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DC-DC Charge install Reflection 29RS

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  • DC-DC Charge install Reflection 29RS

    I recently installed a Renogy 20 amp DC-DC charger, along with Solar, so here is the install.

    The Renogy DC-DC charge takes battery voltage from the factory charge circuit of the tow vehicle and increases the power to what would be a max of 20 amps. Most tow vehicle charge circuits only have about 5 or 6 amps output and there are some videos and posts about the possible damage from trying to charge Lithium batteries with the wet cell batteries found in tow vehicles, or vice versa, so I decided to do the install to not only have added charge amperage to the Lithium batteries but also not damage the tow vehicle battery ( I am not totally sure that this is needed but it is what I wanted to do).

    Here is the final install picture.
    Click image for larger version  Name:	DC-DC 2.jpg Views:	32 Size:	100.6 KB ID:	78003


    The input is on the lower right of the charger, out put on the lower left. The yellow wire from the switch , upper left, is the trigger wire required to turn on/off the charger. I wired this from the marker lights of the RV, from the junction box located under the pin box on a fifth wheel, to the switch and then to the charger. I did this because I always tow with the trailer lights on and if I do not want the charger on I can turn it off. Using the trailer lights as the trigger came from MidwestCamper Jim and information from his install, I just added a switch.

    The input wires, lower right, are from the factory wiring that was located at the self resetting breakers located under the black plastic cover, below the fuse block that I had installed in the picture. There is a white wire with red stripe that I found was the factory charge wire, which I traced to the junction box along with the white ground wire. The junction box is where the 7 RV pigtail connects to the RV. The ouput side just goes to the battery positve, the negative goes to the shunt from the BMV-712. If you have a shunt in your system it is paramount that all negative/grounds go thru the shunt in order to get proper readings of usage and charge. It is also important to trace the wires to make sure that the correct wire is used. I have not tested this system yet as it has been winter but I feel confident that it will work. Jim has used this same system for a while and has noticed that the 7 RV plug does produce a little heat, gets warm to the touch from use, so this would probably be the max that one would want to use when using the stock wiring, I will keep an eye on this and this is another reason I added a switch. There is also a trigger input on the charger to allow the user to cut the amperage in half, that would be 10 amps so would decrease the draw on the tow vehicle wiring which I can add if needed. If it comes to cutting the amperage in half I will run a dedicated set of wires that will handle the full load.

    Brian
    Last edited by Country Campers; 03-06-2022, 12:44 PM.
    Brian & Michelle
    2018 Reflection 29RS Oct.2017 build date, EMS-HW50C , Lippert Remote
    2015 Chevy 3500HD CC LB Duramax , Reese Elite 18K
    630 ah battery, Victron Multiplus 2, 800 watts solar

  • #2
    Nice. I've been really happy with mine (the 60A version). Now even wondering if I should put in solar... but I don't think I can help myself.

    Comment


    • #3
      Originally posted by TravelHabit View Post
      Nice. I've been really happy with mine (the 60A version). Now even wondering if I should put in solar... but I don't think I can help myself.
      Just say NO! It is hard to resist solar.

      Brian
      Brian & Michelle
      2018 Reflection 29RS Oct.2017 build date, EMS-HW50C , Lippert Remote
      2015 Chevy 3500HD CC LB Duramax , Reese Elite 18K
      630 ah battery, Victron Multiplus 2, 800 watts solar

      Comment


      • #4
        I'm new to the RV scene (first TT coming in at the the month), so I'm trying to learn everything.

        That said I'm confused by this post.

        The Renology (or any device) can NOT boost amperage unless voltage is changed in the process (i.e. going from 24V 5A then a DC to DC converter could go to 12V 10A). But the power remains the same.

        To create additional current at the same voltage, the device would have to be a power creation device, and would need a power conversion "engine" (i.e. using a fuel, or a chemical reaction process).

        This Renology device will take the Voltage supplied at the 7 pin and transform it to the required 3 voltages required during the charge phase of your specific type of batteries. The stages are Bulk, Boost and Float, and are different for each type of battery (i.e. Lithium vs AGM, etc.).

