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--- electrical:12v:b2b [2024/03/23 23:42]
frater_secessus [Victron]
+++ electrical:12v:b2b [2025/04/29 00:55] (current)
frater_secessus [Renogy]
@@ Line 32: / Line 32: @@
 See [[electrical:12v:mandatory_dcdc|this companion article]]
 ===== sizing =====
@@ Line 44: / Line 45: @@
 The DC-DC should be big enough to meet your charging targets given the amount of driving you do and the
 contributions of [[electrical:12v:alt_and_solar|other forms of charging]]. It should be small enough that the [[electrical:12v:alternator_details#current|alternator can provide the power continuously]].((Some DC-DC can be derated in the settings in 5A or 10A increments.  IOW, you might run your 50A DC-DC at 35A after observing how the system operates.))  **An oversized DC-DC charger cannot protect the alternator**.
+==== harvest ====
+Ah = Amps x hours.  If your DC-DC charges at 20A and you drive for 2.5 hours it can replace 50Ah (20A x 2.5 hours).
 Note that [[opinion:frater_secessus:charging_faster|bigger is not always better]];  different battery chemistries and capacities accept current at different rates.  Buying more charging capacity than the battery wants((or should have for its own good, see Li below)) is a waste of money. Buying more charging capacity than your alternator can deliver constantly can overheat/damage the alternator.
@@ Line 52: / Line 57: @@
   * **AGM lead-acid** accepts a max of about 0.33C, or 33A per 100A of battery capacity, and requires a minimum of 0.2C (20A).  In this case, **20-33A of charging capacity would be appropriate**.  Less than 20A would be insufficient for battery health  and more than 33A would be wasted expense.((Exception:  high-end AGM often have very high current minumums like C/2))
   * **Lithium** has very low internal resistance and //may// be able to slurp up all the alternator has to give.((in practice, due to wiring resistance and other factors [[electrical:12v:directcharginglfp|Li tends to charge at about the same C-rate as AGM]]))  0.2C-0.4C charging may be the sweet spot between charging time and longevity, which would be **20A - 40A charging**.  If you are charging by alternator alone and have limited time to do so, some BMS allow up to 1.0C charging (100A).  The bank will not be expected to last as many cycles or stay balanced under aggressive charging but the option is there for people who need it.
+===== triggering  =====
+The general idea is to feed power from the chassis (usually the starter battery) to the house battery **only when the alternator is making power**, and isolate the two from each other when it is not.  The DC-DC will handle this in one of two ways:
+  * **voltage sensing** - watching chassis voltage like [[electrical:12v:alternator#voltage-sensing_relays|a VSR]]
+  * by receiving a **trigger signal** (AKA "D+", "IGN", "ignition", etc) from the chassis:  signal = ON, no signal = OFF.  This method requires the user to find a chassis circuit that has power only when the key is turned (IGN, ACC) or when the alternator is actually making power (D+).  Caveat:  leaving the key in the ACC ("accessory") position can trick the DC-DC into starting before the engine is running;  so don't do that.
+  * **voltage sensing + trigger signal** - this is often used to tell voltage-sensing DC-DC that the alternator is smart (variable voltage).  IOW, "voltage is weirdly low but the D+ signal tells me this is a smart alt //and// the engine is running so I can charge regardless."
+Product documentation will tell you how the unit is triggered.((sometimes both methods are used together))
+===== installation =====
+A DC-DC charger is installed as close to the battery bank as practical, in order to minimize [[electrical:12v:voltage_sag|voltage sag]].
+To simplify the installation and minimize expense you may be able to run the input NEG to the chassis rather than all the way back to the starter battery NEG.  If the chassis introduces too much resistance to allow hitting the desired charging output you can punt and run heavy NEG wire all the way back to the starter batt.
+The product manual will give specific guidance on wire gauge, fusing, mounting orientation, etc.
@@ Line 72: / Line 98: @@
 ===== examples - combo with solar charge controller =====
-Combining the [[electrical:solar:charge_controller|solar charge controller]] and DC-DC charger in one unit can have benefits in cleaner/simpler installation, starter battery maintenance from solar, and perhaps cost over separate components.   The downsides are less configurabilty((you aren't choosing your own highly-configurable components)), single points of failure, and limited options on solar input.
