How does the Sterling Power battery to battery charger work?

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The Sterling Power battery to battery charger is installed “between” the van battery and the house battery (more installation details further in this article). There is no switch or button to initiate the charge! You see, when you start your vehicle, the alternator kicks-in and raises the voltage of the van battery in order to charge it. The B2B charger senses the higher voltage and turns itself ON automatically. Now when you turn your vehicle OFF, the alternator stops and the voltage of the van battery drops; the B2B charger senses the dropped voltage and turns itself OFF. All of that happens without user intervention (well, except the part where you drive your vehicle!).

What are the benefits of a battery to battery charger?

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Each type of battery (Gel, AGM, Lithium, etc.) requires a specific charging profile (bulk, absorption, float). Charging with the wrong profile might result in:

• Incomplete charge (cannot reach 100%);
• Reduced lifespan (waste of $);
• Sulfuration (reduced total capacity) of Lead Acid batteries (AGM).

If a lead acid battery doesn’t get a proper multi-stage charge (bulk, absorption, float), it loses its total capacity and that’s non-reversible (knowledge is power: we recommend reading the Charging Profile section of our Electrical System page to really understand what that means). Bad charge = wasted money (the battery has to be replaced more often), so we think the B2B charger pretty much pays for itself in the long run.

Battery to battery charger vs Isolator: what’s the difference?

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• A B2B charger provides the adequate charge profile to the house battery (see paragraph above for benefits); in other words, it charges and keeps the battery in good health in the long term.
• An isolator is simply an automatic “switch” that connects and disconnects the house battery to the starter battery. An isolator does NOT provide an adequate charge profile (bulk, absorption, float), and, therefore, might not be able to charge the house battery to 100%, might reduce its lifespan or reduce its total capacity. The only real advantage of an isolator is that it’s cheaper upfront (but not in the long term as you might have to change your house battery more frequently).

Are solar power AND alternator power (battery to battery charger) both needed?

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Here’s what we think about that:

• If you live full time in your van, we say a B2B charger is a must. Energy is a basic need, it’s not cool worrying about running out of it…
• If you take your van for adventures in summer only, you can probably live without it as solar can provide the bulk + absorption charge on its own.
• For fall and spring adventures, we highly recommend it as the solar days get shorter and weaker. Alternator power is a good way to quickly go through the bulk charge, then solar power can complete the absorption stage.
• For winter there’s no question about it, our opinion is that you want it. The sun angle is too low, the solar day is too short and overcast weather is more common (for USA and Canada at least).

What we Like…

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• Surprisingly easy to install (scroll down for installation write-up).
• Install-and-Forget!
• Fast Charge.
• Provides a nice multi-stage charge that keeps the battery (Gel, AGM, Lithium, etc.) healthy in the long run.

What we Don’t Like …

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• The internal cooling fan is quite noisy; think of a tiny hair dryer. If possible, install the Sterling charger further back away from driver/passenger seats to minimize the noise.

Models & Where to Buy

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There are a few variants of the Sterling Power Battery to Battery charger, so make sure to select the appropriate one according to:

1. Input voltage (most likely 12V…)
2. Output voltage (most likely 12V…)
3. Input current (30A, 60A or 120A).

It basically comes down to either BB1230 (Input: 12V, 30A. Output: 12V, 22A), BB1260 (Input: 12V, 60A. Output: 12V, 45A) or BBW12120 (Input: 12V, 120A. Output: 12V, 90A). We highly recommend the BB1260 for a faster charge (so a short drive goes a long way 🙂 ), unless of course 60A is over the maximum current recommended for your battery.

*But before selecting the BBw12120, please consider the following:

1. Batteries generally have recommended and maximum charge current. Going overboard is a waste of space (this charger is bigger) and money.
   • Check your battery manual or data sheet to find out.
2. Make sure your alternator can handle that much current so that you’re not draining your van battery.
   • For example there are two alternator options on the Ford Transit: basic (150A) and Heavy-Duty (230A). It is believed (not official info) the Transit needs roughly 70A for itself (lights, radio, etc.), so we’re left with 80A extra current with the basic alternator and 160A extra current with the Heavy-Duty alternator. If you have the basic 150A alternator (80A extra current) and you’re charging your house battery at 120A, it probably means you are “borrowing” that extra power from the van battery…
3. Overworking an alternator might reduce its lifespan.
4. The BBW12120 has, according to Sterling Power, reduced cooling capacities due to the fact that it’s waterproof. Therefore it’s not ideal to install that in a van. Instead, they recommend installing two BB1260 in parallel to get a higher output.

Breakers

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Sterling Power recommends to use the following breaker/fuse size:

• BB1230: 50A breakers (Buy on Amazon)
• BB1260: 100A breakers (Buy on Amazon)

Installing the Sterling BB1260 battery to battery charger

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First of all, as always, make sure to read the manual (choose the latest version). The manufacturer knows their product better than anyone else.

