Do Propulsion Engine alternators also Charge House Battery?

[gofast24]

The answer is yes, they do. After wondering about this for about 3 years finally determined last Sunday that both propulsion engine alternators do charge the house battery! Simple test, turn off house battery charger at dock (on shore power), put a some DC load on the house battery (fridge, stereo) for 5 minutes, check house battery voltage on a Blue Seas OLED voltmeter at helm (12.6 VDC), start one propulsion engine (voltage went up to about 13.1 VDC), shut that engine off, start other engine, and same results (13.3 VDC). Now the real question= Since we replaced a group 8D flooded battery with a 8D AGM house battery we changed the switch on the back of the Charles House battery charger from Flooded (wet) to the AGM position. But dont know what effect the propulsion engines alternators , not being adjustable from flooded to AGM, will have on the house battery? Both propulsion engines are also on group 27 AGM batteries as well, but in 3 years, no problems with any of the starting or house batteries? All this just FYI or any comments?

[xixp]

Valid question, im almost sure that main difference for the charger configuration change is becuase wet and AGM have different flotarion voltage requiremets. Therefore for the alternators that parameter is not critical because they dont continuously charge the batteries. (Only when engines are running and there is the engine integrated voltage regulator that is not adjuatable either).
My boat have VSRs as well (voltage sensitive relays) to direct where the alternator power is directed depending on what battery is more depleted so again i think you shouldn't be concerned. (Your boat must have VSRs too).

[Chris_in_Texas]

If the 4160 is original they would have a dual alternator and triple bank battery isolator. Would be a Promariner version (that is unless it has been replaced due to failure.) The thing with them depending on age the batteries will never fully charge even on flooded cell, because of the voltage drop across the diode (either 0.3 or up to 0.7v) depending on what they used. If you change to AGM then it males it worse. However as XIXP pointed out you don't run the engines long enough to make a dent in the larger battery unless your running all day.

The isolator would be located on the firewall and there should be some 8AWG red wires running to them. This is were traditionally Regal ties the battery charger to as well. So you will have a lot of heavy gauge wire running in and out of it. Both alternators will directly run there, and at the alternator if they use the factory harness from the engine manufacture they disconnect the power lead from the starter to the alternator. That is how a single engine with dedicated starting battery would charge.

The only way that I am aware of to fix the alternators is to use an alternator with an external voltage regulator that is adjustable, and put the sense wire after the isolator.

[gofast24]

Thanks guys! I still have the original Charles SP5000 series 60 amp / 3 bank output house/starting battery charger that was installed new on the boat at Regal in 2001, not sure if I have isolation diodes or not, will check next weekend. Also, comment from xixp, the most time at sea is about 1 hour or less, our lake isn't big enough to cruise all day unless wanting to use up a couple $100 in fuel If I think back a year or two i believe I checked the float voltage requirement between AGM and flooded and posted something to this effect. Cant find my own post . There was only 0.1 VDC difference between the flooded and AGM batteries float voltages (12.7 vs. 12.8). Just happy to know that the two AGM starting batteries and the AGM 8D house batteries are still doing fine! Just a note= getting the old original flooded 8D out and the new 8D AGM in was a PITA! Glad I have two local sons (36 and 38) to do this kind of stuff! Just turned 70 last Tuesday.