+Combining the [[electrical:solar:charge_controller|solar charge controller]] and DC-DC charger in one unit can have benefits:
-Combo units typically have much **lower maximum panel input voltages** (as low as 23v) than a standalone charge controller would (60v - 150v).  This limits the solar configuration in a few ways:
+  * cleaner/simpler installation
+  * starter battery maintenance from solar (see the write-up on each unit below)
+  * simplify the enforcement of combined charging current limits
+  * sometimes reduce cost over separate components.
+The downsides are less configurabilty((you aren't choosing your own highly-configurable components)), single points of failure, and limited options on solar input.
+On the last point, combo units typically have much **lower maximum panel input voltages** (as low as 23v) than a standalone charge controller would (60v - 150v).  This limits the solar configuration in a few ways:
   * [[electrical:solar:series_vs_parallel|series panel arrangements]] are effectively ruled out
@@ Line 85: / Line 118: @@
 === DCC series ===
+**Heads up**:  the specs on the DCC line (30A and 50A) have changed but the model numbers appear to be the same.  Most important change is the PV input voltage limit;  see below. Doublecheck which one you will be getting BEFORE ORDERING if this is a critical spec for you.
 [[https://amzn.to/48L6r1f|{{ https://m.media-amazon.com/images/I/41B+GcTmbyS._AC_UY218_.jpg?125}}]]
-  * DCC50S [[https://amzn.to/48L6r1f|50A model with MPPT charging]]. MPPT input limited to 25v.((per the manual)) - [[https://www.renogy.com/content/RBC3050D1S-G1/RBC3050D1S-Manual.pdf|manual]] (pdf)  Total output is limited to 50A from either independent source (see below).
+  * DCC50S [[https://amzn.to/48L6r1f|50A model with MPPT charging]]. MPPT input limited to 25v on original version and 50v on new version.((per the manual)) - [[https://www.renogy.com/content/RBC3050D1S-G1/RBC3050D1S-Manual.pdf|manual]] (pdf)  Total output is limited to 50A from either independent source (see below).
-  * a [[https://amzn.to/3fSFDD2|30A combo model]] is also available
+  * there is no D+ trigger for smart alternators.  Instead, the owner adjusts the cut-in voltage setpoint to make it work as desired:  "...you can connect to DC Home or Core via Bluetooth, and then **adjust the appropriate input voltage value of the charger** according to the characteristics of the working voltage of different types of alternators."((https://ca.renogy.com/renogy-ip67-50a-dc-dc-battery-charger-with-mppt/))
+  * a [[https://amzn.to/3fSFDD2|30A combo model]] is also available.  25v input on older version and 30v input on newer version.
   * low temp charging cut-off supported in Lithium profile when external temp probe is present
   * [[electrical:12v:voltage_sensing|voltage-sensing]] available
@@ Line 107: / Line 144: @@
 This device's behavior regarding solar+alternator charging is widely misunderstood.
-The 50A dual-input charger prefers to charge by solar if possible, up to **50A**.  If it cannot meet charging demands alone and the engine is running it will will charge up to **25A by solar and 25A by alternator**:
+The 50A dual-input charger prefers to charge by solar if possible, up to **50A**.  If it cannot meet charging demands alone and the engine is running it will will charge **≤25A by solar** plus **≤25A by alternator**:
 Consider this snippet from the manual;
@@ Line 126: / Line 163: @@
 Note:  some have reported better alternator charging performance with the D+ (smart alternator) wire connected, even with plain alternators.  Oversizing cables from the alternator may also help. ((https://www.youtube.com/watch?v=LtIe2rIfpW8))
-== disconnecting the solar ==
+== preventing solar from hobbling the alternator side  ==
-Because of the behavior described above, people who want maximum alternator charging sometimes add a way to disconnect solar panels.  This is typically done by adding some kind of disconnect on the panel POS wire going to the solar charge controller:
+Because of the behavior described above, people who want maximal charging can approach the problem one of two ways:
+**Max out the solar side** so it's never failing to make it's fair share.  This would be 400w of panel on the 30A and ~600w on the 50A.
+**Add a way to disconnect solar panels**.  This is typically done by adding some kind of disconnect on the panel POS wire going to the solar charge controller:
   * manual switch
@@ Line 143: / Line 184: @@
 === RBC series ===
+NOTE:  there are two distinct versions of the RBC line.  Both appear to have PV input limits higher than 25v found in the older DCC line.  Major differences appear to be:
+  * DS - built-in Bluetooth, support for both 12v/24v banks.  New case.