        But it does not take the max (as stated in the OP) current of 5 or 6 amps coming from the vehicle power thru the 7 pin connector and boost it to 20 amps.

        The 20 amp rating on the Renology device is specifying the max current this device can handle (not create).

        To say another way:

        Taking the 12V (nominal) pin from the trailer connector can power 12v devices (up to a power limit). If this was tied directly to your trailer battery you might get some charging, but would not be very effective.

        The Renology device takes the 12V and changes it to the different required voltages to charge a battery. For example on a Lithium it might be Bulk Voltage will be 14.6V until about 80% charges, then drop to Boost (adsorption) of 14.4V then finally when at 99% charge drop to Float of 13.6V

        But it cannot "boost" the power/amperage.

        Comment


        • #5
          Originally posted by BLoflin View Post
          I'm new to the RV scene (first TT coming in at the the month), so I'm trying to learn everything.

          That said I'm confused by this post.

          The Renology (or any device) can NOT boost amperage unless voltage is changed in the process (i.e. going from 24V 5A then a DC to DC converter could go to 12V 10A). But the power remains the same.

          To create additional current at the same voltage, the device would have to be a power creation device, and would need a power conversion "engine" (i.e. using a fuel, or a chemical reaction process).

          This Renology device will take the Voltage supplied at the 7 pin and transform it to the required 3 voltages required during the charge phase of your specific type of batteries. The stages are Bulk, Boost and Float, and are different for each type of battery (i.e. Lithium vs AGM, etc.).

          But it does not take the max (as stated in the OP) current of 5 or 6 amps coming from the vehicle power thru the 7 pin connector and boost it to 20 amps.

          The 20 amp rating on the Renology device is specifying the max current this device can handle (not create).

          To say another way:

          Taking the 12V (nominal) pin from the trailer connector can power 12v devices (up to a power limit). If this was tied directly to your trailer battery you might get some charging, but would not be very effective.

          The Renology device takes the 12V and changes it to the different required voltages to charge a battery. For example on a Lithium it might be Bulk Voltage will be 14.6V until about 80% charges, then drop to Boost (adsorption) of 14.4V then finally when at 99% charge drop to Float of 13.6V

          But it cannot "boost" the power/amperage.
          I think you are missing the big reason for the low current on the charge circuit. Battery charging current is proportional to the charging voltage. The long run from the alternator to the trailer battery through a small wire results in significant voltage drop making charge current low as well. By boosting the voltage at the trailer battery, charge current is increased, but still limited by the capacity of the DC-DC converter and the vehicle charge circuit.

          Available power isn’t the limiting factor on stock setups. It’s voltage.

          John & Kathy
          2014 Reflection 303RLS
          2014 F250 SC SB 6.2

          Comment


          • #6
            BLoflin -- technically you're right. The Renogy cannot (and does not) "boost power".

            The rest of this post may make the eyes of the reader roll back in their head--so why read it and try to comprehend the math? Because it is important to understand why anyone doing this mod must ensure the 7-pin connection and associated wiring in their vehicle and trailer can support the higher amperage when using the Renogy.

            Power is measured in watts (the product of voltage and amperage). So...power out must equal power in (assuming no loss in the Renogy itself). So watts in = watts out. What can change (and does change) is the volts and amps.

            Since power out = power in, and we'll assume the truck's output voltage (the input to the Renogy) is constant, the amperage from the truck through the 7-pin must increase. How does the amperage increase from the truck? The apparent resistance of the circuit drops. (Voltage constant but amperage increase = resistance decreases.)

            Example below is not representative of actual numbers (but they are close):

            Stock Configuration
            Truck Voltage = 12.9vDC
            Measured amperage = 9 amps
            Wattage to battery (12.9 * 9) = 116 watts
            Apparent resistance of the circuit (12.9 / 9 ) = 1.43 ohms

            20A Renogy
            Truck Voltage = 12.9vDC
            Truck Amps = ??? (will be calculated)
            Renogy Output Voltage = 13.6
            Renogy Output Amps = 20
            Wattage to Battery ( 13.6 * 20 ) = 272 watts

            Note in the next equation the Renogy's output wattage is used to calculate the truck's amps because power in must equal power out (again, assuming no losses).

