Unattended Battery Smart Charger

[eialm]

Our Oceanis 393 was delivered 12 years ago and has been in the water ever since and charger is always connected when in harbor. Big advantage is that also the fridge has been running since, and we can leave food for a reasonable time on board, and beer’s always cold.

[Sailmonkey]

We don't even have a battery charger. Solar wind and alternator take care of the batteries.

The only time the boat is even plugged in summer at the dock to run the midget air conditioner when were aboard, and winter at the dock to run the dehumidifier. 3-4 months of winter excepted we don't leave the shore cord attached at all.

If it were my boat, I'd slap a small solar panel on the boat to keep the batteries healthy, and if left in the water a loud bilge alarm with instructions left on a visible part of the boat to call a number if an annoying noise is heard.


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[Muckle Flugga]

Originally Posted by Harry Brown

I just worry about all battery chargers! Hence the reason to put one somewhere where it will cause the least amount of damage, IF the small chance of it ever going wrong happend. And I'm talking about leaving it somewhere for many months, hence the concern. I'm probably worrying about nothing though ;-)

I think your concerns may be justified. Chargers are rarely "perfect", and small variations in the bank can lead to cooking off hydrogen, and electrolyte depletion. If you do do this, make sure your bank is well ventilated. Overcharging in the case of LIthium Ions carries a serious risk of explosion.

But why not simply deep charge and then disconnect the bank altogether? This serves to protect your batteries without the worry. Running an auto bilge pump? What is the source of water ingress if so? I have seen bilge pumps stick on due to faulty or jammed switches and burn out, melting pipes and objects around them… everything carries risk. Guardienage is a better bet…

[Muckle Flugga]

Originally Posted by Akapeterc

The only problem I find with leaving my battery charger on a closed up boat is the CO detectors go off

They are actually detecting hydrogen.

[donradcliffe]

I would leave the boat in a yard or marina for months at a time. Sometimes I left the smart charger plugged in, sometimes I left a single solar panel (with simple controller) connected, and sometimes I just disconnected the batteries (gels).

It was not a scientific study, but my conclusion was that the batteries lost less capacity by leaving them disconnected.

I did come back one time to a burned out bilge pump...was lucky that the boat didn't go up in flames.

[Victory 28]

Enclosing a battery charger in any kind of box is a real bad idea, especially one that has zero ventilation (not that you would actually able to do that with out cable glands, though I have seen dumber things than that done aboard)

If the manufacturer thought it was worth the trouble they would likely have provided some manner of thermal compensation charge control (hence smart) that might also provide a unit shutdown for any range of operational temperatures deemed excessive. This would happen well before any possible point of combustion. The truth is you can easily damage even destroy a lead acid with a regulated charger in a month or less if you are completely unaware of what current actually represents, which is heat. This is especially true for automotive starting batteries which is what many people have aboard in spite of the fact that they believe they are deep cycles,

anyhoo here is the math:

2.5 amps trickle at 14.2 volts=35 watts

2 typical starting/deep cycle batteries rated 100ah each for 200ah total capacity. (5 hr rate)

2.5amps * 24 hours= about 60ah a day

Capacity 200ah/60ah=3.34 days

Add some 20% for losses 3.34+.67 = 4.01 days to 100% SOC

And note that, this is starting with a "trickle" current which invariably won't happen because the charger will do what it was meant to do which is to charge the battery up ASAP.

And yet people will leave these chargers on continuously for months, heating up the plates, boiling off electrolytes needlessly and losing both capacity and battery life all the while. A true tapering 3 stage should back current down to roughly 500 or less milli amps or .5 amps.

I have been working professionally with UPS, DC-DC converters, MPPT, PWM SLA, LA, Li-Ion, NiMH and occasionally more exotic chemistries for about 20 years in mission critical and telecomm system power applications. When I do a power design for a yacht there are no troubles, period. some people just like to fiddle about endlessly and some to enjoy sailing with the confidence of knowing that their navigation, security and communications systems are supported by an excellent DC power design.