Generator Charging with Magnum MS Inverters

Written by: Alan Smith

Question:  I started my generator, and the inverter/charger went straight to Float stage, skipping Bulk and Absorb.  Why?
When starting generator charging with a MS series inverter, an operator should first look at their battery bank’s voltage.  If the voltage is higher than a normal resting voltage; the Magnum inverter will skip the Bulk and Absorb charging stages, and go straight to Float.

From the manual in the Operation/Battery Charging section:

“If the DC voltage is high (>12.8 VDC/12-volt models, >25.6 VDC/ 24-volt models, or >51.2 VDC/48-volt models), the charger will skip the Bulk and Absorb charge stages and go directly to Float charging.”

This scenario, where voltage is higher than normal resting levels is common enough.  An operator may want to run their generator on a sunny day, when the solar array is already charging the batteries as well, elevating the voltage above resting levels.  Magnum’s intention with this design/feature is to prevent overcharging the batteries.  In many cases though, an informed operator can safely have both charging sources feeding the battery bank.

There is a relatively simple work-around.  Disconnecting incoming solar power to the solar charge controller, with a solar disconnect breaker, will essentially mimic nighttime.  With no incoming solar power, the battery bank voltage will settle to resting levels in a short time.  At that point, an operator can engage the generator, observe the inverter for ~5 minutes to confirm that the inverter is in the Bulk charge stage, and THEN reconnect the solar disconnect breaker to the charge controller.  Now that the inverter has made it to Bulk, it will continue to move through the rest of the charging cycle.