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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 chargers were first marketed for cruisers (boats) since they run the engines for hours each day.

Charger throughput is generally limited to 20-30A since higher rates would dictate $$$ internal components. This isn't as big a limitation as it might seem, since lead-acid current acceptance drops substantially throughout Absorption.

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_51hu4-7nxol._ac_ul160_sr160_160_.jpgRenogy makes b2b chargers in 20A and 40A versions.

This charger has preset profiles for battery types.


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: 2019/11/12 09:48 by frater_secessus