+  * D1S -  no built-in Bluetooth, 12v banks only.  Uses traditional DCC case.
+== RBC2125DS ==
+{{ https://cdn11.bigcommerce.com/s-fhnch/images/stencil/640w/products/2063/26190/1__10088.1706872952.jpg?125}}
 Note:  some manual versions brand this unit as part of the "Rego" line.
-The [[https://www.renogy.com/renogy-12v-24v-ip67-50a-dc-dc-battery-charger-with-mppt/|RBC series 50A charger]] has a 50V PV input limit and built-in bluetooth.  It can also boost 12v panel voltage to charge 24v banks.  A RBC30 is reported to exist.
+This version is for both **12v and 24v banks**.
-The existing [[https://store-fhnch.mybigcommerce.com/content/RBC2125DS-21W/Manual_RENOGY%2012V%2024V%2050A%20Battery%20Charger-2.pdf|manual]] is minimal and specs/behavior are largely undocumented as of Jan 2024.
+The [[https://www.renogy.com/renogy-12v-24v-ip67-50a-dc-dc-battery-charger-with-mppt/|RBC series 50A charger]] has a 50V PV input limit and built-in bluetooth.  It can also boost 12v panel voltage to charge 24v banks.
+>> Ensure that the open circuit voltage of the solar panel/solar panel array does not exceed 50V
-== solar+alternator behavior ==
+Update:  [[https://store-fhnch.mybigcommerce.com/content/RBC2125DS-21W/Manual_RENOGY%2012V%2024V%2050A%20Battery%20Charger-2.pdf|the manual]] has been updated.
+= solar+alternator behavior =
@@ Line 159: / Line 214: @@
+== RBC30D1S and RBC50D1S ==
+The D**1**S series appears to be a DCC charger with higher PV input limits:
+>> For [the] 30A battery charger, ensure that the working voltage of the solar panel / solar panel array does not exceed **30V**. For [the] 50A battery charger, ensure that the working voltage of the solar panel / solar panel array does not exceed **50V**.
+[[https://www.renogy.com/content/RBC3050D1S-G1/RBC3050D1S-Manual.pdf|manual]]
+== RBC40D1S ==
+A DC-DC w/MPPT that appears very similar to the Redodo/LiTime/etc 40A combo units.
+  * 30v PV input
+  * smart and traditional alternators
+  * no float in LFP profile, rebulking at 13.6v
+[[https://store-fhnch.mybigcommerce.com/content/RBC40D1S-US/Renogy%2040a%20dcdc%20user%20manual%20v1.0%2020240320.pdf|manual]] (pdf)
+= starter battery maintenance behavior =
+not described, and presumed not present
+= solar+alternator behavior =
+When both are present it defaults to alternator priority (only).  It can be set to solar priority.
@@ Line 204: / Line 285: @@
 >> For DMT1230, 1250 using CH 2 (Solar Array/Panel): Turn unit off. Use a proper jumper to temporary connected CH2 “+” to Ch 1 “+”. Remove the jumper when CH 1 is above the unit start up voltage (8Vdc) and restart the unit.
+=== disabling the Kisae ===
+  * tricking the Battery Temperature Sensor port  - [[https://www.promasterforum.com/threads/kisae-dmt1250-dmt1230-low-temp-cut-off-and-couple-of-advanced-wiring-options.97444/|Kisae DMT1250/DMT1230 low temp cut off and couple of advanced wiring options]]
+  * modifying the existing ON/OFF switch - [[https://diysolarforum.com/threads/kisae-dmt1250-partial-disassembly-and-remote-disconnect-addition.15454/|Kisae DMT1250 partial disassembly and remote disconnect addition]]
+The brute force method would be a battery cut-off switch or relay on the POS wire coming from the chassis.
@@ Line 209: / Line 296: @@
 This unit also seems to be sold under the Ring and Merlin brands.
+==== LiTime ====
+{{ https://m.media-amazon.com/images/I/71UNjnxThrL._AC_UL320_.jpg?125}}
+LiTime makes [[https://amzn.to/3xHGjq5|a 40A DC-DC/ MPPT combo]] that looks identical to the Redodo below. Specs appear to be the same:
+  * Pv input 13.0v - 26v, max 600w
+  * Alternator Input Voltage 11.3-24VDC, max 600w
+  * Smart Alternator Input Voltage 12-24VDC , max 600w
+=== solar+alternator behavior ===
+According to the Amazon listing:
+> The DC-DC charger will choose the DC input automatically rather than charging the service battery with both the solar and DC inputs
+=== starter battery maintenance behavior ===
+> When the starting battery voltage is between 3-12V and the living battery voltage is greater than 12.5V, press and hold "REVERSE CHARGE" for 3 seconds to start reverse charging. It is recommended to start the battery when the voltage is greater than 13V and exit reverse charging when the charging current is less than 10A or the voltage of the domestic battery is less than 11V.
