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Passage Maker - - Ask the Experts -

How­ever, this de­pends on the ab­sorp­tion volt­age (the reg­u­lated volt­age once the ini­tial bulk charge phase of charg­ing is over) and how long this is sus­tained be­fore the charger trips to float. The more ag­gres­sive the cy­cling, the higher the ab­sorp­tion volt­age should be, and the longer the ab­sorp­tion charge should con­tinue be­fore the trip to float on those oc­ca­sions where ex­tended charg­ing is pos­si­ble.

In your sit­u­a­tion I would think an ab­sorp­tion volt­age of 14.4 volts would be ap­pro­pri­ate (in some ap­pli­ca­tions with very limited charge times and only in­ter­mit­tent full-charge cy­cles, it pays to go as high as 14.7 volts). If the tripto-float pa­ram­e­ter is based on time, you might want to set this as high as eight hours. If it is based on the charge rate (amps) into the bat­ter­ies, some­thing as low as a trip thresh­old of 200 mil­liamps per 100 amp hours of bat­tery ca­pac­ity would be ap­pro­pri­ate (as op­posed to the more con­ven­tional 2 amps per 100 amp hours of ca­pac­ity). If you set the amps this low, you will def­i­nitely also want a time limit on the ab­sorp­tion charge in case the bat­tery charge rate does not fall this low.

This will keep the charger from boil­ing the elec­trolyte out of the bat­ter­ies on those oc­ca­sions when you are plugged in for days at a time.— Nigel Calder


My 2002 Main­ship 430 has two Cat 3116 diesels and an elec­tri­cal setup con­sist­ing of one 8D 1200 MCA start bat­tery with a 55-amp al­ter­na­tor and one dual-pur­pose 8D 1450 CCA start/ deep-cy­cle house bat­tery charged by a 105-amp al­ter­na­tor that also charges the two 1000 MCA AGM thruster bat­ter­ies through a Vic­tron iso­la­tor. There is also an 8kW gen­er­a­tor with its own 27-se­ries start bat­tery and a Xantrex 3000 in­verter/charger with a bank of three 8D bat­ter­ies. At our ma­rina dock we have 50-amp power to both the boat bat­tery charger and the in­verter/ charger, and all is well.

How­ever, when we haul the boat for the win­ter, our yard power is only 110 volts/15 amps through a GFCI socket. I change the in­verter power share from 30 amps (the max) in the wa­ter to 15 amps on shore, but ev­ery time we put power on, the shore socket GFCI trips. The only way we can keep power to the boat to feed the charg­ers, air cir­cu­la­tors, etc., is by by­pass­ing the shore­power ground, which I don’t like to do.

One pos­si­ble the­ory is that the boat has sev­eral in­ter­nal GFCI sock­ets fed by ei­ther shore­power or the in­verter. So the over­all sys­tem has on­board GFCI sock­ets fed from a shore­power GFCI socket, and you can’t have one GFCI down­stream from another. Is that right?

If so, how do we get around that and

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