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lawrosa's avatar
lawrosa
Explorer
Feb 13, 2018

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

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.
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So I removed the 40 amp fuse and replaces with 100 amp breaker

So 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 battery

Upon 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 exide

Short video.


Charging off alternator


Pics







  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Feb 14, 2018
    First we need to establish a baseline.

    Disconnect the 2 batteries on the trailer and fully charge them. Disconnect the charger and let them "rest" for at least 30 minutes.

    What is the voltage on each battery ? If there is even a small difference in voltage on each battery, the lower voltage battery will drain the higher voltage one, even with no load. You can prove this with you ammeter !

    With the engine running, what is the voltage at the truck battery terminals ? Now what is the voltage at the Anderson connector ?

    Now plug the vehicle and RV together and measure the voltage at the RV batteries with no load from the RV. Last measure the voltage from the vehicle batter positive terminal to the positive terminal on the RV batteries. If life was perfect, the voltage drop would be zero.

    REMEMBER, CURRENT FLOWS FROM HIGH VOLTAGE TO LOW VOLTAGE.

    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.

    You will never be able to "balance" two power sources that are separated by a cable that has more than ZERO ohms resistance and voltage is being sensed at only one location. These two power source need to be SEPARATED and some electronics employed at each end to properly regulate the voltage. They do make DC-DC converters that can do this, but a high current one would be VERY expensive.

    Something worth trying. Wire an Anderson connector off of the feed to the inverter. When you want to use the truck as the primary power source, connect it up directly to that connector, bypassing the RV batteries. Assuming the inverter is also powering your RV converter/charger AND the converter/charger is still wired to the RV batteries, they will be properly recharged.
  • SoundGuy's avatar
    SoundGuy
    Explorer
    Feb 14, 2018
    lawrosa wrote:
    The chevys also use the ad244 145 amp alternators... Very good..

    Not sure if and when they stopped using that model.


    Glove box RPO sticker for my 2012 Silvy says it has a KG3 alternator, which according to this list means it has a 145 amp alternator. :B

  • lawrosa's avatar
    lawrosa
    Explorer
    Feb 14, 2018
    I used these adapters with my old set up. I use one now on my new set up to attaced to neg battery as I couldn't find a good ground close enough.

    Sourcing properly mounted fuses was problamatic hence why I mounted the 100 amp breaker..

    The chevys also use the ad244 145 amp alternators... Very good..

    Not sure if and when they stopped using that model.

    Side terminal to 3/8 stud

  • SoundGuy's avatar
    SoundGuy
    Explorer
    Feb 13, 2018
    lawrosa wrote:
    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?


    No, my existing 10 yr old flooded G27 has finally died so I've decided to replace it with a single G31, an AGM so I can mount it in the front pass through storage compartment where I can then connect to the inverter with short 18" 1 gauge starter cables. The battery box just aft of the tongue jack holds my fresh water transfer pump ... when camping the trailer's Bargman plugs into this box to provide power to the pump while protecting the connector from the elements.

    No fuses with the booster cable that will only be used a few minutes at a time - really no different than using a booster cable for boosting another vehicle.
  • SoundGuy's avatar
    SoundGuy
    Explorer
    Feb 13, 2018
    lawrosa wrote:
    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.


    I'm not familiar with KFI but those sure look much like the Anderson SB-50 connectors I used ... if so, no way are they rated to carry 120 amps but rather just 50 amps. Anderson does make other heavier duty models but naturally they're much more expensive which is why I think this time I'll just use a booster cable with it's own clamps and just forego connectors entirely.
  • lawrosa's avatar
    lawrosa
    Explorer
    Feb 13, 2018
    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?
  • SoundGuy's avatar
    SoundGuy
    Explorer
    Feb 13, 2018
    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.
  • shastagary's avatar
    shastagary
    Explorer
    Feb 13, 2018
    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.
  • lawrosa's avatar
    lawrosa
    Explorer
    Feb 13, 2018
    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.html



    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***** 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




  • SoundGuy's avatar
    SoundGuy
    Explorer
    Feb 13, 2018
    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.

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