I see 14.5 volts at the 7 pin. And during my test the truck ramped up to 15.3 volts. There is a sulfation mode on these trucks. I got 11 years out of the original batterys.Its a very good charging source for camping IMO.RVC system Silverado

electricity follows the path of least resistance. so when your truck is off the easiest less resistance path is from the camper batteries. when your truck is running the alternator is putting out 14 or more volts at whatever current it can produce at the rpm of your alternator pushing it to the camper. that is why it works great with the truck running. can you make it work better with out the truck running? you could lower the resistance by increasing the size of the 6ga wire. or others have talked about using buckboost dc to dc converters.

This is the 4 gauge load support cable I made up using Anderson connectors and yes, each connection is soldered. Closeup pic of this one connector isn't the greatest but I can assure you it is severely burned, as are the other 3 I used to make up this cable.When I went looking recently for a new booster cable I would have preferred 2 gauge or even 1 gauge but anything sold around here in those gauges are too long and way to expensive so I settled on a reasonably priced 4 gauge that's 16' long. I'll be mounting my new G31 AGM in the front pass through storage compartment so connecting to it with this booster cable won't require opening up a locked battery box. If it turns out I don't need all 16' to reach from the truck to the trailer battery I can always shorten the booster cable and thereby further reduce voltage drop under load. I just ordered a clamp meter which will allow me to determine how much support the truck is providing with it running but based on my previous use I'm sure it will support my new G31 just fine when powering my toaster or coffee maker with the inverter. It's certainly a cheaper option than investing in two G31 AGMs and although not a practical solution for those who dry camp all the time this will work just fine for my limited requirements.

Sound guy,Very nice. Im glad someone else thinks like me.. LOL..Any fuses?So you have a 31 now and you are adding a 31? Whats that box all the way forward? Brakes?

Second battery doesn't pull amps but I can push 70+ amps

theoldwizard1
Explorer II
Mar 20, 2018
lawrosa wrote:
theoldwizard1 wrote:
What you really want is about 13.8v-14.0V AT THE RV BATTERY TERMINALS, but you have no way to control this ! The vehicle voltage regulator is "sensing" voltage far from those batteries. If you had an alternator with an externally adjustable regulator, you could crank it up to the desired voltage, but the battery in the vehicle would probably be seeing close to 15.0V and it will be boiled dry.

Thats the thing. With the truck running and all batts full anyload comes right off the alternator. The battery itself was only getting .3 amps when I had the 2.3 amps as shown in the pic above..

I would need to test when the batts are at 50%. Test the amps through anderson to RV batts, and test amps going into truck aux batt.

IMO should it split and what the batts want? Like 60 amps to RV batts and 20 amps to truck batt?

After a night of camping with all 3 hooked up I assume all 3 batt voltages should be the same. Say, 12.5 in am for example?

Read this DC-DC battery charging

If you want really fast/high current charging of the second battery in addition to the CTEK D250SA you will need CTEK SMARTPASS 120[/].
SoundGuy
Explorer
Feb 16, 2018
CA Traveler wrote:
This has the real potential to wake up with 3 dead batteries and the truck won't start.

Not only is the OP only talking about an auxiliary battery in his truck that he's connecting to the trailer, not the starting battery, there's still no need for anyone to ever be left stranded with a dead starter battery and no way to start the truck with the common availability of small, moderately priced, easy to store lithium battery jump starters, such as the PowerAll Deluxe I keep in my truck at all times.
lawrosa
Explorer
Feb 16, 2018
CA Traveler wrote:
Suggest you read up on unbalanced wiring and understand why those long wires from the truck have voltage drop especially at higher loads and charging and is part of the reason for your results. Battery amps will not split evenly (with 3 equivalent batteries) due to your unbalanced battery wiring.

lawrosa wrote:
My set up is only for when parked at camp. Truck will be plugged in during PM hours.

A quick start of truck for 30 minutes or so to get some amps in the batts in AM and let solar continue from there.
This has the real potential to wake up with 3 dead batteries and the truck won't start.

