Charger separated for AGM

[KARL]

Hello, I have a 2015 RT27 classic with 4 AGM Group 31 batteries. One is a cranking battery for starting and the others are deep cycle, one for the Thrusters/anchor windlass and the other 2 for the house bank. When I am using the Promariner charger with shore power, set on the AGM setting, is my boat wired to separate the batteries charging? In other words, if the start battery is fully charged it can be overcharged and damaged while charging the other batteries. I'm not gettng the life span on them that I thought I would. Hope you can shed some light on this. Thank you.

 

[Rode Trip]

Your charger is probably the ProMariner 12-20P model. It is a 3 bank charger. It can charge house, thruster, and start batteries independently. It won't overcharge them as long as the setting on the front is set to 'AGM'. It will go through 3 steps, Bulk, absorption, and float with it safely holding them all on a float charge once fully charged which won't damage the batteries.

 

[KARL]

Yes, it is a Promariner 12- 20P. Thank you for the response. It is set on the AGM setting. Good to know they are being charged properly.

 

[BB marine]

You will not get the life expectation that you would expect with the standard Ranger Tug installation. For one reason the standard 20 amp Promariner charger is not nearly large enough for a battery bank as large as yours. Four batteries at a rated 100AH per battery is 400AH of battery. AGM batteries have a lower resistance than a standard LA flooded this allows them to be charged faster without the fear of excessive heat. It is better for an AGM to charge at a higher amp charge while in Bulk. The minimum charger I would use in a four battery bank AGM would be 40 amp and prefer to be 60 amp. The engine battery is not usually in need of charge like the house bank is and the thruster battery depending on how much you use it is not either. The problem with the Ranger install is the three bank charger that puts out in your case 20 amps is charging the batteries all at the same rate basically as if the charger is a single bank charger. Why? Because the way Fluid motion wired it. There are ACR's used to isolate the engine battery, house battery and thruster battery. When there is no charge and battery voltages are at 12.7 Volt +/- .3V all batteries are independent. When the charger is on and the battery voltage of any of the batteries reaches 13V for 90 seconds or 13.6 for 30 seconds the ACR joins the batteries as if they are wired in parallel. Now all batteries charging as one battery. If all batteries are in like kind and all batteries are of the same age and AH this is ok. The charger needs to be large enough to maintain the bank. 20 Amps IMO is not. If one battery is older and has a higher internal resistance than the other ones this is not the best way to maintain longevity of the newer batteries. If one battery has a weak cell it will eventually damage the other batteries by over charging the batteries. AGM are expensive batteries and one would expect to get twice the use out of them when compared to cheaper Flooded LA batteries. In my experience that is not the case with an installation like what you have. I had the same in my Cutwater and did not experience longevity out of AGM batteries. I used the boat and anchored a lot and used battery. The 20 amp charger was not big enough and the battery configuration worked but it is not the best.

The way a Ranger is set up I would purchase Flooded LA batteries and plan on replacing them every 3 years. Leave the install as is. Many have used it this way with no issue. I know how you used your boat in the past. The same way I did in My Cutwater. The AGM did not give me good service. I had the same set up as you. I switched to LA Flooded and got the same service life if not better than I did the AGM. When I sold my Mainship Pilot last fall it had the same batteries that I installed in August of 2021 Group 31 Flooded La. Inexpensive Duracell (East Penn) 105AH batteries. I had spent 14 months living on board while doing the Loop and 3 more months the following year cruising the Great Lakes anchoring and using battery all the time. The LA Flooded still tested with a low internal resistance and maintained a good full charge after four years of full service. I did have a 40 amp charger and a 50 amp solar Charger which helped.

 

[KARL]

Thank you for the response, Brian. I am going with your advice and replace all 4 batteries with LA flooded. One more question, though, regarding the alternator. I'm assuming that the alternator only looks mostly at the state of charge of the start battery and it being fully charged most of the time, causes the alternator to back down on the amps and this hinders the charging of the deep cycle bank? I notice that when running, the alternator is putting out 14.1v continuously according to my monitor but it does not tell me the amp reading. Will slower charging at 14.1v at lower amps be detrimental to the lifespan of my new batteries? And we have about 220 watts of solar to use for charging at anchor...
Marc
Ranger Tug 27
KARL

 

[BB marine]

Thank you for the response, Brian. I am going with your advice and replace all 4 batteries with LA flooded. One more question , though, regarding the alternator. I'm assuming that the alternator only looks mostly at the state of charge of the start battery and it being fully charged most of the time, causes the alternator to back down on the amps and this hinders the charging of the deep cycle bank? I notice that when running, the alternator is putting out 14.1v continuously according to my monitor but it does not tell me the amp reading. Will slower charging at 14.1v at lower amps be detrimental to the lifespan of my new batteries? And we have about 220 watts of solar to use for charging at anchor...
Marc
Ranger Tug 27
KARL

When the engine is running and alternator is charging once the engine cranking battery reaches 13.6 V for 30 seconds the ACR closes. There is a ACR for the Thruster bank and one for the house bank. When they close all batteries are wired in parallel. The alternator now is charging all batteries. The Voltage regulator is set to bulk charge to between 14.1V to 14.4V at that point the voltage regulator will kick in and out maintaining the voltage adding amps that are removed from 12V users refrigerator, electronics, fans...... When the voltage regulator maintains the 14.1V think of this as Bulk/absorption mode. That is the best that a standard alternator can do. This is where a AGM looses some of its longevity. The proper charging cycle should be 14.4 bulk and the same for absorb then once the battery is fully charged it should reduce the voltage and float at 13.6. This doesn't happen with the standard alternator. The bottom line the alternator D3 Volvo is large enough to charge your bank. It is IMO better suited for flooded than AGM. When I did the Loop in PORT-A-GEE Pilot 34. I had 4 LA Flooded changed with alternators with 1/2 the output that your D3 has. I had 600W solar (100V/50 amp solar charger.) The 4 year batteries still in good usable condition.

I did change their use of the 4 year batteries. I removed my old thruster battery and my original engine start batteries that were purchased in 2019 both Flooded LA. I used my house batteries Dual Purpose for start two in parallel for each engine for start. I converted the House bank to LiFePO4. That was a Game changer. My designed install used two 8D Epoch 460AH Essential batteries 920AH bank with 820AH easily usable. When I finished and tested the system I could use all 120V users including marine air. The engine batteries had DC to DC chargers connected to them to charge the LiFePO4 and the 600W solar was much more efficient charging the LiFePO4 than it was for charging the LA flooded. The solar controller throttled the charger down for LA. The solar controller let the LiFePO4 have everything the panels could produce. The only reason to go to a marina now fuel, water and pump out. Game changer !! I wish I did the install before doing the Loop we would have anchored a lot more !! Something to think about if you plan on keeping Karl.

We could boondock in PORT-A-GEE which was awesome. Unfortunately we changed gears and decided to down size and purchase a winter home in Florida. PORT-A-GEE leaves on another Loop this year with new owner. He will now appreciate the LiFePO4.