Location

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Make sure to install the B2B charger in a well vented space, and do not obstruct the hot air exhaust:

Wiring and Electrical

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It’s honestly quite simple. Here are the required connections:

1. Positive Input (From vehicle battery)
2. Positive Output (To house battery)
3. Negative (Common to vehicle and house battery)
4. Optional Temperature Sensor (Recommended for lead acid batteries (AGM), but not for Lithium. Connects to house battery negative post. This is to correct the voltage according to temperature change)

Follow this wiring diagram (faroutride.com/wiring-diagram) to make sure your B2B charger works as it’s intended to. The wiring diagram had a built-in calculator for fuses/breakers, wire gauge, and wire length/terminal count. Pretty neat!

Ford Transit Connection:

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POSITIVE:

This official Ford SVE Bulletin shows how to connect to POSITIVE for the SINGLE or DOUBLE battery variant: SVE Bulletin Q-226 (.pdf):

Ford Transit with twin batteries configuration, year 2020 & up:

Since 2020, the Transit with dual batteries configuration comes with two (2) CCP (Customer Connection Point) located on the driver seat pedestal (on the door side). The CCP2 is rated for up to 175A, so it’s an ideal connection point (positive) for a B2B since there is no need to remove the seat:

Negative (ground):

Ideally you want to use a ground point recommended in the BEMM (BEMM included in our Builder’s Package), and it’s a good practice to use one as close as possible to the battery (which is located under the driver seat). In our van, we are using the ground point located between the passenger/driver seat:

Mercedes Sprinter Connection:

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Please check the Mercedes Sprinter “Body And Equipment Guideline” on how to use the battery power (alternator):

Default Options

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Here are the factory options for the Sterling BB1260 Charger:

• MODE: 1
  • (Mode 2 is identical to mode 1, except it needs a live signal on the ignition feed input in order to charge)
• ACTIVATION VOLTAGE: vehicle battery above 13.2v (for 5 seconds)
• TURN-OFF VOLTAGE: vehicle battery below 13.2V
• TURN-OFF TIMER: 240 seconds
  • (A timer is required to complement the regenerative braking aspect of modern Euro 5 / 6 + engines – where the alternator’s voltage can drop below 13V for a short period of time)
  • Because our Ford Transit 2016 does not have regenerative braking, we changed the turn-off timer to 30 seconds (procedure in manual). This prevents draining the van battery, especially when running errands (multiple short drives).

First Time Use

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The unit will enter “config” mode at first startup; this is your opportunity to change the charging profile according to your battery type.

• The configuration can be changed later, check the manual.
• To find out which charging profile to select, check your battery manual.

First Time Use Configuration Sequence:

1. To initiate the first startup, turn on the vehicle and wait a few seconds. To indicate the battery to battery charger has turned ON, LEDs will light up, a beep will sound, and the fan will run for 5 seconds. If none of that happens, try to “force-start” the unit: simply press and hold SETUP/ENTER for 5-9 seconds.
2. At this point, an LED is flashing to indicate the battery type (default = lead acid).
3. To change the battery type, press and hold SETUP/ENTER buttons for 10-12 seconds (up to 20 seconds); all LEDs are now flashing.
4. Scroll down (SELECT button) or up (ENTER button) to select your battery type; Press and hold SETUP/ENTER buttons for 2-3 seconds to confirm the selection.
5. At this point, the B2B charger will restart.
6. If you have a battery monitor, such as the Victron (faroutride.com/victron-review), you can observe that the B2B is charging the house battery…
7. That’s it! Go for a ride!

To change the configuration later or for advanced options, check the manual.

Operation

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Once the installation and initial setup completed, just drive and let the Sterling Power battery to battery charger do its thing!

Reliability

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We installed the Sterling Power BB1260 battery to battery charger in October 2018; so far so good! We will keep you updated if anything happens! Subscribe to our Mailing List to be notified.

Resources

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• BB1260 Manufacturer Website (product info, manual, regenerative braking compatibility, etc.)

Runner-Up

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New for 2019, Renogy is now offering a DC to DC charger (B2B). We haven’t tested it ourselves, but Renogy is known for their good, reasonably priced products, so it’s most likely a safe buy. That being said, READ THIS BEFORE BUYING:

• The Renogy B2B starts the charge when the ignition is set to “ON”, even if the engine is not running. Consequently, you could drain your starter battery (when listening to music, for example). For this reason, we would personally stay away from it.
• The Renogy B2B requires a connection to the ignition signal of the vehicle, making the installation a bit more complicated than with the Sterling Power.

Renogy also released the DCC50S which combines a DC to DC charger & Solar (MPPT) charger. As opposed to the Renogy B2B charger above, this model starts the charge based on the starter battery voltage (so it won’t drain your battery when your engine is not running, that’s better). Looks like a sweet product, but be aware of the limitations:

• Maximum alternator charging current: 25A
• Maximum solar charging current: 25A
• Maximum solar voltage: 25V (so if using multiple panels, series connection is not possible)