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Battery to battery chargers

A b2b (or dc-dc) charger is a type of isolator that boosts charging voltage to the house battery. These typically cost more and are rated for less current than normal isolator types.1)

images-na.ssl-images-amazon.com_images_i_3131jbgz9ll._ac_us218_.jpg This kind of controller boosts the chassis voltage to voltage appropriate for proper lead-acid Absorption.


Lead-acid batteries require two things to get fully charged:

  1. a high enough Absorption voltage (Vabs)
  2. enough time at that voltage for the battery to stop accepting much current.2)

DC-DC chargers address the first requirement, but unless you are driving for hours the isolator won't have enough time to fully charge the batteries. DC-DC charging is very effective on cruisers (boats) that run the engines for hours each day. They will, however, put more current into the bank due to their higher voltage.

CTEK D250 series

The most common b2b charger with 'dwellers is the CTEK D250SA, a 20A solar/alt controller. It has connections for both alternator and solar panel input + MPPT function, although the MPPT algo may not be partcularly robust.

The SmartPass accessory bypasses the D250SA when the house battery wants > 20A of current. This will generally happen in the first half of Bulk mode. When the house battery demand drops below 20A control is handed back to the D250SA for boosting to Absorption voltage.3)

Note: the CTEK D250SA4) panel voltage (Vpanel) maximum is 23v.5) It requires >= 80w of solar for reliable solar charging.6)7) There are reports that the MPPT algorithm is not particularly robust and is better thought of as an add-on for the alternator charging circuit.8) FIXME


images-na.ssl-images-amazon.com_images_i_41ic_8sivjl._ac_us218_.jpg The Sterling Pro Batt Ultra series is alternator-charging only, but can be configured to exact setpoints. The BB1260-12 is a 30A example and costs about $50 more than the D250S above.


images-na.ssl-images-amazon.com_images_i_417f858gcdl._ac_us218_.jpg Redarc makes a 25A b2b charge with MPPT similar to the CTEK.

Ring Automotive

Ring makes a 30A DC-DC charger.

electrical/12v/b2b.txt · Last modified: 2019/06/02 13:58 by frater_secessus