+==== Redodo ====
+{{ https://m.media-amazon.com/images/I/71PVPwKPJxL._AC_UL320_.jpg?100}}
+Redodo makes [[https://amzn.to/3JhGtqN|a 40A combo DC-DC/MPPT]]:
+  * Pv input 13.0v - 26v, max 600w
+  * Alternator Input Voltage 	11.3-24VDC, max 600w
+  * Smart Alternator Input Voltage 	12-24VDC , max 600w
+No manual located as of this writing.
+=== solar+alternator behavior ===
+unknown
+=== starter battery maintenance behavior ===
+Amazon listing claims "supports reverse charging the starter battery through the service battery".  A seller answer later says:
+> When the starter battery voltage is between 3 to 12V and the service battery voltage is >12.5V, press and hold the “Reverse Charging” for 3 seconds to initiate reverse charging. It’s recommended to exit reverse charging when the starter battery voltage >13V and charging current <10A, or when the service battery voltage <11V.
 ==== SRNE ====
@@ Line 214: / Line 357: @@
 {{ https://www.srnesolar.com/wp-content/uploads/2020/10/MPPT-Solar-Charging-Controller-MD1250N05-3.jpg?150}}
-SRNE makes [[https://www.srnesolar.com/product/12v-mppt-solar-dc-charging-controller-50a-md1250n05|30A and 50A combo unit]] similar to the Ring and Kisae. Since SRNE makes things that are rebadged by other sellers it is possible they are the original manufacturers.  The BT dongle appears to be the same as the EpEver and Renogy models.
+SRNE makes [[https://www.srnesolar.com/productdetail/DC-DC-Charge-Controller-MD12V.html|30A and 50A combo unit]] similar to the Ring and Kisae. Since SRNE makes things that are rebadged by other sellers it is possible they are the original manufacturers.  The BT dongle appears to be the same as the EpEver and Renogy models.
   * output rating based on solar.  30A will actually do 35A from alternator, 50A will do 60A.
@@ Line 241: / Line 384: @@
 {{ https://cdn.shopify.com/s/files/1/0058/2769/0553/products/004_2ae0ff02-0332-43b3-9ebe-c07b2b0bb989_578x578.jpg?150}}
-Rich makes [[https://richsolar.com/products/50-amp-dc-to-dc-charger-with-mppt|a 50A DC-DC w/MPPT]]. It appears to be very similar to the SRNE listed above.
+Rich makes [[https://richsolar.com/products/50-amp-dc-to-dc-charger-with-mppt|a 50A DC-DC w/MPPT]] and bluetooth. It appears to be very similar to the SRNE listed above.
@@ Line 531: / Line 674: @@
 ==== Renogy ====
-[[https://amzn.to/33HJ8ns|{{ https://images-na.ssl-images-amazon.com/images/I/51Hu4-7NxOL._AC_UL160_SR160,160_.jpg?150}}]]
+[[https://amzn.to/33HJ8ns|{{ https://images-na.ssl-images-amazon.com/images/I/51Hu4-7NxOL._AC_UL160_SR160,160_.jpg?250}}]]
 === DC1212 series ===
-DC-DC chargers in 20A, 40A, and 60A output.  Switched on by ignition circuit on the D+ port, low output mode (12.5% of rated current) triggered by 12v on a dedicated terminal. ((https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf)) DIP switches for battery type, Vabs and Vfloat. [[https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf|manual]] (pdf) [[https://diysolarforum.com/threads/renogy-dcc1212-dc-dc-charger-teardown.10141/|teardown]]  Note:  some versions of the manual [[https://www.reddit.com/r/vandwellers/comments/okfkuk/my_batteries_inverter_and_dcdc_charger_came_in_i/h5899bw/|may have a typo]].
