Re: Battery Charger Manual


I share your experience.  Different batteries specify different voltages for bulk, absorption, and float, and this is often not at all made clear on marketing materials: you must dig deeper.  I am starting speculate some people's early battery failures may be attributable to this.

Take for instance my Trojan AGMs, per the spec-sheet, and double-checked by calling Trojan Tech service:

Bulk and absorption: 28.2-29.4V (at 25°C), I assume 29 for practical purposes
Float: 27V (at 25°C)

The AGM factory default settings of no charger brand that I know of will meet these specs.  Certainly the two Mastervolt chargers on board (100A and 30A) and the external Mastervolt alternator regulator will destroy the batteries even if all three devices are set to the factory "AGM" setting.

The solution?  Products from Mastervolt or Victron, if networked among themselves, and if you install their USB module, let you connect a PC.  Each brand provides its own PC software at no additional charge.  You can then adjust the bulk, absorption, and float values for each device.  Or in the case of Mastervolt, this can also be done from their touch screen modules, if you have one installed on the network, but very laboriously (not recommended).

A further wrinkle: Trojan states that for e.a. 5°C increase in batt temp the voltage must be reduced by 0.2V.  The Mastervolt does this automatically, but only if you have installed the battery temperature sensors that came in the box.  On our boat, the previous owner had installed the 30A charger while neglecting to install the sensor.


SM No. 350
At anchor, Bonifacio

Join to automatically receive all group messages.