DC-DC charger (B2B) options and general discussion

Dzl

Unofficial Forum Librarian
Staff member
Moderator
A very common set of questions in the beginner and the vehicle mounted systems subforums concerns charging a LFP house bank from a vehicles starting system (alternator). The most commonly used and recommended devices for this purpose are DC-DC chargers (also often called Battery to Battery (or B2B) Chargers). This thread is intended to be an index of the various options available as well as a catchall thread for questions and answers, discussion, etc.

Disclaimer (and request for help/collaboration): I do not own and have not used any of these. I have compiled this list because its a very common area of interest and confusion and also for my own interest. Some of these products I have researched in moderate depth, others I have barely read the product description and/or datasheet. There are bound to be errors, omissions, inaccuracies, etc. And there are some aspects that are just hard to represent neatly in a table. So take the accuracy with a grain of salt (especially anywhere you see a red ? or a *) and please help me improve the info if you see something that needs correcting or can think of another specification that should be added.


Charger Only
(DC-DC / B2B)
Brand / ModelMax Current 12/24Input VoltagesOutput VoltagesLFP compatibleParallelable
Victron Orion-TR Smart (Isolated)30A / 17A12, 2412, 24YesYes
Victron Orion-TR Smart (Non-Isolated)30A / 17A12, 2412, 24YesYes
Sterling Power Pro Batt Ultra**70A / 35A ***12, 2412, 24, 36*, 48*YesYes
Renogy DCC1212**60A / --1212Yes?
Redarc DPS40A / 25A12, 2412, 24Yes?
Votronic VCCTBD12, 2412Some Models?
*Not available in all input voltages
**Not all models shown/listed in link or table
***Input current (output current not specified)

Dual Function Charger
(DC-DC + MPPT)
Brand / ModelMax OutputInput VoltageOutput VoltageMax Solar Input VoltageLFP Compatible
Renogy DCC50A / --121225 (?)Yes
Kisae DMT50A / 30A12, 2412, 2450Yes
CTEK D250SE20A / --121223 (?)Yes
Redarc BCDC50A / 20A12, 2412, 2432 / 28 (?)Yes


Triple Function Charger
(DC-DC + MPPT + AC Charger)
Brand / ModelMax OutputInput Voltage (DC)Output VoltageMax Solar Input VoltageLFP Compatible
Redarc Manager 3030A12, 2412, 24 (?)30 (?)Yes
Votronic VBCSTBD1212TBDYes
 
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Reed Cole

Solar Enthusiast
Sterling rates their chargers by their input current for what it's worth. For example I have their 12v-12v 30A model and it outputs about 22.5A.

It's good because you know what the maximum draw on your alternator will be but counterintuitive as most other chargers of any type are rated by their output.
 

Dzl

Unofficial Forum Librarian
Staff member
Moderator
Sterling rates their chargers by their input current for what it's worth. For example I have their 12v-12v 30A model and it outputs about 22.5A.
Thank you for point that out, that is a fairly large difference between input and output, I will update that. I didn't want to overcomplicate the table by adding input and output current but a difference of that amount shouldn't be glossed over. I've found documentation and clarity of specifications to be subpar compared to more standardized components like PV panels and SCC's.
It's good because you know what the maximum draw on your alternator will be but counterintuitive as most other chargers of any type are rated by their output.
(y)
 

Dzl

Unofficial Forum Librarian
Staff member
Moderator
Update 1:
Fixed / amended current specs for Sterling
Added column for LFP compatibility
Crossed out CTEK smartpass for apparent lack of LFP profile.
 

Reed Cole

Solar Enthusiast
I don't know what the actual draw on the alternator is, it would be interesting to know, but alas I don't have a way to measure as of yet.
 

grizzzman

Some say "Why" and some say "Why not?"
Renolgy 40 Amp DC to DC charger. Set for FLA. Truck voltage output 14.0 amps drawn 50. Output 14.7 volts and 39.74 amps. This unit is a buck/boost device.
 

Dzl

Unofficial Forum Librarian
Staff member
Moderator
Some areas for further research/documenting:
  1. Which of these B2B's are isolated (or offer an isolated model)? I am aware Victron does, Kisae doesn't. Not sure about others. Anyone have more info to share?
  2. Power sharing, for the dual and triple input devices, how does the device manage inputs? The sub questions here are is it Solar and B2B or Solar or B2B, or a middle ground, and which source takes priority.
 

Mad_Texan

Solar Enthusiast
Just started playing with my Sterling BB242435 (24v to 24v rated at 35a). So far through the BMS I've seen a max of 27.15a basically at idle. Somewhere I read it could go as high as 40a but I can't find that documentation currently. Still working on the rest of the system...
 
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Dzl

Unofficial Forum Librarian
Staff member
Moderator
Update 2: Added Votronic, have not populated the spec's yet but added them to the table and added links

They have a B2B and a 3-in-1, B2B+MPPT+AC charger! LiFePO4 support looks spotty (some models state they have it, some don't), and 12 to 24v options are limited.
 

riker1

New Member
Hi,
I also experienced 2 issues.
slow charging via alternator. Not sure if Renogy is draining the starter battery with IGN connected, assumed a smart control. But unsure it this is working .

and promised tickle charging of starter battery not working. at least I did not see any current and LED Blinking when battery LED is green and solar is charging.


Anyone having same topic?