Batt on truck is aux battery with isolator. Does not affect start batt.
CA_Traveler
Explorer III
Feb 16, 2018
BTW The "best" solution is to have 3 equivalent batteries on the trailer, balanced wired and then the drain/charge amps will be the same for all 3 batteries.
CA_Traveler
Explorer III
Feb 16, 2018
Suggest you read up on unbalanced wiring and understand why those long wires from the truck have voltage drop especially at higher loads and charging and is part of the reason for your results. Battery amps will not split evenly (with 3 equivalent batteries) due to your unbalanced battery wiring.

lawrosa wrote:
My set up is only for when parked at camp. Truck will be plugged in during PM hours.

A quick start of truck for 30 minutes or so to get some amps in the batts in AM and let solar continue from there.
This has the real potential to wake up with 3 dead batteries and the truck won't start.
lawrosa
Explorer
Feb 16, 2018
You saw my short vid?

https://www.flickr.com/photos/93289479@N04/40251386231/in/datetaken/

My set up is only for when parked at camp. Truck will be plugged in during PM hours.

A quick start of truck for 30 minutes or so to get some amps in the batts in AM and let solar continue from there.

That way I don't need to lug generator out and such.. Generator is only for emergencies.

And frankly I don't want to carry it at all.
CharlesinGA
Explorer
Feb 16, 2018
lawrosa wrote:
Thanks for that... I have an isolator. 100 amps breaker and 6 gauge 11 ft. Why run to back of truck when I can make the connection at the front closer to the battery.

I see a flaw in my design. I need to breaker the RV batt side too...

Ill be getting one of these..

Blue sea makes them.

I was going to mention a Blue Sea ANL fuse or something to use at the tap of the truck batt.

My thinking is largely for charging trailer batteries while going down the road. Anderson connector at the back bumper and cables to the trailer batteries and as you drive they top off, even if very dead from use.

I'm in a Class C motorhome right now, so I have that mentality, but want to move to a 2500/3500SRW diesel truck and 22-25 ft travel trailer for a number of reasons.

Charles
lawrosa
Explorer
Feb 16, 2018
CharlesinGA wrote:
Anderson makes larger, heavier 175 amp connectors. You need to be using those. The 30 amp connectors are not enough.

Will read thru this completely in a moment, but it seems that using something like THIS Surepower Battery isolator, along with some 2 gauge welding cable in plastic jacketing and run along the frame rails, and a 175 amp Anderson connector at the rear bumper, would allow the trailer batteries to charge just like most motorhomes do.

Charles

Thanks for that... I have an isolator. 100 amps breaker and 6 gauge 11 ft. Why run to back of truck when I can make the connection at the front closer to the battery.

I see a flaw in my design. I need to breaker the RV batt side too...

Ill be getting one of these..

Blue sea makes them.
CharlesinGA
Explorer
Feb 16, 2018
Anderson makes larger, heavier 175 amp connectors. You need to be using those. The 30 amp connectors are not enough.

Will read thru this completely in a moment, but it seems that using something like THIS Surepower Battery isolator, along with some 2 gauge welding cable in plastic jacketing and run along the frame rails, and a 175 amp Anderson connector at the rear bumper, would allow the trailer batteries to charge just like most motorhomes do.

Charles
lawrosa
Explorer
Feb 14, 2018
What you really want is about 13.8v-14.0V AT THE RV BATTERY TERMINALS, but you have no way to control this ! The vehicle voltage regulator is "sensing" voltage far from those batteries. If you had an alternator with an externally adjustable regulator, you could crank it up to the desired voltage, but the battery in the vehicle would probably be seeing close to 15.0V and it will be boiled dry.

Thats the thing. With the truck running and all batts full anyload comes right off the alternator. The battery itself was only getting .3 amps when I had the 2.3 amps as shown in the pic above..

I would need to test when the batts are at 50%. Test the amps through anderson to RV batts, and test amps going into truck aux batt.

IMO should it split and what the batts want? Like 60 amps to RV batts and 20 amps to truck batt?

After a night of camping with all 3 hooked up I assume all 3 batt voltages should be the same. Say, 12.5 in am for example?

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Second battery doesn't pull amps but I can push 70+ amps

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