            Truck amps ( 272 / 12.9 ) = 21 amps
            Apparent resistance felt by truck (12.9 / 21) = .61 ohms

            To the best of my knowledge, the forum members that have done the 20A Renogy mod using their vehicle's OEM wiring confirmed the wiring (and fuse) are capable of carrying the increased amperage output.

            I hope this helps anyone reading this thread understand...

            Howard
            Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

            2017 Ford F-350 DRW, '19 315RLTSPlus

            Comment


            • #7
              I guess that "boost" was the wrong word to use. My understanding is that the charger will "draw" more amperage from the tow vehicle instead of just the regular 5 to 7 amps. This has been a good discussion though on how and why.

              Brian
              Brian & Michelle
              2018 Reflection 29RS Oct.2017 build date, EMS-HW50C , Lippert Remote
              2015 Chevy 3500HD CC LB Duramax , Reese Elite 18K
              630 ah battery, Victron Multiplus 2, 800 watts solar

              Comment


              • #8
                Originally posted by Jkwilson View Post

                I think you are missing the big reason for the low current on the charge circuit. Battery charging current is proportional to the charging voltage. The long run from the alternator to the trailer battery through a small wire results in significant voltage drop making charge current low as well. By boosting the voltage at the trailer battery, charge current is increased, but still limited by the capacity of the DC-DC converter and the vehicle charge circuit.

                Available power isn’t the limiting factor on stock setups. It’s voltage.
                Hmmm, but that isn't how electricity works at all. The equation is V=I*R. Also Power has to be conserved. Power In = Power Out - losses (thermal, etc). For Power Out to be more than Power In then Power needs to be created (via a power source, like a fuel or chemical reaction, or in case of the vehicle alternator, fuel into an engine and an engine turns the Alternator).

                For example lets say the Alternator voltage is 14V (just to keep it simple, no decimals) at the Alternator. Lets say when you pull 6 Amps out at the trailer connection the Voltage drops to 12V. That means the wire resistance to the plug is 0.333 Ohms (14 - 12V / 6A). You drop 2V due to resistance along the wire. If you try and pull 12A then the voltage at the trailer connection drops to 10V.

                Also the Power is consistent: At Alternator is 14V x 6A = 84Watts. At Connector is 12V x 6A = 72W + Power loss in the wire resistance is 2V x 6A = 12W which totals 84W.

                Instead if you are trying to pull 12A then power at Alternator is 168W and power at connector is 120W and the power loss in the wire is 48W.

                Now for simplicity lets assume the DC-DC Converter (Renology part) is sitting right at the Trailer Connector (i.e. no additional wire with additional resistance).

                The Convertor will take that 10V with 12A input (i.e. 120W) and step it up (convert it) say to 15V to be able to start a Bulk Charge cycle for the battery (again using rounded numbers for math simplicity). Then the available current DROPS to 8A (actually a little less than 8 as there are some losses in the Renology circuits), 8A x 15V = 120W. Again because you can NOT create power (without a power source).

                The OP spoke of "boosting" the power. You can not. You can boost the Voltage in a Converter, but with the corresponding LOWERING of the current. Or conversely you can boost the Amps by lowering the Voltage ouput, but of course that would not be helpful for charging batteries.

                Also, again the 20A rating on the Renology is NOT the guaranteed current output, it is the highest current (and also highest power rating is nominal 250W based on the 20A and 12V). They also have a 40A (500W) and a 60A (750W). None of these can create power or boost current if you are not delivering the corresponding input current and voltage.

                Comment


                • #9
                  Originally posted by Country Campers View Post
                  I guess that "boost" was the wrong word to use. My understanding is that the charger will "draw" more amperage from the tow vehicle instead of just the regular 5 to 7 amps. This has been a good discussion though on how and why.

