Smart Chargers Are Not That Smart
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I’ve continued my practice of lead/lagging my two house banks even though plugged into the boatyard. I have the same chargers as you and recently completed conditioning of all four banks that have these dedicated chargers. I experienced some of the same frustrating revelations as you. I can isolate my loads and condition banks while the batteries are at rest so it wasn’t quite as challenging as you write. Justin instructs us to condition at 15.5 volts (room temp) for eight hours. The chargers as you know cycle off at six hours so one must set the alarm and re-introduce the cycle for two more hours. Also my chargers must be programmed at 15.7 volts because three of the four held that voltage for the cycle even though the battery temperatures varied ten degrees (F) or so. My battery temperature didn’t rise appreciably so the pre-programmed conditioning voltage was a non issue. One charger refused to enter conditioning mode even when fooled (flooded batt pos), actually it adopted the mode but refused to come above 13.7VDC. I replaced the charger with the spare and all is well again. I agree with your idea that this is an expensive process when away from the dock. I can expect the generator to run 16 hrs or more for this monthly exercise for each house bank. I do not count amps as you know but rather rely on voltage to determine battery condition. I think the amp counting is too complicated and subject to error and it’s one more thing for this old man to manage.
I look forward to your research on alternator charging as this may be my Achilles heel here on Sea Return. We do not use a three step regulator and charge every battery through a Mastervolt battery isolator, hitting all with as much as 14.2 vdc. For the house bank we keep the switch on all while alternator charging because we charge through the switch for the combined house bank. Not all the banks are under load so we may be heating some more than we should but everything stays topped up while underway. With the new engine install we plan to place two 90A alternators on the engine feeding that same Mastervolt battery combiner simultaneously. This deviates from my long time practice of avoiding belt drives but David (ace machinist at Billings) will engineer the two dual belt drives which should be a durable work of art. I also believe in not combining components in a single case so that will begin to explain the two sine wave, one square wave, inverters and four Statpower and one Newmar charger. Good luck with your continued research, we should all benefit in the end.
Great comment, thanks again for sharing your experience.
We elected to use a single larger alternator and carry a spare to keep the clutter on the engine down.
The single alternator charges all the batteries through an automated solenoid that gangs them all together once the voltage is over 13.5. This always worked well on the old engine.
I would still recommend a digital amp meter to measure the amount of charge going into the batteries as the voltage will come up to 14.4 long before the batteries are fully charged. While our meter does count amps but, as you say, not terribly accurately, the big payoff is that it accurately measures the actual amount going into the battery.
I guess I may have missed something in your battery discussion. I have two smaller Rolls. I use an inexpensive Sears 110 charger. It tells me what the outgoing current is. Couldn’t you isolate one battery at a time to charge and use the others to run the ship until that one was fully charged then switch to the next…?
Yes, you could do as you suggest on the batteries, but you would be constantly cycling the batteries while on shorepower and using up battery lifetime in so doing.
With our system, detailed above, we bring all the batteries up to fully charged as soon as we plug in, and then switch one of our three chargers to float at 13.5 volts and turn the other two off. This keeps all the batteries fully charged without overcharging and gassing off electrolyte, which is a finite resource in an AGM battery.
We are getting ready to go to the Arctic with a 24v only boat and would suggest keeping batteries warm with a diesel heating system. How say?
We have never had a problem with low battery capacity due to cold. But then, generally, we don’t let the temp in the boat go below 50F (10C), more for the sake of the crew than the batteries!
However, you do want to make sure that all your charging systems are automatically temperature compensated since when the batteries are cold you need to use a higher voltage to properly charge them.
GPL-L16T Marine Battery, I plan on using 2 of these 6volt bats on my 38 year old 20′ Ensenada. I was wanting to know what is the best way to charge these bats as a 12 v system or isolate and charge as 6 v.
These are 400 amp/hr bats each. Will the system be 800 amp when seried to have my 12 volts? Also, I only have room for one solar panel, I’m thinking 235 watts. What kind of charge controller will have a 3 step charge control for AGM batteries?
Hi Rick,
To answer your questions:
1). It will be best to install the batteries and charge them in series at 12 volts.
2). The bank will be 400 amp hours at 12 volts.
3). See Colin’s chapters on renewable energy in our Online Book Electrical Systems For Cruising Boats for info on charging solar cells.
I’ve installed a new Mastervolt based system on our new boat. This has the advantage that it ties all chargers, inverters, shunts, etc., together with (optional) remote control panel(s). The trick here is that you can tell the charger to interface with the shunt so that it knows how much charge actually goes into the battery.
Yes we looked at Mastervolt. As you say, good equipment. The problem is that their 115 volt chargers top out at 50 amps, so we would need three of them—ouch!
We still think that the world needs a really good three stage charger that can output a total of say 150 amps at 12 volts, senses charge current from a shunt and does not include an inverter.