Or did I miss anything and it is a user error

Thanks T
 

Kesa32

Solar Enthusiast
Deleted, should have watched video first lol,,,,,, though I'll add when I tried mine out via 5m x 8mm connected to vans 6m x 13.5mm , l was getting around 26a , ign wire not connected vehicle running ( ford territory diesel ) , solar was connected but van under a open high pitched roof carport , lm not sure wether that would've throttled the alternator input or not
 
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riker1

New Member
Trickle charge to starter battery only happens when the house batteries are full as far as l know ( from memory,,, which isn't great lol )
Yes, but how to see and control? Battery LED is green, which indicates battery is full but no trickle charging of starter measured?
What am I doing wrong?
Thx
 

Kesa32

Solar Enthusiast
Yes, but how to see and control? Battery LED is green, which indicates battery is full but no trickle charging of starter measured?
What am I doing wrong?
Thx
Hi again , yes l haven't tested it for that function as my 8mm is controlled by the ignition switch , l intend to run new wiring dedicated for the van charging as the 8mm is just a loose lead in the rear to charge the aux battery for the portable fridge
When we went around half of Australia a couple of years ago l found the solar was enough to keep the vans batteries full , though the vans got gas cooking and 3 way fridge , so we don't use a lot of power really anyway ....so never had to connect the vehicle anyway .... even fed power back from the vans batteries to the portable fridge if we were parked up for awhile
Was running redarc / agms back then
 

riker1

New Member
Hi again , yes l haven't tested it for that function as my 8mm is controlled by the ignition switch , l intend to run new wiring dedicated for the van charging as the 8mm is just a loose lead in the rear to charge the aux battery for the portable fridge
When we went around half of Australia a couple of years ago l found the solar was enough to keep the vans batteries full , though the vans got gas cooking and 3 way fridge , so we don't use a lot of power really anyway ....so never had to connect the vehicle anyway .... even fed power back from the vans batteries to the portable fridge if we were parked up for awhile
Was running redarc / agms back then
Hi

ok, but Australia is having a lot of sun.....how man Watts do you have roofed?
 

DerpsyDoodler

Solar Addict
A very common set of questions in the beginner and the vehicle mounted systems subforums concerns charging a LFP house bank from a vehicles starting system (alternator). The most commonly used and recommended devices for this purpose are DC-DC chargers (also often called Battery to Battery (or B2B) Chargers). This thread is intended to be an index of the various options available as well as a catchall thread for questions and answers, discussion, etc.

Disclaimer (and request for help/collaboration): I do not own and have not used any of these. I have compiled this list because its a very common area of interest and confusion and also for my own interest. Some of these products I have researched in moderate depth, others I have barely read the product description and/or datasheet. There are bound to be errors, omissions, inaccuracies, etc. And there are some aspects that are just hard to represent neatly in a table. So take the accuracy with a grain of salt (especially anywhere you see a red ? or a *) and please help me improve the info if you see something that needs correcting or can think of another specification that should be added.


Charger Only
(DC-DC / B2B)
Brand / ModelMax Current 12/24Input VoltagesOutput VoltagesLFP compatible
Victron Orion-TR Smart (Isolated)30A / 17A12, 2412, 24Yes
Victron Orion-TR Smart (Non-Isolated)30A / 17A12, 2412, 24Yes
Sterling Power Pro Batt Ultra**70A / 35A ***12, 2412, 24, 36*, 48*Yes
Renogy DCC1212**60A / --1212Yes
Redarc DPS40A / 25A12, 2412, 24Yes
Votronic VCCTBD12, 2412Some Models
*Not available in all input voltages
**Not all models shown/listed in link or table
***Input current (output current not specified)

Dual Function Charger
(DC-DC + MPPT)
Brand / ModelMax OutputInput VoltageOutput VoltageMax Solar Input VoltageLFP Compatible
Renogy DCC50A / --121225 (?)Yes
Kisae DMT50A / 30A12, 2412, 2450Yes
CTEK D250SE20A / --121223 (?)Yes
Redarc BCDC50A / 20A12, 2412, 2432 / 28 (?)Yes


Triple Function Charger
(DC-DC + MPPT + AC Charger)
Brand / ModelMax OutputInput Voltage (DC)Output VoltageMax Solar Input VoltageLFP Compatible
Redarc Manager 3030A12, 2412, 24 (?)30 (?)Yes
Votronic VBCSTBD1212TBDYes
I would like to suggest adding a “max input (amps)” column to this table. My alternator has a max output rating of 250 amps at 24v. I have no intention of trying to push it to that limit, but I want to be sure that the b2b charger is capable of seeing those amps on the input and not frying... Alternately, if there are reasons this is irrelevant or there are other best practice ways to go about protecting the b2b charger, I am all ears. I have not done a lot of research into this myself, just yet. Only enough know what I want to do and to recognize some of the risks that need to be mitigated.
 

riker1

New Member
I would like to suggest adding a “max input (amps)” column to this table. My alternator has a max output rating of 250 amps at 24v. I have no intention of trying to push it to that limit, but I want to be sure that the b2b charger is capable of seeing those amps on the input and not frying... Alternately, if there are reasons this is irrelevant or there are other best practice ways to go about protecting the b2b charger, I am all ears. I have not done a lot of research into this myself, just yet. Only enough know what I want to do and to recognize some of the risks that need to be mitigated.
Hi do not really understand the difference
in the Specs: DCC50S
  • Designed to charge service batteries from two DC inputs—solar panels and alternator.
Which is B2B and Alternator , right? so looks like Dual and Triple Function?
 
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