                  Brian
                  Yes, correct. That in fact is the concern that needs to be understood, if you are trying to apply say 240W to charge your battery (e.g. something like 15V at 16A) you have to be careful as if your truck is supplying say 12V at the trailer connector then your alternator and the wiring to the connector has to be able to supply and transport 20A and the truck wiring to the connector needs to be sized accordingly.

                  This is in fact what concerned/confused me about the OP. As it appears that the solution to only being able to "trickle" charge anything out of the vehicle 12V trailer connector (that was limited in current due to vehicle wiring, fusing, alternator output and demand, etc.) was to use the Renology part to get good battery charging currents by being "boosted". In fact it is the OPPOSITE. The battery charging voltage will be boosted at a corresponding lowering of the charging current (or else you may be over maxing the current draw from the vehicle).

                  If you have a vehicle alternator that is sized big enough to supply an additional 250W to your trailer (after accounting for all it's demand from the vehicle itself) then you need to possibly add a bigger wire from the alternator to the connector (or at least from the fuse box to the connector) and possibly upsize the fuse in the fuse box. But possibly you will be ok. See if you can find in your Vehicle Owners manual to see if that Trailer Connector 12V has a specific fuse and see what the size is. If it is 5 or 10A fuse, that will be a problem. You could change the fuse, but that would imply they built the vehicle with a small wire. If that fuse is 30A then you should be good to go, as the wiring should be sized accordingly.
                  Last edited by BLoflin; 03-05-2022, 05:15 PM.

                  Comment


                  • #10
                    Originally posted by BLoflin View Post

                    Again because you can NOT create power (without a power source).
                    The alternator is the power source. The alternator varies it's output depending on the demand placed on it. Within it's limits. If you change the demand via the dc-dc charger, it will up the output.

                    2018 Dodge 3500 6.7 Cummins w Aisin and 9 cup holders
                    2021 Reflection 303RLS, Haloview RD7, Strong-arms, Micro-Air364

                    Comment


                    • #11
                      BLoflin Howard has it right, and your concerns are valid as well. Those of us that have used the 40 or 60 amp models have run large gauge wire back from the truck battery to the Renogy (I used 4AWG for my 40A), and have alternator capacity to spare (I think Howard and I are both running dual heavy duty alternators). Those that are using the factory wiring are using the 20A model, in a Ford the factory charge wire is 10AWG, and is fused large enough to handle the load. MidwestCamper was I believe the first to do the upgrade with his factory wiring on his GM, and he verified that the stock wiring and fuses were adequate for his calculations.
                      Neil Citro
                      2018 Reflection 28bh
                      2019 F350 6.7L Long Bed Crew Cab

                      Comment


                      • #12
                        Originally posted by BLoflin View Post

                        Hmmm, but that isn't how electricity works at all. The equation is V=I*R. Also Power has to be conserved. Power In = Power Out - losses (thermal, etc). For Power Out to be more than Power In then Power needs to be created (via a power source, like a fuel or chemical reaction, or in case of the vehicle alternator, fuel into an engine and an engine turns the Alternator).

                        For example lets say the Alternator voltage is 14V (just to keep it simple, no decimals) at the Alternator. Lets say when you pull 6 Amps out at the trailer connection the Voltage drops to 12V. That means the wire resistance to the plug is 0.333 Ohms (14 - 12V / 6A). You drop 2V due to resistance along the wire. If you try and pull 12A then the voltage at the trailer connection drops to 10V.

                        Also the Power is consistent: At Alternator is 14V x 6A = 84Watts. At Connector is 12V x 6A = 72W + Power loss in the wire resistance is 2V x 6A = 12W which totals 84W.

                        Instead if you are trying to pull 12A then power at Alternator is 168W and power at connector is 120W and the power loss in the wire is 48W.

                        Now for simplicity lets assume the DC-DC Converter (Renology part) is sitting right at the Trailer Connector (i.e. no additional wire with additional resistance).

