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Old 19-12-2010, 07:39   #1
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Battery Questions

Good morning,
I would appreciate help trying to understand out battery situation. Here goes...

We have a 2003 Lagoon 380 with Yanmar GM30F engines. The alternators and regulators are the original OEM installs. We have approximately 800 hours on each engine.
We upgraded the batterys last year when we bought the boat. Installed 3ea AGM 4D (205amps ea) for the house battery bank and AGM 27 series for each starting battery.
Additionally, we installed a Xantrax TruCharge 2 40amp battery charger and a Xantrax 3000 watt inverter.
The boat already had a Norpro 7KW Yanmar generator.

Things just don't seem right. We are down in the Bahamas. The mechanic we had looking at the systems seems questionable on his expertise.
I am trying to understand if we have a problem.

We also have a BlueSea 3-position battery gauge at the nav station.

When we charge the batteries everything reads properly on the Xantrax remote station - no fault lights. The settings are set for AGM batteries and the temperature setting is for warm weather (middle setting). The Blue Sea readout during the initial charge starge is about 13v for the house bank and 13.2-13.3v on the start batteries. It falls some as the charger goes through the cycles and finishes in the float stage.

When we shut down the generator, the house bank reads 12.5v and the starting batteries 12.7-12.8v. Is this the proper reading, or is it too low?

We are running a 12v fridge, a 120v 2.4 cu ft Waeco freezer (at a low setting), led cabin lights, vacu-flush heads, sometimes a computer or two, sometimes a tv, plus mooring light at night. We are down to 12.0v in the morning. Should we be going down that quickly? How low should the voltage reading be before we recharge? What is the voltage reading that we do not want to go below?

My concerns
1. Are are we getting a full charge at 12.5v, and how do we know other than the Xantrax remote panels indicates everything is OK?
2. Does the battery discharge seem to be in line with the appliances that we are using?
3. Do we have too much battery capacity for the OEM alternators, or the 7kw generator? Does the TruCharge 2 manage this?

I realize that I am asking for a lot of information, however being down in the Bahamas (Nassau) we are at the mercy of unknown boats mechanics and I don't want to have them start replacing batteries, alternators, voltage regulators, generator repairs unless it is truly necessary. Any advice, and prayers, will be appreciated.
Also does anyone know of a honest and capable mechanic in Nassau that can help?

Tom Waier

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Old 19-12-2010, 07:49   #2
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Yours is a common problem.

First off, your battery charger is WAY too small for the AGM house batteries (3 4-Ds @ 205AH = 615AH). These AGMs can take up to about 600 amps charging current rather easily. Many people don't realize that changing to AGMs from flooded -- which I assume you did -- without beefing up the onboard charging systems (alternators, battery chargers, solar, wind, etc.) is asking for trouble.

Second, yes, 12.5 volts is likely too low. A fully charged AGM battery should show not less than about 12.7 volts AFTER RESTING OVERNITE with no charge and no load. Many will show 12.8-12.9 volts.

I suspect that you are not fully charging your AGMs, and that's a problem because they need to reach a full charge as often as you can get them there. Because of the time required to charge the last 10-15% of capacity, you're not likely to be able to do this regularly with either the engines or the generator/charger. Takes too long. Large solar panels or an overnite using dockside power are two ways to help reach full charge.

You definitely do want to find a way to reach full charge, because failure to do so will result in heavy sulfation and loss of battery capacity. In other words, you'll kill the AGMs quickly.

That said, you didn't give any details of the way your alternators are set up -- capacity, internal or external regulators, combiners, etc., so it's hard to say much more. Also, battery voltage should be measured with a good digital multimeter directly at the battery terminals to be sure you're seeing the right voltages.

Hope this helps a bit.


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Old 19-12-2010, 10:45   #3
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If I understand correctly your maximum charge voltage from the battery charger is 13v for the house batteries and decreases from there.
This is much too low and something is wrong.
Are you sure the battery charger is ever getting out of the bulk phase? It should not be going to the absorption or float stages at these low voltages.

You need to do an energy budget, but my guess is that you are using something like 175-200AHrs day. With a 40A battery charger you need to run the generator something like 5 hrs a day to replace this!
I agree with Bill you need a larger battery charger and I would also recommend a smart regulator on your alternators. I donít think there is anything wrong with the equipment (although the batteries will be damaged quickly by this treatment)
You need to match your energy input and output and there seems to be a mismatch at the moment.
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Old 19-12-2010, 11:30   #4
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I agree with all that has been said before. I assume that you have the OEM alternators on your Yanmars and you use your genset to supply power to the 40 amp Truecharge charger. Either the Truecharge is so small that it never is getting your batteries anywhere near 90% of full charge (the last 10% isn't worth running a genset to achieve) or its charge algorithm isn't working. A decent charger should peak at about 14 or so volts at the 90% charge level in the absorption phase.

Both problems can be fixed with a bigger charger. As others above have said, AGM batteries can accept a lot of charge. Ufortunately it isn't easy to buy a single large capacity battery charger.

If you are unhappy with your Xantrex inverter then replace it with a Victron or Mastervolt inverter/charger that has at least a 100 amp charger capacity. Both are solid brands. Anything Xantrex is suspect IMO.

If the inverter is ok then replace the Truecharge with two 75 amp IOTA chargers. That is the lowest cost solution.

BTW the larger charger whether it is part of an inverter/charger or stand alone will help load your genset. Watch its current output. When it drops below 20 amps AC (about 1/3 load) then shut it off. Letting it run at low loading will eventually glaze the cylinders and carbon up the injectors and exhaust elbow.

If the only AC load that you have connected while running your genset now is the Truecharge charger, then you are probably loading your genset at only 10%.

Finally if you motor for a few hours every other day or so then consider upgrading one of your Yanmar alternators with a high output unit with an external regulator. But if you mostly hang out on the hook, definitely increase your charger capacity.


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