+DC-DC chargers in 20A, 40A, and 60A output.  Switched on by ignition circuit on the D+ port, low output mode (50% of rated current) triggered by 12v on a dedicated terminal. ((https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf)) DIP switches for battery type, Vabs and Vfloat. [[https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf|manual]] (pdf) [[https://diysolarforum.com/threads/renogy-dcc1212-dc-dc-charger-teardown.10141/|teardown]]  Note:  some versions of the manual [[https://www.reddit.com/r/vandwellers/comments/okfkuk/my_batteries_inverter_and_dcdc_charger_came_in_i/h5899bw/|may have a typo]].
 These chargers appear to have a 3 hour absorption duration.  This is usually insufficient for lead chemistries, but still longer than the 2 hour duration of the DCC series above.  From the manual:
@@ Line 553: / Line 696: @@
 [[https://store-fhnch.mybigcommerce.com/content/RCB1260DO-100506PR/RBC1260DO-12B_UserManual_A0.pdf|manual]] (pdf)
+=== RBC series ===
+{{ https://cdn11.bigcommerce.com/s-fhnch/images/stencil/640w/products/2177/27702/_01__78889.1721714867.jpg?150}}
+  * seems to be in [[https://www.renogy.com/12v-40a-dc-to-dc-battery-charger/|40A]] and 20A versions
+  * configurable output current via the app
+  * Voltage-sensing (with D+ for smart alts)
+  * can use [[https://amzn.to/47kjqqD|BT-2 module]]
+[[https://www.renogy.com/content/RBC40D1U-US/QG_RENOGY%2012V%2020A40A%20Battery%20Charger_A0.pdf|manual]]
 ==== Redarc ====
@@ Line 647: / Line 804: @@
-==== examples - without current limiting ====
+===== examples - without current limiting =====
 The [[https://sterling-power.com/products/alternator-to-battery-chargers-up-to-130a|Sterling A2B]] uses DC-DC conversion to boost voltage but has no ability to limit current.
@@ Line 664: / Line 821: @@
 Also see the Votronics section above for their DCC 25A 1224 charger.
+===== examples - power stations =====
+Power stations often suffer from low DC input limits.  DC-DC chargers (//boost converters// in this case) can work around the limit by increasing the voltage to the power station input.((also see [[12v:sg_troubleshooting#maxxing_out_the_solar_input|this subarticle]] about solar input.  The source of the charging is different but the math and concepts are the same.)) If separate DC inputs are present these typically feed power to the solar input;  see your power station's product documentation for specifics.
+**Warning:** exceeding the power station's **input voltage limit** will/may damage it.  Verify specs //before// purchasing, configuring, or installing.
+  * [[https://amzn.to/3DCGu9m|Bluetti 560w charger]] - Adjustable output voltage in the app.  Presets for Bluetti products, or you can manually set the output voltage.
+  * [[https://amzn.to/3PlwcNv|Ecoflow 800w charger]] - Adjustable output 40V-60V.  Starter battery maintenance charging/maintaining modes. Firmware updates may be available.
+  * [[https://amzn.to/41XDQ8o|Etaker 1000w charger]] - ≤500w alternator + ≤500 solar (up to 48v and 20A input).  Output ≤42V, 25A
+  * [[https://amzn.to/3Pidm9V|Pecron DC1242-500]].  500w, 42v.
+Functionally, the ones with a set output voltage are akin to [[https://amzn.to/4fNKrpe|this]] and the ones with configurable output voltage are akin to [[https://amzn.to/3BRoQxZ|this]], plus a method to [[electrical:12v:b2b#triggering|trigger]] the device when the engine is running.
+==== a word about nomenclature ====
+These are listed in the DC-DC article because that is how they are used and how many people think of them.  They are really voltage boosters that output a steady voltage, whether configured by the user or set at the factory.
 ===== installing inline with a relay =====
@@ Line 697: / Line 871: @@
   - repeat forever
-The workaround is to either charge the house battery first or to buy a big enough starter battery maintainer to support both the starter battery and DC-DC charger loads.
+The workaround is to either charge the house battery first or to buy a big enough starter battery maintainer to support both the starter battery and DC-DC charger loads. Or (if the model has [[electrical:12v:self-jumpstarting#maintaining_starter_batteries|starter battery maintenance]]) apply the maintainer to the house battery instead.
 ===== further reading =====
 [[https://diysolarforum.com/threads/dc-dc-charger-b2b-options-and-general-discussion.17211/|DC-DC charger (B2B) options and general discussion]] on DIY Solar Power Forum.

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