                        The Convertor will take that 10V with 12A input (i.e. 120W) and step it up (convert it) say to 15V to be able to start a Bulk Charge cycle for the battery (again using rounded numbers for math simplicity). Then the available current DROPS to 8A (actually a little less than 8 as there are some losses in the Renology circuits), 8A x 15V = 120W. Again because you can NOT create power (without a power source).

                        The OP spoke of "boosting" the power. You can not. You can boost the Voltage in a Converter, but with the corresponding LOWERING of the current. Or conversely you can boost the Amps by lowering the Voltage ouput, but of course that would not be helpful for charging batteries.

                        Also, again the 20A rating on the Renology is NOT the guaranteed current output, it is the highest current (and also highest power rating is nominal 250W based on the 20A and 12V). They also have a 40A (500W) and a 60A (750W). None of these can create power or boost current if you are not delivering the corresponding input current and voltage.
                        You are missing the entire key point. A battery is not a fixed load. Boosting the voltage at the battery INCREASES the current flowing into the battery. 100% absolutely and always. You can’t increase the voltage without increasing current, and you can’t increase the current without increasing the voltage.

                        The voltage drop in the wiring causes the battery to draw less current. That means the battery is not getting all of the power that the tow vehicle charging circuit can provide. By boosting the voltage, the battery draws more current and receives more power, up to the ability of the charging circuit to provide power because the alternator sees a load it responds to.

                        Numbers you might see with direct wiring to the trailer might be 13V and 6A providing 78W to the trailer battery. With the DC-DC converter you’d theoretically see 14.6V and 20A, though the circuit usually is current limited to more like 12A, providing ~175W to the battery.

                        Last edited by Jkwilson; 03-05-2022, 09:16 PM.
                        John & Kathy
                        2014 Reflection 303RLS
                        2014 F250 SC SB 6.2

                        Comment


                        • #13
                          Jkwilson John, someone else will probably chime in to help clarify also. Most of the people running DC-DC chargers are not running lead acid batteries. Instead they are running LiFePO4 which finish charging at a higher voltage. Without the DC-DC charger the LiPO will only charge to about 80% (IIRC) capacity. By using the DC-DC charger they ensure that they get the 100% charge needed.
                          Joseph
                          Tow
                          Vehicle: 2018 GMC K2500 Denali Diesel
                          Coach: 303RLS Delivered March 5, 2021
                          South of Houston Texas

                          Comment


                          • #14
                            Originally posted by Jlawles2 View Post
                            Jkwilson John, someone else will probably chime in to help clarify also. Most of the people running DC-DC chargers are not running lead acid batteries. Instead they are running LiFePO4 which finish charging at a higher voltage. Without the DC-DC charger the LiPO will only charge to about 80% (IIRC) capacity. By using the DC-DC charger they ensure that they get the 100% charge needed.
                            Likely correct. The issue is even more pronounced on lithiums because their open circuit voltage is closer to the charging system maximum output so the voltage drop on the run to the trailer is much more critical. In this application, the DC-DC converter is functionally a battery charger with a DC input. Typically these DC-DC converters will work with an input voltage as low as 7 or 8 volts.
                            John & Kathy
                            2014 Reflection 303RLS
                            2014 F250 SC SB 6.2

                            Comment


                            • #15
                              Country Campers howson

                              Brian, Howard, nice posts on the installation and operation.

                              After testing my 20amp Renogy outside the rig as an initial test, I measured up to 27 amps at startup if my memory serves me. Running current was at 25amps. With the low internal resistance of the LiFeP04 battery, the Renogy delivered the specified 20amps to the rig. For folks that are not confident in the 7 way to operate at the full capacity of the 20amp Renogy, the charger can be configured via a jumper wire to result in a 50% reduction in output. So in this case, the Renogy will output 10amp while drawing as much as 15amp from the TV through the 7 way. This will still allow for proper LiFeP04 charging while isolating the two different battery chemistries between the RV and TV.

                              Jim
                              2017 Imagine 2600RB
                              2015 GMC Sierra 4x4

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